Shownotes

Could we theoretically image continents on extrasolar planets?

• How to Take Snapshots of Distant Worlds — Planet Quest
• First Image of Planet Around Sunlike Star — Universe Today
• Moon Reveals New to Find Oceans, Land on Other Earths — Universe Today

What does an infinite universe mean?

• Is the universe infinite? — WMAP
• Interpretations of quantum mechanics — Wiki
• Multiverses – Ars Technica

What is your opinion of what is in a black hole?  Could we be inside one?

• The science of black holes -- STSci
• Universe Today’s Guide to Space articles about black holes
• What happens inside a black hole? — About.com
• The Anatomy of a Black Hole -  UIUC

If I’m standing still at the Earth’s equator, how fast am I moving?

• Introduction to the Cosmic Microwave Background — U of Chicago
• How Fast Are We Moving When We’re Sitting Still – Universe in the Classroom

Is there any limit to when photons would experience time?

• Discussion of photon and time — Physics Forum

What’s Fraser’s life story?

• Who is this Fraser Guy Anyway? — Universe Today
• Fraser’s Wikipedia page
• StarStryder (check out the new look!)
• Carnival of Space
• The Future of Making Money as a Blogger — David Risley

How likely are the planets in sci-fi where the moons are huge and can be see during the day; or binary planets?

• Tatooine – Star Wars Wiki

In rocketry what does specific thrust measure?

• Specific thrust – NASA
• Ion propulsion FAQs -- NASA

Transcript: Questions Show: Imaging Extrasolar Planets, Infinite Universe, Inside a Black Hole

Download the transcript

Fraser Cain: Welcome to the AstronomyCast questions show where we answer your questions about space and astronomy. If you have a question for the AstronomyCast team please email it in to info@astronomycast.com and we’ll try to tackle it for a future show. Please include your location and a way to pronounce your name.

Hi, Pamela, how you doing?

Dr. Pamela Gay: I’m doing well. This has been a marathon session. The people out there listening don’t realize that we are on episode 4 for today.

Fraser: So this is what we have to do when you’re not traveling.

Pamela: I know. I know

Fraser: Maybe we’ll get to 6, who knows? One little note is thanks for everyone sending in questions. Someone mentioned that they hoped that their question makes it into the question lottery. And that’s actually a pretty good way to describe it. [Laughter] From last night to this morning, I counted like seven or eight questions. When I last checked my e-mail at 11 o’clock at night, to when I woke up this morning around 7 and looked at my e-mail again, there was about seven or eight questions that had piled in.

We do get a lot of questions. We apologize if we don’t get to everyone’s questions. I don’t know what the ratio is, but we get through as many of them as we can. The best way to get your question answered is to make me – I get to be the question chooser – for me to go “Hah, that’s a really good question. I want to know the answer to that too.”

So, if you have a question do a quick search on the site because many of the questions have already been answered and if we feel like we’ve already answered that question, we’ll skip it. The other way is if I can’t quite understand the question, and I’ll put it off because I don’t really get it. Sometimes I’ll sit down and rewrite it but in some cases I don’t get it and I’ll avoid it. That’s maybe to help you make your way through the question gauntlet and win the question lottery.

Alright, so this week, what will we eventually be able to see on extra solar planets? What does an infinite universe mean? What is down there inside the black hole?

Our first question comes from Andrew Branch from Rochester, NY: “Based on our ability to image extra solar planets, especially Earth-like planets over the next 100 years, could we theoretically image continents, rivers, canyons, or even cities on other planets? Are there just not enough photons reaching us?”

Alright, Pamela, how far will we be able to go with imaging extrasolar planets?

Pamela: Well, the problem comes down to two different things. One is contrast. Just how easy is it to tell this bit of orange rock from that bit of red rock?

The other problem is resolution. How small of an object can we see? It will probably be feasible for us to go ooh, land versus ocean on planets that don’t have too many clouds or to say what fraction of the planet might be covered in clouds.

When it comes to getting down to city sizes, that starts to get beyond reasonable resolution abilities.

Fraser: Now, we’re saying reasonable. We’re thinking terrestrial planet finder?

Pamela: Yeah.

Fraser: Technology right? Where you’ve got like a bunch of really big telescopes connected as an interferometer trying to glimpse some planet.

Pamela: Right. Even with potentially using something on its way out to Jupiter in conjunction with something orbiting the Earth where you start getting into really difficult fringe problems.

With radio you might still be able to do it. Even with that getting to city sizes with things that are nearby it starts to become intractable. Continent sizes, that’s nominally feasible in the next 100 years.

Fraser: I think what’s neat though is that scientists are ahead of the curve on this. Figuring out clues on how you might know what is on a planet. It’s the same way that scientists first discovered extrasolar planets, right?

Originally, they were like eventually we’ll have to build a telescope big enough to see Jupiter going around another planet, another star. In fact they figured out well no we just have to detect the motion of the star and detect the planet’s influence through its gravity. We can’t see the planet, but we know it’s there.

It’s very similar to some of the things that are being figured out for actually resolving things on the surface of extrasolar planets, right? Just by the changes of the brightness of the planet we might be able to know where the continents are and where the oceans are.

Pamela: That is the easiest way to start picking these things apart. You look for periodic changes in brightness, and you say ah ha, I get the exact same within a couple of percent change in brightness every day. That tells us the continent versus ocean or at least the bright versus dark albedo difference between different parts of the planet.

Fraser: How it is changing, you would be able to tell whether there is cloud cover. You could, for example, here on Earth we have the heat islands around cities so maybe you could detect strange points of heat going around at a regular basis.

[Laughter] Well you couldn’t see the buildings but maybe you could detect that there is a heat island there.

Pamela: That’s still awful tiny. We’re really looking at continent size things where you might be able to tell the difference between oh I know that half of the planet is supposed to be cold and we have a imagine the density of London or Mexico City spread over all of Europe.

On that scale it really isn’t that dense. If it was that we might be able to see. What we have currently on the planet Earth if we imagine other worlds with that density of humans, we can tell the difference between land not land, forest not forest, on continent size of blobs.

Fraser: You know and that is sort of the reasonable technology. Are there any real limits? Could I build a telescope that is on the moon and is a kilometer across?

Pamela: Even a kilometer is not enough to get there.

Fraser: Really.

Pamela: To be able to discern a 3000 mile wide blob just a couple of light years away you start needing to have telescopes that are hundreds of thousands of miles separated.

Fraser: Right, or a hundred thousand kilometers across.

Pamela: Right.

Fraser: A great big mirror.

Pamela: Yes and I don’t think we’re going to build a mirror that big just due to that we don’t have that many resources. Separating them that much is feasible, but that only gets us to 3000 miles. We want to get to 3 miles. So we have to just keep increasing the size, and increasing the size. Eventually you run out of solar system.

Fraser: I’m going to put my bet on scientists being able to figure out clever tricks to figure out that stuff’s there. [Laughter] Not necessarily to see it like you’re looking at a photograph and there is a city on another world, but to infer that a city is there.

That’s where my bet is going to be. They are going to infer pollution into the atmosphere [laughter] and try to figure out what is going on.

Pamela: I’m with you that they are going to be able to say oh there’s light pollution on that planet. It should be way darker than it is right now.

However, being able to say ah ha, there is a city on that continent. There is another city on that continent. I don’t see us getting there in the next 100 years.

Fraser: Okay. Then the challenge is on. [Laughter] I can’t wait to find out which way it goes. The next question comes from Ninako Shirashi from Tokyo, Japan: “I often hear that in an infinite universe anything is possible. I don’t understand how anything is possible logically follows infinite universe.”

Okay. We have had this conversation before. Is the universe finite or infinite? If it’s infinite, we imagine there are an infinite number of Frasers and Pamelas having an infinite number of podcast recordings on an infinite number of worlds and every gradiation from there. Every slight minor change is also there. There are also an infinite number of Freds and Pamelas recording their podcasts, spacecasts. So, how does this work?

Pamela: The basic idea is there are two different ways of looking at this. First of all there is the Oxford interpretation of quantum mechanics that says that every decision that ever could be is made, and when it is made the universe splits. This is part of the premise of the WebMage book by Kelly McCullough.

There is also the if you make enough planets; every possible type of way of making that planet will happen. In terms of you and me, there you are looking at all the different possible mutli-verses in an infinite universe.

When you start looking at eventually I am going to sit on a chair and you’re going to sit in a chair, and someone else is going to sit in a chair, and somewhere in the universe someone is going to sit on a chair and all of the atoms are going to line up and they are going to fall through the chair.

That one comes with just if you roll the dice enough times, you get every possible combination including if you roll 40 dice simultaneously enough times eventually they are all going to come up ones, even if they’re not loaded. So in an infinite universe, you have the space to roll the dice as many times as you want and have them come up with a world with green eared vulcans.

You have the possibility of having all sorts of just random combinations that we say due to quantum mechanics are very improbable; due to genetics are very improbable. Eventually, given enough worlds, given enough time, given enough space, everything that could be will be.

Fraser: I guess using your dice analogy is a good one, right? If I give you 40 dice and say roll ones and roll it once, chances are you’re not going to get it. But if I say you are allowed to roll those dice as many times as you like, you will eventually come to a point where they will all be ones.

It will require a certain number. I’m sure someone can do those calculations. Because we’re here having this conversation, recording this podcast, means that it’s possible.

Pamela: Yeah.

Fraser: Because it’s possible, it means that it can happen an infinite number of times with every variation that possible. I guess the trick is that you can’t do things that are impossible, right?

We can’t have this conversation and then realize that there is a way that we can move faster than the speed of light and go make a spaceship, right? [Laughter] If from what we understand right now the laws of the universe prevent any than faster than light travel so that will never happen, right?

Pamela: Yeah.

Fraser: I guess the mind kind of boggles at the size and scale of the universe that might be required. The distance you would have to travel to find another Fraser/Pamela having a conversation on that other world.

It’s just enormous. Yet, if the universe is infinite, it has to be happening an infinite number of times. Whoa.

Pamela: [Laughter]

Fraser: Peter McLaughlin from Northern Ireland asks a similar question: “If the universe is infinite, would it be infinite in all directions?” When we have this conversation, we are thinking yeah, head up, head down, head right, head left, North, South infinitely.

Pamela: The thing is infinite does not require that. In mathematics it would be still an infinite universe if it was only infinite in north and south.

Fraser: So there would be a boundary right and left, or up and down, but one dimension could go infinitely.

Pamela: The only thing is I can’t think of any theory that would lead to an infinite universe that wasn’t infinite in all directions.

So, simply saying the universe is infinite isn’t saying it’s infinite in all directions. However, I can’t find a way for physics to build an infinite universe that isn’t infinite in all directions.

Fraser: Right. Okay. Jacob Friday from Ingleside, Texas, asked: “I know there are many theories on what is in a black bole, but what are both your opinions on this matte? What’s in the center? What can it do time wise? What are the possibilities that we are inside it?”

For me, I think my opinion doesn’t matter one iota. It matters nothing. I’m not an astrophysicist. I haven’t done the research. I think that opinion in science can give you some insights and maybe some directions.

A lot of the times your own opinion is kind of a too much opinion is a dangerous thing. I have no opinion. I only have an accumulation of the articles that I’ve written about it. That’s sort of all I’ve got right now. Where do you stand?

Pamela: Yeah. Opinion only comes in when you’re looking at two possible realities that both match experiment, both match theory and you need to run a few more tests. Then you can say my gut tells me this one is more likely to be correct once we’re done running tests.

You can’t base anything on that other than saying this is the one I’m hoping for. You still have to go with whatever the actual final experiment says is true.

Fraser: I’ve got an analogy: it’s like baking a cake and you’re following the recipe and someone forgot to tell you what temperature to bake it at and how long to bake it. So you don’t know.

Should you bake it at 350 or 375 or 400, and for 20 minutes, for an hour? You don’t really know. You have some opinions. You think well probably 375, and probably and hour, but you don’t know until you bake it. Then you bake it and you’re like uhh, I burnt it. That didn’t work.

Pamela: And there’s only one right answer for the perfect outcome.

Fraser: Right. And your opinion can guide you a bit but at the end of the day it doesn’t really matter. You could be totally wrong.

Pamela: And, as far as black holes go, once you’re inside the event horizon we don’t know.

Fraser: Then if you could synthesize the opinion held by astrophysicists, what’s in the middle?

Pamela: The best that we’ve got currently is that there is a new state of matter. Something that is denser than neutron gas.

Something that is denser than anything that we know how that’s mathematically handled. There are people who say it’s a quark soup. There are people who say it is just something we don’t know. I can tell you what it’s not.

Fraser: Right, and we have to stay in that place until an experiment has been devised that will get at the answer. Of course, the big problem is that with a black hole nothing comes back out.

Pamela: Right. The best we can really do is to try and replicate the densities using things like the Large Hadron Collider and the future accelerators that will follow it and see if we can achieve that new state of matter.

Large Hadron Collider is not going to get there. The future colliders that get to the as dense as the center of the black hole with significant enough mass to experiment with new states of matter.

Fraser: Right. Jacob wanted to know: “What a black hole can do time wise?” That I think we have more information, right? How a black hole interacts with time.

Pamela: Basically once you’re inside you’re going fast enough that time is approaching zero. It’s one of those neat quandaries. The closer to death you get the less time is passing for people watching you fall in. You’re slowly experiencing time as though nothing strange has happened.

Fraser: What are the possibilities that we are living in a black hole right now?

Pamela: Yeah, we’re not.

Fraser: We’re not. Okay. There you go. What are the possibilities that we are living inside a car crusher right now? A trash compactor right now? Yeah, you could imagine what the possibilities would be. I think you would know.

Pamela: Yes.

Fraser: If you were living inside a trash compactor as it is crushing you? You’d go hmmm. Jason Davis from Springfield, Illinois (isn’t he from The Simpson’s?) [Laughter]: “If I were standing still at the equator, how fast am I moving? Not just the Earth’s rotation, but all the movements into consideration, like Earth’s rotation, Earth’s orbit around the sun, the galaxy, expansion of the universe. How fast am I going?”

Pamela: The question really comes down to how fast are you moving relative to what? This is one of those problems that we run into is how fast relative to what. The ultimate frame of reference is really the cosmic microwave background.

It’s the farthest away thing that is in all directions and we can measure our motion with them. Relative to the cosmic microwave background, we’re moving about 10 kilometers per second. That’s I guess the best thing to go with.

Fraser: Right. Because everything else is relative to what? If we want to talk about standing on the surface of the Earth, how fast are you moving compared to in orbit around the Earth as it were?

Pamela: If you’re standing at the equator and just hanging out on the surface of the planet, you’re moving about a half a kilometer per second, so it’s nothing to sneeze at.

Fraser: Right, okay. But as you look at all of those numbers, the orbit around the sun, the galaxy, etc., it all averages out to 10 kilometers a second relative to the background radiation of the universe.

Pamela: Right.

Fraser: In some cases they cancel each other out. I guess that movement is so great it really overcomes all the other movements.

Pamela: It’s the one we can measure against a solid non-moving fence.

Fraser: Right, okay. Mitchell Shaiat from Oakland, CA asked: “If there is no time for a photon then the frame of reference of the photon it is both at its place of origin and its destination simultaneously. So, is there a limit at how far away this destination could be?”

This is one of those big head scratchers that we’ve talked about. That because a photon is moving at the speed of light it experiences no time. I guess it experiences when it begins and when it ends at the same time. Is there any limit until it would finally experience time if you created a photon year, let it travel for 13 billion years, would that change the no experience of time?

Pamela: Nope.

Fraser: Nope?

Pamela: Nope. It goes splat. As far as a photon is concerned, it’s created, it goes and it splats. And that going part is instantaneous.

Fraser: So if you were a photon you would experience creation and destruction.

Pamela: And nothing in between.

Fraser: And nothing in between.

Pamela: It goes splat.

Fraser: Is there any time from the creation to the destruction? When a photon is emitted let’s say, is there any time there, or is that instantaneous as well?

Pamela: It’s all one breath in a way. It’s created, it’s destroyed. It experiences no time between those two instances.

Fraser: The time from when it is created to when it is destroyed, it doesn’t accelerate. It just goes from zero to speed and then back again.

Pamela: Right. And since it’s never moving at the speed other than in vacuum 300,000 kilometers per second, it never experiences time, ever.

Fraser: Alright. Kyle Lee from Charlottesville, Va., asked: “We know a lot about Dr. Pam’s past and what she does when she’s not recording Astronomycast, but what about Fraser? What’s your story, Fraser? Is running Universe Today your full time job, and how did you go about it? And can you support a spouse and kids doing that? Any tips for the rest of us who are looking to leave our regular jobs?”

You can Google me. You can Google my history. I ran a bunch of software companies. I worked for a web development agency and was doing Universe Today in the part-time. Over sort of enough time, I was having so much fun with it that I just sort of transitioned over to a full time job thanks to my wife continuing to work.

Can I support a spouse and kids doing that? Half. I support this half of the household, and she supports the other half. It’s not a great salary. I definitely was making a lot more money doing software development, but there is some money.

I make money from advertising on Universe Today. I think I beat 99 percent of the bloggers out there in being able to do that. So that’s great. It took 10 years to get from nothing to having this site, be able to support me as my only job. So, that’s pretty cool, I’ve got to say.

Do I have tips for anyone else looking to leave their regular jobs and be bloggers? [Laughter] I think that another blogger, Pamela, can tell me sort of, and can say what it’s like. Do you make a lot of money from Starstryder?

Pamela: I have to admit the International Year of Astronomy has all but killed Starstryder. It’ll come back, it really will. So the year when I was regularly, regularly, posting Starstryder was paying for itself.

Fraser: Like its hosting fees?

Pamela: It was paying all of its own host fees and was paying enough money that I went out and bought buttons from ButtonStar. I love buttons from ButtonStar. That’s not really enough to do anything with other than poke people with stick pins which can be fun, but it’s not useful.

The real side effect for me has been, I’ve gotten to travel to a whole bunch of really cool places because of the doors that being a blogger has opened for me. I think for many of us that is really the biggest benefit.

It’s not that we’re earning a living through blogging. There are a few people out there who are. I’m not one of them, never have been. But it does open up doors to things like Dragon*Con and that’s just cool.

Fraser: Uh, huh. Yeah, I think, as you said, the benefits are that you’re in this great community. You make all these friends. You get to have these great conversations with people and you get to spend your day thinking about the things that most interest you, and the places where you want to play a part.

Pamela: There are times when I think all of us have had that day where we’re the first to find some really cool story, and we blog about it. We don’t just blog the story. We blog what we feel about the story and we encourage action.

Then to see people go out and act on that or think about it or engage in conversation in the comment sections and to start dialogs, that’s one of the really powerful things. The blogosphere is a community where you can start threads of conversations scattered across the Internet and across your comments and you can affect people’s actions. That’s a lot of fun.

Fraser: Uh, huh. So I would think that I have 10 years of experience doing this and I started doing it early enough where I was able to get a lot of links and traffic and stuff like that.

At the same time, there is enough, everyone has these experiences that you can learn from other people’s mistakes. If you wanted to start up today, you could absolutely make a name for yourself in either blogging or news or in the space industry, or any of that. Because everything is so transparent that you can see what we all did, you can see what we’re doing, do it better, and start to attract readers. And…

Pamela: And, join the carnival of space.

Fraser: And there is money to be made. It’s hard to catch up to me and Phil, but at the same time, you can learn what we’ve done and do a better job and do as good as job, and be able to jump up to the top of the queue.

There are a lot of bloggers that have only started a couple of years ago and they are doing really well. It is absolutely possible to make your living through the Internet. There are some wonderful benefits of doing that. All it requires is that you work really, really hard.

Pamela: Yeah.

Fraser: You put in a lot of time, and are able to think long term and able to chip away at what you’re doing. I think we all have to, I know this is going to sound really dopey here, but you have to do what you love.

Pamela: Yeah.

Fraser: If you do what you love and you do it long enough, the money starts to show up. That’s just the reality. If you don’t do what you love, then it’s really hard to get ahead.

So, for everyone listening to the show, just try to do in your life more of what you love and less of what you hate. If there are things you feel like you have to do, you’d be surprised at how you can chop those out and minimize the amount of time of stuff that sucks, and really emphasize doing the stuff that you really enjoy.

In some cases it has to be a hobby and you’ve got to do your job and then that funds your hobby, or sometimes your hobby can be your job. So, they both work.

Alright. Aaron Goodkin from Seattle, WA asked: “Sci-Fi flicks often show Earth-sized, life-supporting planets with multiply gravitationally rounded moons, some orbiting so near that they are visible during the day time. So how likely are these kinds of systems to form? Is it just Sci-Fi?”

I know what Aaron is talking about. You’ve got these you’re standing on the surface tattooing this gigantic moon in the sky. If you go and actually hold out your hand the moon covers the size of your pinky finger now. That’s it. Sometimes it seems like it’s truly big but it’s actually teeny tiny in the sky. So is that possible?

Pamela: Well, it comes down to densities, and it comes down to probabilities. It comes down to how big is the star. Sure, it should be totally possible. In fact, we should be able to even have binary systems where you have two planets that are the same size co-orbiting a central point between the two planets.

We just haven’t found a system like that yet. Now, one thing I do have to point out though is the Earth’s moon is visible during the day. You just go out and look at a quarter moon. It rises at noon or sets at noon, depending on if it’s first or third quarter. You can see the moon most of the day in a crescent form of one shape or another. You’re just never going to see it as more than a quarter during the day except during the summer when the sun stubbornly refuses to set.

This means if you go far enough north you can see a full moon and daylight at the same time during the summer. Or far enough south you can see it during the other summer.

Fraser: Right. But if you get a big moon that is orbiting very close so that it’s huge in the sky, it’s probably not going to be that stable or last that long, right?

Pamela: Well, there’s actually no reason to think that. What it comes down is that you end up with tidal forces and you end up with the two planets tidally locked, but as long as the atmosphere of the one planet isn’t creating drag on the moon, you’re fine.

If the two objects are big enough you can stick them far enough apart that you can still have this amazing size in the sky for an observer, but the two objects are far enough apart that there isn’t any of this drag due to atmospheres.

Fraser: Right we talked about this before. The trick is that the moon can’t orbit the planet faster than a day on the planet, right? If you get below that then that same tidal process that’s happening with the Earth and the moon, where the Earth is slowing down and the moon is drifting away from us, you get that in reverse.

Pamela: Right.

Fraser: The planet speeds up and the moon spirals inward. So that just doesn’t last. As long as your moon orbits slower than a day of the planet, you’re good.

Pamela: Right and, like I said, you also have to be out of the atmosphere. That one kind of comes without saying.

Fraser: Right. That is the situation you have with phobos and Mars. Phobos is within it and it goes around the planet more quickly than the planet takes a turn once on its axis and so it’s on a decaying orbit. In a few million years it’ll crash into Mars.

Pamela: It’s on a death spiral.

Fraser: A death spiral. Austin Adams, from Brisbane, Australia, asked: “I actually had a fairly long question, but I tried to shorten it down. In rocketry, what does specific thrust measure?” So, what is specific thrust?

Pamela: If you look at the total change in velocity and momentum, which aren’t the same thing. Change of momentum is: I have this mass and this velocity at the beginning, and I have this mass and this velocity at the end, which with a rocket your mass is changing and your velocity is changing, so your total change in momentum is a little bit different than we’re normally used to thinking about.

If you take that total change in momentum, that gives you the total force that happened. If you divide that force by your original mass that gives you a mass corrected sense of just how much oomph your rocket has. The specific thrust is: take that total change of momentum, divide it by the original mass of the system, and that gives you the specific thrust.

If you have something that was able to have this enormous change of velocity and very small change in mass, it’s going to have a giant specific thrust. However, if you have a system that has this huge change in mass for the exact same change in velocity, it is going to have a much smaller specific thrust.

Fraser: Right. Okay. What is something then that gives more specific thrust? Is that when we look at say an ion engine versus a chemical rocket?

Pamela: Well, chemical rockets, you’re throwing everything out. But with an ion drive you’re accelerating some sort of an ion, some sort of a charged particle using magnetic fields and spitting it out the back at extremely high velocities.

The amount of mass you’re throwing out isn’t that much. You’re able to given a long enough distance, a long enough time, get your spacecraft going extremely fast. Specific thrust for an ion drive is very high. Specific thrust for a chemical rocket is very low.

Fraser: Alright. I think that’s all we have time for this time. So we’ll talk to you on the next show. Maybe we’ll record more today.

This transcript is not an exact match to the audio file. It has been edited for clarity. Transcription and editing by Cindy Leonard.

Shownotes

Why was there a difference between the amount of matter and antimatter at the beginning of the Universe? Do black holes have something to do with this?

• Why there’s more matter than antimatter in the Universe — Universe Today
• Discussion of the anti-matter black hole paradox – Astronomy forums

Mathematically, we can have a velocity greater than the speed of lights lets us travel faster than light speed, so why can’t we?

• Can anything travel faster than the speed of light?  PhysOrg

Can stars form in accretion disks around black holes?

• Accretions Disks -- NASA
• Cataclysmic variable stars — NASA

How much precision is needed to keep space telescopes focused on one spot?  I have a hard enough time keeping my camera steady!

• How Hubble Works — HubbleSite
• How Gyroscopes Work for Hubble -- ESA
• Fine guidance sensors — HubbleSite

How can matter exist with antimatter?

• Antimatter- CERN

What causes sunspots and do they influence Earth in any way?

• Sunspots — Exploratorium
• Solar Flares – GSFC
• Coronal Mass Ejections — Cosmicopcia

How do we know what the speed of light is?  How can we measure something that fast and how did scientists figure that out?

• Speed of Light , history of our knowledge about
• Ole Christensen Rømer
• Armand Fizeau

Would life as we know it be able to survive around a Red Dwarf?

• Living with a red dwarf – Astrobiology Magazine
• Tidally locked exoplanets – Martian Chronicles

Could matter escape from the event horizon of two black holes colliding?

• What happens when two black holes collide? — Universe Today
• No Naked Singularity After Black Hole Collision — Astroengine
• Intro to Black Holes
• Movies from the Edge of Space Time — UIUC

Why is it so bright in the center of the galaxy with a black hole there?

• The Milky Way’s Hidden Black Hole — Scientific American
• Sagittarius A*

What is behind a black hole?

• What is On the Other Side of a Black Hole? — Universe Today
• More about black holes – CWRU

Transcript: Questions Show: Matter Balance, Jumping Light Speed and Black Hole Star Formation

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Fraser Cain: Welcome to the AstronomyCast questions show where we answer your questions about space and astronomy. If you have a question for the AstronomyCast team please email it in to info@astronomycast.com and we’ll try to tackle it for a future show. Please include your location and a way to pronounce your name.

Why was there a difference between the amount of matter and antimatter at the beginning of the universe? Mathematics lets us travel faster than light speed so why can’t we? Are there stars forming around black holes?

The first question comes from Scott Wells from Grand Forks, ND: “Is it possible that the slight imbalance in matter and antimatter was created not at the moment of the big bang but shortly after the universe formed by primordial black holes?”

That’s a complex question there. We’re talking about the slight imbalance at the beginning of the universe where all the matter and antimatter were generated and there was like one part per billion off and so they all collided, turned into energy but there was a little bit of matter left over and that’s what our whole universe is. Scott is asking could that matter actually be formed by primordial black holes. What?

Dr. Pamela Gay: This sort of falls into the let’s use black holes as a cure. [Laughter] They’re not. Black holes don’t care if you’re matter or antimatter. They eat you either way.

When they evaporate they give off matter and antimatter in equal parts. Black holes are kind of the ultimate neutral destruction device. They just destroy everything and then they spit out everything. They don’t care.

Fraser: Right, that’s kind of like that question that we had before. What if a black hole and an anti-black hole collide? You would just get a double the size black hole. [Laughter]

Pamela: Yeah you just get a lot of mass.

Fraser: Double the mass black hole, right.

Pamela: No, sadly we’re still stuck with for whatever reason this one part of physics is asymmetric and we have an asymmetric universe. It worked out for us.

If it wasn’t for that asymmetry everything would have annihilated and our universe would be pure energy and we wouldn’t have life. So we’re kind of glad for whatever went wrong in those beginning moments.

Fraser: Right. Shaun Crandall from San Antonio, TX asked: “According to special relativity we know that nothing with mass can reach the speed of light because the math and physics break down at velocity equals light speed. But at least mathematically it is quite simple to have a velocity of greater than the speed of light. Is it possible that you could jump over the velocity equals light speed and be able to move faster than the speed of light?”

Pamela: No.

Fraser: No. Even though the mathematics works out?

Pamela: Math allows lots of things. Math has no boundaries on it other than certain rules like 2 plus 2 must equal 4. Math isn’t constrained by physical reality. It doesn’t care that you have infinite mass. It doesn’t care that you’re dividing by zero. It simply is.

So while the math will let you have whatever velocity you want the reality of the universe says no c is the ultimate speed and you can’t go any faster than that. It’s very unsatisfying.

Fraser: It’s not that math and physics break down it’s that our understanding is what’s doing the [laughter] breaking down.

Pamela: In this case physics simply says you can’t go faster than the speed of light and the math will let you play but once you start looking at the mass you now have nonsense.

Fraser: Dawn Hoverson asked: “Since black holes can generate temperatures and pressures in their accretion discs is there an appreciable amount of nucleosynthesis taking place?”

I guess what Dawn is asking is around black holes can you have the accretion disc get hot enough and have high enough pressure that you get nucleosynthesis like we have at the core of our sun or even more hotter stars?

Pamela: Yeah and what’s really cool is you don’t even need a black hole. When white dwarfs get too close to a companion star in binary systems – we call this a cataclysmic variable because they’ll start gravitationally grabbing matter off of their companion star sucking it toward them and filling up an accretion disc. Periodically this accretion disc will fill up and undergo nuclear reactions.

We can end up with these nuclear reactions going on not just in the accretion discs of black holes but in the accretion discs of neutron stars and the accretion discs of white dwarfs. When you ask is there appreciable Nucleosynthesis that’s a kind of vague adjective.

It’s like asking have I drunk a lot of water today. I’m not sure. It depends on whose definition you use. There is a fair amount of nucleosynthesis in terms of given how long reactions take place and how much matter is involved. It’s kind of like dealing with a star and that’s kind of cool.

Fraser: Ronald Chan asked: “How much precision is needed to take those long exposures with a space telescope in orbit? I have enough trouble keeping a camera from moving around on Earth with a sturdy tripod and sandbags. How can you keep a space observatory pointed at a subject with enough precision to get a clear image?”

That’s absolutely true you may have Hubble staring at the same object for hours and hours and hours. In some cases with the deep field, it was hundreds of hours. How can you get it not even jiggling just a tiny little bit?

Pamela: It’s a combination of gyroscopes and more gyroscopes – well you can do it with two gyroscopes. They also use a fine guidance camera. The gyroscopes if you’ve ever taken a bicycle tire and held on to both sides of it while it’s not touching the ground and spun it and then tried to rotate it, it’s really hard. Things that are rotating are naturally stable.

On the Hubble space station they have a set of six different gyroscopes that can control the space station very precisely using any two of them. They also have a Fine Guidance camera. The Fine Guidance camera locks on a bright star and it stays centered.

The gyroscopes can be used to make fine corrections to the space telescope’s position. So, you’re constantly imaging using the Fine Guidance camera and you’re using the gyroscopes to keep yourself locked in position.

Fraser: Those gyroscopes actually resist the movement. It’s almost like you’re trying to push the telescope uphill away from where it wants to be to actually make it to move.

Pamela: These gyroscopes are floating in fluid and they actually use the fact that the gyroscopes don’t want to move to rotate the space telescope around the gyroscopes.

Fraser: That’s why you need at least two so you can move in two directions, right?

Pamela: Yes.

Fraser: Three is better.

Pamela: Three is better but they’ve figured out how to use things like the Earth’s magnetic field and other stuff to keep track of where we are in that third dimension.

Fraser: Right but without the gyroscopes those long images would be really hard to take.

Pamela: It would never happen.

Fraser: Okay, next question comes from Joshua Eagles from Australia: “How can matter exist? Shouldn’t we be annihilated by antimatter so that there is no overall net force? Are we in a small unfortunate part of the universe that may have large quantities of matter but over the universe as a whole there is no net value?”

I guess what Joshua is asking is is it really that the universe is all matter? You know after that original – we talked about early in the show – you have the matter, you have the antimatter, they collided and there was a little bit of matter left over and that’s why the whole universe is matter.

Is that the case? Or is it like pockets of matter here and pockets of antimatter over there and later on we might get overrun by a pocket of antimatter.

Pamela: As far as we know we actually live in a universe that is dominated by regular matter. While we do actually interact with antimatter all the time there are only certain reactions that are allowed.

For instance, antimatter neutrinos don’t react at all with normal matter electrons or protons. You probably have antimatter neutrinos of one variety or another flying through your body all the time and your body’s matter just doesn’t care.

You can have positrons and electrons, the antimatter version of the electron and the regular matter version of the electrons. They’ll instantly annihilate against each other.

Proton, antiproton – instantly annihilate against each other. There are only certain types of reactions that are allowed.

What antimatter is flying around all the time we don’t generally have to worry about too much? We live in a matter-dominated universe so we’re okay.

Fraser: We can see matter and antimatter collisions happening around the universe. It gives off very specific energy characteristics. If we looked up in the universe and we saw that kind of energy happening we would say oh wow there’s still lots of matter and antimatter colliding all around us. Get ready for a cloud of antimatter to come through the solar system.

We don’t see that at all. We see some places where there is matter and antimatter colliding but it’s more like it is being caused by something else. We see some around the center of the Milky Way.

Pamela: This is just a matter of different places are producing antimatter and the universe takes care of it for us. We’re okay.

Fraser: Paul Williams from Hong Kong asked: “What causes sunspots and does it influence our Earth in any way?”

Okay a sunspot is a black spot on the sun, what’s causing those?

Pamela: Those are actually places where the sun’s magnetic field has for one reason or another decided to poke itself up to the surface. The sunspots pretty much always appear in pairs.

One has basically a north magnetic pole and the other one has a south magnetic pole. You can imagine the magnetic field arcing between the two different locations on the surface of the sun.

They look dark but they’re actually just a thousandish degrees cooler than their surroundings. If you could see one of these sunspots all by its lonesome they are hotter than an arc welder.

Fraser: Right, they’re only 5,000 degrees Kelvin as opposed to almost 6,000 degrees Kelvin. [Laughter]

Pamela: Right. These are places where the energy has gotten all tangled up in the magnetic field. Periodically these magnetic field lines disconnect and reconnect in the process giving off huge amounts of energy.

They release vast amounts of plasma and high energy particles and high energy electrons all into the space around the sun. That stuff sometimes does head our way and create if we’re lucky, just nice northern lights, nice aurora that we can observe; southern lights.

Sometimes there is too much stuff and it can be dangerous for astronauts. It can wipe out satellites. If the magnetic field of the Earth gets whacked too hard the oscillating magnetic field can generate electric current in already overburdened power lines and take out the power grid.

That is a rather dramatic bad thing, so we generally try and keep an eye on the sun so that we can moderate where the astronauts are, what is the power on the power grid? All of this is in response to the sun’s activities.

Fraser: Right but the sunspots are often the sources of these flares. The coronal mass ejections so they don’t influence us temperature-wise or things like that.

Yes you sometimes get these flares and sometimes these flares give us a pretty light show. They influence our hearts. [Laughter]

John Painter from Millbrook, Ontario asked: “How do we know what the speed of light is? How is it possible to measure something going that fast? It seems as if scientists have known what the speed of light is for at least 100 years, so how did they discover it?”

Okay Pamela, so what is the speed of light?

Pamela: The speed of light is 299792.458 kilometers per second.

Fraser: Is that from memory?

Pamela: No. From memory it’s 300,000 kilometers per second.

Fraser: That’s fast. That’s here to the moon in a second.

Pamela: By definition we have actually defined a meter using and thus defined a kilometer as well, using the speed of light. By definition, the speed of light is 299792.458 kilometers per second. It’s fast.

Fraser: Right, that is fast. You can’t – Channel 9 okay and then I press a stopwatch [laughter] and then the light comes past me and I press the stopwatch again, because the speed of me seeing the light is the speed of light.

Even if I had a car going the speed of light I wouldn’t know to press start until it had just got past me. [Laughter] How on Earth, a hundred years ago did these people figure out the speed of light?

Pamela: It was actually more than a hundred years ago. People first started making measurements of the speed of light back around 1676.

Fraser: Wow.

Pamela: [Laughter] That’s kind of amazing to think about. First we needed the telescope but once we had the telescope it started to become practical.

I’m going to pronounce this poor soul’s name; someone whose name vaguely resembles Ole Rømer was looking at eclipses of the moons of Jupiter. What he noticed was if the moons were traveling toward us the eclipses lasted one amount of time and if they were moving away from us they lasted another amount of time.

He didn’t know the distance to Jupiter very precisely and thus didn’t know the sizes of the orbits very precisely. What he was able to figure out was that the light travel time would be longer if the object was moving in one direction than the other because it would have gotten further away by the time the eclipse ended or gotten closer by the time the eclipse ended.

This ends up changing the duration of the eclipse. He ran all the math and ended up with the speed of light at 214,000 kilometers per second which isn’t bad.

Fraser: That’s not bad at all.

Pamela: No, so that was simply based on looking at the moons of Jupiter. A more precise way is to instead use basically a spinning wheel and mirrors. The first particularly precise measurement that was made was by Armand Fizeau in 1849.

He took a mirror eight kilometers away from where he was planning to stand and had a wheel with teeth – think of a gear basically. He started it rotating and shined a light through it. If he had the rotation rate of the wheel just right, the light would go through the tooth and reflect right back through the next tooth.

He was able to essentially send a pulse of light and measure the pulse coming back. He was looking for basically the travel time for a ball of light which is something that you can figure out.

Fraser: His was very accurate, right?

Pamela: Yeah he was able to actually get 298,000 kilometers per second. He was able to get very precise.

Fraser: This was still a couple hundred years ago so this is an experiment that you could probably do in university? If you had enough careful manufacturing and set up the experiment it’s something that you could replicate, right?

Pamela: You don’t even need careful equipment. This is stuff that people were making prior to having big fancy machine shops. It’s possible to basically go out, buy yourself a nice big mirror, get yourself a chunk of wood and cut notches out of it and attach it to an axle and start it spinning very precisely.

You just need to have some sort of a mechanism to measure the frequency at which it is spinning. You can do that simply by counting how many times does it rotate per minute using an egg counter of some sort.

Fraser: I love it. This is one of the how do we know what we know questions. I think it’s great that people call us on it and ask how do we know and we can go back and look up the history and see the experiments and explain them.

Steve Davis from Rico, Australia asked: “I want to know if life as we know it would survive on a planet orbiting a red dwarf. With the advantage of a long life a red dwarf would seem like a logical place to find advanced life and if so, perhaps we should be listening to them with SETI.”

Red dwarf stars are stars with a fraction of the mass of our own sun. I guess since we have planets going around the sun and one of those planets happens to have life and it is likely there are planets going around a red dwarf.

Red dwarfs are thought to last hundreds of billions maybe even a trillion years. That might be the place where life could really get a chance to take time and evolve and become advanced. Are there any problems with that idea?

Pamela: Yeah, red dwarfs are very angry in their youth. These are stars that when they’re in the process of forming give off massive amounts of x-rays. That’s fine, stars do that no big deal but with a star like our own sun planets like Earth got to keep their distance.

We were a fair distance away from our angry young sun. The planets around red dwarfs that are going to be capable of eventually supporting life have to be just about on top of their parent star. They have to be in extremely close to get enough warmth to be able to have liquid water.

The angry youth of a red dwarf lasts about a million years. It is going to destroy any proto-life that starts to form on a planet that is close enough to have liquid water for those billion years of anger.

It is possible that a planet close to one of these red dwarfs could eventually form life or could be seeded with life from someplace else. We can’t rule them out.

The other thing we do have to worry about though is the planets are so close to their parent star that the probability that they get tidally locked, that just like our moon only one side of the planet ever faces its star is pretty great.

When you end up with tidally locked planets you end up with really weird, really harsh weather patterns. That would make life much more difficult to evolve. But, it’s non-zero. It’s just another place with another set of challenges.

Fraser: But I think a few years ago everyone was like no, there’s no point. It’s not hot enough or the stars are too violent. I know that even at the last couple of AAS meetings there were some really interesting discussions. I saw some neat poster presentations where people were talking about maybe it is not quite so violent.

Maybe you could have a planet move in from further away after the violent period and then settle into a nice orbit. I think there is some really interesting research that’s going on right now to answer that exact question.

You’re right, the implications are if it does seem that they are viable places for life there is lots more regular stars out there than there are stars like the sun. Some of them are very close.

They would make really good candidates for pointing your SETI telescopes out to listen for communications. I think that’s a really good path that scientists are considering.

Pamela: And at the end of the day what we’re finding is any type of a star pretty much can support planets. It’s just a matter of always looking everywhere.

Fraser: Peter Kajodik from Serbia asked: “Is it possible for matter or energy to escape from an event horizon during the collision of two black holes?”

Hmm I guess you’ve got normally, nothing no matter, nothing no light, no energy, no matter can ever escape from within the event horizon of a black hole. But if you have two black holes colliding could you get a scenario where something could escape and leak out?

Pamela: I have to admit I was doing back of the envelope force diagrams. From what I can figure out if you have in isolation two black holes that are in the process of merging, they’re spiraling and spiraling in toward each other. You will end up with things that had had an escape velocity that was speed of lightish and was thus inside of an event horizon.

Because you now have the gravitational pull of the two black holes that escape velocity will sink down so that it is lower and thus you could, if you were able to fire off rocket engines or something, escape. The problem is I couldn’t think of any way to easily induce the force necessary to get that sucker to escape.

You have things spiraling together, spiraling together in the event horizons will move. But I couldn’t figure out how to get something that had previously been inside an event horizon happily orbiting or at least as happily orbiting as you can happily orbit inside of event horizons.

Fraser: Terrified, leave orbiting. [Laughter]

Pamela: Right. I couldn’t figure out how to get any of these terrified orbiting objects to get a force to suck them out in a different direction.

So, yeah you can have something that suddenly is no longer within an event horizon but then I wasn’t sure how to get it out of the system.

Fraser: Right, I guess I don’t know, instinctively and I know when you’re talking about black holes and relativity it’s all pointless, but it feels like if you’ve got an event horizon for one and you have an event horizon for another and you put them together..

Pamela: What you end up with is..

Fraser: Something bigger with a bigger event horizon but it would still encompass both objects, am I right?

Pamela: No that actually, so back of the envelope again what you can imagine is one black hole in isolation ignoring spin is going to have a nice symmetrical event horizon around it.

Another black hole in isolation is going to have a nice spherical event horizon around it. If you imagine bringing these objects closer and closer together what you end up with is basically a flattened event horizon on the sides closer to the two objects because they’re both trying to yank from the other one the point at which you have to exceed the speed of light to escape ends up getting closer to the black hole on the side where the two are closest to one another.

It ends up going out in a teardrop shape away from the center of the two systems. You can imagine basically two teardrops coming toward each other trailing the droppy bits to the outsides.

As they get closer and closer the event horizons flatten more on the side that are facing each other until they reach the point that you end up with one event horizon around both objects. It’s complicated and then once you start adding motion in, it gets even more complicated.

Fraser: You’re saying then that maybe it is theoretically a way you could extract something back out of a black hole. Hit it with a bigger black hole.

Pamela: Well, the problem is then where you get the extra force that gets the thing to come out and a third direction going.

Fraser: Right so it has to be able to use energy then to get out. You’re not going to get it just from the collision itself.

You would have to have something with an antimatter drive that is going to try and push at the right moment [laughter] to take advantage of this unique situation.

Pamela: Or something. The fact of the matter is in general, once something is inside the event horizon it is spiraling towards its death.

Bringing two black holes together you’re going to muck up the distribution of the event horizons and it is possible you’ll move one in.

It’s possible you can yank something around somehow but setting it completely free of the system – no. Not without extra forces.

Fraser: Justin Song from Chicago, IL asked: “Why is it so bright in the centers of galaxies if there are supermassive black holes that suck up that light?”

I know we’ve answered this question in various flavors before but this is an easy one, we’ll tackle it. So Pamela, there’s a black hole at the center of a galaxy, why is the center of a galaxy bright?

Pamela: Because there’s stuff in there other than the black hole that gives off light.

Fraser: Right, stuff waiting to die; stuff being mushed around the black hole.

Pamela: Stuff waiting to die. Even in our own Milky Way as you look towards Sag A stars – you look towards the constellation Sagittarius through all the dust and gunk between here and the center of the galaxy. The inner part of the galaxy is really dense with stars.

It’s that density of swarming stars that in normal galaxies makes the quark quite bright. In quasars in active galactic nuclei that center is even brighter because you have an accretion disc in there that could potentially be so dense that it is undergoing nuclear reactions.

Even if it is not, it is being frictionally heated and generating its own lights. So, it is stuff waiting to die that’s giving off a lot of the light.

Fraser: The black hole itself – it is totally black. Everything around the black hole – we use that analogy of the water going down the drain, right? There’s only so much water that can go down the drain of your bathtub and the rest of the bathtub water starts to spin around the drain waiting for its turn to go down the drain.

The light that we see from the center of a galaxy is that stuff waiting for its turn to be destroyed by the black hole. Black holes are greedy but they’re just only so greedy.

Pamela: Just to make it clear though the center of our galaxy is bright because there is lots of stuff happily orbiting there.

It is waiting to die because everything dies eventually but it’s not necessarily all going to fall into the center of the supermassive black hole.

Fraser: That’s the difference between an actively feeding black hole and a quiet black hole. I guess the center of galaxies there is just a lot of stuff there. There’s a higher concentration of stars, more stars, brighter.

Pamela: It’s like looking at the downtown district of a city. Why is the downtown area so bright? Well there are lots of people with lots of light.

Fraser: Even if someone goes and turns off the lights at the biggest building downtown you’re still going to see all the other buildings. That’s a good analogy. We’ll go with that one.

Mario Massera asked (one of our favorite questions): “What’s behind a black hole? In other words if you go inside a black hole what will you see on the other side? What is on the other side?”

I guess this is sort of a two part question. I guess on the one hand Mario is asking let’s see, I’m standing and looking at a black hole and I orbit around to the other side, what do I see?

Pamela: The same thing.

Fraser: The same thing.

Pamela: Yeah, ignoring spin black holes are nice symmetric round blobs we don’t know what.

Fraser: [Laughter] Blobs of no light escaping, right.

Pamela: Exactly.

Fraser: So anywhere I want to look at it, what I’ll see is nothing. In fact I’ll see sort of a ring of light being pulled in towards it.

The second question is if I actually hop into the black hole what’s on the other side? Like the black hole is a tunnel and I go through my tunnel and I come out the other side, what do I see?

Pamela: You’re just dead.

Fraser: It’s not a tunnel.

Pamela: No it’s death. The big thing is black holes are just big things. They squish you a lot. They squish you to the point that your atoms are no longer atoms.

They’re some extra state of matter that we haven’t figured out how to define yet. So you’re just dead and a new form of matter.

Fraser: Once again helpful analogies, what’s on the other side of that blender? What’s on the other side of that trash compactor? What’s on the other side of that tree trimmer? [Laughter]

Nothing, horrible death is what’s on the other side of it. You won’t be able to get through the other side of that blender and really consider your surroundings.

All it is is a place where a black hole is just a place where things get squished together. Trash compactor, we’ll go with that. What’s on the other side of that trash compactor?

Pamela: Yeah, the trash compactor that never gets emptied, it just gets bigger.

Fraser: Right. That’s all the time we have for questions this week Pamela so we’ll talk to you again later.

Pamela: Sounds good Fraser.

This transcript is not an exact match to the audio file. It has been edited for clarity. Transcription and editing by Cindy Leonard.

Shownotes

Why are black holes black?

• “Why are black holes black? Though the history of the term is interesting, the main reason is that no light can escape from inside a black hole: it has, in effect, disappeared from the visible universe.”  — from Black Holes and Beyond by UIUC
• All about Black Holes – space.com
• How Black Holes Work — HowStuffWorks
• Pwn — Wiki

Can a huge mass of people jumping at once make the Earth wobble?

• Short answer: no
• Earth’s Mass: 5.9736×1024 KG

What’s so bad about space pollution anyway?

• Why Can’t We Launch Garbage into Space? — Universe Today
• Space Debris Illustrated:  The Problem in Pictures — Universe Today
• Universe Today’s Guide to Space : Space Junk
• Contaminating Other Planets — Science Friday (Radio show archive)

What measurements do astronomers use to measure distances in space?

• Lightyear = 9.4605284 × 10¹⁵ meters(distance light travels in one year)
  
• Astronomical Unit 1 AU = 149,597,870.691 kilometers (distance from the Sun to Earth)
• Parsec = 3.08568025 × 10¹⁶ meters (distance from the Sun which would result in a parallax of 1 second of arc as seen from Earth.
• Kiloparsec (kpc): = 1,000 parsecs
• Megaparsec ( Mpc) = 1,000,000 pc
• How are distances measured in space — Ask an Astrophysicist

How can we tell the difference between gravitational pull between objects and the expansion of the Universe?

• The Big Bang and the Expansion of the Universe — Atlas of the Universe
• Cosmological Principle: Universe is homogeneous and isotropic
• The Cosmic Void: Could We Be In The Middle of It? – Universe Today

Could energy condensed in a small space create a black hole with its own event horizon?

• Condensed Matter Physics
• Large Hadron Collider
• 5 Things You Need to Know About the LHC — Popular Mechanics
• Despite Rumors, Black Hole Factory Will Not Destroy Earth — LiveScience

If you had a flashlight in space and turned it on, could it propel you?

• How Light Propulsion Works – HowStuff Works
• The Momentum of Light
• Does light have momentum without mass? UIUC
• How Solar Sails Work – HowStuffWorks

How can you use degrees from Swinburne Astronomy Online and other online courses?

• Swinburne Astronomy Online
• A great list of other online astronomy degree programs

The closer an object accelerates to the speed of light, the more mass it has; if an object accelerates away from the speed of light it should loose mass.  Photons have no mass, so what happens?

• Is the speed of light constant?
• Do Photons have mass?
• Rubidium
  

If a black hole can have spin doesn’t that imply that the mass distribution inside has a finite radius and not a true point singularity?

• Anatomy of a Black Hole
• Black Holes Spin — GSFC
• Conservation of Momentum
• Black Holes Seen Spinning at the Limits Predicted by Einstein – Universe Today

Could we get the technology to look for planets around other stars and to see pictures of life on those planets and could they look back at us?

• Angular resolution — Wolfram
• The significance of oxygen
• New Technique Could Find Another Pale Blue Dot — Universe Today
• Moon Reveals How to Find Oceans, Land on Other Worlds – Universe Today

Transcript: Questions Show: Black black holes, Unbalancing the Earth, and Space Pollution

Download the transcript

Fraser Cain: Welcome to the AstronomyCast questions show where we answer your questions about space and astronomy. If you have a question for the AstronomyCast team please email it in to info@astronomycast.com and we’ll try to tackle it for a future show. Please include your location and a way to pronounce your name.

Hi Pamela, another batch of questions – let’s roll. Why are black holes black? Can a huge mass of humanity make the Earth wobble? What’s so bad about space pollution anyway? From Dave Johnson: “Why are black holes black?” So, are black holes black?

Dr. Pamela Gay: Yes.

Fraser: They are black, okay why are they black?

Pamela: Basically black is defined as the absence of all light. In the case of black holes, light can’t get through them. It can’t come out of them. They just sit there and to use an internet term pwning the light.

Light just can’t get away from them and without light being able to get away they can’t shine so they define the absence of light.

Fraser: Alright, that’s it. They won’t let light go so you don’t see any light and so you don’t see any color. You just see nothing.

T.J. from Ft. Worth, TX asked: “Let’s say in a hundred years there are ten times as many people on the Earth and a vast majority of them were to move over to one side of the planet. Would the weight of those people change the axis of the planet? Would that have any affect on the rotation of the Earth? Would the Earth get thrown out of orbit and go hurtling through the cosmos?”

Let’s imagine a hundred years there’s ten times – so we’ve got 60-70 billion people and they all move over to one side of the planet would that significantly change the rotation of the planet?

Pamela: No. Your typical average not overweight American is about 60 kilograms in mass. The planet Earth is six times ten to the twenty-four kilograms in mass.

When I opened up the calculator on my computer and did 60 billion times 60 and divided it by six times ten to the twenty-four, my calculator came back and said zero. It’s such a small percentage of the Earth’s total mass that it has absolutely no affect on anything.

Fraser: I think there are probably mountains that weigh more than that.

Pamela: Yeah, pretty much.

Fraser: You can’t say nothing because everything has an effect. If you did gather that many people over it would have an affect. It would just be impossible to measure. An impossible to measure number wouldn’t throw the Earth out of orbit.

Pamela: It would be a negligible effect. It’s sort of like the difference in your mass between now and the half a second from now when a grain of dust has settled on the tip of your nose.

Fraser: I think that question of could you throw something out of orbit is even interesting. If you somehow found three more Earths and glommed them onto the size of our existing Earth that would affect our rotation but would it affect our orbit?

Pamela: It wouldn’t actually affect our orbit; now if you whacked the Earth with them.

Fraser: No, no gently sort of pack them together like a bunch of snowballs.

Pamela: Right so say that you had four or six – six is probably a friendlier number – you had 6 more Earth-massed objects that come in and gently attach themselves to the planet Earth. Coming in exactly on the x y and z plus and minus axis so all the momentum cancels out.

If you had this miraculous absolutely no transfer of momentum, no forces, everything sums to zero the Earth plus 6 more Earths would continue orbiting the sun exactly the way we’re orbiting it now. Our mass actually has absolutely nothing to do with it.

Fraser: So where the mass moves over to has no affect. Nothing can kick us out of our orbit from on the Earth. It would have to be some body hitting us from outside the Earth.

Pamela: Right. Some sort of a force would need to be imparted upon the planet with violence.

Fraser: Jordan Jamison from Nashville asked: “Why is pollution in space bad? It’s better than polluting the Earth, right? Aren’t there much worse things in the universe than a relatively small amount of Earth metal, plastics and anything else we might leave? What’s the worst that could happen if we shot our trash to the sun or out into the depths of space?”

Pamela: Trash into the sun actually isn’t all that bad of a thing in terms of just wow, okay that’s one way to get rid of really nasty polluting awful chemical things.

Fraser: That’s also one way to really spend your money.

Pamela: Yeah, it’s kind of expensive. It’s also one of these things of eventually we’re probably going to have to mine our garbage dumps to get resources from them. We only have so many easily accessed resources on the planet Earth.

Everyday we throw away metal. Everyday we throw away rare elements just in our old cell phones, old computers and even the nails in our shoes when we toss them out. Someday that may be necessary material.

If we start shooting all of our garbage off toward the sun, we’re going to be depleting our planet of natural resources. So, yeah garbage is horrible. It smells bad, looks bad and takes up real estate that could be used for other more interesting things.

Someday we’re going to need that stuff. Let’s keep it. The organics will recycle themselves, the metals at least we’ll know where they are. Recycling is by far the best thing anyone can ever do.

Fraser: I actually did an article about this about a year back. I actually did the math. The U.S. produces 208 million metric tons of garbage every day. I figured out that to launch that would cost about 208 trillion dollars a day to launch the garbage.

It worked out to about 5,800 times the United States gross domestic budget just to launch trash into space – all of its trash that it generates. I think the issue is if you fire garbage into the sun, great you’ve gotten rid of it and it is no problem. The sun doesn’t care. The sun has all that stuff already and it will dismantle the chemicals, no problem.

It’s outrageously expensive so it’s not really a great idea. I think when they talk about space pollution we really think about the stuff right around the Earth which is colliding and crunching into each other and breaking up into smaller pieces. Really it’s a risk for astronauts. It’s a risk for the vehicles that we launch out.

Every time the space shuttle comes back down from space it’s got little nicks and dings. A lot of times they have to move the International Space Station or the space shuttle because some glove is going to be coming within [laughter] a kilometer of the space station and they have to move it a little bit to make sure that it’s safe.

The thinking goes that the more junk that gets up there the more cluttered the area is going to be and the more chances there are that something is going to get hit catastrophically. It would really be awful if the astronauts were killed because somebody didn’t clean up their garbage very well.

Pamela: A lot of people will say well space is a big place. So are the oceans of the world and any of you who have ever gone out on a ferry or on a cruise ship there is garbage everywhere. It’s really discouraging to for instance when I’ve taken the ferry from Bar Harbor to Nova Scotia, you’ll be out where you can’t really see land and there are soda bottles everywhere.

If we can manage to systematically cover our oceans in garbage it’s not that hard to systematically fill the space around our planet with garbage. While a cruise ship versus a soda bottle the ship wins, in space you’re dealing with much larger velocities. That soda bottle-sized chunk of satellite that hits the U.S. space station could destroy it.

Fraser: I think the last issue is that a lot of people are worried about spacecraft and stuff from Earth happening to land on Mars or Europa or any of the icy moons around Saturn. The risk here is that life on Earth could contaminate these places.

You might get some bacteria that hitched a ride on a spacecraft, made its way maybe over a million years slowly orbiting the solar system happen to crash land on Europa. It might negatively affect the environment there. While that’s a long shot of course, why take chances?

Pamela: We are our own worst enemy in some ways. We could create biohazards and go off and start all sorts of interstellar inbreeding of bacteria. Yeah, it’s just not something to do. We avoid it as best we can.

Fraser: Lynn Long asked: “What are the measurements astronomers use to measure distances in the universe other than the speed of light?”

Do astronomers use the speed of light as a measurement? I get light years, right?

Pamela: Right. In general we use the speed of light to create our meter stick. Light goes this far in a nanosecond, it goes this far in a day, and it goes this far in a year. You know human beings don’t think in terms of the speed of light.

We do things like within our solar system we measure things in terms of astronomical units. That’s the distance from us to the sun. We also in space tend to measure things in a distance called a parsec. One parsec is a little more than 200,000 times the distance from the Earth to the sun.

Then we just start throwing words in front of it. We have things like kilo-parsecs which is a thousand parsecs. We have mega-parsecs which is a million parsecs.

You can still if you dig through the literature occasionally find really silly to my mind references to huge distances measured in centimeters just because the math doesn’t care.

Fraser: Right this is the number of ten to the power of 27 by all means do it in meters or whatever. It makes the math easier.

Pamela: We don’t generally use feet or miles but everything from centimeters to astronomical units to kilometers to mega-parsecs. All these different things are fair game.

Fraser: There you go. Ahmed Arsen from Chicago, IL asked: “How can we tell the difference between everything being slowly pulled towards a large unseen mass by gravity versus the universe expanding?”

I guess because we see all of these galaxies moving away from us the theory goes that this is the result of the big bang and the universe is expanding. How would that be different from these galaxies it’s almost like they’re sliding off a table towards some mass and that’s why they’re pulling away from us?

Pamela: We can’t actually tell this difference. This is actually one of the new questions that have recently come up. It’s possible if our universe is small enough and you believe in amazing coincidences. If all the right things lined up we could be in the center of basically a bubble of mostly empty universe.

The other stuff in our mostly empty section would be attracted outwards toward things that we can’t see. It’s that gravitational mass of the higher density parts of this giant universe that could exist that things could be attracted to. That could happen. It’s a void hypothesis.

I personally have some problems with this because it does require a huge coincidence. It requires that there is a void that we are roughly centered in that’s at least the size of the visible universe. If we’re not centered in it, it’s absolutely huge. It can incorporate everything in the visible universe.

Fraser: That would be almost like imagine you took a whole bunch of marbles and you put them on top of a beach ball and held one at the very top and let go of all the other marbles. They’re all going to roll away down the hill of the beach ball.

The marble on top is going to say everyone’s moving away from me! I’m at the center of this. That would be true, right? Those marbles all would be moving away from you. That says I guess I’m at the center of the universe. I’m important.

Pamela: [Laughter] Right and just the whole coincidence of it all that it is more than just the expansion of the universe. This is actually the acceleration of the expansion of the universe and is caused by this freak alignment.

That’s a bit hard to stomach when so many of us have spent our entire careers teaching okay they used to think the Earth was the center of the universe but it’s not.

Then they thought the sun was the center of the universe – but it’s not. Then we thought the Milky Way – again it’s not. This would suddenly have us going but we are the center of this giant void. That just is uncomfortable.

Fraser: I guess the solution to that then is to very precisely measure the speed that things are accelerating away from us to see if there is some kind of asymmetry.

Pamela: Asymmetry.

Fraser: Yeah, a lack of symmetry. Then if it is perfectly symmetrical you can feel pretty comfortable that we’re not at the center of anything. If it is asymmetrical then you can say wait a minute it’s kind of weird.

Pamela: We need more supernova observations in all directions so that we can systematically recreate the measurements of the expanding universe more importantly the accelerating expanding universe along many different directions.

Fraser: Krishna from University, MI asked: “Einstein showed us that matter and energy are two sides of the same coin. Does that mean that energy itself if made to condense in an extremely small space can form a black hole with its own event horizon?”

Whoa.

Pamela: Yes.

Fraser: Yeah so if you could squeeze energy down you could make a black hole.

Pamela: In fact the Large Hadron Collider produces enough energy to do this. That’s kind of cool. We can do this with stuff here on the planet Earth we think.

Fraser: Wow, that’s pretty crazy. That’s when they talk about how the Large Hadron Collider is going to be creating black holes.

It’s going to be taking the energy of the particles that it’s smashing together and it will generate enough energy in a small enough space that it will in theory make a teeny weenie black hole for a second.

Then it will dissipate. It’s not even theoretical, it’s like we’re gonna do it.

Pamela: What’s cool is these black holes would, we believe decay very rapidly. This might be that final little bit of experimental evidence that’s needed to give Hawking a Nobel Prize. That would be cool too.

Fraser: I think he totally deserves one so that would be great. David Biltcliff asked: “If you took a flashlight into space and turned it on would the light coming out push the flashlight?”

I guess could it push you? Could you use it as a little propulsion system if you’re out in space?

Pamela: Yes you would just get propulsed – if that’s a word – very, very slowly. In fact you don’t even have to be in space. It’s just here on the planet Earth the friction is a bit much to overcome.

Anytime you emit light in one direction you create a force in the opposite direction. This is a serious problem with some of the big mega-lasers that they build here on the planet Earth.

We have the pettawat lasers for instance that some of the military and research facilities here in the United States when they fire those lasers it makes the entire building shake.

This happens because you have light momentum going in one direction and conservation momentum trying to push the laser in the opposite direction.

Fraser: We don’t want to make people do math but what is the calculation that you might want to make for how much force you’re feeling?

Pamela: The way to look at it isn’t so much with force as with momentum. You have your energy going in one direction at a velocity you know. Take that energy, convert it to mass using the whole e=mc² thing. Use the speed of light and get the velocity.

Then figure out the momentum of that light going in one direction. Then look at your own mass and solve for what velocity you might end up going in the other direction. It’s kind of sad, pitiful.

Fraser: You would be able to calculate at least how much force it’s emitting back on to your laser or your flashlight while you’re in space.

Pamela: Yeah.

Fraser: That’s how a solar sail works right? A light beam striking the solar sail imparts a force as well.

Pamela: It’s all in something had to either stop moving or get absorbed and the velocity and the momentum imparted by that had to go somewhere.

Fraser: Yeah. You’re going to love this next question. Conley Deacon from Brisbane, Australia asked: “My son is only 8 and recently asked me to explain what e=mc² means as it has been on the wall at school this term. I have enough trouble understanding relativity and anything mathematical that I am unable to explain to him that he will understand. We don’t want to put him off astronomy for good so can you help me?”

Okay Pamela, can you explain e=mc² to an 8 year-old?

Pamela: I hope so.

Fraser: Maybe I should get Chloe to come into the room and have her just like [laughter] watch us and then if she gets it she can give you the thumbs up.

Pamela: Here’s how I look at it. Energy and mass is the same thing with a constant. One good way to look at it is if you want to have a bowl of jello you need water and powder. There’s always the same ratio between the jello and the water.

The constant that allows you to get from the water to the jello is the box of powder. Jello and water, same thing with a constant that causes them to change basically you go from liquid to mostly solid stuff.

With e=mc² the constant that allows you to figure out how much energy can you get out of this mass is the speed of light squared. It’s just a constant, it’s a special constant but it’s just a number.

The way you’re able to figure out how much jello you get out of a thing of water is you have to multiply it by the of powder. Does that work?

Fraser: I think I get it but then I sort of went into it. I think what you’re driving at is that matter and energy are two sides of the coin – they’re the same thing. They’re just two different ways to look at it, right?

Pamela: There’s always this multiplier of if I mixed water a larger amount with a box and a half of powder I’ll get more jello.

You always have to have things in the exact right amounts. If I mix half as much water with the box of powder I don’t get jello.

Fraser: Right you get very weak jello.

Pamela: [Laughter] You get slime going across your counter.

Fraser: Let me take a shot at it too. I think that if you could take matter, anything, sugar cubes and you could convert that into pure energy that would be like nuclear bombs going off. That would be like electricity to run your house. That would be pure energy, rocket launches.

The e=mc² just tells you how much matter, if you take a sugar cube how much energy you’re going to get out of that. Matter, energy, what’s the number? If you have a car it will give you more energy. If you have a sugar cube it will give you less energy.

I think the most amazing thing is how much energy, because the speed of light in the calculation is so big. You get an enormous amount of energy out of that transformation.

Pamela: Last time I ran the calculations, admittedly New York City was a bit smaller but we were also more energy polluting, but the last time I ran the numbers you could power an entire city off of the energy in basically one potato’s worth of mass.

Fraser: Mark Fritz asked: “Can you offer any advice on Swinburne or any other astronomy programs available? I’m looking for something that is more technical and mathematical.”

Mark already has a PhD.

Pamela: And it’s in the form of engineering.

Fraser: In engineering, yeah. Swinburne – we should disclaim that Swinburne is a sponsor of AstronomyCast.

Pamela: Also I’m one of their instructors and have been one of their instructors since 2000.

Fraser: Right.

Pamela: So we’re fully .

Fraser: Absolutely. Working with Swinburne, anything we say about Swinburne should be taken with a kilogram of salt [laughter] which could then be turned into energy.

Pamela: All of that said, I keep running into past students at science conferences. They’ve gone off, they’ve done great things. They’re still involved in the community in a variety of ways.

They’re mostly involved in the community either teaching at community colleges, working at science centers, working in education and public outreach with a few exceptions. There are some amazing exceptions.

The majority of people who go to Swinburne Astronomy Online are getting a degree because they want to do outreach in education work, not because they want to be research astronomers.

As someone who has a strong technical and mathematical background a terminal Masters Degree designed to help you teach astronomy to non-majors might frustrate you because it will teach relativity from a conceptual standpoint with math.

It won’t go into all of the hard-core math that you need if you’re going to become a researcher in relativity. If you’re looking for the level of mathematical rigor that you’d get in courses that are designed for people who might potentially go on to become researchers in each of those fields versus people who are interested in learning about it and interested in being able to teach things at a popular level and communicate it very effectively to the public so they understand it.

If you want that extra level of mathematical rigor, check out your local state university. There are a lot of universities – my own being one of them – that offer their graduate courses as night courses so that the graduate students can teach classes during the day and do research during the day.

Fraser: If you already had a PhD in a math-intensive area something like engineering, you’ve got to be pretty close to being able to then turn around and go get your PhD in astronomy or astrophysics.

You don’t have to go back from square one, right?

Pamela: No but you do need to go back to day one of graduate school. There is a lot of content knowledge where once I hit graduate school I didn’t take any more math courses except on how to statistically analyze my data. That was a very specialized stats cap class.

Other than that I was doing things like the quantum mechanics of the interstellar media, evolution of galaxies, stellar atmosphere, and stellar evolution. All of these things from a very detailed take the courses you learn as an undergraduate that are general across all of the physics, astronomy and engineering majors and apply them very specifically to astronomy.

There are series of courses that pretty much all astronomers end up taking at the graduate level with varying levels of mathematical rigor depending on what your goal is. People who are going into astronomy education research or education public outreach or people who are going into science communications need enough mathematical rigors to understand the concepts of their core.

They don’t need that extra layer of mathematical rigor that you need if you’re then going to be applying those concepts to going in new directions that no one else has ever gone before. It sounds like Mark might be interested in that extra evil step of okay let’s figure out how to do things no one has ever done before.

Fraser: Would you think he would have to go back to get a new Masters or do you think he could just start with his Doctorate?

Pamela: He’d need a new Masters. Unfortunately in fact astronomy is pretty evil in general where say I had after I got my Masters at the University of Texas had I wanted to go to the University of Arizona to do my PhD, nine out of ten times they’re going to make me redo my Masters.

Masters aren’t generally transferable. You start over. It’s kind of sad but that’s the way it is.

Fraser: Something like Swinburne might be a little more not mainstream I’m trying to think. There’s more focus on outreach and education and rounding you out to be a better communicator for astronomy and teaching what you’re already doing.

You really would need to go back and redo the Masters and redo your PhD switching from Engineering over to Astronomy. That would be like how many more years? Another 2 years for your Masters and another 3+ years for your PhD?

Pamela: Yeah.

Fraser: Another five years at least to get a PhD in astronomy.

Pamela: It’s more typically six to eight actually.

Fraser: [Laughter] Right.

Pamela: It’s kind of bad.

Fraser: Would any of the courses that Mark has with a PhD in engineering be applicable to astronomy?

Pamela: At the graduate level? Only if you wanted to build instruments.

Fraser: Okay, so, Swinburne or go get another PhD. Rack ‘em up.

Pamela: It’s fun. That’s what the astronauts do.

Fraser: Next question comes from Nathan Dye: “I know that the closer something accelerates towards the speed of light the more mass it has. It seems to make sense then that an object that accelerates away from the speed of light loses mass. But photons have no mass and they travel at the speed of light. If a photon is slowed down it can’t lose mass so what happens?”

Can a photon be slowed down?

Pamela: No. They’re quite nice about traveling at the speed of light. There is a caveat here and that is speed of light changes depending upon what media you’re going through.

Fraser: Right so vacuum or atmosphere or water a glass or some ruby crystal.

Pamela: Yes so if you want really slow moving light shoot it through some sort of Iridium gases. Once you compensate for the fact that the speed of light changes from media to media the speed of light is the speed of light is the speed of light.

You can’t slow down photons except by changing what they’re moving through which doesn’t actually change their mass.

Fraser: So, can’t slow them down, so don’t worry about it. Joe Conti from Newton, MA asked: “If black holes can have spin doesn’t that imply the mass distribution inside a black hole has a finite radius and not a true point singularity? So if it was a true point singularity could it not have spin because it doesn’t’ have a radial dimension? There would be nothing to spin.”

Okay I guess this is the question that’s like what is a black hole deep down inside? Is it a singularity where mass is continuing to compress down infinitely small or does it sort of gets to some small size and then just stop into some new exotic form of compressed matter? Would there be a difference between whether those things would spin? Do we know that answer yet?

Pamela: No we don’t. We do know that black holes can spin. In the case of a singularity, it’s actually they’re dragging space time around. You can end up basically twisting up space time which is kind of cool.

What’s spinning is everything. Space, time, frame of reference, everything is getting squinched up and it actually ends up changing the shape of the event horizon depending on how fast it is rotating.

Fraser: Black holes definitely spin. I know that we’ve done a bunch of articles about supermassive black holes that are spinning at the limits predicted by Einstein.

Einstein said here’s how fast a black hole should be able to spin and what do you know, astronomers have found them. Einstein – right again. They’re spinning but how do they know that they’re spinning?

Pamela: We know that black holes are spinning because of the effects of the interface between the event horizon which would be spinning with the black hole and the stuff that’s falling into the black hole.

Depending on the rate of rotation of the black hole itself and the frame of reference around it and everything else it’s able to do neat and interesting things to the accretion discs around it. The way to think of it is if you stick a blender into the center of a thing of cake mix – apparently I’m hungry while talking about this episode – if you stick a cake mixer into the center of a thing of non-moving cake batter and you turn it on and start it rotating first the center is going to start rotating.

Then frictionally it will cause more and more of the cake batter to rotate until pretty much you get this nice rotating cake batter. It’s rotating faster at the center than it is out at the edges. We see the same thing with material falling into a black hole where at the very center the rate at which it’s rotating has to do with the rate at which the black hole is rotating.

Fraser: The fact that we see a black hole spinning doesn’t tell us whether it’s a singularity or it’s some small ball of exotic matter.

Pamela: No.

Fraser: Either one could spin.

Pamela: Yes.

Fraser: Even if a singularity has no width it can still spin.

Pamela: Yes.

Fraser: There you go. The conservation of energy has to happen. The conservation of momentum has to happen. Adam Cordova asked: “We’re seeing light from stars emitted four to13 billion years from the time they were emitted and so then the reverse would be true. From other vantage points our sun is being observed in the past. Could we get the technology to observe planets around other stars and look for evidence of life? Could other civilizations look at us and see evidence there’s life here and even see it in the past?”

Yeah we know that astronomy is a great big time machine. Any star that we look at we’re just looking at what that star looked like in the past. If we look for the light we’re seeing the universe as it looked at that point in time. If you’re looking 12 billion light years away you’re seeing the universe just a billion and one half years after it was formed. So, could we see cities on other planets?

Pamela: No.

Fraser: Like not ever, or just not today?

Pamela: Probably not ever because this is where you start getting into the finite speed of light problem. You need to have such high angular resolution that you’re starting to talk about putting two different spacecraft so far apart trying to image the exact same thing that it’s no longer really useful. Just trying to communicate with the two satellites, get everything lined up it’s just not going to happen.

That said even though we can’t feasibly start looking for individual cities on the surface of distant worlds what we can do even today is start looking at their atmospheres. Right now with little tiny planets we’re not going to really be able to even find them.

With Jupiter-size planets that are close enough into their stars we can start looking at their atmospheres and measuring what’s the composition of the atmosphere. We look for pollution. We look for the signs of organics. We look for loose oxygen.

Oxygen is produced by plants and doesn’t tend to hang out by itself in the atmosphere unless it’s being readily produced on a regular basis. The other thing we can do that’s a bit sad is if the alignments are just right we can start looking for light pollution from other planets. [Laughter]

We can start looking for planets that when we look at them they’re giving off more light than they should. That might be a way to be able to say aha, I found something that appears to have cities on it.

Fraser: Maybe even match it up to additional light to continents and map out the continents. I think once again you’re being trapped by boring reality [laughter] and you’re not really thinking this through to its logical conclusion.

It would be hard but not impossible just hard if you filled the solar system with spacecraft and figured out a way timing perfectly to have an image with a great big telescope you could get some pretty cool angular resolution.

Maybe you would even see something on Alpha Centauri. Maybe the image of the planet’s surface if there’s a planet there. If you could wouldn’t you be seeing what life was like on Alpha Centauri four years ago?

Pamela: If you could overcome all the technical difficulties and all the time lags and everything else including

Fraser: It’s done, I just did it.

Pamela: Okay. If you can overcome all of those difficulties and get the spacecraft far enough apart yet you could image stuff on the surface of other planets given large enough telescopes.

Fraser: You would see it in the past?

Pamela: Yes.

Fraser: Right and so let’s say that the poor folk on Alpha Centauri for some reason lost their history couldn’t we looking at their planet right now be able to record it and go oh well here’s what happened four years ago if they came and asked us.

Pamela: [Laughter] If we knew that we needed to do that.

Fraser: If we knew that we needed to, right, of course. Once again information has to travel the speed of light so they have no way to tell us that they needed us to make a back-up for them. The further out we look a hundred light years away we’d be looking at planets imaging their surface a hundred years ago.

Pamela: Using an even bigger telescope.

Fraser: An even bigger telescope, yeah whatever. It’s the size of ten solar systems whatever. Here, done there I just imagined it so it’s real. The technical problems obviously are staggering, astonishing and a much easier feasible solution is to look for chemical compounds and measure amounts of light and all that.

There are some really amazing research articles being done. I try and write these up whenever I see them. They are really cool ideas on how you might recognize that there is life on a world. They figured out ways to map out the continents and the oceans by the reflected light bouncing off of a moon going around a planet.

As you say, chemical ways to say if you see this chemical compound it has to be pollution. It has to be an industrial civilization. There’s like no other way that could be in the atmosphere of that planet.

You don’t need to see a city. You don’t need to see a car if you see the right pollution in the atmosphere which you could see with a telescope then that’s all you need to know. There are cars, alien space cars but it’s got to be pollution.

Pamela: They’re burning up the same nasty hydrocarbons we’re burning up here on Earth.

Fraser: Then someday they’ll build some ridiculous telescope and really be able to see even better and better. They’ll just look further and further out. I think we’ve run to the end of these questions so we’ll talk to you next time Pamela.

This transcript is not an exact match to the audio file. It has been edited for clarity. Transcription and editing by Cindy Leonard.

Shownotes

Could we transfer our consciousness to robots so the human race could survive the destruction of the galaxy and the heat death of the universe?

• Robot Power Regulations – Society of Robots
• Tutorial:  How to Build a Robot — Society of Robots
• Ep. 86 End of the Solar System
• Ep. 87:  End of the Universe

If galaxies are near to each other, will they orbit each other or collide?

• Colliding Galaxies — UTK
• Dwarf Galaxies Orbiting the Milky Way — PhysOrg
• Tidal Tails are ‘Skid Marks’ from Famous Galactic Collisions – Universe Today
• Binary Galaxies – Caltech
• Ep. 26: Largest Structures in the Universe discusses colliding galaxies.

If solar radiation is a problem on Mars, isn’t it a bigger problem on the Moon?

• Radiation levels on the Moon and Mars — Health Physics Society
• Radiation on the Moon — Universe Today
• Problems with solar flares for people on the Moon — Science@NASA
• Standards for Protection Against Radiation — US Nuclear Regulatory Commission
• STEREO Mission
• Study of Radiation Doses Experienced by Astronauts on EVA — NASA
• Radiation Dose Limits for Astronauts (paper, subscription required) – Radiation Safety Journal

If I were located on one of the most distant galaxies from Earth, one  that is only exceeded by the Cosmic Microwave Background, what would the sky look like?

• Cosmic Microwave Background — NASA
• Ep. #5 — The Big Bang and the CMB

Why didn’t you mention Herschel in Ep. #132?

• Herschel website
• Ep. #132: Infrared Astronomy

I see pictures of stars with bowshocks around them.  Does our sun have one?

• Hubble image of bow shock around LL Ori
• Bow shocks – Wiki

I’d like to pursue a career in science journalism — suggestions?

• All about Pamela Gay (from Star Stryder)
• Pamela’s Wikipedia page
• Astronomy Magazine
• Sky and Telescope
• Knight Science Journalism Fellowship
• Carnival of Space
• Fraser’s story
• Universe Today’s 10th anniversary story
• Fraser’s Wikipedia page
• Science journalism:  Supplanting the Old Media? –Nature

Would geostationary satellites work on other planets?

• Geostationary Orbits
• Rotation of Mercury
• Retrograde rotation of Venus — Universe Today
• Rotation of Saturn — Universe Today
• Rotation of Jupiter — Universe Today
• Mars’ Rotation — Universe Today

The Universe is expanding at an ever greater rate, so doesn’t this constitute adding energy to the Universe?

• Dark Energy — NASA
• Dark Matter — NASA
• Energy for an Expanding Universe — Department of Energy “Ask a Scientists”

If the redshifting of light indicates all matter is moving away from us, how do galaxies and superclusters collide?

• How do galaxies collide in an expanding Universe? — Cornell U
• Why do galaxies collide if they are moving away from each other? –Naked Scientists Forum

Shownotes

How can I find a Galileoscope?

• Galileoscope website
• IYA

Does time stop inside a black hole?

• Time in a black hole – Ask an Astrophysicist website
• Does time slow down near the event horizon of a black hole? — Ask an Astrophysicist
• The Anatomy of a Black Hole –UIUC
• Interactive Anatomy of a Black Hole — Think Technologies
• Nancy Atkinson (hi everyone!)

What exactly is energy?

• Energy - Wiki
• The different forms of energy — NMSEA

Can energy be converted back to matter?

• Can energy be converted to matter — Newton Ask a Scientist
• Large Hadron Collider
• The End of Everything -- Universe Today
• Episode #87:  End of the Universe, the End of Everything

Why don’t we put space telescopes like the Hubble or JWST on the International Space Station so that it would be easier for astronuats to service them?

• Vibration Isolation systems for the ISS
• Google book:  Guidelines for Noise and Vibration levels for the Space Station — National Research Council
• ISS
• Hubble Servicing Missions
• James Webb Space Telescope
• WMAP

Is there a limit to how far in space we can see?

• Cosmic Microwave Background — U of Chicago
• Can we look far enough back in space and time to see the Big Bang? – Cornell U

Why can’t the most powerful photons like gamma rays and X-rays make it through our atmosphere, but on Earth we need lead to protect ourselves from them, while less powerful photons like light come through the atmosphere but can’t make it through a piece of paper?

• Gamma rays coming through the atmosphere – Ask an Astrophysicist
• Solar EM Radiation in Earth’s atmosphere (about 1/3 of the way down the page) — Windows to the Universe
• Ep. 132 — Infrared Astronomy
• Ep. 133 — Optical Astronomy
• Ep. 134 — Ultraviolet Astronomy
• Ep. 135 –X-ray Astronomy
• Ep. 136 — Gammy Ray Astronomy

We’ve heard about the tidal heating of Europa, Enceladus and Io, but how much of Earth’s internal heating is due to lunar and solar tidal forces, and how much is due to radiation energy and heat left over from the Earth’s formation?

• What heats the Earth’s core? –Penn State
• Radon — Wiki
• Tidal Force — Hayden Planetarium and Neil de Grasse Tyson

Questions Show: Galileoscope, Black Hole Time, and What Exactly is Energy?

Download the transcript

Fraser Cain: Welcome to the AstronomyCast questions show where we answer your questions about space and astronomy. If you have a question for the AstronomyCast team please email it in to info@astronomycast.com and we’ll try to tackle it for a future show. Please include your location and a way to pronounce your name.

Hi Pamela, more and more questions. [Laughter]

Dr. Pamela Gay: They just won’t stop coming.

Fraser: Oh and I just wanted to give you a quick prop. There was a recent review of astronomycast on iTunes which was wonderful. Thank you everybody who has been sending them.

We may have like 600 and something. Someone said sometimes the shows seem a little scripted. I just want to make it clear – there’s no script.

Pamela: Yeah.

Fraser: We’re too lazy for scripts. That would be work. In many cases you have no idea what I’m going to ask you.

Pamela: No. I have absolutely no idea.

Fraser: In some cases we fix when we go down in some wild goose chase in editing and maybe we’ll re-record. But most of the time it’s one cut. I’m asking whatever I want and you are answering them from your vast repository of knowledge which I think is amazing. There’s no script.

It’s time to test you one more time. How can you get a Galileoscope of your very own? What happens to time inside a black hole? What exactly is energy anyway?

The first question comes from Chris Lingre “Fraser and Pamela mentioned a $15.00 telescope in a question show. What are they talking about? I haven’t been able to find one and had no luck locating one online.”

What are we talking about? We’re talking about the Galileoscope.

Pamela: Yes. This is a wonderful project that comes out of the International Year of Astronomy. A group of entirely volunteer folks sat down and designed an amazing telescope that is being sold for about $15.00 plus shipping through galileoscope.org.

We’ll have a link in my twitter feed and the astronomycast twitter feed and as well as on our website. This telescope comes with a Barlow lens, two different eyepiece lenses. You can do all of the observations that Galileoscope did with it and you can do better than Galileoscope.

What’s really cool about it is with one of the eyepiece combinations you’re looking through a system absolutely identical to Galileo’s. Everything is upright. It’s really bad eye relieve, really tiny field of view. It’s just miserable and gives you a real appreciation for what Galileo was able to accomplish.

Take that out, replace the eyepiece and all of a sudden you’re seeing through this really nice 50X telescope. What’s cool is we’ve had Alan Nagler look through it. He actually put one of his really nice eyepieces on it and he was amazed by the view that he saw.

Some really good folks including Rick Fienberg, Editor Emeritus of Sky and Telescope, Steve Pompea of the National Optical Astronomy Observatory, Doug Erin up in Wisconsin, a whole team of people worked together, tested this.

Not only is it a really good telescope but if you’re a school teacher you can also take the telescope apart and use it as an optical bench. You have an optical kit. You have a diverse telescope that mounts on a standard tripod. It’s just a really nice system. Like I said, it’s $15.00 plus shipping.

Fraser: And we’ve both tried them out. I tried it out at the last AAS in winter in California and it was great. It was just great. We looked at Jupiter and we could see the moons of Jupiter. We could see bands on the planet.

You can see the rings of Saturn. You can see beautiful craters on the moon. We looked at the Orion nebula. This is the real deal, it’s a $15.00 telescope, and it works.

Pamela: You can use it with a webcam. It’s really lightweight so if you’re trying to mount a heavy camera on it, not so good. For a standard webcam for a lightweight digital camera it works excellent.

They’re awesome. Buy them for your entire school. That’s the cool thing about this. There are a lot of communities that have gotten together as a community and bought a telescope kit for every single kid in say the 6^th grade, in the 8^th grade when they’re still young enough to be interested and enthusiastic.

At $15.00 each you can host a local star party for a local classroom of kids and get the local supermarket to sponsor sending the kids home with the telescope they used at the star party.

Fraser: Definitely check it out at www.galileoscope.org and order one, ten, the more people can order then that can help bring the cost down for the volume and make them really stick around.

I think this is going to be a great way to just get more and more people involved and interested in astronomy. It’s the International Year of Astronomy. This is a great way to get involved.

Pamela: Just like with the one laptop per child, you can buy a scope for yourself and buy a scope for a kid in a third world nation that otherwise would never get to use a telescope. Buy one for yourself and buy one for someone you don’t even know and give them a chance to look up and see the stars.

Fraser: Awesome. We have our second question from Nancy Atkinson. If anybody doesn’t know who Aunt Nancy is, she’s a senior editor over at Universe Today and does a lot of the writing on the Universe Today. She actually does the show notes for Astronomycast and is the producer for 365 Days of Astronomy. She’s a part of the team.

Pamela: She keeps us sane. [Laughter] We couldn’t do this without her.

Fraser: Oh yeah. But her other job is a librarian and she got this question at the library. “Does time stop in a black hole?” Which I guess is a good question.

Pamela: It’s a really good question.

Fraser: Why would it stop? Why is it even possible?

Pamela: In the limit that velocity goes to the speed of light the speed of time goes to zero. This is a kind of squirrelly way of saying that the passage of time for someone who is traveling at the speed of light – which you can’t ever do – but if you were able to go at the speed of light – which you can’t do – then your watch would stop ticking.

Your perception of time as neurons in your brain fire would stop as well because well everything would stop for you. Since things can’t actually go the speed of light as long as they’re regular matter time will still exist.

The thing is we don’t know what happens to matter when it becomes part of the black hole. There is stuff falling in – it’s still normal matter. It’s not traveling at the speed of light. It’s just stuck inside the event horizon. Once you start to get to the physical stuff that makes up the black hole, it’s not regular matter in any way that we understand.

We don’t know how to understand it. We know that with normal matter you have regular stars. You collapse it down and it becomes degenerate gas and you get white dwarf stars. Collapse it down more and you get neutron stars.

Collapse it down more and we don’t know what it is. It’s a black hole and it’s made of stuff. We don’t know what to call that stuff because quantum mechanics and gravity don’t speak nice to each other so we don’t know what to do.

As long as the stuff is stuff with mass it’s not traveling the speed of light. It still has some perception of time. It’s probably really slow because we’re dealing with gravitational red shifts.

We’re dealing with it is moving fast before it goes splat. If it becomes pure energy somehow, energy is light and light travels at the speed of light. Light does not experience time so if stuff that becomes part of a black hole becomes pure massless energy then time can stop.

Fraser: I guess part of it though is we don’t even understand does the contraction inside of a black hole ever stop, right? One idea is that the black hole is just some super exotic matter that just sits there and more gets munched on top of it.

It’s very small and very dense but we don’t really know what it is. Another theory is that it’s a singularity that it never stops collapsing.

Pamela: Right and we don’t know.

Fraser: We just don’t know. Good, we don’t know. Moving on, Robert Elms from Brisbane, Australia asked: “Can you please spend a few minutes to explain what exactly energy is?”

The universe is filled will all types energy including matter which we mention is frozen energy. Okay so let’s just deal with that. What is energy?

Pamela: That is one of the hardest questions. We were actually back the first year we were recording astronomycast on a morning radio show in Australia and they asked us this question and we stumbled over it for a while.

At the end of the day the best definition I have for what energy is would be it is something that can do work. It is something that can change direction. It is something that can change velocity. It is something that causes things to happen.

That’s rather unsatisfying but that’s really at the most general level. Energy creates light, causes vibrations, increases velocity and changes the direction of velocity. Energy does all those things.

Fraser: We can have potential energy which is just a rock sitting on the top of a hill, waiting to do work. It has energy in the system. If you let it roll down the hill and if you ignore friction, the waiting energy will turn into moving energy.

Then when it crunches into something it will turn into other kinds of energy. So, it is the ability to do work. I think then Robert is trying to ask “But what is it really?”

Pamela: [Laughter] that’s a question for a philosopher. At some point we need to store up all these questions and find a philosopher and hold them hostage.

Fraser: Naw, a philosopher would be no good to us. But so a photon is energy, a rock sitting at the top of a hill has energy. An elastic band stretched out has energy.

Pamela: The gas in the room that each of us is in – the gas that we’re breathing – it has energy.

Fraser: Yeah, now Robert has sort of a second question which is: “Can energy be converted back to matter?”

Pamela: Yes.

Fraser: It can?

Pamela: Yes. This is actually what happens in particle accelerators. You take two protons or two particles in general – you can do this with all sorts of different particles depending on which accelerator you use – but in general you can take two protons and get them in circles really fast in opposite directions.

One is going clockwise the other is going counterclockwise doing parallel donuts, going really, really fast. Then using magnetic fields you change their paths so they collide exactly head-on.

That’s what is really amazing is they can take two protons, accelerate them to a significant fraction of the speed of light and then get them to hit head on into one another. That’s just cool.

In the process of accelerating we’ve given them kinetic energy. The faster they go the more kinetic energy they have. Kinetic energy is defined in the classical sense as one half the mass times the velocity squared.

When they collide they come to a sudden grinding halt. In the collision all the energy that was in their kinetic energy as well as the energy that was tied up in their mass gets changed into all sorts of crazy stuff including in some cases we hope, the Higgs boson. This is what the Large Hadron Collider is hoping.

Fraser: But you get a shower of particles that are frozen energy. The speed of the particle – the velocity – gets turned into new particles.

Pamela: Yes, new particles that flash out in all different directions. We catch them in webs of fiber optics and we measure the velocity, their passage through the fibers. We measure their mass. We measure as many different things as we can.

Then we backtrack and put the pieces together and go aha, there was one particle here. That one particle decayed into these two particles and light. We’re able to reconstruct how the matter and energy flashed back and forth between having mass and being light and being both mass and light throughout the process of the collision and the shower of particles and the decays that follow after.

Fraser: Right now with our current technology all you can do is smash protons together and get a shower of particles. It is theoretically possible that you could smash particles together out could come trucks and puppy dogs and water and sandwiches.

Pamela: Right. At a certain level you and I are converting mass into energy every moment. We’re just not doing it via nuclear processes. We’re doing it via chemical processes.

Fraser: That’s the other way, right? That’s the opposite. We’re talking about how we’re getting energy turned into matter.

Pamela: Right that’s true.

Fraser: Then obviously we can turn matter into energy using a chemical process or just take antimatter and matter – put them together.

Pamela: That’s a bit violent but it works.

Fraser: Don’t you get two pieces of matter turning purely back into energy? [Laughter]

Pamela: Right you get two bits of mass – one matter and one antimatter – that if you have the right channel so electron and positron work really well at this. You collide them together and you get pure energy.

Fraser: Or a sandwich and an anti-sandwich. [Laughter]

Pamela: Exactly.

Fraser: Those will turn into pure energy. We can go from energy to matter and we can go from matter to energy and in a nuclear explosion, right? That’s matter to energy.

Pamela: Right.

Fraser: I guess Robert’s last question: “Will energy that exists today turn into matter or will matter turn into energy, or are we just kind of stuck with what we’ve got?”

Pamela: It’s a little bit of both. We use energy in all sorts of different processes. Some of the stuff that exists as energy today – that’s getting generated and a star getting generated, nuclear processes – some of that energy is going to freeze out into different particles eventually.

At the same time when you look really long term, when you look at the inevitable death of the universe – which has to come up once per episode – one of the things that a lot of particle theorists think may be true is that protons will decay.

This means that we’re looking at an eventual future where all matter decays. We’re left with basically a fuzz of energy spread out across this extremely, extremely large cold, cold universe.

Fraser: Right and so that might be the future that all the matter will just turn into energy and then it all gets spread out and that’s that. Energy – what is it? [Laughter]

Let’s move on. Mitchell Shyat from Oakland, CA asked: “Why can’t we just attach telescopes like Hubble or James Webb to the International Space Station or at least placed in an orbit nearby and that way if something goes wrong it could be fixed immediately?”

So, why didn’t they attach Hubble to the International Space Station somehow? The astronauts could just stick their eyes up right up to the eyepiece of the Hubble Space Telescope and take a look. [Laughter]

Pamela: People move – that’s the real problem. Because people do things like bump into the sides of the International Space Station and tap their fingers on the side of the station, the station constantly is vibrating.

The station has fans to control the air processing system. It has fans to control the waste processing system. It has all these different things that generate all sorts of different vibrations. All those vibrations would wreck images. You don’t want to attach telescopes to anything that human beings are attached to.

In fact when we build big observatories here on the planet Earth they’ll actually build the telescope on its own pier that isn’t attached to the building. There is usually an air gap of several inches all the way down through the center of these big observatory buildings between the floors that people work on and the actual pier of the telescope which goes all the way down to bedrock.

You’ll have this separate foundation for your telescope and for the building built around that telescope just to isolate the vibrations.

Fraser: You’re going to have heat coming off the space station which is going to cause problems. There’s going to be light pollution perhaps coming off the station.

Pamela: And then there’s just the well you have to contend with astronauts. You have to contend with the space shuttle.

You have to contend with the different supply vessels. The International Space Station is pretty complicated. Let’s not add a telescope.

Fraser: They sort of split the difference with Hubble. They put it in Earth’s orbit and made it so that it could be picked up and serviced by the shuttle. I think with James Webb they just said what’s the best place to put a telescope? Let’s put it there and not think about how we’re going to repair it.

This is what was done with WMAP. It is out in the LaGrange Point. A nice stable, dark place free of electromagnetic radiation and heat and all that. That’s just a good place for a telescope.

I guess that’s it, right? Some places are good for telescopes and some places are good for you to go and work on them. In the case of those telescopes they’re going with best place for telescopes – science first.

Pamela: Exactly.

Fraser: Daniel Ebdriptasked: “In episode 136 Fraser said that there is no minimum to the wavelength of the radio spectrum but isn’t the Planck length a theoretical minimum of anything including radio waves?”

I had said that I guess no minimum wavelength. In other words you could go past gamma rays and get smaller and smaller wavelengths.

Pamela: Which we’d still call gamma rays.

Fraser: Which you’d still call gamma rays even if they were 100 times more powerful, 1000 times more powerful, a billion times more powerful. Those would still be gamma rays.

You could keep on going forever shortening the wavelength and still be well within the laws physics. Daniel says: “Whoa not so fast. Isn’t the Planck length the limit?”

So what’s the Planck length?

Pamela: The Planck length is length scale at which gravity should be quantized. This is when we start trying to figure out if I look for natural units, if I start figuring out at what point does everything get quantized? At what point does everything start behaving following quantum mechanics?

I end up with certain Planck masses, Planck times and a Planck length. In theory you can’t ever get smaller than any of these things without entering pure quantum mechanic chaos. Everything is determined by probabilities slant.

The Planck wavelength is four times ten to the minus 35^th of a meter. It’s really, really tiny. He’s right, he caught us. We goofed. You in theory shouldn’t be able to have a wavelength that is smaller than this ten to the negative 35^th of a meter.

Kudos to him. If you do go the other direction, if you start looking at longer and longer wavelengths, there I don’t think we have a limit other than the size of the universe.

Fraser: Right so a universe length. Ramez Nadum from London asked: “Is there a limit to how far into space we can see even if we built the most powerful telescope possible?”

Is there a limit?

Pamela: Yes.

Fraser: There is a limit. What is that limit?

Pamela: The cosmic microwave background. It is this kind of impervious wall behind which we can’t see. It’s where the universe becomes opaque. Prior to the cosmic microwave background radiation decoupling from matter the entire universe was as opaque as the densest fog that you’ve ever been in with your high beams turned on.

Light tried to move through space but it was constantly getting absorbed and readmitted by the extremely dense material around it. So you have this complete coupling of light and matter and we can’t see through that opaque dense period in the universe. We can only see the moment at which they decoupled and the cosmic microwave background is released.

Fraser: So we already have instruments that can see this limit.

Pamela: What we’re working to build now is instruments to allow us to see really well the stuff between us and that limit.

Fraser: Right and that’s where we can only see galaxies with any resolution out to a few billion light years away and use special tricks. The James Webb telescope is going to come along and extend that view much, much further out.

What would you say right now is sort of a limit for what we can see with our best telescopes? Like with Hubble doing its deep field view?

Pamela: We’re able to see things from a few million years after the cosmic microwave background. We’re limited to only being able to see the very brightest, very largest objects that are in the process of forming.

It’s the Holy Grail is being able to start seeing the normal objects at the beginning of the universe. To start seeing regular galaxies in their infinite stages as they’re just starting to collapse out of many different combining small blobs of gas.

Fraser: Right to try and get a sense of what those first stars were.

Pamela: Exactly. We’re struggling right now to be able to see the normal stuff at the beginning of the universe as well as the big giant really glowing bright stuff.

Fraser: Okay. John from Milbrook, Ontario asked: “Why is it that the most powerful photons, gamma rays and x-rays, can’t make it to the surface of the Earth through our atmosphere but they require lead to protect us on the ground? Why can the less powerful make it through the atmosphere but can’t get through anything thicker than a piece of paper, like light?”

That’s a good question. Gamma rays will blast your DNA out if you let it and yet it can’t make it through the atmosphere. Light can make it right through the whole atmosphere but can’t go through a piece of paper.

Pamela: The beauty of this is the depths of which we expect things to travel through. Our atmosphere is conveniently thick. This is one of those really nice things that allow airplanes to be able to fly several miles up.

The higher up you go on a mountain the more radiation you’re actually going to start encountering, the more UV you’re going to be able to pick up. We can actually fly balloons high enough still within the atmosphere that they’re starting to pick up microwaves that are otherwise blocked by our atmosphere. They’re able to start picking up gamma rays.

The reason that we don’t get blasted with gamma rays and x-rays here on the surface of the Earth is we have different characteristics of our atmosphere predominantly the ozone when it comes to things like the ultraviolet that are absorbing different colors of light.

If you only have the amount of air that is between me and my computer screen, between me and the other side of the room, that amount of air isn’t enough to guarantee that all the x-rays and gamma rays are absorbed. If instead I have several miles of atmosphere, this several miles of atmosphere are able to make sure that pretty much none of these dangerous particles reach the surface of the Earth. It just takes a lot of distance.

Now at the same time, those molecules in the atmosphere don’t care about visible light. They happily let all the visible light pass through. Water in the atmosphere is another one of those things that likes to absorb. Happily, visible light passes right through all of the water vapor in the atmosphere.

At the same time a piece of paper goes nope, visible light is too thick to go through me, the gamma rays and x-rays are able to snake right between the atoms and molecules in the piece of paper.

Visible light can’t do that. It’s all about what absorbs what colors. What absorbs what wavelengths? Molecules in the atmosphere specifically absorb the gamma rays and the x-rays but they let through the visible light. A piece of paper the stuff in the paper is dense enough to block the longer wavelengths the bigger wavelengths of visible light but the x-rays and gamma rays pass right through.

Fraser: Hmm. It is counterintuitive. You think it’s so powerful but in many cases it just comes down to what absorbs what.

Pamela: Exactly and there are very specific fingerprints of colors which we talked about a couple episodes ago that are absorbed by different atoms and molecules.

We got lucky and live on a planet that’s safe for life because the specific contents of our atmosphere absorb these dangerous wavelengths.

Fraser: Like a radio will go through a piece of paper.

Pamela: Radio will happily go through a piece of paper.

Fraser: So will infrared.

Pamela: Infrared actually won’t go through that piece of paper.

Fraser: Oh that’s right, but radio for sure.

Pamela: Radio for sure. You can’t block your cell phone signal with a piece of paper.

Fraser: Right and so on both ends of the spectrum ha-ha it gets through. That is kind of neat. Okay, let’s move on.

Dawn Hoverson asked: “We’ve all heard of the tidal heating of Io and Europa but what I want to know is how much of the Earth’s internal heating is due to the lunar and solar tidal forces and how much is due to radioactivity and leftover heat from its formation?”

Io is a great example, right? Io is locked in a tidal battle with Jupiter. It’s getting squished and squeezed and this tidal heating makes it the most volcanic object in the solar system.

It would be cold and dead but because it’s getting smushed and squished the friction of this is keeping it hot and very volcanic. Is that going on with the Earth at all?

Pamela: You know I did a quick search trying to find heat generated with the Mares Plate Tectonics due to tidal forces and I just couldn’t find anything that talked about this as being anything significant.

What it turns out is the major reason that the Earth is actually warmer than it should be based strictly on how much light we receive from the sun. It actually turns out that things like radon, the radiation released by decaying particles in granite just all sorts of random decaying stuff scattered all throughout the Earth’s crust is the major source of heat here on the planet Earth. We do still have residual heat from when the planet was formed.

Fraser: Okay so if you took the Earth as a blob of molten rock, let it cool but kept shining the sun on it to warm it up a little bit and let it cool and let it cool we’re hotter than we should be after 4.6 billion years because of radioactive rocks inside the Earth.

Pamela: It’s all about the energy released by all those nuclear decays that cause radon in your basement. Or at least radon in my basement, I don’t know if you have radon in your basement.

Fraser: I don’t think we have radon in our basement. [Laughter]

Pamela: So yeah our planet is rather radioactive and granite is one of the major sources at least of day to day background radiation. We have all sorts of pockets of radioactive materials scattered all through our crust. All of those decays are releasing heat and keeping our planet nice and toasty warm.

Fraser: If we were moved into the orbit of Io then it would switch over to tidal heating would be the major force that is going on.

Pamela: But luckily we’re not there and so we have a much more stable planet and we’re happy for this.

Fraser: Yeah. I think we have run out of time. We will pick this up next week with more questions and more regular shows. Thanks a lot Pamela.

This transcript is not an exact match to the audio file. It has been edited for clarity. Transcription and editing by Cindy Leonard.

Shownotes

Telescope Suggestions:

• Oceanside Photo and Telescope
• Telescope Reviews on Universe Today
• Orion Dobsonian Telescopes
• TeleVue Telescopes
• Celestron Telescopes

Would a black hole the same size as the sun give off the same amount of energy as the sun?

• Do black holes give off energy?  This articles says, perhaps, yes. — Wired
• The Isaac Asimov book Fraser talked about was likely in the Galactic Empire of the Foundation Series.  Anyone know which one?

How do we measure time if we leave Earth?

• Cesium Fountain Atomic Clock
• Episode #117:  Time

How do heavy elements like iron end up in the inner rocky planets but not in the outer solar system or in the sun?

• Gas giant planets could have core of iron and nickel – UK Astronomy Expert
• Sun does have some heavy elements, but a very small percentage — Cornell U
• Our Amazing Solar System — How Stuff Works
• Episode #123: Homogeneity w/Chris Lintott

Why doesn’t a photon have mass?

• Photons do not have mass, but they have momentum — NASA
• Higgs Boson — CERN

Is an open universe infinite? What shape do we think the universe is? Did the early universe inflate at infinite speed?

• Geometry of the Universe — UTK
• Shape of the Universe — Wiki
• Episode #78:  Shape of the Universe
• Episode #79: How Big is the Universe
• Episode #58: Inflation
• What is the Universe expanding into? — Cornell U.

How to use binoculars:

• Binoculars for Astronomy — Universe Today
• How to Focus Binoculars – Appalachian Mountain Club

What are the processes that limit star size, and why don’t black holes have that limit?

• Upper Limit on Star Mass-  Universe Today
• “Don’t Supermassive Me:  Black Holes Regulate their Own Mass” — Universe Today
• Solar Radiation Pressure – Wiki

Is the expansion of the Universe caused by decaying matter?

• Dough and raisin analogy discussed here – Cornell U. (same as above)
• Paper:  Bulk Viscosity, Decaying Dark Matter and Cosmic Acceleration -- Astro-ph
• Conservation of Momentum — NASA

If the age of the Earth is derived from the decay of primordial material from when the sun condensed from a supernova, aren’t we just dating the supernova and not the sun?

Shownotes

What would happen if the Moon was rotating fast enough that it was not tidally locked to the Earth?

• Tidal Locking – Wiki
• Dark side vs. Far side of the Moon — Bad Astronomy
• Geosynchronous Orbit — Centennial of Flight

When light and matter go into a black hole, where do they go?

• PhysLink answers this question
• 87 FAQs about Black Holes – Astronomy Cafe
• What is on the other side of a black hole? — Universe Today
• Episode 18:  Black Holes Big and Small
• Frog in a blender was referenced in Questions show #6

Why does the space station’s orbit seem to oscillate between 60 degrees north latitude and 60 degrees south?

• Image showing ISS orbital track
• ISS orbital tracking
• More on the ISS orbit and its inclination — Sky and Telescope

What do telescopes pick up when they look at different objects — is it light waves or individual photons?

• Waves VS. Particles – University of Colorado
• Episode 83:  Wave Particle Duality

Is Dark Matter “out there” or it is all around us?

• Dark Matter — NASA
• Dark Matter halo around the Milky Way — Universe Today
• Neutrinos — UCI

Did time pass so slowly during the Big Bang that it occurred infinitely long ago?

• Is the Universe Infinite? — WMAP
• Is the Universe Finite or Infinite? Interview with Joseph Silk of the University of Oxford
• Did time pass slower at the Big Bang than it does now? – Mad Science

If the sun classified as yellow, why is the color of daylight white?

• What color is the sun? — SETI League
• The Color of the Sun part 1 — Scientific Blogging
• The Color of the Sun part 2 – Scientific Blogging

Since the beginning of the show, has any of the science discussed changed?

• If you can think of anything, send an email to us!

Could Hubble or Cassini be boosted out in to space to save the spacecraft from destruction?

• Hubble’s Soft Capture and Rendezvous System — NASA
• Discussion:  Possible Hubble End of Life Scenarios — NASASpaceflight.com forum
• Cassini FAQ’s, including what will happen at the end of the mission — Cassini website
• Episode 82:  Space Junk

Transcript: An Unlocked Moon, Energy Into Black Holes, and the Space Station’s Orbit

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Fraser Cain: I can’t believe that, while we were getting ready you’re like uh I might cut out a bit because there are tornado warnings.

Dr. Pamela Gay: [Laughter] Yeah, it’s pretty amazing and right now it’s all sunshine and birds chirping until the next wave of the storm come through.

Fraser: Yikes!

Pamela: It’s the Midwest.

Fraser: Okay so let’s kind of like this leads into I guess it doesn’t really lead into the show. What would happen if the moon wasn’t entirely locked to the Earth? And what happens to all that mass and energy disappearing into a black hole? How can we explain the space station’s crazy orbit?

If you have a question for the astronomy cast team please e-mail it in to info@astronomycast.com and we’ll try to tackle it for a future show. Please include your location and a way to pronounce your name.

First question comes from John dweAngelo location unknown. “What would be the impact of the Earth/Moon system if the moon was rotating fast enough that it was not currently tidally locked?”

Alright so I don’t know why listeners love the tidal lock of the moon. They can’t get enough. We get so many questions about this.

In the current situation the moon always displays the same face to the Earth but the Earth rotates and doesn’t display the same face to the moon. Now what would happen if the Earth was rotating and also the moon wasn’t displaying the same face to the Earth? If neither was tidally locked would there be any difference?

Pamela: Not in any appreciable way although we’d get to see what we call the dark side of the moon on a regular basis you would assume. Right now as the moon goes around it rotates once for every time it orbits the Earth. This way everything is kept in lock-step and we only get to see about half of the moon.

There are some vibrations and oscillations that allow us to see an extra few percent. In general we only see the same one half. If it was rotating faster or in fact slower such that it wasn’t tidally locked, we’d get to see that other side. Other than getting to see that other side, there’d be no appreciable difference here on the planet Earth. We’d just get to see a little bit more.

Fraser: I’m going to correct you before people kill you. It is not the dark side of the moon but the far side.

Pamela: Well and I’m thinking Pink Floyd here. It in fact [laughter] the far side of the moon gets just as much daylight as the side that we get to see on a regular basis but it’s been referred to as the dark side of the moon because of our understanding of it. We don’t know what’s there so that’s where the word dark comes from.

Fraser: There is always a dark side to the moon because there’s always half of the moon in shadow.

Pamela: Sometimes that’s the side that we get to see. So that’s the side we well understand when it’s in the shadow.

Fraser: Perfect. When Pamela says the dark side of the moon she means the mysterious other side of the moon that we can’t see from here on Earth. Of course we sent spacecraft and have it perfectly mapped. That’s the dark side of the moon.

I guess a long time ago nobody had any idea? It could be a big smiley face. Nobody knew what was on the other side of the moon. Anyway I digress. I have a question though, what would happen though if the Earth and the moon were tidally locked to each other?

Pamela: This is the case where if you were on the moon you’d see the exact same side of the Earth all the time and here on Earth we already see the exact same side of the moon all the time. For that to happen today without changing the rotation rate of the Earth so that we still had 24-hour days you’d have to bring the moon in way, way closer.

Here you’re actually going to have to stick the moon in a geosynchronous orbit. It’s going to make its way up to where we stick weather satellites and communication satellites. It’s still far enough away that it isn’t going to get broken up by the tidal effects of Earth’s gravity shredding it to bits. But it would certainly fill a much larger segment of our sky.

We’d have much higher tides except the tides wouldn’t actually ever change. You’d end up with the exact same tide always on the same place beneath the moon. One way to think of it is one part of the Earth would have higher water tables than another part of the Earth.

Fraser: But it would never really change, you’d never really notice. There would be no tides because this would be over the shore of where the ocean is.

Pamela: Exactly. If you’re sitting in New York you’d always have the waves hitting one height on the shore. If you’re sitting in California you’d always have the waves hitting another different part of the shore where the sun would suddenly become the primary source of the tides and it really doesn’t affect the tides that much.

Fraser: Okay but in the case where the moon is not tidally locked just rotating normally there’d just be no change.

Pamela: Exactly.

Fraser: There’d be no difference whatsoever. Being tidally locked not tidally locked, it doesn’t change the Earth at all. If the two were tidally locked together then we would have a different situation, very cool.

Erin Warner from Fergus, Ontario, Canada asks: When light or matter goes into a black hole where does it go and what happens to it?

[Laughter] I think we covered this earlier but I guess the question is when stuff goes into a black hole where does it go?

Pamela: Well to state the very stupidly obvious it goes into the black hole. Basically it’s going down and we assume – we can’t get inside of the event horizon of a black hole and send information back out, we assume that down within the event horizon there is a collapsed star or a section that is like the combined mass of a lot of collapsed stars eating gas, stars that didn’t even bother to collapse before getting consumed.

Supermassive black holes are going to have bigger guts than normal stellar mass black holes. Once you’re inside that event horizon you just have this giant blob of mass that has a state that we don’t really understand. We know that normal stars are made up of electrons, neutrons, protons.

We know that white dwarfs are made up of condensed matter where the electrons actually form what we call a degenerate gas where they’re packed in as tightly as they can. The nuclei themselves are in some cases forming a crystal.

With neutron stars we get an even higher density environment where protons and neutrons and electrons, it’s actually such that the electrons and protons combined give off energy and all become neutrons. Everything just becomes in this case a neutron gas.

Once you condense things further we’re not sure what happens. The state of matter inside of black holes is one of those things we’re still trying to figure out. We’re not there yet.

Whatever that weird new state of matter is the light, the mass, everything that falls into a black hole gets glommed in to this blob of matter and energy that has this new state of matter.

Fraser: It all turns into increasing the mass of the black hole.

Pamela: Exactly.

Fraser: If a planet falls into the black hole, the black hole gets more massive. If a whole lot of light falls into the black hole, the black hole gets more massive.

Pamela: It’s all the energy in mass. It’s two sides of the same coin and it just makes the gravitational pull of the black hole all that much bigger.

Fraser: I think we’ve used this analogy in a few shows before. A black hole is not a portal. A black hole is not a doorway to another dimension. It’s not a hole in the ground. It’s not a conduit to another world.

A black hole is a car crusher. A black hole [laughter] is a garbage compacter. When you put a car into a car crusher and go where does the car go? The car has gone in to the car compacter and has been compacted. That’s it.

As we said early on in the show, I think our black hole show, it’s like a frog thinking about that blender going wonder where that blender goes. I’m going to jump in and be transported to a magical dimension. Really when you go, you go into the blender and turn into blended. [Laughter] That’s where it goes. So black holes – same thing there is no place. A black hole is not a transportation system. It is a destination.

Jim Dennis from Chapel Hill, NC has a question about the ISS orbit, the International Space Station orbit. Why does its orbit appear to oscillate from about 60 degrees north latitude across the equator and down to about 60 degrees south latitude and back again? I thought when you were traveling 27,000 kilometers per hour in orbit you’d be traveling in a straight line. Is this a function of the flat map on my flat computer screen?

I know what Jim’s talking about here. If you look at a – NASA has this they have a listing of the space station’s orbit and it does, it’s like this ‘S’ curve that’s on the map. You can see it follows this path that takes it way up and then way down and then back again. So Pamela, what’s going on?

Pamela: The space station is moving in a fairly circular orbit around the planet Earth. That circular orbit is inclined relative to the equator so at one point in its orbit it’s directly over the equator. At another point in its orbit it is down well south of the equator. At another point in it its orbit it is up over Canada somewhere visiting you. The problem is the Earth is rotating beneath all of this.

We have International Space Station going around and around going north and south on its inclined orbit. The parts of the planet Earth that are beneath it when it is at its most northerly point, when it is at its most southerly point, those points on the planet Earth are constantly changing. On one orbit it may be up over Canada on the next orbit the International Space Station may be up over Siberia.

If you were able to take that map that you see on your two-dimensional screen and cut it apart, tape its two edges together you could trace that orbit around and around and see that it is really just a rotating circle that is inclined. You can actually do this with a hula hoop over your head.

If you take that hula hoop and you hold it in a fixed position and slowly rotate inside of that tilted hula hoop you’ll see that the uppermost part and the down-most part of the hula hoop map to different parts of your body. They’re over different parts of your body as you rotate beneath the hula hoop.

Fraser: Right. Makes sense to me, let’s move on. Stuart Kinear asked: I know that light can be a particle or a wave. What I’m confused by is what our telescopes pick up when they look at distant objects? Is it a light wave like a ripple in a pond when my back yard telescope picks them up or are they individual photons hitting my eyes? Are photons waves and particles at the same time? Are they forced to be one or the other depending on how they’re observed?

This is the question that has plagued physicists for hundreds of years [laughter] right? We have a certain Swiss patent clerk who helped us come to the answer. What is it, when you’re looking through a telescope and you’re seeing light, what are you seeing?

Pamela: You’re seeing both a particle and a wave. And I know that’s highly unsatisfying.

Fraser: How can it be both? It’s got to be one or the other.

Pamela: No it doesn’t have to be one or the other. The thing to think about is when you’re seeing the array disc around a really well-focused star. That array disc is formed by the different waves in all of the different photons hitting your telescope interacting and interfering with one another.

When you have all of the different points all of the different particles of light coming to focus in a single point and chemically reacting with your eye they’re acting as particles. At every moment we have both particle and wave phenomena going on at the same time.

Different effects of your telescope are caused by different parts of the phenomena. When you’re seeing COMA that we generally treat as a particle problem where the different particles of light are coming to a focus at different points due to the lenses involved in the system.

When you’re dealing with chromatic aberration though, you’re dealing with light acting as a wave and the different colors of light are bending in different ways. All the time we’re seeing photons as both particles and waves.

Fraser: Okay and we’ve done a whole show on that called Wave Particle Duality which is episode 83 of Astronomycast. We go into that in more detail and yeah, it is both and that’s confusing and [laughter] sucks to be human and try to understand it.

The universe doesn’t care. This is how it works and if we’re having trouble understanding it that’s too bad.

Pamela: Reality is far more amazing than anything we can imagine. That’s what hurts to take quantum mechanics.

Fraser: Which we haven’t done a show on yet. So we should do that at some point.

Pamela: Sounds like a plan.

Fraser: Mike Maswich sked: is dark matter something that’s ‘out there’ or is it all around us? I guess what Mike wants to know is we know that dark matter is in these vast halos that surround galaxies but if we could somehow pull out our dark matter detector and detect it right here in the solar system or right here on Earth would there be any here?

Pamela: Yeah. That’s one of the cool things is there are actually theorists out there who are working to calculate how much dark matter there probably is within our own solar system.

We probably interact with dark matter on a regular basis. It just passes right through us.

Fraser: Don’t you mean don’t interact with it on a regular basis [laughter]?

Pamela: Well that’s probably the case. We are co-located in the same room as dark matter on a regular basis. We’re still trying to figure out what dark matter is.

One of the particles that make up part of dark matter we think might be the neutrino. We know that we’re interacting with neutrinos all the time. We just need to find the rest of its siblings and build up a model.

All the models we have include dark matter existing everywhere just in differing amounts everywhere. Everywhere happens to include right where we are today.

Fraser: Then right now there could be millions of particles of dark matter streaming through my body?

Pamela: Yes.

Fraser: Or not [laughter] if we don’t understand how dark matter works at all and that it’s just a function of gravity.

Pamela: What we do know is the amount of dark matter inside the solar system at any given moment is very, very small. We don’t have to include it in any of our gravitational calculations.

The possibility of high speed, fast moving not contributing a lot of matter, particles that is non-zero. If neutrinos are part of it we know that there are neutrinos passing through you every second.

Fraser: Yep so it is both out there and all around us. Probably. Thomas William Pawlett from Essex in the UK asked: under general relativity we know that time slows as the gravitational field increases. In a singularity that was the big bang mass and gravity were infinite. Does that mean that time passed so slowly in the big bang that it was really infinitely long ago?

Okay, was in the big bang mass and gravity infinite?

Pamela: Only if the universe itself is infinite.

Fraser: Aha! Okay so you’re saying that if we have a finite universe then there was a finite amount of material so you have a finite amount of mass and a finite amount of gravity.

Pamela: Yes, when astronomers talk about the amount of mass in the universe we usually talk about the mass-density, the amount of mass in a cubic meter of space in a solar system size volume of space.

We worry about how much density is there within some volume not how much stuff is there in the entire universe. We still don’t know for certain if we live in a finite or an infinite universe so we have to deal with densities instead.

Fraser: Okay, I see.

Pamela: When it comes to the big bang everything that is was combined down to a single point. Even if it wasn’t infinite, time breaks. In fact we talk about time starting the moment after the big bang.

Within the stuff that was the pre-big bang singularity we don’t even try and talk about time. It wasn’t even defined as far as our equations go at that point.

Fraser: I guess maybe the question is does that help us know whether the universe is finite or infinite?

Pamela: No, not really. All we know is we can’t describe anything less than about ten to the negative 47^th of a second after the big bang. Our ability to understand physics before that, we’re not there yet.

Fraser: But if it was an infinite amount of mass in an infinite universe as Thomas is saying, wouldn’t that never expand because it was an infinite amount of mass?

Pamela: We have no clue what started the big bang. So now you’re starting to get into a philosophical debate.

Fraser: No, I’m saying after the fact. If you have an infinite amount of mass trying to expand away from itself with an infinite amount of gravity wouldn’t that mean that thanks to general relativity you would have an infinite amount of time for it to happen?

Pamela: Right but how do we know that there wasn’t an infinite amount of dark energy or inflation that played havoc on the equations? We just don’t have a way to get there from here.

Fraser: Right infinity minus infinity is zero.

Pamela: In dividing by infinity and multiplying it’s what does it cancel out to, what is it the limit . We don’t know all of the whereins and wherefores of those first moments.

Fraser: We have no way to describe before that one times ten to the negative 42^nd of a second after the big bang. So we have no way to describe what came before and the expansion of the universe is evidence that time is happening. That’s kind of all we can do right now. We don’t know yet whether the universe is finite or infinite.

Pamela: Right so more to learn, more to discover. More reasons to continue being an astronomer.

Fraser: Whew! I’m glad. We were almost out of reasons. [Laughter] Steve Arch from Wales (I’m not going to pronounce his town in Wales – Dugavolche there we go) if our sun is classified as a yellow star and it looks yellow if you look or glance at it with eye protection why is the color of daylight white on the surface of the Earth? Oh good one. Is the sun a yellow star?

Pamela: This depends on who you ask. It’s actually a fairly controversial question. You wouldn’t think it’s a controversial question but it is.

Fraser: Wow.

Pamela: If you ask me what color is the peak wavelength of light emitted by the sun, it’s actually green. If you then ask me what color does the human eyeball perceive the sun to be from the surface of the planet Earth then it is yellow.

If you ask me what color would the sun be perceived to be if you were on orbit and stupid enough to look directly at it then the answer becomes white?

What color the sun is actually depends on where you’re looking at it from and what you’re using to say what color it is. It is kind of complex.

Fraser: It sounds like the yellow color is coming from the atmosphere somehow.

Pamela: Right, the sunlight passing through the atmosphere, we’re scattering blue light out. That’s why we end up with blue sky. There are other different things.

We’re losing the ultraviolet, bits of the infrared and all of these different filtering processes of our atmosphere lead to sun straight overhead mostly white. Sun on the horizon pretty red, sun in-between the two appears yellow.

When you go out into space where you no longer have the filtering of the atmosphere now your eye is going to combine all the different amounts of light coming off in all the different colors to see it is a white star.

Fraser: Then the classification of the sun is a huge controversy let’s not go there. [Laughter] Seen from space the light is white. Seen from Earth the color of the sun changes depending upon how much atmosphere it has to go through and how much of the blue end is taken out of the spectrum and you’re left with the red.

Pamela: Yes.

Fraser: Okay that makes sense. I think astronomers need some new controversies because that one doesn’t sound like that exciting.

Jean Sullivan asked: since the beginning of the show has anything been said that was thought to be right at the time that has now been discovered to be wrong?

Pamela: Wow, we’ve but I remember thinking oh that changed since we did a story on it. But I can’t remember what so I guess this is one of those things where we should issue a challenge out to our listeners.

In just a few months we’re going to be coming up on our third anniversary. It would be really cool to do an everything that has changed. We have 150 something transcripts sitting online.

Those of you who’ve recently listened to all of our episodes or who have memories better than our memories are proving to be today, tell us what’s changed. Help us put together a retrospective show to air sometime in September.

Fraser: It’s true because we’ve been going at it for almost three years now. We always talk about how everything has changed from when you took your bachelor’s and even when you got your PhD.

That wasn’t that long ago and yet as I sit and think about the stuff that we’ve reported on and the science that we’ve explained there haven’t a lot of changes in it since over the three years. [Laughter] What killed the dinosaurs? No I get nothing; black holes, supermassive black holes; quasars? No.

Pamela: Yeah we’ve known that one since around 2000.

Fraser: Do people think that quasars, Seyfert galaxies and radio galaxies are all the same thing?

Pamela: That’s true.

Fraser: Yeah, new mass for the Milky Way.

Pamela: Number of arms of the Milky Way.

Fraser: Thickness of the Milky Way bulge was increased. The number of arms of the Milky Way but I think we covered it right when we did. Listeners help us out, we’ve got nothing.

If you can think of anything that has radically changed since we started doing the show or even slightly changed, that would be great. We could talk about some of the new changes. We can go back and revise our old episodes with one episode.

Ryan Peterson from Vancouver, BC (nice town – lived there most of my life) asked: I’ve read that as part of NASA’s latest and final service mission to Hubble they attached some sort of docking device to assist in crashing Hubble into the ocean. I’ve also read that Cassini will meet a similar fate at the end of its lifetime by crashing into Saturn. I was wondering if it would be feasible for satellites like Hubble and Cassini to instead be safely blasted out into space once they’re retired.

This is true. Hubble has had a retrorocket fitted to it by the most recent space shuttle mission. This is where the time of the show is getting kind of weird because by the time we’re recording this, the Hubble mission will have already landed and everything went fine. Yet by the date of the show it wasn’t sure, anyway.

It’s got a retrorocket attached to it. At the end of the mission it’s going to be crashed into the ocean. Cassini will also be crashed probably into Saturn by the end of its mission. Why do they do that?

Pamela: We’re looking at a couple of different reasons here. With Hubble what they attached was called the soft capture and rendezvous system. It actually will potentially allow us to go out with either robots or humans if we get a better manned space program with that capability going to go out and grab hold of Hubble and do something interesting with it.

Exactly what happens? Well the current plans are yes let’s destroy it. Let’s plunge it through the atmosphere someplace where the biggest chunks will probably not hurt anyone. We really don’t want to do that so this soft capture and rendezvous doesn’t close all the doors. We don’t have to destroy Hubble.

The real issue is we can’t afford to have a dead mission orbiting the planet where it doesn’t have the ability to control itself where if it gets hit by something it might go into an unstable orbit. Space is a dangerous place. We don’t need to be leaving school bus size junk around to potentially collide with future missions.

Fraser: No disrespect to Hubble. You’re a beautiful wonderful school bus size piece of junk that we’ll love very much.

Pamela: Exactly. [Laughter] Someday it’s just not going to be functional. We need to have plans on how to handle it. The energy necessary to boost it into a really high orbit is costly. Additionally then we just have a larger orbiting piece of space junk waiting to potentially hit something someday in the far future.

Bringing it back to Earth, either destroying it in the atmosphere or figuring out someway to rescue it someday and bring it back down to the planet is really the best bet in terms of not creating a disaster for the future.

With Cassini it’s a bit more complicated. There is always why don’t we just jettison it out to the outer regions of the solar system? There’s a lot of that empty space out there right? There are also potentially a lot of moons that might harbor life.

We don’t want Cassini which has been handled and touched by human beings and potentially is carrying germs and bacteria landing on Titan or anyplace that might potentially have its own bacteria.

The best way to prevent Cassini from potentially being a bio-weapon is to plunge it into Saturn. Saturn itself we’re not worried about supporting life so we’re going to use it as a garbage disposal unit.

Fraser: I think that the argument for Hubble is pretty straightforward. It costs half a billion dollars to launch a mission to Hubble. You have to say do you want to spend half a billion dollars to just have something you could put in a museum or would you rather spend that money on a couple of low-cost missions. Some of the missions that we love a lot – WMAP cost us less than half a billion dollars.

There are some important scientific questions that could be answered but yeah, you’re going to have to lose Hubble. Could you launch it into a higher orbit? Same deal you’re going to have to expend a lot of money and you still have to worry about that thing.

The best solution when it is non-functional is to crash into the ocean where nobody will be harmed and thank it very much for its wonderful service to science.

I think with Cassini the explanation, once again it’s sort of like clean up after yourself. When you’re done with Cassini, it’s no longer functional, kicking it to Saturn and that way we just don’t have to worry about what’s going to happen to it from here on out.

At the same time NASA also abandoned spacecraft on big long crazy missions all the time. The Pioneer and the Voyager spacecraft are zipping out of the solar system. There’s a bunch of other spacecraft that are on these big long elliptical orbits in the solar system.

They sometimes do that. I think in these cases where the spacecraft is trapped around a planet that’s how they get rid of them. That’s what they did with Galileo into Jupiter.

Pamela: On that note I think I’m going to have to request we end the show so I can hide in my basement because we have tornado sirens going off [laughter] here.

Fraser: Okay then we’ll talk to you next week. Bye Pamela.

This transcript is not an exact match to the audio file. It has been edited for clarity. Transcription and editing by Cindy Leonard.

Shownotes

Are new stars dark until their photons reach the surface?

• Nuclear Fusion in Stars – Universe Today
• Light from Stars -  SDSS
• Pre-Main Sequence (PMS) Stars — Wiki
• Main Sequence Stars – Australia Telescope

Can we measure how fast do neutrinos travel?

• Neutrino Mass Discovered (1998 article) — PhysicsWorld
• The three “flavors” of neutrinos:  electron, muon &  tau — Wiki
• Neutrino Speed -- Ask a Scientist
• MINOS Detectors — Wiki

Are all the implications of General and Special Relativity understood?

• No
• General Relativity — UIUC
• Special Relativity –  HowStuffWorks
• Gravity Probe B
• Frame Dragging – Duke U
• Previous questions show (that caused so much distress!) about accelerating matter.

Shouldn’t the Universe be Absolute Zero everywhere?

• Absolute Zero — Wiki
• CMB radiation is very cold, only 2.725° above absolute zero… more from WMAP
• Article about studying Absolute Zero — Smithsonian Magazine

What can’t human eyes see in the Electromagnetic Spectrum?

• Radio
• Infrared
• Ultraviolet
• X-ray
• Gamma ray

How can we measure the rotational rate of galaxies since they are rotating so slowly?

• Rotation of galaxies — University of Michigan
• Galaxy Rotation Curve — Cornell
• Doppler Shift

Is it possible there is no Dark Energy and we are just in a cosmic void?

• Dark Energy — NASA
• Cosmic Void – Could We Be in the Middle of It? — Universe Today
• Voiding the Cosmic Void :  We’re not at the Center of the Universe after all — PhysOrg

What is our velocity relative to the center of the galaxy?

• AllExperts answers this question
• Sgr A*
• Tangential Velocity
• Dynamical Models of the Inner Milky Way – Dehnen and Binney 1999.

If space is a vacuum then the speed of light should be without limit.  So what limits the speed of light?

• Michelson-Morely Experiment – Wiki
• Ether
• Discussion of this question on PhysicsForum
• Speed of light:  299,792,458 m/second  (It’s the law!)

Transcript: Hidden Fusion, the Speed of Neutrinos, and Hawking Radiation

Download the transcript

Fraser Cain: We’ve recorded four episodes in three days. Time is all relative now. Einstein would have to figure this out [laughter] we’re going to record a few more episodes because you’re going to be traveling.

Dr. Pamela Gay: Yeah, recording at the speed of sound.

Fraser: Before I go into the questions I want to remind people a couple of rules for the questions. I have refined them a little bit. The first one is just one question per e-mail. We’re still getting kind of like three questions at a time.

The way this works there are so many questions, literally we get ten questions a day probably. We can only answer about fifteen a week and so they’re piling up.

If you put in three questions in your email I have to bump out two of them and keep my favorite. If that’s okay with you, if you’re alright with me and Pamela choosing which of your three questions is the one we want to answer then that’s fine, but just send one per e-mail.

The second thing is we sort of avoid the heavy calculation ones just because they require a lot of Pamela’s time to calculate. Usually we’ll only throw in one or two of those in a week.

If you’re asking a question that requires some calculation there are some great ones that require a lot of calculation that I would love to answer.

Pamela: When you send us a question that would require me to do a second doctoral dissertation we’re going to procrastinate.

Fraser: Yeah, we’re going to push it down no matter how cool the question is.

Pamela: Life is short and we’ll get there eventually but I have six research papers ahead of the question you’re asking.

Fraser: Now you might get a Nobel Prize for it but these things take time.

Pamela: Yeah and I prefer computational to calculus.

Fraser: The ideal kinds of questions are the ones where we can handle them more not computational, not calculating, more just sort of discussing broad themes and such. Let’s get on. Are new stars dark until the photons reach the surface? How fast to neutrinos travel? What’s the story with Hawking radiation? William Stewart from Chester, UK asks: I understand that a new star is formed when the temperature and pressure at the center of the collapsing gas become high enough for sustained nuclear fusion. I also understand that it can take tens of thousands of years for a gamma ray photon to randomly walk its way from the center of the star to the outer surface. Does this mean that if a new star is forming nuclear fusion would go on inside the star for tens of thousands of years before the star itself begins to shine?

I guess what William is saying and we’ve talked about this before the nuclear fusion inside the star produces gamma rays and the gamma rays are emitted and absorbed many, many times.

Pamela: Changing color as they go in a lot of cases.

Fraser: Right and they make this long walk from the center of the star to the surface. When they finally emit from the surface there’s a visible light that we can see. But a single photon can take a hundred thousand years, maybe even more to go from the core of the star where the fusion happens to the surface.

Is this true? Will we get a situation where the gas will get to the point the fusion will ignite but then you still have to wait about a hundred thousand years before you see the light from the star?

Pamela: Well the question is when do you see light from the star and when do you see light from the particular nuclear reaction. From any given nuclear reaction you might have to hang out and wait a good long time. But the star itself is formed from many different reasons.

One of those reasons is just it is compressed. When you compress gas it heats up. The same way that when you let it expand out of like a can of air that you might use to dust your computer that expanding gas cools. Compress that exact same gas back down and it’s going to get hot.

Stars just compress gas and it thermally heats up through this process. You see that thermal heat, that infrared heat, that radio heat well before you start seeing the light from the nuclear reactions in the core. The star will actually start to shine before it starts to have nuclear reactions and then even before you start to be able to see those nuclear reactions.

Fraser: In many cases when the stellar nebulas first come together and you’ve got that first I think it is a couple of hundred thousand million years after the protostar is formed you’ve got a pretty hot object that’s purely heated from the compressing gas. It is visible to telescopes and I think you may even have a hard time to tell the difference between the star and when the fusion finally comes out.

Pamela: You can tell. You do get a color change when you start to get the nuclear reaction. This is where the star goes from being a pre-main sequence to a main sequence star. It is a gradual process and the exact moment is just a turning point that you don’t really see until you’ve had a chance to watch the star for awhile.

Fraser: Right so some photons would a little quicker, some would take a lot longer. The star would change in color over time. Then it is mostly now the light is coming from the fusion where before it was mostly coming from the heat.

Pamela: The entire star becomes a specific temperature and hangs out at that temperature for awhile once you have nuclear reactions going in the core.

Fraser: Right. Okay Carlton Brown from Maine asks: Neutrinos were originally assumed to travel at the speed of light and to be massless. It now appears that neutrinos do have mass. Has anybody established what the neutrino velocity is?

Pamela: Yes.

Fraser: Yes but neutrinos are the nearly massless particles that are streaming out of the sun. They can go through a light year of lead and not interact with any atoms. There are millions of them passing through your body right now. They do have mass?

Pamela: Yes and that’s one of the coolest discoveries that has been made probably in the last ten years. There’s lots of really cool stuff that’s going on. This is one of the ones that fundamentally we finally knew something totally new and it answered a whole lot of questions.

Since neutrinos have mass they can convert their total mass plus energy to allow them to go from having one amount of mass and one amount of energy to having a different amount of mass and a different amount of energy as long as the whole thing adds up to the same number the whole time. Because of this you can have one flavor of neutrino an electron neutrino decide I want to be a new neutrino. I want to be a neutrino.

They go back and forth between these different types as they fly through space. This finally allowed us to understand why we weren’t seeing as many of one flavor of neutrinos we thought should from the sun. It was either we didn’t understand neutrinos or we didn’t understand the sun which was really, really disturbing. It turned out neutrinos have mass and that answered almost a hundred years of confusion and that’s just cool.

Fraser: Back to his question then, what’s the speed?

Pamela: The speed is almost the speed of light. If you take the velocity that they’re going minus the speed of light, divide it by the speed of light, you get a number that is pretty much one times ten to the minus four, minus five.

We’re looking at a 10,000^th – a very slight difference between the speed of light and the speed of the neutrino. This is entirely consistent with the very, very small amount of mass that they have.

Fraser: Right, they’re going 99.9999 percent the speed of light.

Pamela: Life is good.

Fraser: Yeah, it’s because it’s not the speed of light.

Pamela: That’s all that really mattered. What allows this to happen is we know how to make neutrinos. We finally know how to detect them with instruments like MINOS.

It was the MINOS detector that ran this experiment. They let loose a beam of neutrinos and waited to see how long it would take them to go several hundred kilometers and you can measure that and we did and it’s cool.

Fraser: Alright, Javid Bride asks: Hawking radiation – it seems to me that just as many regular particles would fall in as anti-particles bouncing up with the boiling effect. If energy is produced by the mutual annihilation of the particle and anti-particle and the energy does not escape the black hole wouldn’t it stay in and simply feed the mass?

I’m going to try and do some explaining here. Stephen Hawking is the person who came up with the theory that black holes evaporate. You get these virtual particles appearing right at the event horizon of the black hole. Normally the virtual particles self-annihilate, you know it’s a particle and anti-particle but in this situation one particle goes into the black hole and one particle stays out. Because this happens it actually evaporates mass from the black holes.

I guess what Javid is asking is, who cares? Shouldn’t [laughter] the particles just fall back in? It doesn’t matter whether it’s the particle or the anti-particle these particles should be actually adding to the mass of the black hole not evaporating.

Pamela: I actually read this question differently. The way I read it is you should have as many regular particles escaping the black hole and flying off into the middle of nowhere as you have anti-particles escaping and flying off into the middle of nowhere. If you have as many matter particles and as many anti-matter particles escaping how does that change the mass?

Fraser: The answer is?

Pamela: Here the issue is – if that’s what he meant to ask – anti-matter and regular matter both has mass. An electron and a positron weigh the same amount. If they touch each other they release a huge amount of energy. If you could put a positron an anti-electron on a scale without destroying it and weigh it on the Earth it would weigh the exact same amount an electron weighs.

Having anti-matter particles fly away decreases the mass, decreases the total mass energy of the black hole just as much as having a regular electron fly away. Whether you have a regular virtual particle or an anti-matter virtual particle, either one will decrease the total mass energy of the black hole.

Fraser: Right, I see so if the particle falls in it just gets added to the mass of the black hole but because the anti-particle got away, it’s actually evaporating.

Pamela: Right.

Fraser: If the anti-particle falls in it probably strikes a particle and self-annihilates. The energy though is stuck and you get the same situation.

Pamela: Right. Either way you’re losing some of the mass. It just may be more destructive mass or not.

Fraser: Phil Harler from Chicago, Illinois asks: have all the implications of general and special theories of relativity been understood? Even beyond the difficulties reconciling with quantum theory, are there aspects of relativity that are still not fully grasped?

Pamela: No. [Laughter] One of the wonderful things about science is you can never fully know what you don’t know. The more we learn about the universe the more we find interesting applications for relativity; interesting applications for special relativity.

I don’t think that we can ever safely say to anything more complicated than what happens when you drop a rock on a 2 x 4? Anything more complicated than that I suspect will always have implications that we never fully grasp. Even dropping a rock on a 2 x 4, there are probably implications here on the planet Earth that something is going on at the quantum level that we don’t understand.

Something is going on somehow that we don’t understand. We’re always gaining new information. We’re always gaining new understanding of the universe that we live in. It’s an ongoing process and we still have lots and lots left to learn.

Fraser: You’re saying that there are aspects of relativity that are not fully grasped?

Pamela: I am saying there are aspects of everything that aren’t fully grasped.

Fraser: Including relativity?

Pamela: Yeah.

Fraser: Right and there will always be and that’s all about science.

Pamela: We’re still trying to learn so many different things. The more we study Mars the more we learn that there are plate tectonics and geology and different concepts that play on Mars and on Venus that we never imagined because of our understanding of the planet Earth.

The more we understand about how planets form around other stars the more we realize there are things that we could never have understood just by looking at our own solar system.

The more we study galaxies beyond our own galaxy the more we realize they come in stranger astrophysical patterns than we can see in our own Milky Way. The more we learn about everything the more we realize there are things we never thought of. The universe is way cooler than any science fiction writer ever imagined.

Because of that there’s always going to be some implication that isn’t understood because no one thought to try and figure it out. That’s what keeps being a scientist interesting. There’s always some new question that you never even realized you were going to have to ask.

Fraser: But weren’t there some predictions that were made by Einstein that theorists still haven’t had a chance to test out yet?

Pamela: We’re still working on some things with Gravity Probe B. They’re hard to test so we’re still working on yes frame-dragging. We’re still working on some of the how many decimals can we poke things out to but we at least have the ability now to pretty much test all these predictions that were made.

In terms of what are the implications of light always travels at the same speed to every observer. Just the question we had a few question shows back of if you take a 1 kilogram mass and accelerate it until its relativistic mass creates a short shield radius that is greater than the size of the 1 kilogram mass. One of our department’s best mathematicians who is a theoretical physicist is still struggling with that question.

That’s a direct implication of special and general relativity that we can’t find someone who has solved the math for. There are lots of neat things out there waiting for someone to sit down and do the math, do the models, do the theories and understand the implications.

Fraser: Alright, well then back at her, sorry Phil. There’s more to be discovered. [Laughter] Abduseved Ahmed from Saudi Arabia asks: how can the universe not be absolute zero everywhere? Shouldn’t it be absolute zero an inch above the supermassive hot star? How can nothing be hot? Photons don’t have mass so how can they store energy or be hot?

Okay, so if we go one inch above a super hot star and there’s nothing there.

Pamela: Well there’s light there.

Fraser: Right there’s light there but there’s no mass there, right? What is the temperature?

Pamela: This is where defining temperature is one of the most complicated things that you can do. You have the radiation temperature which is what is the energy stored in the light that’s coming out at you. An object of a characteristic temperature has a characteristic color. We can talk about that based on the primary color of light what is the temperature. It is more complicated than that. I probably made my quantum mechanics prof roll over with that one.

There’s the energy that is stored in light. Light doesn’t have mass. It is actually pure energy. That’s all it is and when that energy hits something it can impart momentum. It can increase velocity which is part of the increasing momentum. If you hit something with enough light and are able to cool it off you can actually make it weigh more, give it more mass.

Light itself we would say it isn’t coupled with the Higgs field and thus it doesn’t have any mass. At the same time it does have energy. That energy is the same thing as temperature. When we talk about temperature beyond talking about what color is the light we can also say how fast the atoms and a molecule vibrating are. We can say how fast an electron is moving through space.

We can say all sorts of different things involving the motions of particles and how they’re colliding with walls. All of these different motions, vibrations and the light itself is all part of what defines temperature.

Fraser: So is it kind of a nonsense question to ask? Temperature has to kind of go hand-in-hand with matter, right? If you stuck your thermometer out in front of a star it would heat up because the thermometer itself would heat up because of the photons that were imparting energy into the thermometer. If you had someway to have a thermometer that didn’t absorb energy somehow, ah.

Pamela: But then it wouldn’t be a thermometer so now you’re changing your definitions.

Fraser: Right, that’s all I’m saying. I’m saying that if there is no mass to be measured, the temperature to be measured of the matter then to ask what the temperature of that area is is kind of a nonsense question.

Pamela: Not really because you can say so this energy, how much work could it do. There’s a matter of temperature is also a way of communicating energy, energy can do work. Energy can expand our universe.

Fraser: Sure but there’s no way to see energy flowing past unless you interrupt it, right?

Pamela: So now you’re asking does a tree in a forest make a sound if no one is there to hear it.

Fraser: No, I guess what I’m saying is that if in the spaces in between atoms of hydrogen for example floating in the middle of space where there is no atoms at all, is there a temperature?

If you measured the atoms you would say oh this space is very close to absolute zero. If you were trying to measure the not atoms in between those atoms would that give you an answer?

Pamela: People who study interstellar media actually end up talking about many different types of temperature. You can have a cloud of gas that has a gas temperature and then the light passing through it from a star has its own characteristic temperature.

You’re dealing with different temperatures also in some cases of different populations of particles. You could even say that puppies have a temperature based on their kinetic energy. If you have a room full of sleeping puppies that are being hit with infrared light to keep them warm and comfy the puppies have one temperature and the light has another temperature.

Give the puppies food and a small child to invigorate them and the puppies now have a different temperature because of their kinetic energy, because of their motion. We talk about the motion and the collisions as one temperature. Then we also talk about the temperature of the radiation.

It’s a complicated thing where there are mathematical definitions that allow there to be temperature even when there isn’t mass present. The cosmic microwave background is everywhere. That alone says everything has to be at least the temperature of the cosmic microwave background.

Fraser: Terry asks: what can’t human eyes see in the color spectrum?

Pamela: The best way to think of this is anything that has any light that doesn’t trigger a chemical response in your eye we can’t see. For us it is radio which is a good thing because if we could see all the cell phone signals, it would blind us. Imagine if every time your phone rang it was light having a floodlight go off.

We don’t see radio, we don’t see infrared. We don’t see ultraviolet and we don’t see x-rays and gamma rays. The energies of those lights are wrong to trigger chemical reactions in our eyes and this is good.

Fraser: So is there any part that we don’t see in between that color range? Say from red through blue, do we see everything in that range, invisible light?

Pamela: Yeah, one of the nice convenient things about the eyes is the photoreceptors have overlapping sensitivities for the colors. We also have these light/no light sensors as well in our eyes. They simply go aha something off somewhere in this large frame of possible wavelengths hit me I’m going to trigger now.

Fraser: Okay, moving on Chuck Hammond from Mount Pleasant, SC asks: how can we measure the rotational rates of the galaxies? Since galaxies are rotating so slowly many of our lifetimes, how can we actually measure the speed that they rotate?

That’s a good question. I know the Milky Way takes 220 million years to rotate once on its axis. How could we wait for that to happen?

Pamela: Luckily its Doppler shifts. When we look out specifically with the edge-on galaxies this is really easy. When you look out at an edge-on galaxy you can say the right side is moving toward me. You can measure how fast it is moving towards you by measuring the change in color of the lights of the stars.

You then look at the left side of it and go aha that side is moving away from me. Measure its rate. What you usually find is there is also the center is moving at some rate so you have to subtract off the motion of the center toward and away from you.

Once you make that correction for the fact that the whole galaxy is moving you can then get at the right side and the left side are moving forward and away from you which gives you the rate at which the whole system is rotating.

Fraser: That sounds like a project that you might have to do in astronomy class.

Pamela: Yeah, it’s actually something that a lot of small and large colleges have educational radio telescopes. You can do this by looking at the light from the gas in the discs of galaxies and just happily measure the rotation rates.

Within our own Milky Way it allows you to look at the fact that we have lots of dark matter and things aren’t moving at the rate you think they should.

Fraser: How do astronomers measure the rotational rate of the Milky Way since we’re in it?

Pamela: Well here what we do is you look out and you have to look for stuff that is moving toward or away from you. Then you make corrections. Okay this has this angle relative to me and the center of the Milky Way and I measure it moving this way. You have to do lots of trig. You can do it, it’s not fun but you can do it.

Once you build up all of the pieces of okay I’m looking at this crazy angle. I see this motion. I’m looking at this angle I see this motion. You can build up a distribution of how fast things are moving all the way around the Milky Way. You just look at things at different distances.

Fraser: Do astronomers use the cosmic microwave background radiation for this?

Pamela: We don’t use that to measure our rotation rate. Well, you can get there but it is much harder. The easiest way to get at how the whole Milky Way is moving versus just the sun is to only look at things within our Milky Way and measure their motion relative to us and do lots of corrections.

When you’re trying to figure out the bulk motion of sun relative to center of galaxy’s sun relative to local group, galaxy versus local group you start measuring all of this relative to the cosmic microwave background. That’s really the best frame of reference that we can measure our motion relative to.

Fraser: Alright, let’s move on. Chad asks: I’ve recently read some information on the thought that there was no dark energy and the reason we’re seeing red shift from supernovae is because we’re in a cosmic void. This would make more sense than dark energy but what evidence is there to suggest this is true? So, dark energy, mysterious force accelerating the expansion of the universe.

The way that astronomers detected this was by measuring the distance to really distant supernovae and they found that the supernovae were further away than they should be if the expansion of the universe was just the leftover momentum from the big bang. So I guess the first question is when he says that we’re in a cosmic void what do you think he’s talking about?

Pamela: One of the things that we talked about in our last episode on large scale structure was that overall the whole structure of the cosmos is one of walls and voids and junctions. We look like Swiss cheese. We look like very lacy mostly air Swiss cheese.

The idea is that what we’re in is actually a collection of bubbles that are inside a much bigger bubble and that there are actually areas of much higher density beyond what we’re able to see.

You can imagine that the entire visible part of the universe which is probably four percent of the universe or less depending on whose models you’re paying attention to is inside of a large empty space inside of a much greater cosmos. It is the fact that we’re an empty area surrounded by much higher masses is pulling the trail outward.

The problem is that one of our basic premises in doing cosmology is that we don’t live in a special place. We don’t live in a special time. The only way this theory works is to assume that we’re in a very special location.

There are a lot of people who are simply going no; we can’t even get there from here. It comes down to the fact that dark energy is very uncomfortable so what other explanations could there be. This is one of the ones that there could be but like I said it breaks the basic tenet of you can’t live in a special place.

Fraser: So if we had a configuration of matter around us in such a way that it was accelerating our local group I guess in a way that would be different from the way every other galaxy out there is being accelerated then that would help explain it.

Pamela: Okay. Yes.

Fraser: That violates this rule so I guess in the one case we say well we live in the most special place in the entire universe or [laughter] something weird is happening to everybody and we still just haven’t figured out what that is yet.

Pamela: There’s always going to be someone out there trying to make us the center of everything.

Fraser: Right. I guess that’s sort of what it is. It’s just like geocentricism; I don’t know local group.

Let’s move on, Bob Able asks: what is our velocity in relation to the center of the galaxy? I know we travel approximately 18.5 miles per second around the sun but how fast are we moving around our own galaxy?

I mentioned that before, right that we are orbiting the center of the galaxy. It takes us about 220 million years to complete an orbit. How fast are we going?

Pamela: This is going to sound kind of sad but our motion relative to the center of the Milky Way relative to age A star has us with a tangential velocity. This means if you draw a straight line from the center of the galaxy to us and then draw a line at a right angle to that we’re moving at about ten kilometers per second.

Fraser: So, less than what we’re traveling around the sun.

Pamela: Yes but that’s our sun relative to the center of the Milky Way. So, we’re going around and around our sun and our sun is chugging along moving its way around the center of the galaxy.

That chugging around the center of the galaxy is carrying us along at about ten kilometers per second.

Fraser: Alright, well that gives us the answer. I think this is our last one, Shawn Irwin from Mesa, AZ asks: the Mickelson – Morely experiment failed to detect an aether of any sort, however if space were indeed a complete vacuum the speed of light should be without limit. So, what is it that limits of the speed of light?

Aether, what’s that?

Pamela: Well there’s this original idea that in order for a wave to travel through space it has to have a medium in which to move. We’re used to seeing this with water. We’re used to this with sound. In the vacuum of space no one hears you scream. It’s one of those famous sci-fi lines.

The thought was that in order for light which has wave-like characteristics to travel through space there has to be some sort of a medium for light to travel through. They looked and they couldn’t find it. No matter what people have done they can’t find the median that light is traveling through. So it really looks like light electromagnetic waves really don’t need anything. They just happily exist and move through a vacuum.

This is a completely new way of thinking of things because what it says is you can have a wave that has a built in speed limit. It appears that within our universe there is a built in speed limit that’s just part of how space is defined. That’s the rate at which light moves in a vacuum.

According to Einstein this is how we define time. This is how we define everything. In our universe there is a built in definition that says light shall and it does even when there’s no medium for the wave to move through.

Fraser: When you ask what defines the speed of light, the speed of light is the speed of light and that’s all you can really say right now.

Pamela: Two hundred and ninety-nine thousand seven hundred and ninety-two kilometers per second. It’s the law.

Fraser: Alright. Well that’s it. I’m sure that bugs some people and they still are certain there’s some kind of aether but I know the [laughter] experimenters haven’t found anything like that. That’s it, that’s the law.

Okay, thanks Pamela. I guess I’ll talk to you tomorrow for another show but to most people it will seem like it has been a few days.

This transcript is not an exact match to the audio file. It has been edited for clarity. Transcription and editing by Cindy Leonard.

Shownotes

What would happen if the Moon disappeared — would that change Earth’s orbit?

• Skeptic’s Guide to the Universe podcast
• Galileo’s experiment at the Leaning Tower of Pisa
• Video recreating that event
• The Sun, Earth and Moon and their orbits

How do planets get atmospheres?

• Planetary atmospheres — U of Washington
• Chemistry and Spectroscopy of Planetary Atmospheres — NASA
• Titan’s atmosphere
• Mars’ atmosphere

I see a faint glow after sunset in the East — what could it be?

• Zodiacal Light
• Paper:  Unusual Cloud-Glow After Sunset
• Book by Brian May:  A Survey of Radial Velocities in the Zodiacal Dust Clouds

Can light get stuck in orbit around a black hole?

• Anatomy of a black hole — UIUC
• The Kerr Black Hole – Astrophysics Spectator
• Videos, “Journey into a Schwarzchild Black Hole”

Where on Earth would I weigh the most?

• GRACE Satellite (Gravity Recovery and Climate Experiment)
• Earth is an oblate spheroid
• Does gravity vary across the surface of the Earth? — Cornell

How much less would I weigh if the moon was directly overhead?

• Tidal Forces –Windows to the Universe
• XKCD comic on Centrifugal Force
• The gravitational force of the Earth and Moon on each other

How is ionized hydrogen detected in space?

• Ionized Hydrogen – NRAO
• Paper:  Ionized Hydrogen at Large Galactocenter Distances
• Star forming regions and ionized hydrogen — Caltech

Do we live in an unbalanced Universe?

• The Unbalanced Universe – Time Magazine
• Baryon Asymmetry
• Physicist Investigate How Time Moves Forward – PhysOrg

Why do some celestial objects form in disks and others don’t?

• Angular Momentum
• Dynamics in Disk Galaxies — U of Alabama
• Oort Cloud – NASA

Could a spacecraft perform a “solar system assist,” in the way we do gravity assists?

• Gravity Assist Primer -  JPL
• How does gravity assist work to change the trajectory of a spacecraft? – Scientific American

If Earth had no axial tilt, how eccentric would its orbit have to be to have  seasons like we have now?

• The Reason for the Seasons –ASD Planetarium
• Kepler’s laws of planetary motion

Does light have mass?

• Answer from previous question show
• Answer from UIUC

The Cosmic Microwave Background is a redshift of the Big Bang.  If one could travel near light speed, would that counteract the redshift?

• Things would get blueshifted looking ahead, more redshifted looking behind, and looking to the side would look the same.
• CMB – WMAP
• FAQs on the CMB — UBC

Is repulsive gravity real?

• No
• Repulsive Gravity, Cosmological Constant
• Evidence of Dark Energy in the Early Universe – NASA

Transcript: The Source of Atmospheres, the Vanishing Moon, and a Glow After Sunset

Download the transcript

Astronomy Cast Questions Show:

Fraser Cane: Pamela it seems like it’s been so long since we talked.

Dr. Pamela Gay: [Laughter] All of about 20 minutes.

Fraser: All of about 20 minutes yeah. As I mentioned my computer died, we’re catching up all the episodes using the wife’s computer. We will get the full list of episodes into your hands we promise. This is the next round.

This week, how do planets get their atmospheres? What would happen to the Earth if the moon just disappeared? What’s that strange glow that we sometimes see after sunset?

Let’s get on with the first question. Samuel Rankert from Fuquay Verena, NC asks: I’ve heard another podcast Skeptics Guide to the Universe, (this is a shout out to them, listen to their podcast) that if the moon vanished the Earth would get along quite nicely. I thought that the moon would change the total amount of the mass in the Earth-Moon-Sun relationship and the Earth would change its orbit.

Okay so for starters is there any way that the moon would suddenly vanish?

Pamela: No.

Fraser: Okay, whew! [Laughter] So this is just purely theoretical.

Pamela: Our moon is there to stay and if something were able to remove it, it would destroy the Earth in the process probably. It would be bad.

Fraser: Some black hole whisking past it would take us out as well. But let’s imagine you that you did whisk away its mass would that affect our relationship with the sun?

Pamela: No. In fact how much mass the Earth has doesn’t really have any affect whatsoever on how it orbits the sun. What matters is how fast we’re going. It just happens to be that the two equations the mass of the Earth cancels out and all that matters is the mass of the sun.

As long as we keep our velocity, as long as we keep trying to have the same speed at the same place as we go around the sun we’re just going to keep orbiting merrily the way we’re orbiting today.

Fraser: This is what Galileo proved, right?

Pamela: Yes.

Fraser: Dropping objects off of the leaning tower, that it doesn’t matter how much mass it is it always accelerates towards the Earth at the same speed.

Pamela: In this case the Earth always accelerates toward the sun at the same speed.

Fraser: Right so it doesn’t matter if you replace the Earth with Jupiter, it would still go the same speed. As long as it was going that speed then everything would be fine.

Ben Oliver from Brisbane, Australia asks: how do planets get their atmospheres? I guess are there different ways that planets get atmospheres?

Pamela: There are two different ways that the gases get into the atmosphere. One is you import your atmosphere. You take a planet, any planet and you clobber it with comets and in the process have the comets release all of their volatiles, their oxygen, their nitrogen, their frozen carbon dioxide. Have them release all of that through melting sublimation processes out into the atmosphere and that’s one way to make an atmosphere.

The other way that you can get gases into the atmosphere of a planet is through out-gassing of the planet itself. Planets that are geologically active often have trapped gases beneath their surfaces. These gases can get spit out all different ways. Many of us have seen bubbling steam pots, volcanoes giving off gas, gurgling springs. All of these different things have different methods that often sulfurous nasty smelling gases can escape from the inside of the planet Earth.

Fraser: I guess you get a situation like Venus where that stuff just builds up. It’s not going anywhere. It comes out of the Earth and goes up almost like it is floating. Imagine that the Earth is the bottom and it’s letting out it’s like in water right?

Gas floats up in water while a rock will go down. It’s like the Earth is separating itself. It’s pushing out the gas but the gas is still being held by the gravity so it can’t go anywhere but it’s floating up on top of the rock.

Pamela: This is something that we see with Saturn’s moon Titan. It has an amazingly methane rich atmosphere and we think that a lot of this methane is coming out from internal processes within the moon. We see methane on Mars that we think most likely comes from geological processes.

Here on the Earth we have volcanoes that belch and burp all the time. You can get things either externally through comets or you can get things internally through the natural release of gases that are trapped within the surface of the planet.

Fraser: Earth is a little bit different because we have organisms that can process stuff out of the atmosphere and even in some cases sequester it away back under the ground. But in most situations sort of once that stuff gets out it is out, right?

Pamela: Right.

Fraser: I guess one of the situations is well you have the situation with Mars where it doesn’t have enough of a magnetic field to hold on to the atmosphere against the sun’s solar wind.

Pamela: We think that Mars used to have a much richer atmosphere than it has today but various processes from solar winds battering away at the atmosphere to just over time particles collide and getting a little bit too much velocity and flying away on their own. All these different processes have slowly wiped away Mars’ much thicker in the past atmosphere.

Fraser: So there you go. Srdevi from India says: there’s a faint glow, it is quite bright in the eastern sky after sunset and it continues through the night. What could be causing it?

I think we’re going to assume that we’re not talking about just the sunset because the sun is still there in the sky after the sun sets. Of course, he’s saying this is in the eastern sky.

Pamela: Right and that was what actually threw me. When I first looked at this I went aha zodiacal light! Then I went, wait zodiacal light is in the west.

Here I think the culprit is likely that if you drove east you’d find a large city there. Light is staying in the same

Fraser: [Laughter] That’s what I was wondering too.

Pamela: Yeah, it’s kind of a sad response but I suspect that if he gets in a car and drives toward the light he’ll find a city. Here we have a really bright glow that’s off in the northeast and it happens to be a large oil refinery that makes a lot of noise and makes a lot of light.

You can end up with natural sources of light. For instance if he’d said that instead there was light that was in the west shortly after sunset that would have been zodiacal light. You have sunlight lighting up dust in the plane of the solar system. That scattered sunlight we’re able to see far after the sun has already set.

This is actually what Brian May of Queen did some of his dissertation work on. That sadly is on the other side of the sky so I think here we’re just dealing with light pollution.

Fraser: Right, the sun rises in the east and sets in the west so you’ll have the light in the west after the sun has set. Usually the east is the dark side so that would have to be light pollution.

Martin Szwanveldt7:59 from the Netherlands asks: if light can be captured by a black hole is it also possible the light can get stuck in orbit around a black hole? If so would we be able to detect it? Jason K. asked the same question and we’ve actually already answered this question in the past.

If you do have a question for us do a search because we’ve answered a lot of questions now and some of them are starting to double up. Which, we don’t blame you; there are hundreds of shows to listen to. [Laughter] Let’s give the quick answer, can light go into orbit around a black hole?

Pamela: Yes.

Fraser: Yes – that’s crazy!

Pamela: [Laughter] But it’s kind of cool. It’s the fact that light is energy. Energy and mass are the exact same thing and gravity affects both of them. You can end up with photons quite happily orbiting a black hole and we can’t see them because the light is orbiting instead of coming toward us.

Fraser: You wouldn’t see the light being emitted from the black hole because it is orbiting a black hole. Where would it be? Would it be outside the event horizon or inside the event horizon?

Pamela: When I ran the calculations last time I have to admit I didn’t make any crazy corrections or anything. A straightforward quick calculation has the light actually inside the event horizon.

Fraser: So it is doomed anyway but it could be orbiting I guess in sort of mathematically perfectly it could be orbiting at exactly the right spot. It just goes around and around and around.

Most likely it’s just going to spiral inward except if it gets bumped or absorbed by other material falling into the black hole.

Benjamin Dale from Christchurch, New Zealand – this is the international edition have you noticed that?

Pamela: Yeah it’s really cool. We have questions coming in from all over the globe.

Fraser: He wants to know: at which point on or near the Earth would I weigh the most and why there? There is a second part of the question which we’ll to in a second.

We know that your weight changes where you are. If you’re right in the middle of the Earth you’re weightless but would you weigh more somewhere inside the Earth, right at the surface or up in the air?

Pamela: I’m actually going to take the where on the surface of the Earth do you have the largest gravitational pull? This is a straightforward way of looking at this question. There’s some really neat data that came from the GRACE satellite the Gravitational Recovery and Climate Experiment. While it orbited the planet it measured slight variations in the gravitational force.

What we found is there are all sorts of different variations in the pull of gravity that are directly related to previously in some cases unknown changes in density beneath the surface of the planet. We find that you weigh more along the north Atlantic mid-Atlantic ridge.

You weigh more when you’re in the Himalayas. You weigh less in India than you do in Algeria. There are strong variations as you go all around the planet. From looking at their maps as near as I can tell the place that you would weigh the most is if you were out around Iceland.

Fraser: So, there’s something dense underneath Iceland or the way it is positioned on the planet that is the spot where you would weigh the most. What if you lifted up into the air somehow, you’re going to be weighing less because you’re moving away from the gravity.

Pamela: This is a what is the gravitational anomaly at the surface of the planet as you travel around question. The gravitational anomaly is the largest positive value when you’re around Iceland.

Fraser: Then if you somehow sink into the ground you’re going to weigh less as well because?

Pamela: The amount of mass below you is decreased.

Fraser: Is decreased and now you’ve got mass above you that is counteracting the pull down below. That’s it. On the surface of the Earth in Iceland you’re going to weigh the most. I’m sure there’s a joke there.

[Laughter] Benjamin’s second question then was: how much less would I weigh if the moon was directly above me with its gravity pulling me up?

Pamela: Here the catch is, in general remember the moon is not straight overhead unless you’re on just the right part of the planet. The moon is generally somewhere in the sky above you but it may be off at some crazy angle relative to you in the center of the planet.

So if you managed to be on the line where the center of the Earth is directly below your feet and the center of the mass of the moon was directly over your head, in that one very most powerful deviation situation your weight would change by about three parts in a million. This really isn’t something that will help you discount the amount of candy that you’ve been eating recently or anything like that.

Fraser: Yet that force of gravity is what affects the tides and causes the Earth to lift up and down by a meter. It’s amazing.

Pamela: It’s a meaningful affect. The tidal force is where you start looking at the combined changes to the gravitational fields. In general in terms of just the variation that you’re going to see on your bathroom scale, you actually get more variation when you take into account the change in how much you weigh on that spring scale when you’re at the equator of the planet versus the north pole of the planet due to the rotation. You get more of a lift off of being spun than you do from having the moon straight overhead.

Fraser: That’s right you weigh less on the equator than you do on the north pole.

Pamela: That’s just because well as XKCD points out centripetal force really is not completely imaginary. Nor is centrifugal or so just pick your set of names, run your equations. It does affect how much you weigh.

Fraser: Alright. Matthew Maddox asks: how could one detect ionized hydrogen in space? It seems that hydrogen has no electrons to change energy states and give off light so it would be very difficult to detect. Now, ionized hydrogen – what is that?

Pamela: Ionized hydrogen is where that one lone sad electron that is trying very hard to orbit its helium nuclei which are generally just a single proton. Ionized hydrogen is where that last lonely electron is given enough energy that it flies off into space and is no longer attached to the hydrogen.

Fraser: The hydrogen is now just a bare proton?

Pamela: Right.

Fraser: With no electron orbiting it?

Pamela: Right.

Fraser: Then the electron is off and away?

Pamela: Yes.

Fraser: How can we detect that then?

Pamela: We can only detect it when the electron decides it’s going to reattach itself to the hydrogen atom and release a photon in the process.

Fraser: We only detect when the electrons connect to the protons again?

Pamela: Right and other than that, no if you get a hot enough gas we can’t see the hydrogen because there is no transition taking place.

Fraser: Why is it important to find ionized hydrogen?

Pamela: It’s one of the most common things in space and it’s always nice to know where the hot spots are. When you have star forming regions, when you have bubbles around hot stars this is where you start to get the hydrogen gas. It’s a temperature indicator.

You start looking at where are all the transitions of all the different atoms that you can see in that region. By comparing this number of hydrogen transitions you see this number of silicon transitions.

By looking at all the different transitions of all the different levels you can start to figure out the exact temperature of the gas.

Fraser: That’s different from the cold molecular hydrogen which is the stuff that stars are made from.

Pamela: Right.

Fraser: There you go. Stephen DeSousa asks: is it possible that while we see an unbalanced universe of matter traveling forward in time is in fact balanced by anti-matter traveling backwards in time?

Whoa. [Laughter] Do we live in an unbalanced universe of matter traveling forward in time? What does unbalanced mean?

Pamela: I think what he’s referring to is for reasons that we can’t fully explain when the universe formed for every roughly one billion particles of antimatter there was one billion and one particle of regular matter.

The billion versus the billion annihilated on one another it released a lot of energy and left behind that extra one piece of regular matter. We’re not entirely sure why the universe would have formed with this slight asymmetry in the in the amount of matter and antimatter. This is something that theorists are working very hard to try and figure out. They’re not quite there yet.

I think what he is referring to is that slight asymmetry. There are a couple of problems with what he is talking about. One is that by definition time started at the moment of the big bang and time only moves forward.

The other is that antimatter has all the same basic properties in terms of how it interacts with things like gravity that regular matter has. There’s no reason to think that the two of them would have had any reason to be going in opposite directions in time.

Fraser: I guess what Stephen is imagining is some situation where you get that balancing in at the same time as you’ve got that one left over piece of matter moving forward.

You also for some weird reason had an alternate near universe where you had one extra antimatter. I guess what you’re saying I think is that matter and antimatter are both happy to move forward in time.

Pamela: Right and they both interact with things like gravity just the same so they’re not going to preferentially segregate or act differently. It’s just that when they touch they tend to annihilate one another.

Fraser: The fact that we can form antimatter now in supercolliders and so on that we have the antimatter here in our universe with us. It’s not like it just disappears every time you make some antimatter it just vaporizes and off it goes into its backwards journey through time. Okay thanks for the question.

Tim Vickey from Washington, DC asks: why do some celestial objects form into discs and others don’t? Are there solar systems that aren’t in a disc shape like our own? Or galaxies? Do planets usually form in a disc shape with their moons? What about local clusters? Why all these discs?

Pamela: In general it’s this terrible thing called angular momentum. Unless two objects manage to hit such that their velocities and their centers of masses are exactly aligned, you’re going to end up with some sort of rotation. Anytime you have something rotating it naturally forms into a disc.

Anyone who has ever tried to make pizza by throwing a blob of dough into the air and giving it a bit of rotation knows this. Take any round thing and rotate it fast enough and it’s going to become oblate, become more oblate and eventually form a disc. Even our sun and Jupiter because of their rotation aren’t perfect spheres.

Fraser: Well even the Earth.

Pamela: Even the Earth.

Fraser: Yeah the Earth is I think it is like 20 kilometers or 15 kilometers around the equator is about that further from the center of the Earth than the poles.

Pamela: You can end up with things forming a spheroid due to collisions. For instance the oort cloud we think is a spheroid of chunks of ice that orbit around the entirety of the solar system.

We have random rogue comets and asteroids that due to past gravitational interactions and collisions and other off-centered flinging processes they ended up forming a spheroid. They ended up forming non-disc motions.

Fraser: You get like giant elliptical galaxies where you have – even this will happen with the Milky Way and Andromeda – when our two galaxies collide. You’re going to get this sort of ball-shaped, egg-shaped galaxy which is the mixture of the velocities of the stars.

Pamela: What’s happening here is you take two discs, collide them violently and all of the different angular momentums end up randomizing. You can end up with a spheroidal result.

If you have just two things colliding or two blobs of gas and dust colliding you can generally form a nice friendly disc. Once you get two discs of sufficient enough mass and what’s kind of cool is out of the Sloan Digital Sky Survey they’re finding that there seems to be this distinctive mass where any collision above this particular combined mass results in an elliptical galaxy.

Solar systems are small. They form basically out of a single blob of gas and dust getting knocked somehow and collapsing down and spinning up. It’s through that spinning process that you end up with solar systems having all of their planets generally in one nice simple disc.

Fraser: Do galaxy clusters form into discs as well?

Pamela: So far we haven’t seen any that are truly discs. You have some galaxy clusters that are flatter than others but with the galaxy clusters forming you have objects falling in from all different directions.

It’s from that falling in from all different directions that you end up with we say a relaxed spheroidal system if you just wait long enough.

Fraser: Right. Lee Anthony from Manhattan, NY asks: since we do gravity assists with spaceships all the time around other planets is it possible to do some kind of solar system assisted speed boost by going around the sun as it rotates around the Milky Way?

I guess we would launch a spacecraft from Earth and it would somehow use the momentum of the sun going around the Milky Way to get a boost. Is that possible?

Pamela: Not easily if you start out on the Earth. If you imagine instead that you have some extraterrestrial spacecraft capable of moving at the types of speeds that are comparable to the sun’s speed relative to the center of mass of the galaxy, if you’re capable of starting off with one of these huge velocities then you can use the sun to either accelerate yourself or slow yourself down depending on what direction you’re going relative to the center of the Milky Way.

But within our own solar system you’re starting off with velocities that are more planet-like and the sun within that particular frame of reference really isn’t moving. You have to move so that your motion is more in the same frame as the sun relative to the Milky Way versus spacecraft moving relative to the planets.

Fraser: So you’ve already got the boost because you’re here with the sun going around the Milky Way that’s it. You’re enjoying that velocity and you have to go to some other place that’s moving at a faster speed than the Milky Way that you can then absorb some of its velocity.

Pamela: Right.

Fraser: This is that same situation with the thought experiment with how the gravity system works here in the solar system. You launch from the Earth, you fire your rocket towards Jupiter. As you move towards Jupiter you get pulled into by its gravity well.

Then you have to sort of climb back out of it again as you’re moving past Jupiter. The point is that Jupiter has also pulled you up to its speed in its orbit. In fact you as a spacecraft have slowed Jupiter down in its orbit, but not very much.

Pamela: Right, it is such a small amount.

Fraser: You’re losing the speed that you got on the inbound trip when you made the up bound trip. The thing you get to keep is you get to keep its orbital velocity around the sun.

Pamela: So, not quite. We’re sorry. You’re already moving at the same pace as the sun and your really have to have a significantly different velocity before you’re able to take advantage of the boost.

Fraser: I think we mentioned this in a previous show as well which is that you could go from star to star and even galaxy to galaxy boosting up your velocity. As long as somebody else has got some velocity you can exploit. [Laughter]

Pamela: Exactly.

Fraser: Then you’re set. Robert Wilson from Brisbane, Australia asks: if the Earth had no axial tilt how eccentric would the orbit have to be to produce seasons equivalent to our axial induced ones?

Okay let’s unpack this one. The Earth’s seasons are caused by the tilt of the axis?

Pamela: Yes.

Fraser: Summer in the northern hemisphere especially if the question is coming from Australia I have to answer about the southern hemisphere as well… [Laughter]

In the northern hemisphere the summer is in June-July when the pole is tilted towards the sun. Winter happens when the northern hemisphere is tilted away from the sun and that’s reversed in the southern hemisphere.

Pamela: The seasons are basically caused by how tightly packed the rays of light are when they hit planet Earth. You can sort of play with this with a flashlight.

If you beam the flashlight straight down on the table and make a little tiny circle of light because you’re pointed straight down, that circle of light will get warmer faster than if you tilt the flashlight at the surface of the desk and make this really long much fainter pattern of light. That is going to be a much cooler surface.

Fraser: The same numbers of photons are hitting the surface they’re just stretched out over a larger surface area.

Pamela: So it has nothing to do with the distance from the sun. It has everything to do with the angle at which the sunlight is hitting the planet Earth.

Fraser: But the distance to the sun has to have some effect.

Pamela: The thing is the Earth’s orbit is mostly a circle. It has slight deviations but it turns out we’re actually closest to the sun during January. Here in the northern hemisphere we enjoy a slightly, slightly milder winter than you get down in the southern hemisphere but the effects are very small.

You can ski in both hemispheres. We have glaciers in both hemispheres. It is as the orbit gets more and more elliptical that you start to see significant variations from hemisphere to hemisphere.

Fraser: Let’s sort of do that thought experiment then. If the Earth had a much more elliptical orbit what would we see?

Pamela: It gets complicated because of with Kepler’s laws of orbital motion you’re tracing out what we call equal areas and equal time. This means that when you’re up close to the sun on a highly elliptical orbit you’re going to be whipping around the sun very quickly so that in one say hundred hour period the triangle that is formed by where you started, where you ended and where the sun is, is going to have the exact same area as the triangle that is formed when you’re far, far away from the sun moving much slower and you travel for that same hundred day period.

When you’re far away from the sun you’re going to orbit very, very slowly. As you orbit slowly your planet has a chance to radiate away all of the heat that it gathered up during the summer. You have to start taking into consideration now remove all axial tilt and have seasons that are caused strictly by the distance from the sun. Change everything.

In this case you’re forcing your winters to be longer which is going to allow them to have the oceans cool more, have everything cool more, lose more of the heat that you stored up during summer and it radically changes the way the seasons work. You can’t easily do a one for one correlation.

You also have to start worrying about how well the atmosphere insulates the planet. A planet that has a thick atmosphere is going to have one set of effects than a planet that has a thinner atmosphere.

Fraser: It’s almost like winter is caused by the orbital eccentricity are just completely or very different and much harsher when you have an elliptical orbit. I can kind of imagine in my mind a comet going around the sun in a very eccentric orbit. It kind of whips around the sun and then slows down as it goes out into the great big orbit. Then it whips around the sun and then goes back out again.

That’s the situation. You’d have a summer that was a few days long [laughter] and then you’d have this winter that went on and on. I guess it’s almost impossible to calculate, right?

Pamela: It becomes a problem for atmospheric physicists or geophysicists. That’s not me but I can say I’m much happier having seasons that are due to the axial tilt of a planet that has a mostly circular orbit. We have nice symmetric seasons.

This is also one thing to think about is the reason that August is so much hotter than June which is when we actually are getting the most light from the sun. The sun keeps shining on us and we retain that heat and the rocks heat up and the oceans heat up.

The coldest part of the winter lands in February. The hottest part of the summer lands in August for us in the northern hemisphere. This is all because of the lag in the thermal cycle.

Fraser: Right it’s too complicated to calculate or I guess for this show. But I guess if there are any geologists or climatologists who want to have a shot at it we’d love to hear your calculations.

Pamela: Or send us a reference to the journal articles.

Fraser: Right or give us some time on the super computer that you’ve used to run your calculation. It’s a great thought experiment to think about how it is different.

Sorry we couldn’t answer it Robert but we want to at least cover it. Ryan Flores asks: does light have mass?

Pamela: No.

Fraser: Moving on. [Laughter] Really, no mass?

Pamela: Yeah. Light has no mass. It does have energy which means gravity affects it.

Fraser: Okay explain that.

Pamela: E = mc².

Fraser: Right, light has energy and therefore gravity can pull on energy.

Pamela: Yes, energy and mass are just different forms of the exact same stuff.

Fraser: We’ve done a bunch of shows on this. If I take a bunch of energy turn it into matter, it will experience the same amount of gravity either way.

Pamela: Yes.

Fraser: Thanks Einstein. [Laughter] Brad Goodspeed from Toronto, Canada asks: I understand that the cosmic microwave background radiation is the red shifted remains of a much higher energy emission, that being the big bang. The expansion of the universe and the Doppler effects simply appears to make it into looking into longer wavelengths to us because of our very low relative speed. Does that mean that if one could travel near the speed of light the entirety of space would begin to get pushed back into visible light thence the opposite affect?

Okay, so cosmic microwave background radiation is the afterglow of the big bang that has been because of its velocity moving away from us. It has been red shifted from the visible light it was when it was created to the microwave that we see today.

I guess that’s the first part of it. If you we were moving towards I guess moving at close to light speed would the microwave background radiation shift back into another spectrum?

Pamela: Yes but it would shift differently depending upon what direction we’re looking. Let’s say that we’re moving straight north. In that straight north direction we’d see everything eventually as we move faster and faster popped back into the visible light.

At the same time if we were to look straight south looking behind us we’d see that that light would have disappeared out of the microwave and gone further and further into the radio.

Then if we looked perpendicular to the direction of our motion, if we looked left, right and east and west what we’d find is that light didn’t change color at all. The Doppler Effect only affects things along the direction of our motion.

In fact we see that right now when we look out at the cosmic microwave background. We can measure our relative velocity against the cosmic microwave background and figure out how fast are we moving relative to the center of the Milky Way.

How fast is the Milky Way itself moving relative to the cosmic microwave background? It sort of provides us a last ditch way of measuring our own motion through the cosmos.

Fraser: It’s almost like a universal sort of landmark.

Pamela: We’re not supposed to say that there’s any one default frame of reference. That’s one of those things that you learn from Einstein. It does provide us a final check on here’s one frame of reference that we can use to measure ourselves against.

Fraser: Right so if you think you’re moving a certain speed in this direction you can check it against what you see with the cosmic microwave background.

Then I’m just trying to imagine what I would see. I’m on my spaceship, I look ahead and things would get bright.

Pamela: Things would get blue.

Fraser: Things would get blue and I would look behind and things would get redder. I would look out the sides and everything would look the same.

Pamela: Exactly.

Fraser: Wow, and then how far would they go? The faster and faster I go things would just get bluer and bluer in front of me in other words shifting back towards visible back eventually what they would just turn into gamma rays?

Pamela: If you’re moving fast enough.

Fraser: The stuff that’s going behind me even though there’s gamma rays coming at me they could turn into radio waves.

Pamela: Right.

Fraser: That’s cool. J. P. L from Heartland, Michigan asks: is repulsive gravity real?

Pamela: No.

Fraser: But isn’t it no but maybe?

Pamela: Here’s the thing. Gravity itself means one very specific thing. It is the force between two objects of mass where energy and mass are the same thing that pulled two objects together. That’s gravity.

When we start talking about dark energy, it is some sort of a repulsive force that is pushing the universe apart. There are ways of looking at the equations that have it as a force. There are ways that have you looking at the equations as this is some sort of an extra energy that is exerting pressure but it’s a different thing.

You have gravity which is always, always an I’m going to pull two things together force. Then you have dark energy that this mysterious something or other that is causing the universe to push itself apart. That’s not repulsive gravity. It is something different.

A lot of people popularize it as saying oh it’s repulsive gravity. No that’s just sort of like saying that kangaroos are a different form of mouse. No, they’re not genetically similar to mouse at all.

I don’t know why someone would say that but it is equally ludicrous. Dark energy is something completely different. It is a completely different force. Gravity is a very specific mathematical G * m1 * m2 over r² - always attractive.

Fraser: Gravity always sucks.

Pamela: Yes.

Fraser: Right. That’s it for the questions this week Pamela.

This transcript is not an exact match to the audio file. It has been edited for clarity. Transcription and editing by Cindy Leonard.

Shownotes

Can our sun generate a solar flare that could wipe out life on Earth?

• Solar Flares – NASA
• Stellar evolution — UCSD
• Solar Superstorm — Science@NASA
• The most severe space weather (power grids compromised, etc)
• When the Sun Spat Death — Bad Astronomy
• Book: Death From the Skies by Phil Plait

Has the Large Hadron Collider answered any questions about the Higgs Boson?

• What is the LHC?
• Higgs Boson
• Current status of LHC
• Fermilab

What would happen if you shone a flashlight out the front window of a spaceship going near the speed of light?

• Speed of light is relative to the viewer
• Relativity tutorial — UCLA

Could a wormhole form in your brain?

• Wormhole
• White Holes and Wormholes

Can’t we look in the opposite direction of the expansion of galaxies and determine the approximate center of the Universe?

• Episode 77: Where is the Center of the Universe
• Episode 28: What is the Universe Expanding Into?

Does the size of a star affect the speed/velocity/distance that a body requires to maintain a stable orbit around that star?

• Simple Orbital Mechanics
• Mass of star is what matters

When a galaxy is found in the far reaches of the Universe, can astronomers figure out what is occupying that space today?

• A very hard concept in astronomy!
• Project o map far reaches of Universe

How does one become an astronaut?

• NASA’s astronaut selection page
• ESA’s “How to become an astronaut” page
• CSA’s Astronaut page
• JAXA’s Astronaut page
• How do I become an astronaut? – How Stuff Works
• Blog: How I am Becoming an Astronaut

How do scientists accurately account for Earth’s plate tectonics and other movements of Earth-based facilities?

• Plate tectonics — Windows to the Universe
• Movements of Earth’s Crust Detected with GPS – SpaceRef

If the Moon broke apart and became a rubble pile, would that change its gravity effect on Earth?

• How Earth and the Moon interact — Astronomy Today
• What if the Moon didn’t exist? Universe in the Classroom

If the Universe is expanding, couldn’t it be older than we think?

• The Cosmic Microwave Background
• Episode 86: End of Everything part 1
• Episode 87: End of Everything part 2

Could interferometry be used in space?

• Interferometry
• SIM — Space Interferometry Mission
• Terrestrial Planet Finder

Why are Saturn’s rings disappearing?

• Universe Today answers the question

Transcript: Dangerous Solar Flares, Higgs Boson Insights, and Light Speed Flashlights

Download the transcript

Fraser Cain: More questions Pamela. Here come the questions.

Dr. Pamela Gay: These are always so frightening [Laughter] and so wonderful all at once.

Fraser: Can our sun generate a solar flare that would wipe out life on Earth? Has the Large Hadron Collider answered any questions about the Higgs-Boson? What would happen if you shined your flashlight at the front window of a spaceship going almost the speed of light?

Let’s get on with the first zinger – I mean question. Alejandro from North Caldwell, NJ asked a bit of a spoiler so I’ve kind of re-written the question so that nobody really knows what he’s talking about. Could the sun generate an enormous solar flare that kills all life on Earth?

Pamela: Present tense not so much; past tense yes.

Fraser: And how?

Pamela: [Laughter] When stars are young they go through this violent period of massive x-ray emissions and massive coronal mass ejections, flickering evil, ill-tempered nasty to your old type behavior. During that period of time nothing existed on the planet Earth.

Luckily stars settle down and start to behave and our sun is going to be a well-behaved star for awhile longer. While it will eventually destroy the Earth it won’t be through a giant enormous solar flare. It will more like just bake us unendingly until there is no water left.

Fraser: Right but not from a killer solar flare. Don’t you worry.

Pamela: Yeah the closest to a killer solar flare we can get nowadays is a really bad solar flare can take down the power grid. You can imagine if Canada or Siberia or any of the extreme north countries lost all of their power during the winter that could have terrible, terrible effects.

Without heat, people will die. That’s a secondary effect and you can always burn wood. It is something to be feared but we’re not going to have all life on Earth eradicated just potentially a few unfortunate people. That is something to worry about and something to work to protect ourselves from. Society itself is safe.

Fraser: If you want – I know we’ve interviewed Phil Plait with his “Death from the Skies” book – he’s got a chapter on that talking about solar flares and how they aren’t going to kill us all. Although as you said on some stars the solar flares can be quite impressive.

James Sagan asks: has the Hadron Collider given us any insight into whether or not the Higgs particle exists?

Pamela: No.

Fraser: Yeah, it is broken, isn’t it?

Pamela: Yeah this is one of the unfortunate things is they fired her up and something went boink and they shut her off. They’ve been in the process of trying to rebuild and rebuild and redesign some of the mechanisms in the process of rebuilding. They haven’t really gotten a full explosion, a full colliding of particles yet. They haven’t been able to look for the Higgs yet.

Fraser: When is the collider supposed to finally come back online?

Pamela: Sometime next year.

Fraser: Then finally, that would be like we’re in 2009 so sometime in 2010 we may finally know if the Higgs-Boson exists. Or we may find new and interesting ways that the collider can break itself. [Laughter]

Pamela: Fermi Lab is nipping at its heels and it could be that instead the U.S. Accelerator will get its new experiment going. We now have a race of the accelerators.

Fraser: Kate Neilson from Adelaide, Australia asks: if you were traveling in a spaceship that was going the speed of light and you’re standing in a window in the ship and had a flashlight in your hand and you turn on that flashlight out the front window what would happen?

Pamela: I’m going to momentarily ignore the fact that you can’t get things with mass going the speed of light.

Fraser: Right, in her question Kate said that if you had your spaceship going the speed of light and that’s not possible.

Pamela: That’s not possible, but even if you could if you’re chewing along through space at the speed of light time has now stopped for you.

Fraser: Time has no meaning.

Pamela: If time has stopped you can’t turn something on because that requires motion and time and there is no time so you can’t move that extra thing. You can’t actually turn on the flashlight.

Fraser: Okay so let’s say then that you can move at the speed of light [Laughter] and time does have meaning, what would happen to the flashlight that you’re firing out the front window?

Pamela: It would sit there going I’m a flashlight and I’m not going to do anything. The photons can’t move fast enough to get out of me.

Fraser: Right so the photons wouldn’t go anywhere. However I think maybe a more interesting question and is perfectly possible is if you made your spaceship go a fraction of a percentage slower than the speed of light.

Pamela: Yes, now we’re in a universe that makes sense.

Fraser: That makes sense. Let’s say that we use up all of the energy in the whole universe to accelerate our spaceship to almost the speed of light and then you walk up to the front window and turn on your flashlight. What happens?

Pamela: In this case time has slowed down for you so much that it looks just like what would normally happen when you turn on a flashlight. You see the beam shine. You’re not at all aware of how long it takes the beam to go from on to off to shining on distant wall.

Everything appears just like it appears when you’re walking around your house. As long as you’re chugging along at not the speed of light no matter how fast you’re going you’re always going to see the flashlight behave in the exact way.

Fraser: The trick is that people watching you do this somehow are going to see something different.

Pamela: To say you’re moving in slow motion, that’s an understatement. They’ll see that thumb flick that turns on the flashlight as taking years and years to transpire.

Fraser: When it actually works and the beam of light comes on it is going to go at light speed. You’re going to see it from outside. You’re going to see the light beam go exactly the normal speed.

It doesn’t matter that it is inside a spaceship that is already moving at close to the speed of light. It doesn’t matter. This is the whole trick with relativity.

Pamela: Yeah, it’s just the process of turning on the flashlight is excruciatingly boring to watch. Once it is on everything behaves normal no matter who the observer is.

Fraser: Let’s keep going. We have this question from Gopal from Fremont, California. He wants to know: can worm holes form inside the brain and if so would they be really small micro-nano-wormholes carrying bits of information?

Is that some kind of way that information can come into your brain from the universe? Alright let’s talk about what’s a wormhole?

Pamela: The idea of a wormhole is that it is possible to pinch space and time so that you essentially can grab the space over on this side of the universe, the space over on that side of the universe and pinch them together and tunnel through the topography of space.

Fraser: Theoretically possible, right?

Pamela: Theoretically. When you work these out using the geometry that we live in they turn out to be utterly unstable. They self-destruct instantly. You can’t construct one of these things that are stable, they just don’t work.

They’d also require in the case of this question microscopic black holes and white holes. The white holes don’t exist. Microscopic black holes if they did exist probably should have decayed by now.

In general no, no on so many levels wormholes, not stable; microscopic black holes, not stable and would have decayed by now. White holes don’t happen so we’re kind of left with no.

Fraser: But if you were going to try to send information, could you send information through a wormhole?

Pamela: No.

Fraser: Even that would collapse a wormhole? Even just like sending photons, you know radio waves through it would collapse it?

Pamela: Just the existence of it collapses it. They’re not stable in the geometry we have for space and time.

Fraser: Although they are kind of theoretically predicted it is sort of the same thing as white holes, right? They would just collapse as you say instantaneously if you actually were able to create one.

I’ve read varying research and seen articles about it that a wormhole would take the better part of the energy of the universe to try and open up and then as you said collapse instantaneously wasting the better part of the energy of the universe.

Pamela: Not something to be encouraged so close to Earth Day.

Fraser: So no possibility. Let’s move on. Oliver Clap from Australia says: you mentioned that we know that the universe is expanding by a specific speed and that we can determine a direction of movement, but do we know where the center of the universe is or where the origin of the big bang is? Can’t we just look in the opposite direction of the expanding galaxies and determine an approximate center of the universe?

We did a whole show on this which is I believe ‘Where is the Center of the Universe”, but we can kind of give a quick version. Is there a center of the universe?

Pamela: No.

Fraser: No so if I look off to my left and see galaxies expanding away from me and then I look off to the right and see galaxies expanding away from me, doesn’t mean that I’m at the center of the universe?

Pamela: No.

Fraser: Right, and why not? [Laughter]

Pamela: You said you wanted the quick answer. Just sort of like imagine and this is an analogy I keep going back to that all the galaxies are the raisins in a rising thing of raising bread dough. We’re just the microbes on the raisin.

As the dough expands you can be anywhere inside the blob of dough and you will see all the raisins moving away from you as the dough between the raisins gets bigger and bigger.

If you were able to somehow reverse this yeasty process all of the raisins would feel themselves getting closer and closer to one another as the stuff between them gets smaller.

It doesn’t matter which raisin you’re on just like it doesn’t matter which galaxy you’re in anywhere in the universe. You always perceive everyone moving away from you and everyone moving towards you if you go backwards in time.

Fraser: To sort of do this experiment in two dimensions, keep in mind this is just two dimensions. Take a balloon blow it up a tiny little bit and then put a bunch of dots on it at equal distances and then blow up the balloon some more.

You’ll see that every dot moves away from every other dot the exact same amount. If you were on any one of those dots on the balloon looking at the other dots you would see them all moving away from you at the exact same speed.

Obviously a balloon is a 3-dimensional object and it has a center point in the middle of the air in the middle but from a 2-dimensional standpoint there is no center to the 2-dimensional surface of the balloon.

Pamela: There is no center to the 3-dimensional universe that we live in. We can’t discuss what we’re expanding into. Just like the balloon if you live on the surface of the balloon it has no knowledge of what it is expanding into. It’s just expanding and our universe is just expanding.

Fraser: We did a show called “What is the Universe Expanding Into”? You might want to check that one out as well.

Phil Courtney from Newburry UK asks: Does the size of a star affect the speed/velocity distance that a body requires to maintain a stable orbit around the star?

Pamela: Yes. It is good to say yes.

Fraser: You got to say yes! [Laughter]

Pamela: The thing about stars is to be stable at a given diameter they have to have a certain amount of mass. If I have two main sequence stars, two stars that are both burning hydrogen in their cores into heavier and heavier elements these two stars, if one has a larger diameter than the other one, the one with the larger diameter is going to have to have a larger mass as well. It is actually the mass that matters. If you have a more massive star, an object orbiting around it is going to have to go faster in its orbit at a given distance to stay there.

If we were to take the Earth, keep it where it is and replace the sun suddenly with an object that was twice as massive our Earth would go spiraling in towards the sun and it would end up on an elliptical orbit plunging closer to the sun than it currently gets. If we wanted to stay where we are now we’d have to increase our velocity.

Fraser: Yeah but Phil’s question is about the size of the star. So if we replaced our sun with a black hole of the same mass would that affect the orbit of the Earth?

Pamela: No.

Fraser: So your answer was no?

Pamela: Well but I wanted to say yes so I used diameter to give it mass.

Fraser: Alright, isn’t there some point like say with the Roche limit of the star? If you had a star that had the same mass as the sun but was almost out to the orbit of the Earth would the Earth orbit in the exact same way?

Pamela: There would be more frictional forces, more tidal forces if we’re just about grazing because we’d have our atmosphere and its atmosphere touching and all sorts of touching slowing things down. That would start to have an effect.

That’s not just the gravity that is making it stable. This is where you’re starting to basically yank the things due to friction. That’s a different kind of affect. If you’re looking strictly at does the orbital mechanics equation balance out the diameter won’t matter.

Fraser: Right so the diameter of the star doesn’t matter for what orbit the planet or some object has to go around a star. It’s all the mass, only the mass of the star is what matters.

Pamela: Exactly.

Fraser: Timo Marcannon from Victoria, B.C. asks – that’s on my island! When a galaxy or group of galaxies are found in the far reaches of the universe can scientists figure out what is physically occupying that space today? Can we not see it because the light was sent billions of years ago and they’ve been destroyed or galaxies have merged together?

So can we when we look at objects that are billions of light years away we’re seeing them as they were billions of years ago, so can astronomers know what’s there today even though what we’re seeing has been long gone for billions of years?

Pamela: This is such an amazingly complicated question. There are two different problems. The first is defining occupying that physical space because the universe is expanding.

So are you asking me what is occupying the co-moving volume of space that is expanding away from us and has been carried away from us by the expansion of the universe, or are you asking me what is filling the space that is the same distance from me today that that object was when it emitted the light?

Fraser: Okay, I can imagine an analogy. I take a photograph of one let’s say of a spot on an escalator and then I come up to you and say can you tell me what’s in this spot on the escalator right now?

I guess you’d kind of have two questions: do I want to know what’s on that stair right now or do I want to know at that exact same spot of the escalator? Although it is going to be different stairs there now, right?

Pamela: That’s exactly the problem.

Fraser: I guess those are the two questions then. Let’s go with both, why not answer both?

Pamela: If you’re asking me what’s on that stair that’s getting carried away I can say well that group of galaxies has probably been carried off toward the nearest cluster of galaxies.

But if it happened to have been the largest thing in its neighborhood it might have just stayed put where it is. The galaxies inside of it have merged, evolved, have changed.

If it is the biggest thing in its neighborhood it has probably consumed some of its nearby neighbors. We know how space in general is evolving. The diffuse background of galaxies in the far past where we had small clusters, we had in many cases even small galaxies originally. Things have been merging and building and the voids have been getting bigger as the clusters themselves have been getting denser.

It is where the small things went that gets to be more difficult because then you have to start figuring out what was all of the stuff that might have been yanking on this small thing.

As for what is in that particular place on the escalator if instead of asking about that stair that is carrying the cluster of galaxies further away.

If instead you want to know what is in that particular place relative to the landscape, I can’t answer that one.

Fraser: Because the expansion of spaces continue to go on and you don’t really know what’s there now.

Pamela: Exactly.

Fraser: Liz Frasek from Pawhuska, Oklahoma asks: how does one become an astronaut?

Pamela: Very, very carefully.

Fraser: Yeah, that’s a whole show on its own. Maybe we should do that as a show. [Laughter]

Pamela: I have to admit that this is one of those things that when you start looking at all the different characteristics of all the different astronauts, they come from such a diversity of backgrounds that there is no one clear recipe.

There are certain factors that turn up over and over again. Military experience, being Eagle Scouts for the men, having the ability to do some combination of medicine, and speak foreign languages and being technologically literate. All of these things all at once go into many of the different people who are selected.

Fraser: Right there are a couple of classifications. There are the people who fly the spacecraft the pilot, the commander. Those people generally come from a military test pilot background. They’ve been in the Air Force, Navy, they have flown aircraft.

They are at the top of their game. Plus they have one or many advanced degrees although you know not necessarily in physics, engineering, medicine and things like that.

Pamela: There are medical doctors.

Fraser: Then they have what are called mission specialists. Mission specialists don’t need to have been a test pilot but then you’ve got to be an amazing human being.

This is where you’ve got multiple PhDs as you said a tremendous amount of real world experience in medicine, science, and physics.

It is amazing to see because so many people want to be astronauts and NASA and ESA can choose from just like the greatest people in their respective countries.

Pamela: You have time to get there. That’s the really amazing thing.

Fraser: Sure but if you’re young and you want to be an astronaut

Pamela: Be amazing today. You have to be amazing for a long time.

Fraser: Yeah, get rolling and you have to put in the same level of commitment to it as to be in the Olympics.

Pamela: Right you have to be physically fit, you have to be intellectually fit. You have to be diverse. You should learn Russian.

Nowadays you probably should also learn Chinese and look to see where you think the next great space faring nation is going to come from. You have time.

The people that they hire to be astronauts are often in their mid-thirties and early forties. To get there especially as a mission specialist you have time.

This is one of those rare exceptions of you really can’t start early enough in terms of both the physical fitness, going to the big schools, going to the good graduate schools, getting the right jobs and just staying after the dream every single day.

Fraser: Or, pay twenty million dollars.

Pamela: That works too.

Fraser: So, one way or the other. I actually think that’s the easier way. [Laughter]

Pamela: Yes.

Fraser: Really, go into business, save up twenty million dollars and buy your way onto the International Space station on a Soyuz flight.

I think that’s the less complicated one that you have more control over. That’s plan B.

Pamela: I bet that there are probably more people on the planet Earth who have those twenty million dollars than are in all the astronaut cores of the world and have gone into space.

Fraser: Now you know what you’re up against. This is John Holmes from Ankara, Turkey: how is it that scientists accurately account for Earth plate tectonics and other movements of our Earth-based instruments and facilities?

So, this is kind of relating to the kinds of things like we talked about how there is the reflectors on the moon and we can detect that the moon is moving by a couple of centimeters a year, drifting away from us.

We also know that for example thanks to plate tectonics here on Earth the plates are shifting apart a couple of centimeters and so you’re moving further away from the moon just on the surface of the Earth wherever you have your laser. How do scientists keep those two things in mind and in balance?

Pamela: GPS. Here’s the thing. We can’t really measure very accurately where we are on the surface of the Earth from the surface of the Earth. The Earth’s crust flexes in response to the moon just as much as the oceans.

We have to be able to take especially with people that are measuring pulsars for instance where they need to get extremely accurate timings; we have to take into account the tides of the Earth.

We have to take into account the flexes of the planet. To do this we have to start making our measurements off of satellites that are orbiting the center of mass of the planet.

It is by measuring how these timings change, by measuring how the orbits of the satellites change that we’re able to very carefully first map the gravity of the planet and also map the motions of the surface of the planet.

Fraser: They do it by taking it all into account. They have to and so they know they’ve measured with GPS how much for example a facility rises and falls with the tides every day even though it is on the ground.

They do take into account I guess plate tectonics and the distance of the moon and all that. They’re very careful.

Pamela: We can calibrate things using pulsars. This is one of the really cool things is the most precise timing mechanism that we know of is pulsars.

By looking at how the arrival time of the pulsars changes we can make sure that we got all the rest of our answers right.

Fraser: That’s crazy. That’s amazing.

Pamela: It’s cool though. [Laughter]

Fraser: Not crazy I mean dedicated and focused and very careful. Jason Parsley from Lakeland, Florida: what would happen if the moon were to fracture into a bunch of tiny pieces like a puzzle and become a giant floating rubble pile? Would that change the affect of gravity on the Earth?

It’s not really possible but imagine someone exploded the moon from inside but not in such a way that it completely blew apart. It just kind of reformed itself into a pile of rubble. Would that change the tides or anything on the Earth?

Pamela: No as long as the moon is in the same place and the chunks are gravitationally chunked together even if the molecular bonds and the minerals and everything else is broken into a zillion little pieces.

As long as the center of mass stays the same distance from the Earth’s center everything is going to be happy. Everything is going to keep moving along.

The issue you now have is this body that isn’t held together any longer. The chunks of moon that are closer to the Earth are going to want to orbit at one rate.

The chunks of moon that are at a more distant place are going to want to orbit at a different rate. Over time this blob of moon unless it gravitationally holds itself together, it just depends on how much energy you give these chunks.

If you give the chunks enough energy that they can escape the gravitational well of this now basically rubble pile, you might end up with something that is more ring-like than moon-like.

As long as those blobs can gravitationally hold themselves together everything is fine. It is going to behave just like the moon; it is just going to be more interesting to look at.

Fraser: Back to the original question that we asked, if we replace a rubble pile with a black hole with the mass of the moon no difference, still get the tides, everything. It just comes down to the mass.

Pamela: No difference.

Fraser: What if you were to stand on the rubble pile? Would it feel any different?

Pamela: No not really because as long as the rubble is held together gravitationally you’re still going to have the same pull from the center of mass of that rubble pile that you have normally from the moon.

You might have a slightly crunchier surface but the regulus itself is pretty crunchy. I think you’re just basically looking at the same sort of experience but much more artistic in its rendering.

Fraser: In a few billion years the rubble pile would all merge into a nice perfect sphere again.

Pamela: Yeah, that’s the nice thing about gravity.

Fraser: You wouldn’t even know that it had ever happened. David Shaun Siever from Montana asks: if the universe is expanding faster than the speed of light and in the future we’ll see less and less of the universe that we can see now why couldn’t it be that the age of the universe older than we think and there’s matter that is beyond what we can see now?

I guess what David is asking as we mentioned in previous shows although nothing can move faster than the speed of light the objects that are being carried away by the expansion of the universe as it is accelerating can eventually be receding from us faster than the speed of light.

At that point they will stretch out into the red and look like these sorts of ghostly artifacts on the edge of the horizon and then eventually disappear. Could it be that that has already happened and that we just can’t see a much larger universe and then that might mean that the big bang didn’t happen how we thought and that there is more universe out there?

Pamela: No.

Fraser: Nope, okay, moving on. [Laughter]

Pamela: Seriously though the cosmic microwave background is there as a check on all of our math.

Fraser: Right.

Pamela: Because we’re able to look out and say ah, cosmic microwave background and then we’re able to say ah, early in the universe we have nice much less chunky distribution of stuff. As we look at clusters that are closer and closer to us we see that they’re more and more clustered.

We can actually see the universe going from not smooth but smoother distribution of galaxies and galaxy clusters to this fine filigree with large voids in-between the structures.

By being able to see the entire picture from the cosmic microwave backgrounds of today we have all these different places that we can check that we understand what’s going on. We can check that yes all of this matches with the universe that’s 13.7 plus or minus .2 billion years old.

Fraser: That isn’t always going to be the case is it? A few trillion years down the road David’s comment is entirely true. Astronomers will be sitting there talking and be like we don’t know how old the universe is.

Pamela: This is one of the things where astronomers hate to say that we live in a special time or a special place. It does appear that we do live in a time that is one of the rare moments given the entire duration of how long the universe is going to last.

We’re lucky enough to live in one of those moments where we can see enough of the history of the universe to understand the history of the universe.

Fraser: There will be a time, trillions of years in the future when the cosmic microwave background radiation will be so red-shifted that we won’t even be able to see it.

Some of the more distant galaxy clusters will be accelerating away from us at faster than the speed of light and we won’t be able to see their light anymore. We’ll have no idea how old the universe is anymore. That’s kind of sad.

We’ve got a whole show on this. We have a 2-part show called “The End of Everything” where in the first part we talk about the end of the solar system all the way up to the end of the solar system. In the second part we talk about the end of the universe and cover this as well. That’s in there.

Mike Robinson from Ontario, Canada asks: you’ve mentioned before that two ground-based observatories can use a technique called interferometry to increase the effective resolution of the combined images. Couldn’t this be used in space telescopes?

Could you make a space telescope where you put observatories on either side of the sun and make a telescope with a resolution of the Earth’s orbit? Are any space-based interferometers in the works?

Pamela: Sort of, kind of I don’t get to say yes or no on this one.

Fraser: Terrestrial Planet Finder.

Pamela: That’s where the sort of kind of comes from. Terrestrial Planet Finder is one of our favorite missions. It is the one that just shows no signs of making it to the launch pad. It is a cool mission.

It actually is three different space telescopes working together as interferometers communicating with a central hub. They’re not exactly spread out on either side of the sun but they’re spread out enough that you can do things that we just can’t do from here on the surface of the Earth.

Fraser: Oh, like detect life on other planets maybe?

Pamela: Right all those cool sorts of things.

Fraser: You know that little thing. [Laughter]

Pamela: Building one of these that sticks things on either side of the sun gets a little bit more complicated because they can’t talk back and forth because the sun is in-between the two of them.

If you got creative and you figured out how to do this with three things, one in front of the sun and one to either side and they were communicating with the one out in front it still doesn’t work quite so well because you want to be able to combine the lights. You want all the light paths to be equal so you can’t quite do that.

You end up having to figure out well then yeah there is no easy geometry that involves orbiting the sun. You can get the groups of them with rockets to keep them together so you have to constantly be correcting the orbits. You can find ways to get them orbiting around the sun spread out enough that you can do really cool things.

Fraser: I guess it is a failure of our current technology and the ability of the precision of our technology but it is theoretically possible to locate three spacecraft in orbit around the sun and create interferometer. If you could somehow sync up these signals you could indeed have a telescope the size of the Earth’s orbit.

Pamela: Yes.

Fraser: Whoa. Now that would be all about resolution, resolving power, right? It would allow you to see how far apart the buildings are on planets orbiting other stars. [Laughter]

Pamela: I don’t think it would be quite that good of resolution but yeah.

Fraser: How far apart the trees or the branches of the yeah.

Pamela: It would be maybe able to let you see if Jupiter has a really cool giant moon. That’s still pretty cool.

Fraser: That would be pretty cool. Last question comes from Dagua from Ghana: I viewed Saturn through a telescope and quickly saw that the rings are hardly visible. Research has shown that Saturn is going to be in this position for quite some time. I was wondering why is Saturn edge on? The rings were nice and visible years ago what made the planet turn edge on? Do the planets roll in their orbits even though they’re also rotating on their axis?

So, is that true? If you looked at Saturn right now in the middle of 2009 would you be able to see the rings of Saturn?

Pamela: Only sort of kind of because he’s right, they’re going edge on right now. In fact this is leading to some really cool images where we’re seeing some really amazing shadowing across the surface of the rings from the Cassini mission.

In general the planet Saturn goes through the cycle where we go from essentially looking so that we can see the north pole of Saturn and see its rings fairly face on to it rotates from summer in the northern hemisphere to seeing the rings exactly edge on. This is more like the equinox for Saturn. Then we start to see the south pole of Saturn.

Fraser: Right and the process that’s going on here is exactly the same as why we have the seasons here on Earth.

Pamela: It just takes a lot longer because Saturn is further out. We’re just seeing it relative to the stars it keeps the same pole pointed towards the same star all the time.

As that entire system orbits around the sun what’s pointed at the sun changes from Earth year to Earth year as Saturn progresses year by year around the sun.

Fraser: Saturn is not rolling or tumbling or in any way changing its orbit. In fact it is being perfectly stable. It is like a top that is spinning.

It’s just that from our perspective we’re seeing various angles of Saturn. If you were to stand on Saturn the same star would be right over your north pole all the time the same way that we have it here on Earth.

Pamela: You can simulate this with a school globe. If you take a globe that is mounted so that it is tilted and put basically a fin all the way around it so it is like the Earth globe has its own ring going around its equator.

If you then hold it so that it is always keeping the north pole pointed at one wall and bring it around your head you’ll see it so that that disc that you’ve artificially put around the planet Earth goes from edge on to face on to edge on to face on again as it goes around and around.

Fraser: Right and I was going to come up with some analogy where you’d have some friend hold their arms out orbit you. [Laughter] Have a hula hoop but that’s it.

Pamela: Yeah, just use your school globe. [Laughter]

Fraser: Use your school globe and that’s the point is that you make sure that the north pole of the globe is always facing in exactly the same direction. Don’t turn the north pole and south pole as you move it around you always keep it in one direction.

You’ll see how for one part of if you’re looking at the bottom of the globe and you’re seeing the rings full on. Then a little after that you’re seeing the side of the globe and the rings are edge on.

Then you’re seeing the top of the globe and you’re seeing the full rings again and then you’re seeing the edge of the globe again and so you’re seeing the other side of the globe and the rings are edge on. That’s all that’s going on.

Pamela: And that’s pretty cool.

Fraser: Alright but if you haven’t seen Saturn in a telescope yet another wake up call you know get out there. I don’t care how, beg, borrow, steal some telescope time with a friend and stick your eye to the eyepiece and see Saturn with your own eyeballs and your own brain for once in your life.

You’re listening to AstronomyCast almost 200 episodes if you include all the questions [Laughter] you haven’t seen Saturn in a telescope with your own eyes? I’ll just have to keep nagging. Do it! [Laughter] It is the greatest thing ever. It completely changes your opinion of astronomy and brings it all home.

Pamela: While this isn’t the best year to do it, the Galileo scopes that are getting sold by IYA which are only about $15.00 are good enough to see Saturn’s rings even as edge on and sad as they are.

Fraser: I looked through one. I saw the moons of Jupiter and bands on the planet of Jupiter. These Galileo scopes are perfectly acceptable. For $15.00 you can get your own telescope. Get on it! Thanks a lot for the questions Pamela and we’ll talk to you next time.