Show Notes

• Cosmoquest’s Moon Mappers for science!
• Google+: Pamela and Fraser
• CosmoQuest Hangouts
• Watch the Astronomy Cast ‘live’ recordings via Hangout (Astrosphere videos)
• Sponsors: 8th Light,  Swinburne Astronomy Online
• Viking Landers — NASA
• The Viking Lander’s Search for Life –UTK
• Perchlorates and Water Make for Potential Habitiable Environment on Mars — Universe Today
• Log of missions to Mars (both failures and successes) — NASA
• NASA Says We’ve Been Looking for Life in the Wrong Places — i09
• Is This Proof of Life on Mars? — Universe Today (4/2012)
• Could the Curiosity Rover Find Life on Mars? — Universe Today
• NASA’s Office of Planetary Protection
  

Show Notes

• Google+: Pamela and Fraser
• CosmoQuest Hangouts
• Watch the Astronomy Cast ‘live’ recordings via Hangout (Astrosphere videos)
• Sponsor: 8th Light
• Viking mission page from NASA
• Viking mission website from Goddard Spaceflight Center
• Viking Orbiters images
• Mariner 9 images
• Chaos Terrain on Mars
• More Evidence for an Ancient Ocean on Mars — Universe Today
• Unmasking the Face on Mars — Science@NASA

Show Notes

Show Notes

• Google+: Pamela and Fraser
• CosmoQuest Hangouts
• Watch the Astronomy Cast ‘live’ recordings via Hangout (Astrosphere videos)
• Sponsor: 8th Light
• Hydrogen Line — Wiki
• Hydrogen energies and spectrum — GSU
• Balmer Series
• Hydrogen Alpha Explained — AstronomyKnowHow.com
• Hydrogen II
• Quantum processes; (absorption and emission, stimulated emission)
• Hydrogen Filters — Society for Popular Astronomy
• Measuring Galactic Rotation — Haystack Observatory
• Bok Globule — Smithsonian Astronomical Observatory
• Tips for Observing in Light Polluted Areas – American Association of Amateur Astronomers

Transcript: Observing Hydrogen

Download the transcript

Fraser: Welcome to AstronomyCast, our weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain; I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University-Edwardsville. Hi, Pamela. How are you doing?

Pamela: I’m doing well. How are you doing, Fraser?

Fraser: Doing really well … having fun recording another episode of AstronomyCast with all of our closest friends here on Google plus, so if you want to watch us live record the show, which we know not many people can actually do because they have jobs, and lives, and things like that, but yeah, you can just go to CosmoQuest.org/hang-outs and you’ll see a list of all of the shows that we do. We do a ton on astronomy-related content and science with us, and Phil Plate, Emily Lakdawalla from Planetary Society, and Alan Boyle from MSNBC, so we got lots of space friends and we’re doing a lot of really good content, so you should come and check it out, and that’s at CosmoQuest.org/hang-outs. We also…we embed the shows there so you can watch them live, you can participate in the conversations, and then, of course, if you can’t watch it live, we do try and mix everything and feed it into the AstronomyCast feed, and actually, I realized we’ve been putting the weekly space hang-out into the AstronomyCast feed and didn’t warn anybody, so…[laughing].

Pamela: [laughing] You suddenly have new content!

Fraser: Yeah! So if you’ve noticed now that you’re getting like an extra hour of audio content every week, that’s this weekly space hang-out that we’re doing on Google plus. No one’s complained, but no one has also said “Hey, thanks for putting that in there. I really appreciate that!” So I don’t know whether people are deleting them, or what. But if you’re getting those and you’re happy, that’s great; if you’re getting them and you’re sad, then also let me know because we could also just break it up. You know, it’s pretty interesting, it’s the kind of content that people always asked us to do, but we never did, which is talk about the news and the current events and analysis of that kind of stuff, which is totally different from AstronomyCast, so anyway, that’s all in there. Sorry about that; hope you’re OK with that. Please let us know if you’re not. Alright, well, why don’t we get cracking then?

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Fraser: So hydrogen is the most common element in the Universe, formed at the beginning of everything in the Big Bang. It’s the raw material of stars, gathering together through mutual gravity into vast nebulae. Astronomers can learn so much looking for hydrogen in the Universe. Well, here’s why and how they do it. Now, we wanted to, sort of, when we first sort of set up this show, I was like “OK, so the topic is hydrogen!” And you were like “No, no, no, that’s too big, that’s too much. Let’s just observe hydrogen.”

Pamela: It’s like 70% of the Universe. There’s a whole lot of stuff going on and…let’s keep focused.

Fraser: Like chemistry, and fusion, and powering cars, and things like that, so…but at least I think we should just have a brief conversation just about the formation of hydrogen and where it all came from, and then I promise we won’t go into the detailed chemistry of it.

Pamela: Well, so hydrogen — talking about its formation is somewhat silly. You take energy, you leave it on a shelf, it becomes protons probably (or other particles), and if it’s enough energy to become a proton, well, one proton that counts as ionized hydrogen, let it near a neutron, you now have a slightly more interesting hydrogen atom. Give it an electron — you now have a neutral hydrogen atom, so basically, hydrogen is that stuff that just formed when the Universe’s energy cooled off enough to start forming particles. Everything more complicated than hydrogen, you have to have some sort of nuclear fusion reaction take place in order to get to it, so hydrogen is just that simple thing that comes out of energy.

Fraser: And so back when the…during the Big Bang, when everything was just too hot, you just had raw energy…

Pamela: Yes.

Fraser: And then as things cooled down, that raw energy turned into protons, and…

Pamela: Protons, neutrons, electrons…

Fraser: …and electrons, and you just, you know, you just gather them together in the simplest possible way and that’s hydrogen. Obviously, we talked about it in a few episodes where you had this moment where the entire Universe was in this state of a star, and the hydrogen atoms were being fused into helium, and that’s where we get the helium from, but really, and then the expansion continued and now we’re just left with all this hydrogen, just this raw material, the building block of the entire Universe, so…and then why is it, then, I guess, important, then, for astronomers to observe hydrogen?

Pamela: Well, it’s not so much that it’s important to be able to observe hydrogen so much as we can’t help but observe hydrogen. It’s out there, and it’s causing us a whole variety of good things, and bad things, so on one hand, every time we’re looking at a star, we’re observing an excited hydrogen atmosphere. Every time we look at a beautiful nebula, we’re observing a cloud that’s rich in hydrogen gas that’s usually glowing red. When we start trying to look through the galaxy in radio light, we find all of the cold parts of space permeated with what’s called the 21-centermeter line of hydrogen. It’s just everywhere. Even when we look at high red-shift galaxies, we find in the spectra of these galaxies all of these places where intervening hydrogen gas has sucked the light out of the spectra of these distant galaxies, so if you study astronomy you’re just going to over and over come across the vocabulary of hydrogen. It can get a bit overwhelming, and that was actually part of the inspiration for this show. We’ve been doing live star parties, and I realized last night we’re talking , “H-II” — all of these different terms, and no one knows what the heck we’re talking about.

Fraser: Right, so hydrogen is the most abundant element in the Universe, so you just can’t help but see it everywhere you look.

Pamela: Yes.

Fraser: And so we might as well understand what it is that we’re looking at. Is it almost like all astronomers are pretty much hydrogen astronomers, you know? Like, a certain percentage of the time is just dealing with the hydrogen in everything they’re looking at?

Pamela: Yes, and one of the hazing rituals of getting a physics degree is learning all of the Quantum Mechanics of the hydrogen atom, and so by the time you finish getting even an undergraduate degree, you are intimately aware of the inner workings of hydrogen at levels you may not want, and you know how to find it all over the Universe.

Fraser: But you’re going to spare us the Quantum Mechanics today.

Pamela: I’m going to spare you the Quantum Mechanics today.

Fraser: OK – good, good. Alright, so then let’s talk about the different flavors of hydrogen that astronomers will observe out in the Universe.

Pamela: Well, the most common way that we confront hydrogen just as we peer through the sky with a pair of binoculars, or with a telescope is what’s called Hydrogen Balmer Lines, so when you look out, you’ll see particularly what’s called either Hydrogen Balmer Alpha Line, or just hydrogen-alpha because we get lazy. This is that bright red color that is associated with most nebulae, and it comes from the fact that the hydrogen’s energy levels are such that that one lone electron it’s got – it can jump between, well, it’s lowest energy level, to its second energy level, and transitions in and out of that lowest energy level. Those occur in the ultraviolet where we don’t see them with our eyes, so those are probably the most common transitions, but the ones we don’t see because ultraviolet gets blocked by our atmosphere. Now, go up one set of energy levels, and look at the transitions in and out of the second energy level. Well, there we have what’s called the 3 to 2 – from the third energy level to the second energy level transition — and that’s at this beautiful, red color that we see in “Open” signs at the local deli, and we see in all of these nebula that are all through the sky, so that red color associated with nebulosity – that is the lowest transition in and out of the second energy level of hydrogen, and this transition was discovered by a dude named Balmer, so it’s called the Balmer energy set, and alpha is for the lowest one, so 3 to 2 is alpha, then if you went 4 to 2 that would be beta, and so on through the list.

Fraser: And just to be clear, I think we talked about this in previous shows as well, right? This is that transition, that energy transition, right? When an atom of hydrogen, where it’s got its proton, it’s got its neutron, and then it’s got this electron, and that electron jumps up or down a level, you can get like a release of energy, and we’re seeing the photons streaming away from these nebula as these electrons are being released.

Pamela: So to get this to happen, you have to have a cloud of gas that’s getting heated up by something. So there’s either a bright star embedded in the cloud, there’s a whole bunch of bright stars embedded in the cloud, and the light from the stars is exciting the hydrogen so that it’s making this transition.

Fraser: Now, sorry, when you say just…I’m trying to be kind of precise here. So when you say exciting, you mean photons are streaming off of this star…

Pamela: Those photons are getting absorbed by the hydrogen atom.

Fraser: Right.

Pamela: And the hydrogen atom in response to absorbing this photon, the electron is jumping to a higher energy level, and it might actually jump a whole bunch of energy levels, depending on what energy it gets hit with, and this actually has a neat effect where if the geometry is such that you look out, you look at the cloud and the star that you’re looking at is on the other side of the cloud, when you look at the cloud, you’ll actually see the hydrogen alpha light, that red light, removed from the colors that you’re looking at. Now, if instead, the star is off to the side and not precisely lined up, then you see that color that red energy from the star is getting absorbed by the hydrogen, re-radiated in all directions, and so you end up seeing the nebula as red.

Fraser: Right, but the point is (and this is where the whole concept of Quantum comes from, right?) that there is this very discreet, very specific step that these electrons take as they jump up the energy levels, and with it there is the corresponding release that comes out in a very specific color, and it’s that color of radiation that we see with our telescopes, and that astronomers are really specifically looking for. They’re actually…they’re limiting the entire spectrum that they could see down to that exact, specific light.

Pamela: And this is actually something that anyone out there listening can experience for themselves. A lot of gag stores, a lot of novelty stores will sell these prism glasses that create rainbows when you look through them. Well, if you get one of these pairs of rainbow glasses, and you walk up to your local deli, you walk up to your local pub, whatever, and you look through these glasses at the neon signs, you’ll see the discreet, specific lines given off by the atoms in that sign, so if you look at a red “Open” sign, you’re going to see this bright red line that comes from the hydrogen alpha, but you’ll also see this gap, and then this bright (they call it “cyan,” to me, I’d call it turquoise)…this bright turquoise line, and that’s hydrogen beta. Then a little bit over to the side from that is hydrogen gamma – this is the 5 to 2 transition (and this is like Crayola blue, or that 00255 if you work in RGB colors), and so you’ll then start seeing closer and closer-spaced, deeper shades of blue as you look at the spectra of that red “Open” sign, and then you’ll see a completely different set of fingerprints if you look at a green sign, or a purple sign, but that red “Open” sign has this distinctive spectra through the novelty rainbow glasses that’s the Hydrogen Balmer series.

Fraser: Right, so I guess what astronomers are doing, right, is they’re filtering out every color of light except for that specific, sort of, in the frequency range that they’re trying to see. The equivalent of putting those crazy glasses on…

Pamela: If we use a hydrogen-alpha filter, yeah.

Fraser: Right, and so that’s the point, right? Astronomers will have a collection of these filters. They’ll have one for hydrogen alpha…how many hydrogen-related filters will astronomers use?

Pamela: So at a certain point, you stop using filters and you start doing imaging spectroscopy, so it’s not too uncommon to have a H alpha filter, a Lyman-alpha filter if you’re working in the ultraviolet, or what will also happen is since these lines are given off by galaxies at different red-shifts, people will actually create special filters tuned to only detect, say, Lyman-alpha. This is the 1 to 2 transition in hydrogen that if it’s nearby we can’t see because it’s UV, but if a galaxy is far away, and its light is getting shifted into the red, that color that’s usually so blue we can’t see it – it gets moved a little bit redder, a little bit redder, a little bit redder until we can see it, and they’ll create filters tuned to see the Lyman-alpha of galaxies that are moving at specific velocities.

Fraser: And I guess this is part of the thing where the amount of that frequency is so tight that if it is red-shifted, you’ve got to push it up and down the frequency. So astronomers know that they want to see this specific kind of frequency of light, and they’ve got the tools to be able to see it, but what does seeing it tell them? Why do they want to do this?

Pamela: Well, it’s… it depends on what you’re doing.

Fraser: Trying to do science.

Pamela: [laughing] And so the thing is there’s lots of different science that you could be doing. For instance, when we’re looking at different nebulae locally, we’re often trying to figure out what is the distribution of temperature in a cloud of gas, what is the density of the gas, and so when we’re looking at the hydrogen alpha light, when we’re looking at the light in all of these different energy levels of hydrogen, what we’re trying to do is figure out just how hot is that gas. And this is where we start talking about things like H-II regions. So an H-II region…the crazy notation we use in astronomy is a letter from the periodic table is clearly the abbreviation for the atom, if it has a Roman numeral “I” next to, that’s something that hasn’t been ionized at all — it’s completely neutral. If it has a “II” next to it, that means we’ve yanked off one electron. If it has a “III” next to it, we’ve yanked off two electrons. So take the number, subtract one, and that’s how many electrons we’ve removed from the atom. So when we’re talking about the H-II region, we’re talking about a region of space filled with hydrogen gas, and that gas is ionized one time to remove that one electron. Now in these H-II regions, this is a cloud of gas that is typically being heated up by really hot, bright stars, so when you look at the Orion nebula with all of it’s O-giant stars embedded in the gas, you’re looking at an H-II region, and in these regions the hydrogen atoms will periodically glom on to one of these free electrons, and as they glom on to the free electron, the electron will cascade down through the different energy levels, and it will give off hydrogen alpha, it will give off hydrogen beta, it will give off all these different parts of the spectrum, and by looking at that, and looking at the ratios of how many of the atoms appear in the different energy levels, we can start to get at the density of the material and the temperature of the material.

Fraser: Now, you mentioned a couple of other things as well. And there’s neutral hydrogen, and cold hydrogen, and those are useful for astronomers to observe as well, right?

Pamela: Right, and so another one of the things that we look at is what’s called the 21-centimeter line of hydrogen, and this is perhaps one of the harder things to try and explain. It’s actually something that when we teach it, we talk about this is something that was originally referred to as “Not going to happen, never going to be observable…” and it’s because it’s a process that takes a long, long time for it to happen, so if you take a hydrogen atom, its proton in the center has what we call in Quantum Mechanics a “spin,” and the spin is either spin up or spin down, and its orbiting electron has the same thing. It either has a spin up or a spin down, and ideally the two little bits — they want to be lined up the same, and so what you’ll have is if you leave hydrogen alone long enough, and it’s not in its lowest possible energy, you’ll end up getting that “spin-flip” and the energy given off in this flip is energy that corresponds to light with a wavelength that’s 21 centimeters long. Now, the probability, in most cases, is that before the atom has a chance for that flip to take place (because it takes a long time for the atom to finally get around to flipping probabilistically), it’s probably going to undergo a collision, it’s probably going to undergo and excitation – something’s going to happen to it. The only way that you’re going to consistently get this spin-flip is if you have a whole bunch of gas, it’s really cold, and thus not moving, so all the little atoms are just sort of going, “not moving, moving very slowly…” and it’s very diffuse gas as well, so you need cold, diffuse gas.

Fraser: Well, that’s kind of interesting though, right, because there’s a way…like, you wouldn’t think if it’s out there, just super-cold in space, just sitting there, not interacting, you would think there’d be nowhere to see it, it would just be invisible, but because there’s this crazy Quantum effect, they just randomly spin-flip, you get a release of radiation that’s very subtle, but it’s there and let’s you detect it.

Pamela: And so this is one of the ways we’re able to measure the rotation rate of our galaxy out to extremely high radii. So what we do is we use radio telescopes, and this is actually the type of thing that undergrads can do, or any amateur who builds their own at-home radio dish, and you can get kits to do that. This is an experiment you can do is identify where the clouds of cold gas are out in the outer wings of the arms of the Milky Way, take a look at them, and measure the Doppler shifting of that 21-centimeter line, and from the Doppler shifting you can get the rate at which the cloud is moving forward and backward in that direction in the sky, and you can use geometry then to start to then get at the orbital velocity of this gas and at the end of the day, this gives you the rotation curve for our galaxy that shows that everything is moving at about the same velocity as you move out toward the outer parts of the galaxy, and thus, you can demonstrate for yourself there is something gravitationally changing. This is dark matter.

Fraser: Well, I think that should be everyone’s homework for this week, then. So everyone should go out and observe the 21-centimeter line, and calculate the Doppler shifting, use geometry to determine the motion, the rotational motion of our position within the Milky Way.

Pamela: Completely elementary!

Fraser: Completely elementary – everyone, get on that! So what are these cold…? I mean, OK, so we can use these cold clouds of gas as weigh points, as places to determine position, but I mean, aren’t these future nurseries of stars?

Pamela: Not necessarily. The thing is that in order to get a star-forming region, you have to have dense gas that has sufficient mass that when you collapse it down and things start forming, you get enough mass leftover to form a star, and some clouds of gas just aren’t massive enough that they’re ever going to form anything meaningful, and in other cases, the clouds of gas as they are right now are so diffuse and so stable that we don’t see star formation in their immediate future. Now, spiral arms do help trigger star formation because what ends up happening is as these clouds of material orbit around the Milky Way, they get pulled in on the one side to the spiral arm, and then as they try and orbit out the other side of the spiral arm, they get slowed down, and as they linger in the spiral arm, there’s a good chance that there’s going to be collisions, there’s going to be compressions, there’s going to be shock waves from supernovae, and all of these effects may cause some of these otherwise far-too-diffuse clouds of gas to have star formation, but in general, our galaxy’s only about 1% effective at transforming gas into stars.

Fraser: So astronomers don’t see…like, don’t really do a lot of searching for great, big clouds of future nurseries. It’s more like waiting until the…you know, I guess it moves into to that hydrogen alpha phase, where you’re actually starting to see the light coming off the nebula that you start to identify these star-forming regions?

Pamela: Well, there’s lots of things that we do look at, and we’re like, “THAT is forming stars right now,” and this is where people who work in the radio and the millimeter, they actually start mapping out some of these clouds. So there are certain, what are called “bok globules.” These are extremely dense, often molecular hydrogen regions, so this is the other form of “H-two” that when you’re doing an audio show, it makes no sense. So you have “H-Roman numeral II,” which is ionized hydrogen, and you have “H-subscript 2,” which is molecular hydrogen, and when you look at these dense, black regions on the sky (Horsehead Nebula isn’t a bok globule, but it’s an example of one of these dense, black regions on the sky)…when you look at these dense, black regions in the sky in the optical, they just look like the never-ending story, “Great Nothing,” ate a part of the Universe, but when you start to look at them instead in millimeter wavelengths, you start to see they’re knots of thermally-radiating areas. These are areas where the gas has begun to contract, and as the gas squishes down, the atoms start hitting each other and this process radiates away, basically, warmth. So this is infrared; this is millimeter to light. You can sort of think of this as if you rub your hands together, it’s going to generate heat, and if you had an infrared camera, you could actually hold your hands up and see that change in temperature from rubbing your hands. Now, when the gas starts colliding like that, you start initially giving off in the radio light. Now, you wait as it continues to collapse, stars start to form, starts to light up in the infrared, and eventually it brings itself all the way into the bright blue UV when you get the youngest stars actually igniting, but so we look for those dark, molecular clouds that are high-density, and those…yeah, they do probe those for star formation, but not every blob of gas is necessarily going to form stars.

Fraser: Can we look for places where, like, hydrogen is absorbing light? You know, like we look for places where certain elements are actually blocking, right?

Pamela: And so when we look at nebula, we talk about there being reflection nebula, we talk about there being emission nebula, and the truth is it’s just a matter of geometry. So if it’s star-cloud-observer, that cloud is going to absorb out the hydrogen lines. If it’s cloud in front of us, star off to the side, then we see emission lines, and so there’s lots of different ways, and it’s all about geometry that controls what we’re able to see.

Fraser: And I think as we’ve been really experiencing with doing these live star parties, and we have one person, we have Gary, who has got this just phenomenal 14-inch telescope, but he’s in this really polluted area — he’s in Los Angeles — and yet he seems to be able to pull together these really sensitive images of nebula. So, why does this hydrogen look so crisp and clear even when you’ve got really bad polluted skies?

Pamela: So he’s cheating in a way. If you’ve ever had one of those kids’ toys, or cereal boxes where you get the little red filter, and you look at this scrambled mess on the side of the cereal box, and then when you put the red filter in front of it you suddenly see a message. Well, what’s happening is, in that case, is you have all this visual noise, and that visual noise gets removed when you put the red filter in front of it — and Gary’s doing the exact same thing. In his case, he’s in the Los Angeles basin, and there’s for the most part sodium lights (those are the yellow parking lot lights that make the sky glow this raspberry color on a cloudy night), and then there’s also…now we’re getting more and more fluorescent lights which are giving off their blue UV light, and all of this is scattering skyward. Sometime it’s because they’re using stupid light fixtures that point the light upwards, or they’re illuminating buildings and it points the light upwards.

Fraser: Hate those people…

Pamela: Right, and sometimes it’s just a matter that you’re shining light down on cement, and the cement reflects the light back up; however, the light’s getting upwards, it’s primarily consisting of the sodium light from the sodium light fixtures, and white light that’s peaking off in the UV from the fluorescents or peaking off towards the UV, not actually in the UV, and what he’s doing is he’s saying, “OK, I’m going to look at the sky, and I know that most of the sky is being brightly lit up by the atmosphere reflecting the sodium, and all of this white stuff that is peaking towards the blue. I’m going to try and get rid of as much of that as possible, and I’m going to focus in on one line of light – the hydrogen alpha light that’s in the red, as opposed to the blue, and the sodium’s yellow…” and by focusing on just that one color, well, suddenly, his background goes to black again because these street lights aren’t giving off hardly anything at all in , so suddenly the light pollution for the most part has been filtered out the same way all that visual noise was filtered out on the cereal box, and what’s left behind is only the hydrogen alpha light. Now, the crazy thing is if he actually went to a dark site, he’d get even more amazing images if he was able to use broader-band filters that were letting in more light all at once, but he does what he can, and he’s found a way to do really good astro-photography in a very light-polluted part of north America.

Fraser: Yeah. So there’s hope for all of us.

Pamela: Yeah, there is.

Fraser: Cool. Well, I think that about wraps it up for this week, so thanks a lot, and we’ll talk to you next week.

Pamela: That sounds great. Talk to you later, Fraser.

Show Notes

• Google+: Pamela and Fraser
• CosmoQuest Hangouts
• Watch the Astronomy Cast ‘live’ recordings via Hangout (Astrosphere videos)
• See the Venus Transit Authority Shirt on AstroGear (lots of other great stuff, too!)
• Sponsor: 8th Light
• Energy From the Sun — Living with a Star, Berkeley
• Video: From Sun to Oort: A solar photon’s journey
• Brownian Motion Demonstration- AIP
• Snell’s Law -- Wolfram
• Refraction — GSU
• How the Eyes See Color – ColorMatters.com
• Apochromatic Lens — Planet Facts
• Skin Effect — LessLoss.com
• Reflection — Wiki
• Diffuse Reflection
• Electromagnetic Waves — Reflection, Refraction and Diffraction — Radio-Electronics.com
• Ep. #37 — Gravitational Lensing

Transcript: Reflection and Refraction

Download the transcript

Fraser: Welcome to AstronomyCast, our weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain; I’m the publisher of Universe Today and with me is Dr. Pamela Gay, a professor at Southern Illinois University – Edwardsville. Hi, Pamela. How are you doing?

Pamela: I’m doing well. How are you doing?

Fraser: I’m doing really well. So once again, we’re recording this episode of AstronomyCast as a live Google plus hang-out. If you ever want to join us and watch us record this show live, you can just go to Cosmoquest.org/hang-outs, and we’ve got a listing of all of the really cool live hang-outs that we’ve been doing, but not just AstronomyCast. We’re doing our weekly space hang-out, we’re live streaming telescopes, we’re interviewing astronomers and…

Pamela: So much more…

Fraser: …space scientists, and you know, you name it, we’ve been covering it, so check that out if you want to participate in any of this stuff. You can interact with us, you can ask us questions, you can jump into our hang-outs…we’re having a lot of fun. And I got one more thing…

Pamela: OK. Go for it!

Fraser: …which is if you’ve never done this, one of the best ways to help out AstronomyCast is to go and write a review on us in iTunes. And so you can go to iTunes, search for AstronomyCast, and then you can leave a review and let people know what you think about the show and the stuff that we’re doing. That’s cool. That was all my stuff for this week.

Pamela: That works. You’re wearing a kind of awesome shirt you can promote.

Fraser: That’s right! I’m a walking, talking billboard for AstronomyCast! But the problem is the people who are listening to this won’t be able to see it, but I am wearing my “Venus Transit Authority” shirt, which, I guess, anyone watching can see it…

Pamela: [laughing] No, they can’t! Your mike is exactly eclipsing the shirt.

Fraser: There. There. That working? Anyway, we’re really excited about this year’s transit of Venus, which is going to be happening in June. Of course, we will be “live casting” that to pieces, but this is going to be the last year for anyone living to watch it.

Pamela: And we’ve created a shirt that will contain all of the pieces of paper you’re most likely to lose on this shirt. It’s…on the front of this shirt, there’s a map of the path of Venus across the Sun, and on the back of the shirt is a map of where on the planet you need to be to see the transit.

Fraser: Right, so that way if all else fails, just wear the shirt and then you’ll know, and you’ll have all the details that you need, and anyone who’s there needs to know where to look and what to see, they’ll be able to do it. So that’s awesome! I love this idea of, like, shirt as instruction manual. That’s really cool!

Pamela: Yes! It’s so…I lose paper. I’m not going to wear the shirt I’m wearing.

Fraser: Yeah, you should have one that just has like your physics formula, you know? And then just while you’re doing your work, if you need to like “How do I calculate this? …spectroscopy of that? Oh, right!” then you just lift up your shirt, and take a look at the right corner and you’ve got the information there.

Pamela: “Maxwell’s Equations” – it’s a great shirt!

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Fraser: Alright, well let’s get on with today’s show, then. So light can do some pretty strange stuff, like pass through objects and bounce off them. It can be broken up and recombined; in fact, everything we see is just the end result of reflection and refraction of light, so it’s time to understand how it all works. So this is the part, this is one of the situations…like, I’ve bent the mind’s of my children when I was explaining to them. You know, the concept that when they see something that is like green, they’re seeing the reflected photons that came from the Sun, and they’re like, “What?!” Right? Furthermore, we’re seeing the refracted photons that have come from the Sun passing through our atmosphere, and again, it’s super-confusing, so let’s start with like the journey of a photon, of a photon that leaves the Sun, travels to Earth, passes through the atmosphere, maybe goes through a window or two, bounces off something, maybe bounces off something again and goes into someone’s eyeball. What’s happening?

Pamela: Well, the first thing to realize is, while you may be following the journey of one ray of light, it may not be the same photon that gets to your eye that left the Sun originally, or in fact, was originally created because there’s also a whole lot of absorption and re-emission processes that are going on, so…

Fraser: Well, we’ll look at those too, but yeah…

Pamela: So you start off with something creates a photon, and the original photon that was created may not be the same photon that reaches your eye, so you have some sort of an event deep in the core of the Sun gives off energy, and this bit of energy as it travels through the Sun is going to get absorbed by an atom, re-emitted in a new direction, absorbed by another atom, re-emitted in another direction, and this entire process is one of what’s called “Brownian motion.” It’s the path…the way they always explained it in physics books, which I think says something about the physics community is “you know how drunk people walk? That trying to get somewhere, but they’re sort of going in all directions? That’s the motion of light as it tries to travel to exit the Sun.” Well, once the light finally breaks free of the surface of the Sun, then it’s mostly a clean path straight to Earth, so assuming it doesn’t end up hitting dust, doesn’t end up hitting, well, Mercury or Venus, or anything else that lies between us and the Sun…

Fraser: Spacecraft…

Pamela: …spacecraft, yeah, Soho does intercept a fair amount of light, SDO intercepts a fair amount of light, but assuming that it hits a straight path toward Earth, then you will have a photon that may be the billionth photon that has been part of a journey of a piece of energy. It’s going to hit the surface of our atmosphere. Now, light travels at different rates, through different materials, and this has a lot of complicated physics behind it which basically boils down to the way the light interacts with the materials, changes both for sound and for light and for pretty much any wave, it changes its velocity based on the composition of the material.

Fraser: Right, and that’s why we always say “the speed of light in a vacuum.” Right? Or you always add that asterisk, right? “In a vacuum”…the speed of light through glass is different than the speed of light in a vacuum, and that’s why they, you know, physicists have said they can slow light down to walking speed.

Pamela: Yeah, and it’s not hard to get light slowed to down to the speed of a Cessna aircraft just using hot rubidium gas. So different materials cause light to travel at different speeds, and different wavelengths of light respond in different ways, so suddenly it’s very complicated, but looking in general, when light hits a material that isn’t a vacuum, it’s going to slow down and this is where something that I consider a bit of the Universe conducting Black Magic occurs. There’s this property referred to as Snell’s Law that basically says if you have light at point A and you’re trying to observe light at point B, the path the light is going to take between those two points, is the path that causes it to have the shortest journey time. Now, the thing that makes this kind of Black Magic is if you can imagine that the light is passing through a series of different materials — a pocket of hot gas, a pocket of cold gas, vacuum from the Sun, or vacuum from outer space, and we’re looking at sunlight, well, as the light passes through each of the materials, its speed is going to vary, and just as you can imagine driving through a city, and you have to make these choices: “Do I get on the highway? Do I get on Main Street? Do I take the back roads with lots of stop signs?” and you optimize your path not for the distance you travel, but how are you going to get there fastest. Well, light does that same optimization, not what is the shortest trip I can take, but what is the fastest trip I can take, and so when you take a look at the passage of the light between those two points, the light is actually going to bend and spend a longer distance in the higher speed material and a shorter distance in the slower speed material to optimize its speed, and it’s one of those “Wait, how did the light know ahead of time that this was the correct option to take?” And it’s a matter of light’s going in all directions.

Fraser: Right, so hold on, you just like blew my mind there, so let me just take a second to unpack it. So if I understand this correctly, that when we see light moving through water, and we see, you know, or like we see…like a you take like a stick and put it in water, and you can see the stick on top of the water, and it’s sort of at one angle, and then as you’re seeing the stick through the water it’s shifted to this other angle, and so in other words, we know that the light that is showing us the stick has bent in the light, and so what you’re saying is that light has chosen this angle because this gives it the shortest travel time?

Pamela: Yes, exactly.

Fraser: And it could be a further travel distance, but at the end of the day, it’s most concerned about the shortest travel time, and that’s when you see it bend?

Pamela: Exactly. Yes.

Fraser: Whoa.

Pamela: Yes.

Fraser: That’s crazy!

Pamela: The thing is it’s not like light is actually making a choice, it just happens to work out this way. And so when you start looking at things mathematically, and this is where I’m wishing I had better props in my office…

Fraser: Well, remember that people are listening to this show, so they will never see your props.

Pamela: Yes, OK, so if you have a surface, and light is going to hit that surface, then the surface has — you can imagine there’s always some line that’s coming out from that surface in a right angle…now, when the light hits that surface, there’s going to be some angle between it and whatever that perpendicular, that right-angle line is, and the way it works is when the light hits the surface, its angle relative to that perpendicular, relative to that — we call it “normal to the surface,” it’s going to bend inwards, so this is where when you look at a pencil, the pencil always appears to bend in the exact same direction. Now, what’s really cool is you can actually change how the pencil appears to bend by adding things to the water, by comparing side by side a pencil or a straw in a glass of alcohol, in a glass of sugar water, in a glass of regular water – it’s very small differences, but it’s still just neat that we can actually play with the path of light.

Fraser: And so if you can actually see the path of light refracting through that Rubidium gas, you would get a different angle.

Pamela: You would get a completely different angle.

Fraser: Right.

Pamela: And what’s interesting about this is it also varies with the color of the light that’s doing this. So say you had a red laser and you had a green laser, one interesting trick to do is to shine them into a cutting board, just one of those plastic-y, acrylic, um, they’re usually a whitish color, boring, cheap cutting boards that you can get at the local dime store.

Fraser: I have one like right in front of me. You can’t see it because my kitchen is dirty, but I have one. I’m looking at one right now, so I know exactly what you’re talking about.

Pamela: Right. So get one of those cheap-y cutting boards that allows light to pass through it, well, shine a red laser into it, and shine a green laser into it, and make sure very carefully that the lasers are absolutely parallel to each other (you can do this by putting a piece of graph paper down), then look at how their light bends as it enters the cutting board, and if you’re very precise you can see slight differences in how the light of these two radically different colors gets bent as it enters the cutting board.

Fraser: Wow! So the light will get bent from the laser passing through the cutting board?

Pamela: Yeah! Because…

Fraser: OK, hold on, hold on, hold on.

Pamela: [laughing] So for those of you who are out there listening, Fraser is in his kitchen, and he is going to go find a laser, and find a cutting board at this moment. This is actually one of those experiments that we used to have our students do as group projects when I taught astronomy, and so…

Fraser: Alright, so here we go…got a cutting board, got a green laser…

Pamela: You need to go in the edge of the laser, you need to go in the edge of the cutting board!

Fraser: What’s that?

Pamela: You need to go into the edge of the cutting board.

Fraser: Like, this way?

Pamela: Yeah.

Fraser: OK. Alright, let’s see…

Pamela: So you need to get the light…

Fraser: Whoa! I don’t know if you can see behind me…

Pamela: So you should be able to see it through the surface of the cutting board.

Fraser: Yeah.

Pamela: Except we can’t see the surface of your cutting board.

Fraser: I can see it. I can see it coming out the top of the cutting board like a line. [missing audio] There we go!

Pamela: Well, I’ll try and do this experiment. I’ll go get a cheap-y cutting board and I’ll post pictures of it later.

Fraser: I don’t know if I can actually do this, though. I love lasers.

Pamela: To do this experiment well, you need one of the really cheap cutting boards that’s also like a quarter of an inch thick, and you literally shine the laser into the edge of the cutting board and you can watch its path across the top of the board.

Fraser: Yeah I could actually see the line of the laser across the top of the board, so that’s really cool. Alright…I just don’t have a red laser.

Pamela: But this is actually one of those things that allows you to understand how prisms work because if you think about prisms that create beautiful rainbows — a lot of people buy them as wind chimes and hang them in their windows and stuff — this is a case of light entering a material,
(in this case glass or crystal), and when that light ray of white light (of all the different colors combined, usually made of sunlight) enters the prism, all the different colors get bent at slightly different angles, and it’s that difference in all the angles that things are getting bent that ends up leading to beautiful rainbows, ends up leading to being able to do spectroscopy, and in this case it’s a matter of the shorter wavelengths are getting bent the most, the longer wavelengths are getting bent the least, and the entire amount that things get bent determines how big a rainbow you’re able to produce.

Fraser: Right, and so you’ve got this situation where you’ve got the sunlight coming from the Sun that contains photons of every color, they’re all hitting that medium (in this case, the glass of the prism), and they’re getting refracted at different angles because of their wavelength, and then they’re coming out the other side and going in their various directions.

Pamela: Now, this is also the problem with refracting telescopes. So if you have a nice, little, cheap, doesn’t-have-fancy-what-are-called-“apro-chromatic lenses,” if you have a nice, normal, cheap refracting telescope, it will have a lens for the eyepiece, a piece for the objective that’s the end that the light comes in through, and as light comes through each of these different lenses, different colors get bent different amounts, so you end up seeing different colors in focus in slightly different places, which causes what’s called chromatic distortion. Now, we get around that by using compound lenses that use multiple materials and try and compensate for all of that. It makes the telescopes extraordinarily expensive, but is usually worth it to spend all that money for an astronomical view.

Fraser: And it’s sort of about trying to bring the light back together, right?

Pamela: Right.

Fraser: Yeah, OK, so we got a little off-track here. So we’ve talked about the light coming through the atmosphere, or glass, or something like that, and its getting refracted, and we talked about the physics of that. Now, what about the reflection part?

Pamela: So the reflection part is actually way more complicated than anyone would ever imagine. It’s one of those things that when I first saw it completely explained out in Quantum Mechanics, I sort of cursed the Universe for its complexity. So when we normally think of reflection, you think of like a photon of light comes down, bounces off of the surface, continues on like a ping…no! No! That has nothing to do with it.

Fraser: No? Nothing?

Pamela: No.

Fraser: OK.

Pamela: You actually have: photon comes down, interacts with the top level of atoms in the material, has all sorts of complicated things that involve skin effect, and the electromagnetic fields, and reversing of polarity, and a new photon comes out in the opposite direction with a completely different phase of the first photon…and so it’s actually a highly complicated process.

Fraser: Can you…? I mean, we don’t want to completely gloss over it, but so are you saying that reflection is…but it’s not absorption, right? It’s not like the photon is being absorbed and a completely different photon is being emitted?

Pamela: Yeah, it is.

Fraser: So all reflection is absorption? Is that what you’re saying?

Pamela: So it’s…it’s an interaction with the surface of the material process, so the incoming photon comes in, interacts, new photon comes out.

Fraser: Completely different photon?

Pamela: Completely different photon, different phase, the whole nine yards.

Fraser: A brand new baby photon, and…but can the…‘cause I mean from what I, you know, what we always talk about, we say, like you see a tree and the tree is green, and so you’re seeing all of the light from the Sun is hitting, you know, all the colors of the Sun are hitting that tree, and then we’re seeing the green, a prevalence of green photons being emitted in our direction, right?

Pamela: So what we’re seeing is the material that the leaves are made of is preferentially re-emitting green photons, based on all of the stuff that’s hitting during the skin effect at the surface of the leaf.

Fraser: And so if it’s getting hit by more colors than just green, is it warming up, is it absorbing that? Is it turning the excess into heat?

Pamela: It’s absorbing it, it’s warming up, it’s undergoing chemical processes…this is where you get into the whole ADP cycle that some of us were forced to memorize.

Fraser: Chlorophyll, it’s making energy… right, right, but just like a regular object, and so but what about something like a mirror that is going to be reflecting the light, you know, almost you know some object with a really high albedo, right?

Pamela: So reflective surfaces — this simply means that most of the photons when they hit that top skin effect layer of the material are ending up interacting and going back off in the other direction in very precisely mathematically described ways. Now, what’s interesting is where you have diffuse reflection. This is where when you look at the light coming off a surface, it gets completely scrambled, and so you have a surface that’s reflecting light, but it’s not reflecting an image. It’s because some of the light’s actually able to pass deeper into the surface before it undergoes this reflection process and comes back out, so the diffuse reflection is where you’re hitting all sorts of different angles inside the material, and you’re hitting different depths inside the material, and so the light is coming out with a whole variety of different angles from what it originally had going in.

Fraser: So can you have situations where there’s, like, reflection and refraction happening at the same time?

Pamela: That’s called binoculars.

Fraser: Binoculars? Right.

Pamela: So think about: grab a pair of binoculars, and on a day, like, grab a friend and go outside and look at a bird, and have your friend look at the front surface of your binocular lens, and they’re actually going to be able to see the daylight scene reflecting back at them because every glass surface actually both reflects some of the light, and allows some of the light to transfer through the material, and the light that’s getting transferred through the material is what’s getting refracted.

Fraser: So, I guess, as always, we try to bring this back around to astronomy, and so what are some of the ways that astronomers will use this? I mean, obviously, we talked a bit about the lenses that we use and the telescope, so what impact does that have on, like, the actual gear that astronomers actually use?

Pamela: So with things like binoculars and telescopes, the whole problem of some of the light getting reflected and some of it getting refracted through the surface means that we want to try and figure out how we can use chemistry to alter the surface of our lenses to make sure that the most light possible gets transmitted through the material, and this is where an expensive pair of binoculars will have this purplish multi-coat on the surface of the objective lens, and that strange-colored overcoating is actually a material that increases the amount of light that gets transmitted through the objective lens of your binoculars. We also worry about sometimes increasing how much light gets reflected, and this is where mirrors for reflecting telescopes also have very special overcoatings on them, so an extremely expensive mirror is going to have usually either a silvering on it or it’s going to be “luminized,” but the combination of atoms that the mirror gets coated with is usually some extremely-patented, highly-worked-out, experimentally-determined recipe that increases – optimizes — the amount of light that gets reflected at the wavelengths that we’re most interested in studying. So the whole point of building modern telescopes isn’t just to make sure that the light gets as precisely focused as possible, but it’s also to utilize chemistry to make sure that every surface that the light has to pass through passes through as optimally as possible, and every surface the light has to reflect off of it gets reflected off as optimally as possible, and altogether we end up talking about what’s the “quantum efficiency” of a telescope, and that boils down to all of the surfaces combined, and then how well the detector (which is really where quantum efficiency comes in)…how well does the detector do at finally detecting the photons that make it to it.

Fraser: And I think we’ve talked quite a lot about the visible light, but obviously, you know, the entire electromagnetic spectrum runs from radio through to gamma radiation, so how does that play into this process as well? I mean, are gamma rays refracting through water? Or will x-rays kind of reflect off of things?

Pamela: Gamma rays kind of do what they want to do [laughing], so these really high-energy wavelengths of light…the surface that you need to use to end up stopping and reflecting a photon – that surface that you need depends on what the wavelength of light is. This is where you can build radio telescopes out of essentially chicken wire because radio wavelengths — they can be several centimeters to several meters across, and so radio happily reflects off of chicken wire. Now, at the same time, gamma rays are extremely small and just want to pass directly through whatever you put in front of them until it gets extraordinarily dense, and this is where you start using lead bricks to stop them, and you can’t really use lead bricks easily to reflect them, but when they start building gamma ray observatories and x-ray observatories, they are using special foils to try and very carefully scatter the light into a narrower and narrower area to detect it.

Fraser: Right. Right, but the point being that, you know, infrared is going to have that same effect, ultraviolet is going that have that same effect, but it’s just going to be changed depending on the medium and depending on its wavelength.

Pamela: Exactly. All light has the same…reacts with the skinning of the material, reacts with…and different materials are opaque and transparent. Glass, for instance, will completely block ultraviolet for you, so any of you out there in the audience that have an iguana, if you’re trying to shine your special solar lamp through the glass of your aquarium, it won’t work.

Fraser: And that’s why you can’t get a sunburn when you’re in the car window, right? Behind the car window…

Pamela: Right, But if you roll your window down, your driving arm will be toasty by the end of the day.

Fraser: Right exactly. Now, we’ve talked about how the astronomers will actually incorporate reflection and refraction into the gear, but how do they bring it into their actual techniques when they’re looking at objects? I mean, are there things that they need to look through, or see reflected from?

Pamela: Well, we have to take into consideration the fact that where the stars appear in the sky is not where they’re actually located, and as an object moves across the sky (because the planet’s rotating it’s not the object moving), the amount of atmosphere that the light has to pass through is constantly changing, which means that the distance the light spends within the atmosphere in the amount of bending that it is experiencing is constantly changing, and this all adds up to we can actually see slightly over the horizon because of the way light is bent, and we have to, when we’re pointing telescopes, compensate for how the atmosphere bends the light, so we have to take all of that into consideration. When it comes to celestial observations, we’re actually somewhat more worried about how gravity bends things at times because we can also get the same sort of refracting, bending of the light, not just from light passing through media, but also from light passing gravitationally near a star, or galaxy, or something else, but we’ve done entire shows on this. It’s called “gravitational lensing.”

Fraser: Right And there’s a lot of situations I know where the reflection of the light…like there’s things like Earth’s shine, light echoes, things like that where you can actually see and learn a bit, you can see x-rays bouncing off, what? Jupiter, and things like that?

Pamela: And one of the more interesting things that’s going on right now is light from Eta Carinae from when it had its 1800s outburst – that light is just now…it hit a background surface, a surface of gas and dust, has reflected off that surface and the reflection is just now hitting Earth, so we’re able to re-observe the reflected light of that nova to actually get whole new observations out of it.

Fraser: Right, so if you miss it the first time around, you can just wait for the reflection, wait for the echo.

Pamela: Exactly.

Fraser: That’s really cool. Alright, well, that’s great, Pamela. Thank you very much again, and we’ll talk to you next week.

Pamela: Sounds good, Fraser. Talk to you later.

Show Notes

• Listener Survey
• Google+: Pamela and Fraser
• CosmoQuest Hangouts 
• Watch the Astronomy Cast ‘live’ recordings via Hangout (Astrosphere videos)
• Sponsor: 8th Light
• Rayleigh Scattering and the blue sky — GSU
• Why is the Sky Blue? — Science Made Simple
• Sun Dogs — University of Illinois
• Red sunsets/sunrises
• Recent paper using Rayleigh scattering to detect the transmission spectrum of an exoplanet
• Chloroflorocarbons – Wiki
• The color of Mars atmosphere – Causes of Color
• Backscattering and Zodiacal Light – Atmospheric Optics
• Rayleigh Scattering in Interstellar Space

Transcript: Rayleigh Scattering or Why is the Sky Blue?

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Fraser: Welcome to AstronomyCast, our weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain; I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University – Edwardsville. Hi, Pamela, how are you doing?

Pamela: I’m doing well. How are you doing, Fraser?

Fraser: Good. I can hear in your voice — you’re a little under the weather, aren’t you?

Pamela: Yeah, colds happen, and our weather has been bouncing back and forth between high 60s F and 20s F, and my body said, “No.” It just said, “No.”

Fraser: Just kidding, but can we recover enough of your brain this week to answer some basic questions about Rayleigh scattering?

Pamela: I think this week’s topic we’re going with “Are you smarter than a fifth grader?” so I am smarter than a fifth grader, even when drugged.

Fraser: OK, Good, good, and so once again, as always, we’re recording this episode of AstronomyCast as a live Google plus hang-out on air, so if you want to join in on the fun, we record these episodes every Monday at noon Pacific, 3:00 Eastern, 8:00 Greenwich mean time. You can go to cosmoquest.org/hang-outs, and you’ll see more information on the show times, the last episodes that we did, and a viewer that you can watch when we record the show live, and a way to participate, so if you want to beyond just listen to the episode, but actually participate and join us because we open it up and people can jump in the hang-out and ask questions about space and astronomy. It’s a lot of fun, so we highly recommend you join us if you want. So, go to cosmoquest.org/hang-outs.

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Fraser: Alright, so next time a kid asks you, “Why is the sky blue?” answer them because of Rayleigh scattering, and if they’re not happy with that answer, feel free to expand based on the knowledge we’re about to drop today right into your brain. Now, Pamela, before we get into Rayleigh scattering, you had an anecdote actually before we even started recording.

Pamela: So I go through a lot of life sleep-deprived on airplanes, and there was one time I was getting on a little, tiny commuter plane, and I was tired, and I don’t know what form of Pavlovian conditioning took over, but for some reason the stewardess hollers, she doesn’t get on her little microphone, she hollers down the aisle, “Why is the sky blue?!” and like call and response, I holler back “Rayleigh scattering!” And I then realized this is a rhetorical question, and I just wanted to like hide under my seat at that moment, but there was really nothing I could do other than pretend to be part of the fuselage. It turned out (she talked to me later), it turned out she and the pilot were having an argument over why the sky was blue, and she decided to embarrass the pilot by asking the entire cabin of passengers, and didn’t actually expect an answer, but was happy that I provided one and was interested to actually know the answer because it turned out neither she nor the pilot actually knew why the sky was blue. I still really felt like that nerd who doesn’t…I was Sheldon. I channeled Sheldon. It’s just that simple.

Fraser: Such a geek, such a nerd, well you know, for that pilot and for the stewardess, why don’t we get into it? So then, where do you want to start with the Rayleigh…so then why is the sky blue, Pamela?

Pamela: The sky is blue because it has sufficient density of stuff in it (gases, particles, things like that) that it scatters all of the light from the electromagnetic spectrum that’s able to get through down to the blue levels, so red comes straight through, yellow comes straight through, green…well green’s green, it doesn’t work in ways the eyes detect sensibly, but the blue light is getting scattered all over the sky such that a photon of blue light or anything with shorter wavelengths than the blue, as it comes through, it will hit a particle of dust, a molecule of gas, and it’s going to get scattered in a random direction, and it’s from all of the different scatterings that the blue light goes through that we end up seeing the entire sky as blue, because eventually, it’s going to get scattered back into our eyes.

Fraser: So, sorry, there’s a couple of things there that you mentioned that I just sort to want to unpack them a bit. So when you say “scattering,” what is…so I imagine a photon is passing into our atmosphere and — what? Bumping into a …you know…

Pamela: It’s…that’s pretty much what’s happening. You can talk about it as an absorption and re-emission process, but in a lot of ways, it’s kind of like throwing a ping pong ball into a room with a lot of different things that it can ricochet off of, so if you send little tiny non-ping pong balls cause they’re little tiny into a room, the way ping pong balls work is the little things are more likely to get straight through, and the bigger things are more likely to get ricocheted. Well, the way it works with light is the shortest wavelengths have the longest frequencies and they’re the things that are most likely to get scattered all over the place. Sorry, I said that backwards, the things with the shortest wavelengths have the shortest frequencies, and it just works out that they’re the things that are most likely to get scattered.

Fraser: Right, but you’re saying like absorption and re-emission, so are these photons that are bouncing into particles in the atmosphere…then they’re getting absorbed and then they’re getting re-emitted? Is that right?

Pamela: Yeah.

Fraser: Right, which is different. I guess what I’m saying is it’s kind of different from refraction, right? When you have water and the light comes through water and the angle of the photons bends…

Pamela: Right.

Fraser: …they’re not being absorbed and re-emitted, they’re just passing through like it wasn’t there except that it’s changing the angle that they’re moving through…but in the case of the atmosphere, they’re actually bonking into particles in the atmosphere, these atoms are absorbing them and then re-emitting them again.

Pamela: And the key for this happening is what the light is interacting with needs to be just the right size, so it’s an elastic scattering process in some cases, where the photon does actually boink and bounce off like ping pong balls bouncing off of each other. You do also have the absorption/re-emission process, so it’s that the elastic scattering is the Rayleigh part, but you also get the absorption and emission – it’s all confusing at times and we have way too many equations to cope with all of this, but in order for this to happen, you have to have sufficiently small particles because otherwise, they’re just going to block the light and nothing good is going to happen.

Fraser: That’s like when you have like a volcanic eruption, or a forest fire, and you’ve got enough dust and large particles in the atmosphere that it actually just starts blocking out the light entirely.

Pamela: But what’s cool is that even with volcanoes and stuff, when they go off, the finest particulates, the smallest dust grains actually add to the amount of scattering that’s going on in the atmosphere, and the way Rayleigh scattering works is first you scatter all the shortest wavelength stuff, so you end up with the blue stuff scattered everywhere, and as you add particles, as the light has to travel through more and more stuff, the probability that you’re going to start scattering yellow light, you’re going to start scattering orange light goes up, and so when you have a lot of volcanic dust in the sky, you end up with much redder sunsets, you end up with…actually the color of daylight changes from that really light blue to a much deeper blue.

Fraser: Right, and just so, sort of, because I’m thick and not smarter than a fifth grader…

Pamela: That’s a lie!

Fraser: …so we’re seeing the blue because it’s the blue particles are getting more scattered?

Pamela: Yes.

Fraser: And then, and so we’re seeing…so the reds, and the yellows, and the lower, you know, the shorter, sort of, the longer wavelengths are passing straight through directly into our eyes…

Pamela: Yes.

Fraser: …but we’re not seeing the light that would have missed us entirely, but is now getting scattered in our direction.

Pamela: And it’s a probability. I mean, this is one of those things where science likes to play with dice, so the likelihood that any particular blue photon from the Sun is going to get straight through the atmosphere is a much lower probability than the probability that a red photon’s going to get all the way through the atmosphere, but the more atmosphere you have, the more scattering has a chance to happen. So it’s like if you throw more and more dice, even though the likelihood that you’re going to throw a Yahtzee is always low, if you throw the dice enough times, you’re eventually going to throw a Yahtzee. Now with our atmosphere, if the Sun is straight overhead, light is coming through the least possible amount of atmosphere. So the atmosphere is a constant thickness around the Earth. When the Sun is straight overhead, it only has to go through the atmosphere that’s straight above you. Now as the Sun goes over towards sunset, as it goes, the angle through the atmosphere that the light has to go gets such that you’re looking through more and more of that atmosphere, and it’s maximum when the Sun is over on the horizon, and when the Sun’s on the horizon, you start seeing red atmosphere, orange atmosphere because so much more scattering has happened that now it’s not just the blue light being scattered, but it’s also the oranges and the reds being scattered as well.

Fraser: Right, and so again it’s that way to think of it that you look up into the sky, and there’s the Sun, and so you’re seeing all of the yellow, and the red photons that are streaming directly from the Sun right into your eye (now, don’t look at the Sun you know that’s a bad thing), but the point being, you’re also seeing, I guess, less of the blue photons that are directly coming from the Sun because they’re getting scattered away, but what’s happening is you’re seeing the whole sky, and so you’re then seeing all of those photons that are getting scattered towards you across that entire sky, and that’s why you see the blue…

Pamela: Right.

Fraser: …because it’s just that it’s such a huge surface area of sky that you’re then able to see, and because the blue is getting scattered away, that’s when you get a chance to see them. There’s sort of a similar effect, although I think this has to do with refraction, like have you ever seen like a moon dog or a sun dog, where it’s really high ice in the sky and you get this circle?

Pamela: That’s actually a refraction process.

Fraser: No, I know it’s refraction, but it’s that same thing that you always see it at a very specific angle because you’re seeing a concentration of the particles in that one angle more than you would see it in any other.

Pamela: That’s actually an interesting case, and we should probably do our next episode on refraction, I’m thinking…

Fraser: Sure.

Pamela: …where with those, when the moonlight hits the ice droplets, ice flakes, I don’t know, they’re falling out of the sky currently where I live, when they hit the frozen bits of water in the atmosphere, they always bounce at the exact same angle and so if you and I are both looking at the Moon in two very different locations, and we see one of these rings around the Moon, we’re actually seeing it through different ice particles because it has to have the exact right angle in order for us to see it. It’s…rainbows have the exact same problem.

Fraser: Yeah, I did an article on this and it’s just absolutely fascinating, and if you ever get a chance to see one… Yeah, but why don’t we do that? Why don’t we talk about refraction, reflection — it’s a whole optical thing. Right, so when we intro-ed this story, we’re going to talk about why is the sky blue, but of course, Rayleigh scattering has a big implication in astronomy.

Pamela: Right, and…

Fraser: So where does Rayleigh scattering come into astronomy?

Pamela: Well, we start seeing it with all sorts of different nebula, so reflection nebula, in particular, are these beautiful, blue objects on the sky, and the diagram that we always draw in Astro. 101 is you take a hot star, so it has no absorption lines in it, so you have a nice, happy, hot star, which is just a continuous rainbow of light coming off of it, you shine that continuous rainbow of light at a gas cloud, and when the light hits the gas cloud, the reds are going to go straight through for the most part, so if you’re on the other side of the gas cloud from the star, you’re going to see a beautiful red cloud. Now, the reality is because lots of clouds are filled with hydrogen, the red isn’t just from this effect. The red is also largely from excited hydrogen emitting red light. Now, the thing is if you’re then at a right angle so that you have the star off to the side, the cloud straight in front of you, and you look at that cloud, you’re going to see it as a beautiful, blue cloud because of all the blue light getting scattered in all different directions through these processes.

Fraser: And so what would scientists use this process for? Like what questions can we answer using this technique, or understanding this principle?

Pamela: Well, it allows us to get at things like what are the sizes of the particulates, what are the densities of the particulates… The thing about Rayleigh scattering is it only works when the particles are significantly smaller than the wavelengths of light, and so by realizing, OK, so we’re seeing this particular amount of light, we know the colors that are going in because the star is over here, we know what type of star it is, we can start to get at the physical parameters of the cloud without actually being able to touch it and poke it, or sense it in any more definitive way.

Fraser: And so when you see the Rayleigh scattering, the wavelength of light that’s being scattered toward you, that tells you the size of the particles in the nebula? I guess if you know the particle size of the nebula that tells you a bit about its composition.

Pamela: Yeah, and the amount of light getting scattered also helps us get at how dense is the material in the cloud.
?

Fraser: And is there like a direct correlation, will it always be if you see this kind of scattering, then you know the particles need to be this size?

Pamela: Well, it’s a range. This is one of those things where I can’t tell you that all because the light that I see is this wavelength that the particles are this size. It’s a matter of as long as the particles are “smaller than,” I’m going to get the Rayleigh scattering, so it places limits on it, but it’s not a definitive thing that allows me to look at the amount of light scattering and say “Aha! That cloud is made of carbon monoxide!” No, I can’t quite get there from here.

Fraser: Oh, you can’t do that? Because that’s sort of what I was driving at.

Pamela: For that we have to use spectroscopy.

Fraser: Right, and spectroscopy is that process where you can see which lines, I guess, in the spectrum are being absorbed or emitted to tell you what the…

Pamela: And the convenient thing here is that if you have that star off to the side, that’s shining light on the nebula, the gas in the nebula is going to absorb only the wavelengths that correspond to transitions in the specific gases, so hydrogen has specific colors it absorbs, ethanol has specific colors it absorbs, crazy things like chlorofluorocarbons have specific wavelengths that they absorb, and when they absorb this out, they absorb the light coming from one direction, but when they re-emit it, they re-emit it all different directions, so we’re able to see emission lines corresponding to what gas is in the cloud when we look at it from off to the side, so this is actually a very convenient geometry.

Fraser: Right, and I guess that’s the question, right? Is because we see them coming from directions, I guess, from a larger area that lets astronomers gather more photons.

Pamela: Well, it’s not so much the more photons issue as if you’re on the other side and you have bright star behind the cloud, you have cloud, and you look at the spectrum of the cloud, you’re going to see the light absorbed out, but it’s easier to detect lines spiking up the emission than it is to get the absorption lines. It’s…so absorption lines are fainter, and emission lines are brighter, and if you don’t have a very powerful detector, emission lines are just easier to find.

Fraser: So if we were able to move to some other planet, if we were able to move to some of these crazy hot Jupiter worlds, or even sort of a…you know, super Earths orbiting other stars, red stars, blue, you know, yellow stars, or hotter stars, would we see a very similar blue sky in any kind of atmosphere that we were living in? I mean, I know you don’t see that on Mars, right?

Pamela: Right, so on Mars you see a somewhat violet sky, and this is because violet is a shorter wavelength. They just don’t have as thick an atmosphere as we have, but at the same time, the sky can get amazingly dusky because of all the dust that will get stirred up during dust storms. So just like here in the American southwest, or if you go out to the desert-y parts of Africa or China, when there’s a dust storm coming, the entire sky turns red from all the scattering of light off the particulates in the atmosphere. Well, when Mars is having its storms, you have the exact same effects of this amazing deepening in color, reddening in color of the sky, but normally it’s just violet because it doesn’t have as much scattering going on. So you can start to get a sense of if you’re on a planet with an extremely thick atmosphere, you’re looking at redder skies, if you’re on a planet with much thinner atmosphere, you’re looking at bluer, or in this case, violet-er skies, like we have with Mars.

Fraser: And so that’s the spectrum that you have to work with, then I’d have the rainbow, and then the thicker the atmosphere, the more it’s going to push into that red direction, the thinner the atmosphere, the more it’s going to go in the violet direction, and it also depends on the size of the particles themselves in the atmosphere, right?

Pamela: Yeah, and having suspended dust can compensate for lack of lots of gas in the atmosphere.

Fraser: Right. So are there any other implications in astronomy? What about back scattering?

Pamela: Well, so back scatter isn’t something we generally have to deal with other than when we’re looking at zodiacal light, which is a case of sunlight reflecting off of dust within the path of the zodiac on the sky that we can see back on the planet Earth, but in general, back scattering just isn’t something that we have to deal with. Other places that we have to deal with this is, unfortunately, we do have an overall reddening when we look at things due to the scattering of the blue light. So when we look through parts of our galaxy that have a lot of material in them – a lot of gas, a lot of dust — when we look through those sections, all of the stuff behind those sections of the sky appear to be reddened, so you’ll often hear not only do we worry about the redshift of a galaxy, but we worry about the reddening, and the reddening is simply caused by stuff in our galaxy, stuff in our atmosphere affecting the color that we see of an object, and we have to correct for that, and so there’s been very detailed maps made of the entire sky trying to figure out what is the extinction, what is the reddening, what is the change in color that is being caused by all of the gas and dust within our galaxy affecting how we see background objects in the Universe.

Fraser: And so you could see a distant galaxy, and you’d want to take the color of that galaxy to find out how much star formation is going on, or how old it is…

Pamela: How fast it’s moving…

Fraser: How fast it’s moving away from us or toward us, and then because there’s intervening gas and dust in the Milky Way, or even in the Universe, maybe in between us and them — that’s going to change your measurement.

Pamela: So we have to apply corrections.

Fraser: And is that done sort of like if you know you’re looking at a galaxy, through part of the Milky Way…

Pamela: You look it up in a table; you apply the table.

Fraser: Really! And then just subtract from your number?

Pamela: [laughing] Actually, it’s just that simple. The tables that we look at are a function of what wavelength of light are you looking at, what is the overall color of the object that you’re looking at, and how much stuff is in that direction, so when I say it’s a look-up table, it’s more than just an “x, y” look-up table; it’s a multi-parameter, binary cube of data that you’re sorting through, but yeah, there’s look-up tables that have been produced that allow you to make the needed corrections.

Fraser: So, does that, you know, we talk about visible light and how we see the sky turning blue, but does it have implications, throughout the…I mean, it must for the entire electromagnetic, I mean, do radio-astronomers deal with scattering in this same way?

Pamela: This is where certain things become transparent to different colors of light, so as far as our atmosphere, as far as radio signals are concerned, for the most part, our atmosphere doesn’t exist, so those colors pretty much just come through, and infrared is largely this way as well. This is where we can actually look through dust clouds using infrared light.

Fraser: Yeah, my house is invisible to radio lights.

Pamela: [laughing] Exactly. So different wavelengths — it just doesn’t matter. So you need to have the size of the particle is commensurate size to the wavelength of the light. Otherwise, this just isn’t going to happen, so once you take all of that into consideration…yeah, radio, we don’t care. Now then, our atmosphere also does things like it doesn’t let ultraviolet through, and this has to do with the composition in the atmosphere. It doesn’t let gamma rays and x-rays through, for which we’re all grateful because that means life can exist, so there’s a lot of chemistry involved, a lot of physical chemistry and quantum mechanics involved, so it’s not just Rayleigh scattering, it’s also what gets absorbed, what gets blocked, what is the different wavelength transparent to, what are the sizes of the wavelengths — all of these things factor together.

Fraser: But, when we get situations where x-rays are getting scattered by nebula atmosphere, atmosphere of the Sun, things like that…

Pamela: X-rays pretty much just get blocked; they’re pretty good that way, so you’ll see areas where the x-rays just aren’t visible, but if you have dense…I mean, it’s also one of these things where extremely dense gas, it’s not that it’s blocking x-rays, it’s that it’s producing x-rays, so there’s all sorts of “if-then” equations involved in figuring this out.

Fraser: Alright, so then let’s wrap this up with a nice, sort of one-sentence answer for someone, you know, “why is the sky blue?” Beyond just Rayleigh scattering… The sky is blue because…

Pamela: …because the gases in the atmosphere scatter the photons like a bunch of ping pong balls trying to get through a crowded room full of chairs.

Fraser: The blue photons.

Pamela: The blue photons.

Fraser: They scatter the blue photons, let all the other ones just pass through.

Pamela: Right.

Fraser: We’re seeing the blue photons scatter.

Pamela: Yes.

Fraser: Alright, alright…I think that works for people. Cool. Alright, well, thanks a lot Pamela.

Pamela: My pleasure.

Show Notes

• Listener Survey
• End of the World NOT Cruise
• Google+: Pamela and Fraser
• Sponsor: 8th Light
• Quantum Theory — The Big View
• Wave Particle Duality — GSU
• Uncertainty Principle — American Institute of Physics
• Angular Momentum in Quantum Physics — Quantum Diaries
• Discussion of Einstein’s quote “God does not play dice,” by Michael Shermer — Big Questions
• DeBroglie Wavelength
• Significance of the uncertainty principle in the real world — discussion on PhysLink
• Faster than light neutrinos  – New York Times
  

Transcript: Heisenberg’s Uncertainty Principle

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Fraser: Welcome to AstronomyCast, our weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain; I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University – Edwardsville. Hi, Pamela. How are you doing?

Pamela: I’m doing well. How are you doing, Fraser?

Fraser: I’m doing really well…working back into our schedule trying to catch up. We’re actually recording this a little bit early than the actual Monday, so I think we’re getting back on track. Again, if you don’t know, for those of you who only listen to the podcast, we record these now as live Google plus hang-outs every Monday at noon Pacific, 3:00 Eastern, and 8:00 London time, so if you want, you can join us live; you can sort of jump in to the podcast at the end, and ask us questions. We’ll hang out for about a half an hour after we record with the audience — really cool, really fun, really neat way to connect with us. You guys get to pick Pamela’s brains to ask her any questions to see just how super-smart she is.

Pamela: Any astronomy question…

Fraser: Any question you like, whatever, you know – the more math, the better.

Pamela: No.

Fraser: Alright, well let’s get on with today’s show. Quantum Theory is plenty strange, but one of the strangest discoveries is the realization that there’s a limit to how much you can measure at any one time. This was famously described by Werner Heisenberg with his Uncertainty Principle how you can never know both the position and the motion of a particle at the same time.

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Fraser: Alright, Pamela I guess we need to reflect back to our Uncertainty principle, or I guess, our Quantum Mechanics conversations. So what is the sequence of discoveries in Quantum Theory that led up to Heisenberg making this very famous principle?

Pamela: So this is actually based on the realization that things, particles in fact, aren’t simply little discrete bundles of matter that fly around like little tiny ping pong balls, but they’re actually made up of waves, and so when I’m talking about a photon of light, I’m talking about something that has a wavelength that gets refracted and interacts with the material around it in much the same way that ocean waves will interact with seawalls as they pass through them, and waves will interact with one another in water creating dead places and places with particularly high waves. This realization that particles are also waves at the exact same time meant that suddenly in trying to describe what does it mean for something to have a location, the world kind of fell apart mathematically and we had to rethink everything. It was no longer a particle that has an edge here, and an edge here, and this radius going off from the center in both directions. Suddenly, it became we’re going to combine wavelengths of various sizes to build up a particle, and that’s a much different thing to try and deal with.

Fraser: So is that kind of like asking what is the position of a wave? I mean, you can imagine a wave crashing on the beach, or imagine a tsunami, right? That causes this huge ocean wave that ripples across the whole ocean, and you know, five hours later, you can ask yourself, “Where is the wave?” Well, how much wave? At which places? I mean there’s going to be some wave. What’s the height of the wave? What’s the power of the wave? You know, it’s almost the entire ocean at that point.

Pamela: Right, and you do have this problem of just, definitionally, what do you use? And you can…with particles you can start to say, well, an electron is made up of this vast combination of wavelengths that all interfere to localize the particle in one place. Now, the only problem with that is once you’ve combined all of these different frequencies to say “the particle is right here,” well, now you’ve started to lose all of the momentum information. It actually turns out that when you have one beautiful, nice wave function, you can very beautifully define what its velocity is. We know how to do that, but when you start combining all of these different wavelengths that all have different velocities, or different frequencies, depending on how you choose to add them up, or what mediums you’re dealing with, when you start adding all this stuff together suddenly you realize, “I no longer know exactly what the momentum of this object is because there’s simply limits on, not my equipment, not my technique, but limits on what I’m able to come up with for the momentum based on all of these wavelengths combining together to tell me where the particle is.”

Fraser: And I think this is a pretty common misunderstanding of this whole Uncertainty Principle is it’s not about the, you know, you getting in and changing the position of the particle as you attempt to measure it, it’s not about a sensitivity of the instruments, there’s actually a…it’s impossible to do both at the same time.

Pamela: Right, and there is a certain amount of you’re interfering with this process as you get involved, so there’s two different ways that this gets looked at. One of the ways that it gets looked at is as a relationship between the energy of an object, and the time at which you’re looking at the energy, and so since …when you measure the energy, well, you’re interfering with the system and you’re probably changing the energy of the system. You’re either able to say very precisely what the energy is, but in the process of making the measurement, you lose the time due to all the general relativistic effects that have to take place — and time and GR are not friendly together, or you run into problems with you can measure the time that you’re making the measurement very, very accurately, but in getting the time just so, you lose track of the energy. It’s pick one, and there’s a “greater than” sign in this, so the way the Uncertainty Principle is written is the accuracy with which you don’t know the energy, the uncertainty, the “indeterminacy” if you’re speaking in German, of the energy multiplied by the uncertainty in the time of the measurement, or the “indeterminacy” in the time of the measurement multiplied together is always going to be greater than an amount that’s set by Quantum Mechanics. Now, you can have more error than that. It’s perfectly reasonable to say, “My equipment doesn’t work that well. My knowledge of the system isn’t that great.”

Fraser: “My big, fumbely fingers keep knocking the particles around.”

Pamela: Right! Exactly! Yeah — “My hadron collider…” but once you put all those pieces together, you can’t get better than a constant set by Quantum Mechanics. It’s easy to understand this when you start looking at position and momentum, so we use momentum because you have issues with “as your velocity changes, so does your mass,” but mass and velocity play together in momentum. That’s a variable that takes into account both of those properties, so here you can actually start to imagine how you’re affecting the system. If I want to know how fast something is going, the best way that I can do it, in some ways, is to actually measure how the impact of that object transfers its energy to another object. Well, I have now just completely changed where that particle’s going to be because I’ve impacted it on something. Now, at the same time, I can very precisely know where a particle is by bouncing things from all directions off of it and looking to see… it’s sort of like how a scanning electron microscope works. You just [missing audio] bouncing particles off of something, you know exactly where it is, but in the process of bouncing all these particles off of it, I have clearly changed its velocity. So in both of these types of measurements, by trying to get at one of the two variables — either the position or the momentum, I’ve affected my ability to know the other one. So since you need two different ways of measuring position and momentum, you can’t get at both simultaneously with accuracy.

Fraser: And so what impact does this actually have on the actual particle itself? As you say, if you are colliding it into something, I guess you’re ceasing its momentum.

Pamela: Yeah…yes, that’s one way to look at it.

Fraser: And discovering its location…but I mean are you actually bonking the particle around with your measurements? But I guess you’ve got this wave-particle duality, you’ve got this situation where things like photons and stuff can act a bit like particles, and a bit like waves, and in many cases, it’s the act of measuring that forces the particle into one state or another. Is there some of that at play here? Is that what the Quantum…sort of, the Quantum part of this is about?

Pamela: And this is where…actually, when people first heard this they got rather annoyed because it just seemed like it shouldn’t make any sense, and Einstein, who really didn’t like Quantum Mechanics at all, was one of the people that tried to say, “No. This doesn’t work. Here’s a thought experiment. Go look at this; I think this says it doesn’t work.” So one of his thought experiments was to actually say, “Let’s consider a particle that’s passing through that narrow slit, and by passing through the narrow slit, you’re taking a wave function and causing it to bend and distribute itself in a different way. We’ve all seen this with seawalls, or at least with pictures of seawalls, where you have this beautiful linear wave approaching the seawall, and then the part of the wave that passes through the hole in the seawall ends up rippling out as a curve. Well, he said that by considering a wave passing through a slit, you end up with uncertainty in the momentum that can be proportioned to the size of the slit, but you can determine the momentum that’s introduced in this very accurately by looking at “Well, how does the wall recoil?” So his idea was you get some of the information by looking at what passes through the slit, we know how to do that, and you get the rest of the information by looking at the wall’s response to the parts that hit the wall, and Heisenberg, in thinking about this, pointed out that we don’t actually know the wall’s position in momentum with sufficient accuracy that we can just throw that out to get the wave perfectly. So once you start putting into consideration the uncertainty in our knowledge of the wall, that’s where our uncertainty comes back into the problem, and no you can’t use that cheat, but Einstein was not deterred by this and he kept coming up with new thought experiments.

Fraser: What was his famous quote: “God does not play dice.”

Pamela: Yeah, and it turns out God may not, but the Universe certainly does.

Fraser: He did not like this…yeah. OK, well, I guess we should step back a bit and really understand how Heisenberg sort of formulated his original principle. And what exactly does his principle state?

Pamela: So his principle states that…when he first wrote this, there was no detailing of constants, but what his principle states is: “The uncertainty…” — and he actually used the word “indeterminacy” in his paper, except in the final footnote, but when the paper, which was written in German, was translated into English, whoever did the translation took the word from the footnote and used it for the entire paper, so while the original paper mostly talks about the “indeterminacy” of the position and momentum, we’ve translated this in English into the “uncertainty of the position and momentum.” It’s semantics. So what he discussed was the accuracy with which we know a particle’s position multiplied by the…I guess it’s lack of accuracy is a better way to put it. The lack of accuracy with which we know its momentum, when you multiply these two things together, those two indeterminacies, those two uncertainties are always going to be greater than some set amount that is defined by the nature of the Universe. He looked at the Planck constant; since then we’ve started using the Planck constant divided by two pie divided by two because we like to divide things up, but some form of the Planck constant is that limiting factor, and this all boils down to looking at the wavelength nature of things, and part of the inspiration for looking at this was the realization by Prince De Broglie — and I love the fact that you’re getting royalty involved in the defining Quantum Mechanics…

Fraser: Not the musician, but an actual prince.

Pamela: Right, yes. He looked at the wave nature of things and realized it’s not just light that has a wave nature, it’s actually baseballs, and human beings, and everything that exists has a wave-particle duality, and we’ve actually experimentally been able to prove this. You can take Buckyball particles, little carbon molecules that…I believe they’re as many as 60 atoms involved in one of these crazy little molecules — you can take one of these carbon Buckyballs, and put it through a slit, and then put a stream of them through a slit, and they form the interference pattern that you would get from sending light through. We can do this with electrons. There’s a whole variety of experiments that have been done showing that matter does behave, does self-interact in the same way that waves of light do. So De Broglie, in thinking about the wave nature of things, was able to describe the wavelength of an article as of a particle, rather, as being equal to the Planck constant “h” divided by the momentum of an object.

Fraser: Yeah, you just “mathed out” on us there.

Pamela: Yeah, so for a human being, our De Broglie wavelength is something like 10 to the -37 of a meter, so we’re talking at like subatomic scales here for human beings’ wavelengths — so we’re not going to interact with one another going through doorways in Quantum Mechanic natures, but the De Broglie wavelength starts to take on more and more importance as you start looking at fast-moving, very small particles, and it was while Heisenberg was thinking about the wavelength nature of particles, while he was thinking about how particles interact with one another, how you measure different interactions that he started to realize that it’s this wavelength nature and our inability to say, “This is in the center of a wave” that means that we can never accurately know the position of a wave, but if we do somehow look at the full wave packet, the combination of all those different wavelengths to see the particle nature of an electron, of a Buckyball, in doing that we’ve removed the momentum information that we get from the wavelength. So it was just in looking at how do we measure these two different things, what aspects of the objects do we rely on…then we realized, “Crud! We can’t get perfect accuracy.”

Fraser: And so what are the implications, then, of the Uncertainty Principle in sort of just modern engineering, modern physics? This is one of those principles that actually does have an implication in electronics and stuff, right?

Pamela: It does, and it runs into annoying things where we actually can’t completely localize particles with CCD detectors and such, where when we have…or the timing – pick one. So if you’re doing extremely high-speed photon counting, you can either know exactly where the photon hit your detector or exactly when the photon hit your detector. You can’t know both.

Fraser: Wow!

Pamela: So I mean, think about how this then affects things like well, those faster-than-light, pesky neutrinos that were, or were not (and I’m on the were-not-detected side of things)…so you can either know the exactly when or the exactly where, but there’s always this uncertainty involved, and you have to start taking into account on, well, you can’t know exactly where the detector was – exactly. You can’t know exactly where the neutrino was – exactly. You don’t know the times and energies – exactly. There’s always this fuzz to everything.

Fraser: Right, and so you’ve got a situation where you’ve got these particles, or I guess you’re dealing with the speed of light, and so the distances they’re traveling is relatively short. I mean, we’re looking at from one part of Switzerland to France, right? So you don’t have a big, long distance, and you can know the distance, you can know where these particles are hitting, which I guess this is key for those neutrinos, but it’s that timing that tells you whether they’re traveling faster than the speed of light that is really hard to get a handle on, so you see it rearing its ugly head with the faster-than-light neutrinos. That’s really cool.

Pamela: And, honestly, I think a lot of the problems are in timing, I mean, one of the issues that comes out of General Relativity is “How do you link clocks?” And this was actually one of the thought experiments that Einstein came up with — sort of kind of. One of the things that he said referring to the Uncertainty Principle in his other “no, this can’t work” argument was consider you have a box with a clock, and you very precisely time the opening and closing of a door on the box, and you let a certain amount of energy out of the box, and you have the ability to measure the amount of energy that came out, and then you can weigh the box, so you know the amount of energy inside, and it’s through this combination of measuring the amount of energy that leaves, and measuring the weight of the box after, and knowing the moment that the energy moved, well, that’s a delta E from knowing how much energy came out, that’s a delta T from the clock, you should be able to get all of this perfectly accurately just by weighing the box. And it was pointed out that the clock and the box are gravitationally tied together, and that this is a gravitational field that will thus affect the ticking of the clock, and so it’s all tangled together, and so now the uncertainty in the time is also coming from Relativity playing a role, and it’s all part of a whole, and at the end of the day it means that even if we do know where every particle in the Universe is, we don’t know where they’re going, and we can’t predict the future.

Fraser: I think that’s a fantastic example because Einstein coming up with a thought experiment, and then someone says, “Oh, but don’t forget this little theory called General Relativity.” Right? That’s going to impact the experiment as well, and I’m sure, again, I’ll bet he was really pleased with that example, and had to go back to the drawing board, but he clearly was puzzled and bothered by the implications of this theory, because as you said, he went on record a bunch of times, and spent a lot of his final years attempting to come up with a Theory of Everything, and trying to, I know, think through the implications of Quantum Mechanics, gravity, and all that together. For every thought experiment that he delivered, the Uncertainty Principle had a perfectly fine way to explain how that still was under the constraints of the Uncertainty Principle. It’s quite interesting that essentially the most brilliant scientist of modern times kept bashing his head against this principle, and it kept defeating him.

Pamela: And it really does say that the Scientific Method does work, that it’s not always a cult of personality. That does happen occasionally, you do occasionally just need to wait for somebody to die to get a theory accepted, but to have someone of the notoriety of Einstein going, “No, really, let’s think this through,” and everyone going, “No Einstein, this is right,” it’s just a brilliant way that the entire community together can be smarter than any one individual when it comes to figuring out what’s true and what’s not.

Fraser: That is really great. So then, you know, does the Uncertainly Principle have any impact on, for example, the search for the Higgs Boson, some of these big particle colliders? Because I’m sure they’re attempting to measure particles very carefully.

Pamela: So here, luckily, we’re mostly interested in the energies of the particles, so we’re looking for the tracks, the light being emitted, the basically, what is the energy of each of these little things that gets created, and so while decay times are kind of awesome to know, it’s knowing what is the energy of the objects that are decaying that is of the most import to us. So while it’s annoying we can’t know everything, just being able to get at “the energy is 125 giga-electron volts per c squared” – that is the information that’s mostly important to us here.

Fraser: Right, but you can imagine, you’ve got these cascades of particles that have half-lives of certain periods, and so knowing that this particle collapsed into those particles, and released this energy at these time periods, that is starting to fall under that whole Uncertainty Principle.

Pamela: It’s not…luckily, it’s not the dominant problem. The dominant problem is just getting all the energy in one place at one time, and letting all of those decays happen.

Fraser: Alright, well I think we’re all done this week, so thanks a lot, Pamela. I really appreciate it.

Pamela: My pleasure, and I will hopefully see you soon, and don’t forget if you’re interested in figuring out a Christmas vacation next year, we’re going to be on “the world is not ending cruise,” and I’m just going to keep plugging that periodically so that we can all, all of you out there listening, hopefully meet in person and explore Mayan ruins together.

Fraser: We’ll plug it until it fills up, and then we won’t plug it anymore.

Pamela: That’s true.

Fraser: Yeah, and that’s going to be over the December 21 holiday – end of the world.

Pamela: Go to “astrosphere;” it’s on the homepage – astrosphere.org

Yeah…astroshpere.org. Alright, well, thanks again, Pamela, and we’ll see you next week.

Pamela: Sounds good. Talk to you later.

Show Notes

• Listener Survey
• End of the World NOT Cruise
• Google+: Pamela and Fraser
• Sponsor: 8th Light
• Charles Messier bio — SEDS
• Messier Objects by Type — SEDS
• Off Axis viewing — Astronomy Shed
• Beehive Cluster (M44)
• NightWatch: A practical guide to viewing the Universe
• The Caldwell Catalogue
• Messier 104
• Owen Gingerich
• Messier Marathon
• Messier Marathon Tips
• Astronomical League; Messier info and certificate 

Transcript: Messier Objects

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Fraser: Welcome to AstronomyCast, our weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain; I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University – Edwardsville. Hi, Pamela. How are you doing?

Pamela: I’m doing well. How are you doing, Fraser?

Fraser: I’m doing well. The weather’s starting to improve — things are getting nice and sunny. I’m good.

Pamela: You know, Spring in January is just plain wrong, Spring in February is still mostly wrong, but yeah, I have to admit my bulbs are starting to come up, so this is a very odd year.

Fraser: That’s good. Alright, so have you ever looked into the sky and noticed a fuzzy blob? That’s a Messier object, carefully catalogued by Charles Messier to make it easier to find comets. We’ll learn about the history of the catalog, Messier’s criteria and some of the prominent objects you might see.

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Fraser: Alright, Pamela, so I’ve done this. I’ve rediscovered many of the Messier objects all on my own — I used to do that. I would go outside look up, you know, really dark skies, and where I grew up we had just beautiful dark skies, great big Milky Way and especially in winter the sky just pops, you get out there at like midnight, one in the morning, and it’s just amazing, and then what I would do is I would look around, and look for stuff just off… sort of that I couldn’t quite see that there was something there, you would see it out of the corner of your eye, and then you look over and maybe you wouldn’t see something, then you look away again and you’d see this fuzzy bit.

Pamela: Yeah and sometimes it’s not even required to use off-access viewing, yeah, it’s…I keep rediscovering the fuzzy blob in the center of Cancer – that’s my special ability.

Fraser: Which one is that?

Pamela: See, this is the problem when I constantly rediscover it. I believe that one’s the Beehive.

Fraser: Right, right, right, and so what you do is you look at these blurry things, and then I would pull out my star chart I had a nice, beautiful…I have Night Watch, by the way, if you want my #1 recommendation for a book that lists all of the objects in the night sky, I love Night Watch. So I had that book, and I would look at it and find the object: “Oh, that’s the great galaxy, Andromeda! Oh, that’s the great nebula in Orion!” And so as you said, for a lot of these things you’re rediscovering them, and these are the Messier objects, and if you ever have seen a comet with your own eyes, you know, that’s something completely different, and you need to keep them straight. So let’s learn about Charles Messier. So who was Charles Messier?

Pamela: Charles Messier was a French astronomer who worked in the late 1700s early 1800s, and he’s like many of us — someone who as a kid just had this moment of “Oh, my God! Astronomy is so awesome – that’s what I want to spend my life doing!” And for him that moment of complete “awesome” was the great comet of 1744. He was 13 years old when it went overhead, and this was an object that ranks as one of the top 10 brightest recorded comets. It, at one point, was reported to have 6 different tails, it was visible during daylight, it was just this absolutely amazing phenomena that impacted him as a teenager, so he went on to actually become an astronomer when he was an adult, and one of his first logged events that he recorded was actually a Mercury transit when he was in his early 20s.

Fraser: And so he set about trying to find comets.

Pamela: Right, so back when he was working, we were still trying to figure out this whole observational astronomy thing. There were planets – understood planets, then there were stars, and then there were fuzzy things and we had no clue what the heck all these fuzzy things were, and the real way to make a name for yourself was to discover comets because, well, there’s always the potential they’re going to be bright enough and big enough that everyone can see them, then of course your name ends up in all the newspapers. It was a good way to become a famous human being, and so Messier, among many other things, set out to discover comets, and over the course of his lifetime he actually was able to discover 13 different comets at different points. One of them he shared the designation with his assistant, Méchain. Another one actually ended up getting named after a different observer, Lexell, but it’s unclear which of the two was actually the person who should get all the credit for it. But the problem with trying to be someone discovering comets, and this was a problem that William Hershel and his sister Carolyn also dealt with, is comets start out looking like little tiny fuzzy patches on the sky, and lots of other things look like little tiny fuzzy patches on the sky, and so the only way to tell if you’ve discovered a comet or not is to wait for the fuzzy patch to move or to have a catalog that lists the fuzzy patch for you.

Fraser: Right, and so you could imagine if you’re just getting into this hobby that you would point your telescope in the sky, you’d scan the skies and find a fuzzy bit, and then you would go “Ha ha! Comet!” And then someone would remind you that “No, no, that’s always been there ever since being have been watching the sky.” Back to the drawing board, so I guess he just wanted to cut out this whole problem and build a catalog.

Pamela: Yeah. Just fix it. And so this is where, working in France, he developed his Northern Hemisphere-centric catalog of fuzzy annoying things — to him, objects on the sky, and because he was working when he was working, all of these objects are extremely bright, and everything in the Messier Catalog can be seen by binoculars if you’re at a dark site. So if you’re out in western Texas, if you’re in the middle of the prairie of the United States and it’s clear, if you’re in one of the random, rare, empty patches that’s fairly dark in Europe, anywhere in Siberia, for the most part, unless you’re in Lake Krasnoyarsk — there’s not much there. So as long as you’re in the north, and you’re somewhere fairly dark, all of these objects are available for you to look at.

Fraser: It’s interesting, though, you said Northern Hemisphere. He was operating out of France, and so there’s going to be huge portions of the sky that he had no way to see, and even though there’s some phenomenal parts of the sky, they’re just not on the Messier Catalog because he wouldn’t notice them, so they just get less publicity unfortunately.

Pamela: Well, and you know, and Sir Patrick Moore actually worked to fix this. So there’s a catalog called the Caldwell Catalog, that Patrick used his mother’s last name, Caldwell, when he published this catalog. I guess the “Moore Catalog” would just sound kind of funny, but the Caldwell Catalog is Sir Patrick Moore working in the 1990s to try and fix this problem. So he looked at the fact that there’s 109 Messier objects, found a matching list of 109 southern hemisphere viewable objects and created the Caldwell Catalog that brings in all the cool things from the Southern Hemisphere, so he has for instance, the Jewell Box Nebula, 47 Tucanae, which is a globular cluster, Omega Centauri, Centaurus A — all of these different objects are tied into his catalog, allowing people to basically go back and forth between the two hemispheres and have equally biased catalogs on either side of the Equator.

Fraser: Yeah, so you know, the people in the Southern Hemisphere – there’s some love there. But that’s how it goes, right, it’s just like whoever gets it out there first, the name sticks and that’s why we have Messier marathons, which we can talk about at some point later on. Right, OK, so he went through this process, he gathered together this list of all these objects so that he could discover comets, and in the end, you know, discovered like you said, quite a few on his own and then…

Pamela: But those aren’t his lasting legacy. His lasting legacy is this catalog of things that annoyed him.

Fraser: Yeah, not the comets, but in fact, the not-comets, which he didn’t discover, he just…

Pamela: Catalogued.

Fraser: Catalogued, which…

Well, in a few cases, he was the one who discovered them. That’s the thing — at the time when he was working, yeah, it’s not to say he was necessarily to first person to view all these objects, but in some cases he and his assistant, Mechain were the first ones to write down these objects, which actually has led to evolving credit on this list (for lack of a better way to put it). When the catalog was first published, there were only 45 objects in it, and then they came out with the second version that brought it up to 103 objects, one of which didn’t exist, which always makes for interesting times, but if you look at it today it’s 110 minus 1 objects, and those additional objects come from folks going through his notes and realizing “Wait, they discovered other things that they deserve credit for. ” So Nicholas Flammerion in 1921 added Messier 104 after finding a note in the margins of one of their catalogs, and 105-107 were added by Helen Sawyer Hogg in 1947. Owen Gingerich was still adding objects in 1960, so this has been an evolving process as people go through the original documentation, and this is where our archivists can play such an important role in making sure people get the right credit for the discoveries, so it became 110 objects based on realizing “Hey! Wait! They’re the ones that discovered this. Let’s make sure they get credit in their catalog for their discoveries.”

Fraser: So in fact the Messier Catalog…so what you’re saying then is the Messier Catalog lived long after Messier’s life himself and other people were able to contribute to it, and I mean, but is it locked and closed down now? Is there any way that people will ever be adding things apart from, say, historical discoveries?

Pamela: Well, there’s always the possibility that someone will be going through letters, someone will be going through notebooks and realize “Oh, wait! Here’s this other thing that was discovered that we just don’t have a record of.” So you can never say never to something like that, but at this point I think, especially after Owen Gingerich, who is an amazing astronomer and an amazing historian — after he went through the all records, I think we can close the door on new things being added, but you never know when another letter is going to be discovered.

Fraser: Or some other object could appear. I mean, some of the objects are supernova remnants, and so you can imagine in the far future we’ll end up with a new supernova remnant.

Pamela: Right, but I don’t think they’ll give credit to Messier for something new.

Fraser: No that’s true, that’s true, but I wonder, you know?

Pamela: So that’s a new catalog at that point.

Fraser: Right, OK, so what kinds of objects would we find in the Messier Catalog?

Pamela: Well, it’s anything, by definition, that could, through a low-power telescope or a pair of binoculars, could cause an observer to go, “Is that a comet?” So all these types of things are either stars that are so close together that their light kind of combines into a cloud, or things that are actually cloudy. So we have open clusters like the Pleiades, globular clusters like M13 in Hercules, which is this tight little cotton ball of stars on the sky, there’s planetary nebula, there’s supernovae remnants, there’s random nebula… So like the North American nebula is this big, beautiful, red object on the sky, gas that has starlight passing through it, and the blues get filtered out so that we see the beautiful reds, and then there’s galaxies and Messier didn’t even know what galaxies were, but he, along with Hershel, is responsible for finding some of the most beautiful ones in the sky.

Fraser: I mean even up until 100 years ago they called them nebula.

Pamela: Yeah.

Fraser: “The Great Nebula in Andromeda,” right?

Pamela: Less than 100 years ago we were still arguing, not we, but, I mean, what’s amazing is you talk to Owen Gingerich, who’s one of the oldest professional astronomers, who’s also done all the history work, and you ask, “What’s the most amazing discovery in your lifetime?” And they say, “Galaxies!” [laughing]

Fraser: [laughing] Galaxies! That’s pretty amazing!

Pamela: [laughing] It’s like – OK, totally new perspective on everything…so yeah, these are all objects that look cloudy until you start to really resolve them with larger and larger telescopes.

Fraser: So then, you know, both you and I have done some visual observing, and so, you know, what are your favorite of the Messier objects?

Pamela: I have to admit M51, the Whirlpool Galaxy. It’s what everyone absolutely adores, and I’m just a follower on this one. It’s one of my favorite objects. I used the McDonald observatory 30-inch telescope, which has a giant field of view, to image this anytime that I couldn’t use the telescope for my science, so while waiting for the Moon to set, I’d be out there happily observing my galaxy, trying to get a beautiful, pretty picture of it.

Fraser: I’m going to say that my favorite is the Ring Nebula.

Pamela: The Ring Nebula…that one’s a challenge because it’s not that large on the sky.

Fraser: Well, it’s not that large, but it is…it’s M57, right…it’s not that large, but it actually…I was able to find it in my…I had a little 4-inch telescope growing up, and that was one of the first objects I was able to find, and I think what was great about the Ring Nebula is it really looks like a little ring, but a lot of the other things, as you say, the Whirlpool Galaxy, yeah, if you’ve got a 30-inch telescope, then you can see, and you’ve got a nice, long exposure then you can see the beautiful spiral nature, but if you’re just doing visual observing, looking through your eyepiece, there’s not a lot of these objects that look like what they’re supposed to look like in the picture, but the Ring Nebula, for me, always really looked like a little ring floating in space…and then I would say the great globular cluster in Hercules.

Pamela: Yeah, that one is…it’s harder to find than you’d think. I don’t know how many nights I spent basically lying on my back, binoculars in one hand, planisphere in the other, trying…you can’t look through both at once, or look at and through both at once, desperately trying to star-hop my way there before I found it.

Fraser: Yeah, you’ve got to go up and down between these two stars on the side of Hercules trying to find it. And then, of course I would say, the great nebula in Orion, which is just absolute beautiful, clearly fuzzy bit in the sky, which is even starting to show some color, which is fairly rare for a lot of these kinds of things.

Pamela: And what’s kind of amazing is the sheer diversity in objects that he found. So you have everything from extremely disturbed galaxies to these beautiful, classic galaxies; you have little, tiny objects like the Owl Nebula, which is another one of my favorites. It’s a little planetary nebula that just happens to have two darker patches that look like owl eyeballs.

Fraser: Absolutely looks like owl eyes! Absolutely, yeah…

Pamela: And it’s just this amazingly rich way to get people engaged in astronomy by saying, “Look at the diversity and the beautiful things that we have in our field!” And the name is kind of fun to play with. As a little kid, and as someone who as someone who has absolutely no knowledge of the French language, other than what you learn from Miss Piggy on the Muppets, which isn’t useful in France, I learned it…Messier — you don’t see it as Mess-ee-ay, you see it as Mess-ee-er, like your “messier” bedroom, and as a little kid, I read it that way. I thought this was the catalog of “messy” objects on the sky, and that’s actually a really neat way to engage people. Look at what the Universe has to offer — not everything is perfect and symmetric and beautiful the way you’d expect the planets to be. Sometimes you have things that look like squished bugs, and then when you start to understand them, you realize they look like that because this is two galaxies that collided into one another, and they literally splattered across the Universe, and this is where Messier marathons becomes so interesting.

Fraser: Yeah, well, I was going to talk about the Messier marathon next as well. So what is a Messier marathon?

Pamela: Well, it’s basically just like the name “marathon” implies, it’s kind of an endurance mission to try to make it through all the objects, and you have to start at the moment the Sun gets far enough below the horizon that you can start to pick these objects up. You need to be in the Northern Hemisphere, and ideally somewhere between about 20 and 30 degrees north, so like Texas, Florida, Mediterranean area…these are all fairly good, northern Africa is fairly ideal, and from these latitudes just as the Sun sets in mid-March, you’re able to start picking up the westernmost objects for that time of year at sunset, and then if you quickly flip through them through the night you can basically hop from Messier object to Messier object and just before the sun comes up, if you’re good, and you’re efficient, and you find things quickly, you’re able to make it through the entirety of the list. Now the problem is you hit certain areas, like the Virgo cluster of galaxies, or the center of the Milky Way and there’s kind of stuff everywhere, and so there’s a whole lot of “Did I find the right thing? Did I find the wrong thing? Did I…?” And so you have to try and leave time for those objects. You’re not actually allowed to linger on anything.

Fraser: No. There’s a certain time of year that you have to do it, right?

Pamela: March.

Fraser: You have to do it in March. March — like a very specific time…

Pamela: Right. And the reason for this is the combination of, well, in March, no matter where you are on the planet, you have basically 12-hour-long days, and so with those basically 12-hour-long days, you have just enough time to get through everything, and the other is there is somewhat of a biased east-west in when you can see objects, and it just happens to work out that in March is when you’re best able to get everything up all at once between sunset and sunrise.

Fraser: Well, What kind of a telescope would you need, you know, to definitely complete a Messier marathon, you know, what would be the bare minimum gear that you would need?

Pamela: Well, if you want to say you’re definitely going to complete it and you don’t care about cheating, I’d say anything with a go-to drive.

Fraser: Well, of course! Yeah! [laughing] Right. You don’t even have to look through the eyepiece! You just make sure it’s polar-aligned, and just press the button and watch your telescope from afar, and you know, update it 100 and whatever — 9 times, 8 times and you’re done.

Pamela: Yeah, so personally, I consider that cheating, so if you want to be a purist, then I’d say you need a good star atlas (paper works!), a red flashlight, and a pair of fairly perfectly reasonable binoculars — so something with a nice 7-degree field of view probably will do it for you. You don’t need anything fancy, I mean, the thing to think about is this was discovered by a guy working through a refracting telescope made by hand a couple hundred years ago. Our everyday spotting scopes are way better than anything he could have imagined. Now, a nice easy way to do this, if you want to use a telescope, is just get yourself a nice 6-inch or 10-inch Dobsonian, and move your light bucket around the sky gathering light, and what’s neat is so many people have spent so much time in trying to figure out how to do this well, and how to do this right that there’s actually, if you search around you can find, “OK so do this object, this object, hop from here to here…” instructions on how to do this efficiently.

Fraser: Yeah, you don’t want to do them in order. You don’t start at one and go to two, you know, you have to start in whatever object is closest to the horizon, although they…

Pamela: Closest to setting…

Fraser: Yeah, but in some cases, you know, the numbers are kind of similar because as he was creating these numbers, he would, like what is it, M81 and M82 are two galaxies, are side by side, and they’re probably actually interacting in Ursa Major, so you know, there’s some that are connected in that way, but in many cases, yeah, you’ve really got to…the only way to possibly do this is to follow someone’s list or checklist, and then do a few practice runs, and try to make sure, you know, different times of the year, and make sure you can find these constellations and find them fairly rapidly, and then, when the time is ready, get your gear and do it.

Pamela: One of the confusing things about the Messier Catalog is it’s not ordered by type of object, so you don’t find all the planetary nebulae clustered together in numbers, it’s not ordered numerically from east to west, it’s pretty much in the order that they found things, and so while there are pockets of numbers that go together — the Virgo cluster stands out rather nicely, the rest of it is just kind of random, so you just need to get yourself a map, and it’s just like taking any tourist trip, you have to figure out what roads you’re going to take to get from one stop to the next.

Fraser: So and this is one of the things that we’re planning. I don’t know if people have been watching, but we’ve been doing these live star parties on Google plus. We’ve been connecting together four or five telescopes all at the same time and streaming into a Google plus hang-out, and so our “maybe” plan in March is to do a Messier marathon, and do it in like a couple of hours to just have astronomers around the world all streaming together their go-to telescopes, and just knock it off get a world record for a Messier marathon.

Pamela: And the thing is we can seriously cheat because we can get observers that are spanning 6 hours apart across the planet, and always get them at zenith.

Fraser: Absolutely! Yeah.

Pamela: So we just wait for the objects to be in the ideal spot in the sky, and then we check them off of our list.

Fraser: Yeah. Exactly.

Pamela: Now, that’s totally cheating. We will not earn any certificates for completing a Messier marathon doing this.

Fraser: [laughing] Are there certificates that you get? Are there?

Pamela: There are actually.

Fraser: Really? OK.

Pamela: So the Astronomical League has put together certificates for how you observed and how many you observed in a given night. I tried really hard to get my Messier certification with binoculars, only I failed. I got lost in Sagittarius, and couldn’t differentiate from one object to the next before I got called off to go do something else.

Fraser: That’s cool. I would like to do that some year. So then like if people really want to just do it, pair of binoculars, sky chart… What would you say if you want to start discovering your Messier objects, and you don’t have to do it in one night because different parts of the sky will be visible at different times of the year, and you’ll have the optimum times to do it and you can just pick away at it segment by segment? There is a…on Universe Today, Tammy Plotner used to do a “Messier Week.” And so she would recommend you take a course of a week to chip away at a Messier marathon, just, you know, don’t try to kill yourself in one night. But then, gear — I just want to talk about that last thing, people want to start doing this and really starting seeing the Messier objects and identify them, you said sort of what? Like 7 x 35 binoculars, maybe a little better than that, right?

Pamela: I think 10x40s is what I’d go for. The larger the front aperture you can get, the better — 50, 60 — just increase that number until they get too heavy to hold. So bare minimum equipment is a good atlas, they make them online, which saves time and energy, just make sure that whatever you’re using has a red mode so you don’t blow your dark adaption, nice pair of binoculars, and then I use…we have one of those hammocks on a stand in our backyard, and so I’m up off the ground and comfortable nested in my hammock unless the dog decides to join me in which case we swing a little bit violently.

Fraser: Yeah, binoculars pointed skyward…

Pamela: Yeah, lawn chair…something like that, something that allows you to lie down and be comfortable without the creepy crawlies crawling on top of you, and the thing about the Messier objects is because they are distributed fairly consistently across the sky (there is a gap), you can go out a couple hours after sunset every night, take in a few, and just let the sky pass overhead, and over the course of the year, you can get to see everything when it’s highest in the sky and easiest to view.

Fraser: So break it up. Don’t get in such a rush.

Pamela: And all you Southern Hemisphere people – Caldwell Catalog.

Fraser: Caldwell Catalog, yeah, Caldwell Marathon — Caldwell/Messier marathon…

Pamela: Exactly.

Fraser: Yeah. Alright, well, thanks a lot, Pamela.

Pamela: It’s my pleasure, Fraser.

Show Notes

• Listener Survey
• End of the World NOT Cruise
• Google+: Pamela and Fraser
• Sponsor: 8th Light
• Faster Than Light Neutrinos
• Particle Physicists Put the Squeeze on the Higgs Boson
• What is Six Sigma?
• A Six-Sigma Signal of Superluminal Neutrinos from Opera — Science 2.0
• ATLAS Experiment
• 2011 Nobel Prize for Dark Matter Discovery

Transcript: Precision

Download the transcript

Fraser: Welcome to AstronomyCast, our weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain; I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University – Edwardsville. Hi, Pamela. How are you doing?

Pamela: I’m doing well. How are you doing, Fraser?

Fraser: Doing very well, very cold, a little sick, so people can hear it in my voice — I’m a little nasal-y today, so I apologize. It should be going away. But now you had a couple of things that we wanted to talk about today. One is you wanted to remind people about the survey that we’re running.

Pamela: Right, so every couple of years we do a general listener survey to find out how we’re impacting you, what you want to learn and exactly why you come and spend spare time listening to the two of us talk astronomy. So if you can spend a few months…spend a few minutes…

Fraser: A few months…

Pamela: [laughing] …answering some questions – spend a few minutes. If you could spend a few minutes answering some survey questions for us, the survey is at http://www.astrosphere.org/Surveys/AstronomyCast/survey_astronomycast.php …we’re just going to put all the links up for you. I’ll be tweeting that in just a minute, and it will be in our shownotes for this episode.

Fraser: OK cool, and then the other thing we wanted to remind everyone is now that it’s 2012 and that the world is ending, we’re going to be on a cruise at the end of the year to celebrate the “end of the world” – not. So, at the very moment that the Mayans predicted…I guess the Mayans ran out of calendar space, we will be cruising around the coast of Mexico, talking about astronomy and celebrating the continuation of the world with all our other skeptical friends, so that’s going to be…David Brin’s going to be on this cruise, there’s going to be astronauts… it’s going to be awesome! We’re going to be there, and we’re going to be doing probably live episodes of AstronomyCast, and you can hang out with us. Play shuffleboard.

Pamela: And all the details are at astrosphere.org, again, and if you sign up, when you talk to the travel agency, tell them you’re part of the AtronomyCast group. We’ll have special freebies and special events just for you on the cruise ship.

Fraser: Yeah, and then we want to know, sort of, how many people are coming for us, so we can sort of accommodate that. Awesome! And know that there’s a limited number of spaces, so it’s one of those things where we’ll keep nagging you until all the spaces are gone, and then we won’t talk about it anymore. OK, and so then one last little piece of work: and so once again we’re recording this episode of AstronomyCast as a live Google plus hang-out. We record these every Monday at noon Pacific, 3:00 Eastern, 8:00 pm Greenwich Mean Time…that’s all the time zones I can think of, so if you want to join us live, we try to sort of get an announcement out ahead of time and then watch the video and participate, ask questions, jump in the hang-out with us, and uh, yeah, it’s sort of the next level of interaction, and big thanks to Google for letting us use this technology. It’s awesome! Alright, well let’s get rolling.

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Fraser: Alright, so accuracy, precision and “reproduceability” – these are the foundations of science that make our progress possible, but how do these play into a scientists daily activities, and just how precise can you get with our measurements? And are we going to talk about scientific notation?

Pamela: No.

Fraser: No? OK.

Pamela: [laughing] No.

Fraser: That stuff was the like the bane of my university existence, but right, so then let’s talk about it. I mean, precision, so where…you proposed this topic this week, so I want to get an idea of where you want to go with this.

Pamela: Well, right now we live in a world where lots of different things are getting discussed about in terms of “is it real?” There’s the “neutrino travels faster than the speed of light” issue, there’s dark energy, dark matter, there’s the Higgs Boson, and the question that people should be asking is “At what level can I believe the things that I’m hearing are true?” And this plays out on so many different things. It plays out also on at what point do you believe a Kepler detection of a planet is real? At what point do you believe the detection of a distant galaxy isn’t just a fluke of your detector on a given day? So as we’re trying to sort out all of these different things, there’s lots of vocabulary that comes into play, and lots of ideas that come into play that we don’t generally have to deal with in everyday life, so I wanted to spend an episode getting into things like, well, what is the different between precision and accuracy? What do you mean you can have a highly precise result that means absolutely nothing? So this is where I wanted to go.

Fraser: So then, I guess, how would you say that scientists define that precision? Like where…how are you going to measure that?

Pamela: So we deal with two basic variables. One is how precise is your measurement? And that basically says, if I take a measurement and I repeat it over and over and over and over, the values are either tightly bundled together, or if it’s not a precise result, they’re spread out a lot. So the example we use when we’re teaching is we’re throwing darts. If you’re a highly precise dart thrower, all your darts are going to land within a half an inch of each other. If you’re an un-precise dart thrower, all of your darts are going to land spread out over two, three meters, maybe, on the wall. You’re taking up the whole wall with your five darts, so precision is how closely spaced are all of your results.

Fraser: And so if you’re, like, doing some kind of scientific research, and you’re looking for some expected outcome, you’re going to want the expected outcome to be precise; otherwise, it’s just going to be random noise.

Pamela: Exactly. And at a certain level, we always start off with a fair amount of noise in our results. As people have worked on trying to define the expansion rate of the Universe, they have gone from plus or minus a few 100 km/second in the early years of trying to make these measurements, to plus or minus a few km/second. So over time, we get our results closer and closer; the error bars on the age of the Universe have gotten smaller and smaller. You always start off with less precise results, and get better and more refined as you go, but precision and accuracy aren’t the same thing, and this is one of the things that we have to worry about when we start looking at things like the “neutrinos moving faster than the speed of light” problem.

Fraser: So I guess in that case, you know, they were very precise in that all of the neutrinos that they detected were moving faster than the speed of light within a very close range; you know, they threw all those darts and they all landed very close to each other, but the question now is are those results accurate?

Pamela: Exactly. So you can imagine the person who throws all of their darts, and they all land within an inch of each other in the very last circle of the dartboard. So they have very precise results that are in entirely the wrong place, and this is one of those problems where….

Fraser: Wrong dartboard…yeah.

Pamela: [laughing] Right, and so this is the type of thing that can come down to…well, I don’t know what it would come down to with the dart thrower, but there have been plenty of experiments that have been done where you don’t realize your meter stick is missing the last three millimeters of the meter stick, you don’t realize your equipment is misaligned by one degree.

Fraser: Right, so you could have something that’s causing noise in your experiment in a very predictable, very…you know, it’s always doing the same thing, and it’s always wrong by the exact same amount.

Pamela: It’s a systematic offset. People who fire guns deal with this when their sites are off, or if you’re playing a video game you may realize “Crud! I always need to click up and to the left 3 pixels in order to actually hit the thing correctly.” So there’s systematic offsets that if you don’t know what they are, you can’t believe any of your results.

Fraser: And there are many situations where it’s those systematic offsets that people didn’t realize they were happening, and then they thought they had accuracy and precision?

Pamela: Well, they keep cropping up throughout all of history. Most people, I think, believe that the “neutrinos are moving faster than light” are actually going to turn out to be some systematic problem with either not understanding the way the Earth is stretching, not understanding the distances, not understanding the GR involved, and the corrections needed to match two clocks in two locations, and so we just look back and we keep finding small things like this. I know there have been cases of “Oh, crud! We forgot to take into account the fact that the Milky Way is moving!” Those sorts of little things add up when you’re trying to figure things out on cosmic scales or even local scales. So it’s the type of thing that we figure it out fast enough that there aren’t too many glaring mistakes.

Fraser: I can think of a good example. Like, remember how Newton made his predictions about the movement of Mercury? And eventually telescopes got better and better and better, and scientists were able to calculate the position of Mercury with great precision, and yet it was always wrong. Matching his theories, right?

Pamela: And that wasn’t so much an error in measurement as an error in understanding.

Fraser: Right, in prediction, yeah.

Pamela: Yeah. We have to worry about two different things. It’s the systematic offsets in our measuring, which is where we worry about the neutrinos, but sometimes we’re just missing a term in our equations, and that doesn’t so much go into precision and accuracy as we just missed a term in our theory, so that’s…different bin.

Fraser: Now, there was a really good example that’s come up quite recently with the possible detection of the Higgs Boson by Cern. They sort of talked a lot and sort of, you know…was it Sigma? Degrees of Sigma?

Pamela: How many…yeah. So this starts to get into noise theory. Any time we make a measurement, there’s going to be some sort of inherent noise in it. There’s going to be…if we’re trying to detect light, there’s just this constant steady stream of photons at all colors that are creating this noisy background. There’s going to be just minor fluctuations when you try and make measurements with a ruler, measurements with a laser, measurements with any tool, and if the noise is truly random, what you should end up with is all of these different variables, all of the different ways that things can go wrong, if they’re random, work out to form what’s called the Gaussian Distribution, a bell curve, a normal distribution, such that the majority of the measurements are going to be pretty close to the same value. And this means that if you take all of your points and you plot them, you’ll end up with plus or minus 34.1% of your values, so 34.1% that are too high, and 34.1% are too low – those count as one Sigma off of accurate. So you end up with a curve where one Sigma is plus or minus 34.1% of your values. Then you end up with another “Sigma” is the term we use – I know it’s all quite confusing. So it’s a bell curve, go plus or minus 34.1%, and that’s one Sigma. Now I know this is hard to understand, so for 3 Sigma, instead of giving you the percentages that we’re looking at, it’s 1 in 370 of your values, so if you take a whole bunch of observations, 1 in 370 of them is going to fall 3 Sigma away from your actual value. So once you start to get to that level of “Wow! That probably shouldn’t have happened.” You start to think “maybe this is something other than the measurement I was trying for. Maybe that’s something above the noise in my values.” So with the Higgs Boson, if you’re looking in a chamber for a particle to randomly come out of the energy of what they’re colliding in the detector, there’s a random chance that something’s just going to happen, and then there’s the “you see it happening more often than random would predict,” and if you see it happening at the 1 in 370 level, that’s a 3 Sigma detection.

Fraser: And didn’t they, I mean, they said…or that maps over to something like a… What was it? Like a 99% possibility?

Pamela: Right, of it actually being real. Now the thing with the Higgs Boson detections is they haven’t actually gotten up to 3 Sigma yet. They’re looking at like almost 2 Sigma detections, and in reality, what we actually really hope for is a 6 Sigma detection. This is where you have a 1 in 507 million of the thing occurring randomly. So once you start to get to something is that rare in random distribution, you start to say, “Huh! Maybe that’s real.”

Fraser: Or it was…remember last week we were talking about the confirmation of the multiverse theory, right? It happened to exist in a universe where all the particles are lining up in the wrong place. But right, it’s funny, if you got…you know, if I’m 99% right, then that’s pretty right, but it’s quite surprising — physicists are so reserving of their judgment that they need a 99.99999…I forget how many nines to be really comfortable that they found the Higgs Boson, and they’ll announce it. And you know, I think when physicists say, “We’ve found a particle,” they are serious.

Pamela: Well, and the thing with the Higgs Boson that I’ve really enjoyed watching is they’re not only doing one experiment over and over at a variety of different energies, trying to prove that it exists with that one detector at that one set of energies, but they’ve actually have a whole variety of different experiments going on, and what’s kind of awesome is through using the Atlas experiment, the CMS experiment, the D-0 group, all of these different experiments that all do very different things that are for an entirely different show — what they’re doing is they’re systematically, with all the experiments, ruling out some energy levels, so they’ve pretty much completely ruled out everything in a higher energy than 128 giga-electron volts/c squared, which is just a number – deal with it. But with all these experiments, they’ve ruled out that region, and with both Atlas and CMS, they’ve managed to say, “there seems to be something going on between 115 and 127 giga-electron volts/c squared” – again just a set of numbers, but two different experiments using two different methodologies have come at the same range of “Huh! There might be something here.” Now the problem is the “it might be something here” is such a weak detection that it’s hard to say it isn’t just something random that’s in the background noise of, well, what the Universe is constantly doing. There’s constantly particles coming in and out of existence. There’s lots of stuff going on at every single moment, and it’s hard to know — are they just detecting the tail-end of the Universe, or an actual detection of the Higgs Boson?

Fraser: So is that an accuracy problem? You’ve got noise coming in that’s pushing everything in the wrong direction?

Pamela: So accuracy and precision refer to your data. Is it…are all of your data coming in at the same energy level? So the range of 115-127 describes the precision of the measurement. Accuracy says whether or not it’s true, but neither of those reflects on the noise. The noise is, well, just how well can you detect this? So it’s sort of like saying you are throwing darts in the dark, and you’re trying to figure out while feeling your board if you actually managed to get everything in the right place. So it’s…you’re just not quite sure what happened because you can’t see it well enough, so this is getting above the noise issues.

Fraser: Right, so what is the method, then, that scientists use to manage their precision, right? And their accuracy? What do they do to, sort of, really in a way that other scientists would say, “Yes, we agree. You’ve found the Higgs Boson.”

Pamela: So here it’s a three-pronged problem. You have accuracy of your results, and that comes from, basically, narrowing a window down and proving nothing’s outside of that window. All of the detections we have are within that window. Precision is getting the window smaller and smaller and smaller, and then there’s the “seeing it above the noise.” The “seeing it above the noise,” that’s the seeing in the dark problem, and to get to that, you just have to build more and more sensitive detectors, so in this case, it’s things like with Atlas, the fiber optics they’re using… I actually worked on building this instrument when I was an undergrad. Didn’t know at all what I was doing; I was just weaving fibers…I was an undergrad.

Fraser: Really?

Pamela: Yeah…

Fraser: Wow!

Pamela: So I was working on it when I was at Michigan State, and one of the things that we had to do was mix optically-perfect epoxy that didn’t have any bubbles in it, and every single fiber was checked to make sure that it had the expected light through-put, so if you put a set amount of light in one end, you get the set amount of light out the other end, and any fiber that didn’t meet “spec” got thrown out, and we had to redo that entire fiber optics assembly. So with things like Atlas, they work very hard to make sure they understand exactly how sensitive the system is, and then make it absolutely as sensitive as possible — basically, the “no photon goes unmeasured” type of a set up.

Fraser: And, I guess, the same thing with the accuracy, right? Which is that, you know, you need to make sure that every piece of your experiment you’re performing as expected to.

Pamela: Right, right, so when you say something is at 114 giga-electron volts/c squared, you actually mean 114, not 122. When you say 115, you don’t actually mean 123, so that’s where the precision comes in is making sure you’re actually… I mean, that’s where the accuracy comes in is you actually know where you are, and the precision is “When I detect it, I’m certain it’s where I think it is.”

Fraser: And the other big concept that we mentioned at the beginning of this show is “reproduceability,” so how does that come into play with science?

Pamela: This is the “neutrino faster than light” problem, where they said, “OK, can somebody else in the world reproduce this?” Because you never know what is a problem with your system. When they first detected the cosmic microwave background, they blamed their equipment, not the Universe. They assumed it was something wrong with their set-up, pigeon poop, something… and so not only did they do everything they could to make sure that it wasn’t noise created by their electronics, but they also went out and they said, “OK, can someone else reproduce this?” When supernovae are detected, the first thing that people do is they put out a call: “Can someone else detect this with their detector?” And it’s by having multiple instruments reproducing the same results where you get your first confirmation. Now when it comes to ideas that change our understanding of the Universe, however, it’s not just enough to say this one experiment has been reproduced with this telescope, this telescope, that telescope, or multiple cyclotrons, or the same type of experiment at multiple institutions. You actually have to come up with complementary experiments, so when we say the Universe is filled with dark matter, we base that bold statement on the fact that we see things rotating at speeds that can only be explained by there being more stuff out there than we can observe. We base it on seeing lensing of distant galaxies — microlensing and macrolensing events of different types. We base it on looking at the cosmic microwave background and at the assembly of galaxies. All of these different lines of evidence go into dark matter. The same thing with the Big Bang — there’s multiple lines of evidence.

Fraser: And eventually we’ll be able to have a “cup of Universe” and sort it by regular matter, and dark energy, and dark matter, and actually have detected it, and know, you know, we also know this is dark matter because we could detect it here with our instruments. And that’s the piece of the puzzle that’s still being worked on. That’s kind of like the next big job.

Pamela: And this is again where we’re starting to see experiments that are making claims that they’re detecting a particle, but we don’t know if that’s really above the noise, we don’t really know “Can you trust that?” And so this is where the repeatability comes into the experiments.

Fraser: So then, where do you think people are, like, hearing and discovering new theories, and hearing them talked about on the internet, either fairly mainstream stuff like the Higgs Boson and you know other dark matter experiments and things like that, but also some of the more interesting theories like the discovery of “faster than light neutrinos?” I mean, who wouldn’t love faster-than-light travel? So lot of this stuff gets announced. When a lay person hears that kind of stuff, what sort of filter should they use, based on what we’ve been talking about today, as a way to put everything in perspective?

Pamela: So any time you hear an announcement that says that it’s going to fundamentally change our understanding of the Universe, you need to ask, “Has this been repeated?” That should always be your first question is “Has this been repeated?” And when I say repeated, I mean by somebody else. So when they first announced dark energy back in 1998, what was so amazing is there were two competing teams that didn’t particularly like one another because they were competing for financial resources. These two different competing teams both came up with the exact same result using supernovae to say our Universe isn’t behaving the way we thought, and it’s not behaving the way we thought for both sets of data in the exact same way; therefore, we have something we’re going to call dark energy. Since then we’ve been able to add more and more credence to that idea by looking at the cosmic microwave background, by looking again at models for how large-scale structures formed over time. So the first thing you ask is “Has it been proven by more than one experiment?” If it’s been proven by more than one group of people doing the exact same experiment, it’s fair to go, “Huh, I can start to think that’s true.” The next thing they should ask is “Well, OK, so it was done by more than one place, but how good was the detection?” So there was, back in 2010, some…what that looked like for about one month, really good evidence for a 2 Sigma detection of the Higgs Boson, where both Fermi Lab and Cern came up with similar results and then realized “No, that was the Universe, not a detection of the Higgs Boson, just background noise that always sits there.” So then you have multiple experiments, and then you have high threshold above the noise so you’re certain there’s something actually there. Once you know there’s something actually there, and it’s repeatedly actually there, and then you start saying, “OK, so can I find another way to detect the same phenomena? Is there another different type of experiment that somebody else has done?” So this is where you get the multiple lines of evidence all proving the same thing.

Fraser: And will scientists typically speak in this “Sigma” way of describing…

Pamela: Oh, yeah.

Fraser: Oh, really?

Pamela: Yeah, we’re really lazy. We like to say it’s a 6 Sigma result, it’s a 2 Sigma result, and so yeah, we’re pretty bad about that.

Fraser: Right, but it’s like 5 stars, 2 stars…

Pamela: Exactly. That’s exactly what it is. Six Sigma is “Wow! OK, I can trust this number!” But you also have to be careful…so sometimes we lie with numbers, we don’t mean to, but we do, so you can have a 6 Sigma detection above background of a bright object, but all because you have a 6 Sigma detection doesn’t mean it is what you think it is. This is where the whole supernova problem comes in. You can have a 6 Sigma bright detection on your image, and what you’ve actually detected is something totally different from a supernova – a cosmic ray hit your detector, airplane flash on your detector, all sorts of different things could have caused a 6 Sigma detection of something radically different than what you claimed it was.

Fraser: And so then based on that, you know, this sort of reliance on 6 Sigma and, etc…what is a way that you could sort of decide if something is sort of complete and total nonsense, right? Just by hearing the vaguest hint of it, you know, what is the thing that a scientist depends on, which a pseudo-scientist will avoid at all cost?

Pamela: If the person doesn’t have error bars on their measurement, they probably don’t know how accurate or precise their measurement is, so you need to have error bars. The experiment needs to have been done more than once, and all because something’s published, doesn’t mean it’s been done more than once. The research journals are completely filled with experiments that were done once, written up, published, and never repeated again, or when they were repeated, didn’t get results, and therefore the null results that came in the future were never published because you don’t publish null results.

Fraser: [missing audio] You should.

Pamela: I know you should, but that doesn’t mean people do. So you need error bars and you need repeatability.

Fraser: So if you could, like, ask some pseudo-scientist, “Let’s see your error bars.”

Pamela: Yeah.

Fraser: If there are no error bars show up… OK, so let’s say they do have a working understanding of statistics, and they’re able to provide you with some error bars, what would you want to ask for next?

Pamela: Well, then you’ll have to start critiquing their experiment. You have to start saying, “OK, did you take into account this? Did you take into account this? Did you take into account this?” The first…what we thought was a detection of a planet going around a pulsar turned out to actually be just forgetting to take into account the Doppler shift of the planet Earth, and so you have to be very careful in how you design your experiments. And if someone has what sounds a like a phenomenal result, you have to make sure they didn’t just rediscover a systematic effect that was there and had nothing to do with what they thought it was.

Fraser: And is that the real value of the peer review process is to look for those error bars for starters, but then to, you know, hammer on each piece of the experiment to find out what’s right and what perhaps could have introduced some error?

Pamela: At the end of the day, none of us remember everything every time, and this is where collaborators help keep you honest. If you have a good collaborator, they’re going to go, “Did you think of…? Did you think of…?” And it’s a harrowing experience if you have a really good collaborator because they will basically beat you up to make sure you thought of everything, but you want a collaborator like that, first because they’re friendly, and then once you and your collaborators have gone through the “Did you think of…? Did you think of…?” peer review should do the next step of “Did you think of…? Did you think of…” and only if you can answer yes, or answer, “This is how it would effect it” to all those “Did you think of’s.” Peer review should help that happen and that’s where good science comes from is that dialogue of “Did you think…?”

Fraser: Well, I think that about wraps up this week. Thanks a lot, Pamela.

Pamela: My pleasure.

 

Show Notes

• Sponsor: 8th Light
• Google+: Pamela and Fraser
• CosmoQuest
• CosmoQuest Hangouts
• Moon Mappers
• Schrödinger’s Cat — Cornell
• An interactive Schrödinger’s Cat
• Video of Schrödinger’s Cat — Minute Physics
• Quantum Mechanics — Stanford
• Boltzmann Equation — Wolfram
• Observations Affect Reality — Science Daily
• Ep. 140: Entanglement
• Ep. 138: Quantum Mechanics
• Ep. 166: Multiverses
• How Quantum Suicide Works – HowStuffWorks
• Quantum Woo — Rational Wiki

Transcript: Schrodinger’s Cat

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Fraser: Welcome to AstronomyCast, our weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain; I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University – Edwardsville. Hi, Pamela. How are you doing?

Pamela: I’m doing well. How are you doing, Fraser?

Fraser: I’m doing really good. Once again, for everyone listening, we are recording this episode of AstronomyCast as a live Google plus hang-out, and the big innovation that we’ve got this week is: 1) a commitment to a schedule, I think, which is important, so we’re going to be recording AstronomyCast usually on Mondays at 12:00 noon Pacific, 3:00 p.m. Eastern and 8:00 p.m. London time, so if you want to try and catch the recording live, that’s approximately the time that we’re going to be doing it; although we’ll, you know, depending on Pamela’s…

Pamela: There’ll be occasional Wednesdays when I travel.

Fraser: Yeah, your travel schedule, and we’re going to try to get shows done ahead of time to catch up, so that’s the plan. The other cool thing is that we’ve now got a page dedicated at CosmoQuest, which is the, well, we can explain that separately, but at CosmoQuest.org/hang-outs, and so what’s really cool about that is that you can then go to that page, and you can, you know, just a few minutes before the show’s going to start, and then when the show starts, it should just appear in that window and then you can actually watch the show. We’re hoping that we can minimize the amount of: missing the show, or people wondering where it’s going on, or they miss when it started, or…all of that. We’re going to try to make it as regular as possible then, now that we have access to hang-outs on air. Now, Pamela, I don’t think we’ve really gone into CosmoQuest. Did you want to take a second and explain the short version? Because I know that you can take an hour to do this, so give us the short version.

Pamela: So the short version is for a couple of years now, Fraser and I have talked about building a community where people are working on doing astronomy, learning astronomy, and basically recreating the idea of an academic learning research environment – a university, basically, but for everyday people working at home in their spare time. So we’ve talked about figuring out how to get telescope time, we’ve talked about “pie in the sky” getting our own satellite, but at the more simplistic level, CosmoQuest launched, allowing you to basically become part of the science team for the Lunar Reconnaissance Orbiter, and we are also working with the Messenger mission, the Dawn mission and the Hubble Space Telescope, and we are going to be providing you things like this show streamed live, star parties, and ways to do science that gets published and is actually really useful and needed by the scientific community.

Fraser: Yeah, it’s really our belief that regular people who are interested in science who haven’t necessarily gone and gotten their Astrophysics degree and their PhD can still contribute to science in meaningful ways: in identifying objects, in classifying things, and even with, you know, with small telescopes and some of the amazing amateur telescopes gathering light from variable stars, searching for supernovae…there’s a ton of things that regular people can do to get involved in actual astronomical research, and so we’re trying to develop tools that will bring researchers together with the public to participate in science and if things work out, well, maybe we’ll be able to actually change some of the ways that science gets done — so I think it’s pretty exciting.

Pamela: …and the way science gets learned. No longer do you have to get signed up for the $1000-credit-or-more university classes. We’re going to be providing you classes right here on CosmoQuest as well.

Fraser: Yeah, so again — great big experiment, and it will take us a while to figure all the pieces out, so if you want to join us you can go to CosmoQuest.org and you can actually sign up, and you can see some of the tools. What do we have right now? We have the Moon Mappers?

Pamela: We have Moon Mappers is “live,” we have Wikies in place but not yet populated with content. The goal is to get information on how to reduce NASA image data. We have lots of content. We have a blog, we have a forum, and if you have ideas for what you want to see, get on the forum and tell us what you want to see, and we’ll work to make it happen.

Fraser: Yeah, but the big one, I mean with the Moon Mappers, people can actually classify objects on the Moon, and that’s used by researchers. So this is some real science happening.

Pamela: And the other thing that’s most important is with Moon Mappers you can fix the output of computer algorithms, so what we’re trying to do is determine what is the most effective way to map the Moon: computers, humans, or some combination of both. And you can be one of those data points that helps us figure it out.

Fraser: Alright, well, let’s get on with today’s show, but you’ll be hearing a lot more about CosmoQuest as we sort of flesh it out more.

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Fraser: Alright, so you’ve probably heard of “Schrodinger’s cat” — that strange thought experiment designed by Erwin Schrodinger to show how the strange predictions of Quantum Theory could impact the real world. No cats will be harmed in the making of this episode – maybe.

Pamela: [laughing] There are no cats near me. Fraser may have a cat; it’s up to him to harm a cat if any cats are going to get harmed.

Fraser: Maybe, maybe, maybe…it’s uncertain. It’s uncertain what will happen in this “multiverse.” Alright. So then, where do you want to start? Let’s just start with the, sort of, the Schrodinger’s cat thought experiment as initially described by Schrodinger. How do you describe it?

Pamela: So the best way to describe it is a thought experiment designed to mock a scientific concept. A lot of people really struggled with Quantum Mechanics while it was being developed, and in fact a lot of people still struggle with Quantum Mechanics.

Fraser: What do they say? Those who say they understand Quantum Mechanics don’t understand Quantum Mechanics.

Pamela: Something like that. So Schrodinger came up with the thought experiment of: say you’ve got a cat — a nice, big, tangible object — you put it in a box, you can’t see inside the box, you can’t hear what’s inside the box, cat is now in a box, you assume that it can breathe, it can eat, it can do all the catlike things it needs to stay alive under normal conditions, but then you put with the cat something that undergoes a Quantum process (in this case, radioactive decay), and all Quantum processes are described through probabilities, and one of the ideas of Quantum Mechanics is until you observe something, it’s in all the probability states at once. So if you have a material, and you’re not sure if it’s decayed or not, well, until you look at it, it has both decayed and not decayed. And this idea that something can be in multiple states at once led Schrodinger to basically say mockingly, and this was all meant mockingly: “The cat is both dead and alive inside the box.” And what’s great is what started out as a way of scoffing the idea has since turned into the way we describe it.

Fraser: Well, so let’s unpack that a bit then. When we say that the cat is both dead and alive, that particles decay and don’t decay, what is the sort of Quantum Theory that’s underpinning all of that?

Pamela: So in this case, we’re talking about the probability tied to radioactive decay. We could just as easily be talking about the Quantum probabilities that a given atom will be in a specific energy level. Lots of different things are…

Fraser: Right, photons going through the slit experiment…

Pamela: Right, so lots of different things are guided by a probability, and the thing is you can’t know a priori — you can’t know ahead of time which atom is going to behave in which way, and because it’s probabilities, there’s always the chance nothing’s going to behave in a certain way, so imagine the radioactive isotope polonium-210; this is an isotope that periodically gets used to murder people because it has 138-day half-life, it gives off a whole lot of energy in the process of decaying. It’s rather potent stuff. Now, if you happen to have, say, about 280 atoms of this on any given day, one of those atoms should decay, and after 138 days, well, half of those atoms should have decayed, but that’s a probability — it’s only a probability, so it could be none of them ever decay, it could be all of them spontaneously decay, it could be that they go off in dribs and drabs where 20 decay in one day, 0 decay in the next several days – it’s all defined by probabilities. And according to Quantum Mechanics, until you observe what happened, everything has happened, and all of those different possibilities co-exist at the exact same time until the observation is made.

Fraser: So how…that’s the weird part, right? I mean, you can take it back to the cat idea, and you can put the cat in a box, and you’ve got particles that decay and…but what is the…what is this process of, you know, “until you observe it?” How…you know, what does that mean? Until you observe it, you don’t know that the thing has happened?

Pamela: So with Quantum Mechanics, stuff (atoms, cats, particles of all different types) exist in wave functions, and all of these different wave functions are said to be interacting with one another, and if you’ve ever been in a room with really awesome acoustics, you’ve walked around maybe speaking or humming to yourself trying to find that sweet spot in the room where all the echoes come back and add together to increase your voice, or walked around looking for that place where when you hum you hear no echoes coming back…well, what you’re hearing is all the waves interacting with one another. Well, in Quantum Mechanics, you have all the different wave functions for all the possible things that can happen, and they’re all resonating together, but you don’t actually hear: Are they growing? Are they killing one another off? You can’t hear the result until you listen, until you make the observation, so all the possible outcomes: the echo that builds the sound up, the lack of echo that is the dead spot in the room — all those possibilities simultaneously co-exist in wave function, and it’s through making the observation that you determine how the waves at this particular moment have collapsed down into reality.

Fraser: And when you say “making an observation,” what are the kinds of things you can do to make an observation?

Pamela: Well, so with an atomic radioactive decay, you look to see which atoms are in which state, so it’s literally a matter of looking to see so how much of the polonium-210 has decayed into lead-206, and so it’s in that atom-counting stage that you make the observation, or alternatively, you can have a detector for alpha particles. These are the high-energy helium nuclei that get flung off in the radioactive process, so you can look for that helium nuclei flying off, and that’s another way of making an observation, or for the cat — you open the box.

Fraser: Right. OK, and so then as Schrodinger sort of originally described this experiment, what are the pieces of the puzzle that he, sort of, in his joke, I guess, the way he put it together because I know its kind of morphed into other things since then, right?

Pamela: So for Schrodinger the idea was you take a cat, a healthy, nice cat, you put it in a box that will generally preserve its life, and you put in the box with the cat something radioactive that is going to undergo a radioactive decay, and you put with it something — a Geiger counter, some manner of detecting the radiation that is given off during that decay process in there with the cat, and you attach to that decay detector a vial of poison, and the second the detector detects a decay, it releases the poison and the poison kills the cat. So the idea is that the entire system is one convolved set of wave functions, where at any given moment, the wave functions that describe all the different possible states of all the different possible atoms are causing the cat’s wave functions to be in states of dead or alive all at the same time…that it all gets entangled together until someone external observes the system and goes, “Cat is dead; therefore, detector detected nuclear decay process; therefore, something decayed.” Now, the reality is the cat does observe its own death; it knows when it died (or the autopsy will determine that), but it’s still one of those “Oh, that’s kind of freaky!” kind of things.

Fraser: So before the observation was made (but I guess that’s the point, right?)…is the cat made the observation, but I guess the way the thought experiment is going is before the experimenter opens up the box, or takes a look to see how the wave has collapsed, the cat is both alive and dead at the same time.

Pamela: Right. And this applies to lots of different systems, so you have it applying for radioactive decays, you also have this applying to the distribution of atoms in different energy states, so for instance, if you grab a neon “Open” sign, it’s not always filled with neon gas, but this tube of gas that glows red, green, whatever color it is when it is that it glows when it says, “Open-Open-Open,” the individual atoms in that aren’t all at the exact same energy state all of the time, and there’s an equation called the Boltzmann equation that looks at the temperature of the gas, looks at the density, looks at a lot of different things and says “How many of the atoms are going to be in each of the different energy states?” But it doesn’t say which atom is in which state, so you have to observe the individual atoms to get at, “OK, did you fall into this probability? Did you fall into this probability?” And so there’s all these different things that follow probabilities, but we can never say which atom behaves in which different way.

Fraser: But how is it different, practically, from the thought experiment? I mean, I know that if you put a cat into a box and did this experiment for real, I mean: 1) you’d get a call from PETA, but 2) you would…

Pamela: Yeah, don’t do this experiment.

Fraser: You don’t do this, but it also wouldn’t work — for real.

Pamela: So the for real problem is while all of the atoms do have all of these different states, the fact that you have the detector making the detection means you know whether or not something happened, and that detector is making the detection. Now, one of the interesting things there’s a Quantum Mechanics paper a few years ago that basically said simply by being in existence and observing our universe, we’re changing the quantum state of the Universe just by observing it, and every time we observe it, we reset the probabilities on different things, so at a certain level, we’re not entirely sure where this breaks down and where it doesn’t. We just know that things are dictated by probabilities and that observing things screws them up.

Fraser: And so then, what is the, I guess, what is actually going on? Like, if this was designed, this thought experiment was designed to highlight how weird Quantum Mechanics is, but what are the implications for this thought experiment in sort of Quantum Mechanics itself?

Pamela: Well, one of the interesting things is you can actually use this to look at how light changes as you pass it through a variety of different polarizers. So you can take a beam of light and pass it through a filter, and all of the light downstream from it should have a given polarization, but you can reset the probabilities through the stream as you go, and there’s lots of creepiness that creeps in. The other thing is you can send atoms, or electrons, or just individual photons of light through a single slit, and as they go through the single slit, their positions where they land they move around and land in different places based on the assumption that they go through as a whole stream, and the most likely place they’re going to land, due to interfering with one another, is in the center of the screen, but those interference patterns cause them to sometimes go off to the left, go off to the right, and build up this what’s called a “fringe pattern,” an interference pattern. Now the thing is you get the exact same pattern if you send 10,000 photons through, as if you send one photon through at a time 10,000 times, so somehow, and we’re not quite sure how, the photons, the electrons, the atoms (I think this has actually been done with Buckyballs now)…they know what their probability distribution is, and it’s like they interact with all of those atoms, or molecules, or whatever that haven’t gone through yet, and so the Universe is simply proving it’s weird over and over and over again, and allowing us to know all these wave functions are out there waiting to interact with one another.

Fraser: There’s a couple of shows that we’ve actually done in the past that people might find interesting. We’ve done a whole episode just on “entanglement,” which is I think what you’re talking about here, we’ve also done one on Quantum Mechanics, and we’ve also done one on “multiverses,” but I think it’s multiverses that there’s a lot of really interesting overlap with the Schrodinger’s cat experiment, and, you know, what could be a possible explanation — a way to resolve it, right?

Pamela: Yeah, so trying to understand, “what exactly does this mean?” leads to a lot of, well, head-scratching, a lot hair-pulling as well, and occasionally, students crying over their homework assignments. One of the interpretations of this is what you’re actually seeing is when something passes through a slit, it takes every possible option, and it’s interacting with itself. Another way of looking at it is through all the different multiple universes that might be out there. We don’t know if we’re single universe or many universes. Every possibility is being realized, so in one reality, the photon goes straight through and hits in that most probable sweet spot, in another universe it goes through and goes all the way to the left, so every possibility is being realized and it’s just a matter of, well, which universe are we in? And what we see just depends on the flip of the coin of which reality it is. Now this means on a macroscopic reality, if I woke up this morning and got out of bed, I could have simply did as I did and actually stand on the floor and make it out of my bed and out of my bedroom, but in another reality I might have put my feet on my dog as I got out of bed, and had the dog explode, and landed on my butt, and had to be taken away in an ambulance. Everything that could happen does happen in a universe, in this multi-universe, is another argument that quantum mechanics…

Fraser: And I guess to take it back to Schrodinger’s cat, the cat in one universe is alive, and in another universe it’s dead.

Pamela: And this leads to the one possible way of testing if we’re in a multiverse or not, which no one should ever do, and this is the suicidal scientist experiment, where you put a scientist in a box instead of Schrodinger’s cat, and there’s going to be some universe where the rules of probability are such that, well, while half of those atoms should decay in a half-life, that doesn’t mean any of them necessarily are going to, and there’s this infinitely tiny probability that if you put someone in a box with radioactive material, none of it is going to decay as it’s supposed to, it’s an infinitesimally small probability, but that means there’s some universe out there where you put that scientist in the box with the polonium 210 with its 138-day half life and 138 x 5 days later, still nothing has decayed, that scientist is still alive, and that means that that scientist is in the one universe that beat the odds, that did that tail-end of the probability distribution. That means in every other universe, though, that poor schmoe is dead, so don’t do this experiment, but it’s the only way we’ve come up with to test the multiverse theory.

Fraser: And so have other thought experiments been put together? I mean, you’ve got that one of the suicidal scientist. Are there any other thought experiments sort of in the same vein as Schrodinger’s cat?

Pamela: Well, those are the main ones. At a certain point you start getting into Quantum entanglement, which we’ve done shows on as well, where you start looking at, “OK, these two things both were emitted in the same experiment. That means that if this one has these set of states, that one has to have that set of states in order for the properties to be preserved, let’s observe them switch and see if we can prove that these suckers stay tied together,” and so then we start getting to messing with the Universe, and it stops being thought experiments and it starts actually being “let’s shoot photons of light down fiber-optics as far as we can to see if we can keep two different photons entangled for as long as possible.”

Fraser: And we can.

Pamela: And we can.

Fraser: Well, not “we” obviously…

Pamela: Other people — I just read the papers. It’s really amazing because as much as people dislike Quantum Mechanics, and what’s strange to me is we get letters all the time from people saying “Relativity is wrong.”

Fraser: Relativity is wrong…yeah.

Pamela: But we don’t get the same ones for Quantum Mechanics. Instead we get the “Quantum mechanics is my religion,” and I’m not quite sure why people get upset about Quantum Mechanics making their stomach and their head hurt, but then embrace it as a religion; whereas, people find Relativity makes their stomach hurt and their head hurt, and therefore they reject it and come up with alternative non-mathematical theories, but for whatever reason, this weirdness, this probability distribution way of describing the Universe is readily embraced by a lot of people out there as, well, “It’s just the probabilities that I had a bad day.”

Fraser: Yeah, we call that “Quantum Wu” when a person takes Quantum Theory and sort of embeds it in their own alternative theories about how the Universe works.
Deepak Chopra does that a lot.

Pamela: Yeah, there are a lot of people try and use Quantum Mechanics to justify belief in a lot of things like telepathy — and we reject that concept.

Fraser: Alright. Cool! Well, thanks a lot Pamela. That’s one of those topics that we get a ton of email from people wanting us to explain it. And, I wonder why people find that…this thought experiment so fascinating.

Pamela: The idea of a cat that is both dead and live is just visually awesome, and sometimes all you need is that thought experiment that has that cool visual, like the twins that age differently from General Relativity. You just need that cool visual that goes on a t-shirt.

Fraser: And so I guess if you’re a physicist and you want your theory to last into the future that everyone’s going to reference, you got to figure out a way to really make it pop.

Pamela: A great thought experiment with a great cartoon sketch.

Fraser: Yeah, then you’re set. That’s great. Alright. Well, thanks a lot, Pamela, and we’ll talk to you next week.

Pamela: Sounds good, Fraser. I’ll talk to you later.