GUY RAZ, HOST:

Come with me. Let's go outside.

A couple of months ago, we bought our son a telescope.

RAZ: (whispering) Okay, we're going outside now, we have to be quiet, okay?

And since then ...

(SOUNDBITE OF DOOR OPENING)

RAZ: ...He's gotten hooked.

(whispering) Okay, walk down ...

... Totally obsessed with the stars.

RAZ: (whispering) Do you want to open up your constellation book?

RAZ'S SON: But, but we can't - but I have to - I have to write something inside with ... Oh, now, I want to see - oh, I see Orion's belt.

RAZ: Where?

RAZ'S SON: The star.

RAZ: Where? Where's Orion's belt?

RAZ'S SON: There's one star there.

RAZ: Oh, yeah.

RAZ'S SON: And another star there.

RAZ: Oh, yeah. There it is.

RAZ'S SON: One, two, three.

RAZ: We got - we learned - Hopefully this cloud is going to move over, but we can still see a lot.

RAZ: On a clear, dark night even in the city where we live, you can still see about a hundred stars in the sky, just by looking up.

What's your - what's your favorite planet?

RAZ'S SON: Mars.

RAZ: How come?

RAZ'S SON: Because red - it - its color is red and red's my favorite color.

RAZ: What's your favorite star?

RAZ'S SON: Polaris and Sirius are my favorite stars. Maybe Sirius is Polaris' neighbor.

RAZ: (whispering) I think they might be neighbors, yeah.

RAZ'S SON: Yeah.

RAZ: Like a lot of kids, my son has this incredible curiosity about something I hadn't really thought about in years - the night sky.

RAZ: (whispering) Look at the moon though, look how bright the moon is.

RAZ'S SON: It seems close to us.

RAZ: Yeah, very close to us.

RAZ: Welcome to the TED Radio Hour from NPR, I'm Guy Raz, and on the show today we're going to hear from TED speakers who never lost that curiosity, people who look up at the sky every night, who think about the infinite possibilities out there in space.

RAZ: (whispering) Are you cold?

RAZ'S SON: Yeah.

RAZ: (whispering) Okay, all right - what do you want now?

RAZ'S SON: May I have some orange juice please?

RAZ: Sure.

So sometime in the future, and we're talking the far future, at some point there won't be anything to see beyond our galaxy. Distant space will appear pitch black, empty, and to understand why, physicist Brian Greene in his TED Talk explained that you've got to go back to the year 1929...

BRIAN GREENE: ... when the great astronomer Edwin Hubble realized that the distant galaxies were all rushing away from us, establishing that space itself is stretching - it's expanding. Now, this was revolutionary, the prevailing wisdom was that on the largest of scales the universe was static, but even so, there was one thing that everyone was certain of - the expansion must be slowing down.

(SOUNDBITE OF MUSIC)

RAZ: Why?

GREENE: Well, gravity is an attractive force, right? You drop anything, it falls to the earth. You throw anything out a window, it falls downward. Gravity pulls things together. So similarly, gravity out there in the cosmos should be pulling each galaxy toward every other. So if they're rushing apart, they should rush apart slower and slower over time. It's sort of like, you know, if you throw a baseball up in the air, it goes up, but it goes up slower and slower, so gravity of the exact same sort should be slowing the exodus of the galaxies.

RAZ: So in 1929, when Hubble figures this out, it must have blown people's minds. I mean, people assume that the universe was basically our galaxy, and then Hubble comes along and he says, it's not and it's growing.

(SOUNDBITE OF MUSIC)

GREENE: Yes, it was totally revolutionary. In fact, there was another fellow named Georges Lemaitre, who was a Belgian priest, who told Einstein that he was studying the math of Einstein's equations and general relativity, and the math seemed to say that the universe should be expanding. Einstein said to him, your math is correct, but your physics is abominable.

He was saying that you can't always trust the equations. In fact, Einstein went back and tried to change the equations so that they wouldn't imply that the universe was expanding. Then Hubble, with these observations, proved that it is, and Einstein turned sharply around and described this picture of the expanding universe as one of the most beautiful things he'd ever encountered.

RAZ: And that became a fundamental principle of astrophysics - the universe was expanding, but the expansion was slowing down. Now, everyone accepted that theory for 70 years, until there was a problem.

ADAM RIESS: There was definitely a moment when we realized that something very weird was going on, something very surprising. But our initial response to this was, oh, this must be a mistake.

RAZ: This is Adam Riess. He's a professor of physics and astronomy at Johns Hopkins, and in 1998, he made an observation that had to be a mistake.

RIESS: Really, you make so many mistakes. I make a hundred mistakes a day working in science. That's your first thought, that it was just a mistake that wouldn't go away after a while.

RAZ: And at exactly the same time, in the different lab, in a different part of the country, another scientist was coming to the same weird conclusion as Adam Riess.

SAUL PERLMUTTER: First of all, does this sound good right now, or does this sound echoey?

RAZ: Saul Perlmutter.

PERLMUTTER: And I'm a professor of physics at Berkeley, and a senior scientist at Lawrence Berkeley National Laboratory.

RAZ: Perlmutter and Riess led different teams of scientists who thought they made the same mistake at the same time. It happened while they were observing distant supernovas to measure changes in the universe over time.

GREENE: So they - after they analyzed the data, both teams found that the expansion is not slowing down over time. It's speeding up over time.

RAZ: Now, if this was true, it would be groundbreaking because remember, for decades, everyone knew the expansion of the universe was slowing down.

That was how you learned about this, when you studied physics, when you were a student, right?

GREENE: Oh, absolutely. This is bread-and-butter material that you learn - now you learn as an undergraduate. I learned it as a graduate student.

RAZ: But to say the expansion of the universe was speeding up? This had to be a mistake. It was such a crazy idea that Saul Perlmutter and Adam Riess could hardly believe their own data.

RIESS: Yes. It was a crazy idea. You had to report what it looked like the universe was doing.

PERLMUTTER: Right, so you were looking at results, but your assumption is that probably something must be wrong.

RIESS: Maybe there's some, you know, sneaky effect that we're both getting tripped up by.

PERLMUTTER: You just figure, well, obviously once we finish doing all the calibrations, cross-checking all of the different parts of the program, the data will end up looking more like what we expect.

RIESS: We didn't think, the first time we saw it, wow, the universe is accelerating; you know, we're going to win a Nobel Prize.

PERLMUTTER: We were aware that we were going to have to be absolutely sure that we were right, because it was such a major issue. Anything that we said about this, we'd have to back up and show that we had checked every possible way which it could be wrong that we could imagine.

RAZ: Now, remember, it was Einstein, a century earlier, who told a fellow scientist who pointed this out. He said, your math is correct, but your physics is abominable.

RAZ: (in unison with Greene) You can't always trust the equations.

GREENE: Literally, it's as if someone said to you, throw an apple up in the air and it's going to go up faster and faster and faster and faster and faster and faster

RAZ: ... and it was just a sense of this can't be right...

GREENE: ... and faster and faster and faster and faster and faster and faster and faster and faster and faster and faster and faster...

GREENE: ...You'd say, oh it's crazy.

RAZ: It was crazy. But remember, there were two teams.

GREENE: Both coming to the same result.

RAZ: Independently of the other.

GREENE: So it's very convincing when different lines of investigation are all pointing to the same result.

RAZ: And within a few years, other research teams began to verify those results.

RIESS: And that's when we started seeing other experiments looking at the universe in totally different ways getting the same results and that's when you say, this is the way it is. I mean, we can't - this isn't going to go away.

RAZ: And that mistake that refused to go away - it earned Adam Riess and Saul Perlmutter the Nobel Prize in physics in 2011.

So what does that mean for us? Well, Brian Greene answered that question when he gave his TED Talk and you'll hear some sound from a video he played on the TED stage...

(SOUNDBITE OF BRIAN GREENE TED TALK)

GREENE: You see we learned that our universe is not static, that space is expanding, that that expansion is speeding up all by carefully examining faint pinpoints of starlight coming to us from distant galaxies. But because the expansion is speeding up, in the very far future, those galaxies will rush away so far and so fast that we won't be able to see them - not because of technological limitations, but because of the laws of physics. The light those galaxies emit, even traveling at the fastest speed, the speed of light, will not be able to overcome the ever-widening gulf between us. So astronomers in the far future, looking out into deep space, will see nothing but an endless stretch of static, inky, black stillness. And they will conclude that the universe is static and unchanging and populated by a single central oasis of matter that they inhabit - a picture of the cosmos that we definitively know to be wrong. Now, maybe those future astronomers will have records handed down from an earlier era, like ours, attesting to an expanding cosmos teeming with galaxies, but would those future astronomers believe such ancient knowledge? Or would they believe in the black, static empty universe that their own state-of-the-art observations reveal? I suspect the latter.

RAZ: Does that ever make you sad?

GREENE: I guess it does a little bit. I mean, when I imagine we're able to sustain life on this planet for billions of years...

RIESS: And in some ways there are lots of ways to feel sad about this small moment that, fleeting moment that we get to see, and all the things that we would miss and...

PERLMUTTER: If there are cosmologists someday that want to make the kinds of measurements we have, they will look out and the landmarks will be gone. I mean, that's what the galaxies are - you know, the mile markers of the universe for us.

GREENE: It doesn't make me sad, because what I think of is, how amazing it is that we little, tiny, puny creatures, who are just crawling around the surface of this little planet, around a nondescript star, in the outskirts of an ordinary galaxy - that we've been able to figure this stuff out. That to me - how should I say - gives me a sense of connection to the universe, a kind of sense of partnership with the cosmos, if you will, that I find thrilling.

RAZ: Brian Greene. Of course, we did leave out one thing here. If the universe is expanding outward, what's beyond it? Brian Greene returns later in the show to answer that question. By way of a hint, consider something he used to do when he was a little kid. He would stand in his room, in between two mirrors, each facing the other.

GREENE: It's the effect that I think we've all experienced. When you have two mirrors that are facing one another, you put any object in between and it gets reflected back and forth, back and forth, between the mirrors. And I would sort of think to myself, what it would be like to have a parallel reality out there, where there's a version of me, but one that had a mind and an ability to do things different from the one that I experience.

RAZ: Why there may be other copies of you, other copies of me, other copies of everything you know. Our show today: the Wonders Above Us.

Next up, the asteroid hunter and his quest to save the earth.

(SOUNDBITE OF PHIL PLAIT TEDx TALK)

PHIL PLAIT: Apophis is an asteroid. It was discovered in 2004, and it's going to pass by the earth in April of 2029, and it's going to pass us so close, that if it's just right, the earth's gravity will bend it just enough that seven years later, Apophis is going to hit us.

RAZ: I'm Guy Raz. More peering into space, in a moment, on the TED Radio Hour, from NPR.

(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.