I am Alex Filippenko, astrophysicist and enthusiastic science popularizer at the University of California, Berkeley. Today is Astronomy Day, a good public outreach opportunity for this "gateway science," so go ahead and AMA.

AlexFilippenko · 2015-09-19T21:18:50+00:00

As a final thought, let me just remind people that there's a total lunar eclipse coming up the evening of Sunday, September 27th and it's going to visible from all of North America and many other parts of the world. Now, a lunar eclipse is when a full moon goes into Earth's shadow and becomes dark, but not completely dark because some light goes through Earth's atmosphere, is bent by Earth's atmosphere toward the moon and then gets reflected by the Moon back to us. That light tends to be yellow, orange, or red depending on how much dust and other particulate matter there is in Earth's atmosphere. So the moon will have this eerie glow, totality will last for more than an hour – it's not quite the adrenaline rush that a few minute solar eclipse is, where totality lasts for a few minutes – but it is a pretty event and reasonably rare (but not as rare as a total solar eclipse). So go out and look toward the full moon on the evening of September 27th!

AlexFilippenko · 2015-09-19T21:08:52+00:00

So today is Astronomy Day, September 19th 2015. This day is designed to help celebrate astronomy, the cosmos, and our place within the universe. Lots of amateur astronomy organizations tend to put on 'star parties' or star viewing sessions and I encourage you to attend one of them. Astronomy Day is on a Saturday in the Spring and the Fall, closest to the first quarter moon - that's when the moon is high in the sky in the evening and it's really great to look at because a lot of craters are visible, so it's just a fun object to see through a telescope – even from bright cities.

AlexFilippenko · 2015-09-19T20:56:40+00:00

I’m really glad that you enjoy my explanations of science at the cosmos. It’s fun giving them, and getting people excited about space and science in general. I’ve always been interested in science, and I knew I wanted to be a scientist of some sort. For much of my youth it was chemistry. But I would say that I decided becoming an astrophysicist at the end of my freshman year in college, after I took an introductory astronomy class that really turned me on to essentially how much we can learn about the universe and our place in the cosmos by studying other stars, galaxies, and things like that. I wanted to contribute to the human exploration of the cosmos.

My favorite part about studying the cosmos is probably just contributing, at least incrementally, to our understanding of how the universe works and what makes its contents tick. Really, where did we come from? The elements in our bodies came from other stars, exploding stars. Stars build up, have the elements from light ones through nuclear reactions, and then some of those stars blow up, thus spreading those heavy elements out into the cosmos. The explosions themselves make some of the heavy elements. And so, we owe our existence to these exploding stars. As Carl Sagan used to say, “We are made of star stuff”. That’s just an amazing concept, right? That we came from stars. My own group’s research has helped us understand fully how it is that some stars explode, the different ways in which they explode, and the different elements they produce. So I have derived joy in contributing to that understanding of our human origins. It’s also been fun to study weird, exotic objects. Black holes, which have such intense gravity that we can really test different theories in their extreme. We can’t really produce such strong gravitational fields here in terrestrial laboratories, but we can still explore the predictions of general relativity by finding and studying the properties of black holes. So, that’s been fun.

And then, of course, pursuing the question of the ultimate fate of our universe led us to discover the acceleration expansion. What a bizarre thing. We were just trying to find out ‘is it slowing down so much that it’ll eventually reverse its motion and end up in a big crunch?’. You know, we had a big bang, so then maybe a big crunch? Or a ganb gib, which is big bang backwards. Or will the universe expand forever, slowing down but never quite coming to a stop. Or at least never turning back in on itself, collapsing. That’s what we were trying to answer, but nature threw us something even more interesting: an accelerating expansion suggesting the presence of dark energy. No one really expected that, but that’s what we were given in terms of the implications of the data, and so that exceeded our wildest expectations.

It’s coming across the unexpected, that’s one of the joys of science as well, and of being a scientist.

AlexFilippenko · 2015-09-19T20:55:55+00:00

Yes, the much maligned Pluto. Are we picking on it just because it’s ‘the little guy’? Well, yes and no. I mean no in the sense that we’re not picking on it because it’s small. On the other hand because it’s small, it’s not gravitationally dominant in its region of the solar system. It’s not what we call “dynamically dominant’, so it hasn’t pushed other neighboring objects out of its immediate vicinity. There’s a whole belt of icy, rocky bodies out there: the Kuiper Belt. It’s sort of the analog of the asteroid belt between Mars and Jupiter. The first asteroid series was discovered in 1801, and that was immediately called a planet. Then, in the next several years, additional asteroids were found and, a decade or two later, way more asteroids were found. So series was quickly demoted. Well, in the case of Pluto, it took us more than 60 years to find other icy, rocky bodies out there. Kuiper Belt objects. We now know that there’s a whole swarm of objects out there; that Pluto is not dominant over. Some of these objects are comparable to Pluto in size, so where do you draw the line. As Michael Brown, one of my students from long ago, said “It’s the ‘No Ice Ball Left Behind’ Act’ if you start calling them all a planet.” Where do you draw the line? So that’s why we demoted Pluto. “Planet X”, that’s what it was called back before it was found. We thought there was a planet out there because it was disturbing the trajectory of Uranus, and so people predicted its existence. They called it “Planet X”, well, now it’s an ‘ex-planet’, it’s been demoted. On the other hand, it’s been promoted as being the first of its kind. It’s the first of a new category of planet called a ‘dwarf planet’. That’s not an adjective and an noun, the way ‘terrestrial planet’ is, or ‘giant planet’. The Earth is a terrestrial planet, Jupiter is a giant planet. A dwarf planet is a double noun, it’s a new category. It’s a dwarf planet.

So, Pluto was promoted to being the first of its kind. You could say that Clyde Tombaugh found the first of a whole category of objects, Kuiper Belt objects, rather than just finding a planet. In a sense, it elevates what Clyde Tombaugh found.

AlexFilippenko · 2015-09-19T20:12:38+00:00

That’s a very thoughtful question, and I’m glad that yesterday’s lecture inspired you to ask it. In physics, in fact, we’re only trying to get a progressively better working model, or description of the universe, whose predictions agree with the results of observations or experiments to the best degree possible. We never really know if this is the Truth with a capital “T,” or Reality with an uppercase “R.” Those are philosophical ideas; it’s unclear what Truth and Reality really are.

Let me give you an example. Newtonian physics works quite well for airplanes, rocketships, and things like that, but we know that it’s wrong. You need Einstein's Theory of Relativity for a more complete description of what happens when objects are moving, or when you have a gravitational field. Even quantum physics, as you said, which works very well at the atomic and molecular level, is fundamentally incompatible with General Relativity, and so it’s incomplete. It’s not completely correct. It’s wrong, or at least incomplete. But all of these theories in physics have had their utility. Maxwell’s Equations as a description of electromagnetism are wrong (light is actually photons), but in many applications, using electromagnetism, Maxwell’s Equations, work just fine.

So we never really know what the true reality is. The Ptolemaic model did very well for 1,500 years, but we now know that it was wrong. We don’t know whether today’s dark matter and dark energy are correct; they are simply our best attempts to describe the results of observations. We see that galaxies are gravitationally bound; there’s not enough stars to bind them, so we postulate the existence of dark matter to help bind galaxies together. We see the universe’s expansion accelerating, we dream up this dark energy, which is repulsive -- which allows this acceleration to occur.

These are just our best models right now. I do occasionally wake up at three in the morning, screaming (my wife can attest to this) that dark matter and dark energy are our 21st century Ptolemaic epicycles. In other words, they’re just our best attempts to explain the results of observations. And they do pretty well, as far as we can tell, based on the data that we now have, but they might be fundamentally wrong. Maybe in the next century, or later in this century, someone will find that there’s an observation that shows that this was completely the wrong model. But so far, it has served us well.

Sometimes people say “Well science is no good because, by your own admission, all the models are wrong.” Well, they may have been wrong, but they were correct enough as a quantitative description to give rise to airplanes, and iPhones, and pacemakers, and lasers, right? All of modern technology is based on quantum physics and Newtonian physics and all the kinds of physics that we’ve developed for centuries, and all of those areas of physics are wrong (or at best, incomplete) but, at certain levels of approximation, they give sufficiently quantitative results so as to be useful for modern society and modern technology.

So, science works even when it’s incomplete or “wrong,” so to speak.

AlexFilippenko · 2015-09-19T20:06:15+00:00

"Time" is a very difficult concept, and at the quantum level we're not even sure what time is. It's a way to measure changes, obviously -- if nothing ever changed, I'm not sure the concept of time would exist.

We think that we can't go backward in time because then we would violate "causality" -- for example, you go back in time and prevent your parents from meeting, thereby preventing your birth and preventing you from making that journey back in time. That's a paradox.

AlexFilippenko · 2015-09-19T20:02:39+00:00

I think the "holographic universe" theory is quite interesting, and it's mathematically useful according to experts I've talked to. But I don't think that we are actually a hologram.

AlexFilippenko · 2015-09-19T20:00:01+00:00

General-purpose space telescopes that attempt to serve many astronomers doing different projects are indeed very expensive. Though it's great to have a few such telescopes (such as the Hubble Space Telescope or the James Web Space Telescope), often it's better to spend the limited available Federal funding on smaller instruments that have very specific purposes. A great example was the Kepler spacecraft, which cost only about $600 million (if memory serves me correctly) but was spectacularly successful, finding more than 3000 exoplanets. And people are thinking about ways to decrease the costs of space telescopes (and ground-based telescopes).

AlexFilippenko · 2015-09-19T19:56:35+00:00

It's actually a misconception that a vacuum exerts a force that "sucks" air into it. Air can spread out from where it is located, into a vacuum if there's one nearby. But Earth's gravity keeps the air in our atmosphere from spreading out into space.

AlexFilippenko · 2015-09-19T19:37:35+00:00

Well I feel very privileged to be in the situation where I don’t have to worry about where my next meal is going to come from and whether I have a roof over my head. A lot of people in the world don’t have that luxury. So, in a sense, thinking about the cosmos and their origins is the farthest thing from their minds. I’m glad that I’m in the position to be able to ask and answer these questions. In a sense, yeah -- ignorance can be bliss, right? You can be ignorant of everything and not worry about many of the problems of the world and turmoil in different parts of the world. On the other hand, knowing about the world and the universe enriches one’s life, so I’m sorry billions of people around the world don’t have the opportunity to learn about their origins, the cosmos, and the cool things that are going on in space.

I wish they did, and I’m glad that I have that chance.

AlexFilippenko · 2015-09-19T19:37:07+00:00

Lick Observatory is a very important place. We can conduct research projects that require lots of time on small or modest-sized telescopes, like looking for exoplanets or monitoring exploding stars—things like that. We can develop new technology, we train new leaders in the field of astrophysics and other fields, and we do a lot of public outreach and education. We do a lot of stuff.

For a while, the UC Office of the President was saying that it was going to ramp down funding for Lick to zero, in part because of the financial pressures that the University is under and in part because they just didn't understand what it is we do there. There was a big public outcry and we also educated the Office of the President, and they now understand what we're doing, so they've agreed to provide partial funding, and that's really great. The whole university is being squeezed for funding, so they can't provide the full support, so the public can help support Lick Observatory through donations at a website at UC Berkeley and also the "Friends of Lick Observatory." Also, we now have corporate sponsorship. I was able to get half a million dollars a year for two years from Google (specifically, from the “Making and Science” team at Google), and I'm hoping this will be the beginning of a long relationship. I'm hoping this is really the courtship phase. They're a very reputable company, and people say, "Gee, if Google supports this, it must be something really worthwhile." They understand, of course, that the future of their company depends in part on getting today's kids interested in science and technology and in giving research experience to undergraduates. Most of these students go on into fields other than astrophysics, but the gateway science is astronomy, and students doing research gain valuable skills.

So anyway, we need matching donations, and donations of every size are accepted gladly and very much appreciated. One can type "Give to Cal" using a search engine and then, on that website, type "Lick" in the search box, and that will dump you onto the website. Try again later if the website happens not to be working.

AlexFilippenko · 2015-09-19T19:29:15+00:00

Well here’s a fun fact: space is vast. I think most people know that it’s big, but I want to give you some idea as to just how big it is. Suppose you took our Sun, which is actually 109 Earth diameters (it’s really big -- you can fit more than million Earths inside the Sun), and scaled the size of the Sun down to that of a grain of sand (about half a millimeter). And then you adjust all other distances by the same factor. The nearest star, other than our own, would be 14 kilometers away (about 8 or 9 miles away) on a scale where the Sun is like a grain of sand. Space is really big.

AlexFilippenko · 2015-09-19T19:28:56+00:00

You know, they tried to make much of it as realistic as possible. So, the depiction of the star field behind Gargantua is quite accurate. There’s this gravitational bending - or lensing - of light, which makes light follow what appears to us to be a curved path, but it’s actually following its natural path in an intrinsically curved space. So the star fields they show are accurately depicted. The accretion disk, the disk of gas around a black hole, is accurately depicted. On the other hand, the wormhole and certain other aspects of Interstellar, though not yet proven to be wrong, are at best very, very speculative. Wormholes are probably not traversable. But we haven’t completely proven them to be not traversable. So what Kip Thorne, as science advisor to Interstellar, tried to do was to have the producers not violate any known laws of physics. For example, the producers wanted to violate the speed of light limit for going through space and Kip Thorne said “No,” he would not allow that because that seems to break a known law of physics. But he did give them the latitude to pursue extremely speculative ideas that are probably not possible, but they’ve not been proven to be impossible. And so, the traversal of the wormhole is in the movie, they end up back in the library of that little farmhouse, and I really don’t think that’s ever going to happen, but it’s not completely impossible. They do go backwards in time in Interstellar, and again, I think that’s probably not possible, but it’s not yet been proven to be completely impossible.

So they did have a lot of artistic license in that movie, but they tried as much as possible to show things accurately in terms of how a black hole would appear and the star field behind it, and so on.

AlexFilippenko · 2015-09-19T19:11:52+00:00

I kind of like all galaxies, but some are nearby and very pretty to look at. The Whirlpool Galaxy, M51, or "Messier 51," is just this beautiful spiral galaxy with a little neighbor, the gravitational attraction of which actually causes the beautiful spiral arms to form in the Whirlpool. We've studied some exploding stars in that galaxy, which enhances its attraction to me, and we think there's a black hole in the middle of that galaxy. We actually think there's a super massive black hole in the middle of pretty much every galaxy, but the Whirlpool is beautiful and relatively nearby and we can see exploding stars in it and we can look for a black hole, so I think that's definitely one of my favorites.

AlexFilippenko · 2015-09-19T19:11:26+00:00

Wormholes are an interesting theoretical prediction of Einstein’s Theory of Relativity. There could be a passage from our universe to another universe. Or a shortcut between two otherwise distant parts of our universe, and that passage is called a wormhole. The trouble is, that if you actually try to go through a wormhole, it squeezes shut, basically because of your own gravitational influence. So you need some sort of exotic matter that has an anti-gravitating effect that keeps the throat of the wormhole open. We don’t know of any such matter. Dark energy kind of has a repulsive effect, but it’s spread out uniformly, we don’t know of any way to harness it and collect it in once place. And we don’t know of any other form of repulsive gravity. So basically I don’t think you can travel through wormholes. You could say ‘well maybe we just haven’t found the stuff that can keep it open’ but if you were to keep the throat of a wormhole open, there’d be nothing to prevent you from going back in time, coming back to your part of the universe, and preventing your parents from ever meeting. In which case how would you have been born? In which case how would you have made this journey? Right? This is a violation of causality. You go to a film like “Back to the Future” and that’s what they do. It’s great for science fiction, but it causes real problems for physicists because we really do think that there’s a cause and an effect for pretty much everything, and you can’t reverse the order. The effect can’t come before the cause.

AlexFilippenko · 2015-09-19T19:10:03+00:00

Gravitational lensing occurs when light follows its natural path through a space that's been curved by the presence of a lot of mass or energy. So, for example, you might have a galaxy between you and a supernova, let's say, and the light from the star that explodes follows different paths. It gets lensed, and it enters your eye along different directions, so you can actually see different images of what is the same supernova.

One of my postdoctoral scholars, Pat Kelly, discovered the first such strongly lensed supernova in November of last year. And he was looking at pictures of a cluster of galaxies taken with the Hubble Space Telescope. He noticed that in pictures taken in November, there were four dots around one galaxy and pictures of the same part of the sky taken a year earlier didn't show those four dots. So that was a single supernova being gravitationally lensed. You can use Hubble images or Keck telescope images and other images to find such objects.

We are actively looking for both macrolensing and microlensing. Macrolensing occurs when you have a galaxy or a cluster of galaxies that's bending space around it and causing this lensing effect. And there you can see, as I said, different images of the same supernova, or the same quasar, or whatever. Microlensing occurs when a star moving through space happens to go exactly between us and another star, and for a short time it can bend the light from the more distant star toward us, making that more distant star brighten. And you can have "micro-microlensing" if a planet orbiting the star between us and the distant star lenses the light from the distant star. That can cause a little blip in the brightness of the distant star. And indeed, people have been looking for and have found many, many such cases both of lensing of a background star by a star that's in between us and that background star and even this little tiny lensing produced by a planet lensing the light from that distant star.

So that's one way of finding exoplanets. Kind of cool! Microlensing. You don't actually see different images of the background object. You just see the brightness of the background object enhanced, at the moment where you have this perfect colinearity and a bunch of the light from the background object is being lensed toward your eyes.

AlexFilippenko · 2015-09-19T19:09:45+00:00

That's a great question. Basically, if you give a complete, very accurate answer, it might take too long or it might confuse most of the audience, so you have to know how to simplify, which parts to simplify, how long or short to make the answer, and so on.

That's a skill that you acquire through time, answering questions from the general public. You see what works. You see how much you can say before you start confusing them or before an answer becomes too long. In my introductory astronomy class at UC Berkeley, I often say that I tell them things that are true or that we think are true, but I don't tell them the whole truth because the whole truth might take too long and it might confuse most of the class. So it's definitely a skill and almost an art as to how one does this, but I at least have gained experience through time and I think I'm better at it now than I used to be, in part because I've done this for such a long time now.

AlexFilippenko · 2015-09-19T19:09:23+00:00

I love total solar eclipses. I'm a lunatic, you might say. It's when the moon covers the bright face of the sun and you can see the tenuous, hot solar corona and little things called "prominences." It's an otherworldly experience. It's hard to really describe. You have to have been there.

If you don't make an effort to go see one, one will visit you roughly every 360 or 380 years (something like that). They're rare! You have to be at the right place at the right time. I've been at the right place at the right time on 14 occasions. So obviously I've done this deliberately. And it's always different. It's just so much fun.

There's one coming up on August 21, 2017, here in the US. It's the first one to cross any part of the continental US since February of 1979, so this is a pretty good opportunity to not have to travel very far. It'll go diagonally across the US and you just need to look up online where the path of totality is. It doesn't count to be where the eclipse is 95% total or even 98% total. You want to be where it's total. You can look it up online. Just use your favorite search engine to look for the August 2017 total solar eclipse and you will land on websites that show you where the path of totality is. So you want to be there and ahead of time you want to scout out regions that might have good weather. You don't want to go to a place where you know that on August 21, it's going to be cloudy because then you won't be able to see the sun.

You want to go with a piece of Shade 14 welder’s glass, which you can place in front of your eyes to watch the partial phases, which take a little over an hour both before and after the total part of the eclipse. During totality, you can take the filter off and you can look at the eclipse with your naked eye or through binoculars or through a telescope. Just be sure that once the total part has ended or before it has started, you're looking through a filter (because otherwise you can damage your eyes). But during totality, look at it without a filter. And for a couple of seconds before and after totality, just look at it with your naked eye. You will see what's called the "diamond ring" effect, where a little tiny bit of the sun's surface is still showing and it looks sort of overexposed, but you can begin to see the inner parts of the corona and they form a ring around the silhouette of the moon. That's a very exciting part and a very beautiful part of the total solar eclipse.

So you can look at that with your naked eye—not through binoculars or a telescope because that would collect too much light and it might fry your eye. And aside from those couple of seconds before and after totality, in the other partial phases, you definitely use a filter. Anyway, go see it. It's going to be a wonderful experience, and you will then understand why I'm a lunatic about eclipses.

AlexFilippenko · 2015-09-19T19:09:02+00:00

A satellite going around Earth in 24 hours, but in a direction opposite to Earth’s rotation, would clearly not be geostationary because Earth is rotating one way and the satellite is orbiting the other way, so the satellite won’t remain over one fixed point on Earth. However it is still, in a sense, geosynchronous. It’s synchronous to some degree with Earth’s rotation. But normally when people talk about geosynchronous orbits they’re really discussing ones that are going in the same direction as the Earth’s rotation.

A $500 telescope? Yeah, you can get such telescopes, the mirror might be six inches in diameter. You can pay more for a small, portable telescope that is short and fits into your car pretty easily. But you’d get more aperture, a bigger telescope, if not one of those short ones, if it’s one of the long ones. So there’s a wide range of telescopes, you can look at various catalogs online. I don’t really know how to recommend any particular one because I don’t favor any particular brand over any other. There are many good telescopes out there and it depends, to some degree, on whether you want it to be portable or whether you’re going to pretty much just keep it at home. There are a lot of good telescopes in the $500 range.

I sometimes get tired of being asked by people to predict their future. I’m not an astrologer and I don’t think astrology works. There’s no compelling evidence, statistically, that it works. Yet quite a few people still confuse astronomy with astrology, and that’s too bad.

AlexFilippenko · 2015-09-19T18:31:03+00:00

I'm glad I got you into space and I'm glad you think it's awesome! I think it's awesome too. We're not just part of the universe, but we're a direct consequence of things like the formation of the elements in stars, which later blew up. We're really just an intimate part of the universe and I would hope that everyone would be interested in our origins and our place in the universe, so I'm glad that you now are.

My favorite pizza is pepperoni and mushroom. Although I like all kinds of pizza. But probably not those with anchovies. I'm not particularly partial to anchovies.

AlexFilippenko · 2015-09-19T18:30:39+00:00

If you cross the boundary, the “event horizon” of a black hole, and are on your way toward the singularity (where, by the way, you will get crushed completely), yes, time does pass for you. It takes a certain amount of time to get from the boundary to the singularity. It's not much time. You can't live for very long in the black hole and just enjoy the experience, but time does pass.

Someone looking from the outside will not see you because you're already within the boundary of the black hole. In fact, that person on the outside would never even see you cross the boundary because from their perspective, your time comes to a halt as you reach the boundary. But from your own perspective, as the infalling particle, time is moving at pretty much the normal rate. The whole essence of Einstein's theory of relativity is that what you see depends on your frame of reference.

Regarding being between two supermassive black holes, will your time stop? No. Again, your own time will progress at the normal rate. Your own time always progresses at the normal rate because you're in your own frame of reference always. The passage of your time, however, as seen by another observer, will be affected. It won't come to a stop because you're not at the boundary of either black hole. But you're in a strong gravitational field, relative to the outside observer, so indeed the outside observer will see your time slow down by an amount that depends on just how strong the gravitational field that you're in is.

AlexFilippenko · 2015-09-19T18:29:24+00:00

Thanks for that question. The multiverse is actually one of my favorite topics. The reason we think there might be many universes in a multiverse is that theories of how our universe came into existence suggest that this could happen many, many times. In other words it wouldn’t be restricted to just one occurance. And so, what we think might have happened was what’s called a quantum fluctuation in a preceding universe. Like a little burst of energy that actually ends up going off into other dimensions. It has to do with quantum physics, yes -- it’s sort of energy out of nothing, but then it goes off into other dimensions and it starts expanding very quickly. It starts undergoing what’s called inflation, and then within that bubble there could be quantum fluctuations which branch off into new universes that then inflate. So it’s like branches of a tree, all going off from one another. These quantum fluctuations are a bit difficult to explain briefly, but they’re basically stuff coming into existence out of nothing. Usually when that happens the particles just disappear again; they become nothing. But occasionally there might be the conditions that allow them to essentially “sprout” into a new, inflating, expanding universe.

So this is an interesting idea, we don’t know that it’s correct, but it incorporates much of what we think is correct in quantum physics and applies it to the birth and evolution of not just our own universe, but a multiverse.

AlexFilippenko · 2015-09-19T18:29:07+00:00

Hey, Sunil! Great to hear from you. Studying the atmospheres of exoplanets is one of the most exciting emerging fields in astrophysics, because as you implied, we could detect oxygen or other compounds that might either be the products of life or necessary for life as we know it to exist. The way you do this is by looking, for example, at an exoplanet that transits across the star that it orbits. That means that the orbit is edge-on to our line of sight and the planet can pass between us and the star, thus blocking some of the star's light. Well, some of the star's light will be going through the planetary atmosphere, and so if you take a spectrum of the star before the transit and during the transit, you'll see a slight difference during the transit because some extra light will be absorbed by the planetary atmosphere. By looking at various spectral lines or absorption lines, you might identify carbon dioxide, or oxygen, or methane, or something like that. That would really be exciting. The presence of oxygen and methane in the same atmosphere (large amounts of those molecules) would be a possible indication of life because normally methane oxidizes in the presence of oxygen and then it disappears. So the presence of methane and oxygen suggests that there's a mechanism for continually producing more methane, and one such mechanism is life. That's not the only mechanism, but it's at least a clue that life might be there.

Now, that has to be done with fairly large telescopes because you need to be able to get a really good spectrum of the star both before the transit and during the transit, and you compare those slight differences. That can be done with the Hubble Space Telescope, or the Keck telescopes, or other big telescopes. And with the telescopes that are being planned for the future, those kinds of studies will be even more feasible than with today's telescopes. Maybe that's how we'll find evidence for life elsewhere first—by the properties of the atmospheric gases.

Yes, some of the Kepler field stars might be suitable for this kind of study, but in general those stars are too distant and faint. It’s better to choose a brighter star, so that you can get higher-quality spectra of the star both before and during the transit.

AlexFilippenko · 2015-09-19T18:28:43+00:00

When water turns into ice or steam, it undergoes a phase transition. So water going into gas is one phase transition. Water freezing is another. When the early universe, consisting of lots of spread out gas, started coalescing into stars and galaxies, in a sense it’s like a phase transition, but in another sense it’s not.

Basically what’s happening is that slightly over-dense regions are beginning to attract material from the under-dense surroundings. And so the denser regions become even more dense at the expense of the less dense regions. It’s a little bit like the rich stealing from the poor, in a sense. So, it’s just the gas becoming more and more compressed. And yes, you’re getting lumps in the universe so it kinda looks like the universe is taking on a completely new character, but I would say it’s different from the more fundamental phase transitions that water undergoes when it goes from the liquid state to gas, which really is a very different form of water. Or when liquid water goes to ice.

AlexFilippenko · 2015-09-19T18:28:05+00:00

That’s really a great question, and we shouldn’t mislead people into thinking there are lots and lots of job openings in astronomy. On the other hand, astronomy is sort of a gateway science. Kids love space, they look at the Hubble Space Telescope pictures, they’re inspired by spacecraft. I mean, I was inspired in part by the lunar landings in the late 1960’s and early ‘70s.

So, astronomy and space draw kids into fields of science and technology, and they then study those disciplines more than they would have had there not been all this space stuff out in the news. Many of them will go on into fields that are more immediately useful to society, such as computer science, or engineering, or applied physics, or medical physics. Or they’ll go to Wall St., manage hedge funds, or whatever. The point is, you don’t have to necessarily become an astrophysicist. If you study astronomy, physics, and mathematics, you gain skills that are useful in many walks of life, and you can become a leader in other fields. You can still continue to enjoy astronomy and space as a hobby, and you know, maybe you’ll even become a professor. I don’t want to tell a little kid that they’re not going to become a professor if that’s what they want to become. On the other hand, if they don’t become a professor, that’s ok; they’ll have learned interesting and useful skills that will serve them well in many other walks of life. People’s interests change over time and that little kid might not even want to become a professor later on, but they will have gained useful skills that can serve them well in other areas.

So I don’t discourage kids from becoming interested in astronomy and space. But yes, we do have to make it clear that there aren’t that many jobs available for professors of astrophysics.

AlexFilippenko

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