DIY Universe

Summary

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Radiolab: “DIY Universe”

Date: March 26, 2009
Hosts: Jad Abumrad, Robert Krulwich
Guest: Brian Greene, Physicist (Columbia University)

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Main Theme

This episode of Radiolab explores the astonishing idea that humans could, in theory, create their own universe. Through engaging conversation with physicist Brian Greene, the hosts investigate the science—and the mind-bending speculation—behind the concept of universe-creation, venturing through topics like inflation theory, black holes, repulsive gravity, and the philosophical consequences of such a feat.

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Key Discussion Points and Insights

1. What Does “Universe” Mean, Really?

• The hosts clarify that for most people, “the universe” means everything that exists—so by definition, there should be just one.
• Physicist Brian Greene introduces the “multiverse” concept:

  “The idea that there might be many universes has surprisingly cropped up in a variety of different contexts in physics…. [The Big Bang] is 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.” (Brian Greene, 01:36)

2. The Multiverse and Modern Physics

• Greene lays out the development of these ideas:

  • The inflationary theory was developed in the 1980s.
  • The concept of “many universes” emerged from this work.
  • No one has “explored” another universe—it’s a conclusion from theoretical work, not direct observation:

    “We are confined to our bubble and we really can't get out and explore the other bubbles… it is a mental exercise, but a powerful one.” (Brian Greene, 03:06)

• Greene highlights the need to move beyond human intuition when considering bizarre physical phenomena:

  “The history of physics…the last century has taught us to strenuously challenge our perceptions…. 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.” (Brian Greene, 03:36)

3. Engineering a “DIY Universe”

• The hosts ask whether humans could actually build a universe as a DIY project.

• Brian Greene explains that physicists haven’t ruled it out; in fact, there are hypothetical scenarios in which it might be possible:

  “People have studied this and nobody's really been able to say that it's impossible.” (Brian Greene, 05:19)

• The underlying mechanism requires understanding a strange feature of gravity:

  • Gravity is not just attractive; under special circumstances, it can be repulsive and push things apart.

  “Gravity can actually be not only attractive… it can also be repulsive. It can push things apart.” (Brian Greene, 06:08)

• This “repulsive gravity” is thought to be what drives the expansion of our universe and would play a key role in creating a new universe.

4. The “Seed” of a Universe

• To start a universe, you’d need to make something “very, very small.”

  “The seed has to be very, very small…. The seed of our universe, we believe from our calculations and our observations, was roughly 10 to the minus 26, 10 to the minus 27 centimeters across, weighed, you know, a few pounds. About 10 pounds.” (Brian Greene, 09:07 and 09:22)

• Surprisingly, even 10 pounds of the right “stuff”—with the right properties—might be enough to seed a universe, because the repulsive side of gravity injects enormous energy into expanding space.

5. Black Holes and Universe Creation

• The conversation turns to black holes as the likely form of the initial “seed.”

  “The seed should come in the form of what he described as a black hole.” (Robert Krulwich, 10:19)

• Contrary to popular belief, black holes can be tiny:

  “There's nothing that you could give me that I couldn't turn into a black hole by squeezing it sufficiently small.” (Brian Greene, 11:26)

• Natural processes—like high-energy particle collisions—can create tiny black holes, and such phenomena might even be produced at the Large Hadron Collider.

6. The Trigger and Safety of Universe Creation

• Creating a universe requires not just a “seed” black hole but also a trigger for setting off the expansion—though the specifics are highly technical.
• The hosts and Greene discuss whether creating a universe would be dangerous:

  “Instead, this universe that you create would, in essence, create its own space…. It would be off on its own, if you will, creating a new bubble universe. That would be a universe in its own right.” (Brian Greene, 13:04)

7. Could We Visit Our Creation?

• 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.” (Robert Krulwich, 14:41)
• Greene speculates that, despite the dangers, the curiosity might prove irresistible:

  “If you could actually do this…. I think I might have a little trouble resisting this possibility.” (Brian Greene, 15:02)

8. Why Bother With “Speculation on Speculation”?

• Greene closes by acknowledging just how speculative the idea is, but stresses its value:

  “I do consider this speculation on speculation…. [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.” (Brian Greene, 16:07)

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Notable Quotes & Memorable Moments

• On the Multiverse:

  “We have learned that the atom is made up of particles that can be both wave like or particle like... None of those things feel right according to our intuition. But I assure you, the experiments that have been done... have confirmed each of those crazy ideas over and over again.” (Brian Greene, 03:36)

• On Making a Universe in a Kitchen:

  “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.” (Robert Krulwich, 08:21)

• On the Motivation to Try:

  “If you could actually do this... I think I might have a little trouble resisting this possibility.” (Brian Greene, 15:02)

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Important Segment Timestamps

• The multiverse concept introduced: 01:36
• Why intuition is a bad guide: 03:36
• Is it possible to create a universe?: 05:19
• Repulsive gravity explained: 06:08
• Universe “seed” size and weight: 09:07–09:22
• Black holes as universe seeds: 10:19–11:26
• Natural tiny black holes & the LHC: 11:36
• Would a DIY universe expand and destroy us?: 13:04
• Could you visit the new universe?: 14:03–14:48
• Why speculate?: 16:07

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Tone and Language

The episode balances playful curiosity (banter between Jad and Robert) with awe and humility at the scale of the universe. Brian Greene brings clarity, accessibility, and a sense of infectious wonder, making esoteric ideas approachable to a curious general audience.

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Summary

“DIY Universe” is a mind-expanding deep-dive into whether people could theoretically craft new universes. Physics, philosophy, and imagination all intermingle as the hosts and Brian Greene explore how our universe might be just one bubble amid an endless multiverse, how gravity could power new realms, and how the pursuit of such far-out possibilities, though speculative, pushes the boundaries of human understanding. This episode leaves listeners with more questions than answers—and a potent sense of cosmic possibility.

Transcript

[Robert Krulwich]

I sh.

[Jad Abumrad]

Quite.

[Robert Krulwich]

You're listening to Radiolab, the podcast from New York Public Radio, Public Radio, WNYC.

[Chad Abumrad]

And npr. Hey, I'm Chad Abumrad.

[Robert Krulwich]

And I'm Robert Krulwich.

[Chad Abumrad]

This is Radiolab, the podcast. Yes. Ooh, that was exciting.

[Robert Krulwich]

And this particular turn of our wheel, we are going to be taking up.

[Chad Abumrad]

A very odd, odd idea, which is.

[Robert Krulwich]

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.

[Chad Abumrad]

Eh? Do you mean like, in theory?

[Robert Krulwich]

No, actually, I'm going to. This is a serious proposition, really. 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.

[Chad Abumrad]

About this, go about building a universe, create a whole universe, as in like a carpenter, like in a carpentorial sort of way. Like here.

[Jad Abumrad]

Build a table in a carpentorial sort of way.

[Chad Abumrad]

No. You know why that's not possible?

[Jad Abumrad]

Why?

[Chad Abumrad]

Because the universe is that which we are a part of. So how can you build something that is that we are already a part of? That doesn't mean anything. Sense.

[Robert Krulwich]

To begin this conversation, we do have to consider this word universe, which to.

[Jad Abumrad]

Most of us, as you just said, means everything, that is everything. And therefore, by definition, there should only.

[Robert Krulwich]

Be one of them. Yes, of course, but for physicists like Brian Greene, our friend Brian Greene Green, 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. For example, Brian says 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 multiverse is a natural word to use to describe the collection of. 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.

[Jad Abumrad]

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 physical physicists in the mid-80s into the 90s, and it's still studied today.

[Jad Abumrad]

So it's kind of a new idea then.

[Brian Greene]

This version of it is new.

[Jad Abumrad]

But no explorer has ever ventured into one of these other universes as best you know.

[Chad Abumrad]

Right.

[Jad Abumrad]

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. So from that point of view, it is a mental exercise, but a powerful one.

[Jad Abumrad]

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 have 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. Has taught us to strenuously challenge our perceptions, 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 Krulwich]

Okay. You with me here, Jad?

[Chad Abumrad]

I am, yes. All right, so let's say begrudgingly.

[Robert Krulwich]

Really?

[Chad Abumrad]

Yeah, if you're like me.

[Brian Greene]

No, no, no.

[Chad Abumrad]

I'm here with you. Where else I gonna be? I'm right here.

[Robert Krulwich]

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

[Chad Abumrad]

Okay?

[Robert Krulwich]

Now the question is, how do you.

[Jad Abumrad]

Go about building one?

[Chad Abumrad]

Yeah, that's what I want to know. You said at the beginning we.

[Robert Krulwich]

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

[Chad Abumrad]

So then how would you engineer one?

[Jad Abumrad]

Let's get to our main Subject?

[Robert Krulwich]

Well, that's what I asked Brian.

[Jad Abumrad]

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's really been able to say that it's impossible. And some have even suggested hypothetical ways that you might actually do it.

[Robert Krulwich]

Well, let me, I mean, the first question I can ask is how one, are there several ways to do this.

[Jad Abumrad]

One way to do this, 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.

[Jad Abumrad]

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, 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 what does that have.

[Jad Abumrad]

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, particularly if it's a fierce repulsive force, which seemed 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's not a universe, so it has to expand, right? 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.

[Jad Abumrad]

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 Krulwich]

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.

[Chad Abumrad]

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

[Robert Krulwich]

Well, the exact nature of the seed thing is actually quite complicated. 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 to the minus 20 centimeters across. 10 to the minus 26 centimeters.

[Jad Abumrad]

That's small.

[Robert Krulwich]

That's really, really, really small.

[Chad Abumrad]

Yeah.

[Brian Greene]

And it wouldn't.

[Jad Abumrad]

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.

[Brian Greene]

Universe scales our universe, according to this theory. Again, you know, 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 to the minus 26, 10 to the minus 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 Krulwich]

Okay, Jeff. 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.

[Chad Abumrad]

The seed is a black hole.

[Jad Abumrad]

Mm.

[Chad Abumrad]

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.

[Jad Abumrad]

They don't?

[Brian Greene]

No, not at all.

[Jad Abumrad]

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, a grape.

[Jad Abumrad]

Can you make. Can you make a grape into a black hole? Absolutely. 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.

[Jad Abumrad]

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 direction, 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.

[Chad Abumrad]

Wow, this is getting kind of interesting. So, okay, you've got a black hole, a tiny one, which we somehow have to impregnate with this anti gravity force. Yeah. What other ingredients do we need?

[Robert Krulwich]

Now we need a trigger, something to turn the expansive force on so that it will go.

[Chad Abumrad]

What's the trigger?

[Robert Krulwich]

Well, the trigger is a very, very complex. Frankly, I only kind of 80% 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, don't ask. But once you've got the trigger, which you add to the little black hole, and now you've got the expansive force lying trigger, and you will get a.

[Chad Abumrad]

Universe of your own right there in your kitchen. But doesn't that worry you? I mean, wouldn't that blow up everything?

[Jad Abumrad]

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.

[Chad Abumrad]

So what do we see from our side?

[Robert Krulwich]

Well, 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.

[Chad Abumrad]

And it's staying little on our side, but getting bigger on the other side. And can we jump through it?

[Robert Krulwich]

Well, that's the interesting thing.

[Brian Greene]

You need to jump in to be able to see what's going on on the other side.

[Jad Abumrad]

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 Krulwich]

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 Krulwich]

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.

[Jad Abumrad]

Could you ever imagine having made a creation on this scale?

[Robert Krulwich]

Could you ever imagine visiting it forever.

[Chad Abumrad]

And never going back home?

[Robert Krulwich]

Never.

[Jad Abumrad]

Well, no radio lab.

[Chad Abumrad]

Oh, no radio.

[Robert Krulwich]

You know how many people would be sad?

[Jad Abumrad]

So many sad.

[Chad Abumrad]

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.

[Chad Abumrad]

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

[Robert Krulwich]

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.

[Chad Abumrad]

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

[Jad Abumrad]

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 Krulwich]

Till next time?

[Chad Abumrad]

Yes, two weeks. We'll see you then. Bye.