Perlmutter: Then you couple camera technology with computers. Consumer demand meant that we finally could afford computers that could scan through millions of images to find the rare things that we’re looking for. In our case, we were looking for supernova explosions to use as distance markers.
Ghez: For me it’s the exact opposite. I know exactly where I want to look, so I don’t need a big field of view. Instead, I want to see as much detail as possible. So the technology that’s changed so much for me is the ability to see this very fine detail. Astronomers are obsessed with building larger and larger telescopes. There are two promises that we make with bigger telescopes: that they can see fainter things and that they see more detail. But it’s been really hard to follow through on that second promise because of atmospheric distortion. The atmosphere is great for people—it allows us to survive—but it’s a real headache for astronomers. We lose about a factor of 20 in detail because of the atmosphere. The technology that has made immense strides in the last decade has been methods for overcoming atmospheric distortion [such as using adaptive optics to cancel out the blurring].
Plait: We have some great questions for the panel that were sent to the DISCOVER magazine Web site. Here’s one for Mike: We’re finding more and more Kuiper belt objects. How soon before we make a direct detection of Oort cloud objects?
Brown: The Kuiper belt is what I spend most of my time studying. It’s the region of space outside of Neptune’s orbit that extends out a good ways. It includes Pluto, it includes Eris and all the other smaller things that I’ve been talking about. The Oort cloud is much, much farther away. It’s a hypothetical region of space where comets come from, about halfway between us and the nearest star. It’s incredibly far away compared with everything else we’ve ever seen. When my students and I have had way too much coffee, which happens daily, we sit around and think, “How are we gonna ever detect something in the Oort cloud?” It’s kind of our holy grail. If the coffee fails, we switch to wine. Still doesn’t help! We cannot figure out any way to make that happen. I would be willing to bet anybody, because I’ll never have to pay off, that there are things the size of Earth, and larger, in the Oort cloud. But I don’t know that in my lifetime we’re ever going to have a way to find out. If anybody here has any ideas, let me know.
Plait: Andrea, I’ll give you an easier question: How does a black hole affect the evolution of a galaxy?
Ghez: These black holes at the centers of galaxies are big [as black holes go]. But compared with a galaxy, they’re really small. So they don’t have that much of an effect; we have nothing to fear. They only affect the very closest stars to them. But recently it was observed that the mass of a central black hole correlates with the mass of the galaxy around it! Before that observation, we didn’t know if the black hole formed first and then the galaxy formed around it, or if the galaxy formed first and then the black hole formed from the galaxy. The correlation means that the black hole and galaxy had to form together. They couldn’t be separate events because a black hole can’t affect an object as big as a galaxy. Whatever gave rise to that galaxy had to give rise to the black hole.
Plait: Now a question for Saul: The discovery that 96 percent of everything out there is dark matter and dark energy would seem to indicate that we need a new theoretical model of the universe. What are the leading candidates?
Perlmutter: What’s amazing is that theories of how to explore dark matter used to come out relatively slowly. But as soon as dark energy came into the picture 10 years ago, the field just exploded. Every three days for the past decade there has been a new paper proposing what dark energy might be. What’s interesting, though, is that I doubt almost any of the authors of those papers would stand up and say, “I think I’ve got the answer.” Almost every one of them would say, “I’m just expanding the range of ideas we have to consider.” They are really throwing the ball back into the court of observers like us to give them some more clues. The theory of everything is unknown—we’re still pretty clueless.
Audience member: Do you think there could be life on other planets?
Fischer: Now we’re playing the role of theorists, imagining what will be. To me, it’s hard to imagine that there isn’t life somewhere else. We look at our galaxy and other galaxies and we see that they are glowing with molecules called polycyclic aromatic hydrocarbons. They become the building blocks of proteins. So the raw material is out there. Biologists look here on Earth at life in extreme environments and say, “Wherever there’s water, there’s life.” I’ll bet you a hundred dollars there’s life—though I don’t know if it’s the kind of life that is scum in a pond or if it’s the kind of life that walks up to a microphone and asks questions!
Brown: I would be willing to bet that hundred dollars that in your lifetime, somebody will actually get to Mars and discover some sort of microbe.
Audience member: The Big Bang started from a pinprick. Could there be something leaking from another side into our universe that is causing the expansion of the universe, and that’s dark energy?
Perlmutter: There’s been a long-standing tradition of using the analogy of an expanding balloon for the expansion of the universe. If you use that analogy and work your way backward in time from now, you end up imagining everything coming from a point—a pinprick. I’ve been on a campaign to get people to stop talking about balloons, because current data indicate that we live in an infinite universe. That being the case, now start working backward in time. In the simplest cosmological theory, you just suck space out between each one of you. As you go back in time, eventually everybody’s right on top of each other, but the universe is still infinite. You can still go as far as you want in any direction. It’s just very dense. Our understanding of physics happens not to work in that very hot, dense regime. That’s as far back as we know. We don’t know what happened before that, and that’s what we’re calling the Big Bang. We’re working really hard to invent ways of figuring out what happened just before that moment, and just before that. This picture is not as fun as the image of a little dot exploding, but I think it’s probably our best picture of what we’re talking about.
Audience member: What kind of mass makes up a black hole?
Ghez: The answer is that we don’t know. We have this interesting problem with black holes. What is a black hole? It is a region of space where you have mass that’s confined to zero volume, which means that the density is infinitely large, which means we have no way of describing, really, what a black hole is! The fact we say things like “the density is infinitely large” means we don’t have our description of physics quite right. I think the question really is about our description of the physical world, as opposed to the matter content of the black hole.
Audience member: What do you think about the existence of wormholes?
Ghez: They’re an interesting idea—that you’ve got black holes that take things in, and maybe something comes out on the other side [possibly in another place and time]. That gets us into the realm of science fiction because we can’t test the idea. So we let it be, without worrying about whether or not it really is possible. It’s mathematically possible, but we’ll never know whether or not it’s true. That’s probably not the answer you want, but it’s an answer.
Audience member: If a person did fall into a black hole, where would he go?
Ghez: The problem with falling into a black hole is that you would never make it. You’d get sheared apart. As you fell in your feet would feel a pull so much greater than your head that you would be torn apart. It would be a really bad ride.
Brown: Like blood spattered everywhere!
Ghez: There’s that gore again.
Fischer: It’s a theme tonight!
Audience: What are your hopes for this year’s International Year of Astronomy?
Brown: If there is anything I can convince people to do, I want people to not just sit here and listen to astronomers and think about astronomy but to look at the sky. So what I want everyone to do when you walk out tonight is to look up. You’ll see Orion, you’ll see Sirius. Just look up at the sky for a minute and think about what’s out there. That’s what I want.