Ask An Astrophysicist The universe is being pushed apart at a faster and faster rate. And the culprit? Dark energy. Astrophysicist Adam Riess shared the 2011 Nobel Prize in Physics for that discovery, and now's your chance to ask him about it--or anything else you've been wondering about the cosmos.

Ask An Astrophysicist

Ask An Astrophysicist

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The universe is being pushed apart at a faster and faster rate. And the culprit? Dark energy. Astrophysicist Adam Riess shared the 2011 Nobel Prize in Physics for that discovery, and now's your chance to ask him about it—or anything else you've been wondering about the cosmos.


Next up, have you had the chance to go camping this summer? Maybe aim your telescope at the night sky or out in the backyard doing that or the driveway is where I do my stuff. If you have, you probably know that if you gaze up at the stars long enough, you can't help but start to wonder about the universe. How far does it go? Is it infinite? Why is it expanding? What is it expanding into? Yeah, what about all that stuff you can't see in the spaces between the stars, the dark energy, the dark matter that's everywhere? Where does it come from?

Well, my next guest knows a thing or two about the universe and where it might be headed in the future. He shared last year's Nobel Prize in physics for his discovery that the universe is expanding at an accelerating rate. And he's here to play ask a cosmologist with us today because it's your chance to chat with a Nobel Prize winner, maybe to run your theory of the universe by him. Try to stay within certain bounds or limits, Flora. Like, we don't want to get too crazy about running your theory by him, but you can - we can all play.

Our number is 1-800-989-8255. You can go to our website at, or you can email us or send us a tweet, @scifri. Adam Riess is professor of astronomy - excuse me - and physics at Johns Hopkins University. He's also senior member of the science staff at the Space Telescope Science Institute in Baltimore, Maryland. Welcome back to SCIENCE FRIDAY.

DR. ADAM RIESS: Thank you for having.

FLATOW: Has there just been one question that's too weird that's been asked of you about the universe?


FLATOW: Or is everything fair game?

RIESS: I suppose anything is fair game. I mean, certainly, some of the more fanciful ideas if there are 10 to the 500 universes, is there really one where everybody is like all the people I know but just the opposite, as we've seen, you know, in many sci-fi plots and things like that? So, you know, those are very speculative.

FLATOW: Yeah. Here's one from a tweet that came in from Will Gillespie(ph), who says: If an infinite universe means going one direction long enough eventually, does that put you on the other side?

RIESS: Well, no. I mean, that would be - pretty much our definition of an infinite universe is you'd head in one direction for a long time, you never come back to the other side. In fact, scientists frequently look for evidence of a finite mist of the universe by looking out in one direction, for example, at the radiation left over from the big bang and they look for a pattern. And it would be amazing if they saw the same pattern on the other side of the sky that would indicate that we had already seen the universe wrapping around.

On the other hand, a lot hidden to us by the horizon of the universe, just like there's a horizon on the Earth where you stand somewhere and you can't see below or beyond the horizon, but you know there's more Earth out there. We experience the same thing with the universe because of the finite speed of light and the finite age of the universe that we can only see out to about 13 and a half billion light years.

FLATOW: This is SCIENCE FRIDAY from NPR. Talking with Adam Riess about - it's your chance to ask a cosmologist. Let me get one more question before we get into some of the questions.

RIESS: Sure.

FLATOW: Here's one that's been asked a lot: As space expands, does dark energy mean that new energy is being created? Or is it flowing into our universe from some place else?

FLORA LICHTMAN, BYLINE: This is one that I'm really interested into.


LICHTMAN: I was just asking this this morning (unintelligible).

FLATOW: What - Dr. Riess, what...

RIESS: Yeah. It's - well, you know, it seems strange at first to think of the universe getting bigger, and if we really believe that there's dark energy and if it is, let's say, constant, so that every time you create a new cubic centimeter of space, you create more dark energy. Isn't that a problem? Physicists are very comfortable with the idea of different forms of energy, and we've never had a problem with energy changing from one form to another. Now, on one side of the ledger can be positive forms of energy, and dark energy would even be included in that.

But on the other side of the ledger, physicists keep track of sort of debts or deficits, and one of our forms of that is potential energy. And so that's usually defined as the energy you would have to put into the system just to make it look very ordinary, for example, to move all the objects infinitely far away from each other. And so we have a debt and we have the positive side of the ledger, and we believe that if you properly do the accounting over the whole universe, that it still remains balanced.

FLATOW: Hmm. Can you put, you know, Einstein was asked, I think, many times the famous question: Can you put your thumb through the edge of the universe?

RIESS: What did he say?


FLATOW: He said it's not like a balloon. You know, in those days, they used to describe the universe as expanding like a balloon. He said that's not really, you know? What - how does the universe - what is it expanding into then?

RIESS: Right. Well, this is a...

FLATOW: That's the question, it's what they're asking.

RIESS: Right. I mean, this is a difficult concept, and we're still not totally sure about the answer. I mean, it is possible. I like to give, as an example, sort of a non-intuitive answer to this to students in my undergraduate class. Imagine a two-dimensional universe that just lives on the surface of a balloon, and it could be ants who live on the surface of the balloon. And imagine every day, the balloon gets a little bit bigger, and so they notice that their - the surface area gets bigger, but it isn't obvious where it comes from.

And the reason it isn't obvious is because the ants can't understand curvature. They can't understand that their two-dimensional universe bends in the third dimension. And so it is possible for our universe still to have some curvature and so - although we can't picture four spatial dimensions, we would understand by math or by analogy it could be this way.

Alternatively, there's nothing wrong with something that's infinite getting bigger. As my father used to like to joke with me: What's bigger than infinity? Infinity plus one. So even though the universe can be infinite, it can also still be locally expanding so that every location is still getting bigger.

FLATOW: A mathematician made a whole career out all of those infinities.

RIESS: Right.

FLATOW: 1-800-989-8255. A quick question from Mark in Washington, D.C. before the break. Hi, Mark.

MARK: Hello. How are you?

FLATOW: Hi there.

MARK: I was just thinking that what dark matter really is just their explanation for not knowing what anything is. And it reminded me of actually, when I was in the science museum in Richmond a little while ago, they equated gravity as a stretching of space-time. I'm wondering whether, you know, when the bang - big bang happened, that stretching in space-time actually also gave it an extra boost just like elastic would, you know, you put - if it's a 10-pound ball, you put in 10 pounds upward force on it. So maybe it's more about the elasticity.

FLATOW: All right. We're going to - Adam, wait because we have a break.


FLATOW: We'll give you some time to come up with a truly mind-boggling answer to that. I'm sure you've been asked this a few times before. 1-800-989-8255 is our number. We're talking with Adam Riess, professor of astronomy and physics at Johns Hopkins University. Flora Lichtman and I will be back after this break. Stay with us, and we'll take your questions also on Twitter, @scifri. So stay with us. We'll be right back after this break.


FLATOW: This is SCIENCE FRIDAY. I'm Ira Flatow.

LICHTMAN: And I'm Flora Lichtman.

FLATOW: And you're listening to Ask An Astrophysicist with our guest expert Adam Riess, 2011 Nobel Prize winner, professor of astronomy and physics at Johns Hopkins University. It's your chance to play the game with us. Well, there are no prizes or anything like that.


FLATOW: Just ask Adam Riess a question about the dark energy, universe, whatever. 1-800-989-8255. And before we went to the break, Adam Riess was trying to answer a question. Do you have - you got the answer. Go ahead.

RIESS: Yes. Well, so I've decided to interpret the question, which had a few different parts to it, in - along the broad class of questions that I'm frequently asked. How do we know that this mysterious stuff - now the caller referred to dark matter, but the same would be true of dark energy, the same would be true of, recently, particle physicist have been looking for, the Higgs boson - how do we know that the mythical thing that sounds like a unicorn, that it really exists or that it isn't something else? It just makes us think that.

And the hard thing is that on the one hand, there is many examples in the history of science where we imagine a mythical thing and it was wrong. It turns out we didn't understand the physics right. And there is other times we have had tremendous success imagining the mythical thing and then finding it. Two great examples I love because they're easy for people to understand and they're opposite signs of the coin are two planets. One called Neptune and one called Vulcan. We've all heard of Neptune, but Neptune was discovered in the 1840s by carefully watching Uranus, the planet inside to it, noticing that Uranus wasn't in the right place frequently. It was going too fast or too slow.

And so astronomers realized or thought there could be another planet that they couldn't see but whose gravity was affecting Uranus. They were actually able to do this with enough mathematical precision that they identified where it should be. And within half an hour of receiving notice of this, Berlin astronomers in the 1840s found Neptune. So that's a great success, and that actually at the time Neptune was a kind of dark matter in the same sense that we couldn't see light from it, only its gravitational effect on Uranus.

Now, the same trick was tried when Mercury wasn't quite behaving the way it was expected to at the turn of the previous century. And again, some of the same people hypothesized an inner planet between Mercury and the sun called Vulcan. And astronomers looked for it for years but never found it, and eventually, Einstein pointed out that that was just an artifact, the strange motion of Mercury, by not having the right law of gravity. Newton's law wasn't quite right, and he came up with a new theory of gravity.

So what we always do in these frameworks is we try the simplest hypothesis and we collect a lot of data, a lot of observations. And so you hear about dark energy and dark matter because they're very sexy and they're very interesting, and we're stumped about, in some cases, finding them. But we don't tell you about the, you know, 100,000 or million times that we do the ordinary tests of gravity that, you know, we wake up each day and a planet is just where it's supposed to be or your GPS device, which is supposed to guide you home, because of general relativity, is accurate to centimeters and not off by miles that it would be off every day.

And so there's an impressive string of victories with these theories of physics, the ones that remain after the sort of survival of the fittest process of going through experiments. And so we are left at this point with a large amount of data and crosschecks and redundant measurements that tell us the universe is 73 percent dark energy and 24 percent dark matter, and we're out looking for them.

And to anybody who's been following the story in recent weeks at the Large Hadron Collider may have read that similarly, physicists hypothesized the Higgs field and the Higgs boson to explain why particles have mass. And Peter Higgs and others hypothesized this 50 years ago, and it wasn't until just a couple weeks ago that finally evidence of its real existence was found. So, you know, this is the process of science. Just because we tell you it's mysterious doesn't mean it's wrong or we're lazy or, you know, we just, you know, came up with the first crazy idea and said it's that. But it usually means that we're still looking. We're still looking for evidence to prove that it exists.

LICHTMAN: It seems like chasing the unicorn is actually kind of the fun part anyway?

RIESS: Oh, absolutely.


RIESS: Especially, you know, in the case when we came across dark energy. We weren't even expecting it. So that's when it's really fun.

FLATOW: Let's go to the phones. Let's go to Doug in Salt Lake City. Hi, Doug.

DOUG: Hey. How are you doing?

FLATOW: You got a question for us? Ask an astrophysicist.

DOUG: Yeah. I've always wondered about gravity. I once heard (technical difficulties) turned out to be salts. But I once heard that gravity has an immediate effect on the - on everything around it. For example, as the sun were to suddenly disappear, the Earth would immediately fall out of its orbit. But I later found out that that's not quite true, that gravity does have a finite speed. And I was wondering if you could expound on how gravity actually has an effect and how soon. And if also that would lead into potentially - are there any theories out there besides, you know, creating a wormhole or whatnot for faster-than-light communications?

FLATOW: OK. Lots of things to think about.

RIESS: All right. Well, right, there are a number of things in there. But, again, I also like to, one - so as the caller pointed out, under Newton theory of gravity, that just depended on the inverse square of the separation between objects, if you - if the sun wiggled, the Earth should wiggle immediately. And even Newton was bothered by this, kind of realized that he shouldn't be able to communicate so instantaneously.

Now, when Einstein replaced Newton's theory of gravity with general relativity, he described space as warped or bent by heavy objects. So when you - so picture the sheet of rubber with a kind depression in it where the sun would sit, as indicating its gravity. So if you move the sun, you could imagine moving this warped location such that a sort of wave or waves would be sent out, indicating the change in the warp. And we call those waves gravity waves. And it turns out that they cannot travel any faster but just about the speed of light.

And, again, we haven't quite found the direct confirmation of these gravity waves we would like. We've been building gravity wave telescopes for a number of years looking for the largest of them, and we're still looking for those. But the theory works so well in so many other areas that we've been able to test. I'm not aware of other mechanisms besides the wormhole trick that one could take a shortcut along this membrane or sheet of rubber to go back in time. I'm not even sure if that's legal...


RIESS: ...not in - in all of the states.

FLATOW: But what about the spooky action at a distance, you know, the entanglement that can go?

RIESS: Yes. Well - so physicists do like to argue about that, and I'm sure it would sound a little like "Inside Baseball" to many of the listeners, but it's, you know, it's the general idea that the outcome of one event is directly caused by or connected to the outcome of another. So...

FLATOW: That's at the subatomic level, though, right?

RIESS: Yeah. But, you know, the same thing has always been true, actually, at the macro level. You know if I take two cards, one's a queen and one's a king and I put one in an envelope and don't show it to either of us and I put the other in another envelope, don't show it to either of us and we go miles apart, and at a certain pre-defined time, we might flip over each of our cards. So I flip over my card and by seeing my card, I instantly know what your card says. But that never really bothered people, I think, before. I guess quantum mechanics takes it to another level or adds some fairly mysterious-sounding words to it.

LICHTMAN: So, Darren Newman(ph) tweeted us and has a question for you and that is: If everything in the universe is expanding, does that mean that we and every other object are expanding, too?

RIESS: Oh, that's a great question or - as a colleague of mine had asked me similarly about this, well, if everything is getting bigger, would we even notice? I mean, you know, the room's getting bigger, I'm getting bigger, but it's all relative. Well, that is actually not quite the way we think it works. The expansion and even the dark energy repulsion that causes things to speed up is an incredibly weak force. So we don't really see it until we look across the vast separations between galaxies.

Now, for most objects here on Earth or even in the solar system, there is a reason that those objects are bound together. It may be the electromagnetic force that binds molecules together. It could be the gravitational force that keeps you on the Earth. And that force, that energy is so much greater than dark energy, for example, that we would not see things get bigger.

In fact, it would be a little like if you were holding hands with another ice skater on an ice rink and somebody started expanding the ice. As long as you held hands tightly, your feet would slide across the expansion so you would remain bound and at the same distance. That's - from the size of these forces, that's what we believe would happen, and does happen in the universe.

FLATOW: Let's go to Jim(ph) in Washington, D.C. Hi, welcome to SCIENCE FRIDAY, Jim.

JIM: Hi. The physicists hypothesize that there have been more than one big bang, and we just can't understand that there have been more than one because we're in the middle of one.

RIESS: This is true that - the first part particularly - that many cosmologists believe that there have been either more than one big bang or that there are - there is more than one universe that formed from the big bang. There's a process in the early universe known as inflation, which once it gets started inflating the universe and other universes, it's almost hard to get it to stop. It's not quite clear how or why it does stop. And so there may be many universes that are separated from each other.

It's very difficult for science to actually prove the existence of them. A universe pretty much defines the region in which you can communicate and have causal connections. And so, our best chance would be if we ever developed a theory, and maybe string theory would be an example of that, that we were able to test so many areas, and then there was this last prediction left over that many universes would form, then we might get confidence in that. But, at this point, it's very speculative.

FLATOW: Mm-hmm. Here's a tweet from Charlie Ross(ph), who says: Does the theory that dark energy is an illusion caused by the rate of time slowing down have any validity to it?


FLATOW: Next question.


LICHTMAN: I have a question for you. Have you, I mean, have you always been interested in this stuff even since you were a kid? Were you sort of a science nerd like I was as a kid?

RIESS: Not really. I would say that I was very interested as a kid in these questions of, you know, how long have we been here, and what's our origin and things like that. I didn't realize that science actually had a way to answer these questions somewhat directly. So, you know, if you had said to me as a kid, you know, well, how long have we been here? I would say, I guess, I don't know, ask a philosopher or maybe a cleric or something. And the fact that we can make measurements of the universe with telescopes and come back and say, about 13.72 billion years, I just - once I heard that we can do that, I knew that I wanted to be involved in those measurements.

FLATOW: I'm Ira Flatow with Flora Lichtman. This is SCIENCE FRIDAY from NPR. So have you changed at all since those days?

RIESS: Well, you know, you have to be more patient than I probably was at early times. I mean, it can take many years to do these experiments. It's a long process. You have an idea, and you write a proposal, and hopefully you get time on a telescope, and you make the measurements and, you know, on and on. And, you know, the - what we learn is usually incremental. The exciting discovery of 1998, that doesn't happen very often but...

FLATOW: Well, let's talk about that discovery a little bit. First, you must've been very - were you surprised by it? And second, and this has been asked by many people, why - if we have a universe that is negative energy or is pushing out, why did it kick in at some point, was it eight billion years?

RIESS: Right.

FLATOW: Why did suddenly the universe decide to go, OK, here we go, zoom?


RIESS: Right. It's - that is - that's a real stumper that we really - I mean, the first part I could say is easy to answer, yes.


RIESS: I was surprised. My colleagues were surprised. Most of the community was totally surprised. And it's taken us about a decade of just being able to reproduce that experiment and many other experiments that keep coming up with this answer that we've learned to accept it. But this question of why now, why so recently, I mean, after all, if this is really the way the universe is going to be, there's going to be, you know, hundreds of billions of years where the universe is just accelerating, and we would not be at this point where we said, why did that just start happening recently? And we really don't know.

FLATOW: Sometimes that's good to say, we really don't know.

RIESS: Yeah.

FLATOW: Yeah. Well, thank you very much, Adam Riess, for taking time to be with us. It's been fascinating.

RIESS: Sure.

FLATOW: We'll have to have you back on Ask an Astrophysicist again, so we'll wait for that day. Adam Riess shared the 2011 Nobel Prize in physics. He's professor of astronomy and physics at Johns Hopkins University and senior member of the science staff at the Space Telescope Science Institute in Baltimore, Maryland. Thanks again.

RIESS: Thank you.

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