[RADIOLAB INTRO]

JAD ABUMRAD: Hey, I'm Jad Abumrad.

ROBERT KRULWICH: And I'm Robert Krulwich.

JAD: This is Radiolab.

ROBERT: The podcast!

JAD: Yes. Ooh, that was exciting!

ROBERT: And this particular turn of our wheel, we are going to be taking up a very odd, odd idea.

JAD: Which is?

ROBERT: Is it possible for a human, a man or a woman, probably a mature man or woman, we'd hope, to build their own universe?

JAD: Eh? Do you mean, like, in theory?

ROBERT: No, actually. This, I'm going to—this is a serious proposition.

JAD: Really?

ROBERT: There are people who are now thinking about it seriously at Stanford, in Israel, in Japan, theoretical physicists who are trying to figure out how one might go about this.

JAD: Go about building a universe?

ROBERT: Create a whole universe.

JAD: As in like a carpenter, like in a carpentorial sort of way? Like, "Here, build a table?"

ROBERT: In a carpentorial sort of way.

JAD: No. You know why that's not possible?

ROBERT: Why?

JAD: Because the universe is that which we are a part of. So how can you build something that we are already a part of? That doesn't make any sense.

ROBERT: To begin this conversation, we do have to consider this word 'universe,' which to most of us, as you just said, means 'everything that is.'

JAD: Everything.

ROBERT: And therefore, by definition, there should only be one of them.

JAD: Yes, of course.

ROBERT: But for physicists like Brian Greene, our friend Brian Greene, who came to my kitchen so we could have this discussion, to physicists like him, he's very comfortable with the idea of more than one universe. And that's been the case for physicists for a while now.

BRIAN GREENE: I don't know the first time, but the idea that there might be many universes has surprisingly cropped up in a variety of different contexts in physics.

ROBERT: For example, Brian says ...

BRIAN GREENE: The expansion of space, the blossoming of a universe that we have called the Big Bang, was not a single event, but it's an event that happens over and over and over again. In distant and far-flung regions of our universe, other universes sprout out, have their own new big bangs, giving rise to a kind of cosmic bubble bath of little bubble universes, of which our universe is simply one. And then this idea of universes, or a 'multiverse,' is a natural word to use to describe the collection of all these bubbles, each of which, if it has inhabitants like us, would think that that is the universe. But now, you see it's only one of many.

ROBERT: And this was something that somebody thought up in 1920, 1930, 1950?

BRIAN GREENE: Well, the inflationary theory itself was developed in the early 1980s, and this recognition that it could give rise to this many universes was developed by a number of incredibly creative physicists in the mid-'80s into the '90s, and it's still studied today.

ROBERT: So it's kind of a new idea, then?

BRIAN GREENE: This version of it is new.

ROBERT: But no explorer has ever ventured into one of these other universes as best you know, right? This is simply a mental—this is a conclusion of a mental process, not of a Columbus or a Magellan kind of process.

BRIAN GREENE: That's true. We are confined to our bubble, and we really can't get out and explore the other bubbles. So from that point of view, it is a mental exercise, but a powerful one.

ROBERT: But you can see how hard it is for somebody who doesn't read the world through mathematics, but just reads through his senses or her senses, that this explanation seems nonsensical, since you've no sensual experience of another universe, the only one you've got is staring at equations.

BRIAN GREENE: That's true, but I'd say that the history of physics of the last century has taught us to strenuously challenge our perception, strenuously challenge the things that intuitively seem obvious. We have learned that the atom is made up of particles that can be both wave-like or particle-like, that in some sense, they can be two places at once. None of us have experienced any of those things. None of those things feel right according to our intuition. But I assure you, the experiments that have been done over the last 80 years have confirmed each of those crazy ideas over and over and over again. So I don't think it's a good guide to use our senses and our intuition to determine what we think is right or wrong. We really have to follow the laws of physics and see where they take us.

ROBERT: Okay. You with me here, Jad?

JAD: I am, yes.

ROBERT: All right, so let's say ...

JAD: Begrudgingly.

ROBERT: [laughs] Really?

JAD: Yeah. No, no, no. I'm here with you. Where else am I gonna be? I'm right here.

ROBERT: All right. So let's say that you can have, just in principle anyway, more than one universe.

JAD: Okay.

ROBERT: Now the question is: how do you go about building one?

JAD: Yeah, that's what I want to know. You said at the beginning we can build them ourselves.

ROBERT: Right. So this is not, you know, anything like an act of magic or a God-like thing. This is just as far as Brian is concerned, this is a practical, albeit kind of crazy, a practical engineering problem.

JAD: [laughs] So then how would you engineer one?

ROBERT: Well, let's get to our main subject.

ROBERT: Well, that's what I asked Brian.

ROBERT: The proposition here is that not only can you have more than one of them, but that you—you, an ordinary human being and some pals, can make one. Is it conceivable to you that there could be something called a man-made universe?

BRIAN GREENE: People have studied this, and nobody has really been able to say that it's impossible. And some have even suggested hypothetical ways that you might actually do it.

ROBERT: Well, let me—I mean, the first question I gotta ask is how one—are there several ways to do this? One way to do this? How many—how many different paths?

BRIAN GREENE: Well, I would say at the moment, there's no one way that anybody has been convinced is really compatible with everything that we know. There are a number of suggested ways, but they all rely upon more or less the same physics. And that physics has to do with a strange feature of gravity that none of us have ever experienced, but the math shows us is true and observations of space seem to confirm, and that is that gravity can actually be not only attractive, it can not only pull things together, it can also be repulsive. It can push things apart.

ROBERT: If that were the case, then wouldn't we all be combusted?

BRIAN GREENE: Well, the repulsive side of gravity only rears its head in very special environments. And everyday life, the Earth, the solar system, and so forth, are realms in which it doesn't rear its repulsive side strongly enough to have any effect. But we have learned that on the largest of scales, even in our universe, we believe that gravity is exerting its repulsive side, which is what's causing distant galaxies to be rushing away from us at an ever-accelerated rate. They're rushing away faster and faster. So the repulsive side, there's actually direct observational support for.

ROBERT: What does that have to do with creating a universe, however? Because it seems to me that creating a universe, you'd want to somehow manage the thing. And repulsive sounds—particularly if it's a fierce repulsive force, would seem to make it be a kind of an unmanageable situation.

BRIAN GREENE: Well, if you want a manageable way of building a universe, what you want to be able to do is build something pretty small. But a small thing is not a universe, so it has to expand.

ROBERT: Right.

BRIAN GREENE: For something to expand, there's gotta be some outward push. There's gotta be some repulsive push. And that's where this repulsive side of gravity comes into the story.

ROBERT: So I want to build something that is a seed of another universe. But inside my seed, there has to be latently and then later actively, some expansive thing, something that just wants to grow. Now is there such a device, such a seed?

BRIAN GREENE: There are conditions which according to the laws of general relativity, the laws that Einstein wrote down a long time ago, well tested, those laws tell us that in this context of the right energy density carried by the right substance, you will have repulsive gravity. Which means if you can build this little seed, this little nugget in just the right way, it will, on its own, roughly speaking, start to expand, grow faster and faster and faster, beginning tiny and sprouting into a gigantic universe.

ROBERT: So I can have, you see, an expanding universe that is born in my kitchen and I don't have to worry about my dishes.

JAD: Wait, wait. You're having a lot of fun here, but you've left me behind a bit. What is this seed thing anyway?

ROBERT: Well, the exact nature of the seed thing is actually quite complicated.

JAD: [laughs]

ROBERT: [laughs] But just to give it a shape for you, the first thing I learned is that in order to start a universe, any universe, even our own universe, the seed has to be very, very small.

BRIAN GREENE: You can calculate that the nugget that we believe perhaps gave rise to our universe, maybe someone created it in their apartment in some other universe, was about roughly 10⁻²⁶ centimeters across. 10⁻²⁶ centimeters. That's small.

ROBERT: That's really, really, really small.

BRIAN GREENE: Yeah, and it wouldn't ...

ROBERT: And it could grow into—in other words, there's enough push inside it, repulsive force or push out to make it grow into a thing like we would associate with universe, universe scales?

BRIAN GREENE: Our universe, according to this theory—again, I'm being facetious that it was created in somebody else's apartment, but who knows? But the seed of our universe, we believe from our calculations and our observations, was roughly 10⁻²⁶, 10⁻²⁷ centimeters across. Weighed, you know, a few pounds. About 10 pounds. You wouldn't really think intuitively that you could build a whole universe from 10 pounds of stuff. I think you would think that to build a whole universe—I'm talking about a universe with stars and galaxies, hundreds of billions of stars and hundreds of billions of galaxies, you'd think you'd need more than 10 pounds of this stuff. But it turns out that that's all you need because the repulsive side of gravity is so powerful that it actually injects energy from gravity itself into the expanding space. So from that point of view, all you need is the seed, and then gravity takes over and does the rest of the work.

ROBERT: Okay, Jad. So we now know the seed has to be small. Now the second thing that Brian told me is the seed should come in the form of what he described as a 'black hole.'

JAD: The seed is a black hole?

ROBERT: Mm-hmm.

JAD: Wait a second. You said that it has to be small, but black holes are huge.

BRIAN GREENE: But it turns out that black holes can be—they don't have to be big.

ROBERT: They don't?

BRIAN GREENE: No, not at all. Relatively.

ROBERT: Well, can you get—I mean, I thought that the reason we get the black hole is because the star collapses. So it's a fairly gigantic beginning, and therefore, it's a fairly gigantic thing. Could you get a black hole the size of a wine cup or a thimble or less?

BRIAN GREENE: Oh, yeah. Absolutely. You give me any object, and if I squeeze it sufficiently small, then according to the classical laws of general relativity, if you make it small enough, it will be a tiny black hole. Now ...

ROBERT: A grape? Can you make a grape into a black hole?

BRIAN GREENE: Absolutely. [laughs]

ROBERT: Can you make a raspberry into a black hole? Can you make a blueberry into a black hole?

BRIAN GREENE: Seriously, there's nothing that you could give me that I couldn't turn into a black hole by squeezing it sufficiently small.

ROBERT: Huh. Would there be any example of a naturally-occurring small black hole?

BRIAN GREENE: Sure. There are processes where particles can slam into each other at very high energies, and the calculations show that if they slam together at sufficiently high energies in the right geometrical configuration, they can create a tiny black hole. And this is not just hypothetical. There's a new machine in Geneva, Switzerland, right now called the Large Hadron Collider. And one of the things that may happen at the Large Hadron Collider is the creation of microscopic black holes in the collision between protons and protons. These will be tiny black holes, but black holes nonetheless.

JAD: Wow! This is getting kind of interesting. So okay, you've got a black hole.

ROBERT: Yep.

JAD: A tiny one, which we somehow have to impregnate with this anti-gravity force.

ROBERT: Yeah.

JAD: What other ingredients do we need?

ROBERT: Now we need a trigger, something to turn the expansive force on so that it will go—boom!

JAD: What's the trigger?

ROBERT: Well, the trigger is a very, very complex—frankly, I only kind of 80 percent got the trigger. And I don't want to bore you with it, but it's something about a compass with only one needle or something like that. But anyway, once you—don't ask.

JAD: All right.

ROBERT: But once you've got the trigger, which you add to the little black hole, and now you've got the expansive force lying—and you pull the trigger, and you will get a universe of your own.

JAD: Right there in your kitchen.

ROBERT: Mm-hmm.

JAD: But doesn't that worry you? I mean, wouldn't that blow up everything?

ROBERT: It just seems that if you create one, you would be—you would be in danger.

BRIAN GREENE: People have studied that issue in great detail and found that, at least according to the proposals that are on the table for how, in principle, you might create a universe, that wouldn't be a worry. That wouldn't happen. Instead, this universe that you create would, in essence, create its own space. It wouldn't encroach on your space by expanding into your domain, into your house, into your region. Instead, it would expand like our universe does, but it would expand by creating new space, space that hadn't existed before. So it would be off on its own, if you will, creating a new bubble, a new bubble universe that would be a universe in its own right.

JAD: So what do we see from our side?

ROBERT:

Well, what we see, probably—I'm not sure, because Brian isn't with me during this particular conversation, but I think Brian would say all we'd see is our little black hole on our side and something going on very large on the other side.

JAD: And it's staying little on our side, but getting bigger on the other side?

ROBERT: Mm-hmm.

JAD: And can we jump through it?

ROBERT: Well, that's the interesting thing.

BRIAN GREENE: You know, you need to jump in to be able to see what's going on on the other side.

ROBERT: So if you could make one of these, you might be able to inspect it.

BRIAN GREENE: You'd be—at a certain cost.

ROBERT: What would be the cost?

BRIAN GREENE: You couldn't come back. You couldn't pass through. But what you're creating on the other side is there, and in principle you could go there.

ROBERT: So if you could make your own universe, you would never, ever, ever be able to come back to visit anyone or anything you ever have known. Could you ever imagine having made a creation on this scale? Could you ever imagine visiting it forever?

JAD: And never going back home?

ROBERT: Never.

JAD: Well ...

ROBERT: No Radiolab.

JAD: No more Radiolab. Whew!

ROBERT: You know how many people would be sad? So many.

JAD: Sad. Yeah. Just a small little sliver of humanity. They'd get over it.

BRIAN GREENE: If you could actually do this, beyond theory, I mean, I have to say, I think I might have a little trouble resisting this possibility just because it's so curious, this idea that through your volitional act in your kitchen sink, you are creating a universe that would give rise, perhaps, to things like we see in the world around us. Really, you can think of our universe potentially as being the outcome of the hypothetical processes that we're talking about. Our universe.

JAD: Speaking of which, we should say our universe—or our corner of it—is funded by the Sloan Foundation, the Corporation for Public Broadcasting and the National Science Foundation.

ROBERT: And also thank you to Brian Greene, who is professor of, let's see, physics and mathematics at Columbia University in New York. He's also the author of The Elegant Universe and The Fabric of the Cosmos.

JAD: One day he may create himself a little bit of cosmos.

ROBERT: Is this, by the way, plausible to you?

BRIAN GREENE: It's very tough to say. I do consider this speculation on speculation. So I think I would stress that the reason for thinking about this is not so much to do it, but it's more to push the laws of physics to their breaking point, because that's often where we learn new things about how the world works.

ROBERT: 'Til next time?

JAD: Yes. Two weeks. We'll see you then.

ROBERT: Bye.

 

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