Physics & Philosophy with Sean Carroll & Neil deGrasse Tyson

Foreign. [Music] This is Star Talk. Neil deGrasse Tyson here, your personal astrophysicist. I've got with me my co-host, Chuck Nice. Jeff, hey, what's happening? All right, it was good to have you there, man, especially when we have Cosmic Queries. Oh, fan favorites. Oh, yeah, fan favorite. We love them. Uh, you get to ask a question with sort of entry-level participation in our Patreon program, just five dollars a month, 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. Of course, you know why? Because it makes them feel like they have a stake and a say. And it's like, because nobody has the answers, 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. Right. Okay, that's the end of our show.

Well, we, we, we're bringing into this, uh, an old friend and colleague, Sean Carroll. Sean, welcome to StarTalk. Hey, thanks for having me on, Neil. Welcome back to StarTalk. I see, I should say, this is, you've been on at least four or five times. Uh, you are one of the world's experts on not only physics, being a physicist, but you're also that subcategory of physicist 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 I don't have to give you nothing but the correct, true answers. So, okay, otherwise Chuck will get on your case. Don't, don't make me go on another diatribe. So you're the Homewood Professor of Natural Philosophy at 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 Institute. And your expertise in quantum physics, space-time, cosmology, love it, emergence, um, entropy, dark matter, dark energy, symmetry, origins of the universe, um, and perhaps most people who know you know you through your Mindscape podcast. So always good stuff happening there. Those things that make you, uh, tilt your head and scrunch your eyes like that's my lane. That's what I do. That's you with that. Oh, I'm gonna keep them in it. Okay. So I say this lovingly and crazily, stay in your lane. Okay. And full of crazy people, but I'm, I'm in it. So tell me, what is, uh, first, natural philosophy? I'd 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, 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 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, but it's clearly different from all other nights. So you are there to clean up the pieces, is what you're saying?

Well, I'm actually there to understand the universe. I think that the common thing, uh, 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 it's kind of foundational, that, you know, takes a step back. Look, physicists, plus their hearts. You've met physicists, Neil. I know this. And ask them, by the way, Chuck, anytime someone prefaces something by "bless their heart," they're about to insult them. In some, nothing good ever, you know, it's just in the same sentence as "bless their heart," especially if you're an old white lady from the South, you know what I mean? They said, "Oh, bless her heart, she's just a little that's all Sarah." You know, that's how it goes. Sarah, you know, it's true. That's how it goes. Okay. I started a book by saying, uh, "You do not need a PhD in theoretical physics in physics to be afraid of quantum mechanics, but it doesn't hurt." And physicists don't want to dig into the deepest questions about quantum mechanics. They want to calculate their differential equations. They show up and calculate. You shut up and calculate. And that's the opposite of what I like to do myself. So the philosophers, humor me on that.

So, just to be, just to make sure all our audience is on the same page, quantum mechanics is, is amazingly successful at predicting and and and 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?

Yeah, absolutely. Just like it drove professors Einstein and Schrödinger back in the day. But there was this, uh, 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 freeing, right, 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, right?

So you, you're the "show your work" part of this whole equation. Explain your work. Show it. Unhide anything. No scene. Yeah, it's okay to come up with the answers, but we got to know how we got there. Absolutely. Yeah. So, Sean, what's been, all the buzz in recent years is 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 all, right? 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. There, I use the word "know." They, they know about each other's existence. And, and the moment you make a measurement of one of them, the other particle's 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?

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

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, then I said, "What are you smoking?" I think that's for sure. That's what I said. Tell us.

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 Schrödinger and Heisenberg and their friends figured out back in the day. 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? Yeah, the events unfold. Yeah, it's changes. It has its dynamics. Whatever it's doing, whatever its behavior is. But then there's a whole another 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.

So, Einstein said, "God does not play dice." That's what Einstein said. Yes. And the universe, or so it kind of looks like you are playing dice. I'm just saying. I'm just. And by the way, what a, what a presumptuous statement on Einstein's behalf. I mean, who knows? Sean, didn't Niels Bohr say, "Stop telling God what to do"? Exactly. I mean, who's to say that God's not down to one knee going, popping these a new pair of shoes? You don't know that. You don't know that.

So it wasn't me. It was Bohr. Somebody said it to Einstein. Who was it? I think 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, yeah, okay. There you go. That, that makes sense. 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 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. That's when I asked, "What the guy was smoking?" Wow.

Now, wait. So these different worlds are in the same realm? Is that the case? Or are we talking about completely different, um, unfoldings that create completely different scenarios that make the whole thing work? Or another way to ask that, do you have access to these other worlds?

There you go. Thank you. You have an 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'll come back with an answer. And you can be guaranteed that there's a whole other universe, which you can never interact with or talk to, in which you do the opposite thing. It's split in that instant. Right. In that instant. Yes. Yeah. At the decision instance. Okay. Okay. It's a physical quantum process. But, and, and that's because of the entanglement because they couldn't exist simultaneously. 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.

Sean, Chuck is about to blow a gasket. And no, because you're freaking me out, man. You are free. Get me out. This is not anything that we, uh, bump into in our everyday lives. If it doesn't make you a little bit uncomfortable, you're not taking it seriously. Okay. All right. I am. Wow. All right. Sure. Let's get to the questions. Okay, man. This is already good stuff. Boy, I'll tell you right. I'm so mad I didn't have an edible before this show. I really should have taken the gummy before this one. Dog gone it. Again, these are from our Patreon supporters. Thank you all for what you do for us. It allows us to experiment and bring new and creative content to you that has yet to be proven to be commercially viable. So that's what would, that's what's going on here. All right, Chuck, you got your, your iPad there? All right, I do. So here we go.

Hi, I'm Neil deGrasse Tyson, your personal astrophysicist. And I'm Lindsay Nix Walker, senior producer of StarTalk. And Neil and I just co-authored a brand new StarTalk book coming out September 12th. 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 pre-order it, you get to gain access to a livestream that Lindsay Walker and I will do from this office. And you have the occasion to submit questions that we will answer. That's right. If you pre-order from startalkmedia.com/books, we'll answer your questions about the book, the universe, Neil's favorite kind of cheese, whatever you want. All right, so we'll see you there and we'll see you then.

This is from Sai. Uh, says, "Hello, Dr. Tyson, Dr. Carroll, Dr. haha. Uh, first-time Patreon member. I know, right? First-time Patreon member here. A huge, huge fan. Uh, I am Sai Anurag U from India. Chuck, if you get my name right, I swear to God, I will double my Patreon membership." Exactly. Yeah. Well, I, I guess you have no, you're in no danger there, are you? Yeah, I think he's gonna have it after what you just did to his name. But all right, that was funny. Uh, my question pertains to Dr. Carroll's research, which says that the universe is infinitely old, and the Big Bang is just one of many events resulting from quantum fluctuations of a vacuum energy in a cold, this 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? Ooh, good. Very good. I love it. You know, hanging out on the wrong street corners. I don't know where they, where they picked 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. We're all gonna die. That's the, 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. It 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, uh, I've long wondered about this. And I wrote a paper years ago now with, uh, uh, a woman who's 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 proposed 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, uh, 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 the story of more and more universes being created with people in them who think that we are in their past. I, I'm gonna tell you right now, uh, if, if Sai understands what the hell you just said, and they need to be the co-host of this show. So, Sean, what you're saying is there's some symmetric point among these universes and these time continua where, in one direction, we're entropy increases, but in principle, there's a whole other realm where entropy decreases?

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 significant. Now, so now that, so we're in their past because they're looking at us and seeing a decreasing entropy, which is, and 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're 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. Chuck gets it. We're done. Yeah, man. [Laughter] Chuck, you're blowing out the volume level. One, that's insane. Okay, wait. So, so Sean, before we get to the next question, what, um, these are ideas. Is there any way to experimentally verify any of this?

Well, we're trying, but the short answer is we don't know yet. We don't have, uh, it's not like a "no." Just say it. Oh, it was very much not a "no." Oh, okay. But all the words matter here. Okay. Yeah. And this, but this is a more, a broader idea, right? Um, there are plenty of tentative, preliminary scientific ideas which are too ill-defined. I'm with you. Predictions. Einstein's, um, gravitational waves. Einstein's gravitational rings. Yeah, I'll give you that. We'll get there. We will get there. Send money. We'll, we'll do it. Just trust us. Yeah. In your lifetimes. Yeah. Every time it's getting shorter. Every year. So I don't know. Yeah. Your life expectancy is dropping every year. Yeah. Yeah. All right, Chuck, what else are you at? All right, let's go on to Doug Sherman. Doug Sherman says, "Hi, Neil. Hi, Sean. Lord, nice." Uh, Doug, this is Doug from Frisco, Texas. All right, all right. 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. Once, 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 probability of a finely tuned universe approaches one." And then it's, oh man, he, he must have cut and pasted because it drops out. Then he, so he, he, 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." So, just for context, William Lane Craig is a proponent of, um, 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. Do they characterize that you're not going to throw down with Pat Robertson or Jimmy Swaggart? That's right. It's not on the debate stage. No. Okay. I do think that the, what is called the fine-tuning argument. Did I characterize your, your opponent accurately? Would you say? Yeah, that's fine. Um, 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've read 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? That the things like the amount of energy in empty space could have been so large that it would rip planets apart before they ever formed. 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? There could be many different parts of the universe, and we just are finding ourselves in the hospitable one. But there's two things. You're not in all the others to have this conversation, right? So they help play an explanatory role in, 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, that 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, 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.

All right, now let me, let me, let me just ask a question here, because I, uh, just, just to further clarify, by what if, instead of needing the laws of physics, the laws themselves are a reflection of what God has done? So it's not necessarily that the, that the laws are needed, it's that the laws exist because they just happen to be a byproduct of the creation itself. That is completely possible. And Neil will raise us in here and say, "How do we observationally test that hypothesis?"

Okay, listen, I'm 100% with, 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 here. It smells like Spinoza's God, right? Which is that the, whatever God is to you, the laws of physics are the manifestation of it. Oh, so I'm not that smart. Somebody already thought of my question. Could have been Chuck's argument. But nice is God. Um, 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 continues to do so. Yes. 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, they tend not to rely on God to account for the things that we observe in the natural world. What is called natural theology, as opposed to natural philosophy. Natural theology is not so popular anymore. Gotcha. All right. Fascinating stuff. All right, Chuck, keep going. We've only gone through two or three questions. Let's see if we can speed up.

Okay, we just have to have Sean back. That's all. This stuff is too good. We can't rush. We cannot rush through this. At one point, get a double-wide episode with him, maybe. Yeah, well, yeah, yeah, absolutely. All right. This is Tom B. Knight. Hello. I'm a Patreon supporter of both StarTalk and Mindscape. We're great to see Sean on the show. Uh, 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. Okay, good one. Every dinosaur is a constellation. I think it's a waterfall, or is it has something to do with water? My memory serves, but anyhow. Sean, what you got there?

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 place. 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 other episode.

Wow. I like the way you said that. You, we, we observe these fluctuations about a 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?" That'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. Well, it's, it's, once again, a reflection of the fact that the early universe had low entropy because gravity was so strong in the early universe. 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.

All right, keep this going, Chuck. Uh, this is Malcolm Marfan. And Malcolm says, "Hello, Dr. Tyson, Dr. Carroll, and Chuck. Maybe, okay, um, okay. I love these people. They love you, Chuck. No matter what they call you. I know nobody I know." [Laughter] "Well, Malcolm Marfan here, all the way from Trinidad and Tobago. And this is nice. He says, 'Dr. Carroll, I came across your 2018 paper, 'Why Is There Something Rather Than Nothing?' and thought, wow, this guy's really dedicated a lot of brainpower 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?"

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. Uh, 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, I don't think that, uh, it is nearly as down-to-earth and simple and physical as certain physicists like to talk about this, make it out to be. It's a, it's a fun, mentally, a philosophy question.

Wait, but Sean, 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?

No, it's something. It's space. It has, 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? Is empty space three-dimensional? I don't know. You just don't want to answer it because. Okay, so let's say, let's say it's three-dimensional and, and exists on a time continuum. Sure. It's, oh, it has a property then. It's not nothingness. It is, there's a way it could have been different. You invoke a way to measure stuff in it. I wouldn't call that an inherent property of the empty space. It's, it's different than four-dimensional empty space. Okay. So how about this? How about this? Okay. Uh, again, one of the reasons why I don't like arguing with philosophers is 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 no thing, nothing there, then that's nothing. Okay. Now, you're saying there's a grid system there that we can invoke or it's inherent. So that's a thing. Okay. Now I add to my inventory of a thing, particles plus grid systems. Okay, fine. Then that's there. No. 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, can't be entirely nothing, because laws of physics apply even though there's nothing there to manifest them.

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 that 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 them separately. It's not a right or wrong thing to ask, right? Yeah.

All right, well, that's all right. Cool. What a great question. 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." I just, so whatever something we have, that's, is side by side with a lot of nothing. And until you start invoking other definitions for what nothing can be. So that's all, that's my only point there. Well, there you have it, Malcolm. We have discussed your question, and we have, uh, we have achieved nothing. [Laughter] All right, all right. Keep it going.

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. Till to the speed of light, we can only see the past while looking into distances of the cosmos. 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." Absolutely. Everybody's been smoking before they said. Let me tell you, man, I told you, I told you. But he says, "I hope you read this message from the past. Please keep looking up." He makes an interesting point that, what is, what is the present even mean if everything we do to interact with the world has some kind of time delay?

Yeah, I'd like that idea of the brain or understanding our senses, our, that's true. My, 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? Yeah, there's a scientist here and a philosophy answer. I'll give you the science answer because it's quite good. Our brain does not perceive 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, because that happens suddenly. So your brain has correcting for it. Holy, 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..." Well, millisecond is a thousandth of a second. So 40 to 50 thousandths of a second would be like five hundredths of a second. There you go. Good method. Excellent. Yes. Right. 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. It's too hard. It's too much. I can't do no more." So you do deal with it. Oh, God. You can't take it. No. So, so, so this is an experimental result, Sean. You know, look, as, as I'm sure you are already know, neuroscience, biology, psychology, that's a whole frontier right there. They like it way harder than physics or astronomy. Way harder. Way harder. Oh, yeah. Okay. I did not know this. So, uh, 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. 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, uh, kind of creating a construct and then painting a picture of what it is. And then it looks for changes in that construct.

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. Absolutely. That's why there are so many black men in prison right now. That's one example. I was going to say optical illusions, but sure. Yes. Racial incarceration, inequalities, that's another one. Yes. This is the philosophy part of the answer, which is that there is, there's a real world out there. I mean, there, 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 a coherent picture. Yeah. And a clever, a clever optical illusion will hijack that ability and make you think something that is not very far from true as being true. Very, but it doesn't quite make sense. Yeah. Yeah. All right. We've got time for one last question, Chuck.

Oh, my God. This is over already? I know, right? Yes. We got to do this again. This is fantastic. I think he's got other stuff to do. You know, he's working on books, you know, the man writes books. Okay, now, what's his latest book? You just wrote, um, on right now during this episode? Yeah, I'm almost done. [Laughter] Oh, that's excellent. Wait, you've got a book, "The Biggest Ideas in the Universe, Volume One," and you're working on Volume Two. And this is a physics book where you, got equations in there. And you, and you are, you are not apologetic about it. No. I mean, we don't assume that you know any math. We teach you the math. So I teach a calculus and what have you, you know, just in case you missed calculus in your school. It's in the first couple of pages, right? A couple of chapters. But yes, and then you move on and you learn tensors and differential geometry and, uh, Einstein's equation for general relativity. And this is for the public. You just want to boost the public's math literacy a bit. 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. 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. The quantum mechanics and quantum field theory and particles and symmetries and gauge theory. Had you had such a book, imagine how much smarter you would be. Yeah, it's all out by now. I let one last quick question go.

Okay, this is Hamed, who says, "This, hi StarTalk. This is Hamed from, uh, Montreal, Canada. My question, are we still chasing the dream of a unified theory of physics, or is that just a dead end? Should it never be achieved?" Love it.

Sean, still chasing it because there is the universe. The universe is telling us what it does. It's just up for us to think up to us to figure it out. So, Sean, it's a philosophical bias that you presume everything can be explained under one field equation and everything derived. That's a, isn't that a bias? Maybe the universe is fractured in this way with multiple forces that can't talk to one another.

Yeah, that's completely fine. I, 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. Because we got bad history there in astronomy where Kepler, he's a mathematician, and he knows that geometry is beautiful and perfect, and there's certain number of Platonic solids. Kids, 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. 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. Hills artist. Kepler. I'd be very, very happy. Okay. Yeah. All right. We got to call it. Chris there. Sean, it's been a delight to see you again and chat with you. And Chuck, always good to have you, man. Always a pleasure. Neil deGrasse Tyson here, your personal astrophysicist. I'm beating you to keep looking. [Applause] [Music]