The Nothing Behind Everything

Summary

Radiolab Episode Summary: "The Nothing Behind Everything"

Release Date: July 25, 2025
Hosts: Lulu Miller and Latif Nasser
Creators: WNYC Studios

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Introduction

In the compelling episode titled "The Nothing Behind Everything," Radiolab delves deep into the enigmatic realms of theoretical physics and metaphysics, challenging our fundamental understanding of the universe and reality itself. Through insightful conversations with renowned physicist Brian Greene and author Jim Holt, the episode navigates complex ideas about the multiverse, the essence of matter, and the limits of human comprehension.

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Segment 1: The Multiverse and the Quest for "Everything"

Hosts: Robert Krulwich and Jad Abumrad
Guest: Brian Greene, Professor of Physics and Mathematics at Columbia University
Reference: Alan Lightman's essay "The Accidental Universe"

Overview:

The episode opens with Robert Krulwich introducing a thought-provoking discussion based on Alan Lightman's article, which questions the theoretical physicists' aspiration to understand "everything" through the lens of the multiverse theory.

Key Discussions:

1. Theoretical Physics and "Everything":

   • Robert Krulwich introduces Brian Greene, highlighting the theoretical physicist's goal to comprehensively understand the universe using mathematical equations.
   • Brian Greene emphasizes that while equations can describe fundamental particles and forces, they aren't designed to predict mundane details—"Now, you can't take that too far. None of us really imagined that if you ask the equations, what are we going to have for dinner tomorrow night? The equations will spit out fried tofu and spring rolls or something like that..." ([01:58])

2. The Multiverse Theory:

   • Krulwich and Greene explore the concept that our universe might be just one among countless others, each with its unique set of physical laws and properties.
   • Greene explains, "There may have been many Big Bangs. There may continue to be Big Bang-like events, each spawning its own universe... vast number of them can be different from each other." ([04:43])

3. Implications for Scientific Understanding:

   • The conversation delves into how the multiverse theory shifts the paradigm from seeking singular underlying principles to understanding a tapestry of diverse universes.
   • Brian Greene asserts, "Is progress, that is understanding. And then it frees you up to ask other kinds of Questions..." ([08:19])

4. Challenges and Criticisms:

   • Alan Lightman, featured indirectly, challenges the notion that the existence of multiple universes undermines the physicists' goal to understand everything, suggesting that it complicates rather than diminishes the pursuit.
   • Greene counters by reinforcing the robustness of mathematical logic in predicting these phenomena, stating, "This is just logic." ([13:55])

5. Faith vs. Mathematics:

   • A critical exchange occurs when Krulwich likens the reliance on mathematical laws to faith, to which Greene strongly refutes, "I couldn't disagree with you more... It has absolutely nothing to do with faith." ([12:40])
   • Greene emphasizes the empirical foundation of mathematical laws, asserting their basis in centuries of observational evidence.

6. Future Prospects:

   • The discussion concludes with optimistic possibilities of experimentally detecting other universes, potentially validating the multiverse theory through indirect observational evidence.
   • Greene envisions, "Measurements, which would be quite wonderful. And in that case, at least there's a chance that we gain observational evidence of the existence of these other realms." ([10:02])

Notable Quotes:

• "Some of them might have atoms, some of them might not have atoms. You could have universes with lots of stars, some with no stars, some could be made of Muenster cheese." — Robert Krulwich ([05:15])
• "This is just logic." — Brian Greene ([14:02])

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Segment 2: The Essence of Reality and the Nature of Matter

Hosts: Robert Krulwich and Jim Holt
Guest: Jim Holt, Author of "Why Does the World Exist?"

Overview:

The latter half of the episode transitions to a philosophical exploration of reality's fundamental nature, featuring an engaging dialogue with Jim Holt. The conversation examines whether reality is composed of tangible matter or abstract mathematical constructs.

Key Discussions:

1. Reality: Substance vs. Thought:

   • Jim Holt introduces the debate between materialism and idealism, referencing the historical clash between Samuel Johnson and Bishop Berkeley over the nature of rocks and the material world.
   • Holt explains, "You're increasingly convinced that the reason you can clap, the reason you don't fall through the floor, the reason that gravity works, is all because of certain ideas that govern." ([28:46])

2. Historical Perspectives on Matter:

   • Tracing back to ancient atomists like Democritus and Leucippus, Holt discusses the evolution of the concept of atoms and the subsequent revelations from modern physics.
   • Holt notes, "The atom is a big empty space... it's effectively a flux of pure information with no further substance." ([27:00])

3. Quantum Field Theory and the Illusion of Solidity:

   • Robert Krulwich and Holt delve into how quantum field theory challenges the perception of solid objects, revealing that atoms are mostly empty space.
   • Krulwich muses, "If my hands are all atoms... why don't my hands just go right to each other like two clouds?" ([25:02])

4. Mathematics as the Fabric of Reality:

   • The discussion posits that what we perceive as tangible matter might actually be manifestations of underlying mathematical structures.
   • Holt elaborates, "It's going to be mathematics and structure all the way down." ([29:07])

5. The Mystery of Subjective Experience:

   • Holt confronts the profound question of how objective, mathematical processes give rise to subjective experiences like pain and pleasure.
   • Holt reflects, "It's still miraculous and improbable that it should produce subjective experience, that it should produce pleasure and pain." ([30:42])

6. Philosophical Implications:

   • The conversation highlights the discomfort and philosophical dilemmas posed by a reality devoid of inherent substance, relying solely on abstract information.
   • Holt concludes, "I've heard one physicist say that the cosmos is ultimately a concept." ([28:53])

Notable Quotes:

• "The atom is a big empty space." — Jim Holt ([24:38])
• "It's all... they're just temporary properties. Of what are called fields." — Jim Holt ([26:33])
• "Maybe in a hundred years from now, when string theory is finally worked out, we might have a very different conception of it." — Jim Holt ([29:07])

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Conclusion

"The Nothing Behind Everything" masterfully intertwines cutting-edge scientific theories with deep philosophical inquiries, inviting listeners to ponder the very fabric of existence. By juxtaposing the ambitions of theoretical physics with the complexities of metaphysical thought, Radiolab challenges us to question the boundaries of human understanding and the nature of reality itself. The episode underscores the delicate balance between empirical evidence and abstract reasoning in our quest to unravel the mysteries of the universe.

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This summary captures the essence of the Radiolab episode, highlighting key discussions, insights, and notable quotes to provide a comprehensive overview for those who haven't listened.

Transcript

[Jad Abumrad]

Yeah.

[Robert Krulwich]

Wait, you're listening. Okay.

[Jad Abumrad]

All right.

[Robert Krulwich]

Okay.

[Jad Abumrad]

All right.

[Jim Holt]

You're listening to Radiolab Radio from wnyc.

[Robert Krulwich]

Rewind.

[Latif Nasser]

Hey, this is Radiolab. I'm Left Hypnosider. And today I have got for you two Radiolab segments that came out before I ever worked here. Both of them do a thing that I find myself craving more and more these days, which is they. They pop you out. They pop you out of the news cycle. They pop you out of whatever interpersonal drama you're stuck thinking about. They pop you out of your own body. These are pieces about dimensions and even universes that are imperceptible, verging on, almost unthinkable. I mean, I think I get it, I think I understand, maybe I don't. But I still found it all really fun. So I hope you enjoy this pre scheduled break from your perceptual reality. It begins with our emeritus host, Robert Krulwich, talking to our other emeritus host, Jad Abumrad, about a conversation he had with a legendary physicist.

[Robert Krulwich]

Okay, so this is about what you do for a living. You know that I have this neighbor and friend, Brian Greene.

[Brian Greene]

Brian Greene, professor of Physics and Mathematics, Columbia University.

[Alan Lightman]

Yes, I do know that.

[Robert Krulwich]

And the thing about Brian is he is a theoretical physicist. Now, theoretical physicists say that it's theoretically possible to know everything there is to know in the universe. So one day they'll be able to explain not only how you could send a rocket to the moon, but the laws that govern space and energy and time and gravity, everything, the whole universe, one day, they think might be totally understandable using logic and mathematical equations.

[Brian Greene]

Now, you can't take that too far. None of us really imagined that if you ask the equations, what are we going to have for dinner tomorrow night? The equations will spit out fried tofu and spring rolls or something like that, but at the level of the fundamental ingredients, the particles that make up the universe, their properties, the hope and the goal is that the theories that we work out will apply everywhere and tell us about everything.

[Robert Krulwich]

You just said everything?

[Brian Greene]

Yes.

[Robert Krulwich]

As in everything.

[Brian Greene]

Yes. That's the big, big goal.

[Robert Krulwich]

This is like playing poker. You're helping me. I don't know what you're gonna do. All right, we'll take it to the next step. Okay.

[Alan Lightman]

Wait, so what do you. What are you up to here, Krolewich?

[Robert Krulwich]

All right, so, well, you know, we argue. That's the fun thing we do. But unlike him, my position has always been that it's gonna be very hard to answer all the Puzzles in the universe. And frankly, it's not a bad thing if some mysteries remain mysterious. Yeah, that's my view. But because Brian's so smart, when I tell him, how do you know this? Whatever, he always wins the arguments. But a few months ago, this is the thing that got this whole thing started. I was reading Harper's magazine and I found an article written by another physicist and a novelist, Alan Lightman. And I thought, oh boy, this is gonna drive Brian bats. Because Alan says there is a group of physicists, and Brian happens to be one of them, who've embraced a very exciting idea with an unfortunate effect. If this idea turns out to be true, Alan writes, it will then be impossible for physicists to know everything. Which I thought, ah, excellent.

[Alan Lightman]

What is the idea?

[Robert Krulwich]

It has to do with more than one universe. You know, there is a very, you know this, we've talked about it before, that there is a vogue now for the idea that instead of one universe encompassing everything, there might be more than one.

[Brian Greene]

Right. So there actually are a number of ways that physics comes upon this idea of other universes. Maybe the most intuitive is to think about the Big Bang that sent space rushing outward and matter could cool and yield the stars and galaxies. That wonderful picture that we've had with us since the 1920s. We have in the interim decades come to the possibility that the Big Bang may not be a one time event. That is, there may have been many Big Bangs. There may continue to be Big Bang like events, each spawning its own universe. If that were the case, then our universe would then be viewed as one of many in this grand collection emerging from all of these Big Bang like events.

[Robert Krulwich]

Now, in this view of things, there could be not just one universe or three or 19. There could be 10,000. There could be trillions. There could be an infinite number. And here's the crucial thing. Each and every one of these universes can be different from its neighbor. Vastly different.

[Brian Greene]

That's right. So when we study the equations for the production of these universes, we see in the mathematics that the other universes could have different features, different particle compositions, different masses of the particles, different forces.

[Robert Krulwich]

Some of them might have atoms, some of them might not have atoms. You could have universes with lots of stars, some with no stars, some could be made of Muenster cheese. I don't know. The fundamental properties of each universe could be very different.

[Brian Greene]

That's exactly right.

[Robert Krulwich]

And that's the key to Ellen Lightman's argument. Well then, going back to the beginning of our conversation, if a Physicist's job is to explore everything, everything that is the universe. Now the universe has just been demoted to a sub universe. Then when you get your diploma from a great university, the president of the university says, my friends, we are gathered here to meet the people who have earned the credentials to describe the sub universe, a little bit of what we could know. It's like you've been demoted. You thought that you were going to get to learn about everything, your words, and now it turns out that everything is very. Is sub.

[Brian Greene]

Oh, I wouldn't describe it like that at all. As you might imagine, rather than view this as an incredible loss of understanding, the right way of viewing it, I think, is to recognize that certain questions that we were asking when we thought there was just one universe were the wrong questions.

[Alan Lightman]

Meaning. Meaning what?

[Robert Krulwich]

Well, he says, here's the way to think about it. This is how it always goes.

[Brian Greene]

We've seen this before in the history of science. Take Kepler.

[Robert Krulwich]

Johannes Kepler was an astronomer and a kind of mapper of the solar system. He was trying to figure out where the planets were and the nature of their orbits and stuff.

[Brian Greene]

And Kepler spent a long time trying to find an explanation for why the earth is 93 million miles away from the sun.

[Robert Krulwich]

93 million. Kepler thought that has to be a really important number, a key to a deeper mystery.

[Brian Greene]

But we now know that he was barking up the wrong tree.

[Robert Krulwich]

Why?

[Brian Greene]

There isn't just one planet. There are many planets, in fact, many planets around many stars. And the distances of those planets from their host star varies over a wide range of possibilities.

[Robert Krulwich]

Mars, for example, is 140, 41 million miles from the Sun. Jupiter, 483 million. And when you start comparing the different distances of planets from the sun, you realize that the fact that the earth is 93 million miles away, it doesn't seem like a deep law of the universe anymore. It just feels kind of arbitrary. And then that forces you to change the question. Not why 93 million? Now, why are all these different planets at different distances from the sun? And yet they all stick around the sun? They're all trapped in the neighborhood. That question puts you on the road to a deeper thought, the theory of gravity. The point is, says Brian, if you're focused on one thing, you're going to think that one thing is the key to everything. When your one turns to many, then you think, ah, well, the one thing really wasn't so special. But the way Brian sees it, that.

[Brian Greene]

Is progress, that is understanding. And then it frees you up to ask other kinds of Questions such as, what's the law of gravity? What is the equation that allows us to understand how the sun forms? So those are real questions. And when you can toss out the ones that are red herrings that you thought were deep, but they're actually just asking the wrong question, that frees you up to make progress.

[Robert Krulwich]

And Brian says you can make the exact same kind of progress if you compare universes. So instead of asking, why is our one universe the way it is now? You can ask, well, what do all. All of these universes, so different one from the other, still have in common?

[Brian Greene]

That would be pretty heavy and exciting to describe the underlying laws that govern all universes, regardless of their detailed features, and what it would be like in that universe or that universe or that universe way over there.

[Robert Krulwich]

But there are an infinite number of them. So if I told you that you could write anything down and it might be a universe, black universes, white universes, green universes, soft universes, hard universes, muscular universes, teeny universes, huge universes, then the only one you know intimately is your own. It seems to me that what do you know about those other universes, other than that they might be very different.

[Brian Greene]

In other words, we don't know very much observationally. Sure, we can't see them. We don't know very much experimentally. So they're definitely on a very different footing from that perspective.

[Robert Krulwich]

But Brian believes that one day we might be able to experimentally detect these other universes and somehow, you know, kind of pick up their distant vibrations, kind of like the way you'd hear your neighbor's music just emanating through the walls. We might be able to listen in, he says, and take a couple of.

[Brian Greene]

Measurements, which would be quite wonderful. And in that case, at least there's a chance that we gain observational evidence of the existence of these other realms. And at that point, I would begin to say, hmm, maybe there's something really to this.

[Robert Krulwich]

So the physics you're doing says, I can't go there. I can't observe it, at least for the moment. All I have is my brain and my math. And I say from my brain, I'm going to just assume certain things are always true. There's always going to be gravity, say there's always going to be some particle or wave that creates matter. There's always going to be. I don't know what else are there. Things that they're always going to be. What are they? They're always going to be.

[Brian Greene]

The things that you were describing need not Always be the case. Yes. What would be the case is that the fundamental governing equations, the mathematical laws, would be the underlying architecture that governs what happens in those places. But environmental details can change things.

[Robert Krulwich]

Gravity. Environmental details.

[Brian Greene]

Yes. That's actually something, you know, at some level right now, right on the moon, you could jump a lot higher than you can here. So if you didn't.

[Robert Krulwich]

But I do think that two bodies do attract each other.

[Brian Greene]

That's right. So there is a fundamental law of gravity that manifests itself in different ways based on the environment.

[Robert Krulwich]

All right, so let me say that again. Let me ask it again. Are there fundamental laws that you think operate in all universes?

[Brian Greene]

Yes, absolutely.

[Robert Krulwich]

And why do you think that that.

[Brian Greene]

Is the starting point when we come upon this possibility of other universes? It's not a crazy idea that we dream up late at night when there's nothing else to think about. These are ideas that emerge from the fundamental equations that we use to describe the things that we do see in the world around us. Then we follow the equations, and the equations suggest to us there might be these other universes. So we have equations, we analyze them, and we interpret what they're telling us about reality. But those are the very equations that come to this possibility of other universes that then those are the equations that govern those other universes. The starting point is, let's assume that these are the fundamentals.

[Robert Krulwich]

This does sound an awful lot like, why is God three in one? Or why was the world made in seven days? Aren't we getting close to some sort of. You're believing in certain things to be always true the way religious people believe certain things are always true. Not because you've seen it, or it's just because you can't. You have a faith in it.

[Brian Greene]

I couldn't disagree with you more.

[Robert Krulwich]

I thought not.

[Brian Greene]

It has absolutely nothing to do with faith. The reason why we trust the equations is because we've got centuries worth of observational and experimental evidence that the equations take us in the right direction here, here. And it's those very same equations that work here that we are following to their logical conclusion to see where the mathematics takes us. Right. So if you remember the train of.

[Robert Krulwich]

Reasoning here, you might have just projected here into there. That's faith talking. No, because you can't go there. All you can do is say, well, what works. But my deep understanding of here has to be there. I don't know why it has to be, but that's what you just said.

[Brian Greene]

No, it's actually the reasoning goes A somewhat reverse order from that, we build mathematical equations to describe here. We then follow those equations and say, oh, my goodness. Those equations that we developed to describe here are telling us that there is something over there. And then we're like, wow, the equations do a great job of describing things here. And the equations have this feature that they tell us there's another place over there. Maybe that's possible.

[Robert Krulwich]

The key thing also logic in your mind, not belief.

[Brian Greene]

This is just logic.

[Robert Krulwich]

Aren't you worried, though, that there's another Brian Greene in universe number 3790,208,600,045, who is sitting there talking to another radio reporter in another university, and he's saying, well, we know all about the other universes because we're assuming that the math here is the same as the math there in that other place. But as it turns out, their math and our math aren't the same. So there will not. You may just be wrong.

[Brian Greene]

Oh, that's always the possibility. In fact, it's likely the possibility. In fact, 99.99% of everything we do is wrong. Not from the point of view we make a mistake, but the wrongness is.

[Robert Krulwich]

A deep wrongness that you somehow are somehow feeling that the math is a clue that. That everything follows your math. If at some point the maths collide and then the universes collide, then that would be very unsettling to both of you, I would assume, in terms of.

[Brian Greene]

Whether the math is somehow contradictory, incoherent.

[Robert Krulwich]

And your tools of learning are not working.

[Brian Greene]

Yes, that would suggest that we were both wrong and that there's a deeper, overarching framework. I mean, I hate to use the word faith, but the one point where I'll give you faith is this. I do have a deep faith that the universe is coherent. And by universe, call it multiverse, whatever word you want to use, the whole thing, I do believe that it's coherent. Now, whether that means it follows mathematical laws, I don't know. It could be the case that, you know, when we talk to those aliens that we encounter one day and they say, okay, show us what you got. We bring out our equations and they kind of laugh at us and say, oh, you guys are still stuck on math, you know, and they said, yeah, you know, a thousand, ten thousand years ago we were doing math too. But here's the real way of describing. Now, what they'd be showing us with the real way of describing it, I have no idea. I can't even imagine what it would be that would be non mathematical. So I do have a deep faith that it's coherent. And the only tool that I know how to encapsulate that coherence are mathematical equations. So if Zantar, Brian, and Brian here come up with equations that code with one another and don't work, to me it just means that both were wrong and there's some bigger overarching coherence that we've yet to find.

[Robert Krulwich]

That's it.

[Alan Lightman]

I don't even. I can't even begin to figure out if you. Did you just win? Did you lose? I can't tell. Wait, so this all came from Alan Lightman's article?

[Robert Krulwich]

Right.

[Brian Greene]

So do you think he beat the.

[Alan Lightman]

Objections in the article?

[Robert Krulwich]

Did he beat the article? Well, I thought it would be fair to ask the author of the article. So I called Alan.

[Jad Abumrad]

Yep.

[Robert Krulwich]

Who happened, as it turns out to be, in Phnom Penh, Cambodia.

[Jad Abumrad]

I make all of my international calls.

[Robert Krulwich]

On Skype, and I sent him the interview with Brian. He listened to and I asked him, well, what do you think about Brian's argument?

[Jad Abumrad]

Well, I don't think that he's wrong, but I think that the problem is philosophically more disturbing than what he is confessing.

[Robert Krulwich]

He said, well, I think it's going to be much harder than Brian thinks to actually sense or encounter or measure these other universes, if they exist at all.

[Jad Abumrad]

We don't even know whether the other universes exist in the same space and time that we do. And there are other physicists who feel that these universes are even, in principle, never, never observable by us, that we will never be able to have any physical evidence of their existence. And that possibility is what I find disturbing. It may be that this is the way nature is.

[Robert Krulwich]

What does that mean?

[Jad Abumrad]

Well, I mean, it may be that we've done as much explaining is this possible.

[Robert Krulwich]

And that we'll never, ever really understand everything.

[Jad Abumrad]

Yes. In other words, we may have pushed the human mind as far as it can possibly go.

[Latif Nasser]

Huge thanks to Brian Greene, professor of physics and math at Columbia University, as well as Alan Lightman up at mit, whose essay Robert read the Accidental Universe. It appears in a book of the same name. When we come back, we have another story that will break your brain in a whole different way. This time it's not distant, unobservable universes, but. But maybe every single thing around you right now. Stick around. Radiolab is supported by Capital One. Banking with Capital One helps you keep more money in your wallet with no fees or minimums on checking accounts and no overdraft fees. Just ask the Capital One Bank Guy. It's pretty much all he talks about. In a good way. He'd also tell you that Radiolab is his favorite podcast too. Oh, really?

[Robert Krulwich]

Thanks.

[Latif Nasser]

Capital One Bank Guy. What's in your wallet? Terms apply. See capital1.com bank capital1 NA member FDIC.

[Amy Beth]

Since WNYC's first broadcast in 1924, we've been dedicated to creating the kind of content we know the world needs. Since then, New York Public Radio's rigorous journalism has gone on to win a Peabody Award and a Dupont Columbia Award, among others. In addition to this award winning reporting, your sponsorship also supports inspiring storytelling and extraordinary music that is free and accessible to all. To get in touch and find out more, visit sponsorship.wnyc.org.

[Latif Nasser]

Latif Radiolab we are back. Today's episode is about the nothing behind everything. And I'll pass it back over to our emeritus hosts, Chad and Robert.

[Alan Lightman]

Let's just start it up. I'm Jad Abumrad.

[Robert Krulwich]

I'm Robert Krylwich.

[Alan Lightman]

This is Radiolab, the podcast. We're gonna continue the conversation we were just having been having all week about, well, perfection. You know, like striving for things which seem perfect versus living in the real world. And recently I got into a bit.

[Robert Krulwich]

Of a kerfuffle with a guy who yearns like you do, for an ideal bliss. His name is Jim Holt.

[Jim Holt]

Okay, okay.

[Robert Krulwich]

And he wrote this really good book called why does the World Exist? And just to get us started, in that book, he quotes a poem.

[Jim Holt]

Yeah.

[Robert Krulwich]

Remember the line?

[Jim Holt]

Yeah. Kick at the rock, Sam Johnson. Break your bones. But cloudy, cloudy is the stuff of stones.

[Robert Krulwich]

Cloudy. Cloudy is the stuff of stones.

[Jim Holt]

Yeah.

[Robert Krulwich]

Meaning what?

[Jim Holt]

It's something. Well, Samuel Johnson, who lived in the 18th century, was a contemporary of Bishop Berkeley. And Bishop Berkeley was an idealist. He believed that the world was essentially pure appearance. It was like a thought, not like a solid reality. It was a thought in the mind.

[Robert Krulwich]

Of God, like the rock really had no substance.

[Jim Holt]

And Samuel Johnson, when he heard this, he thought it was ridiculous. And he went and kicked a stone and said, I refute Barclay. Thus. Anyway, that's the story.

[Alan Lightman]

Wait, One guy thought it was a thought, the other guy thought the rock was a. What are they arguing about exactly?

[Robert Krulwich]

Well, they're arguing about reality.

[Jim Holt]

Just what is this world? What is its essential nature?

[Robert Krulwich]

When you hold a rock in your hand, like, what's it made of?

[Alan Lightman]

What's it made of?

[Robert Krulwich]

Yeah.

[Alan Lightman]

Minerals.

[Robert Krulwich]

No. Is that the mineral? What I'm mainly asking is what is the most essential nature of the rock? So if you look deep, deep, deep down into the rock, do you find something concrete, do you find a little bit of thing? Or do you find something more ethereal, something you can't touch, something you can't pin down, something like, oh, a thought.

[Jim Holt]

This is Jim's notion, and this sounds like a. It sounds like I've been eating lotus leaves to believe it's a pipe dream. But this is what science has increasingly.

[Alan Lightman]

Led us to, that rocks are thoughts.

[Robert Krulwich]

Well, to follow Jim's logic, he goes all the way back to the Greeks, to the first real attempt to get to what's really at the bottom of a rock.

[Jim Holt]

You know, even in ancient times, the atomists Democritus and Leucippus thought that if you keep cutting up the stuff of reality that we see around us, tables and chairs and rocks and so forth, eventually you cut them up into such itty bitty pieces that you can't cut any further. And then you've got atoms. So there you've got. You've clearly got a fundamental stuff, the atoms.

[Robert Krulwich]

Yeah, that sounds very pleasing.

[Jim Holt]

Right. But even going back to Newton, there were reasons to suspect that there was something a little funny about reality. It wasn't quite as substantial as we believed. Newton, of course, came up with a theory of gravity. And the theory of gravity says if you've got the sun and a planet, the sun exerts a gravitational force on the planet. And Newton's contemporaries wanted to know, well.

[Robert Krulwich]

How does it do that?

[Jim Holt]

What is the mechanism by which gravity is mediated? How does the sun as it were, reach out to the Earth and force it to move around in this orbit?

[Robert Krulwich]

So if I were an atomist, if I were looking for stuff, then I'd need some kind of thing that carried gravity.

[Jim Holt]

Yeah, yeah. But the problem is it looks like there's nothing between the Earth and sun except a void.

[Robert Krulwich]

All that Newton had to fill that void was a mathematical equation that told him how the sun and the Earth interact. And the thing is, it worked. You could plug in the numbers and you could know how one was influencing the other. But Newton had no idea at all why the equation worked. He couldn't point to any, like a little particle thing like a graviton and say, there's your reason. It almost seemed like gravity was created from the equation itself. And this disturbed a lot of people because at that time everybody thought that.

[Jim Holt]

Nature has to be made out of hard, durable stuff. You know, gears, sprockets, pushing and Pulling. That's the essence of reality. Then in the 20th century, of course, it got much, much worse. You know, the atom, which was thought to be very, very tiny, and you couldn't cut it any further. It was the limit to this splitting process. And as we know all too well from the 20th century, you can split an atom. Yeah. And it has pretty interesting consequences. But we also discover the atom is almost entirely empty space.

[Robert Krulwich]

Huh.

[Jim Holt]

If you took a baseball and put it in the middle of Madison Square Garden, that would be like the nucleus and the first level of electrons are as far away as the exterior of the Garden.

[Robert Krulwich]

So you can think of this baseball, this nucleus, as a tiny dot all alone.

[Jim Holt]

So it's basically the atom is a big empty space.

[Robert Krulwich]

Well, it doesn't feel that way. Like. Watch this. I'm gonna do this.

[Jim Holt]

Yike.

[Robert Krulwich]

If my hands are all atoms, and as you say, atoms are mostly empty space, then why don't my hands just go right to each other like two clouds? But you'll notice, yeah.

[Jim Holt]

Why don't I fall through the floor here? Because the floor is mostly empty space and I'm mostly empty space. That too. If you look at it on the micro level, this apparent solidity is the product of a purely mathematical relation.

[Robert Krulwich]

Well, that can't. Isn't it more like my electron. Electrons don't like similar electrons, so the electrons in my hand just hate the electrons. On the other hand.

[Jim Holt]

No, it basically comes down to a pair of mathematical relations, the Pauli Exclusion principle and the Heisenberg Uncertainty principle. I mean, all of this gets very abstract.

[Robert Krulwich]

Very good. I understand it perfectly, of course, but I don't want to bore you with the details of his argument.

[Alan Lightman]

You have no idea what he's saying, do you?

[Robert Krulwich]

I'll say this according to Jim. It's not that the electrons in my left hand are repelling the electrons in my right hand. It has to do with a law of nature that says two particles, identical particles cannot be in the same place at the same time. So when you hear that sound, you can hear it as the sound of a law saying, no, not allowed. Not in nature. Exactly.

[Jim Holt]

And here's a slightly different way of putting that.

[Robert Krulwich]

But wait, isn't this law that we are announcing, isn't this law about. About particles? Like we're talking about atoms and electrons? Those are things. So we're still talking about things.

[Jim Holt]

Well, if you study quantum field theory, which is what all physics graduate students begin with in graduate school, you discover that even particles are unreal. They're just temporary properties. Of what are called fields. And fields are just distributions of mathematical quantities through space time. It's all. They're not. They don't seem to be grounded in anything.

[Robert Krulwich]

According to Jim, a field is kind of like a stream of numbers, pure information, numbers that tell you where a particle like an electron might be. So maybe the electron's over here? Oh, no, no. Maybe it's over there. Or maybe it's with this group, or maybe it's with that group. The problem is you can't ever see the thing itself. You can only see the effect it has on other things. So you can't observe it.

[Jim Holt]

And if something is in principle unobservable, you may as well say it doesn't exist.

[Alan Lightman]

Wait a second. No, no, no.

[Robert Krulwich]

What?

[Alan Lightman]

I mean, I'm on his side, but you could say that it's just not observable down there at the microscale. Up here, it's pretty observable. I mean, this table exists, this mixer. I mean, something is happening to give the world substance.

[Robert Krulwich]

Well, according to Jim, what we think happens, and this, admittedly, is a gross oversimplification. But in these fields, you're going to get these little fluctuations, these little events, sudden hiccups of energy, little bursts, and that's where stuffiness flickers into existence. But it's a very flickering existence. Stuff isn't permanent.

[Jim Holt]

So what is a rock? I mean, a rock looks like a good, solid, persisting object, but it's really our perception of it is energy transitions, changes in the distribution of energy from one state to another. When that happens, the energy is irradiated. It goes through my retina, goes through my pupil, rather, and strikes my retina, and I perceive the rock.

[Robert Krulwich]

I don't know if Jim would call a rock, like Bishop Barclay did, a thought in the mind of God, but he might say that deep down, what Iraq is, is an expression of rules or math. It's just here, like a shadow of an idea.

[Jim Holt]

Yeah, yeah. I've heard one physicist say that the cosmos is ultimately a concept.

[Robert Krulwich]

Are you increasingly convinced that the reason you can clap, the reason you don't fall through the floor, the reason that gravity works, is all because of certain ideas that govern. Ideas rule the world.

[Jim Holt]

Yeah, yeah. Maybe. You know, in a hundred years from now, when string theory is finally worked out, we might have a very different conception of it, but what it looks is that it's going to be mathematics and structure all the way down.

[Robert Krulwich]

You're okay with this?

[Jim Holt]

Well, I'm a sort of mathematical romantic. I love the idea that the essence of reality is not stuff. You know, stuff is kind of ugly. I mean, you want to get rid of stuff. There's too much stuff in your apartment. It's flutter, it's gross, viscous.

[Robert Krulwich]

I don't know what to do if I don't have stuff.

[Jim Holt]

Well, this is a temperamental difference between us. I like the idea that reality consists. It's a flux of pure information with no further substance.

[Robert Krulwich]

I don't know why this makes you so happy. I mean, here I would love. If I'm clapping or if I'm hitting someone in the face of. I would love to think the billiard ball of me is hitting the billiard ball of them. And that explains what's going on. Now, you've often.

[Jim Holt]

But we're living in almost in a spiritual realm. You want to live in this gross material realm where there's a lot of.

[Robert Krulwich]

Stuff, but in the spiritual realm, it's literally empty. It feels so intuitively wrong.

[Jim Holt]

But if you go back to the old 19th century view that we're made up of these little hard particle atoms that are all bumping around, is it any more plausible that you and I are just a bunch of dumb hard particles in a certain configuration? And if that's true, you know, how are certain configurations of these particles tantamount to the horrible feeling of pain?

[Robert Krulwich]

You could say pain.

[Jim Holt]

Oh, that's just a lot of elementary particles in a certain configuration.

[Robert Krulwich]

But we all know that explanation isn't enough. So when you look down to the.

[Jim Holt]

Bottom of everything, whether it's a mathematical object or whether it's little billiard balls knocking around, it's still miraculous and improbable that it should produce subjective experience, that it should produce pleasure and pain.

[Robert Krulwich]

And that mystery how you go from the most basic things, or actually the most basic nothings, to everything we see around us.

[Jim Holt]

I find that to be exhilarating to worry about the metaphysics of physics and the nature of reality. Even though it doesn't lead you to any sort of comfortable intellectual closure, it's a good way of idling away an otherwise boring afternoon, as we've just proved.

[Robert Krulwich]

It also explains why when I headbutted him with my very strong forehead, he seemed to think of it as a fascinating thought. Special thanks to Jim Holt, who, actually, we're both too shy to ever headbutt each other, too weak ever to try it. But anyway, he has a wonder. The book is called why does the World An Existential Detective Story.

[Alan Lightman]

Okay, well, I guess that's it for this podcast. Hi, I'm Jad Abumrad.

[Robert Krulwich]

I'm Robert Krulwich.

[Alan Lightman]

Thanks for listening and existing temporarily.

[Susan Orlean]

Hi, I'm Amy Beth and I'm from Longmont, Colorado and here are the staff credits. Radiolab was created by Jad Abumrag and is edited by Susan or in Wheeler. Lulu Miller and Latif Nasser are our co hosts. Dylan Keefe is our Director of Sound design. Our staff includes Simon Adler, Jeremy Bloom, Becca Bressler, W. Harry Fortuna, David Gable, Rebecca Lack, Maria Paz Gutierrez, Sindhu Nyan Sambandan, Matt Kilty, Annie McEwen, Alex Neeson, Sarah Carey, Sarah Sandbach, Anissa Vita, Ariane Wack, Pat Walters, Molly Webster, and Jessica Young, with help from Rebecca Rand. Our fact checkers are Diane Kelly, Emily Krieger, Anna Pujol, Mazzini, and Natalie Middleton.

[Jad Abumrad]

Leadership support for Radiolab science programming is provided by the Simons foundation and the John Templeton Foundation. Foundational support for Radiolab was provided by the Alfred P. Sloan Foundation.

[Unknown]

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