Physics & Philosophy with Sean Carroll

Summary

StarTalk Radio – "Physics & Philosophy with Sean Carroll"

Host: Neil deGrasse Tyson
Guest: Sean Carroll (Physicist, Philosopher, Podcaster)
Co-host: Chuck Nice
Date: June 5, 2026

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Overview

In this lively, mind-bending Cosmic Queries episode, Neil deGrasse Tyson is joined by theoretical physicist and philosopher Sean Carroll to tackle the deep and often perplexing intersections between physics and philosophy. The conversation explores quantum mechanics, the nature of reality, the arrow of time, the multiverse, cosmological fine-tuning, and the very meaning of "nothing." With Chuck Nice providing comedic relief and sharp questions, listeners are treated to a blend of serious scientific inquiry, philosophical debate, and entertaining banter.

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Key Themes & Discussion Points

The Revival of "Natural Philosophy"

• What is Natural Philosophy?
  • Physics was historically called “natural philosophy.” Over time, academia split science and philosophy into distinct silos, often leaving the “in-between” foundational questions unaddressed.

    "Once an area of philosophy starts making progress, it gets spun off to a completely different field so it never looks like philosophy actually makes progress." – Sean Carroll (06:38)

• Philosophical Foundations in Physics:
  • Carroll describes his work as foundational, asking questions like "What is an observer?" "What is infinity?" and seeking to bridge the physics-philosophy divide.

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Quantum Mechanics: Shut Up and Calculate vs. Understanding

• The "Shut Up and Calculate" Attitude:
  • Most physicists are satisfied with quantum mechanics' predictive power, but some—like Carroll—seek deeper understanding.

    "Physicists don't want to dig into the deep questions about quantum mechanics. They want to calculate their differential equations." – Sean Carroll (08:37)

• Historical Resistance:
  • Einstein and Schrödinger were among those dissatisfied with mere predictive success, pushing for a more complete explanation.

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Quantum Entanglement and the Many Worlds Interpretation

• Entanglement in Plain Terms (10:33):
  • Entangled particles behave as a holistic system, their outcomes linked even across vast distances. The predictions are exquisitely accurate, but interpretation is debated.

    "What the world is, is not a bunch of separate particles doing their own thing... It's more holistic than that." – Sean Carroll (11:40)

• Many Worlds as an Explanation:
  • Carroll advocates for the “Many Worlds” interpretation: every quantum outcome actually occurs, each in its own parallel universe.

    "Every possible measurement outcome comes true, but in a different world, in a different part of the overall quantum universe..." – Sean Carroll (15:22)

  • Q: Do we have access to other worlds?
    A: No, but it’s fun to imagine, e.g., the “Universe Splitter” app demonstrates the idea (15:47).

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The Arrow of Time and Eternal Universes

• Why is There an Arrow of Time? (Entropy)
  • Fundamental laws are time-symmetric, yet the universe has a clear direction (entropy increases). Carroll and Jennifer Chen proposed that the Big Bang was not the absolute beginning, but rather one of many events in an eternal, fluctuating cosmos (23:22).
• Two Directions of Entropy:
  • Their model describes a universe symmetric in time—a “U-shape.” Every observer always sees entropy increasing in their direction of time, even if for others (on “the other side” of the U), our past is their future.

    "From our point of view... we always define the past as the direction in which entropy was lower." – Sean Carroll (26:33)

• Experimental Verification?
  • The theory is speculative, with no current experimental confirmation, but Carroll draws parallels to Einstein’s predictions eventually being tested (27:56).

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The Cosmological Fine-Tuning Argument and God

• The Argument:
  • Some claim the universe is too finely-tuned for life to have arisen by chance; ergo, God.

    "The fine tuning argument for the existence of God... is the best argument for the existence of God. I also think it's a terrible argument, but still it's the best of the ones that they have." – Sean Carroll (30:07)

• Replies:
  • Physics increasingly explains apparent “fine-tuning.”
  • The multiverse offers a naturalistic explanation.
  • If God can do anything, then fine-tuning is unnecessary.
• Science and Explaining the Natural World:
  • The explanatory need for God has diminished as science advances (33:05).

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Cosmic Web Voids and the Cosmological Principle

• Do Voids Violate the Cosmological Principle?
  • On large scales, the universe is generally uniform, but “voids” (empty regions) are outcomes of how gravity amplifies tiny initial fluctuations—consistent with expected evolution from a mostly smooth early universe (34:33).
• Open Questions:
  • The source of the very first tiny fluctuations is still unknown. Inflationary theory remains a popular, though incomplete, answer.

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The Layers of "Nothing"

• Why is there something rather than nothing?
  • Carroll challenges the assumption that “nothing” is a coherent alternative to the universe. Even empty space has properties; true “nothing” eludes precise definition (41:41).

    "It is not at all obvious that there is an alternative to the universe existing." – Sean Carroll (41:41)

• Semantics Matter:
  • Physics’ definition of empty space is not the same as philosophical “nothing.”

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The Present Moment and Perception

• Are We Living in the Present?
  • Because of the finite speed of light and neural processing delays, our experience of “now” is always slightly behind real events—about 40–50 milliseconds delayed (49:10).

    "Our brain puts together a picture of the world that is on a slight time delay." – Sean Carroll (48:17)

• Neuroscience vs. Reality:
  • The brain synthesizes sensory input, and at certain ranges, compensates for delays (e.g., sound vs. light), but only up to a point.

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The Dream of a Unified Theory

• Is a “Theory of Everything” Possible?
  • Physicists pursue it, but Carroll clarifies it may not be one elegant equation—it could be messy and fragmented, reflecting the universe’s own nature (53:51).

    "We don't have any right to say that the final theory of the whole universe will be simple or elegant or easily understandable by us." – Sean Carroll (54:20)

• Philosophical Biases:
  • History (e.g., Kepler) cautions against forcing beauty or unity onto nature.

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Notable Quotes & Memorable Moments

• On philosophy and science:
  • "I'm actually there to understand the universe." – Sean Carroll (07:49)
• On the many worlds theory:
  • "You have iPhone. You can download an app called Universe Splitter..." – Sean Carroll (15:47)
• On the brain constructing reality:
  • "Our brain collects things and says, I'm going to put this together into a picture of the present." – Sean Carroll (49:09)
• Chuck Nice, comic relief:
  • "If Psy understands what the hell you just said, then they need to be the cohost of this show because I am not going to lie." (25:42)
• On the difficulty of neuroscience:
  • "Neuroscience ... that's a whole frontier right there. Like, way harder than physics or astronomy." – Sean Carroll (50:15)

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Timestamps for Key Segments

• Natural Philosophy vs. Physics: 06:12–08:37
• Quantum Mechanics Philosophy: 08:37–09:40
• Entanglement and Many Worlds: 10:33–15:22
• Quantum Branching & Universe Splitter: 15:47–17:01
• Arrow of Time & Entropy, Eternal Universe: 23:22–27:19
• Fine-Tuning & God Debate: 30:07–33:22
• Cosmic Web Voids & Cosmological Principle: 34:21–37:06
• "Why is there something rather than nothing?": 41:41–45:59
• Are We Living in the Present? (Neuroscience): 47:37–51:52
• Unified Theory/Philosophical Bias: 53:32–55:20

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Episode Tone & Style

• Thoughtful, energetic, and playful, balancing rigorous discussion with humor.
• Carroll and Tyson riff off each other with both mutual respect and friendly skepticism; Chuck Nice provides accessible comic relief and clarifying questions.
• Jargon is explained, and complex topics are made approachable (though some remain brain-bending!).

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Final Thoughts

This episode epitomizes StarTalk's approach—melding deep science, philosophy, laughter, and audience questions into a captivating journey through the mysteries of existence. Carroll’s expertise and Tyson’s curiosity illuminate the unresolved puzzles where physics and philosophy blur, leaving listeners with new frameworks for contemplating reality and their place within it.

"Keep looking up!" – Neil deGrasse Tyson

Transcript

[Neil deGrasse Tyson]

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[Neil deGrasse Tyson]

Hey, Start talking. Neil here. You're about to listen to an episode specially drawn from our archives to serve your cosmic curiosities. The archives run deep. If you enjoy this, take a peek at the full catalog on your favorite podcast platform. There's a lot there to tickle your geek underbelly. Check it out. Welcome to StarTalk, your place in the universe where science and pop culture collide. StarTalk begins right now. I'm Neil Degrasse Tyson, your personal astrophysicist.

[Lindsay Nix Walker]

And I'm Lindsay Nix Walker, senior producer of StarTalk. And Neil and I just co authored

[Sean Carroll]

a brand new StarTalk book coming out September 12th.

[Neil deGrasse Tyson]

Yeah, this is the third in a series of collaborations with National Geographic Books and this one is titled To Infinity and Beyond and it's available for pre order from the StarTalk website startalkmedia.com books. If you do pre order the book, you have a special access to a conversation that I'll be having with Lindsay Walker. She's been my senior producer for years. She's behind the scenes in practically every StarTalk episode you've ever seen or heard. I look forward to doing a live stream for our audience and they'd be able to submit questions in advance, so we'll see you there. We'll see you then. Startalkmedia.com Books this is Startalk. Neil DeGrasse Tyson here, your personal astrophysicist. I got with me my co host, Chuck. Nice, Chuck.

[Chuck Nice]

Hey, what's happening?

[Neil deGrasse Tyson]

All right. Always good to have you there, man. Especially when we have Cosmic Queries. Fan favorite? Oh, yeah, fan favorite. We love them. You get to ask a question with sort of entry level participation in our patreon program. Just $5 a month.

[Chuck Nice]

That's it.

[Neil deGrasse Tyson]

That we collected them. And you know in advance what you're asking about. Because today's topics involve physics and philosophy. People love just talking about stuff for which there is no answer.

Well, of course.

[Chuck Nice]

You know why? Because it makes them feel like they have a stake and a say.

[Neil deGrasse Tyson]

It's like because nobody has the answer.

[Chuck Nice]

Yeah, nobody has the answer. So I'm just as right as you are, right? Like. No, you're not. You're still an idiot. Okay, see, I have a PhD in Philosophy and physics. I have what's called an informed opinion. You, on the other hand, went on the Internet, saw somebody on Joe Rogan's show say something about something else, and now you think you're an expert. Shut up. Shut up. All right, Sorry.

[Neil deGrasse Tyson]

Okay. That's the end of our show. Well, we're bringing into this an old friend and colleague, Sean Carol. Sean, welcome to StarTalk.

[Sean Carroll]

Hey, thanks for having me on, Neil.

[Neil deGrasse Tyson]

Welcome back to Start Talk. I should say this is. You've been on at least four or five times. You are one of the world's experts on not only physics, being a physicist, but you're also that subcategory of physicists who cares about philosophy and have engaged philosophers on the frontier of our understanding of physics. So it's great to have you for this Cosmic Queries. And dare I say we crafted this Cosmic Queries around your expertise. So you are the Homewood professor of Natural Philosophy at the Johns Hopkins University right there in Baltimore. And you have a joint appointment at the Santa Fe Institute. Now, that institute, everything I know about it, those are deep thinkers about things that it's like what? Like you twist your head like a dog hearing a high pitch. It's like, what? And you're the fractal faculty at the Santa Fe Santa Fe Institute. And your expertise in quantum physics, space, time, cosmology. Love it. Emergence, entropy, dark matter, dark energy, symmetry, origins of the universe. And perhaps most people who know you know you through your Mindscape podcast. So always good stuff happening there.

[Sean Carroll]

Those things that make you tilt your head and Scrunch up your eyes like, that's my lane. That's what I do.

[Neil deGrasse Tyson]

That's you. Okay? So I say this lovingly and crazily. Stay in your lane.

[Chuck Nice]

Okay,

[Neil deGrasse Tyson]

so tell me, what is first natural philosophy. I last saw that term with, you know, 17th, 18th century philosophers. Natural philosophy was the then term for what today we would call physics, right? Because political philosophy and religious. Natural philosophy was physics. So what? Why isn't that just physics?

[Sean Carroll]

Professor, There's a joke in philosophy circles that once an area of philosophy starts making progress, it gets spun off to a completely different field so it never looks like philosophy actually makes progress. But you're right. Newton, Galileo, those folks would have called themselves philosophers. The idea of a physicist hadn't been invented yet. But what happens is that academia loves to categorize and silo people. So they invent a physics department and a philosophy department, and they examine what questions you could ask, and they decide which is which. But what that does is that it means that all the in between stuff, because it's really a continuum here, not a interstitial ideas and things, those just get lost. And we're at a point in physics right now where questions like, you know, what is an observer? What is infinity? Why is the past different from the future? What is emergence like? These are physics questions.

[Chuck Nice]

What makes the night different from all other nights? Sorry.

[Neil deGrasse Tyson]

Yeah.

[Sean Carroll]

Philosophy is pride.

[Neil deGrasse Tyson]

Is that a song lyric? Is that. Okay, all right. So. So. So you are there to clean up the pieces, is what you're saying?

[Sean Carroll]

Well, I'm actually there to understand the universe. I think that the common thing within natural philosophy is we're not studying the process of science or anything like that. We're studying nature, we're studying reality. But there's a way of doing it that is kind of foundational that, you know, takes a step back. Look, physicists, bless their hearts. You've met physicists, Neil. I know this. And ask them about.

[Neil deGrasse Tyson]

By the way, Chuck, anytime someone prefaces something by bless their heart, bless your heart, they're about to insult them in something.

[Chuck Nice]

Nothing good ever. You know, it's just like.

[Neil deGrasse Tyson]

It's in the same sentence as bless their heart.

[Chuck Nice]

Especially if you, a old white lady from the south, you know what I mean? It's just, oh, bless her heart. She's just a little whore, that's all. Sarah, you know, it's. That's how it goes, okay?

[Sean Carroll]

I started a book by saying you do not need a PhD in theoretical physicists in physics to be afraid of quantum mechanics. But it doesn't hurt. And physicists don't want to dig into the deep questions about quantum mechanics. They want to calculate their differential equations.

[Neil deGrasse Tyson]

Shut up and calculate.

[Sean Carroll]

Shut up and calculate. And that's the opposite of what I like to do myself. So the philosophers humor me on that.

[Neil deGrasse Tyson]

So just to be. Just to make sure all our audience is on the same page, quantum mechanics is amazingly successful at predicting and describing reality, but that reality defies all our common sense. And you reach a point where you just say, okay, I'll just live with that and continue to calculate. And, Sean, you're telling me you're not satisfied with that. You want to understand crazy quantum phenomena on some level where we can sit down and say, okay, now I understand it. Is that what's driving you?

[Sean Carroll]

Yeah, absolutely. Just like it drove professors Einstein and Schrodinger back in the day. But there was this consensus that developed in the 1920s and 30s by physicists where, like you say, we have some equations, we can solve them, we can calculate them, we can make predictions. And beautiful, exquisite agreement between the calculations and the predictions without knowing what's going on, without agreeing on what's actually happening in the world. And there's a whole bunch of physicists who will say, oh, no. Understanding what is actually happening in the world, that's not my job. I'm just here to make predictions. I strongly feel that's not right. I'm here to help understand what is going on in the world.

[Chuck Nice]

Right. So you're the show your work, part of this whole equation.

[Sean Carroll]

Explain your work.

[Neil deGrasse Tyson]

Show it.

[Sean Carroll]

Hide anything. No sweeping under the rug. Yeah.

[Chuck Nice]

It's okay to come up with the answers, but we got to know how we got there.

[Sean Carroll]

Absolutely.

[Neil deGrasse Tyson]

Yeah. Okay, so, Sean, what's been in all the buzz in recent years is a quantum entanglement. All right? And let me offer my best explanation, and you correct it, and then. But then give me your understanding of it.

[Chuck Nice]

All right?

[Neil deGrasse Tyson]

You can create two particles simultaneously that have sort of complementary properties, quantum properties to them, and they can separate, and they know about each other. Dare I use the word know? They know about each other's existence. And. And the moment you make a measurement of one of them, the other particles, properties manifest to whoever is observing them, and they manifest instantly, transcending the speed of light. And so we know that happens. But, Sean, you're going to tell me that you understand it, or will you not?

[Sean Carroll]

Well, I think that we have multiple competing ways to understand it. We have not agreed on the correct way. My way is, like I said, Chuck,

[Neil deGrasse Tyson]

in The bar, you just have the beer and nobody agrees. Right? That's the difference.

[Sean Carroll]

But like, like you said, we can make the prediction to exquisite accuracy. People tested the prediction. They won the Nobel Prize for it last year. That was what the physics Nobel Prize was given for. And by the way, the whole reason we know and care about entanglement was because Einstein in 1935 was trying very hard to figure out what really is going on. Right. And he didn't quite succeed. He didn't get the answer there. But it's that drive to understand that led here. And ultimately what we can say, I think, with some confidence, is that what the world is, is not a bunch of separate particles doing their own thing. It looks like a bunch of separate particles under certain very clear circumstances. But in other circumstances, like this entanglement business, it doesn't. It's more holistic than that. So people like me who are advocates of the many worlds interpretation of quantum mechanics, we have a very simple, straightforward way of talking about entanglement. But there's other people out there who talk about it differently. And, you know, that's great. That's what academia and intellectual curiosity is all about.

[Neil deGrasse Tyson]

Remind us of the many worlds hypothesis, because I think that's now 100 years old. Right. We're, we're on the centennial decade of the major discoveries of quantum physics, the 1920s. So if you can just remind us what the many worlds, I think it was once explained to me, and I said, what are you smoking?

[Chuck Nice]

I think that's. Sure, that's what I said.

[Sean Carroll]

When we teach undergraduates quantum mechanics, we say that a quantum system has two different ways of evolving. There's one way it can evolve when you're not looking at it. And that's what Schrodinger and Heisenberg and their friends figured out back in the day. But then.

[Neil deGrasse Tyson]

Well, just to be clear, I just to be precise, I know how you're using the word evolve, but to a biologist, the word evolve means something completely different. So you mean it unfolds? The events unfold?

[Sean Carroll]

Yeah, it changes. It has its dynamics, whatever it's doing, whatever its behavior is. But then there's a whole nother way that we need to describe that behavior when we make a measurement, when we observe the system. Famously, in quantum mechanics, you can't predict deterministically, precisely, with 100% confidence what answer you're going to get. You can predict a probability distribution over different possible answers.

[Neil deGrasse Tyson]

And Einstein said, God does not play dice.

[Sean Carroll]

That's what Einstein said. Yes.

[Neil deGrasse Tyson]

With the Universe.

[Sean Carroll]

Or said it kind of looks like,

[Neil deGrasse Tyson]

you know, you are playing dice. I'm just saying. I'm just.

[Chuck Nice]

And by the way, what a. What a presumptuous statement on Einstein's behalf. I mean, who knows, Sean?

[Neil deGrasse Tyson]

Didn't Niels Bohr say, einstein, stop telling God what to do?

[Chuck Nice]

I mean, who's to say that God's not down on one knee going, papa needs a new pair of shoes? You don't know that. You don't know that. So was it Niels Bohr?

[Neil deGrasse Tyson]

Somebody said it to Einstein. Who was it?

[Sean Carroll]

I think it was Niels Bohr. I think the better advice would be, like, don't play dice against God. You're not going to win if that's, you know.

[Neil deGrasse Tyson]

Okay, there you go.

[Chuck Nice]

That makes sense.

[Sean Carroll]

So what is this going on with this weird thing? You don't expect measurements, observations, looking at things to be part of the fundamental nature of reality. Right. You know, it never was before quantum mechanics came along. So you can ask yourself, what if, like, all of that was unnecessary. This whole idea that we need a separate rule for what happens when we measure something. What if you just erase that from the rules of quantum mechanics? And the answer is that what you find is that every possible measurement outcome comes true, but in a different world, in a different part of the overall quantum universe, you get parallel worlds where different measurement outcomes are true.

[Neil deGrasse Tyson]

That's when I asked what the guy was smoking.

Wow. Now, wait a minute.

[Chuck Nice]

So these different worlds are in the same realm. Is that the case? Or are we talking about completely different unfoldings that create completely different scenarios that make the whole thing work?

[Neil deGrasse Tyson]

Or another way to ask that, do you have access to these other worlds?

[Chuck Nice]

There you go. Thank you.

[Sean Carroll]

You have iPhone. You can download an app called Universe Splitter. And if you're ever stuck on what decision to make, you know, should I have a hamburger, should I have pizza for dinner tonight? Or whatever? Ask the Universe Splitter and it will come back with an answer, and you can be guaranteed that there's a whole nother universe which you can never interact with or talk to, in which you do the opposite thing. So there's.

[Neil deGrasse Tyson]

It's split in that instant, right?

[Sean Carroll]

In that instant?

[Neil deGrasse Tyson]

Yes, at the decision instant.

[Chuck Nice]

Okay. Okay.

[Sean Carroll]

It's a physical quantum process, and that's

[Chuck Nice]

because of the entanglement, because they couldn't exist simultaneous. They have to exist in those positions at the time of the decision so that when one does it, the other does the opposite, or when one does something. So there's an action and There's a reaction, but there can't be action. Action. It has to be so that they're existing and then reacting differently.

[Neil deGrasse Tyson]

Is that Sean Chuck is about to blow a gasket?

[Chuck Nice]

No, because you're freaking me out, man. You are freaking me out.

[Sean Carroll]

This is not anything that we bump into in our everyday lives. If it doesn't make you a little bit uncomfortable, you're not taking it seriously.

[Neil deGrasse Tyson]

Okay.

All right.

Wow.

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[Neil deGrasse Tyson]

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[Chuck Nice]

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[Neil deGrasse Tyson]

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Let's get to the questions.

[Chuck Nice]

Okay, man, we got to digest this. This is already good stuff. Four out of ten tell you, right? I'm so mad I didn't have an edible before this show. I really should have taken a gummy before this one. Dog gone. All right, here we go again.

[Neil deGrasse Tyson]

These are from our Patreon supporters. Thank you all for what you do for us. All right, Chuck, you Got your, your iPad there?

[Chuck Nice]

All right, I do. So here we go. This is from Sai says. Hello. Dr. Tyson, Dr. Carol, Dr. Haha. First time patreon member.

[Neil deGrasse Tyson]

I know, right?

[Chuck Nice]

First time Patreon member here. Huge, huge fan. I am Sai Anurag from India. Chuck, if you get my name right, I swear to God I will double my Patreon membership. Yeah, well, I guess you have no. You're in no danger there, are you?

[Neil deGrasse Tyson]

Yeah, I think he's going to have it after what you just did to

[Chuck Nice]

his name, but all right, that was funny. My question pertains to Dr. Carroll's research which says that the universe is infinitely old and Big Bang is just one of many events resulting from quantum fluctuations of a vacuum energy in a cold de sitter space. Please throw some light on. What kind of space is this? How can I visualize it better in order to understand it more fully?

[Sean Carroll]

Ooh, good. Very good. I love it. You know, hanging out on the wrong street corners. I don't know where they pick these things up. But yes, this is all driven by the very famous philosophy question, why is the past different from the future? Why is there an arrow of time? Because the fundamental laws of physics have no arrow of time in them. The answer is entropy. And the second law of thermodynamics. The universe used to be more organized, lower in entropy. The whole history of the universe is just entropy increasing disorder and chaos developing all around.

[Neil deGrasse Tyson]

We're all going to die. That's the.

[Sean Carroll]

It's not your fault necessarily, but you're contributing to the disorder and chaos all around us. And that started about 14 billion years ago, near the Big Bang. At the moment of the beginning of the universe, our universe was exquisitely orderly. Doesn't necessarily look that way, but you run through the numbers and it's true. Why? Why is that true? Why was the early universe so orderly? And so I've long wondered about this, and I wrote a paper years ago now with a woman who was a graduate student of mine at the time, Jennifer Chen, where we proposed that the Big Bang was not the beginning of our universe. Other people propose that in different contexts, but we made the case that you don't need a fine tuned, special organized, low entropy beginning of the universe. The universe can be eternal. It can last forever. But what happens is it empties out just like our universe is doing. A universe can be completely empty. The future of ours will be, but it still won't be perfectly quiet. There are still quantum fluctuations that can lead to whole new universes coming into existence. And as that happens, they all start in low entropy conditions and the entropy grows and gives that little part of the universe an arrow of time. And the fun part is the far, far past. The same thing happens, but in the other direction. So there's sort of a symmetric shape to the universe where the future is a story of more and more universes being created and the arrow of time pointing in that direction. The past is a story of more and more universes being created with people in them who think that we are in their past.

[Chuck Nice]

I'm going to tell you right now, if Psy understands what the hell you just said, then they need to be the co host of this show because I am not going to lie.

[Neil deGrasse Tyson]

Wait, wait.

[Chuck Nice]

So Sean.

[Neil deGrasse Tyson]

Wait, Sean, you lost me at the end.

[Chuck Nice]

I need you to do the end again.

[Neil deGrasse Tyson]

So Sean, what you're saying is there's some symmetric point among these universes and these time continua where we're in one direction where entropy increases. But in principle, there's a whole other realm where entropy decreases.

[Sean Carroll]

From our point of view, from the people living in it, they will always see entropy increasing because we always define the past as the direction in which entropy was lower. So it's a big U shape that is perfectly now.

[Chuck Nice]

So we're in their past because they're looking at us and seeing a decreasing entropy which is indicative of traveling backwards because we're moving towards a more ordered universe. But we cannot be moving towards a more ordered universe if we are moving into the future because we are always moving towards entropy. So if you are observing that, then you are in my. I am in your past. So because you're looking at me going towards order.

[Sean Carroll]

Chuck gets it. We're done.

[Chuck Nice]

Yeah, man. Yeah. Science. Oh God. And it's insane.

[Neil deGrasse Tyson]

Chuck, you're blowing out the volume level on the microphone.

[Chuck Nice]

That's insane. Oh my God.

[Neil deGrasse Tyson]

Okay, wait. So Sean, before we get to the next question, what these are ideas, is there any way to experimentally verify any of this?

[Sean Carroll]

Well, we're trying, but the short answer is we don't know yet. We don't have that sound like a no.

[Neil deGrasse Tyson]

Just say.

[Sean Carroll]

It's very much not a no.

[Neil deGrasse Tyson]

Oh, okay.

[Sean Carroll]

But all the words, Neil, these. All the words matter here.

[Neil deGrasse Tyson]

Okay?

[Sean Carroll]

Yeah, and this, but this is a more a broader idea, right? There are plenty of tentative preliminary scientific ideas which are too ill for yet.

[Neil deGrasse Tyson]

I'm with you.

[Sean Carroll]

Predictions.

[Neil deGrasse Tyson]

Einstein's gravitational waves, Einstein's gravitational rings. Yeah, I'll give you that.

[Sean Carroll]

We'll get there. We will get There, send money, we'll do it. Just trust us.

[Neil deGrasse Tyson]

Yeah, in your lifetime.

[Sean Carroll]

And lifetime is getting shorter every year, so I don't know.

[Neil deGrasse Tyson]

All right, Chuck, what else you got?

[Chuck Nice]

All right, let's go on to Doug Sherman. Doug Sherman says, hi, Neil. Hi, Sean.

[Neil deGrasse Tyson]

Lord.

[Chuck Nice]

Nice. The Doug. This is Doug from Frisco, Texas. All right, all right. Way to go, brother. Doug says. I thoroughly enjoyed Sean's debate on God and cosmology against William Lane Craig. Although I'm still trying to get my head around everything Sean explained. One amongst many arguments I found interesting was sean's rebuttal against Mr. Craig's technological argument that the finely tuned universe was evidence for the existence of God. I don't recall the specifics, but I believe Sean stated that in some models, the finely tuned universe approaches. Then he says, could Sean once again go through the perspective of the fine tuned argument? I also reject the technological argument, but for more simplistic reasons than my flawed brain can rationalize.

[Neil deGrasse Tyson]

So just for context, William Lane Craig is a proponent of basically a God created universe. And he's not the Bible thumping person in such a conversation as others might be. He's trying to stay grounded in the natural world, taking you to a precipice where you say, okay, God must be there. So I'm pretty sure Sean wouldn't debate just anybody on that subject. So William Lane Craig has some, some debating respectability in that regard. Did I characterize your opponent accurately, would you say?

[Sean Carroll]

Yeah, that's fine. But the, the fine tuning argument for the existence of God is what I think is the best argument for the existence of God. I also think it's a terrible argument, but still it's the best of the ones that they have. So I'm glad when they refer to it. And the idea is that you look around the world, the world in which we live, the universe we find ourselves in, and you say there are features of this universe that need to be the way they are in order for life to exist. If they were different, life couldn't exist, but they easily could have been different, right? The things like the amount of energy in empty space could have been so large that it would rip planets apart before they ever form. But we seem to have gotten lucky. We seem to find ourselves in a universe that allows for our existence. And so the argument is, I know why. It's because God did it, because God created a universe in which that's possible. A very common counter argument is, well, it also could just be a multiverse, right?

[Neil deGrasse Tyson]

You're not in all the others to have this conversation. Right.

[Sean Carroll]

So they help play an explanatory role that in accounting for why our universe looks so fine tuned. So two things going on here. One is the proponents of this argument tend to exaggerate the degree of fine tuning that they need. And that's what the questioner is referring to. There's certain things that William Lane, Craig and others say, oh, I just don't get it. That's so fine tuned. But you can raise your hand and say, actually physics has completely explained that one. Now we don't need to go beyond the realm of physics to account for that. So but in other ways it still looks fine tuned. And my favorite rejoinder is actually this is a great argument for the non existence of God. Because if God existed and God created life, God is not beholden to the local laws of physics. God can create life however God wants to because he's God. God can do anything. You don't need the physical conditions to allow for the existence of life. Unless God does not exist.

[Chuck Nice]

All right, now let me just ask a question here because just to further clarify, what if instead of needing the laws of physics, the laws themselves are a reflection of, of what God has done? So it's not necessarily that the laws are needed, it's that the laws exist because they just happen to be a byproduct of the creation itself.

[Sean Carroll]

That is completely possible. And Neil will raise us in here and say, how do we observationally test that hypothesis?

[Chuck Nice]

Okay, listen, I'm 100%, I'm on board with that. Okay, good. I just wanted to make sure that that could, that that could be an argument to be had, that's all.

[Sean Carroll]

But look, for the last 500 years, as science has done more and more to explain why the universe is the way it is, the role for God as an explanatory move has gone away, has diminished. Right. And so you are.

[Neil deGrasse Tyson]

It continues to do so. Yes.

[Sean Carroll]

And so you're left with if you want to believe in God, and there's plenty of very, very smart people who do, they tend not to rely on God to account for the things that we observe in the natural world.

[Chuck Nice]

Gotcha.

[Neil deGrasse Tyson]

Wow, fascinating stuff.

All right, Chuck, keep going. We've only gone through two or three questions. Let's see if we can.

[Chuck Nice]

Well, we just have to have Sean back, that's all. This stuff is too good. We can't rush. We cannot rush through this. This is too good.

[Neil deGrasse Tyson]

At one point get a double wide episode with him.

[Chuck Nice]

Yeah, well, yeah, yeah, absolutely.

[Neil deGrasse Tyson]

All right, here we go.

[Chuck Nice]

Tom P. Knight says this. Hello. I'm a Patreon supporter of both StarTalk and Mindscape. Great to see Sean on the show. Do voids in the cosmic web like the Eridanus supervoid violate the cosmological principle? What could be the cause of these structures? Thank you for your service.

[Neil deGrasse Tyson]

Okay, good one. Eridinus is a constellation. I think it's a waterfall or it has something to do with water, my memory serves. But anyhow. Sean, what you got there?

[Sean Carroll]

This is a great question, but there's a lot going on here. I'm going to try to keep it brief here. You know, there's something called the cosmological principle that says that if you squint and look at the universe on very large scales, everything looks the same everywhere, right? The same number of galaxies and whatever. It's a dopey thing to call a principle, because it's not a principle. It's just a fact that you see about the universe. It could easily have been otherwise, especially because it's not exactly true. And that's what the question is getting at. There are places in the universe where matter is very dense. There's places where it's very empty and so forth. The way that modern cosmologists think about this question is to say the early universe, it was even smoother than it is now. It was very, very smooth. There was only a difference in one part in a hundred thousand. As you went from place to number one, why was it not perfectly smooth, but number two, why was it pretty darn smooth? And number three, how did it evolve, using the word evolve again from that condition 100,000 years after the Big Bang, to our conditions now, the last one, how it evolved, is the one we have the best handle on. It was gravity doing the work. Gravity turns up the contrast knob on the universe. So if you have a slightly emptier region, it empties out. You have a slightly heavier region, it collects matter onto it. And so we went from very faint ripples, if you look at the cosmic background radiation, to these very vivid voids and galaxy clusters that we see today. We still don't know where those first ripples came from. Inflationary cosmology is a. Is a favorite thing to talk about, but that's a whole nother episode.

[Chuck Nice]

Wow. There you go.

[Neil deGrasse Tyson]

So I like the way you said that you. We. There's. We observe these fluctuations of one part in a hundred thousand, and you say, well, how come it's not perfectly smooth? How come it's one part in A hundred thousand. And how come it's not anywhere near that today? It's a fun way to think about that problem because it's easy to say, oh, here's the answer, and then move on. But wait a minute. Why isn't it something else? Yeah, right. And not enough of that goes on, I think.

[Sean Carroll]

Well, it's a. It's a, once again, a reflection of the fact that the early universe had low entropy because gravity was so strong. In the early universe, a more common generic random configuration would have been wild fluctuations like black holes here and empty space there. And so the fact that it was so smooth does kind of demand an explanation. And we're not sure what the explanation is.

[Chuck Nice]

Okay.

[Neil deGrasse Tyson]

All right, keep this going, Chuck. And that one was from the overlap of the Venn diagram between Mindscape and startalk. Love it.

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[Neil deGrasse Tyson]

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[Chuck Nice]

Why?

[Neil deGrasse Tyson]

Because I've been shopping with Quince for years and I was delighted to see that they are now supporting StarTalk. So if you want to look good like me, if you want to elevate your summer wardrobe, even though let's be for real, you're not going to look as good as me, go to quint.com startalk for free shipping on your order and 365 day returns. Now available in Canada too. That's Q U I n c e.com startalk for free free shipping and 365 day returns. Quince.com startalk and guess what? You're gonna look even better than me.

[Sean Carroll]

Hey, this is Kevin the sommelier and I support StarTalk on Patreon. You're listening to StarTalk with Neil DeGrasse Tyson.

[Chuck Nice]

This is Malcolm Marfan and Malcolm says hello, Dr. Tyson, Dr. Carol and Chuck maybe. Okay, okay. I love these people, man.

[Neil deGrasse Tyson]

They love you, Chuck, no matter what they call you.

[Chuck Nice]

I know. No, I know. Well, Malcolm Marfan here, all the way from Trinidad and Tobago and he says, oh, nice. He says, Dr. Carol, I came across your 2018 paper, why is there Something rather than nothing? And thought, wow, this guy's really dedicated to the lot of brain power, to the concept of nothing. Now, since you've clearly become an expert in nothingness, can you shed some light on the various layers of nothing? Specifically, how do these layers of void stand apart and how are they intertwined with the head spinning realms of cosmology and quantum mechanics? P.S. can I get a philosophy or physics degree with nothing from. With nothing for my thesis?

[Sean Carroll]

I think our questioner missed the point of the title of my paper, which is that there is something like, you know, we can contemplate that there wouldn't have been anything and there's just nothing. But what I say in the paper is, can we really contemplate that. I mean, I think that we have this informal training from our everyday lives, right, where we have boxes with things in them and boxes with nothing in them. And so we think that there's an option, there can be things or there could be nothings. But when it comes to the universe, it is not at all obvious that there is an alternative to the universe existing. What does it even mean for nothing to exist? How does nothingness even exist? I mean, that's kind of what I'm getting at in the paper, which is that it's not at all clear that the reason why the universe exists is the kind of thing that has an answer to a why question. Maybe we, maybe we just have to accept it as a brute fact and be lucky about it. So I do think this stuff is fun to talk about, but I don't think that it is nearly as down to earth and simple and physical as certain physicists who like to talk about this make it out to be. It's a, It's a fundamentally a philosophy question.

[Neil deGrasse Tyson]

Wait, wait. But John, if there were no quantum physics, in principle, you could talk about space as having no particles and none of these virtual particles that quantum physics forces into it. You just say, remove the atoms and all known particles. That's as pretty good and nothing as anyone would hope to describe, isn't it?

[Sean Carroll]

No, it's something. It's space. It has.

[Neil deGrasse Tyson]

Because you have a word for it. Okay, you call the empty space space and I call the empty space nothing. Aren't we just semantically differing there? Not fundamentally differing?

[Sean Carroll]

Is empty space three dimensional?

[Neil deGrasse Tyson]

I don't know.

[Sean Carroll]

You just don't want to answer it because you know.

[Neil deGrasse Tyson]

Okay, so let's say, let's say it's three dimensional and, and exists on a time continuum. Sure.

[Sean Carroll]

So it has a property. Then it's not nothingness. It has. There's a way it could have been different?

[Neil deGrasse Tyson]

Well, you invoke a way to measure stuff in it. I wouldn't call that an inherent property of the empty space.

[Sean Carroll]

It's. It's different than four dimensional empty space.

[Neil deGrasse Tyson]

Okay, so how about this? How about this? Okay, again, one of the reasons why I don't like arguing with philosophers, because ultimately it comes down to how you're defining the words that you're using in your sentence in so many of those arguments. So let me just say if we define something versus nothing as something is, there's a thing there. And I take everything out so that as Chuck said, there's, as you said, there is no thing, nothing. There, then that's nothing. Okay, now we're. Now you're saying there's a grid system there that we can invoke, or it's inherent. So that's a thing. Okay, so now I add to my inventory of a thing, particles plus grid systems. Okay, fine. Then that's there. So now we have to ask, can we take away the grid? What I think is a more interesting question is, do the laws of physics apply in that volume? And therefore it can't be entirely nothing, because laws of physics apply even though there's nothing there to manifest them.

[Sean Carroll]

Ooh, now you're getting deep. So I like it because you're invoking not what the system is, but counterfactual properties of what would happen to the system if you changed it a little bit. Which is fine. It's a fine thing to do. Look, you're absolutely right that there is no pre existing definition of the word nothing to which we're referring here. You could have different ideas. I think at the deepest level of this question is why is there a universe at all versus complete non existence, not even space? I mean, even you had to preface your question by saying, like, imagine there was no quantum mechanics. And for that matter, secretly imagine there's no general relativity either. Because. Okay, yeah, you're throwing away all of known physics to even ask your question. But of course, within known physics, you can ask plenty of questions about why isn't space empty? Why is space three dimensional? Those are perfectly good physics questions. It's a little bit different than the question of why there's a universe at all. You can ask the both of them separately. It's not a right or wrong thing to ask.

[Chuck Nice]

Right?

[Neil deGrasse Tyson]

Yeah. All right.

[Chuck Nice]

Well, that's super cool. What a great question.

[Neil deGrasse Tyson]

Yeah, yeah, because when someone says, why is there something rather than nothing, and I look out in the universe, which is mostly nothing, I say, there's a lot of nothing in the universe. So whatever something we have that is side by side with a lot of nothing until you start invoking other definitions for what nothing can be. So that's my only point there.

[Chuck Nice]

Well, there you have it, Malcolm. We have discussed your question and we have achieved nothing. Okay,

[Neil deGrasse Tyson]

all right, all right. Keep it going.

[Chuck Nice]

This is Javier Ortega, who says hi. You guys are just the best. Greetings from my artificial limbs development lab in Panama. Just a quick question that will not let me sleep due to the speed of light. We can only see the past while looking into distances of the cosmos. And how do we know we are in the quote Unquote, real present. We sense everything with delay, even short distances. Also, there's a delay between our senses and our brain. Are we sure that we perceive now as now? Maybe it's just something relative to us, like movement. Maybe we are five hours in the past or 200 million light years in the past according to some other arbitrary timeline or other alien beings that could be tr. That could travel instantly.

[Neil deGrasse Tyson]

Everybody's been smoking before this.

[Chuck Nice]

Let me tell you, man. I told you. I told you. He says, I hope you read this message from the past. Please keep looking up.

[Neil deGrasse Tyson]

It makes an interesting point that what is. What does the present even mean if everything we do to interact with the world has some kind of time delay? Like, I like that idea of the brain, our understanding, our senses, our.

[Chuck Nice]

That's true.

[Neil deGrasse Tyson]

Our. You know, my hand is not as it. Is it as it was a billionth of a second ago. So what does it even mean to talk about the present?

[Sean Carroll]

Yeah, there's a science answer here and a philosophy answer here. I'll give you the science answer because it's quite good. Our brain does not perceived the present. Our brain puts together a picture of the world that is on a slight time delay. Like our brain wants to be able to bleep out things that it doesn't. Like if you watch someone dribble a basketball and they're right next to you, you will see the basketball hit the ground and you will hear the thump of the basketball against the ground. And they coincide. They go along with each other. If that person walks away still true. You see and hear the same thing at the same time, even though the light gets to you much quicker than the sound. And what happens is if they keep walking away suddenly, they will go out of sync. The vision of the basketball hitting the ground and the sound of it.

[Neil deGrasse Tyson]

Because that happens suddenly. So your brain was correcting for it.

[Chuck Nice]

Holy shit.

[Sean Carroll]

Because your brain corrects for it as long as it's near enough. Your brain says, this is all now. And you can even measure how much it is. It depends on what sense you're talking about and what perception. But roughly think about 40 or 50 milliseconds of time is a little window in which your brain collects things and says, I'm going to put this together into a picture of the present.

[Neil deGrasse Tyson]

A millisecond is a thousandth of a second. So 40 to 50 thousandths of a second would be like 500ths of a second.

[Sean Carroll]

There you go. Good memory. Excellent. Yes.

[Neil deGrasse Tyson]

Wait, so what you're saying is there's A point where the brain just gives up recreating the present and said, I can't compensate for this.

[Chuck Nice]

It's too much. I can't do no more. So you do deal with it. Go on without me. Oh, God. It's just. I can't take it.

[Neil deGrasse Tyson]

So this is an experimental result, Sean,

[Sean Carroll]

you know, look, as I'm sure you already know, neuroscience, biology, psychology, that's a

[Neil deGrasse Tyson]

whole frontier right there.

[Sean Carroll]

Like, way harder than physics or astronomy.

[Neil deGrasse Tyson]

Way harder. Way harder.

[Chuck Nice]

Yeah.

[Neil deGrasse Tyson]

Okay, I did not know this. So interesting. So the brain constructs a present so that we can help make sense of the world in our own moment, that we make decisions.

[Chuck Nice]

It's actually doing that with everything, all the time, your brain. Because there's just too much input for your brain to actually process in real time. So most of what it's doing is kind of creating a construct and then painting a picture of what it is, and then it looks for changes in that construct.

[Neil deGrasse Tyson]

Wait, so, Sean, this tells me that if the brain can't complete the picture, it'll make stuff up to fill out the picture.

[Chuck Nice]

Absolutely. That's why there are so many black men in prison right now.

[Sean Carroll]

I was going to say optical illusions, but sure, yes. Racial incarceration, inequalities. That's another one.

[Neil deGrasse Tyson]

Yes.

[Sean Carroll]

This is the philosophy part of the answer, which is that there is a real world out there. I mean, there is objective physical reality, but there's also the picture, the image, the model of the world that our brain puts together. And they're related, but they're not the same. And our brain is doing a lot of work to take all the many sense inputs that it has and sew them together into coherent picture.

[Chuck Nice]

So cool.

[Neil deGrasse Tyson]

Yeah. And a clever. A clever optical illusion will hijack that ability, make you think something that is not is very far from true as being true.

[Sean Carroll]

Right. But it doesn't quite make sense. Yeah.

[Neil deGrasse Tyson]

Yeah. All right, we got time for one last question. Oh, my God.

[Chuck Nice]

This is over already.

[Neil deGrasse Tyson]

I know, right? Right.

[Chuck Nice]

Jeez, we gotta do this again. This was fantastic.

[Neil deGrasse Tyson]

I think he's got other stuff to do. You know, he's working on books. You know, the man writes books. Okay. What's his latest book? You just wrote one right now?

[Sean Carroll]

During this episode? Yeah, I'm almost done.

[Chuck Nice]

That's excellent.

[Neil deGrasse Tyson]

Wait, you've got a book. The Biggest Ideas in the Universe, Volume One. And you're working on Volume two. This is a physics book where you.

[Chuck Nice]

You.

[Neil deGrasse Tyson]

You got equations in there. And you. And you are. You are not apologetic about it.

[Sean Carroll]

No. I mean, we don't assume that you know any math. We teach you the math. So I teach you calculus and what have you. And

[Chuck Nice]

I love that.

[Neil deGrasse Tyson]

Just in case you miss calculus, you know, in your school. It's in the first couple of pages, right?

[Sean Carroll]

A couple chapters, but yes. And then you move on and you learn tensors and differential geometry and Einstein's equation for general relativity.

[Neil deGrasse Tyson]

And this is for the public. You just want to boost the public's math literacy a bit.

[Sean Carroll]

I. And their self esteem. I love the public. I want them to feel like they can get. They can get this stuff into their heads. It's not so hard, really.

[Neil deGrasse Tyson]

I love what you said to us offline, that when you were 16, you wished someone had written a book like this for you to consume at that time of your life.

[Sean Carroll]

Be quantum mechanics and quantum field theory and particles and symmetries and gauge theory.

[Neil deGrasse Tyson]

Well, had you had such a book, imagine how much smarter you would be.

[Chuck Nice]

We'd have figured this all out by now.

[Neil deGrasse Tyson]

All right, one last quick question.

Okay.

[Chuck Nice]

This is Hamed Daoud, who says this. Hi, Star Talk. This is Hamed from Montreal, Canada. My question are we still chasing the dream of a unified theory of physics or is that just a dead end? Can it ever be achieved? There you go.

[Neil deGrasse Tyson]

Love it. Fun.

[Sean Carroll]

Still chasing it. Because there is the universe. The universe is telling us what it does. It's just up for us to fig up to us to figure it out. So it might.

[Neil deGrasse Tyson]

Sean, it's a philosophical bias that you presume everything can be explained under one field equation and everything derived. Isn't that a bias? Maybe the universe is fractured in this way with multiple forces that can't talk to one another.

[Sean Carroll]

Yeah, that's completely fine. I did not say it was just going to be one equation. I was just about to say it might be a terrible mess. We don't have any right to say that the final theory of the whole universe will be simple or elegant or easily understandable by us. But we can shoot for it. We can try and we can give it our best shot and see what happens. That's what we're trying to do.

[Neil deGrasse Tyson]

Because we got bad history there in astronomy where Kepler has. He's a mathematician and he's. He knows that geometry is beautiful and perfect and there's certain number of Platonic solids. There's like the cube and the pyramid and the dodecahedron, and he thinks that relates to the orbits of the planets and he embeds one in the other. He is philosophically driven with some idea that the universe is beautiful and perfect and he spent 15 years wasting his time until he threw it all. I said no planets just have weird elliptical orbits. And sure enough, that's the answer. So we, we've had to be. We've been through this in my field, John. I'm just telling you, if I feel

[Sean Carroll]

as hard as Kepler, I'd be very, very happy.

[Neil deGrasse Tyson]

All right, we got to call it. Chris there. Sean, it's been a delight to see you again and chat with you. All right, we out of here. Chuck, always good to have you, man. Neil Degrasse Tyson here, your personal astrophysicist. I'm bidding you to keep looking up.

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From furniture to tableware, the best for outdoor living is at Paragould, the destination for luxury home. Elevate how you go al fresco with quality pieces in every style from design's best brands. Shop in store and [e-mail] Eczema is unpredictable, but you can flare less with EBGLIS, a once monthly treatment for moderate to severe eczema. Eczema after an initial four month or longer dosing phase. About four in ten people taking Epglis achieved itch relief and clear or almost clear skin at 16 weeks, and most of those people maintain skin that's still more clear at one year with monthly dosing.

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MGLIS Lebrekizumab LBKZ a 250mg 2ml injection is a prescription medicine used to treat adults and children 12 years of age and older who weigh at least 88 pounds or 40 kilograms with moderate to severe eczema, also called atopic dermatitis that is not well controlled. Controlled with prescription therapies used on the skin or topicals, or who cannot use topical therapies. Ebglis can be used with or without topical corticosteroids. Don't use if you're allergic to ebglis. Allergic reactions can occur that can be severe eye problems can occur. Tell your doctor if you have new or worsening eye problems. You should not receive a live vaccine when treated with Ebglis before starting Ebglis. Tell your doctor if you have a parasitic infection.

[Lindsay Nix Walker]

Ask your doctor about ebglis and visit ebgliss.lilly.com or call 1-800-lilyrx or 1-800-545-5979.