The Edge of Our Understanding with Brian Greene

Are humans smart enough to uncover the secrets of the universe? Neil deGrasse Tyson and comedian Chuck Nice explore the singularity, string theory, free will and more with theoretical physicist Brian Greene.

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

• 0:00Neil deGrasse Tyson?

  Coming up on StarTalk Cosmic Queries, we have a visit from our old friend, theoretical physicist, Brian Greene. And in it, we respond to questions about the Planck length, about measuring the size and position of particles inside of atoms. We talk about string theory, of course. We talk about E equals mc squared. How does it work? Where does it apply? That and more on StarTalk. Check it out.

• 0:31Neil deGrasse Tyson?

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

• 0:44Neil deGrasse Tyson?

  This is StarTalk. Neil deGrasse Tyson here, your personal astrophysicist. I got Chuck Nice with me. Chuck.

• 0:51Chuck Nice?

  Hey Neil.

• 0:52Neil deGrasse Tyson?

  Yeah, we got a Cosmic Queries.

• 0:55Chuck Nice?

  Yes.

• 0:55Neil deGrasse Tyson?

  One that's back by popular demand.

• 0:59Chuck Nice?

  Oh, one of, one of the most popular.

• 1:01Neil deGrasse Tyson?

  Oh, yes. We had my friend and colleague, Brian Greene, theoretical physicist, professor of physics and math at Columbia University, author of the very bestselling Elegant Universe, followed by The Fabric of the Cosmos, followed by The Hidden Reality. My boy's into all kinds of freaky cosmic stuff, and we got him back for more by popular demand. Brian Greene, welcome back to StarTalk.

• 1:29Chuck Nice?

  Thank you. Good to see you guys.

• 1:31Neil deGrasse Tyson?

  Yeah. Yeah, for those who are watching this on video, I think that's a black hole behind your head.

• 1:36Chuck Nice?

  It is.

• 1:37Neil deGrasse Tyson?

  Full wall-sized.

• 1:38Chuck Nice?

  They all look just like that.

• 1:40Neil deGrasse Tyson?

  Did he just emerge from that black hole for this interview?

• 1:45Chuck Nice?

  If I had done that, I would have broken the laws of physics. You know that.

• 1:48Neil deGrasse Tyson?

  Oh, we can't have that.

• 1:52Chuck Nice?

  Yes. But all of your knowledge would still be intact? Or is that, that, that's information?

• 1:58Brian Greene?

  That's a very good point. Subtle point. I don't know how many of your audience just got the subtlety of Chuck's comment, which is quite.

• 2:07Neil deGrasse Tyson?

  Chuck, I gave him a little diploma recently.

• 2:10Chuck Nice?

  I know.

• 2:11Neil deGrasse Tyson?

  For how much he's learned of physics, I created just a little sort of StarTalkian diploma.

• 2:16Chuck Nice?

  Well deserved.

• 2:18Neil deGrasse Tyson?

  Yeah. Oh, yeah.

• 2:19Chuck Nice?

  Yeah, I love it. Let me tell you something. It's, it's, it's the reason I do this job. It damn sure ain't for the money.

• 2:31Neil deGrasse Tyson?

  So speaking of money, I just wanting, so Brian, you have two professorships. Was one not enough, professor of physics and professor of math?

• 2:41Brian Greene?

  Yeah, each department doesn't know about the other, which is.

• 2:46Neil deGrasse Tyson?

  My boy's drawing two paychecks.

• 2:48Brian Greene?

  That's so funny.

• 2:49Neil deGrasse Tyson?

  Okay, StarTalk fans, don't tell anybody.

• 2:52Brian Greene?

  Exactly. We meet every day at a very small cafe.

• 2:57Brian Greene?

  Me and the math department.

• 3:00Neil deGrasse Tyson?

  It reminds me of our colleague, Sean Carroll, who moved from Caltech to the Johns Hopkins University. He has a dual appointment there in physics and in philosophy.

• 3:10Brian Greene?

  Philosophy, yeah.

• 3:11Chuck Nice?

  Yes.

• 3:12Neil deGrasse Tyson?

  Yeah, so they're feeding his interest by those two affiliations. So I guess that's what's happening with you, right?

• 3:19Brian Greene?

  To some extent, yes. You know, I started out as a math kid and then became a physics nerd. So, you know, it goes way back for me. In fact, you know what? I, when I was in junior high school, went to the math department at Columbia. And that's where I first really learned advanced math. I just knocked on people's doors and say, teach me stuff. And one graduate student took me on.

• 3:40Chuck Nice?

  Wow. Wow, you and Neil have something in common. See, kids, you better learn something, okay? These people at universities, I don't care if it's Carl Sagan or the math department at Columbia, they have time on their hands.

• 3:58Neil deGrasse Tyson?

  I'm just saying, if they see someone young and ambitious, you can't, you can't not.

• 4:02Brian Greene?

  Yeah, you can't turn that away. No, no.

• 4:04Neil deGrasse Tyson?

  You can't turn that away.

• 4:05Brian Greene?

  You can't turn that away.

• 4:07Neil deGrasse Tyson?

  Not given the culture we have cultivated here, as just as a nation that values achievement and excellence, or at least, most people do, I think. Okay, some people.

• 4:18Brian Greene?

  Yeah, I was gonna say, I was gonna say, we are two nations.

• 4:20Chuck Nice?

  All about 37% do.

• 4:23Neil deGrasse Tyson?

  So Brian, I remembered, did you tell this to me on the air or was it offline? That you were not interested in a book unless there were equations on the pages?

• 4:37Brian Greene?

  Yeah, we did, I think, talk about that once. When I was in college, I would go to the bookstore to look at the assigned text for a science class. If there were a lot of words, my heart would sink. If it was chock full of equations, I was like, okay. Because, you know, words can be ambiguous, but the equations are so precise that that certainly at that time was what I was drawn to more fully.

• 4:58Neil deGrasse Tyson?

  Okay, so Brian, what you're saying is so that none of us misunderstand you, you should only speak in equations for the rest of the conversation?

• 5:07Brian Greene?

  I should add, I've matured. I've matured since those early college days.

• 5:11Neil deGrasse Tyson?

  Well, okay, you're picking on some vocabulary.

• 5:13Brian Greene?

  Human being has become more important.

• 5:16Chuck Nice?

  I'm just trying to figure out what book is sitting in Brian's bathroom right now. That's all.

• 5:23Neil deGrasse Tyson?

  I remembered my freshman year, because I go way back. I predate you, Brian. I was taking a computer class back before computers had their own department.

• 5:34Brian Greene?

  Yeah.

• 5:34Neil deGrasse Tyson?

  Because it was not yet enough of a thing to justify an entire academic commitment by a university. But anyhow, I was becoming very fluent in Fortran. And then I had my first dream in Fortran.

• 5:46Brian Greene?

  Yeah.

• 5:46Neil deGrasse Tyson?

  And I said, oh, okay, I guess I've crossed over.

• 5:51Brian Greene?

  I've never, I have not had one of those, but I have had my first lucid dreams. Have you had any of those?

• 5:58Neil deGrasse Tyson?

  Oh, these are the kind of people where they, where they meet aliens and things, right? That's where...

• 6:02Brian Greene?

  At least mine wasn't. Mine was a dream, I think the conventional definition is when, in the dream, you become fully aware that you're dreaming. And...

• 6:10Chuck Nice?

  Yeah.

• 6:11Neil deGrasse Tyson?

  Oh, I was thinking, okay, that's different.

• 6:14Brian Greene?

  Yeah.

• 6:15Neil deGrasse Tyson?

  So, okay.

• 6:19Brian Greene?

  It's a very good experience. The first time I said, I know I'm dreaming because the architecture of the building was different from what I knew it to be. I said, this must be a dream. I'm gonna prove it. I'm gonna prove it by waking myself up. And I shook myself in the dream, and I woke up in real life, you know?

• 6:34Chuck Nice?

  Yeah.

• 6:35Neil deGrasse Tyson?

  Wow, so the architecture of the building is what gave it away. That's interesting.

• 6:38Brian Greene?

  Absolutely, yeah.

• 6:39Chuck Nice?

  So you want to know, here's the thing. I had a lucid dream where I was on stage and I was doing material I've never done before. I was literally writing material in my dream. And here's when it, when it dawned on me that it was dream. I was bombing and I was like, I cannot believe I am bombing. And then it occurred to me, wait a minute, this isn't real and I'm in the dream. And I was like, I'm waking up. And then I woke up going, Jesus Christ, you have a dream and you make yourself bomb in your own dream. Like you could have had a dream where you were at Madison Square Garden, but instead you're at the same comedy club you always work at and you're failing.

• 7:21Brian Greene?

  Usually anxiety, anxiety driven dreams, man. But

• 7:25Chuck Nice?

  That's what that is. That's an anxiety driven dream.

• 7:27Neil deGrasse Tyson?

  Yeah. Well Chuck, we got questions lined up for Brian.

• 7:30Chuck Nice?

  Yes.

• 7:31Neil deGrasse Tyson?

  Patreon members, five dollars a month gives you access to the genius of Brian Greene.

• 7:37Chuck Nice?

  Right. Well, listen, and that's a deal you're not getting anywhere, man.

• 7:40Neil deGrasse Tyson?

  You ain't getting anything like that.

• 7:41Brian Greene?

  Five dollars a month, I have to like, you know, calibrate the answers to reach that level.

• 7:47Chuck Nice?

  No.

• 7:48Brian Greene?

  Part of your audience.

• 7:50Chuck Nice?

  No, no, the idea is it's a bargain, Brian. You're not supposed to give them the actual value, which is a value added service.

• 8:00Neil deGrasse Tyson?

  It's the entry level that we people have access. There you go.

• 8:04Chuck Nice?

  There you go. All right. Let's go to Colin Brum and Colin says, um, does quantum mechanics prevent an infinitely small singularity inside of a black hole? I thought nothing could be smaller. Oh, check it out than a plank length.

• 8:21Neil deGrasse Tyson?

  Oh.

• 8:21Chuck Nice?

  So, so if we're infinitely small, you know, how, how do we violate that precept?

• 8:27Neil deGrasse Tyson?

  Yeah, Brian, you got one with a black hole above his head. What?

• 8:33Neil deGrasse Tyson?

  Wait, let me, let me preface that. I think, didn't Einstein? Or was it Hawking? I think Einstein say, there's gotta be something to prevent the singularity. Because that's just not physically, you know, God is dividing by zero there. So there's gotta be something to prevent it. We just haven't discovered it yet. So where does all that land?

• 8:52Brian Greene?

  He's absolutely right. In 1939, Einstein wrote a paper where he basically tried to prove that the mathematics that suggested a singularity at the center of a black hole could never be realized in the real world, in a real world situation.

• 9:06Neil deGrasse Tyson?

  And just to be clear, singularity is infinitely small, infinitely dense.

• 9:10Brian Greene?

  Well, I'd like to rephrase it because yes, that's the language that people often use. But singularity really means any place where our mathematics can't give us insight to what's going on, any place where the mathematics breaks down. So that's an important point because to the questioner, question.

• 9:30Neil deGrasse Tyson?

  I like that, man. When we get to the Planck length. Wait, it's a cop out, but I like it.

• 9:36Neil deGrasse Tyson?

  It feels like a cop out, but I'm, I'm, we'll, we'll ride it. Go, go.

• 9:39Brian Greene?

  The reason why it's not a cop out is because if you take the mathematics too seriously and you push it into infinitely small or infinitely dense, then you do run into the kind of questions that the questioner asks, like, doesn't that conflict with the statement that you can't really go smaller than the Planck length? And those are just two different perspectives. One is going to take the math and just push it regardless of how far it's going to take you. The other says, let's really evaluate step by step whether this math is actually applicable.

• 10:12Neil deGrasse Tyson?

  Okay, so you're saying it's a mathematical singularity, not a physical singularity?

• 10:16Brian Greene?

  That's the best that we can say today. Now, we need to go further.

• 10:20Chuck Nice?

  It sounds to me like it's term, the terms that we use, we're, we don't have the adequate language to actually describe, because when you say infinite.

• 10:29Neil deGrasse Tyson?

  One thing comes to mind, okay? But the fact is that it's really not infinitely small.

• 10:35Brian Greene?

  I just love not. I, I, but, but here's again the point. Since we can't actually do the experiment, we have to rely on equations. Equations just take us so far because the equations are beautiful. They not only give you insight, they also tell you, we can't give you insight into that domain. We're not powerful enough. We're not refined enough. And the equations clearly tell us that going smaller than the plank size or higher than the plank density is beyond the reach of today's equations.

• 11:02Neil deGrasse Tyson?

  Remind everybody about a plank length.

• 11:03Brian Greene?

  So a plank length is a very specific number. It's about 10 to the minus 33 centimeters. It's incredibly small. And you might say, where in the world does that length come from? Well, it comes from combining Newton's gravitational constant, Planck's constant from quantum mechanics and the speed of light. If you put those together in the right way, a length pops out and that length is the plank length, 10 to the minus 33 centimeters. And its importance is, equations pretty clearly say, don't push us smaller than the plank length because we're not applicable in that domain. And people who talk about infinitely small are disregarding that and saying, well, let's just keep on going and see where the math takes us. And it takes you to a crazy place.

• 11:48Brian Greene?

  Infinitely small, infinitely dense, singularity. We need to fill in smaller than the plank length or whatever new idea for length comes into play in order to have a complete theory of the world. We don't have that yet. So we sensibly should stop at the plank length because that's where the math ends its applicability.

• 12:06Neil deGrasse Tyson?

  Okay, so, so what you're saying is that since the mathematics we, we create that represent a physical idea.

• 12:21Neil deGrasse Tyson?

  What you're saying is that mathematics, which is, let's say, general relativity, admits that there's a point beyond which general relativity does not apply.

• 12:32Brian Greene?

  Yeah, especially when you put general relativity and quantum mechanics into a combined theory. So, general relativity alone doesn't have the Planck length in it, because as I mentioned, you need Planck's constant from quantum mechanics. Quantum mechanics doesn't have the Planck length on its own either, because you need Newton's constant from Newtonian gravity or from the general theory of relativity. They both make use of that number. So, it's only when you try to have a more complete description, that you have all of these ingredients, and when they come together, we are told from the math, "Hey, you've got to start thinking differently when you get to the Planck length."

• 13:08Chuck Nice?

  But it sounds like worlds colliding. Worlds colliding, Jerry! Worlds colliding!

• 13:13Neil deGrasse Tyson?

  Yeah, it kind of is. It's kind of is. Right. I'd like your, what did you call it, Brian? A shotgun wedding between quantum physics and general relativity in the early universe, where the two were, had to get to know each other for the first time.

• 13:31Brian Greene?

  Because it was high and dense and small, that you needed both the theory of gravity and the theory of quantum physics.

• 13:37Neil deGrasse Tyson?

  Yeah. So, Brian, my sort of terrestrial version of that, I think of lines of longitude on Earth as separating time zones, 24 or so time zones that we have. But, of course, as you move away from the equator towards the poles, these lines of longitudes get thinner and thinner, right? There's like the slices, like when you slice an orange, from the top down. They get narrower and narrower, and they meet at the pole! So, you can ask the question, "What time is it at the North Pole?" And there is no time. It has no meaning, that question has no meaning at the North Pole, where all time zones meet. And so, that's my baby example of what...

• 14:21Brian Greene?

  That actually pulls out a very important point, because that analogy played out historically with black holes and black hole singularity, because... You know, of course, that on planet Earth, there's really no singularity. There are other ways that you could define time zones that wouldn't run into this particular problem. So it's really a singularity born of human invention because of the way we set up these lines. People early on with black holes thought that certain singularities were real, but they turned out to be the analog of that. Coordinate singularities, bad choices of lines of longitude, if you will. And that's what happens at the edge of a black hole.

• 15:04Brian Greene?

  The edge of a black hole, people thought, might be singular, but it turns out that it is not. But way down at the center, that's a real one, mathematically speaking, if you push all the way down, as we said, to infinitely small size. You can't get rid of that one by a change of lines of longitude, a change of coordinates.

• 15:21Neil deGrasse Tyson?

  So watch your coordinate system.

• 15:23Brian Greene?

  Yes.

• 15:24Neil deGrasse Tyson?

  What that is. Right.

• 15:34Speaker 03

  Hey, I'm Roy Hill Percival, and I support StarTalk on Patreon. Bringing the universe down to Earth. This is StarTalk with Neil deGrasse Tyson.

• 15:51Neil deGrasse Tyson?

  All right, so let's keep going. Chuck.

• 15:53Brian Greene?

  Yeah, let's get to William Silverman. And William says, "Hi, Dr. Tyson, Dr. Green, Lord Nice. From a photon's perspective, does any time pass as it travels at the speed of light? If no time passes, from the photon's perspective, as it makes its journey, but the light years pass from the perspective of the observer, was it, here's the term, predestined to hit my retina when it left its source?"

• 16:20Neil deGrasse Tyson?

  Ooh.

• 16:21Brian Greene?

  From Bill Silverman at Lafayette Hill. So he's getting philosophical.

• 16:24Chuck Nice?

  I like that.

• 16:25Brian Greene?

  My man took the, uh, took the, uh, the physical and got philosophical.

• 16:31Neil deGrasse Tyson?

  Yeah.

• 16:32Brian Greene?

  It's a weird concept when you think about it, but it makes sense. Yeah, you know, it's a good question because when you look at Einstein's special relativity, you find that the faster something is going, the slower time elapses. You know, so if something goes closer and closer to the speed of light and we're watching it, time will lapse ever more slowly for it. So if you take that to its logical extreme, at the speed of light, no time would be elapsing for a photon. Now, poetically, that's true, but when we try to interpret it, we make a real error. Because a photon doesn't have any consciousness, it doesn't have any means of reporting experience, those ideas don't really have any relevance.

• 17:14Brian Greene?

  So to say that time doesn't elapse, that photon doesn't age, is a very human description of what's going on. And this is a perspective that we humans could never have because massive bodies can't ever travel at the speed of light. So there's a barrier for us to ever really know what that experience would be like. But there's a second part of the question, which is predestination. And I don't think that has much to do with the notion of how time elapses at different speeds. It has to do with how the universe evolves. And yeah, I do think that the universe evolves by laws that do not have an opportunity for humans to intercede.

• 17:55Brian Greene?

  And so is there a kind of predestination built into physical laws, even with the probabilities of quantum mechanics? Yeah, I would say yes.

• 18:03Neil deGrasse Tyson?

  But wait, but let me make a practical example of this. So a photon leaves the center of the galaxy, okay? My thesis data was on stars at the center of the galaxy, right? And I'd always think each night that this photon has been traveling for 35,000 years and it hits my detector instead of someone's buttocks on a beach, okay? So I guess I'm giving value to these photons, right? Or a mountainside. But my question is, if someone, if I were able to watch it travel and stick a mirror halfway through to just send it off in another direction, then the photon on being emitted didn't know I was gonna do that.

• 18:48Neil deGrasse Tyson?

  And so it wasn't gonna hit my detector. So the photon that's emitted and absorbed in the same instant, because it has no concept of time, could that have been anything else? Could that have, could that have had a different fate than the one I gave it?

• 19:06Brian Greene?

  No, but I would also say that your act of putting the mirror was also predetermined in, in, in a similar sense that you're a collection of particles governed by physical law, and I don't believe that you have intrinsic control over those particles because you don't control Maxwell's equation, you don't control Einstein's equation.

• 19:26Neil deGrasse Tyson?

  So you think.

• 19:27Brian Greene?

  So, so, yes, the events of the universe play themselves out in a manner that's dictated by physical law. And that means that human freedom of will that we ordinarily feel that we have, I think, is of a different variety than we intuitively think. You know, when I lift up my hand, you know, I feel like I've made the choice to lift it. When I think about it fully, I truly believe that it was the laws of physics that required that to happen, and I just am observing how my particles are moving.

• 20:05Neil deGrasse Tyson?

  All right.

• 20:08Chuck Nice?

  All right. That's, I'm sure that was.

• 20:11Neil deGrasse Tyson?

  Right about now, this is when Chuck pulls out some weed.

• 20:14Brian Greene?

  What are you talking about pull out? They're sitting right.

• 20:18Chuck Nice?

  I don't have to pull it out.

• 20:22Neil deGrasse Tyson?

  All right. What else you got, Chuck?

• 20:26Chuck Nice?

  All right, here we go. Let's go to Liam Cochrane. And Liam says, hey, this is Liam from Rhode Island. What is it that string theory proposes that the fundamental particles we know, quarks, gluons, etc., are comprised of a combination of strings vibrating at different frequencies rather than just another type of particle? What is the purpose of the string idea behind an analogy to help people understand the theory in more simple terms? So why not a particle that makes up the smallest particles instead of this idea of

• 21:08Chuck Nice?

  a vibration or string that causes it to be more easily understood?

• 21:15Neil deGrasse Tyson?

  And Brian, let me, let me prepen that by asking. Are you proposing that everything's made of strings just so that it's more elegant?

• 21:26Brian Greene?

  No.

• 21:27Neil deGrasse Tyson?

  The man who wrote the book The Elegant Universe? Is this a philosophical motivating force for you? Because Kepler had his own philosophically motivating mathematics, where the planets were platonic solids, and it was beautiful because it was math. And are you, why, what confidence do we have that you are describing reality and not a reality you want to be true so that the universe becomes elegant so that you can sell more books?

• 21:57Brian Greene?

  Ooh.

• 21:59Brian Greene?

  We're hip to you, you, you and the industrial string complex.

• 22:05Brian Greene?

  We know what you're up to, Brian.

• 22:10Brian Greene?

  So, that is a key question, not the selling of books one, but what is the role of aesthetics in making these decisions? And I would say that we theorists do use mathematical aesthetics at times. But in the end of the day, it's observation, it's experiment, and real tension in existing understanding that drives our ideas. So we began this conversation with a questioner asking about the Planck length and this tension between gravity and quantum mechanics. And I said, we need to go further because just saying that they come to loggerheads at 10 to the minus 33 centimeters is not enough, it's not an answer. It's simply letting you know that you can't trust anything beyond that point.

• 22:56Brian Greene?

  String theory is an attempt to fill in the gap, to try to put general relativity and quantum mechanics together. And at least on paper, and we've known this now for many decades, it succeeds in putting general relativity and quantum mechanics together.

• 23:12Neil deGrasse Tyson?

  Whereas if it's just a portfolio of particles, you don't get that benefit.

• 23:15Brian Greene?

  Well, here's the interesting thing. If you said that to me seven or eight years ago, well, maybe 10 years ago, I would have said, yes, you're absolutely right.

• 23:25Brian Greene?

  There's a lot of progress that's happened. And now we realize that a lot of the qualities of string theory have a dual description, a sort of mirror image version, in which point particles do play a role in that description. It's a description that differs from the way we described point particles in the 70s and 80s in certain very specific and important ways. But we're beginning to learn that string theory is one language for describing this unification, but there are other languages, languages sometimes doing both point particles. So it's all kind of coming together in a beautiful tapestry. And we're still trying to, you know, figure it all out.

• 24:06Neil deGrasse Tyson?

  And Brian, it's been 50, 40 years, so I'm very disappointed. I thought you ought to have this solved back in the 90s, just FYI.

• 24:14Brian Greene?

  But you know, do you mind if I actually address that? Because I know it's like partly a joke, but there are people who with a straight face really do say that. You guys said you'd wrap it up in five or seven years, what's going on? And I just have to keep educating them that science is not like, you know, a company where you lay out your product development timeline.

• 24:36Neil deGrasse Tyson?

  Right.

• 24:37Brian Greene?

  You know, you have goals, and as you're going toward those goals, new ideas emerge. You follow those new ideas, they take you to wonderful, crazy places. And as long as you're not stuck, and we're far from stuck, that's what exploring the unknown is all about.

• 24:54Chuck Nice?

  Yeah. But you know, what's weird is like, when you put it that way, it kind of sounds like someone is saying to you, now the assignment was figuring out the entire universe. Why are you late? Why is your paper late? All I asked you to do was figure out the entire universe, and yet here you are saying you need more time.

• 25:13Neil deGrasse Tyson?

  Okay, so I have said this publicly to Brian onstage. So this is not differently mean sounding than when I first said it. It's the same. It's, okay, I've asked string theorists, what's taking you so long? And they say, it's a hard problem. And then I said, wait, wait. So then I said, maybe you are all just too stupid. This is, that's not a consideration here, that we need a different crop of people to enter your field?

• 25:44Brian Greene?

  Well, I'd say it's somewhat different.

• 25:45Neil deGrasse Tyson?

  Of course.

• 25:48Brian Greene?

  We always want young students, you know, who are vibrant and energetic. So I agree, but could it be that the species is too stupid?

• 25:55Chuck Nice?

  Okay.

• 25:56Brian Greene?

  Yeah, that's a real possibility.

• 25:58Chuck Nice?

  I mean, there's a lot of evidence to back that up. I'm just saying. You know, as track records go, let me just come down that I'm in the camp, the too stupid camp. I'm down to believe that.

• 26:11Brian Greene?

  No, we can even go, we didn't even take it out of our species, right? I mean, I respect the intelligence of dogs. They do some remarkable things, but they don't do quantum mechanics. So there's a species that has a limit on how well it can understand the people of the universe. And so why would we be any different?

• 26:31Neil deGrasse Tyson?

  We have some limit of understanding here. Right, of course.

• 26:34Brian Greene?

  Yeah. I think it's a miracle.

• 26:36Chuck Nice?

  Is that problem also exacerbated by observation? The inability to actually observe? Because I mean, honestly, that's what we do. We observe first.

• 26:46Neil deGrasse Tyson?

  Right. So here's how it goes. Ready? All right. So Brian, what particle accelerator do you need now?

• 26:52Chuck Nice?

  That was funny.

• 26:57Brian Greene?

  It's good to have a sense of scale. So take that Planck length that we mentioned before, okay? Just to give a feel for how small that crazy number, 10 to the minus 33 centimeters is. If you take the Planck length is to an atom, right? As a tree is to the entire universe.

• 27:17Chuck Nice?

  Damn.

• 27:18Brian Greene?

  So that's how small, even on atomic scales, we're talking about. And so, yeah, we can't probe there directly. We don't have accelerators to probe that kind of tiny distance. So we, from what we measure here, and we use our mathematics to push as far as we can, and that's a tall order. And so it is a tough problem.

• 27:36Chuck Nice?

  That analogy you just gave, gave me an entirely new perspective and respect for the entire field. Because my answer to that, once you said that, is, oh, to hell with it then.

• 27:50Neil deGrasse Tyson?

  Take up something else.

• 27:52Chuck Nice?

  Let's talk about something else. That's insane, man. That's insane.

• 28:03Brian Greene?

  Yeah, but as we saw in the first question, it comes into play at the deep center of a black hole or the moment of the big bang. So these aren't questions that are irrelevant. They're just pretty extreme.

• 28:28Neil deGrasse Tyson?

  All right, Chuck, let's try to do some rapid round here.

• 28:31Chuck Nice?

  Yeah, who cares? This is so good. I mean, the questions are so good. The answers are so good.

• 28:38Neil deGrasse Tyson?

  We got good people. We got good.

• 28:39Chuck Nice?

  Yeah, these people are on point today, man. They're just on point. All right, let's go with Bruce Ryan. Bruce Ryan says, hiya, gents. Bruce Ryan here from Alexandria, Virginia. Everyone knows E equals mc squared, but how is it the formula actually used in practical terms? How is the formula actually used in practical terms? I mean, if you want to determine the energy of an object, what values do you plug into that equation? Is the mass in grams or pounds? Is the speed of light miles per second or kilometers per hour? Or does any of that even matter? Thanks.

• 29:15Brian Greene?

  Yeah, so where to use that formula? You don't use it much, of course, in everyday life. But if you're looking at a nuclear reactor and you want to know how much fuel needs to be put in, it gives you an order of magnitude sense of what it will require. If you're trying to understand the sun and the amount of energy that's produced by fusion reactions, it gives you a sense of the scales that are involved. Now, how to actually use the formula? Well, the key thing that you learn in science is you have to use consistent units. So kilogram meters per second is the units that we typically will use. And so if you want to use those for mass and for the speed of light,

• 29:59Brian Greene?

  that's a really good way of getting an answer out in joules, which is a particular unit for measuring energy.

• 30:07Neil deGrasse Tyson?

  But just to be clear, the meters per second would be the speed of light, but then you square that. It'd be kilogram meter squared, second squared. Here's the unit of a joule. Right, okay.

• 30:17Brian Greene?

  Precisely. Now, I said that you typically don't use it in everyday life, but there is something misleading there. And I had a lot of arguments with chemists about 10 years ago about this point. They were all wrong.

• 30:29Neil deGrasse Tyson?

  I bet I know what kind of argument we're having. They were thinking that the energy in their things had nothing to do with equals mc squared. I bet that that.

• 30:36Brian Greene?

  Yeah, exactly. Yeah. For instance, you know, an example that I use is if you take a flashlight, you turn it on and you put it on an incredibly sensitive scale. The reading on the scale will go down over time because energy is going out of the beam of light. And that energy has a mass equivalent and that mass equivalent will register on an incredibly.

• 30:59Neil deGrasse Tyson?

  I've had the same, I've had the same debates with them. Interesting, Brian.

• 31:03Brian Greene?

  Yeah. They said, if only nuclear, if it's not nuclear, it has no role.

• 31:07Chuck Nice?

  That doesn't make any sense. We don't even have to go to the flashlight in an incredibly sensitive scale. Set something on fire. Okay. There you go. I'm being serious.

• 31:17Neil deGrasse Tyson?

  Wait, wait, wait, but there is energy contained within nuclear atomic bonds. Okay. So Brian, in your conversation with the chemist, they surely mentioned that they have exothermic and endothermic reactions. Energy coming in and out. Is that your equals mc squared going two ways there?

• 31:34Brian Greene?

  Equals mc squared is at work all the time. For instance, in the simplest example, take a pot of water and turn on the gas, right? As the pot of water gets hotter, if you were on a sensitive scale, it would register a bigger number. A small, bigger, a small change, but a bigger number because energy is going in. And if energy is going in, then the overall mass of this entity called the pot of water is increasing. It's always.

• 32:04Neil deGrasse Tyson?

  So I did this calculation. So I drive an electric car. And so I wanted to ask myself, how much more does the car weigh on a full charge? Right, right. And so I ran some numbers on that, some back of the envelope numbers, and it was so small. I was gonna tweet it, "Hey, look what I found!" It was like, "No, I'm not tweeting this." It was like a thousandth of an ounce or something.

• 32:28Brian Greene?

  Yeah, ridiculously small, but it's an important point because so many students, obviously some in the field, conflate equals mc squared only with nuclear particles.

• 32:40Neil deGrasse Tyson?

  It's a physics thing, yeah.

• 32:42Brian Greene?

  In fact, there's one chemist came back to me after a year of arguing and said, "This has been a year of soul searching. I now realize that you're right, and I didn't really understand so much of what I thought I understood," which was sort of an honest...

• 32:56Neil deGrasse Tyson?

  Yeah, and physics, there's no real understanding of chemistry without physics, and there's no real understanding of biology without chemistry. So Brian is justifiably cocky in that role.

• 33:11Chuck Nice?

  Plus, we all know that chemists are dead.

• 33:14Neil deGrasse Tyson?

  Of course.

• 33:15Chuck Nice?

  Come on, come on. Let's just be real.

• 33:18Neil deGrasse Tyson?

  That's just common knowledge.

• 33:20Chuck Nice?

  That's just common knowledge.

• 33:23Neil deGrasse Tyson?

  All right, keep going. What else do you have? That was not lightning round speed, by the way.

• 33:29Chuck Nice?

  But guess what? That was...

• 33:31Brian Greene?

  I keep slowing it down.

• 33:32Chuck Nice?

  It does make a difference. We keep getting in the areas that we otherwise would never get into on the show, which is fantastic. And we can just have Brian back again, people, okay? You know, it's a real simple thing.

• 33:44Neil deGrasse Tyson?

  He's got agendas in his own life. We're not...

• 33:47Chuck Nice?

  I know, I know he's got his life, but you know, I'm selfish. So what can we do? Here we go. This is Surge. Surge says, "Hi, my question is regarding the subatomic world. If we could scale up an atom, what would it look like? Would it have some kind of shell? If yes, what would the shell consist of? The same question regarding the smallest particles. What is their composition and what is their appearance? If the quark is the smallest particle, what do you get if you divide it into smaller pieces? Oh, man, that's really cool. What does the subatomic world look like, man? What does it look like?"

• 34:21Brian Greene?

  Yeah, I think this really challenges our intuition because our brains and our eyes evolved for the purpose of survival, and to survive, we just need to be able to see on the scales of everyday life.

• 34:37Neil deGrasse Tyson?

  Just to not get eaten by a lion, that's it.

• 34:39Brian Greene?

  Not eaten by a lion, you know, so the language that we developed and the senses that we have are attuned to the kind of physics that dominates the scales of everyday life. And those physical principles are not the same ones that come to the fore in the subatomic realm. So when you're talking about an atom, if you imagine we have an electron cloud, it's a probability cloud, now what does that mean in terms of visualization? Mathematically, I know what it means. There are a lot of locations where the electron might be found, but to actually see it, literally, I need to bounce some light off of it. When I bounce light off of it, quantum mechanics tells me I have affected the thing that I'm

• 35:21Brian Greene?

  observing, so I'm not seeing the probability cloud any longer, I'm simply seeing the electron at whatever location the photon hit it.

• 35:28Neil deGrasse Tyson?

  Can I add something there, which is spooky? I mean, not spooky, it's disturbing when you think about it. You, everything we see is larger than the wavelength of light that's reflected off of it, right? So

• 35:44Brian Greene?

  Yeah.

• 35:44Neil deGrasse Tyson?

  Yeah, yeah, so if you, if you have things that start becoming smaller and smaller, then the wavelength of light we use to detect it with, the thing will just not, will basically disappear. So, so, so Brian, you need light waves with wavelengths on the scale of the things in the atom you're looking at, isn't that correct? If we're, if we're gonna see it.

• 36:06Brian Greene?

  That's right. That's right. And so, and those are, those are more energetic than we're used to, and, and they have more of an impact than the kinds of things, you know, you've shone a light on a wall, the wall doesn't move, right? You know, we don't feel the light bouncing off of us, but an electron feels the light bouncing off of it, and that interaction affects how it then subsequently looks. And so it's really hard to give an everyday visualization that's at all accurate for what things are like in a realm that we don't inhabit directly. I wish we could.

• 36:44Chuck Nice?

  Wow.

• 36:45Neil deGrasse Tyson?

  I like it. I like it.

• 36:46Chuck Nice?

  Okay. All right. Here's a lightning round question. Travis Knopp says, hi, Doctors Tyson and Green. Thank you for taking my question. I would like to know if there's a geometric center of the universe. And what might we find there?

• 37:00Brian Greene?

  Me?

• 37:03Chuck Nice?

  Is that you? You're there? You're there at the center of the universe?

• 37:07Neil deGrasse Tyson?

  Well, I have to say, one of my highest retweeted tweets ever was a simple sentence. I said, because the universe has no center, you can't be it.

• 37:21Neil deGrasse Tyson?

  Somehow, that deeply resonated with like, everybody.

• 37:25Chuck Nice?

  Yeah.

• 37:25Brian Greene?

  Yeah, it's great.

• 37:27Neil deGrasse Tyson?

  So Brian, can't we talk about a center of the universe? If we include the time coordinate? And so we say, that's the direction of the center of the universe. Go there and you'll see it. And that direction is back in time to t equals zero. Isn't that a... Can I say that?

• 37:44Brian Greene?

  Well, you see, center, to most people's minds, is a special location within a larger reality. It's like, you have all these other points that are somewhat secondary. And then you've got the center, which is primary. And that, we don't think, applies anywhere or any when. So if you even go back to the Big Bang, the conventional story, although there are modifications of this, but the conventional story is, all of space is in this point. It's not as though it's a point in a pre-existing realm.

• 38:20Neil deGrasse Tyson?

  Got it, got it.

• 38:21Chuck Nice?

  So there's no construct? You don't have a construct?

• 38:24Neil deGrasse Tyson?

  There's no construct with which you would find the center, even at the beginning.

• 38:28Chuck Nice?

  Even at the beginning.

• 38:28Neil deGrasse Tyson?

  Everything was at, quote, "the center." But then we have to rethink how we use the word "center."

• 38:33Brian Greene?

  Center, yeah.

• 38:34Chuck Nice?

  And then even once that comes, once that, I want to say explosion, but once the expansion takes place, it's like, what is the center of a ball? Where is the center on a ball?

• 38:46Neil deGrasse Tyson?

  On the surface of the ball.

• 38:47Chuck Nice?

  On the surface of the ball.

• 38:48Brian Greene?

  Yeah, on the surface. That's the key thing. Because if you then imagine the center of it, then you're misled. But on the surface of a balloon, all points are equal, and there is no central point.

• 39:00Neil deGrasse Tyson?

  But if you do point to the center of the ball, that's where the whole ball was at the beginning. And then we're back to the original issue about defining the center.

• 39:08Chuck Nice?

  You can do that at any point on the ball.

• 39:11Brian Greene?

  Yeah, yeah, exactly. Any point of the ball, you could do it. So the retort to your tweet might be because the universe doesn't have a center, you and everyone else occupy the center. There's no location that's more special than the one that you occupy.

• 39:28Neil deGrasse Tyson?

  Uh, that's not as fun.

• 39:30Brian Greene?

  Wow.

• 39:32Brian Greene?

  Yeah, that doesn't make people feel stupid.

• 39:37Brian Greene?

  Makes them feel special. Nobody wants that. Okay. Okay, this is Andrew Coffey. Andrew says, hello to the best science communicators together. Creating cosmic vibrations that will radiate knowledge, cultivate curiosity and enhance our understanding. Please help me understand our limits. Will we ever reach a point where theoretical physics can no longer be explored, probed or even proved experimentally? Maybe we are already there. Thanks. Andy C. from Vancouver, British Columbia. And he says, I truly love your work.

• 40:17Neil deGrasse Tyson?

  Excellent. So, so Brian, we, we all know a cocky physicist a century ago, but, but, you know, the turn of the previous century saying, uh, physics is done. There's no more physics to be discovered, just a few decimal places and a few touch up some constants and we should take on another field. So are you, do you see, where do you see the field right now?

• 40:43Brian Greene?

  Well, there's a huge amount of progress, but I can certainly envision that if we don't build new accelerators and if we were to stop building powerful space telescopes, we wouldn't have any new data. And without new data, I can imagine, I don't know, 10, 20, 100 years of totally abstract theoretical research might grind to a halt. And it wouldn't be that we'd sort of reach the end, we'd simply reach the end in that era until we had the wherewithal to explore more fully. There has to be an interplay between observation, experiment and theorizing. And so, yes, I, I, we're far from there now, but can I envision that if we lose the will?

• 41:27Brian Greene?

  To put the effort and the resources into understanding the micro world and the macro world with greater precision, could we reach an end for a while? Sure, absolutely.

• 41:37Neil deGrasse Tyson?

  Chuck, I just have to, I gotta praise Brian in this moment, because there are many theorists, he's a theorist, who hardly ever mention, talk about, or think about experimentalists.

• 41:50Neil deGrasse Tyson?

  They're in their own world. And, and, and who, Brian, who was it that said, "Never trust an observation unless it's supported by a good theory"?

• 42:00Brian Greene?

  Yeah, I know the quote, I don't know who said that.

• 42:02Neil deGrasse Tyson?

  Yeah, somebody said that. That's, you know, that's an asshole theorist talking it. But, but Brian is humble and he knows that at the end of the day, good observations of the universe not only will constrain where he can or should think, but can also extend what, what new ideas might be, come out of that, so.

• 42:24Chuck Nice?

  Awesome. Well, on, on that note.

• 42:26Neil deGrasse Tyson?

  Let's flip in one more, we think, we got time for that.

• 42:28Chuck Nice?

  This is, this is a good last one to dovetail on that last thought. David Lees says, "Hi, this is David residing in Chiang Mai, Thailand. What do you think will be the next major breakthrough or shifting of our understanding with respect to the universe"?

• 42:52Brian Greene?

  Yeah, I think everybody will have a, have a different answer on this, but I think that in the next, who knows, next few decades, we're gonna have a much more refined understanding of the Big Bang. The work that's being done in, in understanding quantum mechanics and gravity and black holes, I think ultimately the lens will be turned fully on cosmology. And I can envision that we will have a different, or at least more refined, version of the theories that we currently have on the table. And in the best of all worlds, we'll finally be able to answer questions that we began with, like, what really do we mean by the singularity of the Big Bang? What really happened there? I think there's a chance that we'll have progress on questions like that.

• 43:37Neil deGrasse Tyson?

  Do you think there's anything, any understanding we have that we feel good about that is at risk of being dismantled by? New or better observations? So in other words, is there a shift in the paradigm, as they would say in the lingo?

• 43:51Brian Greene?

  Yeah, so two things. One, I mean, you know, inflationary cosmology is the most refined version of cosmology. There are competitors now, and who knows? The scales may shift, and our view on that may change. The other thing I would say is quantum mechanics, many people are quite comfortable, been around for 100 years and it works, but there are unresolved questions that many physicists don't really spend much time thinking about. And I can imagine that in the coming years, those problems, and they are real, I assure you they are real problems, may flare up, causing us to rethink the foundations of quantum theory.

• 44:33Neil deGrasse Tyson?

  Hmm, I like that, flare up.

• 44:34Brian Greene?

  Interesting.

• 44:35Neil deGrasse Tyson?

  Up in your face. Well, Brian, it's been a delight to have you back on StarTalk. You know, I don't want to assert my preferences on our audience, because they express their own, but this is where my preferences and their preferences intersected and overlapped, getting you back on the program.

• 44:56Brian Greene?

  Thank you.

• 44:57Neil deGrasse Tyson?

  There's no end of cosmological queries that we have for you.

• 45:01Chuck Nice?

  Well, the truth is, every time we say that you're coming on and we put out a call to the listeners for queries, we get like six or seven pages of them.

• 45:10Neil deGrasse Tyson?

  They lose their shit.

• 45:11Brian Greene?

  Yeah, so. Always happy to do it. All good questions.

• 45:19Neil deGrasse Tyson?

  All right, and your books are still out there. Elegant Universe, give me the other two.

• 45:25Brian Greene?

  Fabric of the Cosmos, Hidden Reality, but the most recent is Until the End of Time, and my most favorite, so.

• 45:32Neil deGrasse Tyson?

  And is that out yet, Till the End of Time?

• 45:33Brian Greene?

  Yeah, that's out, yeah.

• 45:34Neil deGrasse Tyson?

  Oh, cool. And who published that?

• 45:36Brian Greene?

  That was Knopf.

• 45:37Neil deGrasse Tyson?

  Knopf, very nice. Until the End of Time, we'll look for them. All right, dude, thanks. Chuck, always good to have you, man.

• 45:44Chuck Nice?

  Always a pleasure.

• 45:45Neil deGrasse Tyson?

  All right, this has been Cosmic Queries with the one, the only, inimitable Brian Greene, friend and colleague, professor of physics and math, right up the street here in New York City at Columbia. This is Neil deGrasse Tyson, as always, bidding you to keep looking up.