Physics & Philosophy with Sean Carroll

Why is the past different from the future? Neil deGrasse Tyson and comedian Chuck Nice explore the universe’s deepest questions like why is there anything, how we know we are in the real present, if there could be a unified theory of physics and more with theoretical physicist Sean Carroll.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Neil deGrasse Tyson?

  Hey Startalkians, 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.

• 0:24Neil deGrasse Tyson?

  Welcome to StarTalk, your place in the universe where science and pop culture collide.

• 0:33Neil deGrasse Tyson?

  StarTalk begins right now.

• 0:46Neil deGrasse Tyson?

  I'm Neil deGrasse Tyson, your personal astrophysicist.

• 0:49Speaker 01

  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.

• 0:58Neil 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 preorder from the StarTalk website, starTalkMedia.com/books. If you do preorder 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, and we'll see you then. StarTalkMedia.com/books.

• 1:46Neil deGrasse Tyson?

  This is StarTalk. Neil deGrasse Tyson here, your personal astrophysicist. I got with me my co-host, Jack. Nice, Jack.

• 1:53Chuck Nice?

  Hey, what's happening?

• 1:55Neil deGrasse Tyson?

  All right, always good to have you there, man, especially when we have cosmic queries.

• 2:00Chuck Nice?

  Fan favorite.

• 2:01Neil deGrasse Tyson?

  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.

• 2:10Chuck Nice?

  That's it.

• 2:11Neil deGrasse Tyson?

  And we collected them, and you know in advance what you're asking about, because today's topics involve physics and philosophy.

• 2:20Neil deGrasse Tyson?

  People love just talking about stuff for which there is no answer.

• 2:25Chuck Nice?

  Well, of course, you know why? Because it makes them feel like they have a stake and a say.

• 2:30Neil deGrasse Tyson?

  And a say, because nobody has the answer.

• 2:32Chuck 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.

• 2:59Neil deGrasse Tyson?

  Okay, that's the end of our show.

• 3:03Neil deGrasse Tyson?

  Well, we're bringing into this an old friend and colleague, Sean Carroll. Sean, welcome to StarTalk.

• 3:11Sean Carroll?

  Hey, thanks for having me on, Neil.

• 3:12Neil deGrasse Tyson?

  Welcome back to StarTalk, 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.

• 3:53Neil deGrasse Tyson?

  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, spacetime, 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.

• 4:29Sean Carroll?

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

• 4:35Neil deGrasse Tyson?

  That's you.

• 4:37Neil deGrasse Tyson?

  Okay, so I say this lovingly and crazily, stay in your lane, okay?

• 4:44Neil 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 philosophy. Natural philosophy was physics. So what, why isn't that just physics professor?

• 5:08Sean Carroll?

  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-

• 5:45Neil deGrasse Tyson?

  The interstitial ideas and things.

• 5:47Sean Carroll?

  Yeah, 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.

• 6:01Chuck Nice?

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

• 6:07Sean Carroll?

  Philosophy and fraud.

• 6:09Neil deGrasse Tyson?

  Is that a song lyric?

• 6:12Neil deGrasse Tyson?

  Alright, so, so, so you are there to clean up the pieces, is what you're saying?

• 6:17Sean 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-

• 6:42Neil deGrasse Tyson?

  By the way, Chuck, anytime someone prefaces something by bless their-

• 6:45Chuck Nice?

  Bless your heart?

• 6:46Neil deGrasse Tyson?

  You're about to insult them in some-

• 6:48Chuck Nice?

  Nothing good ever, you know, it's just like-

• 6:51Neil deGrasse Tyson?

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

• 6:53Chuck Nice?

  Especially if you're an old white lady from the South, you know what I mean? It's, oh, bless her heart, she's just a little whore, that's all.

• 7:02Chuck Nice?

  That's how it goes.

• 7:05Neil deGrasse Tyson?

  Okay.

• 7:05Sean Carroll?

  I started the book by saying, you do not need a PhD in theoretical physicist 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.

• 7:21Neil deGrasse Tyson?

  Shut up and calculate.

• 7:23Sean Carroll?

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

• 7:29Neil deGrasse Tyson?

  So just to be, just to make sure all our audiences are on the same page. Quantum mechanics is amazingly successful at predicting and describing reality. But that reality defies all our common sense. And you can 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?

• 8:08Sean Carroll?

  Yeah, absolutely. Just like it drove professors Einstein and Schr ö tiger 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 book beautiful exquisite agreement between the calculations and the predictions without knowing what's going on, without freeing 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.

• 8:49Chuck Nice?

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

• 8:53Sean Carroll?

  Explain your work. Show it, play it, hide anything, no sweeping the rug.

• 8:57Chuck Nice?

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

• 9:01Sean Carroll?

  Absolutely.

• 9:01Neil deGrasse Tyson?

  Yeah. 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, 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 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.

• 9:40Neil deGrasse Tyson?

  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?

• 9:54Sean Carroll?

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

• 10:02Neil deGrasse Tyson?

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

• 10:08Sean Carroll?

  But like, but 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, their 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

• 10:52Sean Carroll?

  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.

• 11:14Neil deGrasse Tyson?

  Remind us of the many worlds hypothesis, because I think that's now 100 years old, right? We're on, we're on this 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 do you smoke? Sure, that's what I said.

• 11:34Sean 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

• 11:50Neil deGrasse Tyson?

  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.

• 12:02Sean 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.

• 12:27Neil deGrasse Tyson?

  And Einstein said, God does not play dice.

• 12:30Sean Carroll?

  That's what Einstein said, yes.

• 12:31Neil deGrasse Tyson?

  With the universe.

• 12:32Sean Carroll?

  Or

• 12:33Neil deGrasse Tyson?

  Kind of looks like, you know, you are playing dice. I'm just saying, I'm just.

• 12:37Chuck Nice?

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

• 12:43Neil deGrasse Tyson?

  Sean, didn't Niels Bohr say Einstein, stop telling God what to do?

• 12:48Chuck Nice?

  Exactly. Who's to say that God's not down on one me going popping these new pair of shoes? You don't know that. You don't know that.

• 12:57Neil deGrasse Tyson?

  So wasn't Niels Bohr, somebody said it to Einstein, who was it?

• 13:00Sean Carroll?

  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, you know.

• 13:07Chuck Nice?

  There you go. Yeah, that, that makes sense.

• 13:09Sean 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.

• 13:51Neil deGrasse Tyson?

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

• 13:52Chuck Nice?

  Wow. Now, wait a minute. So that 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?

• 14:10Neil deGrasse Tyson?

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

• 14:13Chuck Nice?

  There you go. Thank you.

• 14:16Sean Carroll?

  If 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.

• 14:37Neil deGrasse Tyson?

  And it's split in that instant.

• 14:39Chuck Nice?

  Right.

• 14:39Sean Carroll?

  In that instant, yes.

• 14:40Neil deGrasse Tyson?

  At the decision instant.

• 14:42Chuck Nice?

  Okay, okay.

• 14:44Sean Carroll?

  It's a physical quantum process.

• 14:46Chuck Nice?

  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. Is that?

• 15:14Neil deGrasse Tyson?

  Sean Chuck is about to blow a gasket.

• 15:17Chuck Nice?

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

• 15:22Sean 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.

• 15:29Chuck Nice?

  Okay, all right.

• 15:40Neil deGrasse Tyson?

  I've always wondered why Hollywood aliens tend to have two eyes, a nose, a mouth, ears, head, shoulders, neck, arms, legs, fingers, toes. Maybe it's because an actor is donning a costume. That's one of the reasons why I wrote Take Me to Your Leader. It's to explore all that is possible in this universe beyond what has yet to be imagined by Hollywood. So that for your first alien encounter, you'll be prepared. You'll have some anticipation of what they could look like, what kind of ship they arrived in, what you should or should not say, or should or should not presume. I narrated the audiobook. The print version is available as well.

• 16:25Neil deGrasse Tyson?

  You better get the book now before you have that first alien encounter, because afterwards, it'll be too late.

• 16:40Neil deGrasse Tyson?

  Chuck, let's get to the questions.

• 16:41Chuck Nice?

  Okay, man.

• 16:42Neil deGrasse Tyson?

  We've got to digest this.

• 16:44Chuck Nice?

  This is already good stuff, boy. I'll tell you right, I'm so mad I didn't have an edible before this show.

• 16:53Chuck Nice?

  I really should have taken a gummy before this one. Doggone. All right, here we go.

• 16:59Neil deGrasse Tyson?

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

• 17:05Chuck Nice?

  I do, so here we go. This is from Sai, says, "Hello, Dr. Tyson, Dr. Carol, Dr. Ha Ha. First time Patreon member." I know, right? "First time Patreon member here. Huge, huge fan. I am Sai Anurag Lakajur, Lakarju, from India. Chuck, if you get my name right, I swear to God, I will double my Patreon membership."

• 17:40Chuck Nice?

  Yeah, well, I guess you have no, you're in no danger there, are you?

• 17:44Neil deGrasse Tyson?

  Yeah, I think he's gonna have it after what you just did to his name.

• 17:50Chuck Nice?

  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 disliter, disitter 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?

• 18:19Sean Carroll?

  Good, very good. I love it, you know, hanging out on the wrong street corners. I don't know where they, 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.

• 18:55Neil deGrasse Tyson?

  We're all gonna die, that's the.

• 18:56Sean 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 proposed that in different contexts, but we made the case

• 19:36Sean Carroll?

  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,

• 20:21Sean Carroll?

  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.

• 20:37Chuck Nice?

  I'm gonna tell you right now.

• 20:41Chuck Nice?

  If, if Psy

• 20:44Chuck Nice?

  understands what the hell you just said,

• 20:48Chuck Nice?

  then they need to be the co-host of this show.

• 20:53Chuck Nice?

  Because I am not gonna lie.

• 20:57Neil deGrasse Tyson?

  Wait, wait. So Sean, wait, Sean.

• 20:58Chuck Nice?

  You lost me at the end. I, I need, I need you to do the end again.

• 21:03Neil 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.

• 21:28Sean 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 symmetric.

• 21:41Chuck Nice?

  I get it now. So we're in their past because they're looking at us and seeing a decreasing entropy, which is, 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.

• 22:15Sean Carroll?

  Chuck gets it. We're done.

• 22:16Chuck Nice?

  Yeah, man.

• 22:22Chuck Nice?

  And it's insane.

• 22:26Neil deGrasse Tyson?

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

• 22:28Chuck Nice?

  That's insane. Oh, my God.

• 22:32Neil deGrasse Tyson?

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

• 22:42Sean Carroll?

  Well, we're trying, but the short answer is we don't know yet. We don't have, uh...

• 22:46Neil deGrasse Tyson?

  It sounded like a no. Just say it.

• 22:49Sean Carroll?

  It was very much not a no.

• 22:50Neil deGrasse Tyson?

  Oh, okay.

• 22:52Sean Carroll?

  All the words, Neil. These are all the words that are here.

• 22:55Neil deGrasse Tyson?

  Okay.

• 22:56Sean 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-thought-out yet.

• 23:08Neil deGrasse Tyson?

  I'm with you.

• 23:09Sean Carroll?

  Predictions.

• 23:10Neil deGrasse Tyson?

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

• 23:17Sean Carroll?

  We'll get there. We will get there. Send money. We'll do it. Just trust us.

• 23:22Neil deGrasse Tyson?

  And your lifetime?

• 23:25Sean Carroll?

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

• 23:29Neil deGrasse Tyson?

  All right, Chuck, what else you got?

• 23:31Chuck Nice?

  All right, let's go on to Doug Sherman. Doug Sherman says, "Hi, Neil. Hi, Sean. Lord nice." Doug, this is Doug from Frisco, Texas.

• 23:41Neil deGrasse Tyson?

  All right.

• 23:41Chuck Nice?

  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 arguments, but for more simplistic reasons than my flawed brain can rationalize."

• 24:24Neil 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 debating respectability in that regard. Did I characterize your opponent accurately, would you say?

• 25:02Sean Carroll?

  Yeah, that's fine. But 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 formed.

• 25:46Sean Carroll?

  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?

• 26:05Neil deGrasse Tyson?

  You're not in all the others to have this conversation, right?

• 26:08Sean Carroll?

  Well, they help play an explanatory role 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 Liam 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.

• 26:50Sean Carroll?

  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.

• 27:11Chuck Nice?

  All right. Now, let me, let me, let me just ask a question here, because I, just, just, just to further clarify. 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.

• 27:44Sean Carroll?

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

• 27:50Chuck Nice?

  Okay. I'm, and listen, I'm a hundred percent with, with, I'm, 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.

• 28:00Sean 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 It 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.

• 28:29Chuck Nice?

  Gotcha. Wow, fascinating stuff.

• 28:33Neil deGrasse Tyson?

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

• 28:36Chuck 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.

• 28:44Neil deGrasse Tyson?

  At one point, get a double-wide episode with him.

• 28:47Chuck Nice?

  Yeah, well, yeah, yeah, absolutely. All right, here we go. 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 Iridanus supervoid, violate the cosmological principle? What could be the cause of these structures? Thank you for your service. Okay.

• 29:17Neil deGrasse Tyson?

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

• 29:28Sean 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 100,000

• 30:13Sean Carroll?

  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.

• 30:59Sean Carroll?

  We still don't know where those first ripples came from. Inflationary cosmology is a favorite thing to talk about, but that's a whole nother episode.

• 31:10Sean Carroll?

  Wow, there you go.

• 31:11Neil deGrasse Tyson?

  So I like the way you said that. You, 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? 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?

• 31:32Sean Carroll?

  Yeah.

• 31:33Neil deGrasse Tyson?

  Right. And not enough of that goes on, I think.

• 31:35Sean 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.

• 31:59Neil deGrasse Tyson?

  Mm hmm.

• 32:00Sean Carroll?

  Okay.

• 32:01Neil deGrasse Tyson?

  All right, keep this going, Chuck.

• 32:04Neil deGrasse Tyson?

  And that one was from the overlap of the Venn diagram between Mindscape and StarTalk. Love it.

• 32:18Sean Carroll?

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

• 32:29Chuck Nice?

  Uh, this is Malcolm Marfan, and Malcolm says, hello, Dr. Tyson, Dr. Carol. And Chuck, maybe? Okay. Um.

• 32:40Neil deGrasse Tyson?

  Okay.

• 32:40Chuck Nice?

  I love these people, man.

• 32:41Neil deGrasse Tyson?

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

• 32:43Chuck Nice?

  I know, no, I know.

• 32:46Chuck Nice?

  Well, Malcolm Marfan here, all the way from Trinidad and Tobago. And he says.

• 32:53Neil deGrasse Tyson?

  Oh, nice.

• 32:53Chuck 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 cower 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?

• 33:31Sean 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,

• 34:13Sean Carroll?

  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 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 fundamentally a philosophy question.

• 34:44Neil deGrasse Tyson?

  Wait, but Sean, if there were no quantum physics, in principle, you could talk about space as having no particles or 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 a nothing as anyone would hope to describe, isn't it?

• 35:05Sean Carroll?

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

• 35:08Neil 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?

• 35:19Sean Carroll?

  Is empty space three dimensional?

• 35:22Neil deGrasse Tyson?

  I don't know.

• 35:25Sean Carroll?

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

• 35:27Neil deGrasse Tyson?

  Okay, okay, so let's say, let's say it's three dimensional and, and exists on a time continuum. I'm sure it's.

• 35:31Sean Carroll?

  So it has a property then, it's not nothingness, it, it has, there's a way it could have been different.

• 35:36Neil deGrasse Tyson?

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

• 35:42Sean Carroll?

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

• 35:45Neil deGrasse Tyson?

  Okay, so how about this? How about this? Okay. Uh, 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 where it's inherent. So that's a thing. Okay, so now I add to my inventory of a thing, particles plus grid system. Okay, fine, then that's there.

• 36:30Neil deGrasse Tyson?

  Now, 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.

• 36:47Sean 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 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.

• 37:27Neil deGrasse Tyson?

  Okay, yeah.

• 37:29Sean Carroll?

  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 both of them separately. It's not a right or wrong thing to ask.

• 37:49Chuck Nice?

  Right, yeah.

• 37:51Neil deGrasse Tyson?

  All right.

• 37:51Chuck Nice?

  Well, that's so cool. What a great question. Yeah.

• 37:55Neil deGrasse Tyson?

  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.

• 38:06Neil deGrasse Tyson?

  So whatever something we have that's side by side with a lot of nothing. Until you start invoking other definitions for what nothing can be. So that's all. That's my only point there.

• 38:17Chuck Nice?

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

• 38:30Chuck Nice?

  All right.

• 38:30Neil deGrasse Tyson?

  All right. Keep it going.

• 38:31Chuck 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 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.

• 39:14Chuck Nice?

  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, that could travel instantly to our place.

• 39:27Neil deGrasse Tyson?

  Everybody's been smoking before.

• 39:29Chuck Nice?

  Let me tell you, man, I told you, I told you.

• 39:34Chuck Nice?

  He says, I hope you read this message from the past.

• 39:40Chuck Nice?

  Please keep looking up.

• 39:42Neil deGrasse Tyson?

  He makes an interesting point that.

• 39:46Neil deGrasse Tyson?

  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, I like that idea of the brain, our understanding, our senses, our-

• 39:58Sean Carroll?

  That's true.

• 39:59Neil deGrasse Tyson?

  Uh, our, uh, 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?

• 40:08Sean Carroll?

  Yeah, there's a science answer here and a philosophy answer here. I'll give you the science answer, cause it's, it's quite good. Uh, 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.

• 40:53Sean Carroll?

  The vision of the basketball hitting the ground and the sound of it, because-

• 40:57Neil deGrasse Tyson?

  That happens suddenly, so your brain was correcting for it? Holy shit.

• 41:00Sean 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, 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 gonna put this together into a picture of the present."

• 41:20Neil deGrasse Tyson?

  A millisecond is a thousandth of a second. So 40 to 50 thousandths of a second would be like 5 hundredths of a second.

• 41:27Sean Carroll?

  There you go. Good man. Excellent. Yes.

• 41:29Neil deGrasse Tyson?

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

• 41:37Sean Carroll?

  It's too much.

• 41:39Neil deGrasse Tyson?

  It's too much.

• 41:40Sean Carroll?

  I can't do no more.

• 41:42Neil deGrasse Tyson?

  No, you do. Deal with it.

• 41:45Sean Carroll?

  Go on without me.

• 41:49Chuck Nice?

  Oh God, it's just, oh, I can't take it.

• 41:56Neil deGrasse Tyson?

  So, so, so this is an experimental result, Sean.

• 42:00Sean Carroll?

  You know, look, as, as I'm sure you are already know, neuroscience, biology, psychology.

• 42:05Neil deGrasse Tyson?

  That's a whole frontier right there.

• 42:07Sean Carroll?

  Be like way harder than physics or astronomy.

• 42:09Neil deGrasse Tyson?

  Way harder, way harder.

• 42:11Sean Carroll?

  Yeah.

• 42:12Neil 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.

• 42:22Chuck 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 a kind of creating a construct and then painting a picture of what it is and then it looks for changes in that construct.

• 42:43Neil 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.

• 42:51Chuck Nice?

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

• 42:59Sean Carroll?

  I was gonna say optical illusions, but sure, yes, racial incarceration and inequalities, that's another one.

• 43:07Sean Carroll?

  This is the philosophy part of the answer, which is that there is 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 coherent picture.

• 43:31Chuck Nice?

  So cool.

• 43:31Neil deGrasse Tyson?

  Yeah, and a clever, a clever optical illusion will hijack that ability.

• 43:38Sean Carroll?

  Hacking the brain.

• 43:38Neil deGrasse Tyson?

  Make you think something that is not, is very far from true as being true.

• 43:42Sean Carroll?

  Right, but it doesn't quite make sense. Yeah.

• 43:44Neil deGrasse Tyson?

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

• 43:46Chuck Nice?

  Oh my God, this is overall ready?

• 43:49Neil deGrasse Tyson?

  I know, right, right?

• 43:50Chuck Nice?

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

• 43:55Neil 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 this lady's book you just wrote?

• 44:02Sean Carroll?

  One right now during this episode. Yeah, I'm almost done.

• 44:10Sean Carroll?

  That's excellent.

• 44:11Neil deGrasse Tyson?

  Wait, you've got a book, The Biggest Ideas in the Universe, Volume One, and you're working on Volume Two.

• 44:16Sean Carroll?

  That's right.

• 44:17Neil deGrasse Tyson?

  This is a physics book where you, you, you got equations in there and you, and you are, you are not apologetic about it.

• 44:25Sean 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.

• 44:32Neil deGrasse Tyson?

  I love that.

• 44:35Neil deGrasse Tyson?

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

• 44:39Sean Carroll?

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

• 44:46Neil deGrasse Tyson?

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

• 44:50Sean 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.

• 44:56Neil 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.

• 45:05Sean Carroll?

  It'd be quantum mechanics and quantum field theory and particles and symmetries and gauge theory.

• 45:10Neil deGrasse Tyson?

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

• 45:16Sean Carroll?

  We'd have figured this all out by now.

• 45:21Neil deGrasse Tyson?

  All right, let, one last quick question. Go.

• 45:22Sean Carroll?

  Okay, this is, uh, Hamed Dawud, who says this, "Hi, StarTalk. 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?"

• 45:37Neil deGrasse Tyson?

  I love that.

• 45:38Sean Carroll?

  Can it ever be achieved?

• 45:39Neil deGrasse Tyson?

  There you go. Love it.

• 45:41Sean Carroll?

  Yeah, still chasing it because there is the universe. The universe is telling us what it does. It's just up for us to figure, up to us to figure it out. So it might-

• 45:52Neil deGrasse Tyson?

  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.

• 46:10Sean Carroll?

  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.

• 46:28Neil deGrasse Tyson?

  Because we got bad history there in astronomy where Kepler has, he's a mathematician and he knows that geometry is beautiful and perfect and there's certain number of platonics 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 away. He said, no, planets just have weird elliptical orbits and sure enough, that's the answer. So we've had to be, we've been through this in my field, Sean, I'm just telling you.

• 47:10Sean Carroll?

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

• 47:12Neil deGrasse Tyson?

  All right, we got to call it quits 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, bidding you to keep looking up.