Fraser Cain: Now we’re at the third part of our trilogy on the human exploration and colonization of Mars. Humans living on Mars will inevitably tire of living underground. They will want to stretch their legs and fill their lungs with fresh air. One day they will contemplate what it will take to reshape Mars to suit human life. Is it even possible? What technologies would be used? And what is the best that colonists could hope for in changing Mars? 

Pamela, we talked about last week about how Mars is very hostile to life. The temperatures can be 150 degrees below zero at the poles. Even on your best hottest summer day you’re not going to get but a few degrees above freezing. The pressure is one percent of what we experience here on Earth. There’s radiation, essentially a long-term lethal dose of radiation. It’s cancer for everyone living out on the surface of Mars.

So, we’ve talked about people living underground in essentially pressurized space suits or in pressurized chambers where you can keep the pressure, the temperature, and protect them from radiation. That’s a really hard way to live. So inevitably the question is: Could we change Mars? How possible is it with the laws of physics to change Mars?

Dr. Pamela Gay: Well with the laws of physics, you can do it. The question is can you afford to and if you can’t afford to, should you? There are a lot of ethical questions to consider when you start thinking about completely changing the nature of another planet that just might harbor fossil life or actual life somewhere within its soils.

Fraser: Why don’t we deal with the ethical issues later? Imagine that you were some superpower human being and some advanced civilization with tremendous access to power and all of that and you want to sorta quickly modify Mars to make it more appropriate for human life. What are the things that you could do with a snap of your finger?

Pamela: [Laughter] If you want to do it quickly…..

Fraser: No, I don’t want to say do it quickly, but the point is if we could change Mars to be more appropriate for human life, what are the things that need to change on the planet?

Pamela: Well, there are basically three issues. First of all you have to give it a thicker atmosphere. Then you have to give it warmer temperatures. These two are actually coupled to one another. Third, you need to find a way to deal with the whole lack of a magnetic field and that one gets much trickier to deal with. Dealing with the first two, the low temperatures and the very thin atmosphere, can be dealt with by first releasing a lot of greenhouse gases into the atmosphere of Mars. Either by perhaps crash-landing rockets filled with chloro-flora carbons onto the surface of Mars or use some other mechanism that some chemical engineer still needs to imagine.
 :
By releasing all of these greenhouse gases onto the planet you can systematically increase the planet’s ability to retain its heat. Right now, sunlight hits Mars, it reflects off and a lot of this heat is lost back into Space as infra-red light.
 :
You can imagine being able to essentially wrap an atmospheric blanket around Mars such that sunlight hits the planet, starts to reflect off the soil, hits the atmosphere and then reflects back down. This heat stays with Mars and continues to build up and warm the planet over time. Sorta like heat that’s released by the coils in your oven is kept in by the walls of your oven allowing the temperature in your oven to continually increase.

Fraser: You could really see that when on your car. When you keep the windows up, even on a not very hot day, it’s amazing how hot the car will get inside. If you even crack the window just a little bit to let that heat escape, then the car will cool down quite a bit.

Pamela: And right now Mars’ atmosphere is so thin that it is essentially a convertible with the top completely removed. By simply dumping a bunch of chloroflorocarbons on to the planet, we can raise the roof of that convertible. That small change will allow more of the water ice on Mars to melt and add water vapor to the atmosphere of Mars. Water vapor itself is a greenhouse gas so here we’re starting to roll up the windows of our convertible.
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Over time as you build up more and more gases that have been previously trapped as various ices within the soils and at the north and south poles of Mars, you can convert these ices into atmospheric gases which will continue to heat the planet. Pretty soon we might be able to get something that at least in terms of temperature is suitable for human life.

Fraser: Right, so you would be able to put on a jacket, head outside, and the temperature wouldn’t be really awful. But, you’ve still got the atmospheric pressure so you’re saying that you really can’t thicken the atmosphere really too much?

Pamela: Well, you can thicken it but getting it thick enough that it is comfortable for a human being used to living at ground level here on the planet Earth is unclear. We don’t know if there are enough gases trapped within ices on Mars that you can, using just what is there, get that thick of an atmosphere on a useful time scale. The problem is these gases are continually escaping from Mars.
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It is a little planet with very little gravity, light elements that are released into the atmosphere just through normal particle to particle collisions they are accelerated to escape velocities. Then you have the Sun blasting the atmosphere of the planet and in turn blasting away bits and pieces of the atmosphere. So, you have to be able to release these gases quickly. Even then, they might only hang around for a thousand to a few thousand years without being restocked. You have to start asking where do you restock the gases from?
 :
You start considering ways to capture comets and otherwise bring oxygen, carbon dioxide, and nitrogen all to the atmosphere. There is also no natural buffer gas. Here on Earth we have an atmosphere rich in nitrogen that doesn’t totally get involved in building molecules on a regular basis.
 :
The types of gases that the Martian atmosphere would be rich in are things that like to form molecules. Thus, you need this buffer gas as well to make a nice happy atmosphere.

Fraser: So, the problem you’re getting here is that Mars has no magnetic field, right? The Earth’s magnetic field forms a protective bubble that buffets away the Solar Wind and keeps it from really interacting with our atmosphere. If we didn’t have our magnetic field, the Solar Wind would be blasting away our atmosphere just like it did to Mars.
 :
You would need some way to constantly replenish the atmosphere on Mars or you might have it incredibly thick in the beginning and then over time it would just be eroded again. You would no longer have reserves on the planet you could be using to rebuild it. Without that magnetic field it’s a lost cause. And also with a lower gravity, that sounds like a pretty big problem.

Pamela: Yeah. But it’s not something that if you throw enough energy at the problem isn’t unsolvable. As I said, you could conceivably go out and start capturing comets. Comets are rich in things like water that you can tear apart and turn into atmospheres.
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It’s not exactly a trivial problem to go out to the Quaker belt and capture yourself a whole bunch of large icy objects and tote them back to Mars. While we’re wandering out in the dreamland of terraforming, it’s possible to conceive that on the thousand year time scales things like this might be possible.

Fraser: But it almost sounds like with that problem and the lack of a magnetic field is going to come back to haunt us for another part as well. It might make sense to just get more mass on the planet, right? [Laughter] Smash Mars and you know all the Asteroid Belts gather. Crash that into….you know? [Laughter]

Pamela: There is actually an even more interesting solution that I read about. There weren’t any real descriptions of how you do this but one of the ideas I saw kicking around on the internet was you find a way to build a giant magnifying lens. The biggest magnifying lens ever and place it in an orbit such that it focuses the light of the Sun on Mars and melts Mars until it has a liquid core again. You wait for the planet to cool off enough that you can stand on the surface again.
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Now that you have a new version of the planet Mars with a new liquid core having destroyed everything else and probably lost all the atmospheric particles in the process of vaporizing the planet, you at least have magnetic fields now. It was a suggestion that needs to be thought out a bit better but it did amuse me.

Fraser: Right – it almost sounds like domes are your way to go, right?

Pamela: Yeah.

Fraser: You build a dome and then boom. You’ve got protection from the radiation; you have the temperature and pressure. You’ve got everything you need. Okay, so we’ve talked about the temperature and the pressure like rise in lock step. You give the impression that there is a limit to the pressure, right?

Pamela: There’s a limit to the pressure until you start bringing in things from other places. As you heat the planet up, you’re going to be melting ices and the gas from these ices slowly pop up the atmosphere. They add pressure to it by adding additional molecules.
 :
This is similar to taking a balloon and dropping in a piece of dry ice and tying a knot. As that dry ice changes from ice to gas the balloon will blow up. With Mars, gravity acts as the walls of the balloon helping hold that gas to the surface of Mars. As you melt the ice the atmosphere gets thicker and thicker.
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But, the thickness of the atmosphere is limited by how much material there is to melt. We’re still not fully sure of just what reserves there are within the soils that we can release. There is a limit – a limit defined by what ice is trapped within the soil on Mars and at this point in the studies I’ve found, it looks like you’re going to get maybe a tenth of the atmosphere of Earth tops.
 :
And that is standing at the bottom of the deepest chasms of Vales Marineris which I’m sure I’ve mispronounced thirty times in this series, standing down in the base of that chasm you might be able to start to get something that will at least allow you to stand outside and not have your skin bruised to badly as it is subjected to too low of a pressure.

Fraser: Right. Let’s talk about the third problem then, which is the lack of a magnetic field and the radiation that’s coming.

Pamela: Here is where we’re not sure how huge of a problem it is. We know that the radiation is such that you’re going to just blow right past the United States’ recommendations on radiation levels in the workplace. In a matter of days you will get the recommended level for a year. That’s bad.
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At what point it becomes cancer causing, we don’t know. That’s an experiment that we haven’t done and can’t do because it is slightly immoral you might say. There’s a radiation problem. You can probably walk around on the surface a few hours at a time in a space suit without worrying for your life, but you do need a way to protect yourself during your day-to-day activities.
 :
Burying yourself underground is sufficient. Air actually helps deter radiation but you’re starting to need a hundred meters or more of the atmosphere to get out (and that’s sea level what we have down here on earth atmospheric pressures) to start getting the radiation down to acceptable levels.

Fraser: Right, that’s what I was going to mention is that the atmosphere itself does help protect against the radiation. So that thickening of the atmosphere will really serve triple duty.

Pamela: If we can come up with a way to do what’s called either para terraforming or creating a world house, a giant greenhouse that combines a thick (defined as like a hundred meters) atmosphere beneath a lead-lined glass or leaded glass canopy that itself is fairly thick to help deter from radiation.
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There are different types of high-energy particles that can’t penetrate through glass. Through this sort of combined construction that allows sunlight through that stops things like alpha particles from coming through, beta particles from coming through, it may be possible to lower the risks to the point that they’re acceptable.

Fraser: What about plants? Would you be able to grow plants on the surface of Mars?

Pamela: This is one of the cool ideas. I highly recommend anyone who is interested in terraforming go read the excellent book “Red Mars” by Kim Stanley Robinson. There are different people who have hypothesized ways to basically take algaes that are perfectly happy to live on Mars today, release them and then slowly genetically engineer high altitude grasses, arctic grasses to get something that is both happy in the extremely frigid temperatures and in the extremely low pressures.
 :
You also start finding ways to suppress the different plants’ chemical responses to trauma, putting the plants essentially on “happy pills”.

Fraser: Like giving them some Prozac.

Pamela: Through a combination of “better living through chemistry and genetic engineering” it may be possible to create agricultural products that will live beyond domed protection on Mars.

Fraser: And that could start fairly soon, right? As you said, there are algaes here on Earth that are almost able to live in the Martian environment.

Pamela: And there are those who think that actually we probably could just dump some of the algaes found on Earth on Mars and they would happily go off and do its little algae thing.
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It’s somewhat frightening to imagine that just a cavalier accidental transportation of green slime from Earth to Mars could create new forms of life living on another planet. This is where the ethical considerations start to come in.
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It’s not impossible to imagine piggybacking life here to there and if it hasn’t already happened via rocks which is probably possible. We certainly send enough metal debris over to Mars with our own contaminations on it. We might have already started the terraforming process without realizing it.

Fraser: Sure, there’s no doubt that we have sent bacteria to Mars from Earth on the Rovers, on things that have crashed on the planet. I know that for example when bacteria were on one of the Lunar missions, the Surveyor mission was sitting on the surface of the moon. When the astronauts landed near it, they pulled off its camera and brought it back to Earth and scientists were able to find bacteria that had made the journey, sat perfectly dormant on the surface of the Moon for five years or more and then they brought it back to Earth and were able to get it going again. It survived no problem.
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So, who knows I guess if the kinds of bacteria that we have shipped off to Mars are the kind that can survive and even thrive in that kind of environment. So, I think you’re right we may have already begun that process.
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It is an interesting ethical debate. I think it’s not one that we have much of a conversation about on Earth. We do it and that’s that. Humans have modified the environment of Earth to suit our needs and I a lot of people are concerned about what impact we’re having on the environment with the species lost, temperature changes through global warming and all those kinds of things. At the end of the day, it’s not should we not at all build houses or cut down forests or that kind of thing but rather to what extent.
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It’s interesting to me to hear people say we shouldn’t modify Mars at all because we’re going to. It’s just inevitable. We will get to a point where Earth is full and colonists are living on Mars and they’re going to want to go and plant a plant outside. It’s just going to happen. [Laughter] I see it more.
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It’s like we have a whole Solar System here that we have existed and it is just inevitable to the point that we are going to reshape the Solar System to match human needs. So, on the one hand I think it’s an interesting ethical debate, but for me it feels inevitable that we will reshape the whole Solar System to meet human needs.
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There will come a day when we will control all of the energy output of the Sun. We will reshape the planets to provide as much habitable living space as possible. Ideally, we’ll keep some amount of green space and natural environments as we can but we will have torn apart the entire planet Earth, turned it into a ring or a sphere or who knows what it would be to collect every piece of sunlight from the Sun.
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It’s a matter of when, when along that time-line do we want to reshape and destroy every environment in the Solar System. [Laughter]

Pamela: I think that this falls into the same category of keeping an archaeologist on hand when you’re digging around, building a new building. It’s worthwhile as we look to take over new environmental niches within the Solar System to have the biologists on hand to go in first to dig through first to figure out what is it we’re about to destroy and let’s scrape some up and stick it in a bottle and try to understand what it is within the environments that was there originally.
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Let’s document the history of our Solar System before we remove the evidence for future generations. It’s a chance to be able to look back and see there used to be a dead Dodo bird on the planet Earth. We know there is nothing as exciting as the Dodo bird on the planet Mars unless it lives deep underground where the Rovers would fail to find it. Really I don’t think there is anything as exciting as the Dodo bird on Mars but I’ll always leave room for the amazing.
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As we go and explore Mars it would be good for us to keep track of the microbes before and the potential algaes and lichens. I don’t think we’re going to find anything that complex either. But if we do, it needs to go somewhere like one of these preserve all the DNA we can crypts that exist here on Earth already.

Fraser: I think the other possibility is that as our technology improves and changes we’re going to have more and more robotic, artificial life happening in the Solar System. It’s very possible that on the time scales, we’re looking at hundreds and hundreds and maybe thousands of years to terraform Mars.
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I would be very surprised if human beings were still the same hundreds of years from now that we really need to change Mars to suit our current form and that we may very well have a future form that is more integrated with technology and doesn’t need the planet to be changed so much. Our technology, the Mars Rovers are suited to live on Mars today. That might be what the future of life is going to look like so we have the old fleshy humans living here on Earth [Laughter] and the new robo-humans living on Mars and maybe the needs for terraforming aren’t so great.
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I think a lot of this stuff is very interesting. As the technology improves, as our science improves, it completely changes our understanding of what’s involved and what the ethical issues are. I’m looking forward to see how these debates go in the future but….

Pamela: Yeah, and you have a very creepy future living in your head with robo-humans living [Laughter] living on Mars.

Fraser: I know, just passing time until that last plucky black hole gives away to the future. [Laughter] Anyway, Mars is the most natural target that we would want to consider to terraform. But that’s not the only place in the Solar System we could have a go at. Venus strikes me as much closer. It has the mass, a thick atmosphere, what could we do to change Venus?

Pamela: The problem with Venus is it had a runaway greenhouse event at some point in its past where the atmosphere didn’t just trap some sunlight, it trapped all of it. In the process it boiled off any water that was in the soil to the point that plate techtonics can’t even exist anymore.
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The soil has been completely desiccated of moisture and all that moisture went into continuing a run away greenhouse effect and now we have a planet with a temperature on the order of 500 degrees Celsius and that’s just not a way for any planet to be.
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To fix that particular planet we need to strip the greenhouse gases out of its atmosphere finding some way to sequester all of the carbon-based molecules, the carbon monoxide, and carbon dioxide. Certainly we want to get that sulphuric acid out of the atmosphere as well while we’re at it.
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Exactly how to do all of this is something that is not a well-defined pathway. It is not as if we can plant redwoods on the surface of Venus that will happily absorb all of these toxins. The planet is 500 degrees.

Fraser: Yeah, we drop spacecraft made of metal onto it and it barely survives more than a couple hours before they die.

Pamela: They melt.

Fraser: In this case, our happy Mars Rovers would be burned alive if they were dropped on the surface of Venus. [Laughter] You need some mechanism for extracting and sequestering carbon out of the atmosphere of Venus. You would need to do a lot. The atmosphere on Venus is thicker than Earth, right?

Pamela: Yeah, so we would need to find a way to take these tens of atmosphere’s atmosphere and suck a lot of the gas out of it. There are different ways to imagine doing this using chemical reactions and catalysts where you basically rain through the atmosphere some sort of chemical that as it falls through the atmosphere, bonds with the different greenhouse gases.
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This has huge energy requirements. This has huge requirements of just taking resources from planet Earth or resources that we figure out how to mine out of asteroids or comets that make the mistake of getting in our clutches.
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Then we use those resources to rain chemical fear on the surface of Venus by changing everything. By changing its entire atmosphere, by transforming gases back into solids. That’s not an easy process. Again it’s something to keep the chemical engineers out there who like to dream big very busy.

Fraser: And I think I mentioned this before that in Venus if you can reach an altitude of about 50 kilometers, the temperature and pressure are the same as Earth. So, you could actually set up a floating balloon station on Venus and live there and go outside with just a breathing mask and feel perfectly normal.

Pamela: You can call yourself Lando Calrisian.

Fraser: Yeah exactly living in your cloud city. That would be awesome. [Laughter] Okay, so Venus you have to extract the carbons and maybe send it all to Mars. Pull out chunks of carbon in your cloud city and [Laughter] fire off rockets to Mars delivering fresh carbon to thicken Mars’ atmosphere.
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Is there anywhere else maybe in the Solar System that could use a little terraforming?

Pamela: Well, there is a discussion that perhaps you could take Europa with its liquid seas, but the problem with Europa is while it has water, it also has high radiation.
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A poor astronaut on the surface of Europa would have ten minutes to live before the radiation killed him. They probably wouldn’t want to be alive all of those ten minutes.

Fraser: Now this is coming from Jupiter, right?

Pamela: Yes, it’s the radiation field of Jupiter that unfortunately Europa has to deal with and any astronauts going there would have to deal with as well. There’s also discussion that maybe we could do something with Titan again. It’s a planet with a thick, organic rich atmosphere but orbiting Saturn, it’s kinda cold out there.

Fraser: Right, the temperatures are so low that hydrocarbons and methanes freeze out of the atmosphere and form lakes.

Pamela: It’s so cold out there and the Sun is so far away that Solar energy is no longer a particularly useful way of generating energy. Especially not once you get to the bottom of the big thick, fairly opaque atmosphere.
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As you start to look at Titan you have to ask how exactly to get a large enough nuclear power source out there with me. While you’ve moved far enough away that Solar radiation is less of a problem, you no longer have a good way to keep yourself warm and again it has very low gravity. Humans tend to like to have gravity. It makes our bodies happy.

Fraser: As we go forward though, in time as the Sun’s energy output increases and especially as it nears the end of its life, a lot of these worlds are going to suddenly become very habitable, right?

Pamela: The moons of Saturn are going to become very appetizing.

Fraser: Yeah, as the habitable zone of the Sun expands outward, suddenly they will melt and will have oceans and maybe even atmospheres?

Pamela: It’s going to be a brave new Solar System. What will be interesting to see is with these moons that are extremely rich in ice just how much moon to you have left once you heat them up. That will be an interesting question to sort the answer out to.

Fraser: Yeah, a lot of them are half ice, right?

Pamela: Yeah. So we’re going to be melting the outer Solar System, which is an interesting picture.

Fraser: And then in the far future as the Sun nears its very end and its habitable zone extends out it might even include like Pluto and some of the Quaker Belt objects?

Pamela: Yeah, the things that are going to melt.

Fraser: I know you can imagine some far future when people are sitting on the beaches of Pluto [Laughter] right, where the Sun is completely different and it could actually be briefly the only place to live.
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Once again there would be some terraforming involved to try and make it as human habitable as possible. But once again, if humans are the same six or seven billion years from now [laughter] we have a problem.
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I would be quite amazed. I think that goes through the terraforming argument. I know this is sort of a sacred cow for a lot of people that we must terraform Mars and reshape it to our will so I look forward to your e-mails.

Pamela: And go read Red Mars by Kim Stanley Robinson.

Fraser: Absolutely, Red Mars, Blue Mars and Green Mars, right?

Pamela: Yeah, the whole trilogy.

Fraser: There are also some interesting articles written. The Mars Society has done a lot of thinking on this. There is great stuff on Wikipedia and a lot of other interesting books have been put out. Even some thinking was done at NASA.
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We’ll have a whole bunch of links in our show notes that people can chase down. All right Pamela thanks again for a cool show. I think we’re done with Mars. We’ve given it six episodes so [Laughter] I think Mars’ Phoenix Lander can feel like we’ve given it a tribute and it will be awhile before we return back to Mars.

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

Fraser Cain: Hi Pamela.

Dr. Pamela Gay: Hey Fraser, how’s it going?

Fraser: Good. So you’re going to be off on another trip shortly another Astronomy conference?

Pamela: Well, the reality of it is by the time people are listening to this, I will be in Munich, Germany. And on Friday, I will be in Cambridge, England.

           In fact, if any of you are interested in going to a Pub with me, I will be at a Pub in Cambridge and the exact Pub will be listed on the BAUT Forum and on StarStryder.com.

Fraser: Okay. Once again, I wish I could make it but it’s kind of expensive to fly to Germany.

            [Laughter]

Pamela: Yeah.

Fraser: Okay, so this week, it’s going to be another rough one.

            [Laughter]

           I think we’ve been putting off this side of science, so let’s go. Have you ever heard that light behaves like both a particle and a wave? That is a crazy dual nature of light. What does that really mean? How did scientists figure it out?

           Today we’re going to get into it and try to explain one of the most complicated and non-intuitive concepts in science. Get ready for a little lesson in quantum physics. Can you explain how does light behave like a wave and how does it behave like a particle?

Pamela: Well, if you hit something with a photon of light it will move just like if you hit it with a soccer ball or something like that. This whole idea that you can hit something and it bounces and it moves just like you’d hit it with a particle is the particle nature of light.

Fraser: Right and that’s the action that is keeping stars ballooning out. The photons are bumping against each other and trying to get out of the star and that’s what keeps the star up.

           That’s how solar sails work. You take the sail and put it in space and just the pressure of the photons bouncing into it will move the sail through space. Are there any other examples where we use this?

Pamela: Well you can use it for imaging in fact. You can’t see something except for the fact that photons are coming from some light in the room and bouncing off of whatever you’re looking at and then going into your eye.

           So just that little thing, the fact that eye glasses work can explain the way that light reflects or refracts or the way rainbows are formed.

           All of this is explained initially by Newton through the particle idea of light.

Fraser: So then how is light like a wave?

Pamela: Now here’s where things get screwy. If you take a golf ball and you hit it the exact same way a thousand times, in a no wind environment, it will always fly the exact same way.

           If you take a thousand photons and you fling them through a slit a thousand times, they’re going to go all over the place. The pattern that they end up forming on the other side of the slit is the pattern that you would get from waves going through a slit.

Fraser: Right, I’ve seen this. You have a sea wall and your waves are bumping up against the sea wall and there is a hole in the sea wall.

           Where the wave hits the hole then you get another little wave that comes out the other side of the hole and continues to propagate through the water.

Pamela: And what’s really cool is you can have a perfectly straight wave front hitting this wall and the wave that comes out on the other side of the slit is round. So you end up with these round wave fronts radiating away.

Fraser: Even an individual photon will still make that shape?

Pamela: Well, not only that but if you have two slits, just like with two slits in a wave wall, you end up with interfering waves. In some places the waves get especially big and in some places they get especially small.

           With light when you have two waves that are interfering you can end up with places where you see no light. Where the light seems to cancel itself out and you end up with other places where the light seems to be especially bright.

           You get this interference pattern with only one photon going through at a time. So, how does one photon at a time manage to interfere with itself?

Fraser: Hold on a second. One photon interferes with itself? I don’t understand.

Pamela: No one does.

Fraser: Okay, then what do you see? What’s the experiment to make one photon interfere with itself?

Pamela: The experiment is actually kind of simple to set up. You just need to have a very precise light source. You can do this with a set of razor blades in fact. You take four razor blades and you very carefully set them up so that you end up with two razor-edged slits that the light can go through. Then you set up a screen on the far side of the room.

           Or if you want to do this with one foot on time, which you can’t see with your eyeball, you put a detector there, a CCD or something that will detect light. Then you take a laser and you put so many filters in front of it that all that’s getting through from that laser to hit that set of razor blades is one photon at a time.

           When you do this, the one photon goes out, through the slits, hits the detector on the other side and ends up leaving a single point of light on the detector. No big deal. But, if you let a second photon through, a third proton, and a few thousand photons through, it will build up a pattern of interfering waves.

           It’s in fact the exact same pattern that you get if you allow a few thousand photons to go through those two slits all at the same time and you can see the light and dark patterns with your eyeballs.

Fraser: If you only had the one photon, it would actually be creating an interference pattern. You just can’t see the whole pattern yet because you’ve only pushed one photon through. But the pattern is essentially there.

Pamela: What’s happening is when we detect that photon, it decides where it’s going to be, its wave function collapses. Its probability collapses and it picks a place and that’s the place it lands.

           All photons have the same set of probabilities. It’s most likely it will end up here. It’s least likely it will end up here. And just like if you roll the dice enough times you end up getting all the different numbers on the die.

           If you send enough photons through you end up building up the full pattern. When you send them through one at a time they each land where they land and the full pattern of all of them going through over time builds up this interference pattern.

Fraser: So, does that mean that each individual photon, because they are building up that interference pattern, each photon is going through both slits at the same time?

Pamela: This is where it gets philosophically confusing. You could either say there is a statistical probability that the photon is going to go through in all these different ways and the photon goes through in one of them.

           Or, you could say that the wave is passing through both slits interfering and the wave function is collapsing in a specific location on the screen.

Fraser: Right.

Pamela: So you can look at either statistically as it’s just picking a place and going through there just like you’re rolling the die and you can’t get one through six all at the same time. It picks one.

           Or you could say that when the observation is made, the wave function collapses and you have detection.

Fraser: Right, but aren’t there ways that you can split up or block the photon from going in through one of the slits and you can get a better sense of what’s actually an impossible thing seem to be happening?

Pamela: No. That’s the weird thing. There are some really cool experiments that have been done with this. If you block one of the slits, you get a completely different pattern for where the photons land. That’s one cool thing. You have to have both slits there in order for the photons to build up this distribution.

Fraser: Yes, you just don’t get the interference pattern until you have both slits there.

Pamela: Right. I saw the coolest demo a few years ago. One of the neat things about this is if you have two slits and you shine a laser through them you can actually see on the wall a diffraction pattern of bright spots separated out scattered across the wall.

           Now, if you put a lens in front of the slits, instead of getting the diffraction pattern, you can actually focus the two slits and get an image of the slits on the wall. This is one way that we say the lens forces the light to behave like particles instead of like waves.

           This is where we get into the whole “it’s both” argument. The slits make the photons interact with each other or perhaps with themselves and build a diffraction pattern, an interference pattern on the wall. The lenses force them to work like particles and you end up getting images of the slit on the wall.

           If before you put the lens in you very carefully take a grid of wires and you arrange the grids so that the wires are in the dark points on the diffraction pattern. Then when you’re looking at your screen all you are seeing is the diffraction pattern.

           When you’re looking at your experiment, you’re seeing laser shining on two slits and then this grid of wires that appears to do absolutely nothing. It’s just hanging out there. Then you see the pretty diffraction pattern.

           If you put that lens back in you just see these focused two slits. The wires in the experiment seem to have absolutely no affect on anything. You don’t see them at all.

           If you cover one of the two slits and the wires aren’t there, then the lens causes you to just see one image of one of the slits. But, with the wires there, if you cover up one of the slits, and you get rid of the interference, all of a sudden you can see the wires in the lens.

           It’s the creepiest thing ever to watch. There are videos of this.

           There’s a man in New England, his last name is Afshar, who has been doing this experiment. No one is quite sure they understand his interpretation of the experiment.

           But what it is showing is a photon is simultaneously a wave and a particle. It’s just cool.

Fraser: All right, now let’s go into the how we know what we know part. How on Earth did scientists figure this out? As I mentioned in the intro, this is completely [Laughter] non-intuitive to come up with the answer that light behaves as both a particle and a wave is about the last thing that you would rationally conclude.

           It’s not surprising that it took so long for scientists to get to the bottom of this or to the top of it. [Laughter] So, how did they even go down this road?

Pamela: We’ve been arguing over it for about 400 years. This is one of those things that made people feel queasy to their stomachs starting as early as Christiaan Huygens.

           He was playing with light and noticed this cool if you shine light through a slit, you get an interference pattern. If you shine light through two slits you get a different interference pattern.

           It’s just cool. It can only be explained with waves.

Fraser: Right, so I guess he said “that’s it, case closed, it’s waves.”

Pamela: Right. Except Newton working not that differently in time said “no. It must be a particle. Look light reflects.” It reflects light particles. You hit a mirror at a 45 degree angle. The light goes off at a 45 degree angle.

Fraser: Right, ocean waves don’t reflect in the same way particles do.

Pamela: Right. Because of this difference in how waves reflect and how light reflects, Newton said no, particle. He was able to go on and build beautiful mathematical explanations for reflection for refraction, for light going through prisms and forming rainbows all based on a particle understanding of light.

           We have Huygens explaining interference and diffraction patterns using a wave nature to light and we have Newton explaining lenses and reflection and rainbows using a particle theory of light. We have these two competing theories. Things continued and continued.

           Then finally, in the 1800s, there were two more scientists who did a bunch of experiments using interfering light again; Thomas Young and Augustin-Jean Fresnel.

           Fresnel is the person who came up with the perfectly flat, weirdly textured pieces of plastic that allow you to essentially magnify what is behind your motor home or something. Those funky little magnifying flat things use interference of waves.

           Young and Fresnel said “interference patterns, it’s a wave.” Maxwell came along and with his theories of electro-mechanics and his equations of electro-mechanics he built into all of this mathematics which explained electricity, magnetism and all the cool stuff of the day, he built in the idea of waves. The dominant scientific way of thinking was waves in the 1800s.

           Then things changed again. In the early 1900s, from about 1901-1905, we had people doing more experiments. This is where we keep getting into problems. One set of experiments says particles while another set of experiments says waves.

           The people then working in the early 1900s were saying weird. This now acts like particles, sort of. So we had Max Planck who was trying to explain the distribution of the colors of light that come off of heated objects. This is black body radiation.

           If you’ve ever seen an old generation episode of ‘Star Trek’, when Captain Kirk heats up a rock with his phaser and it glows red that’s black body radiation. Any of you who have ever used a kiln when you heat things up and they glow in the kiln, that color is directly related to the temperature of the kiln.

           Hot coils on your stove are again black body radiation. He was trying to explain mathematically why you get the distribution of light that is observed.

           The only way he could explain it was to say that it looks like the energy allowed must have specific values. It must have what we call quantized values. He came up with a model of the oscillators and the atoms having quantized energies.

           Today we understand this as atoms have different allowed energy levels and they release photons with specific energies related to those allowed energy levels. This was a particle idea.

           We also had Einstein come along with his photoelectric effect which is what he got for his first Nobel Prize. What he found with the photoelectric effect is that if you have a sheet of metal and you shine a blue light on it, you can often get it to conduct electricity by hitting the atoms with light that causes the electrons to leave the atoms.

           If you use pretty feeble blue light, the metal just sat there and went, ‘yeah, I don’t care”. But if you hit it with brighter blue light current would flow.

           If you used red light, you could blast it with as much red light as you wanted and nothing would happen. This seemed to indicate that different colors of light carried different individual energies.

           So that when you look at a light beam, the brightness that you see is related to how many particles of light there are. The energy in each individual particle is related to the color.

           What was happening in the red light versus blue light case was: If you have a power pitcher imagine with like cricket or baseball, and they’re throwing a fast ball, that fast ball is going to hurt when it hits and if in this case we have this powerful blue photon and it hits a piece of metal’s atom just right, it will fling off an electron and it’s going to fly somewhere.

Fraser: Like in your analogy, the ball is hitting so hard that a catcher lets it drop back out again. Or let’s something drop back out again.

Pamela: Exactly. [Laughter] The brightness is how many balls you have flying at one time.

Fraser: But if you have a little leaguer throwing that ball the catcher is not going to let go of it.

Pamela: Yeah, so it’s just going to hold on. You can have as many little leaguers as you want throwing baseballs and they’re probably not going to hurt anyone.

           But, if you have only one power pitcher out there, and there are 40 catchers, he may not be able to get past those 40.

           If you get ten power pitchers out there, they probably have a chance at to get at least one of those catchers to drop a ball.

           What’s happening is with the blue light, it is able to knock electrons out and the brightness just says how many pitchers you have going. The color is how powerful the throw and the brightness is how many throwers.

Fraser: So we’re back to particle.

Pamela: We’re back to particle. There is this terrible moment of “oh no, oh dear”. Max Planck has these great equations that say wave, wave, wave, wave. But Einstein has this great explanation that’s particle, particle, particle. Wow, it’s both.

Fraser: There must have been just some awful fights. [Laughter] Can you imagine the battles? Because they’re both right and so when you’re both right and the evidence supports you, the battles must have just been ferocious.

Pamela: Yes. That’s an understatement.

Fraser: Enemies must have been made. Funding must have been cut. [Laughter] Oh, it must have been awful.

Pamela: And it gets even worse. With light, yeah fine, it doesn’t have mass let’s let it be both a wave and a particle. Okay, it’s just this weird thing.

Then a guy by the name of de Broglie came around in 1924 and he says no, everything has a wavelength. You have a wavelength Fraser.

Fraser: So not just photons, but larger things like electrons or atoms…..

Pamela: Buckeyball.

Fraser: So, I’m both a particle and a wave. That’s what you’re saying. All of our listeners are both particles and waves or a collection of particles and a collection of waves.

Pamela: Yes. Isn’t that cool?

Fraser: Well then, I mean don’t [Laughter] get to the buckeyball yet. So you’re saying that like a proton….let’s say an atom, a hydrogen atom. How is that both a particle and a wave?

Pamela: It’s hard to explain. The way that we look at it is every object has this wavelength over which it exists. It is capable of interacting and things like that.

           This is in part defined by our uncertainty in being able to figure out where things are. The way I figure out where you are is I look at you which requires me to look at you with light. Light is coming from some source and hitting you and coming back to me.

           If I try looking at you in radio light which has huge wavelengths, I can only figure out where you are within the wavelength of that radio wave. But if I start looking at you with x-ray light, I’m probably going to give you cancer, but I can really figure out where you are because my uncertainty is the same size as that x-ray wavelength which is very tiny.

           Now if your wavelength is such that your specific uncertainty in you is something that is commensurate with the wavelength of how I’m trying to look at you. You can interfere with yourself.

           It gets to what are the spacings between the slits, what are the sizes of the slits, what is your wavelength.
Your wavelength is defined by well, this is the de Broglie wavelength. It’s defined by this constant called the Plancks constant divided by your momentum.

Fraser: Is it almost like an averaging out of all the particles in my body?

Pamela: It’s that everything has this intrinsic uncertainty in where’s it’s located. This intrinsic little jiggle is what we refer to as the de Broglie wavelength. The catch is that for you, you large human being you, this uncertainty is so small that it’s actually smaller than if I turned you into a black hole what your short shield radius would be.

           There’s basically no uncertainty in where you are because I can’t measure anything that tiny.

Fraser: But for single particles, for instance, haven’t scientists been able to make hydrogen atoms behave like a wave?

Pamela: We can make hydrogen atoms behave like waves, we can make actually the smallest bacteria if we wanted to we could make behave like a wave. We’ve actually, not me personally, but there was an experiment in 1999 in Vienna where a group of scientists took buckminsterfullerenes.

           These are molecules made up of 60 carbon atoms. They were able to make these buckminsterfullerenes behave in this wave-like interfering way and get this diffraction going on.

           This statistical uncertainty in position led to a distribution on how they were measuring where these things ended up on the other side of two slits. That’s just kind of cool.

           You have these 60 carbon atoms in this soccer ball like shape that are perfectly happy to interfere with each other. That’s a pretty big atom.

Fraser: Yeah. That’s amazing. So your ability to detect that or the ability to interfere or the precision with where you are gets harder to measure the more mass that you have, the more particles that you have. Right. Okay.

           So, what is the current research into this? Where are scientists trying to push the limits of this right now? Apart from making fullerenes behave like waves.

            [Laughter]

Pamela: It’s always fun to see what new and interesting things you can get to diffract. There’s also the question of how do we interpret this? One of the classic things that people say is: individual items are wave functions and they move through space in packets.
Wave packets is one way that we look at things and we can either know how fast that thing is moving or we can know where it’s located but we can’t know both and that when we make an observation, we’re collapsing a wave function. So you can never observe something as both a wave and a particle.

           People are trying to figure out if that is true. Can you really not observe the wave function and the particle at the same time? This is where the arguing over the experiment I explained earlier with the wires and the diffraction and the lens comes in. We’ll put some links to some stories on that.

           There’s also well … really the wave function only collapses into a particle when an observation is made or is it really a just a particle all the time and there is this statistical wierdness. There are still philosophical arguments going on as well. Then there’s the old are we really limited to you can either know where something is located or how fast it is going and not both.

           Is there any magical way using enough technology to get around what is called the Heisenberg Uncertainty Principle? That’s where you start to get into things like we can’t have Star Trek transporter beams until we figure out the uncertainty principle, because how do you put someone back together.

           Trying to figure out if these are actual limits or things that there is always somebody trying to do?

Fraser: Right, and there are some other aspects of this like entanglement and like that concept of Schrödinger’s cat, the uncertainty, so I think we’ll come back to this in future shows and have another go at it.

           I think we wanted to get across today just how to understand that when you hear that wave particle duality, what are we talking about and how do we figure it out and what were the experiments that brought that into play. I think that was a really good explanation.

           I’m sure we’ll get a lot of questions but there’s going to be more shows on this. I know this is an astronomy pod cast, but there is so much physics involved that there are many times where we have to bring this stuff in as well. So bear with us.

Pamela: Spectrographs wouldn’t work without light interfering. Stars wouldn’t support themselves without waves acting like particles. Everything that makes astronomy work goes back to the wave particle duality of light.

Fraser: Well there you go then, there’s our explanation.

Pamela: And it’s just really cool that the uncertainty in you and I is smaller than our short shield radius. I just think that’s cool.

Fraser: Right. That’s the event horizon of a black hole. If you took my mass, turned me into a black hole, the size where nothing, not even light could escape, that’s my uncertainty – smaller than that.

Pamela: And that’s just cool.

Fraser: We’ll talk to you next week Pamela. Have a good trip.

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

Transcript: Questions Show #8

Download the transcript

Fraser Cain: We’ve been so crazy following our own whims through the universe that we’ve neglected your questions. That ends today. It’s time to dig deep into our overflowing email box to retrieve the puzzling questions our listeners have sent in.
 
Let’s start with what I think is our best question ever.
 
[laughter]
 
This is it, this is the greatest question. Justin Craig sent in an awesome email. He says, “I was wondering, if you had enough anti-matter and you put it into a black hole with an equal mass, would the black hole disappear or just become twice as heavy?�
 
Now, before we go into the actual answer of question, let’s give the listeners background on anti-matter. I don’t think we’ve done a show on anti-matter, so what is it?

Dr. Pamela Gay: Anti-matter is basically the “Spock has a beard� universe of matter if you’ve watched old generation Star Trek. An electron of antimatter has the opposite charge. It has all the opposite physical characteristics that a regular electron has. So you have an electron and a positron, take one and turn it inside out in every way you can (except for the mass – you can never have negative mass, it’s always a positive quality), and it’s exactly the opposite. Opposites often annihilate one another.

Fraser: This isn’t just some crazy, calculated theory. This is real stuff – you can calculate it in the lab, you can smash it together, it annihilates and produces a gigantic amount of energy. This is real stuff.

Pamela: Yeah, we’ve produced positrons – I think they’ve even put together anti-matter hydrogen and helium anti-atoms in various laboratories. You’re just very, very careful to suspend them away from everything else while you’re working with them. But we can create these things.

Fraser: So this isn’t some theoretical concept. Astronomers see the presence of antimatter out in the universe, being produced naturally. In fact, it was recently announced there’s a cloud of antimatter in the Milky Way.

Pamela: There’s a bunch of natural processes that it’s just part of how energy settles out when it’s becoming matter. If you take energy and you say, “okay, let’s change it into matter� you’re going to get a regular matter particle and an antimatter particle. Everything is created in the yin and yang, in terms of you have to have a positive charge and a negative charge. All of these things have to balance out in these energy goes into matter reactions. In some cases it can actually create clouds of antimatter.
 
There’s a cloud here in the Milky Way that we detect because of the very specific gamma ray light it gives off, that has a colour that you pretty much only get when you have these matter/antimatter reactions. We think this is perhaps coming from low-mass x-ray binaries that are creating this cloud of antimatter.

Fraser: All right. We know there’s antimatter, but just creating clouds which are annihilating instantaneously. We’re not actually clumping together gigantic quantities – enough to say, create a black hole. But let’s say we could. We’ve pulled it all together and fashioned it into a ball of antimatter with exactly the same mass as our target black hole. Then we smash them together.

Pamela: Here’s where I said it’s really important that mass is always a positive quantity. If you take a pile of matter and a pile of antimatter, they’re both going to have the same gravitational effects on things, they’re both going to have the same style event horizons… they’re going to have the same everything.
 
The thing is, with a black hole, you can’t tell if it’s matter or antimatter.

Fraser: Whoa.

Pamela: Yeah.

Fraser: Right, of course. So an antimatter black hole would, in all cases, feel identical to a regular black hole, if you’re trying to orbit it or whatever.

Pamela: If you basically went around with some sort of antimatter vacuum cleaner and collected antimatter into a bigger and bigger and bigger pile until the pile had enough mass (regular mass with antimatter characteristics), that it condensed down to a black hole… it’s a black hole. When you take an antimatter black hole and a matter black hole and throw them together… we don’t know what’s going on within the event horizon. From the outside perspective, you just made one really large black hole. Which is kind of cool.

Fraser: Hold on, let’s break this down a little bit. Say we have our antimatter black hole and we’re streaming planets and asteroids at it, they’re just disappearing into the antimatter black hole. Now, there would’ve been an explosion going on as these asteroids are striking the antimatter, right?

Pamela: The problem is you’re starting from the assumption the matter inside a black hole is normal. It’s not – at least, we can’t think of any way that it’s normal. So the whole idea that you have electrons goes away. The whole idea that you have protons goes away.
 
What you have is some surreal quark soup that all the different bits and pieces that make up both matter and antimatter are slammed together and forced into these really small volumes. Things lose their identity in the process.

Fraser: We’ll get that question in a second – we’ve actually got another question on that identity and information. I guess my question – sorry to not let go here – let’s imagine you had your antimatter black hole and your regular matter black hole, wouldn’t your antimatter black hole be the exact same configuration as the regular black hole, just the antimatter version of that/
 
Say it’s some kind of soup of particles which no longer look like protons/electrons/whatever. Wouldn’t they just be anti-versions of whatever’s in the black hole, and wouldn’t that still create the explosion?

Pamela: How do we know, because it’s in the event horizon, that these particles are able to hold on to that level of identity? How do we know they haven’t turned into pure energy as they cram themselves in there?

Fraser: Let’s say we do know. Let’s say they do remain as a mere version of the particles that are in a black hole. What happens then?

Pamela: Well, it’s just energy being released, but that energy can’t get out because it’s a black hole.

Fraser: Well that’s the question isn’t it – the energy can’t get out because it’s a black hole which would stop even energy. So obviously you’re not going to have an explosion of chunks of things because they would just be sucked down. You’re not going to have radiation because it’s going to get sucked down. You’re not going to get sound…. Anything. There may very well be an explosion, but you wouldn’t know it happened. Is that right?

Pamela: Exactly. Basically, what goes in stays in and we can’t find out anything beyond that. Since the antimatter systems have positive mass, you just have a bigger black hole.

Fraser: Right. Wow.
 
All right. I think that’s it – I guess, that’s the question at the heart of it. The hope was maybe the two would cancel each other out and you’d be able to break past black hole-ness, right, and the whole thing would explode and turn into a release of energy. Even energy can’t escape this black hole, so even if there is a release of energy, no one’s the wiser.

Pamela: Exactly.

Fraser: Awesome question. Best question ever.
 
[laughter]
 
Let’s get on to some other best questions ever. Let’s go with that – continuing on the information.
 
We had a question from Maureen Egan, and she wants to know, “in terms of information not being able to escape the gravitational pull of a black hole, what exactly is information? When I imagine information I think of data like that stored on a floppy disk or CD.�
 
I think astronomers do use that term quite loosely – all the information is lost, so who knows what happens to it. But what is information?

Pamela: I’m not sure so much that we use the phrase loosely as we just throw it around a lot without ever telling anyone what it means.

Fraser: Oh, fine – yeah.

Pamela: Which is a little bit more evil on our part.

Fraser: Yeah, no – I just throw around, “information’s gone – moving on�
 
[laughter]
 
“Stop, what does it mean?� So really – what does it mean, information loss?

Pamela: It’s an idea that came out of quantum mechanics. It’s this whole idea that particles have varied states in them. If you take an atom – let’s talk about helium, which is nice and simple. In a helium atom, you can have two different electrons. One is going to have spin-up and the other will have spin-down if they’re both in their lowest energy state. This is something that comes from the poly-exclusion principle, which says you can’t have two electrons with the same spin in the same orbital.
 
The fact that one is spin-up is information. The different states particles take on, or the different wave functions, all of this is different types of information. It’s the quantum states that are tied up in particles that people try and figure out how to take advantage of in building the next generation of hard drives where we store information in the spins of electrons.
 
How do we figure out how to tap into this so that we can build atoms that store the genetic code of the human genome, or something crazy like that. I don’t think you can actually do that one.

Fraser: Maybe we could do an analogy in star trek, like where you hop in a transporter and you’re going to be teleported from where you are to the moon down below. You want to make sure that the teleporter can rebuild you, atom by atom, and for it to be able to do that it’s going to be able to put an atom here with this quantum state, an atom there with that quantum state, etc. It’s got to get it exactly right or you won’t be you anymore. You’ll be somebody else, or even just a mess.

Pamela: All of this can include information such as what the polarization of a photon, what is the orientation of the waving of the electric and magnetic fields of that photon as it passes through space.

Fraser: So there’s any number of ways you could measure an atom or a photon or a particle or anything and that’s the information that is thought to be destroyed when it goes into a black hole.

Pamela: It’s the most basic way of putting this is what are the quantum states of the particles – that’s the information the particles carry.

Fraser: So the thinking is that if you could somehow pull that stuff back out of the black hole, there would be no way to re-create that information. No way to ever know what its quantum state was.

Pamela: Yeah.

Fraser: Why is that bad?

Pamela: Well, we like to think that no information is ever lost. Ever particle in some way, holds its entire past inside of it. It couldn’t exist if a whole series of different things hadn’t existed. You take energy and that energy has to split into a positive and negative charge, different spins that are conserved… you have all these different things that have to get conserved in the creation of matter and reactions and there are very specific processes that are the only allowed atomic processes, as particles decay from one to another through time.
 
If this information could get lost, it’s sort of like erasing the history of the particle, which is kind of sad and also implies that there’s information about our universe that gets lost forever.

Fraser: Right, but astronomers aren’t boo-hooing about lost information. This information loss breaks something, right?

Pamela: Well, one of the tenets we start with is no information can ever be lost or destroyed. If black holes can lose or destroy information, there’s one of our basic tenets gone, and that makes people uncomfortable.

Fraser: Okay, I think we could talk about this all day. Hopefully that gives you the information you were looking for, Maureen, and we’ll come back around and talk about information in black holes… that’s a whole show, I’m sure.

Pamela: Yeah. The short answer is, as near as we can tell, black holes don’t eat information – it has ways of escaping. But that’s for another entire episode.

Fraser: Right, right. Okay. But when they’re talking about information, that’s what they’re talking about – the quantum state of the stuff that gets consumed.
 
Let’s move on and go to our next question. This is from Mark Maultby. “If gravity is the force of interaction between objects, what is the smallest object that could noticeably be said to have gravitational attraction?�
 
I just want to set some scale here. If I have the Earth, with the Sun… Here we are on the Earth, feeling its gravity. If I go across the universe, to the other side of the universe, I’m still feeling the effect of gravity from the Sun, right?

Pamela: Oh yeah.

Fraser: Now, not much, obviously.

Pamela: Not noticeably.

Fraser: It’s so miniscule you can’t even have numbers to describe it, but it is there. Every piece of matter in the whole universe is interacting gravitationally with every other piece of matter in the whole universe. That’s true?

Pamela: That is exactly true.

Fraser: Okay. All right, and then that doesn’t matter for any size – for a planet, a moon, a proton, an electron, a neutrino… anything, there’s still a gravitational force that’s being done across the universe. I guess the question is, is there some point where that doesn’t happen anymore?

Pamela: No. It’s either you have mass – and if you have mass, then you affect things with gravity. Or you have no mass, in which case you can fly across the universe at the speed of light.

Fraser: Is there a minimum amount of mass you can have/

Pamela: Nope.

Fraser: But, we had this conversation just a couple of weeks ago about the Higgs-boson. I know there’s the concept of gravitons. Is there some number where, if you’re smaller than the Higgs-boson, then you won’t have mass? Like, you need to have one Higgs-boson to have mass – I’m speaking gibberish, right?

Pamela: That’s one of the crazy things. Higgs-bosons have a fair amount of mass.

Fraser: Theoretically.

Pamela: Or at least, they have a fair amount of energy (and energy and mass are kind of interchangeable, which makes the way we talk kind of confusing). The real question comes down to what is the least massive particle that we know about? That’s probably quarks. Three quarks combine to make a proton.
 
I think the real question is what the particle is with the smallest mass out there. Here you have to start remembering there’s quarks, and they combine to create protons and basically have mass (in a sort of weird kind of way). Electrons have mass, neutrinos have mass. Then there’s this stuff called dark matter that we don’t know what the heck it is. It has mass. It gravitationally effects things.
 
I’m not sure we know, yet, at this point in time, exactly what the smallest particle out there is, because we’re still discovering particles. We’re still trying to figure out what this weird stuff called dark matter is. But it’s basically, when you start getting down to these… this is a single lepton, a single boson, a quark… these individual units have slightly different masses, but these are the smallest things (smaller than atoms), that are capable of gravitationally affecting other things in the cosmos.

Fraser: But that kind of feels like you’re not quite answering the question.
 
[laughter]
 
You’re kind of saying that these are the smallest particles that we know about – that we know exist for sure – and we know that those particles have mass, and therefore they can gravitationally attract. If you had one quark on one side of the universe and another on the other side of the universe, if they weren’t being expanded away from each other, they would eventually come together, over a long time.
 
But the question is, is there some theoretical limit where you just can’t have any less mass?

Pamela: When defining the smallest possible things, we often say, “there’s the Planck unit of time� (the smallest discernable unit of time), or there’s the Planck length… You’d think there’d also be a Planck mass, which would be a limit to how small mass could get. But there’s not.
 
As far as we know, there may not be a limit to how small something can get in terms of mass, but we’re still figuring out the particle world. We still haven’t found the Higgs-boson (if it exists). We still haven’t found the graviton (if it exists). There’s this whole realm (potentially) of different particles that don’t interact via the electromagnetic force like electrons and protons do, that are making up dark matter. For all we know, the least massive particle out there is also the most common particle out there and happens to be whatever it is that makes up dark matter.
 
We’re still learning. Particle physics, the standard model, these are things we’re still working to define. As far as we know, no – there is no mandated-by-the-cosmos boundary on how small a mass we can get. We’re still exploring.

Fraser: I guess the question will maybe help to be answered by upcoming work with the Large Hadron Collider.

Pamela: Yes.

Fraser: We don’t really know. That was a good question too.
 
[laughter]

Pamela: These are the ones that stump me.

Fraser: I know, I know. Let’s move on. Something I think is a little simpler – this comes from Sabre Rosewood and the question is: “since the tides on Earth are part of what causes our moon to slowly move away, what will happen once the oceans are gone? Will the Moon stop moving away from the Earth?�
 
We talked about this in our show “Where Does the Moon Come From?� and discussed that – the Moon is slowly moving away from the Earth. What’s the cause of that?

Pamela: It boils down to conservation of angular momentum. The Earth isn’t a perfect sphere: it has mountains, it deforms itself due to the gravitational pull of the Moon. As the planet rotates, it bulges out so that part of it bulges toward the Moon and part of it bulges in the opposite direction because the gravity is not so strong over there.
 
This deformity basically gives the Moon a gravitational handle to hold on to our planet and say, “no – don’t rotate past me, keep the bulge pointed this direction!� The rotation of the Earth is constantly trying to carry the bulge past the Moon. Gravity grabs that bulge and pulls it back. This pulling back on the bulge that’s trying to rotate past the Moon is slowly, slowly, slowly, slowing the rotation of the planet.

Fraser: You’re talking about a bulge that’s coming from mountains or one side of the Earth is a little more bulged than the rest of it. Oceans move huge distances – more than the mountains ever move. There’s a gigantic amount of ocean on the planet, so does that play a significant role in this?

Pamela: It plays a significant role, but it’s not the only role. So, 50 million years from now, when our oceans start to evaporate away, we’re still going to have these tidal effects. We’re still going to have this planetary flexing that prevents us from becoming a perfect sphere ever. This planetary flexing is going to continue to slow the rotation of the planet until eventually we’re completely locked so the same face of our world is always facing the same face of our moon.

Fraser: And the moon will stop moving away.

Pamela: It will stop moving away.

Fraser: Right, so the oceans are part of the bulge on the Earth, but they’re not the whole thing. Eventually, even when the oceans boil away, the Earth and the moon will still go through this dance until they figure it out – until the Earth and moon are facing the same side toward each other forever and always. Which I think would be longer than the lifetime of the Sun, right?

Pamela: Yeah, that’s what we think right now at least.

Fraser: It’ll be a red giant before it happens.
 
Okay, cool question. Let’s move on. Paul Barnett asks “Since the universe is expanding and we believe that matter cannot be created or destroyed but only changed from one form to another, I’m curious to know where the new matter comes from to occupy the new space that’s created. Is there new matter being spontaneously created?â€?
 
Now, let me try and rephrase the question, because I think he made a couple of mistakes there. We talk about the universe expanding, the expansion of the universe, both from the big bang but also from the additional dark energy that’s helping to push the universe apart. We’re getting more space in between the galaxies and galaxy clusters and interstellar space. But we’re not necessarily getting any space in between the galaxies because they’re held together.
 
I guess the question is, let’s look way out into the most unpopulated part of the universe where space is expanding apart and we can measure the density of how many atoms per cubic kilometre there are out there. As the space is expanding from dark energy, is there any more matter coming into existence?

Pamela: No, that’s the cool thing. The universe is basically diluting itself over time.

Fraser: So it’s like you’re pouring water into something that was quite thick, and it’s just making it more and more dilute – more and more thinned out.

Pamela: Or, the way I like to think about it, if you imagine blowing up a balloon, the balloon has very thick walls when it’s small, but the more and more you blow it up, the thinner those walls get, the fewer atoms there are per square centimetre of area on the surface of that balloon.

Fraser: Until it pops.

Pamela: Until it pops.

Fraser: Our universe isn’t going to pop, is it?

Pamela: No.

Fraser: Okay.

Pamela: But it’s going to get pretty empty.

Fraser: Right, and that’s it – there could be some point in the far, far future where everywhere you look, there’s no atoms around. Right now, I forget – did you mention how dense space is?

Pamela: It’s on the order of nothing per cubic meter?

Fraser: Right, okay. The occasional particle per cubic meter, but you could eventually get to the point where there’s one particle per light year.

Pamela: What’s weird though is this is true of atoms of normal matter. There’s this thing called dark energy, and near as we can tell, dark energy is constant at all times. When we look at how much energy there is per cubic meter of space, it works out to a few protons worth of energy at all points in time, even though the total volume of the universe has increased.
 
That means the amount of energy, the amount of dark energy in the entire universe, is somehow increasing as the universe gets larger, because its staying constant as a function of volume. This gets confusing.

Fraser: I’ve got a zinger for you now, then. We always talk about the fact that matter and energy are interchangeable. So, is dark energy interchangeable with matter? Could you freeze it into matter?

Pamela: As far as we know, no. Dark energy is this weird enigma, currently. We don’t know what causes it. As near as any theorist that I can understand has gotten, dark energy is basically a field of energy that permeates all of space and time. If you can imagine this mesh of energy that is everywhere, all at once, and not getting all metaphysical on me… if you can imagine this lowest possible energy state (that isn’t zero) it permeates everywhere. One of the fears is something will come along and trigger that wave, that field that permeates everywhere to crash down to zero and no one knows what will happen.

Fraser: Now you’re freaking people out here.
 
[laughter]

Pamela: Theorists do scary things with their mathematics sometimes. Like I said, we don’t really understand it right now. So, give us a few years.

Fraser: Okay. To summarize then, with the expansion of the big bang and the addition of dark energy, the universe is growing but the amount of matter in the universe isn’t changing, so it’s really just getting diluted. So, back to the question where’s the matter coming from, it’s not coming from anywhere – there’s no additional matter. All the matter in the entire universe was created in the big bang, and that’s all we’ve got.

Pamela: That’s all we’ve got.

Fraser: All right. Speaking of all we’ve got, there’s one more question. This is a good one too, in fact this is a question I was going to ask you about and I never got around to it.
 
This one comes from the forum, the Bad Astronomy & Universe Today forum. “I can’t wrap my head around the physics of gravity assist. Why does travel in the same direction of an object’s orbit speed something up, while travel in the opposite direction slows it down? I keep thinking the approach push and depart pull would cancel each other out either way and not change the speed at all.�
 
This is great – I’ve thought about it too. You’ve got a spaceship going toward Jupiter and it’s going to get a gravitational assist to pick up velocity and go much faster. As it approaches Jupiter, Jupiter is speeding it up. I get that – it’s velocity might be changing as it’s falling into Jupiter’s gravity well. As it does its fly past, and starts to move away from Jupiter again, now Jupiter’s pulling back on it. It should be slowing back down. Shouldn’t you just end up with the same velocity? It’s like going down a hill and then back up it on the other side, shouldn’t you end up going the same speed you were going before?

Pamela: That would be exactly right if the object you were having the gravity assist from wasn’t moving.
 
The key is you are gravitationally falling into the gravity hole of some object in motion. If it’s not in motion, you go in, come back out and your energy hasn’t changed at all. If you imagine a completely frictionless, gently curved valley in the road. You go down a hill, up a hill, no friction occurs so you’re going the same speed on both sides of the hill even though you speed up going in and slow down going up… it all cancels out in the end.
 
The catch is, if the object’s moving, the amount of time that it is either able to gravitationally pull on you to speed you up or gravitationally pull on you to slow you down changes. If you’re moving in the same direction as the object that’s giving you the gravitational assist, as you’re moving toward it, it’s saying “yes! Catch up with me!� and pulling on you to get you to catch up to it. So the whole time, you’re approaching it, it’s running away from you. As it’s running away, it’s pulling on you to help you catch up.
 
Once you catch up to it, you’ve gained all this velocity, so you’re able to zip away from it with extra velocity you didn’t have before, because the extra time you had catching up with it lead to you getting some of its velocity and spending extra time falling in and not extra time falling out.

Fraser: So, you’re slowing down Jupiter by a teeny-tiny little bit, to slow it down in its orbit, and its speeding you up to pull you up to its speed.

Pamela: Yes.

Fraser: Right. So the amount that you get falling into it and the moving back away from it do cancel out, but it’s that process where it’s pulling you up to its speed in the orbit which is what adds to your velocity.

Pamela: If you’re going in opposite directions, then you end up putting the extra effort into slowing down to meet its speed. Then you end up going slower on the other side. Same thing.

Fraser: Right, and I know the MESSENGER space craft is using that method to be able to go into orbit around Mercury.

Pamela: Yes.

Fraser: They’re using this process to be able to slow themselves down, as well – if you just go the opposite direction, you slow yourself down.
 
That totally makes sense. I honestly didn’t have it thought through, so thank you.

Pamela: It’s a really cool affect.

Fraser: You know what, I said that was the last one, but we’ve enough time for one last, quick little question. I think this is a quick one. Rich from New York wants to know “if the Sun were to suddenly vanish, would we feel the effects of gravity instantaneously, or would it take approximately 8 minutes, just like light?�

Pamela: It would take 8 minutes, just like light. Fast enough?

Fraser: The speed of gravity is the speed of light. If the Sun disappeared, we would see the light disappear and we’d also suddenly feel the gravity disappear.

Pamela: It would appear as if all of a sudden all the stars became visible and they’re moving in the wrong way. That’s kind of cool.

Fraser: Yeah.
 
And that effect works the same for us moving around the Milky Way, the Moon going around the Earth… it waits for the speed of gravity. Cool.
 
I think that plays into our recent show about gravity waves, that’s what the whole trick is about. You’re watching as waves of gravity are released from objects as they wash over the planet. That’s it – that was quick.

Pamela: Cool.

Fraser: Perfect. I think that covers everything.

Transcript: Cosmic Rays

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Fraser Cain: We’re going to return back to a long series of episodes we like to call: Radiation that Will Turn You Into a Superhero. This time we’re going to look at cosmic rays, which everyone knows made the Fantastic Four.

 

These high-energy particles are streaming from the Sun and even intergalactic
space, and do a wonderful job of destroying our DNA, giving us radiation
sickness, and maybe (hopefully!) turning us into superheroes.

 

Pamela?

Dr. Pamela Gay: No.

Fraser: All right.

 

[laughter]

 

I guess we’ll have to wait for the next episode – perhaps gamma rays. We’ll
keep moving.

 

So where do cosmic rays come from?

Pamela: They come from as near as our Sun, and as far away as some of the most distant
angry, active galactic nuclei. Wherever we have strong magnetic fields you have
particles getting accelerated. In fact, in some cases we also get what are not
cosmic rays, but they look similar. They’re cosmic ray-like things from granite
and other rocks that are embedded with radioactive materials here on the planet
Earth.

Fraser: What is a cosmic ray? Some come from the Sun, some come from deep space…
break it down for me.

Pamela: It’s basically a fast-moving, subatomic particle. You get protons, electrons and
in some cases you even get alpha particles, which are helium nuclei. If you
accelerate them at high rates, when they collide with things they expend all their
energy. If the thing they’re hitting happens to be DNA it can do damage. If it
happens to be a digital imager such as a CCD detector it creates streaks in your
image (in graduate school cosmic rays were the bane of my existence and I
learned to hate them with great vigour.

Fraser: You’re saying the word particle. That doesn’t sound to me like a ray. When I
think of a ray, I think of a piece of the electromagnetic spectrum, but it doesn’t
even fit on the spectrum, right?

Pamela: Yeah, that’s one of the weird things about this. Cosmic rays are flying particles:
they’re a single thing that gets flung at you, or the planet Earth, or something
that can detect them, at high velocities.

Fraser: So think bullets, not waves.

Pamela: They’re bullets not rays.

 

Now, I have this sneaking suspicion, and I have no way of confirming this that I
know of, that the name cosmic ray may have come from the fact that they leave
streaks on detectors. So you get one basically coming to a grinding halt across
your photo-detector, across your photo-sensitive whatever it is you’re working
with. When they come grinding to a halt, their energy creates a streak on
whatever image you’re trying to take, that looks like a ray.

Fraser: All right, so give me the origin of a cosmic ray. What kind of conditions exist
and what will happen to actually generate one of these?

Pamela: So you have a proton minding its own business happening around the universe –
perhaps in a star, perhaps somewhere else.

Fraser: Sure – lets start with the ones that come from our Sun. will you have a free-
floating proton?

Pamela: A free-floating proton is nothing more than the hydrogen atom that’s been
stripped of its electrons.

Fraser: Okay, so how did it get stripped of its electrons?

Pamela: You heat it up and it gets naked . it’s kind of cool that way.

Fraser: All right. And a star is known to heat things up – so a star can strip a proton of its
electrons so you just have a naked proton.

Pamela: So you have this naked proton wandering around in the extremely hot outer,
outer atmospheres of the stars. They get trapped in magnetic loops.

 

When you look at the Sun through and H-alpha filter, you’ll sometimes see
these loops – these different neat filamentary structures on the edges of the Sun.
you can’t see them face-on, because they get lost in the glare of the Sun. they’re
getting accelerated through these magnetic loops, and when these loops break,
we get all sorts of particles flung at our planet. When they hit, we get things like
the northern lights.

Fraser: so the magnetic loops we see on the Sun, those are almost like if you take a
magnet and put it in a bunch of iron filings, the filings will move in the shape of
the magnetic field lines that are coming out of the magnet. So those loops on the
Sun are kind of the same thing?

Pamela: They’re very similar. Another way to think of it is as an electromagnet. If you
take a wire and loop it around a piece of PVC pipe (use the thickest wire you
can find and a skinny pipe), attach it to a car battery, you can use it if you attach
and detach it quickly to fling small objects that are metal. Don’t do it with sharp
objects, but it’s fun to do with little BB’s or something in an open space. This is
a project I like to give to students.

Fraser: So in that situation you’re turning on the magnetic field and the BB or whatever
is trying to align itself into the magnetic field, and just as its about to get there
and be slowed down and pulled into its correct position, you turn off the
magnetic field and its just got the momentum to carry it along.

Pamela: In particle accelerators here on the planet Earth, like CERN which we talked
about in our show about the Large Hadron Collider, they have pulsed magnetic
fields where they’re constantly turning the magnets on and off in sequence to
drag the particles in circles around and around in these loops.

Fraser: So you’ve got these protons hanging out on the Sun, they get accelerated or they
get pulled into these magnetic field lines, and then the magnetic field lines
change and you get this snap and the particles are flung out. Is it just protons?
How fast are they going? …I just asked two questions there. Is it just protons?

Pamela: It’s not just protons. It’s protons and electrons, its even helium nuclei (alpha
particles) in some cases.

Fraser: It’s whatever was trapped in the magnetic field line when it snapped.

Pamela: It’s always ions

Fraser: Water at the end of your wet towel.

Pamela: The key is its always something that has charge. It’s going to be a light atom
because it takes a lot more energy to accelerate a heavy atom.

Fraser: Oh, because they have to have charge to be picked up by the magnetic field line
anyway.

Pamela: Exactly. So you take a charged nuclei, interact it with a magnetic field, snap the
magnetic field and off flies the charged particle, the charged ion… and you have
a cosmic ray.

 

These things vary in energy. You can get pithy little tiny ones, but you can also
get some where you have a single proton that is carrying as much energy as a
tennis ball going 50-60mph. That’s a lot of energy.

Fraser: Especially if it hits your precious DNA.

Pamela: Yeah. Imagine how much it hurts your skin if you get hit by a baseball. Imagine
instead all that energy being focused and nailing a piece of your DNA.

 

Luckily, these are itty-bitty little tiny things. They’re parts of atoms. Even
though we look like solid objects, human beings are mostly empty space –
everything is mostly empty space. Most of the time these protons will happily
sail through your entire body and not interact at all. Occasionally, damage can
occur.

Fraser: Right, but aren’t we protected by the Earth’s atmosphere?

Pamela: We’re mostly protected by the Earth’s atmosphere. The magnetosphere is
what’s doing most of the protecting. Our planet has its own magnetic field, and
when these charged particles interact with the magnetic field, in many cases
these particles get their direction changed and they veer off so we don’t get hit
by the majority of them. Some of them do make it through the magnetic field of
the Earth and hit us down here on the planet Earth. There’s actually been some
possible relationships between spikes in the number of cosmic rays hitting the
planet Earth, and the frequency of cancer.

Fraser: So when the cosmic rays hit the Earth, they don’t stream straight in – they get
stopped by the atmosphere. Could we talk about our natural defences – how is
our planet protecting us from those awful rays?

Pamela: It’s primarily our magnetic field. Just like magnetic fields can accelerate these
particles, they can decelerate them and change their direction. They can funnel
them into the Van Allen Radiation Belts.

 

Our atmosphere can help as well. When these cosmic rays hit the atmosphere,
they end up reacting with things in the atmosphere, creating Cherenkov
Radiation. We get streams of different types of particles that we can then detect
with different telescope facilities that are specially built to detect these cosmic
rays.

 

There are still some that make it through, completely unaltered, waiting to nail
my CCD when I’m trying to take high-resolution images of the cosmos.

Fraser: That’s what you talked about next. You’re using your CCD and not trying to
detect them… but what’s the method astronomers use to detect them when they
go looking for them?

Pamela: There’s a few different ways. One method you can use is you can take a large
tank of often heavy water. You can actually get muons produced when cosmic
rays hit the heavy water. We can detect these through their child particles and
the flickering of light they give off.

 

Another way that we can detect this is through the chain of particles they
produce in the atmosphere. You can have a high energy proton coming in and it
collides with a molecule in the atmosphere and gives off what are called pions
which then decay into things like muons and gamma rays and neutrinos.
Through all these different chains of events, we eventually get things we can
actually detect. There are different observatories like the Whipple Observatory.

 

There’s a new facility, the Pierre Ojet Observatory, which is actually a pair of
observatories, one in the United States and another in Argentina. They’re
working to use a whole different array of methods so they can compare how
they’re detecting cosmic rays and hopefully work to figure out where on the sky
these cosmic rays are coming from.

 

Figuring out where cosmic rays originate is actually a real problem. As they’re
flying through the cosmos, every magnetic field they interact with is going to
change their direction. Some cosmic rays we’ll never be able to figure out
where they originated.

Fraser: That’s part of the mystery. You talked about the fact that we know most of the
cosmic rays hitting the Earth are coming from the Sun. That’s not all of them –
where are the rest coming from?

Pamela: Some are coming from galactic origins. Unfortunately, the galactic ones we
have no way of figuring out where they came from. The galactic magnetic field
scrambles all of that information.

 

Based on their energies and based on the shocks we see around things like
supernova, we believe most of the galactic cosmic rays originate in supernova
blasts. Some of them though have such high energies we can’t really find
anything in our galaxy that they could be coming from. We’re still trying to find
all the origins.

Fraser: Weren’t some of the energy levels in the cosmic rays higher than physicists
thought was even possible? Wasn’t it more than was theoretically predicted by
the most extreme events anyone could imagine?

Pamela: Oh, totally.

 

So sometimes (not often, but occasionally), you get physicists that come up with
humorous names for things. The Higgs Boson is nicknamed the God Particle.

 

It’s the one we’re looking for that will give mass to everything, and we need to
know where mass comes from.

 

After finding these ultra, oh-my-god-high energy cosmic rays, they got
nicknamed the “oh my god” particles, because nothing can explain what created
these things.

 

We’re starting to get some clues. We think many of them have extragalactic
origins, so they’re travelling to meet us from other galaxies. We think it might
just be that they’re coming from super massive black holes that are angrily
feeding in the centres of galaxies. These are active galactic nuclei. It’s a family
of galaxy related to quasars.

Fraser: What might be the process that’s whipping up these particles with that much
energy?

Pamela: It’s all about the magnetic fields. Active galactic nuclei, in many cases, have
these amazing jets. They appear as radio lobes in surveys like the first NVSS
surveys done with the VLA in Mexico. You look at these images and when you
super-impose the radio images on the optical images, the optical part of the
galaxy might be 20 pixels across, down in the centre of the image. Then you get
these huge radio lobes that will go out a couple hundred pixels in either
direction.

Fraser: When you say lobes… what is a lobe?

Pamela: We call them lobes. It’s the name we gave the shape. Take ice cream cones and
attach them to the top and bottom of a spiral galaxy. At the end, have the
material coming out billow as it hits the intergalactic medium.

 

We have these jets of material in some cases very tightly wound and we can
actually see twisting and winding of the material. As the material travels away
from the galaxies, it eventually ends up colliding with the dust and gas between
galaxies and it billows out when it hits, sort of like a waterfall hitting the ground
and creating a cloud of splashing water.

Fraser: So when you see the picture from a telescope of a quasar or active galactic
nuclei, the visible part may be a small little part of the screen, but then the part
that’s actually radiating radio waves is gigantic around the galaxy, and that’s
coming from the jets that are interacting with its surroundings?

Pamela: They originate from the jets. So these quasars have powerful magnetic fields
being generated in the accretion disk of in-falling material around them. You
have this spiralling charged material driving huge magnetic fields. Sometimes,
particles get flung out the poles of the magnetic fields. This acceleration creates
the jets, and it can also help create, in this chaos of magnetic fields, these ultra

 

high-energy cosmic rays that are packing a wallop of a high school student’s
tennis ball that’s getting hit at 50-60mph.

Fraser: There’s actually some brand new research that we reported on at the AAS, where
astronomers are now calculating that many super massive black holes are
spinning at the very limits of relativity as predicted by Einstein. You can just
imagine something with hundreds of millions of times the mass of our Sun
spinning close to the speed of light.

Pamela: Yeah.

Fraser: In a disk of material and with a giant magnetic field it’s building up. You can
just imagine the forces its building up. Just like the Sun, it’s scooping up
particles in these magnetic fields and snapping them like a towel at us? Maybe.

Pamela: That’s pretty much exactly what’s going on. One of the numbers I found in
preparing for the show was that in some cases, these high energy accelerated
particles are moving so fast, at so close to the speed of light, that if one of these
high energy cosmic rays – a proton – left a supernova at the same time as a
photon and they travelled for one year, the proton, which because it has mass
can’t travel at the speed of light, will only be about 46nm behind the photon that
is travelling at the speed of light.

Fraser: That’s what I heard – that one of the important things astronomers were able to,
with their latest research they were able to see some event at a super massive
black hole in a galaxy far away, and then later, see the associated cosmic rays
from it.

Pamela: This is one of the neat, new, forefront areas of science where we’re just starting
to build the detectors, we’re just starting to figure out how to detect these things
and how to triangulate where they’re coming from, and in may cases we can’t
tell where the cosmic rays are coming from, but with our optical, radio, gamma
ray, x ray telescopes we can see that a really cool event went off and then a few
minutes later, with our cosmic ray detectors, we see this flood of cosmic rays.
So we’re using the probability alignment of “if we see this and then we see this
over and over, then they’re probably related”.

Fraser: That makes sense.

Pamela: Works for me.

Fraser: Now, what kind of an impact do cosmic rays have on spaceflight for astronauts
heading to the Moon? If humans are going to be buzzing around the solar
system in the future, are these pretty dangerous?

Pamela: Yeah. This is actually a fairly serious problem we have to figure out how to
address as we look to send men and women further and further across the solar
system. Today on the International Space Station, they actually have one part
that is much better protected than others. When there’s a solar storm, they lock
everyone in that one area because it will protect them better.

 

As we start heading out… Mars doesn’t have a magnetosphere. The Moon
doesn’t have a magnetosphere. We’re going to have to develop spacecraft that
will allow astronauts to not only survive solar storms but as they spend longer
and longer periods of time in orbit, they’re going to need to not get blasted with
too many REMs of radiation.

 

Alpha particles are one of the forms of cosmic rays. They’re also one of those
things that can cause radiation poisoning if you encounter too many of them. So
we need to protect them, and we need to worry about how long people spend in
space.

 

Anyone who’s worked in a lab with radiation knows you can experience a
certain amount of radiation before you have to start worrying about the
consequences of the radiation. All of us can get our teeth x-rayed, all of us can
go down to the granite quarry now and then. But if you live in new England,
you’ve probably done a radon test in your basement because you don’t want to
live in a house that’s filled with radon. It will eventually cause increases in
cancer rates.

Going into space is the same as building your house inside the granite quarry,
where your entire house is filled with radon.

Fraser: What kind of warning will we get? Do we have mechanisms for detecting a solar
storm coming past, and a way for the astronauts to run and hide? How much
time do they have?

Pamela: People are trying to figure out ways to do this. Luckily for the solar ones they’re
not going at the speed of light. Often we have a day or so – a few hours, to get
people prepared. It depends.

 

At last year’s AAS, or perhaps over the summer, someone was talking about
ways you can tune in to coronal mass ejections, and depending on the radio
spectrum, depending on all the different colours of light and how they come off
of the Sun, you can say, “this one is going to hit us with a blast of particles, and
this one isn’t.” that’s useful information. It allows us to do things like put
telescopes into safe mode when we know they’re in trouble.

 

Now, the problem is there are these ultra-high energy cosmic rays that are
coming from beyond the Sun that we have no way of predicting. As you get out
of the Earth’s magnetosphere, the number of those that are going to hit your
body are increasing.

Fraser: The astronauts in the space station, they’re protected because they’re within the
magnetosphere.

Pamela: In many cases yes.

Fraser: Right. But if you get out of the magnetosphere and off to the Moon or off to
Mars, then you’re on your own.

Pamela: Exactly.

Fraser: I think that’s going to be a pretty big problem, and I can imagine us having these
heavily armoured (and, I guess, heavy) spaceships trying to minimize the
radiation risks the astronauts are going to be facing. That’s just going to
increase the expense of getting things into orbit.

Pamela: Yeah, and people in the international space station are only up for a few
hundred days. Going to Mars, you’re looking at 3 years.

Fraser: Right, and it’s not like once you get to the planet you can sit there and be safe.
It’s just as dangerous down on the surface of the planet as you are in space.

Pamela: So we have to figure out how to effectively protect people, lower the risk of
cancers and mutations. One of the problems with this is it’s not necessarily the
astronauts that get the cancer, but it could also be their children. You don’t want
to say astronauts can’t have children, but we have to consider the generations of
damage we can do.

Fraser: There’s one last thing that was quite interesting. One of the writers on Universe
Today did an article, and scientists had been able to track the link between
cosmic rays and cancer rates.

Pamela: Yeah, this is what I was hinting at. There was a cycle determined using ice core
samples. It’s possible to go through and determine where and when in the past
there were increased numbers of cosmic rays. In the United States, Canada, the
UK, and Australia, we have fairly good data for who had cancer and died of
cancer in the past 100+ years. Going through this data, they were able to find
there’s basically a 28 year lag between a peak in cosmic rays and a peak in
cancer deaths.

 

They also found that when there was extremely low rates of cosmic rays, 28
years later there was extremely low rates of cancer. All because there’s a link
doesn’t mean cosmic rays are causing the cancer – it could be something else. It
could be that cosmic rays are causing something else. But there is this
relationship we’re noticing.

 

One of the ideas they put forward is you have a woman who’s pregnant. While
pregnant she gets blasted with cosmic rays. She has millions of cells – she’s’
okay. But her unborn child might be a few dozen cells at the time. When you
damage one of those few dozen cells, that damage propagates to the entire
future human being. Then that future human being has a child, and it’s that child
that ends up getting and dying of the cancer.

Fraser: Wow. So is there a Suntan lotion I can get when the cosmic rays are on the
increase? Lead, right?

Pamela: Or glass – glass in some cases can be useful.

Fraser: Glass, lead, underwater.. live in a subterranean home…

Pamela: That little room the x-ray technician goes into.

Fraser: Yeah, that should be safe.

Transcript: The Large Hadron Collider and the Search for the Higgs-Boson

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Fraser Cain: When it was first developed, the standard model predicted a collection of particles, and thanks to more and more powerful colliders, physicists have been able to find them all except one: the Higgs-Boson. It’s an important one because it should explain how objects have mass. The European Large Hadron Collider should have the power and sensitivity to find the Higgs-Boson.
 
All right Pamela, can you give us a bit of history on the standard model without explaining the whole thing?

Dr. Pamela Gay: For a long time, scientists tried to figure out how to piece all these crazy different particles we have and all the forces we have into one coherent model. The standard model is about the best way we have of doing this. It is able to combine electromagnetism, the strong force and the weak force (it unfortunately can’t quite get to gravity) in one coherent framework that explains things like why an electron and a proton are stable, while other particles like muons just fall apart on very short timescales.
 
In the process of pulling all these different things together, they realised photons carry the electromagnetic force, the force that causes magnets to stick to your refrigerator and your lights to light up when you flow electricity through them. They were able to figure out that gluons glue together the centres of atoms and that W- and Z-Bosons are part of the process that allows different atomic decays to take place.
 
In the process, they realised we still need something to give mass to different particles.

Fraser: It’s funny when you think about that. Mass just seems like such a part of reality, everything has mass – you pick it up, it’s hard to move – and yet, there has to be some underlying framework. Even in the vacuum of space, it’s harder to move something that has more mass than something else.

Pamela: This is one of the things that has been extremely troubling. Why is it an electron’s mass is so much smaller than a proton’s mass? How do photons not have mass at all, whereas W- and Z-Bosons, which, just like a photon, are force carriers, have a lot of mass.
 
What scientists figured out is there’s a field called a Higgs field that permeates all of space. The field contains energy. Different particles are coupled to this field in different ways, depending on how they interact with this Higgs-Boson (if it exists – and we really think it does).

Fraser: I can imagine all of space as molasses, and particles are stuck in that molasses, and it’s hard to get them moving in that background.

Pamela: But once you get them moving, it’s hard to stop them. One of the standard ways of trying to explain this is imagine you have a room full of people. They’re all just hanging out. If a movie star comes into the room, and is amiable to signing autographs and things, and has a large entourage, that movie star is said to have a lot more weight. As the movie star tries to move through the room with her big entourage attached to her, it’s hard to stop that moving swarm of people.
 
If the movie star stops and people collect around her, it’s very hard to get that movie star moving again because there’s so much mass to try and get moving.

Fraser: I’ve never heard that analogy before, that’s a good one.

Pamela: It’s a really neat way of thinking of it, just in terms of the more bosons, the harder it is for you to move, or once moving, the harder it is to stop moving.

Fraser: Why hasn’t this particle been seen so far?

Pamela: The problem is, it has a lot of mass. In order to discover new particles, what scientists have to do is take a whole bunch of energy and force that energy to fall out into new particles. What they typically do is take a couple of protons, a couple of positrons and electrons – some sort of small, easy to accelerate particle, and accelerate it extremely fast.
 
As that particle is usually flying in a circle in some sort of a cyclotron device, it’s getting faster and faster and faster because of magnets. We take these charged particles and you can actually use a magnet to move charges. So we accelerate the charges faster and faster and faster. The energy they have, it’s tied up in their velocity. That energy adds to their mass, so in a way the faster the proton or electron is moving, the more mass-energy it has.
 
At the end of this, we slam (with great violence) that particle that has been accelerated into a target or into another accelerated particle. When they collide, all of a sudden all that velocity is gone. All that energy ends up freezing out as new particles. This is how the top-quark was discovered at Fermilab. This is basically how all the large particles that we know about that are extremely unstable have been discovered.

Fraser: So the particle is destroyed, and all of the energy that was in the particle turns into whatever sub-particles it has energy for.

Pamela: What’s cool is there’s basically this rain of particles. If you collide together two electrons, they create a shower of new particles that are initially unstable. Those unstable particles will collapse into more particles, and if any of those are unstable, they’ll collapse into more particles. As they do this, they’re raining out of the target chamber, where the collision took place, and passing through different types of gasses and crystals. They interact with the material in the detector and often give off faint flickers of light.
 
Particle physicists and experimental cosmologists use these flickers of light to create trails of the particles as they pass through the detector to try and figure out where different things are at different points in time, and to figure out what that entire rain of particles was – what were all the different things that came out of the collision.

Fraser: Before, you said it was a matter of mass, that the Higgs-Boson is very massive, and that’s why they’re not able to find it yet. Can you explain that?

Pamela: With your standard collider, for instance the one at Michigan State University, you take a particle and you can accelerate it only so fast. It’s sort of like my Jeep Wrangler that really doesn’t go faster than 95mph. So if you accelerate something as fast as you can and slam it into a target, the combination of the mass in that particle and the energy in the form of kinetic energy (velocity) in that particle can get transformed into new particles.
 
You only have as much energy as was stored in the mass of the original particle, and that you were able to give the particle by accelerating it. That number usually has some maximum value, and anything that has a mass that has an equivalent energy greater than what you’re able to get out of that particle, you can’t make. It’s sort of like you can’t make a two-layer cake if you only have enough mix for one and a half layers. If you have a particle that has more mass than that initial particle plus all that energy you gave it by accelerating it, you can’t ever create that larger particle.

Fraser: So, there has never been a collider that’s had enough energy to generate particles with that high enough amount of mass.

Pamela: They tried really hard with the last detector they had at CERN. CERN is the world’s largest particle accelerator. It straddles the border between France and Switzerland, located near Geneva.
 
They used to have the Large Electron Positron Collider, LEP. In its final days, when they weren’t so worried about breaking it, they pushed it past all of its limits, and tried really hard to find the Higgs-Boson. If you look down in the noise, there’s stuff that people (if you squint really hard and force your statistics really hard) think might be hints of the Higgs-Boson. But no one’s really sure.

Fraser: Is that one of the situations where there are a bunch of predictions for the particle, and you’re able to at least knock off some of the predictions? It may be its mass is between this amount and that amount, and if you don’t see it with the most powerful collider that you have so far, that doesn’t mean it doesn’t exist: it just isn’t in that range, right?

Pamela: Yeah. It’s sort of like if your eyes can only see things that are as bright as a lightening bug. If something’s half as bright as a lightening bug, you can’t see it. All you’ve done by looking for it is saying that is has to be fainter than a lightening bug.

Fraser: Right.

Pamela: With LEP, they tried and tried and tried. They were able to say it must be greater than about 200 giga-electron volts. That’s a really weird unit to be talking in.
 
When talking about these particles, we talk about them in terms of their equivalent energy: how much energy does it take to make this particle. An electron, for instance, has an equivalent energy of 0.5 mega-electron volts (a million electron volts). We’re looking for something substantially bigger than that – on the order of billions of electron volts.

Fraser: All right. Let’s talk a little bit about the Large Hadron Collider then. What capability is it going to have?

Pamela: It’s going to be able to get into the hundreds of giga-electron volt values.

Fraser: So before… what was the number?

Pamela: Before we were just barely starting to get to about 200 giga-electron volts when they pushed the system beyond its safety limits, where you’re in danger of not hurting yourself but hurting the equipment. Now we’re going to be able to get substantially higher than that.
 
Just to give some more scale to this, the equivalent of 725 milli-joules is the type of energy you can get out of these collisions. That’s the equivalent of 157kg of TNT. So we’re looking at very large amounts of energy, coming out of streams of these giga-electron volt particles.

Fraser: This is microscopic particles colliding together, generating the force of dynamite explosions.

Pamela: They’re looking at having billions of collisions per second, in some cases.

Fraser: All right. Is the Large Hadron Collider purely looking for the Higgs-Boson?

Pamela: No. We wouldn’t have spent so many billions of dollars building one apparatus if it was designed just to look for one lonely particle that we’re all pretty sure is there.

Fraser: We should talk about a scale – sorry, I know I asked you a question, and now I’m asking a different one – but we need a little background because it’s gigantic.

Pamela: It’s huge. The tunnels they accelerate the particles through are 27 miles long. There’s a pair of these circular tunnels, one next to another, to accelerate particles through.

Fraser: They go through multiple countries.

Pamela: Two different countries. America alone has over 1000 scientists working on this one detector system, this one giant facility. It actually has multiple detectors in it, but this one accelerator facility.
 
We’re looking at something that cost on the order of about $3 Billion. It’s a bit expensive.

Fraser: Okay, now we’ll go back to the original question. So what else is it going to be looking for? It’s so much of an investment just to look for one particle.

Pamela: It’s going to be looking to see if there’s a theory that’s superior to the Standard Model. It’s going to be looking for things like this particle called a neutralino. These hypothetical particles come out of super-symmetry theories.
 
The Standard Model, a lot of scientists are kind of uncomfortable with that has all these different parameters they actually have to go and measure. A lot of theorists don’t want to have to measure things. They want theories to make solid predictions of “this is going to be this big and have this value and nothing has to be measured in a lab, everything comes from some magical first principle�.

Fraser: So they make their predictions of the particles, but they find it frustrating that they’ve had to actually go and perform the experiments to find out how much those particles weigh, or how much energy they take to show up.

Pamela: Right. So for instance, the Higgs-Boson, we think we know how much mass it has: we think it’s around 200 giga-electron volts, but it could be much bigger. What’s worse, it could be the Higgs-Boson is actually a family of different particles, so there’s more than one version. We don’t know – we have to go measure that, which annoys a lot of theorists that want everything to be nice, clean and predicted entirely from mathematics.

Fraser: It doesn’t include gravity, right?

Pamela: Right, and that’s always a problem.

Fraser: Yeah.

Pamela: People would like gravity to fit into their grand unified theories of the universe.

Fraser: Right.

Pamela: Or at least into their grand unified theories of particle physics.

Fraser: Right, so there’s a whole force we’re well aware of, that we see everywhere, which isn’t predicted or explained at all by the best-known model of physics. So what is super-symmetry?

Pamela: The super-symmetric theory basically says all these different particles have super-particles. They have this other set of particles that have matching, but flipped characteristics. For every one particle we know of now, there must be a second particle: a matching, super-symmetric particle. They’ve come up with all sorts of crazy names for them.
 
The lightest of these is the neutralino. If we can find it, then we’re going to find it with the Large Hadron Collider. It’s actually very close in mass (we think) to the Higgs-Boson. One or the other of them is going to pop out very early on in the experiments, if we’ve made our predictions correctly – rather, if these brilliant, mathematically gorgeous theories they’ve come up with have predicted correctly, we’re going to find one of these.
 
We also might end up creating microscopic black holes. That’s also kind of cool. So, if the super-symmetry model is predicted, then there’s going to be some new Nobel Prizes handed out for that, probably.
 
Theorists can’t get the Nobel Prize until someone actually finds the particles that were predicted, so if we find the Higgs-Boson, Peter Higgs will get the Nobel Prize. If we find the super-symmetric particles, the people who worked on the super-symmetry theories will get a Nobel Prize. If we create a microscopic black hole that, in fractions of a second, decays via Hawking’s Radiation, then Stephen Hawking might finally get his own Nobel Prize as well.

Fraser: I did an article about microscopic black holes one time. These are black holes that could’ve been formed at the very beginning of the Big Bang, when you had a high concentration of mass. Since then, since only large amounts of mass can collapse, you’ll never get those microscopic black holes since then. Now, physicists might be able to re-create them in the lab.

Pamela: This is one of the few times that you can refer to an astronomer as an experimentalist. In general, we’re not experimentalists: we can’t go out and build stars and stick probes in them and control variables. We’re observationalists, sort of like a lot of animal behaviourists who go out into the wild and observe creatures in their natural habitat. They’re not experimentalists, they’re observers.
 
With particle physics, you can have a cosmologist who’s trying to study the first moments of the universe go into one of these facilities (CERN, Fermilab, or any one of the many different colliders scattered around the planet) and set up situations that only existed in the earliest moments on the universe and play with particles in a way that no longer necessarily happens in the universe. They can also simulate things that happen in supernovae. They can actually do experiments on what happens in different astronomical conditions.

Fraser: So, with the neutralino being the first particle they should be able to tease out, where will they go from there?

Pamela: That’s the question. There’s so many directions things could go. We could start finding things that prove or don’t prove super-symmetry. If super-symmetry isn’t true, that’s going to lead to a lot of head-scratching.
 
We can also start chasing things predicted by both super-symmetry and string theory, and maybe narrow down which versions of string theory may and may not be true.
 
We can start working with the baby black holes. That’s just an odd idea, and who knows where that idea could go. At this point, we’re all sort of holding our breath going, “what is the very first result going to be?� Once we have those first results, the theorists can go to work and start making predictions for the next rounds of particles, as we chase down super-symmetry.
 
There’s so many different things we don’t know, that we really need to find Higgs, find the neutralino, make the baby black holes. Then we can see what we’ve eliminated and what we can move on to discover next.

Fraser: I’ve heard some people kind of freaked out about the possibility – of course, they worry about this with every new particle collider – that it’s going to…

Pamela: That we’re going to destroy the universe?

Fraser: Yeah, that it’s going to instantaneously destroy the universe and turn it all into some form of ice or something like that.

Pamela: Yeah, no.

Fraser: Uh, no? Can you put everyone’s concerns to rest, and explain why the Large Hadron Collider isn’t going to destroy the universe?

Pamela: At most, they’re going to destroy part of their building. That’s only going to happen if they’ve had some sort of safety mishap and a beam drops in the wrong place. That’s where you get the air-dropped bomb energy coming out of the beam.
 
In general, this thing is built 100m underground and anything it creates is going to be completely unstable and will decay before it can really leave the building. So yeah, there are going to be radioactive particles created. There might be microscopic black holes created. There will be (hopefully, hopefully), Higgs-Bosons created.
 
All of these things are unstable, and it’s sort of like taking an ice cube and shredding it into ice. If you throw that ice up into the air, it’s going to be water before it hits the ground (if it’s a hot day, at least). With the Higgs-Bosons, if you create one it’s decayed into something completely safe before it hits the ground. We’re creating unstable things and watching what happens as they decay.
 
They do it over small distances, the detector is completely buried, surrounded in cement and lead. They have done everything they can to make it a completely safe facility. If something goes wrong, the worst that will happen is they blow up one of their own detectors. That really sucks because you have to spend the money to rebuild the detector, but humans don’t generally get hurt except when things like cranes drop. That’s been the biggest danger in building these facilities: not the radiation, but the fact that you’re working in compact spaces, with machines that are multiple stories tall, and you’re doing it all underground between walls, wedged into tight spaces. It looks like human beings crawling around like ants on these detectors, when they’re working on them.
 
The danger you’re looking at for humans is more like what you get when you’re building buildings than what you get even when you’re taking x-rays in a medical facility. We’re safe.

Fraser: It feels like people have been talking about the Large Hadron Collider for years and years and years, as it’s been constructed. When is it finally going to go online?

Pamela: It is about 2 years behind schedule. It’s had different financial crunches, different changes… yeah. Big science sometimes gets delayed. They’re currently in the process of doing test runs. They’re looking at doing their first science starting in May. Things are going, starting to go well and they’re just ticking down their checklists and they have particle beams going and their equipment is working.

Fraser: So we could be six months away from learning some of the new results.

Pamela: Yes. It’s going to be a great new year in 2008.

Fraser: No kidding. That will be big news. Even if they don’t find anything – that’ll be big news.

Pamela: One of the cool things is if they do find the neutralino, it’s by many considered to be a candidate for dark matter. We may actually finally be able to identify a particle that could be associated with a lot of the dark matter that we otherwise have no way of detecting. We might be creating dark matter in a laboratory and finally be able to study it.

Fraser: That’s cool. Thanks, Pamela.

Fraser Cain: This week is going to be one of those foundation episodes that we’ll be referring back to time and time again in the future, so pay attention, take some notes, we’ll try to make this as entertaining as possible but it’s going to be some work so listen carefully.
 
So as human beings, we perceive the Universe in visible light. We can feel infra-red as heat, and our skin burns because of ultra-violet (although that’s not a very good scientific instrument). There’s a whole electromagnetic spectrum out there, ranging from radio waves to gamma rays. Different kinds of objects and events produce different kinds of radiation and tell us more about the story of the Universe.
 
So Pamela, let’s start with a really simple question: what is light?

Dr. Pamela Gay: Light is a particle and a wave that is called a photon. It’s this little bit of energy that’s capable of moving at the speed of light that we perceive as light. It can have all sorts of different wavelengths or energies, which correspond to the colours that we see.
 
If you have a low-energy bit of light, a low-energy photon, you might perceive it as a radio wave by turning on your radio and seeing what incoming signals your antenna can apprehend. You might perceive it as visible light, by taking a picture of your child during the holiday season and then sending it to all of your relatives. You might perceive it as microwave light by turning on your microwave and sending lots of photons with a microwave wave-length at your food and watching your food cook.

Fraser: So our eyes are just photon detectors.

Pamela: That’s all they are.

Fraser: And a radio is a photon detector at a different wavelength.

Pamela: And our microwave is a light just like our lights are lights. Radio antennas out in the middle of fields, those are a different type of light. They are emitting radio waves.

Fraser: So what’s the difference between a radio wave, and why can’t I see a radio wave when I can see visible light?

Pamela: Different detectors are sensitive to different colours. Our eyes are sensitive to the specific colours around 400-800 nanometres that correspond to optical light. Those nanometres are how long the given wavelength is. At the same time, light that comes from say, my favourite radio station here, 90.7MHz (it’s an NPR station), its wavelengths are 33 metres long. So we’re going from something that is 0.000 000 0007 nanometers – a really, really red colour your eye can perceive, out to 33 metres long, which is what your radio antenna can receive when you turn your radio on at home.

Fraser: So is it that your eye isn’t equipped to see the photon because it has such a long wavelength, it can’t put it together?

Pamela: That’s exactly what it is. What’s cool is, different creatures eyes are actually sensitive to slightly different colours. Some forms of snake can actually see slightly redder colours. They can see into the infra-red more than the human eye can because they’re adjusted to be able to find mice at night and mice are basically warm little objects running around in a cold forest at night. Anything that’s warm gives off infra-red light. You and I are giving off infra-red light as we’re sitting in our offices, just because we’re warm.

Fraser: Okay so, how does this move to astronomy then? How do astronomers use this for finding stuff in space?

Pamela: The different colours correspond to different types of interactions. The colour of an object can depend on how hot it is: warm things like human beings, we give off light in the infra red. So do stars that are forming – really young stars that haven’t really started to generate a lot of heat on their own, they give off light in the infra red.
 
Really hot stuff starts to give off light that is optically visible. So things that are visible to the human eye typically have temperatures between 3600 and 7200 degrees. So hot things (really hot things, things that would more than cook your car if you touched them) those are visible to our eyes.
 
Even hotter things, things that are capable of giving you sunburns and stuff, those correspond to larger temperatures greater than 10 thousand degrees. Really, really hot, young stars give off the majority of their light in the ultraviolet.

Fraser: Hold on. So, if I’m in my room in the dark and turn on a light bulb and can see everything in my room, that doesn’t mean that everything in my room is 5 thousand degrees.

Pamela: No, but what it means –

Fraser: But the lightbulb –

Pamela: The light bulb has light that corresponds to temperatures that are really really hot, and those photons are flying off of your really hot light bulb and reflect off surfaces. Some photons will reflect and some will get absorbed. What we see as colour is simply the characteristics of what photons get reflected and absorbed by different surfaces.

Fraser: Right, so it all depends on the source of the photon, it can then bounce around from that point on, but the photon has been given that energy.

Pamela: What’s cool about light bulbs is some light bulbs are actually cool. Some fluorescent bulbs, you can touch them – no big deal. These aren’t giving off light because of temperature, they’re giving off light because the electrons inside are getting excited by electricity. Excited electrons have high energies, but nothing can stay excited for a long time. We all crash eventually, including electrons. When those electrons come down from those excited energy levels, that energy has to go to something. In human beings, we generate heat. Electrons generate photons when they drop to lower energy levels.
 
The fluorescent light bulbs give off photons because the electrons inside are changing energy levels, and that’s another way we can get light: through electrons transitioning from energy level to another, either while roaming around free (that’s called “free-free”, or “bremsstrahlung” emission (that’s just a fun word to say)) and we can also get atomic molecular lines and just plain old atomic lines, where you have an atom or a molecule and the electrons are changing energy levels and give off very specific colours. This is where we get “Open” signs that are red made out of different gasses. We can get all sorts of different neon lights that correspond to different gasses with different energy levels.

Fraser: Okay, let’s go back to astronomy then.

Pamela: Okay. So, when we go outside, we can use all sorts of different instruments to look up at the sky and detect all these different colours of photons. Any of you, who’ve seen the movie Contact with Jodi Foster, saw that she used an array of giant radio dishes, as well as one ginormous dish in Puerto Rico. She actually filmed (along with everyone else in the crew) at the Arecibo Observatory in Puerto Rico as well as the Very Large Array in New Mexico. These are both radio observatories, and they use their dishes to look for all different colours of radio light coming from stars, galaxies and cold gas.
 
So radio emission comes from a bunch of different things. One of the neatest places it comes from is molecular transition lines. We don’t think of it very often, but the sky is filled with things like ammonia and formaldehyde and carbon monoxide. When these molecules have electrons that change energy levels, they give off radio emissions. For instance, ammonia has a 12cm wavelength, or 23 GHz radio line. So we can go out, tune our antennas to 23 GHz and tune in to listen for ammonia in giant clouds of gas and dust.

Fraser: So do most objects in space give off radio waves?

Pamela: Most cooler objects give off radio waves, due to these molecular transitions. Molecules are kind of fragile. If you heat them up, they turn into their individual, constituent atoms. These individual atoms often give off light at shorter wavelengths, for example in the optical or ultraviolet. But molecules have these lower transitions and those are visible in the radio.
 
We also get radiation in the radio from star forming regions where we have electrons that are running free that as they change directions, there’s actually energy involved in changing directions, and that can get given off as radio emission. We also have star-forming regions that give off radio emissions. So galaxies that either have active galactic nuclei (which means there’s a black hole consuming things – but that’s two shows away, when we talk about black holes), and places where stars are forming, we get this radio emission.

Fraser: And also, we know that the further away you look at things, things can be redhsifted away, so can’t things that maybe started out in a different spectrum be redshifted out to the radio spectrum?

Pamela: You have to be moving away from us at a fairly large rate to get redshifted all the way into the radio, but there are lots of optical things that get shifted into the infra red, and UV things that get shifted into the optical and near-infra red. So, we do see things at colours other than the ones that they’re actually giving off due to this Doppler shifting of our Universe’s expanding, so further away objects appear to be moving away from us and their light gets shifted because of that.

Fraser: I guess you explained a bunch of interesting things in the radio, aren’t there pulsars and stuff that are giving off radio waves?

Pamela: A lot of that comes from the electrons interacting, these free-free / bremsstrahlung reactions. Electrons that are excited into different states, when they de-excite, they give off the radio emission and we find this in some cases around pulsars. The magnetic fields in the pulsars can cause the electrons to change directions and the effect is we see radio emission. It’s just a really neat way of seeing what’s going on at the atomic level in objects that are so far away we can’t really make out the details of what they look like, but we know what their atoms are doing.

Fraser: Okay, let’s pump up our photons, a little more energy. What else can we see now as we move up the electromagnetic spectrum?

Pamela: The next chunk of the electromagnetic spectrum we hit is microwave radiation, and this is where we find our Cosmic Microwave Background. One of the things we haven’t talked about in detail is how temperature and wavelength and frequency are all intertwined.
 
So when we’re talking about the colour of something, we can use a lot of different terms. We can say that it has a wavelength of 14.48 GHz, that’s formaldehyde. Or we can say it has a wavelength of 21cm. You get these two numbers because wavelength times frequency just happens to work out (because of the way the Universe was formed) to be the speed of light. One of the other neat things that comes out of physics, is if you heat an object and it’s what’s called a perfect black body… a rock is a good example.
 
If you heat a rock, it gives off light in all different colours, but the maximum colour it gives off, the colour that gives off the most number of photons is going to correspond to the temperature of the rock. If you go back and watch some of the original Star Trek episodes, you’ll see Captain Kirk heating rocks with his phasor, because that’s what he did. As you heat the rock it gets brighter and brighter in the reds. It’s a warm object. If he keeps shooting it with his phasor, it will eventually turn blue. That colour that we see corresponds directly to the temperature.

So when people talk about the Cosmic Microwave Background, they usually talk about its temperature, which turns out to be about 2.7 degrees Kelvin. If you look at the equation that describes the maximum wavelength that corresponds to a given temperature, that works out to be about one millimetre, so the wavelength of the Cosmic Microwave Background is one millimetre, which is microwave. So in theory, you could use the Cosmic Microwave Background to heat food – not effectively, it’s not tuned exactly right, but still, it’s just microwave radiation.

Fraser: And the microwave background radiation is what was redshifted from the visible light back at the beginning of the Universe.

Pamela: That’s one of those cases where something that was once really hot, bright temperature, good, easy to see (probably quite dangerous to the body) radiation, over time has gotten stretched out, now being in the microwave.

Fraser: Is there anything else that we can see in the microwave spectrum?

Pamela: There are these neat things called “mazers”. These are cases where you have some sort of molecule hanging out either sometimes in a comet, sometimes in galaxies, in molecular clouds, and these molecules are hanging out in an excited stage.
 
Molecules and atoms are allowed only to have specific energy levels. It’s sort of like stair steps. They jump from one level to the next and they can’t be anywhere in between. It works out that if one of these molecules is at a higher step and a photon comes along with the exact energy corresponding to between that high energy and the energy below it, it can hit it just right that the molecule jumps down an energy level, gives off a photon, and that original photon (or at least, some photon with the exact same energy) also comes off. So one photon comes along and suddenly it turns into two photons. Those two photons can hit another excited molecule, and now we have four photons. This ends up magnifying the amount of light at a given colour that’s coming out in a straight line. It’s sort of like a laser beam, except in this case it’s in the microwave radiation.

Fraser: Is that because the energy is being spread out? Sort of one photon has a lot of energy, but then it gives it to a whole pile of other photons, but they’re going to come at it with a lot lower energy.

Pamela: It works out as this weird amplification process. You have all these things that are hanging out at a higher step, and one thing comes along and it knocks something off a step and it gets another photon with it. It comes along, hits something else on a higher step, knocks it down, now we have more photons at that same energy going along. It’s causing a cascading reaction of all of these excited molecules that are in an unusual state. They cascade down, and then give off this photon as they go.

Fraser: So we’re seeing “mazers” in the microwave spectrum.

Pamela: We see them in the microwave spectrum and they’re just kind of cool. The Universe creates its own lasers, but in the microwave regime.

Fraser: All right, let’s keep crawling sort of up the spectrum. What’s next?

Pamela: The next place we land is in the infrared. This is generally just warm stuff. What’s neat about the infrared is dust and gas scatters light. Light is more likely to get scattered if it has a very short wavelength, or a high frequency. Stuff we can see with our eyes easily gets scattered by dust. Stuff with really long wavelengths, like in the infrared or radio, can pass right through dust – not a big deal.
 
When we look out in the Universe using the infrared, we can see through a lot of different dust clouds, and we can see things that are embedded in the dust clouds that we can’t normally see using optical light. So we look out and we can see stars embedded inside of nebulas, we can see background objects, we can peer into the centre of our galaxy just by going into the infrared and looking at this light that doesn’t easily get scattered.

Fraser: The invention of infrared was quite a revolution in astronomy, wasn’t it?

Pamela: It allowed us to suddenly see things that we never thought we’d ever be able to see. It’s just a matter of getting detectors that are tuned to the right colour photons. Nowadays, it’s common technology. Night-vision goggles are just infrared detectors. They allow you to see the cooler photons that come off of warm objects. This is why you see warm bodies as ghostly shapes where the dark spots correspond to cold objects on the person’s body.
 
This allows us to see things with temperatures in the range of human body temperatures. We look out and can also find things like stars that are just starting to form, things up to 1 thousand degrees, 2 thousand degrees – not a big deal in terms of hot objects, but a big deal in terms of the science that comes out of it. We can see stars before they have nuclear reactions going on, and start to figure out what are all the different stages in star formation.

Fraser: You could have an object, say even a planetary system. There’s nowhere near enough energy there for us to be able to see with a visible light telescope, but it’s getting warm enough just through the friction of the dust that it’s starting to form and we can see it in the infrared spectrum. Maybe even, it’s covered in dust – enshrouded in dust – and the infrared lets us peer through that dust when normally it would be blocked in other telescopes.

Pamela: It’s this wonderful form of the old “get your x ray glasses” comic book glasses, but in this case it was really the infrared that was needed. We’re peering through dust that was otherwise opaque to see objects that were otherwise invisible.

Fraser: And most of the new instruments htat are being built are focussing on a lot of the infrared – Spitzer, I know the new James Webb telescope is going to be significantly in the infrared

Pamela: This is for a couple of different reasons. One of them is it allows us to look through dust, and that’s just useful. It opens up whole new areas of the sky, places we can now go and explore. It lets us look at star and planetary formation.
 
The other reason is the most distant galaxies have had the majority of the light they’re giving off redshifted into the infrared, so now things that may be bright blue on the very edge of the Universe, far back in the past, their light has gotten shifted as it travelled toward us, so now it appears in the infrared. We can see the earliest days of the Universe by looking in these other wavelengths.

Fraser: So next up…

Pamela: Next is the good, old fashioned, boring optical.

Pamela & Fraser: Boring!

Pamela: This is what we see everyday of our lives. Again, nice. Warm temperatures, again. Here we’re looking at the few thousand to about 7 thousand degrees. This is where our Sun gives off a lot of its light. It’s just good old fashioned thermal emission.
 
Now you also start to get atomic lines in here. You get some neat – the hydrogen bomber series, which is a good way of looking at a star and telling how fast it’s moving because you know exactly where these lines are.
 
It’s a good way of telling the temperature of the star, because the strengths of the lines vary with temperatures. You get things that are very excited at high temperatures, or very excited at lower temperatures because as they go up to the higher temperatures the electrons fly away and you no longer have transitions.
 
There’s all sorts of really cool quantum mechanics going on. You start to get things like iron atoms get excited. You get metallic lines going on.
 
So there’s lots of neat ways that when you spread out the light of a star and look at the individual colours, you can start telling exactly which atoms go into making up stars. This is all very easy to do in the optical. You have lots and lots of lines to deal with and easy to detect because our technology’s driven in some cases by what is commercial and most useful.
 
Everyone wants to take a picture of their kid, so we figured out how to make optical detectors. All of that commercial technology has gotten transformed and used in astronomy. We have all of this great equipment we can use to study the stars, and study what atoms make up the stars, what light is getting absorbed and emitted by the individual atoms in those stars.

Fraser: All right, let’s move beyond the visible light. What’s next?

Pamela: Next is where we get our sunburns, that’s the ultraviolet light. This is again, a good place that we can study the individual atoms in the stars. We also get UV light specifically in its largest amounts, in really hot places.
 
When you have lots of star formation going on, you have lots of young, really, really hot, really, really massive stars just blasting ultraviolet radiation. It’s these hot, dense areas with these young, young stars that give off lots of UV light. So when we look at starbursting galaxies, they’re not just blue, they’re ultraviolet. Ultraviolet is you just keep going hotter from the blue and you land there.
 
It’s a dangerous place interms of the human body doesn’t cope so well with ultraviolet. These are high energy photons, so when they hit things, they can knock electrons out, they can do lots of damage. Ultraviolet photons can actually damage your DNA if they hit one of your molecules in just the wrong way. We need to be careful when we start getting into these high energy photons.
 
We also start to see ultraviolet in places like the cores of galaxies that have active galactic nuclei that are doing lots of consuming and there’s high density gas. Anyplace where the gas gets really dense you start to get high energy photons.

Fraser: So we’re going to be seeing ultraviolet in fairly exciting places.

Pamela: Very exciting places. We also start to see x rays in some of thse very exciting places.

Fraser: Right, that’s next on the list.

Pamela: X rays, we start to get from hot gas. We also get x rays when you heat metals up really, really hot. When we look at the cores of clusters of galaxies, in these places, the gas gets compressed so much, and the temperature gets so high that they start giving off x ray emission.
 
We also get x rays in places where there’s really strong magnetic fields. As electrons get accelerated by the magnetic fields, this acceleration… you end up with an energy change. This energy change corresponds to photons – to light being given off. We end up with magnetic fields being sources of x rays. When we look at stars with really large magnetic fields, we also start finding x rays. When we look at supernova remnants, where we have, in some cases, magnetic fields, and where we definitely have lots of accelerated stuff, we find x rays.

Fraser: So the magnetic fields are boosting the energy levels of the photons around them.

Pamela: They’re accelerating them.

Fraser: and hurling the mass.

Pamela: Exactly.

Fraser: Wow. There’s more?

Pamela: There’s one final category; Everything that is higher energy than x rays is called a gamma ray. No matter how much higher you go, it’s still going to be called a gamma ray.

Fraser: That’s how we get the Hulk, right?
 
[laughter]

Pamela: Something like that.
 
Gamma ray emission is again, something we find associated with magnetic fields. We find gamma rays in supernova remnants again, but gamma rays also come from the most magnificent explosions in the Universe. When you have some supernovas that funnel the majority of their energy along the axis of rotation of the star that’s exploding, if we just happen to be along that axis, we can see this burst of high-energy light, high energy photons, gamma rays, funnelled straight at us from the explosion. These are the mysterious gamma ray bursts that had been befuddling astronomers for decades, that we think we finally have a handle on. If you get a couple of neutron stars to collide, they give off gamma rays because the energy of the explosion is so high, the photons get accelerated to the point that they become gamma rays.

Fraser: Wasn’t there a mystery that gamma rays have been detected with energies so high that we don’t even know where they might be coming from?

Pamela: There’s always these mysterious “what could have done this?” It could just be that you hit something with a photon that’s going at a really large rate. This is the old what happens when you send a two-year-old on rollerskates at a sumo wrestler? They bounce off. Now, if the little kid goes into a running sumo wrestler, they bounce off with a really high velocity. If you have a regular, everyday, happy electron chugging through the Universe at not to high a rate, and it gets blasted by a high speed photon, a cosmic ray from some sort of an explosion or something, the energy change could correspond to ginormous levels that end up giving off gamma rays. We’re not entirely sure what would cause that to happen. There’s always these mysteries.

Fraser: I know there’s a new observatory being built in Chile

Pamela: There’s all sorts of different ways for studying the Universe. There’s new telescopes coming on everyday. It’s going to be interesting to see what technology allows us to discover in the next 10 years or so.