“Is Our Universe a Simulation?” with Brian Greene

Neil deGrasse Tyson investigates the nature of reality, from quantum physics and string theory, to the multiverse and “The Matrix.” With theoretical physicists Brian Greene and Stephon Alexander, philosopher David Chalmers, co-host Maeve Higgins, Chuck Nice and Bill Nye. NOTE: StarTalk All-Access subscribers can listen to this entire episode commercial-free. Find out more at https://www.startalkradio.net/startalk-all-access/

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

• 0:01Neil deGrasse Tyson?

  Welcome to StarTalk. Your place in the universe where science and pop culture collide. StarTalk begins right now.

• 0:22Neil deGrasse Tyson?

  Welcome to the Hall of the Universe. I'm your host Neil deGrasse Tyson. I'm your personal astrophysicist. And tonight, we are featuring my interview with bestselling author and theoretical physicist, Brian Greene. He is an expert on all manner of weird physics phenomenon, especially in quantum physics and in cosmology. And I picked his brain on everything from the multiverse to the matrix. Is our universe a simulation? Let's do this.

• 1:00Neil deGrasse Tyson?

  And as you know, I never do this alone. I've got my comedian co-host Maeve Higgins. Maeve, welcome back to StarTalk.

• 1:06Speaker 01

  Thank you.

• 1:07Neil deGrasse Tyson?

  Yes. And you're still growing accustomed to being in America, being a native of Ireland.

• 1:12Speaker 01

  Yep.

• 1:13Neil deGrasse Tyson?

  Yeah, but I like your observations of America because they're things we forget to notice.

• 1:18Speaker 01

  Yeah, now I'm worried you're gonna tell me there's a whole other universe that I have to get used to.

• 1:21Neil deGrasse Tyson?

  Yeah, that's right.

• 1:22Speaker 01

  Well, let's find out.

• 1:23Neil deGrasse Tyson?

  You're gonna get jokes for that universe, right.

• 1:24Speaker 01

  Oh, my goodness.

• 1:25Neil deGrasse Tyson?

  Also, to help me out here is professor of philosophy David Chalmers. David, welcome.

• 1:32Neil deGrasse Tyson?

  And at New York University, you're not only philosophize, you're also co-director of the Center for Mind-Brain-Cognitive-Brain-Minds? Mind-Brain and Consciousness. And Consciousness. A lot about the mind. Okay, consciousness. Yeah. That's ambitious. It is. Because everyone says they understand consciousness, and at the end of the day, nobody does. None of us understand a thing. Okay, so get back to work. What are you doing here? But you're here in particular because you're not just any philosopher to us. You've done a lot of thinking on whether or not we live in a simulation that we otherwise think of as our universe.

• 2:07Brian Greene?

  It's possible.

• 2:07Neil deGrasse Tyson?

  It's possible. Well, we'll get to the bottom of this. Now, Brian Greene, he's best known to the public for popularizing string theory. His earliest book, The Elegant Universe, was a mega bestseller back in 1999, and it was followed up with a book called The Fabric of the Cosmos: Space, Time, and the Texture of Reality. Now, that touches on so much, and it enables him to think about so many interesting branches of physics that intrigue us. And in 2003, there was a paper published by a philosopher from the University of Oxford on whether or not the universe is a simulation. And I had to ask Brian Greene if he thought this could actually be possible, just to get

• 2:50Neil deGrasse Tyson?

  a professional opinion on this. Let's find out.

• 2:55Brian Greene?

  If it's the case that one day we can have computers that can recreate a reality in bits and bytes that has such verisimilitude that their inhabitants of those simulations that feel that it's real, if that's possible, I think many of us agree that it might be.

• 3:11Neil deGrasse Tyson?

  Sure.

• 3:12Brian Greene?

  We're getting closer already. Just let's assume that's possible. It's so much easier to create a simulation than it is to create a real universe. I mean, how are you going to create a real universe? So if you wait long enough, there are going to be many, many more simulated universes than there are real ones. So any sentient being, if they're rational, will think that the odds are that they're in one of those simulations because there's so many more of those compared to real ones.

• 3:37Neil deGrasse Tyson?

  Statistically, you're in the simulated one, not the real one.

• 3:40Brian Greene?

  Yeah, yeah, exactly. So how do you know? And it would be very hard. I mean, some have suggested, sort of like in The Matrix, look for glitches. Like, real universes don't have glitches, but computers can have them. But I say to that-

• 3:51Neil deGrasse Tyson?

  Well, glitches because presumably a fallible entity programs that.

• 3:56Brian Greene?

  It could be that, it could be that. It could also be there's an electric current glitch that happens in the real universe and screws up what's happening inside the computer. But I don't buy that argument because if it's a really good simulation, it should be able to rewind, erase the memory of a glitch, fix it, and then the simulated beings have no memory of it ever happening.

• 4:20Neil deGrasse Tyson?

  Wow, okay, we should start there.

• 4:23Speaker 01

  I got so excited when he said about glitches and that that's how you know. Because I always feel like I should be with Michael Fassbender, do you know that actor?

• 4:30Neil deGrasse Tyson?

  Yeah, yeah, of course, yeah.

• 4:31Speaker 01

  But I'm not, and it makes no sense to me.

• 4:34Neil deGrasse Tyson?

  Oh, I got you.

• 4:34Speaker 01

  And that's a glitch in the...

• 4:35Speaker 03

  That's a total glitch in the matrix.

• 4:37Speaker 01

  Thank you.

• 4:37Neil deGrasse Tyson?

  A glitch in the matrix, because you're not with Michael Fassbender. So, David, what do you have here?

• 4:43Speaker 03

  I don't know, I think it's science fiction philosophy, and a lot of people think it's way out, but I think you've got to take that statistical argument seriously, that there will, there may be many simulations created in the history of the universe, many simulated universes, many simulated people, only a relatively small number, non-simulated people.

• 5:04Neil deGrasse Tyson?

  But what's the best argument against that?

• 5:06Speaker 03

  I think it's probably the argument from simplicity. Basically, that the universe is much simpler if we're not in a simulation. If we're in a simulation, you've got to postulate levels, beyond levels, beyond levels.

• 5:19Neil deGrasse Tyson?

  Anyone who's played a well-programmed video game goes levels upon levels upon levels.

• 5:24Speaker 03

  Scientists say you should go for the simplest hypothesis that explains the data, and they say the simulation hypothesis is not very simple, it's a complicated hypothesis, let's just go with what the physicists are saying.

• 5:34Speaker 01

  But I thought scientists said, like, "We don't understand that, let's check it out."

• 5:37Speaker 03

  That's true, and scientists late at night, after a few drinks, say, "Hey, maybe that simulation hypothesis doesn't look so bad."

• 5:43Neil deGrasse Tyson?

  Oh, I see, so it depends on the state of alcohol in your veins.

• 5:46Speaker 03

  Yeah, absolutely.

• 5:47Neil deGrasse Tyson?

  Yeah, okay, I didn't know that. David, I want to know, what is the evidence that we are not in a simulation?

• 5:56Speaker 03

  I think there could be no proof that we're not in a simulation, there's a simple reason for that. Any evidence we could get that we're not in a simulation, that could be simulated. The simulation could provide, could simulate that evidence for us, so we can never know for sure.

• 6:11Neil deGrasse Tyson?

  Would you want to know, if you could?

• 6:16Speaker 03

  I would like to know if we are in a simulation, because if we are in a simulation, there's a whole world out there, you know, right now, we've got people exploring space and exploring other galaxies. Whoa, now here's Morpheus to take me to another world. It's all right, Morpheus.

• 6:33Neil deGrasse Tyson?

  Maeve, will you want the red pill or the blue pill?

• 6:43Speaker 01

  Can you explain which one does what?

• 6:45Neil deGrasse Tyson?

  Oh, I guess I should explain that first.

• 6:47Speaker 01

  The red one, are those M&M's, Neil?

• 6:50Neil deGrasse Tyson?

  Take the blue pill.

• 6:53Neil deGrasse Tyson?

  No, these are real pills.

• 6:54Speaker 01

  Okay.

• 6:55Neil deGrasse Tyson?

  Okay, they just look like M&M's that we just bought two hours ago. But they're real pills.

• 7:01Neil deGrasse Tyson?

  Maeve, take the blue pill. You return to your life. You don't even know that you're living in a simulation and you're happy with all that surrounds you. Take the red pill and you'll see how deep the rabbit hole goes.

• 7:15Speaker 01

  Blue, please. Oh, my God. I'm sorry, I'm...

• 7:19Neil deGrasse Tyson?

  David, she left you the red pill.

• 7:21Speaker 01

  I feel bad.

• 7:22Neil deGrasse Tyson?

  Boring. Okay, let's see what happens.

• 7:27Speaker 01

  Oh, I'm allergic to peanuts.

• 7:29Neil deGrasse Tyson?

  The next universe up looks remarkably like this one. Yeah, sorry. So those pills actually had peanuts in them. I hope you're not allergic to peanuts. Because your alternative universe would be death.

• 7:40Speaker 01

  It's so pretty. No, I'm fine.

• 7:44Neil deGrasse Tyson?

  So, if we're in a simulation, given all that we know and see about our universe, what does that say about the concept of a creator? And I ask that very question of Brian Greene. Check it out.

• 8:00Brian Greene?

  If you're going to think about theological explanations of the world and try to make some argument that might be compelling, the one that feels compelling to me is we really could be in a simulation of a 15-year-old kid from the far future in his garage.

• 8:17Neil deGrasse Tyson?

  Or her garage.

• 8:18Brian Greene?

  Or her garage, of course, yeah. Thank you very much. And in some sense, that individual is the creator of this universe. There's nothing supernatural about this. You don't have to go outside the laws of physics. You don't have to do the things that we as scientists recoil from. But nevertheless, there is somebody, a real-life person, who is responsible for this world that we're in.

• 8:40Neil deGrasse Tyson?

  So our creator is a snot-nosed...

• 8:43Brian Greene?

  Pimply kid, and that's right, man. That kind of brings it down to earth, you know? The problem with that as a real explanation, of course, is you could apply that to any mystery that we encounter. And then it becomes less satisfying.

• 8:58Neil deGrasse Tyson?

  Right.

• 8:58Brian Greene?

  Every time we've pushed forward on previous mysteries, we've found deeper explanations that didn't require a god or a kid in a futuristic garage. And that's where we're driven to look.

• 9:11Neil deGrasse Tyson?

  David, if we're created by a pimply kid in a garage from the future, or from another civilization on another planet, then what are the implications of that?

• 9:21Speaker 03

  Well, I think, you know, it's got a whole lot of theological implications. In fact, I think it might explain a whole lot of that stuff. The god of the Old Testament, all those floods and fires and pestilence. I can totally see my five-year-old nephew doing that stuff. When he's playing Sim Life and Sim Universe and so on. "Yeah, let's rain down the floods."

• 9:42Neil deGrasse Tyson?

  So, that series of games, the Sim series, in those you can heap disaster upon the life forms that you've created?

• 9:49Speaker 03

  And little kids are really into it, so...

• 9:52Neil deGrasse Tyson?

  So, what you're saying is our universe comes very close to the temperament of a child?

• 9:59Speaker 03

  I think we may be getting evidence that a teenager is running this thing.

• 10:04Neil deGrasse Tyson?

  So, do we know... We, as scientists, try to find the rules that they have programmed into the game. And do you think that's ultimately doable?

• 10:14Speaker 03

  Well, you know, a really smart creator is not going to have left too many traces. So, let's hope that the creator is, you know, not too quick and too far ahead of us here.

• 10:26Neil deGrasse Tyson?

  And what I wonder is, if you're playing a game and there isn't turmoil and stress, and then it's less interesting, isn't that right? So, here in the real world, we have storms and tornadoes and earthquakes, and we have real, live things, leaving me to wonder whether they're all there for the entertainment of the creator, just so that they don't get bored playing this game. Do you have any reflections on that?

• 10:53Speaker 03

  Well, I hope you're enjoying this.

• 10:57Neil deGrasse Tyson?

  We'll figure you out eventually. So, David, tell me about the possibility that you can create a simulation within which simulations are created.

• 11:09Neil deGrasse Tyson?

  So that it's a nested set of universes. How realistic is that?

• 11:15Speaker 03

  Well, if every, probably every universe can create simulations. Probably those simulations will not be as complex as the original universe. You know, maybe the original universe has only got so much capacity, you know, like one billion gigabytes or something, then, okay, the next one down, maybe you can create a thousand simulations of a million gigabytes each, and so on and so forth. So probably simulations within simulations are gonna gradually get less complex than each other.

• 11:44Neil deGrasse Tyson?

  So eventually you just have stick figures punching one another and that's it. So, no, I think that's profound and it smacks of the Gödel's incompleteness theorem, where can you create a more complex universe than the universe from which you create it? And maybe not. Maybe it has to be sub-complex to the complexity from which it is derived.

• 12:12Speaker 01

  Why? Because you can't imagine it?

• 12:14Neil deGrasse Tyson?

  Well, I don't know, I'm just, I'm exploring that now. Can you create something that's smarter than yourself? Can you create something more complex than anything, than any complexity in the world from which you created it? Is that even possible?

• 12:30Speaker 03

  I think I could create something more complex than me in principle by, you know, doing an amazing job of programming, but I might have to exploit the complexity of the world around me. Could a universe create something more complex than itself? It's hard to see how that's possible because what you create is still on a computer running within your universe. If it's complex, then our universe is more complex because it contains that computer and more besides. So I think inevitably, you cannot exceed the level of complexity which our universe can support.

• 13:00Neil deGrasse Tyson?

  So I just realized something, we're creating these things on a computer. So if you create a universe, the creatures in that universe, if they're gonna create another simulation, they have to invent a computer.

• 13:11Speaker 03

  Yeah.

• 13:11Neil deGrasse Tyson?

  And learn how to program the computer in the simulation.

• 13:16Speaker 03

  Yeah.

• 13:16Neil deGrasse Tyson?

  And then whatever they create in that computer has to itself invent a computer.

• 13:21Speaker 03

  Yeah, computers within computers within computers. But I hope these are really efficient computers, otherwise they're gonna be giving off a lot of, you know, power loss and so on, and the energy's gonna run out somewhere. Hey, I think I'm, I think it's all slowing down around me now.

• 13:34Neil deGrasse Tyson?

  So, so, so, wow, so, evidence of power shortages could tell us something.

• 13:40Speaker 03

  There are energy crises left and right. Does that mean something?

• 13:47Speaker 01

  The latest.

• 13:49Neil deGrasse Tyson?

  Okay, so, even if our universe is real and not simulated, it might not be the only universe. Welcome to the concept of the multiverse when StarTalk returns.

• 14:15Neil deGrasse Tyson?

  Welcome back to StarTalk. We're here in the hall of the universe beneath the Hayden Sphere, and we're featuring my interview with theoretical physicist Brian Greene, who thinks that the notion that our universe might be one of a multitude of universes might not be as far-fetched as it sounds. Check it out.

• 14:36Brian Greene?

  You know, people often say, "You guys are just like overworked imaginations coming up with this idea of the multiverse." And I say, "No, we look at the math. The math kinda grabs us by the lapel and slaps us around and says, 'Look at what the equations are telling you.'" The fact that quantum physics naturally yields this possibility that all of the probabilities allowed by the math of quantum mechanics might yield definite outcomes with the electron 50% chance here, 50% chance there, means that there are actually two universes, one in which the electron is here and one in which it's over here. That's the oldest version, perhaps, 1957, but since then, they are understanding of the Big Bang. Right, we used to consider the Big Bang to be a singular event, one event that gave rise to one universe.

• 15:21Neil deGrasse Tyson?

  The Big Bang.

• 15:22Brian Greene?

  The Big Bang. But, but the math shows that you don't use up all of that fuel in a single Big Bang. In fact, the bang itself winds up generating more of the fuel, which generates other bangs, other universes. So there's two variations right there. Quantum physics and cosmology naturally yield this possibility of ours being one of many universes. They come right out of the math.

• 15:43Neil deGrasse Tyson?

  So he's using his math to create universes, and he believes them. Not kinda, you know, he's a smart guy, so I'm kinda, I'll, I'll, I'll hang with him on this. So, so David, do your people, uh, cause you have people, right?

• 15:57Speaker 01

  He's Australian.

• 15:58Neil deGrasse Tyson?

  He's Australian. Do, do your philosopher people, do they think much about multi, the multiverse?

• 16:03Speaker 03

  Oh yeah, we think about possible worlds all the time, different ways the world could have been, and the idea that maybe all of those worlds are in some sense real, so.

• 16:14Neil deGrasse Tyson?

  And there's a universe where Maeve marries Michael Fesman.

• 16:16Speaker 01

  It makes me think of the movie Sliding Doors. I don't, the one where Gwyneth Paltrow and some guy who's not as good-looking as her, which is a constant in Hollywood. Um, but the thing that isn't constant is she meets him once he gets on the train, and then he doesn't get on the train, but she meets him later.

• 16:34Neil deGrasse Tyson?

  So that's, that's a split in the universes, they're just different universes.

• 16:37Speaker 01

  Yeah, but it has the same, uh, result, which I don't know what you think about that.

• 16:42Speaker 03

  All the universes end up converging, I think, you know.

• 16:44Speaker 01

  Yeah.

• 16:45Speaker 03

  In the philosophical model, every single possible universe, well, it's the one where Michael Fesman, that marries you, and then you dump him, and then.

• 16:52Speaker 01

  Yeah, and then take him back.

• 16:53Speaker 03

  You have five kids.

• 16:55Speaker 01

  Yeah, five kids.

• 16:56Speaker 03

  He runs off with Neil, and they get married, it all happens.

• 16:58Neil deGrasse Tyson?

  Now, this is, this has reached into pop culture from this film that you're describing.

• 17:03Speaker 01

  Sliding Doors.

• 17:04Neil deGrasse Tyson?

  Sliding Doors. Uh, there's a, there's a fun and famous scene in Family Guy where they talk about the multiverse. Uh, Star Trek will do this, did this in a few episodes. So, I, I'm, I'm impressed that pop culture has tapped this for their storytelling, because what intrigues me is if you have multiple universes. Might they ever intersect in some testable way? Rather than just hypothesizing their existence and washing your hands clean of whether any experiment will ever deduce this? And I always wonder, you know, could dark matter, this mysterious source of gravity in our universe, and we don't know anything about it, other than it has gravity, could that be like regular gravity in another universe that is adjacent to ours, whose gravity we feel? Leaking into ours?

• 17:49Neil deGrasse Tyson?

  And I, the best example I can think of is very simple. Just imagine a sheet of paper, and we all live inside that flat sheet of paper. And we just deduce the nature of our world just by looking at things. And watch what happens. You see a dot appear, out of nowhere. We say, "Wow, ooh, ooh, where did that come from?" We don't know. We bring out our best theoretical physicists, they're poking it, probing, they don't know anything. And what does the dot do next? It gets bigger, turns into a circle. And the circle gets bigger to a maximum size, and then it shrinks back down, goes back to a dot, and then disappears. Then all the academics go back to the chalkboards and they try to figure it out. And all it is? Is a sphere passing through the two dimensions of your universe.

• 18:33Neil deGrasse Tyson?

  So if you sat in a higher dimension, it is patently obvious what's going on. But if you're stuck in the two dimensions of that universe, it is a mystery. Leaving me to wonder what mysteries might lie out there in our universe that are simply other universes bumping into us.

• 18:52Speaker 03

  I mean, the more these universes interact with each other, though, the less clear it becomes why we should think of them as parallel universes. If they're like interacting all the time, and there are people can go back and forth, then suddenly, why not think about it as one big universe? So if they're interacting, then the question is, why so little interaction?

• 19:11Neil deGrasse Tyson?

  Ooh. You've got me there. Yeah, so I think we're driven to this by the fact that in the quantum realm, there's so much weirdness going on that we can't explain. And maybe it's just, it's just some other universe messing with us. More on the mind-bending reality of quantum physics, when StarTalk continues.

• 19:43Neil deGrasse Tyson?

  Welcome back to StarTalk. We are here in the hall of the universe of the American Museum of Natural History. And we are talking about quantum oddities. And one of the most famous of all quantum oddities was devised, was proposed by quantum physicist Erwin Schrodinger in 1935. And it's a thought experiment involving a cat that is simultaneously dead and alive. I brought that very question to Brian Greene, theoretical physicist. Let's check it out.

• 20:18Brian Greene?

  He was pointing out that the weirdness of quantum physics, which normally we think of as only applying to like particles like electrons, he said, "There's no way to protect everyday life from that weirdness." He was basically saying that if you have a probabilistic description of electron, it could be here or here. You say, "Well, okay."

• 20:36Neil deGrasse Tyson?

  And it's completely legitimate.

• 20:37Brian Greene?

  That's right.

• 20:38Neil deGrasse Tyson?

  That is the world.

• 20:39Brian Greene?

  That is the world, according to quantum mechanics. But you don't seem to have a cat that's like a mixture of being dead and alive. So he's like, "Well, how might you bridge the gap between them?" He says, "Look, what if, if the electron's over here, it releases some poison, cat dies. If the electron's over here, it doesn't release the poison, cat lives. So if the electron has a 50/50 chance of being here and here, you're forced to contemplate a cat being in a mixture of dead and alive." It's called the quantum measurement problem, technically. And it's basically the idea that we don't still, even today, know how to go from the probabilistic description of the micro world to the definite reality of the macro world in which you don't seem to see cats in a mixture of here and there, or in a mixture

• 21:24Brian Greene?

  of dead and alive. And this is, this is a real puzzle.

• 21:27Neil deGrasse Tyson?

  By the way, we don't mean half-dead, half-alive. You mean completely alive and completely dead.

• 21:31Brian Greene?

  That's right. Because the electron is not...

• 21:32Neil deGrasse Tyson?

  Because you could be dying, and that would be some...

• 21:34Brian Greene?

  Sure, sure. Totally right. But you see, it's not that the electron is half here and half here. It's a mixture of being here and a mixture of being there. And that's the difference that you're pointing out, which would then imply that the cat would be actually a mixture of being fully alive and fully dead. But yeah, this is a real issue in quantum mechanics that I consider to be unresolved.

• 21:56Neil deGrasse Tyson?

  If I just give a brief primer on quantum physics. It was discovered in the 1920s. What we noticed was that as we started probing matter on smaller and smaller scales, molecules, atoms. We realized that they were behaving differently from any of the classical physics rules and regulations, laws, that we had formulated up until then. Newton's laws of gravity and, and all the equations of electricity and magnetism. None of those worked in the realm of tiny particles. And so whole new formulations to account for the behavior of nature had to be laid to page. And thus was the birth of quantum physics.

• 22:40Neil deGrasse Tyson?

  And in there, there's strange phenomena. Particles pop in and out of existence. They transmutate from one form to another. They start out here and they show up there and they get there faster than the speed of light. It's called quantum tunneling. And all, it's like, this is weird. And, and it freaked people out because we were in the habit of understanding what we were describing. And when quantum physics came around, we could describe it, but not understand it. We had precise mathematical formulations for what was going on. And you could predict quantum phenomena every time perfectly, but it completely defied everybody's common sense. And so there it was in the 1920s, a curiosity.

• 23:25Neil deGrasse Tyson?

  No one knew, why, like, why are you wasting your time on this? You'll never see atoms, you'll never see molecules. I work with wood, wood is fine. I don't need to know quantum physics. I work with metal, I build bridges. Why do I care? It would take several decades, a full 40, 50 years after quantum physics, before we would realize that quantum physics would become the foundation of all modern information technology. The creation, storage and retrieval of information as we know it today would not be possible without the exploitation of quantum physics and the rules that describe it. So there is no modern life without quantum, there'll be no lasers, there's no, be no

• 24:06Neil deGrasse Tyson?

  semiconductors, there's no, there's no imaging in hospitals, the MRI, all of this exploits quantum phenomenon. It's stunning. It's a lesson that whatever science is going on today, you could easily judge it as being irrelevant, but then take a cue from quantum physics and say, it is too early for you to decide. Let the future history of the world be the judge of the value of this science that we are now conducting. So let me ask you, David, how do your philosophical friends think about Schrodinger's cat being half-dead and half-alive?

• 24:41Speaker 03

  Well, it's amazing, actually, because physics in the 20th century threw out a new philosophical mystery to rival any of the existing philosophical mysteries. What's the nature of the mind? What is reality? What on earth is going on in quantum mechanics that can, because it works so well in predicting the results of our experiments, but it does not deliver an answer really to what's actually going on in reality. Is the cat dead? Is the cat alive? Is it both? It talks about a quantum wave function where the deadness of the cat and the aliveness of the cat coexist, but every time we look, every time we open the box and look, the cat's dead or the cat's alive.

• 25:26Speaker 03

  So how does that transition happen from the wave function where the particles are here and there to the moment of observation where we look and everything is in one place, not two? For me, that raises questions about consciousness and the role of the mind in reality, which is wonderful.

• 25:43Neil deGrasse Tyson?

  Well, I'm not satisfied with you telling me it simply raises questions, because I brought you on the show for you to have answers.

• 25:47Speaker 03

  Alas, then I got a Nobel Prize coming for this if I have good answers.

• 25:52Neil deGrasse Tyson?

  And by the way, it's not, it's not a, an odd fact, you can have very famous physicists in the past reflecting on the non-understandability of quantum physics. In fact, Richard Feynman at one time said, "I think I can safely say that nobody understands quantum physics."

• 26:10Speaker 01

  Oh, I'm so glad he said that. I was feeling so dumb.

• 26:15Neil deGrasse Tyson?

  But he didn't mean that no one knew how to calculate with it and get right answers. Understand meaning can I make sense of it?

• 26:20Speaker 01

  Mm-hmm.

• 26:21Neil deGrasse Tyson?

  And, um, so I remembered, uh, both Brian Greene and I, uh, when we grew up, we read a book series called Mr. Tompkins, Mr. Tompkins in Wonderland. And this was a brilliantly conceived series. It's for, for, for curious kids, where Mr. Tompkins occupies a world where the laws of physics are slightly different. So that things that will otherwise be hidden from you in our world are completely manifest in his world. And so he basically explored concept and theoretical physics in this, in this, in this fascinating way. And the author was George Gamow, who's written a bunch of other books that enchanted me growing up. I, I, I brought, I raised the topic with Brian Greene in my interview with him. Let's check it out.

• 27:02Neil deGrasse Tyson?

  One of the stories I remember, they changed the value of Planck's constant to be something that produced macroscopic phenomenon.

• 27:11Brian Greene?

  Right.

• 27:11Neil deGrasse Tyson?

  So you would walk-

• 27:12Brian Greene?

  Macroscopic quantum phenomenon.

• 27:13Neil deGrasse Tyson?

  Macroscopic quantum phenomenon. So you, you'd walk through a doorway and then you would refract.

• 27:18Brian Greene?

  Yeah.

• 27:18Neil deGrasse Tyson?

  The way light would do it.

• 27:20Brian Greene?

  Or you play pool in the pool hall and you hit the cue ball and it passes through the ball that you're shooting at. A quantum tunnel. You know, uh, yeah.

• 27:28Neil deGrasse Tyson?

  Yeah, that'd be like a really cool universe to live in.

• 27:29Brian Greene?

  It'd be totally a cool universe.

• 27:30Neil deGrasse Tyson?

  Yeah.

• 27:31Brian Greene?

  You know, and that actually is our universe, except we don't play pool on that tiniest scale to witness that. But if that's how it would be.

• 27:38Neil deGrasse Tyson?

  I tell people all the time, if we were that size-

• 27:40Brian Greene?

  Yeah.

• 27:40Neil deGrasse Tyson?

  Then quantum physics would be intuitive to us.

• 27:43Brian Greene?

  We're mind melding. I'd say the same thing.

• 27:45Neil deGrasse Tyson?

  Oh, yeah.

• 27:45Brian Greene?

  I'd say if we were born 10 to the minus 18 meters across, this stuff would be obvious.

• 27:49Neil deGrasse Tyson?

  Yeah, it would be, it would be life.

• 27:51Brian Greene?

  Yes.

• 27:52Neil deGrasse Tyson?

  It'd be, just be life. Whereas now, when you, you know, I, I hold a pen and I let go, let go of it, it drops and that's gravity doing its thing. And that becomes what forms my sense of the world.

• 28:03Brian Greene?

  Totally.

• 28:04Neil deGrasse Tyson?

  And therefore, if it doesn't agree with that, I say it does not make sense. But that doesn't mean it's not true in the universe.

• 28:08Brian Greene?

  That's right. In fact, it goes deeper, right? Because your intuition not only comes from your experience, but it's kind of built up from the human species, right?

• 28:16Neil deGrasse Tyson?

  Yes, yes, yes.

• 28:16Brian Greene?

  That's what our brains have evolved to understand. And out there in the wilderness, those of us who knew Newtonian physics survived and those who thought quantum mechanically were eaten.

• 28:29Neil deGrasse Tyson?

  How to be removed from the gene pool, get a wrong sense of reality.

• 28:32Speaker 01

  Yeah, that bear is just gonna go through me.

• 28:36Neil deGrasse Tyson?

  No, yeah, not in this universe. So, it seems to me there ought to be some whole world of video games that you can just adjust knobs of the various physical constants to change what is a phenomenon that you experience and what you don't. So, other things that happened to Mr. Tompkins in Wonderland, he changed the speed of light to be 60 miles an hour. So, as you're driving down the street, all these relativistic phenomenon would happen because you're nearing the speed of light, just staying within the speed limit of the road. And in the case that we began that conversation, Planck's constant, which was discovered by

• 29:13Neil deGrasse Tyson?

  a guy named Planck, Max Planck, in 1900, he noticed that light does not come in continuous ranges of energies, it comes quantized. You can have this much energy, or that much energy, or that much energy, but not anything in between. And that quantization of energy became the founding syllables that tells us what the name of this new branch of physics would be called, quantum physics. And so, if you change the value of Planck's constant to be something big, rather than the tiny value that it has, all of a sudden, quantum physics manifest in everyday life.

• 29:55Neil deGrasse Tyson?

  That would just be cool to develop a new sense of what is normal. Do you guys practice that as philosophers, just to take yourself out of your comfort zone?

• 30:04Speaker 03

  Yeah, we call it a thought experiment, you know, like use your imagination to think about ways the world could have been, but isn't. But I think it's actually now, might eventually become practical to do this. People are now building computers based on the principles of quantum mechanics, quantum computing. And as in the early days, yeah, people are still just rigging together the way to get the quantum bits to interact, but you can imagine in a few years, we're gonna have whole video games really based on quantum computing, and we'll be able to use that to actually use quantum processes to develop a real intuition for the quantum world.

• 30:41Neil deGrasse Tyson?

  Now, since we don't understand why quantum physics behaves the way it does, and we don't understand consciousness, I'm intrigued that many people want to explain consciousness with quantum physics. Two things that we don't really understand very well at all, but you'd want to use one to explain the other.

• 30:58Speaker 03

  It was right there.

• 30:58Neil deGrasse Tyson?

  There's no excuse for that, I just want you to know.

• 31:00Speaker 03

  Yeah, yeah, yeah, yeah. Two mysteries, they've got to go together. But actually, it was right there at the beginning of quantum mechanics, because they really put so much weight on the notion of measurement. Brian Greene was just talking about the measurement problem. In quantum mechanics, they say something special happens when a measurement occurs. And then that raises the question, what on earth is measurement? And it sounds like most people treat it as an observation by a human, conscious observer. And does that play a role in physics? Well, okay, so the next thing that happens is the physicists freak out and say, no way can the human mind play a role in physics. We've got to find some way to get the mind out of there, because physics is meant to be objective and...

• 31:38Neil deGrasse Tyson?

  Well, I build a machine that makes the measurement, and then we see the chart recorder later.

• 31:42Speaker 03

  Yeah, but then no one knows where to draw that line. What counts as the machine that can truly make a measurement, as opposed to the quantum system that doesn't make a measurement? No one knows where to draw that line.

• 31:52Neil deGrasse Tyson?

  So you're folding this into a theory of consciousness?

• 31:54Speaker 03

  I'm saying, if you want to find a role for consciousness in the physical universe, which is one of the great traditional mysteries of philosophy, quantum mechanics may provide a promising place to look. And I've actually been thinking about this lately, seeing if we can make that precise. And I'm not promising you it's going to work, but I think it's worth thinking about.

• 32:11Neil deGrasse Tyson?

  Okay, when you figure it out, you come back on the show?

• 32:13Speaker 03

  Totally.

• 32:14Neil deGrasse Tyson?

  Okay.

• 32:15Speaker 03

  Right before I get my Nobel Prize.

• 32:16Neil deGrasse Tyson?

  Okay. So, right now, one of my favorite segments, it's time for Cosmic Queries. Yes. In this segment, we answer questions that we solicit from our fanbase. I've not seen these questions. Maeve, you have them in your hands.

• 32:31Speaker 01

  Yes.

• 32:32Neil deGrasse Tyson?

  And since philosophy is one of the categories of what we solicited, I got a philosopher with me, so I don't know the answer. We're going to David here. Okay, Maeve, give it to me. Cosmic Queries.

• 32:40Speaker 01

  All right. First cosmic query from Keilia Silvestre in St. Paul, Minnesota. What experiments could provide hard scientific evidence for the multiverse hypothesis?

• 32:49Neil deGrasse Tyson?

  David?

• 32:51Speaker 03

  Quantum mechanics is already showing signs that electron can be in two places at once, that a cat could be dead or alive. Some people think the best explanation of that is multiverse. Is it proof? No, but it's evidence for taking the idea seriously.

• 33:08Speaker 03

  Yeah, you want more than that?

• 33:10Speaker 01

  No.

• 33:10Neil deGrasse Tyson?

  No, no, David, that was an awesome, succinct answer.

• 33:12Speaker 01

  Perfect.

• 33:13Neil deGrasse Tyson?

  Yeah, that was a perfect answer.

• 33:14Speaker 01

  Okay.

• 33:14Neil deGrasse Tyson?

  I can neither add nor subtract from what he said.

• 33:16Speaker 01

  Okay, great.

• 33:17Neil deGrasse Tyson?

  Yeah, yeah.

• 33:18Speaker 01

  You're winning.

• 33:21Speaker 01

  The second question is, do the findings of the double slit experiment prove consciousness creates reality?

• 33:29Speaker 03

  I don't think the double slit experiment on its own can come close to doing that. That is where you see the electron.

• 33:36Neil deGrasse Tyson?

  You sent an electron through one slit, but what you see on the other side is as though the electron was a wave passing through two slits, and you see the wave interfering with itself on the other side, even though you knew you sent electrons.

• 33:47Speaker 01

  Yeah.

• 33:48Neil deGrasse Tyson?

  Yeah.

• 33:48Speaker 01

  So...

• 33:49Neil deGrasse Tyson?

  The double slit experiment, yeah, so is that a... so the crux of the question is...

• 33:53Speaker 01

  Does that prove that consciousness creates reality?

• 33:57Speaker 03

  It doesn't prove anything like that, but it does suggest, let's say, because if you look at the slit, then it looks like the electron goes through one slit. But if you look at the backboard where the electron ends up, you see something completely different, an interference pattern that suggests it goes through both. So to some people, that has suggested that what measurement you make, what observation you make, makes a difference to the results of a physics experiment. And if you want to call that consciousness creates reality, well, there are ways to go there.

• 34:29Neil deGrasse Tyson?

  So however real that is as a physical description, that is very tasty to new age philosophers. They... it's irresistible to them to try to explain all manner of other things. So there's a risk of how that information is used and tapped by others who want to claim access to reality.

• 34:46Speaker 03

  I think you're right. And in the 1970s, this brought a bit of a bad reputation, this kind of idea, because people were writing books like The Dancing Wu Li Masters and The Tao of Physics. Yeah, consciousness, quantum mechanics, it's all so cool. So I'm thinking maybe a sober reassessment of these ideas, though. But I do think consciousness is cool, and it may well... we do need to understand the connection between consciousness and physics, so let's bring the volume down. But I think there are ideas here worth taking seriously.

• 35:11Neil deGrasse Tyson?

  And you have to think consciousness is cool because it is in the title of the... Department you run.

• 35:18Speaker 03

  It is.

• 35:18Neil deGrasse Tyson?

  Okay, just to clarify that. One more, last question, go.

• 35:21Speaker 01

  From Nicole Brooks in Philadelphia. What is reality?

• 35:28Neil deGrasse Tyson?

  Yeah, David, why don't you take that one? I could do it, but I just, I'll let you take this one.

• 35:33Speaker 03

  What is real, Neo? If reality is what you sense and perceive and taste, then reality is just a bunch of neural electrical signals in your brain. Their Morpheus is spouting the philosophy known as idealism. Reality is all in the mind. I don't think reality is all in the mind. Reality is something out there in the external world. The mind creates our perception of reality. What we don't understand is how something outside the mind and something inside the mind somehow come together to create all of our amazing experience of this universe.

• 36:09Neil deGrasse Tyson?

  I have a very pragmatic definition of reality. It is that which multiple people can agree upon as being real, which gives you some confidence that it's not simply going on in someone's head. That would be your personal truth. But the objectively established reality are what experiments can show exist without a dependence on who is actually making the measurement.

• 36:32Speaker 01

  So you're like, is this milk sour? Will you smell this?

• 36:35Neil deGrasse Tyson?

  Yeah, and we all agree it's sour, it's sour milk.

• 36:37Speaker 01

  Yeah.

• 36:38Neil deGrasse Tyson?

  Yeah, if you think it's sour and no one else does, it's in your head. That was, that is not a, an objective reality. It's just what's going on in your head, and none of us should have to give any credence to it at all.

• 36:48Speaker 03

  So reality is just a consensus?

• 36:50Neil deGrasse Tyson?

  Yes!

• 36:50Speaker 03

  And if you're outside the consensus, then what? You're mentally ill?

• 36:53Neil deGrasse Tyson?

  Yeah, basically, yeah.

• 36:53Speaker 03

  Okay.

• 36:54Neil deGrasse Tyson?

  Yeah. Or mentally different.

• 36:59Neil deGrasse Tyson?

  So, we gotta catch up with my, my man Chuck Nice, because Chuck goes to the street. He, he, he takes this stuff to the street. So let's catch up with him, Chuck Nice.

• 37:10Chuck Nice?

  Hey Neil, I'm on the streets of New York City, finding out what regular people know about theoretical physics. I have a theory, it's nothing. What is theoretical physics?

• 37:20Speaker 05

  I have no idea. I guess it has something to do with physics and theories.

• 37:24Chuck Nice?

  Theoretical physics. Theoretical physics. Theoretical physics. How are you, my friend? True or false? On a subatomic level, particles can exist in two places at the same time.

• 37:38Speaker 06

  Uh, well, I would say true, but I know nothing.

• 37:40Chuck Nice?

  No, you're right, sir! You are right. And now for 1 million points, how?

• 37:45Speaker 06

  How? By visualizing yourself, or the particle, outside. To become the projection of what you visualize, and that becomes the realer one.

• 38:00Chuck Nice?

  Uh, are you familiar with the idea of parallel universes? I am. What is happening to you in your parallel universe, right now? Bill Murray is my dad.

• 38:10Speaker 07

  Maybe robbing a bank or something.

• 38:11Chuck Nice?

  Oh, so you're the evil you in your parallel universe? Yeah! Theoretical physics, that's what we are talking about. Higgs boson walks into a church. The priest says, "Hey, we don't allow Higgs boson in here." The Higgs boson says, "Hey, but without me, there can be no mass."

• 38:27Speaker 05

  Uh...

• 38:28Chuck Nice?

  What is the most frequently given answer in quantum physics? I really have no clue.

• 38:36Speaker 07

  I have no idea.

• 38:38Brian Greene?

  I don't know.

• 38:39Chuck Nice?

  Correct!

• 38:42Neil deGrasse Tyson?

  Chuck, nice!

• 38:47Neil deGrasse Tyson?

  So, up next, we're gonna find out what string theory has to do with string music, on StarTalk.

• 39:06Neil deGrasse Tyson?

  Welcome back to the American Museum of Natural History. We are doing StarTalk, featuring my interview with theoretical physicist Brian Greene. And he once explained string theory while there was a string quartet going on behind him, and he connected the two. And I had to ask him, "What's up with that?" Let's check it out.

• 39:29Brian Greene?

  We as physicists have used musical metaphors forever. The harmonies of nature, the music of the spheres, and string theory. The metaphor really is so close to the theory itself. We are talking about vibrating filaments that look like vibrating strings. So it was natural to have a string quartet, not to illustrate the ideas. I hate that, take science and illustrate it with music. But rather, allow an audience to absorb the ideas, both cognitively from someone describing the science, but also emotionally. All right, I mean, you care about that a lot too, that people feel the emotion. Feel the physics. Feel the strings, right? I mean, that's what it's about.

• 40:06Neil deGrasse Tyson?

  And then they want more of it. So, I'm a violinist, and I strike a note, and you hear it in one way. I strike a different note, you hear a different frequency. And together, they make music. In string theory, the vibrations of your strings manifest as particles in our physical universe. Vibrated another way, it's a different particle.

• 40:29Brian Greene?

  Yes.

• 40:30Neil deGrasse Tyson?

  And together, you make the Symphony of Life.

• 40:31Brian Greene?

  Yeah. Everything in the universe, every particle, electrons, corbs, neutrinos, everything represents the different notes that strings can play if the theory is correct, which you need to underscore. But that's the basic idea of string theory.

• 40:45Neil deGrasse Tyson?

  Now, it turns out, there happens to be a guy out there who wrote an entire book on the connection between physics and music.

• 40:54Neil deGrasse Tyson?

  An entire book. His name is Stefan Alexander. And he's standing by right now, live on video call. You guys, you have him?

• 41:02Speaker 08

  I'm here.

• 41:03Neil deGrasse Tyson?

  Stefan, hello.

• 41:04Speaker 08

  Hey Neil, what's up?

• 41:05Neil deGrasse Tyson?

  Hey, well, welcome to Startalk.

• 41:07Speaker 08

  Hey, good to be here. Thanks for having me.

• 41:09Neil deGrasse Tyson?

  So, so you wrote a book, uh, The Jazz of Physics, Stefan Alexander. The Secret Link Between Music and the Structure of the Universe. That's kinda, that's a, that's a, that's a, that's a badass title, right there. But what I want to know is, is there something about physics that you can tell me? So that henceforth, I will always think of jazz when I encounter it.

• 41:31Speaker 08

  I can give you one cool example, and it has to do with improvisation. So, what an improviser has to do is spontaneously create something cool while the music is going on, while the chords are changing. And different jazz musicians have different strategies for doing that. And one thing I discovered is the idea of targeting notes. So, for example, if I start off on a G, and some bars later, I end up with a D, that's sort of the beginning point and the end point. And in between targeting those two notes, meaning the end point note being the G,

• 42:14Speaker 08

  I can imagine playing many different paths, many different notes. And that's a very good analogy to Feynman's conception of, um, quantum mechanics.

• 42:23Neil deGrasse Tyson?

  Do, do you have the sax in arm's reach? Maybe you can play sort of a particle improvisation for us, just briefly.

• 42:31Speaker 08

  Sure, I can try something. Hold on a second.

• 42:34Neil deGrasse Tyson?

  Okay.

• 42:45Speaker 08

  How was that?

• 42:46Neil deGrasse Tyson?

  Nice, alright.

• 42:50Neil deGrasse Tyson?

  So, alright, that works for me. Because it's not just simply the music of physics, it's the jazz of physics. Because jazz is famous for improvisational riffs.

• 43:00Speaker 08

  And according to Feynman's conception of quantum mechanics, that particle will actually traverse all paths between the beginning point and the end point.

• 43:09Neil deGrasse Tyson?

  Yeah, and so when you talk about the Feynman, these path integrals that they are, where you can get from this point to this point, and it kind of doesn't matter how you get there, if you end here, you're good to go. Then jazz has beginnings and ends, but where they go in between, that's the journey. Well, Stefan, thanks for joining us on StarTalk.

• 43:27Speaker 08

  Thanks a lot, Neil. Thanks for having me.

• 43:28Neil deGrasse Tyson?

  Alright, Stefan Alexander.

• 43:32Neil deGrasse Tyson?

  We're featuring my interview with theoretical physicist and bestselling author Brian Greene. And in this last clip, he and I assess the meaning that comes from probing the depths of quantum theory. Let's check it out.

• 43:48Neil deGrasse Tyson?

  When you work on string theory, are you really feeling to yourself, "I am nearing an understanding of the nature of reality"?

• 44:01Brian Greene?

  Rarely.

• 44:03Brian Greene?

  You know, but when it happens, though, and it has happened on occasion. You know, I think every scientist, I mean, you know, Einstein had breakthroughs all the time. But, you know, an ordinary scientist, a handful of times in your life, you're gonna have a moment where you feel like you've really seen something that no one else has seen.

• 44:19Neil deGrasse Tyson?

  Even if it's just a handful.

• 44:20Brian Greene?

  That's right.

• 44:21Neil deGrasse Tyson?

  Yeah, it could be one or none.

• 44:22Brian Greene?

  That's right. And those moments, when you're staring at something, you're like, "Wow, I cannot believe that this is coming together this way. No one's ever known this. This is really..."

• 44:30Neil deGrasse Tyson?

  Before that moment.

• 44:31Brian Greene?

  Before that moment, yeah. And you're staring at something, you feel, at least I have felt, a connection, a communion with the universe that otherwise you just don't have. It makes it feel like we really are a part of the bigger picture. I mean, we always say it, right? You know, we're star stuff, it's all true. But to have that feeling that you've connected in, in a deeper way, is thrilling.

• 44:54Neil deGrasse Tyson?

  David, do you ever feel a communion with the cosmos?

• 44:57Speaker 03

  Yeah, you know, even in philosophy, I think you get this, uh, this feeling of trying to understand how everything fits together. Trying to understand, for example, how consciousness fits into physical reality. And every now and then, it just seems the pieces just fit. And for that moment, it's like, this is amazing. I've really got something.

• 45:15Neil deGrasse Tyson?

  Let's catch up with my friend and colleague, Bill Nye, the Science Guy, and see what he has to say about quantum theory and reality. Check it out.

• 45:31Bill Nye?

  Video games, where you battle the bad guys. It's all good gaming fun. But suppose there's more represented here than meets the eye. People have speculated that humankind is doomed. We're gonna wipe ourselves out, one way or the other. Could be a worldwide thermonuclear war. Could be we're so busy playing games on our phones that we fail to deflect an asteroid which comes in and destroys the Earth. No matter how it happens, the argument goes, our demise is so likely that the only reasonable explanation for our existence is that we're part of a computer simulation. Obviously. That's why there's this universe, or a parallel universe, or multiverses, or the indivisible nature of subatomic particles, or the quantum.

• 46:15Bill Nye?

  It's all because we were created by some entity for kicks. If we're just sims, do we really have conscious experiences? Is what you're watching real? Is this video game real?

• 46:30Bill Nye?

  Am I real?

• 46:40Neil deGrasse Tyson?

  Bill Nye.

• 46:44Neil deGrasse Tyson?

  So, let me just solicit from you guys your parting thoughts on this. Maeve, just about quantum realities, multiverses. What's your stand on this?

• 46:55Speaker 01

  I'm against it.

• 46:59Speaker 01

  It's all wrong. It's so confusing. I cannot figure out this universe.

• 47:04Neil deGrasse Tyson?

  Uh huh.

• 47:05Speaker 01

  No, it's fascinating. And really, I love what you were saying too about when you're trying to figure something out and then things line up just for a second. That's a really fun part of writing and being creative and doing comedy too.

• 47:16Neil deGrasse Tyson?

  Okay. So David, where are you on this?

• 47:19Speaker 10

  You know, the moral I draw from this is space is big, but the imagination is bigger.

• 47:24Neil deGrasse Tyson?

  Ooh. No one will take that from you. So when I think about all that has come before us, I find quantum physics entertaining because it's real, yet we don't understand why it's real. It's a different kind of reality. And it leads me to wonder, how much of the world are we missing simply because we are absent the senses to recognize it? Before we had science, we had our five traditional senses, you know, sight, hearing, touch, taste, and smell. And so everything about the world that was real came filtered via those five senses. And what is science?

• 48:09Neil deGrasse Tyson?

  It is a tool that enables you to probe nature in a way that's better than your senses, that's outside of your senses, so that we can all contribute to understanding our place in nature, our place in the universe. You've been watching StarTalk. I'm Neil deGrasse Tyson, your personal astrophysicist. And as always, I bid you to keep looking up.