Quantum Anomalies with Lara Anderson

Why does string theory need ten dimensions? Neil deGrasse Tyson and comic co-host Jordan Klepper sit down with Lara Anderson, string theorist and associate professor of physics at Virginia Tech, to tackle intersecting dimensions, the nature of gravity, and a unified field theory.

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

• 0:00Speaker 00

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• 1:40Neil deGrasse Tyson?

  So Jordan, I'm just convinced I'm a string theory ignoramus.

• 1:44Jordan Klepper?

  You know what? Hearing you say that makes me realize I maybe don't know as much about string theory as I could. But if you know nothing, I can't wait to find out how little I truly know.

• 1:55Neil deGrasse Tyson?

  Coming up, one of the world's experts on that subject. Check it out. Welcome to StarTalk, your place in the universe where science and pop culture collide. StarTalk begins right now. This is StarTalk, Cosmic Queries Edition. I got with me Jordan Klepper. Jordan, Daily Show, Jordan Klepper. What would that show be without you?

• 2:24Jordan Klepper?

  It would still be Daily. They would replace me probably pretty quick.

• 2:28Neil deGrasse Tyson?

  Okay.

• 2:29Jordan Klepper?

  I had no illusions. You know, I'd like to come at you with more confidence. Yeah, geez, Neil, what would it be? It would be fine. It would be fine.

• 2:36Neil deGrasse Tyson?

  They'd get along just fine.

• 2:38Jordan Klepper?

  Oh my God, they really have, they have a formula. They don't need me whatsoever. Why, why do you give me such a gotcha at the top of the interview here, Neil?

• 2:45Neil deGrasse Tyson?

  Sorry, sorry, I take it back, I take it back. And you got a touring show, I just learned.

• 2:49Jordan Klepper?

  Yes.

• 2:50Neil deGrasse Tyson?

  Jordan Klepper Live.

• 2:51Jordan Klepper?

  Jordan Klepper Live.

• 2:52Neil deGrasse Tyson?

  Live, and we find you on...

• 2:53Jordan Klepper?

  Well, you find me on stages, you'll find my information at officialjordanklepper.com. And then you'll see me up on stages, telling stories about my time at The Daily Show, time on the road, time growing up. You'll get a lot of media.

• 3:06Neil deGrasse Tyson?

  All right, all right, that's how we like it. So this Cosmic Queries is all the physics that I never learned in graduate school.

• 3:16Jordan Klepper?

  This is, so this is sort of an attempt for you to get smarter because you didn't want to pay the extra money, or because there was just a failing at the higher education level.

• 3:25Neil deGrasse Tyson?

  Well, so there's a saying that I first heard from my sister, who got it when she worked for Michael Dell of Dell Computers, now Dell whatever, Industries, whatever. It's, if you ever find yourself to be the smartest person in the room, change rooms.

• 3:41Jordan Klepper?

  Terrible advice. I have worked my entire life to be the smartest person in the room. Here's a, the opposite advice: if you find yourself the smartest person in the room, stay in that room. Lock the doors. You are king. Enjoy being king. If you find yourself in a room where you are not the smartest person, try another room. There's a lot of rooms. I'm sure there's smaller rooms, there's other rooms you can find an advantage. Intellect is an advantage that you can wield for your own advancement. Get in a room where you can wield that. So, potato, patata.

• 4:16Neil deGrasse Tyson?

  So, what we have here, we went to Virginia Tech. We found a string theorist, she's been on before, Associate Professor of Physics and an affiliate in the math department. The physics wasn't enough, throw in some extra math.

• 4:33Jordan Klepper?

  It's a definite brag. Oh, that's not enough at a cocktail party.

• 4:37Neil deGrasse Tyson?

  Everyone, help me welcome back to StarTalk Lara Anderson. Lara, welcome back to StarTalk.

• 4:42Speaker 03

  Thank you so much, I'm excited to be here.

• 4:43Neil deGrasse Tyson?

  Excellent, excellent. And you not only do research there, but you also teach classes?

• 4:49Speaker 03

  I do indeed, yeah.

• 4:50Neil deGrasse Tyson?

  Yeah, yeah, there it is.

• 4:51Speaker 03

  I teach from beginning level all the way up through graduate students.

• 4:53Neil deGrasse Tyson?

  There you go. And it says here, your research includes the geometry and particle phenomenology in string theory.

• 5:02Speaker 03

  Yes, it does.

• 5:03Neil deGrasse Tyson?

  Duh, obvious.

• 5:05Jordan Klepper?

  Yeah. Yeah, I'm mostly interested in the particle phenomenology.

• 5:10Neil deGrasse Tyson?

  Okay.

• 5:11Jordan Klepper?

  The geometry, that's old hat, so we're just gonna skip by that. We're gonna be, we're phenomenology the entire time.

• 5:18Neil deGrasse Tyson?

  So, I got some questions for you, Lara, because occasionally some questions come up that are a little beyond my reach, or a lot beyond my reach. What's, what's the latest on the Higgs boson? Can you just catch us up on that?

• 5:28Speaker 03

  Well, the Higgs boson, I would say, is thoroughly discovered. You know, in the, in the recent years since the detection of this, this was something that, you know, theory had predicted roughly 50 years before, so my experimental colleagues would be annoyed at me for saying this, but by the time of, you know, the actual discovery of the Higgs boson, N years ago, roughly, yeah, 15 years ago, you know, this, this was something that we really expected to be there. The thing that everybody is, is waiting for is, is there any physics beyond the Higgs boson that we can discover with accelerators like the LHC? And that, the jury is still out.

• 6:03Neil deGrasse Tyson?

  I like your phrase you said, thoroughly discovered.

• 6:05Speaker 03

  We're sure, we're feeling really confident on that one.

• 6:09Neil deGrasse Tyson?

  Well, let me interpret that and you tell me if...

• 6:11Jordan Klepper?

  That's like phraseology. After I lost my virginity, I was using words like that. Mom, I've been thoroughly discovered.

• 6:16Neil deGrasse Tyson?

  No, but thoroughly, I think, because when you discover a particle, there's, it's, there's a statistical confidence that you have in that discovery. And how strong is the statistical support for it? So, would you say, Lara, that no one is doubting the discovery? Of course, there's been a Nobel Prize given for it, so that would be egg on their face.

• 6:36Speaker 03

  That's a pretty good indication that, that people are pretty happy with that one.

• 6:38Neil deGrasse Tyson?

  Yeah, excellent, excellent. And are its properties of the Higgs boson intact?

• 6:45Speaker 03

  Yes, so as the, the particle that is giving mass to the rest of the particles in our standard model zoo of particle physics, the, the sort of key role of the Higgs boson is very much confirmed in all the experiments that have come since. And yeah, seeing that so cleanly at experiments like the LHC has been a very exciting part of particle physics in the last 20 years.

• 7:07Jordan Klepper?

  Oh, what do you say?

• 7:08Neil deGrasse Tyson?

  LHC?

• 7:09Jordan Klepper?

  The LHC.

• 7:10Speaker 03

  Large Hadron Collider.

• 7:12Jordan Klepper?

  The Large Hadron Collider.

• 7:13Neil deGrasse Tyson?

  I'm testing Jordan.

• 7:15Jordan Klepper?

  I know about the Hadron Collider, Geneva hanging out underground.

• 7:19Neil deGrasse Tyson?

  You didn't let me test Jordan.

• 7:21Jordan Klepper?

  This is no, please, no acronyms, no acronyms.

• 7:24Neil deGrasse Tyson?

  So when you say physics beyond it, could there be some completely hidden physics awaiting us at even higher energy levels from our particle accelerators? Energy levels we have yet to reach?

• 7:37Speaker 03

  Yep, we certainly hope so. So in terms of, of energy scale as sort of a resolution of nature, we think about, you know, the wavelengths of light that we see every day around us from things like, you know, visible light, or microwaves, or radio waves. All of those wavelengths are very long comparatively, so the photons involved are lower energy. And if you talk about trying to probe deeper and deeper into subatomic structure, you might have heard of something like X-ray diffraction, where you're trying to see inside atoms using X-rays, right, which are more energetic. That's a distance scale of like 10 to the minus 10 meters that X-ray diffraction works.

• 8:15Neil deGrasse Tyson?

  Just to be clear, you can resolve at those scales because the wavelength of X-rays is so tiny...

• 8:20Speaker 03

  Yep.

• 8:21Neil deGrasse Tyson?

  ...that it's commensurate with what you're trying to see, so that detail can be revealed. The tool has to match the task.

• 8:28Speaker 03

  Yeah.

• 8:29Neil deGrasse Tyson?

  Right, and so you need shorter wavelengths, you can't use visible light or microwaves, you gotta go down into X-rays.

• 8:34Speaker 03

  Yeah, so one, one analogy might be like, why can we hear around corners but we can't see around corners? Right? And that has to do with the length of sound waves relative to the size of the door, right? Sound waves are bigger than the door, so they kind of bend as they go around it, and that's why we can, we can hear around doors. Light waves, obviously much smaller wavelength, and they go straight through the door, we don't see around the corner. Same for when we're trying to resolve this really small structure in, in atoms, or, you know, even smaller, down to, you know, quarks or what's beyond that. So, the LHC, the big Large Hadron Collider, and this is, is probing energy scales of like a TEV, or you know, tera-electron volt, up to like 13 TEV. So we can see really small stuff, but not all the way down that we might want to ask.

• 9:16Speaker 03

  So this is a distance scale of maybe, you know, 10 to the 19th meters, but we could try and ask what happens even smaller. Smaller distance scales are higher energies.

• 9:24Neil deGrasse Tyson?

  Okay, so we're, we're currently blind to that whole, to what's beyond what we've already probed. That's a, the blunt way to say that.

• 9:32Speaker 03

  In terms of experimental direct seeing of it, yeah. Of course, theoretically, we can try and play games and say, you know, depending on what that structure should be at a smaller scale, what would be the signatures of it? How would we know? What would happen when you smash these atoms together?

• 9:46Neil deGrasse Tyson?

  That's when the theorists jump in and, and play.

• 9:49Speaker 03

  Yeah.

• 9:51Neil deGrasse Tyson?

  Now, one last question before we go to our Patreon supporters, who each paid $5 to be able to ask a question.

• 9:59Jordan Klepper?

  Well-invested money.

• 10:00Neil deGrasse Tyson?

  I think so, too. So, let me just get up in your face for a minute.

• 10:05Speaker 03

  Please.

• 10:06Neil deGrasse Tyson?

  Okay. The first murmurs I heard of string theory was dates back to the 1980s. And that was 40 years ago. Forty years. Forty years. Albert Einstein comes up with general relativity by himself in 10 years, and we have dozens of string theorists around the globe working on this thing, and you still haven't solved the problem.

• 10:33Speaker 03

  That is a very, very fair question. You know, where is this going? Is it leading somewhere interesting? Have we come up with structure that is actually delivering on something worthwhile?

• 10:42Neil deGrasse Tyson?

  You're trying to find the most basic constituents of the universe and account for everything, so it's basically a unified theory of the universe. That's fair, right?

• 10:54Speaker 03

  Yeah, well, trying to describe all the forces and particles that we see in nature.

• 10:58Neil deGrasse Tyson?

  Okay, and you haven't done it yet.

• 11:00Speaker 03

  This is true.

• 11:01Neil deGrasse Tyson?

  Either that solution is not waiting for us, or it's too hard for our species to figure out, or the string theorists working on it are just too dumb to figure it out.

• 11:17Speaker 03

  All of the above.

• 11:18Neil deGrasse Tyson?

  All of the above.

• 11:20Speaker 03

  I mean, actually, what you just described there, this question of like, you know, where's this going? Am I going to make a breakthrough? Is it worthwhile? That's something that researchers in any form of research really have to ask, right? You're trying to solve a hard problem, and you have to ask, am I making progress? You know, what's this going to deliver? And on what time scale? Is it worth the trip? And I would say, you know, comparing this to Einstein's theory. Einstein's theory, amazing brilliance, you know, yes, general relativity, you know, one of the greatest intellectual accomplishments of the 20th century. But also, in terms of testability, we had a lot of data and measurements ready to go on gravitational physics on the scale of our solar system or nearby solar systems, stars, planets, galaxies, that we could try and compare to very rapidly. The hard part about what string theory is trying to do,

• 12:05Speaker 03

  and where I would argue that, you know, this progress is sort of innately on a different time scale, is we're trying to describe quantum gravity. And that involves physics from the very, very smallest distance scales all the way up to the large-scale structure and history of the universe. So, it's a really hard problem. Is it one that we may not actually solve at all? I think string theory has already demonstrated that it's a consistent theory of quantum gravity, which by itself is interesting in the same way that we idealize the things like, in physics, you know, you pretend that all the shapes are spheres in order to make the math easier. You pretend that, you know, you're in an idealized system where you can ignore air resistance or whatever. You know, that idealization in string theory is very valuable. But the question of whether that theory of quantum gravity exists in our universe,

• 12:50Speaker 03

  I think, is not one that isn't capable of delivering answers. It's just really hard. It's really hard to push the theory all the way through to decide, you know, is this right or wrong? And obviously, I made the judgment call, because this is what I'm spending my time on, that I think we are making progress. I think that there is a hope that this will either be a model of our universe in a way that we can understand, or that we'll learn something about how quantum gravity works, even if it's different than string theory in our universe.

• 13:15Neil deGrasse Tyson?

  Yeah, but nowhere in there did you say, "We're waiting for someone much smarter than everyone else who's working on it to solve the problem the way Einstein did it 110 years ago."

• 13:24Speaker 03

  I mean, hey, if there's somebody in the sidelines who wants to come in and solve all the problems, like, be my guest. That'd be great. But we're working on it.

• 13:31Neil deGrasse Tyson?

  All right, I'd have to get that off my chest.

• 13:34Speaker 03

  It's a fair question.

• 13:35Neil deGrasse Tyson?

  Thank you for taking us there. So, Jordan.

• 13:39Jordan Klepper?

  We got some questions.

• 13:40Neil deGrasse Tyson?

  Bring it on.

• 13:42Jordan Klepper?

  All right.

• 13:42Neil deGrasse Tyson?

  And these are, people knew you were going to be on this show. And so, these questions are direct, occasionally one leaks in my direction, and I'm happy if it's got some astrophysics-y things in it. But these came in for you.

• 13:57Speaker 03

  Well, I'm honored, and I'll give it my best shot.

• 14:00Jordan Klepper?

  If there's any satirical comedy questions, I'm more than happy to take a swing at it as well.

• 14:04Speaker 03

  We're counting on you.

• 14:05Jordan Klepper?

  Yeah, okay, so I'm around. I'm on the bench.

• 14:08Neil deGrasse Tyson?

  You got backup for us.

• 14:09Jordan Klepper?

  Yeah, yeah, let's see where we go with this. This one's coming in from Germany. This is Josh in Bonn, Germany. "In my search for more ways to visualize the madness that is string theory, what actually is a string? If it's a one-dimensional object, how can it vibrate? It intersects with another dimension, making it not exactly a one-dimensional object. With that in mind, is it fundamentally possible to have any motion and thus transfer of energy without it intersecting at least one higher dimension? Thanks, Neil and Co., I'm still looking up."

• 14:41Neil deGrasse Tyson?

  Ooh.

• 14:43Speaker 03

  That's a good question, Josh. Yeah, the question of dimensionality is something that actually gets like, kind of brushed under the rug a lot when people talk about string theory. So, we talk about the basic building block of matter, the thing that's replacing these point-particle descriptions as this extended 1D object. But that doesn't mean that the space that it moves in is one-dimensional. So, for example, you know, three-dimensional space or four-dimensional spacetime, or indeed, as string theory suggests, maybe even more dimensions of space and time. These strings can move through those dimensions. And indeed, the way that we actually describe them isn't even as that one dimension. The way that we really describe them is something two-dimensional called a world sheet. So, in relativity, you talk about where something is moving in space as well as time.

• 15:28Speaker 03

  So, you might have heard in like, you know, sci-fi movies, people talk about your timeline, right? You can imagine a point particle like moving forward, making a line through time. If you have an extended one-dimensional string, as that moves through time, it's going to create a surface or a world sheet. So, in some sense, the strings are actually more two-dimensional in terms of their description and how they vibrate in terms of that spacetime description. And even just to confuse matters more, we actually believe that things like where the endpoints of strings can go are actually part of the dynamical information of the theory. So, these are things called membranes that can be all sorts of different dimensions. And those are also part of how string theory is specified. So, I'm going to say, my short answer is, it's kind of a cheat to say that string theory is about one-dimensional objects. There's actually a lot of different dimensions

• 16:13Speaker 03

  that go into describing how these things move and how they interact.

• 16:16Neil deGrasse Tyson?

  So, if you take a string, which is one-dimensional, and then move it in a time dimension, and you get a sheet, as you were describing, we are three-dimensional creatures moving in time. What do we make?

• 16:33Speaker 03

  This would be some four-dimensional spacetime surface for the sort of history of how we have moved through the universe.

• 16:39Neil deGrasse Tyson?

  Okay.

• 16:40Speaker 03

  Yeah, that's hard to visualize.

• 16:41Neil deGrasse Tyson?

  So, you have to bring in the higher dimension. It'd be a fourth spatial dimension.

• 16:46Speaker 03

  Three spatial and extra time. But the way that we sort of, you know, plot that is, you know, you imagine for the particle, you would have, you know, time versus space, and there's your line. So, in order to count the motion in time, you need another axis. You need another direction to talk about. And that's what the fourth direction would be, is your motion in time.

• 17:04Neil deGrasse Tyson?

  Okay.

• 17:12Speaker 04

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• 18:43Neil deGrasse Tyson?

  Here's yet another fact from Lost in Space, the latest collaboration between StarTalk and National Geographic. 1995, we discover the first authentic exoplanet, a planet orbiting another living star. So, anyone born from 1995 onward? I now declare each one of you to be Generation X. O planet.

• 19:16Neil deGrasse Tyson?

  If you like that fact, you can find 4,999 more in Lost in Space. 5,000 facts to help navigate the universe. Lost in Space is now available wherever you get your books.

• 19:48Neil deGrasse Tyson?

  So Jordan, can you think of higher dimensions in your day?

• 19:52Jordan Klepper?

  I struggle with even getting past two. Going into this fifth or sixth. No, I mean, I was, I was just told about a book that, what is it? The, the, not Flat Earth.

• 20:03Neil deGrasse Tyson?

  Flatland?

• 20:04Jordan Klepper?

  Flatland, yes.

• 20:05Neil deGrasse Tyson?

  Flatland, wonderful book.

• 20:06Jordan Klepper?

  Yes, which I was like.

• 20:07Neil deGrasse Tyson?

  Should be on everyone's shelf.

• 20:08Jordan Klepper?

  It should be on my shelf.

• 20:09Neil deGrasse Tyson?

  I probably have it somewhere here, actually.

• 20:11Jordan Klepper?

  Will you let me borrow it? Promise to return it, Neil. But because I do have such a hard time visualizing this, like the idea of string theory in and of itself is so compelling to me, and yet the idea of getting beyond this fourth dimension is, is, I don't know what to do visually inside my head with it. So I usually zone out.

• 20:30Speaker 03

  You and every other human, right? Our brains are not, not designed to do that.

• 20:34Jordan Klepper?

  So what, what do you do? What, what is your note to a person like me? Yeah, how do you do it? What's your trick? Is it, which, which, which drug is it?

• 20:41Speaker 03

  I mean, in terms of being able to visualize more than three dimensions, my brain isn't good at that either. Mathematically, it's not so bad in that, you know, the, the math generalizes really easily to higher dimensions for lots of things. But another way that I like to think about things is in terms of their shadows. So if you think, you know, if I have a three dimensional object and I look at its shadow on the floor, you know, on a table, right? On a two dimensional space, you can still learn something from that, you know, 3D thing from what its shadow looks like in 2D. And so for higher dimensional things, we can, you know, imagine what would their 3D shadows be like, even if we can't visualize their whole four dimensional shape.

• 21:19Neil deGrasse Tyson?

  Right, so a four dimensional object casting a shadow into three dimensions would be a full three dimensional shadow?

• 21:26Speaker 03

  Correct, yeah.

• 21:27Jordan Klepper?

  It's the lesson of the, this Plato's string theory cave theory, right?

• 21:31Neil deGrasse Tyson?

  I think it's the Plato's cave.

• 21:32Jordan Klepper?

  Yeah.

• 21:33Neil deGrasse Tyson?

  There's a little bit of that in there. Right, right.

• 21:35Speaker 03

  So, yeah, this analogy that gets used a lot in, in these kinds of things is if you imagine the relationship between, you know, a square and a cube, right? You could imagine something that's four dimensional that has as its shadow, something like a cube. And this is where all these cool pictures of things like tesseract's come in, which are just, yeah, fun things to visualize in terms of what four dimensions, their three dimensional shadows might be.

• 21:59Neil deGrasse Tyson?

  And they're fundamental to the Marvel universe, the tesseract.

• 22:02Jordan Klepper?

  They really are.

• 22:03Speaker 03

  No Marvel powers that I am aware of, but.

• 22:06Neil deGrasse Tyson?

  So, but one of the, one of the elements of that question was, how can a string accomplish anything if it's not interacting with another string in a higher dimension?

• 22:17Speaker 03

  And indeed, we expect they do. So strings in string theory can, they can break apart. You can have one string that could break into two pieces. It can break, you know, they can merge into each other.

• 22:27Neil deGrasse Tyson?

  I did not know that.

• 22:28Speaker 03

  Yeah, you can also have things like, as I mentioned, the endpoints of the strings are actually dynamical. So where the strings are, that's part of the theory too. And so things can kind of dissolve into their endpoints and come back out again. And there's all sorts of weird, silly putty games you can play with these, these 1D objects.

• 22:44Neil deGrasse Tyson?

  And if you take two endpoints and join them, what happens?

• 22:48Speaker 03

  You can have, depending on the, the shape of the string, you can have things like closed strings where they form little loops and they can merge together and form bigger loops. You can have, you know, a, a single string that can be open and then become closed. You can join two strings together and get, you know, another string of a different, you know, configuration. So lots of possibilities.

• 23:07Neil deGrasse Tyson?

  Okay. However, if you have an open string, you can vibrate it in whatever way you want. If you close the loop, you can't fit an arbitrary set of waves in a closed loop.

• 23:21Speaker 03

  That's right. It does change the vibrational modes. So just like, things like the lengths and configuration of violin strings, as you mentioned, or the standing waves that can exist on them. All of those change for classical strings and they change for quantum mechanical strings too.

• 23:34Neil deGrasse Tyson?

  Okay, so they are affected. Okay.

• 23:35Speaker 03

  Yeah.

• 23:36Neil deGrasse Tyson?

  Just making sure. Okay.

• 23:39Neil deGrasse Tyson?

  So Jordan, what else you got?

• 23:40Jordan Klepper?

  Well, I got Ethan Brady here. Ethan Brady says, "Hey, StarTalk, I'm currently a student at a community college. Recently, my entire class got sparked into a debate due to the following question. If a higher dimensional object intersected our spacetime, could it appear to us as a black hole?"

• 23:56Speaker 03

  That's such a cool question. I want to hang out in your, your community science class. That's, that's really cool. So I, short answer is, yeah, sort of. So what we, first caveat is, we don't know what's happening inside a black hole.

• 24:10Neil deGrasse Tyson?

  Well, go find out.

• 24:11Speaker 03

  Yeah.

• 24:13Jordan Klepper?

  You don't have a, a free weekend or something to just go sneak out there? Check it out? Take an iPhone with you? Like, take some pics?

• 24:22Speaker 03

  I've seen the sci-fi films on this. If anybody is, is sending, you know, sending folks, I'm ready.

• 24:28Speaker 03

  But in, in general relativity, in Einstein's theory of gravity, one of the ways that we characterize black holes is through singularities. So where, you know, the sort of smooth trampoline surface of spacetime that we understand gravity to be, where that starts breaking or getting, you know, crisscrosses, you know, creases, spikes in it. And so one thing that is certainly true is that if you have a singularity in some subset of your dimensions, so imagine that you have a singularity that we would see as something like a black hole in three dimensions, that can be quote, "resolved" or smoothed out by having higher dimensions available. So one way of, of sort of visualizing that is if you imagine you had like, two lines that cross in a plane, like if, you know, a plane of a piece of paper,

• 25:12Speaker 03

  where those two lines cross is mathematically a singularity from the point of those, those curves, because, you know, what happens right at that intersection point doesn't look like a smooth curve anymore. But if you had an extra dimension where you could pull those two apart, then it doesn't have to be singular anymore. Now you just have two separate, you know, smooth curves sitting there. So the same could be true for spacetime and that things that look singular in our universe could actually be smoothed out by having extra dimensions available.

• 25:37Neil deGrasse Tyson?

  So the answer is yes?

• 25:38Speaker 03

  The answer, yeah. Great question and, and great conversation.

• 25:42Neil deGrasse Tyson?

  But why not take it, take an extra step? Could most of the things we see, think of and interact with in our three dimensional universe be the shadows of higher dimensions cast into our world?

• 25:55Speaker 03

  In terms of the size of those dimensions, this gets tricky because we know that if there were big things, big extra directions for things to move in, that we would have seen those with the way that all sorts of experiments run. So for example, in atom smashing experiments like the Large Hadron Collider, right? You know, you're smashing two protons together and you watch all these pieces fly out and you calculate their kinetic energy and how they're hitting all these detectors. And if there were large extra dimensions that, you know, were the same size as the rest of our universe, things would fly off into them and you'd watch all these pieces just disappear all the time. You'd watch energy and mass disappear. So we know that doesn't happen.

• 26:34Neil deGrasse Tyson?

  Interesting.

• 26:35Speaker 03

  So we have bounds on how big those extra dimensions could be based on the fact that we see most of the mass and energy that we experience in our universe contained to our universe.

• 26:45Neil deGrasse Tyson?

  Oh, so if the extra dimensions were just sitting there available to the experiment, you would lose information into those dimensions?

• 26:54Speaker 03

  Yeah, or stuff. You could lose, you know, mass, energy, all sorts of stuff.

• 26:58Neil deGrasse Tyson?

  You can lose stuff?

• 26:59Jordan Klepper?

  I mean, this is, you just, that, that movie I want to see. We're living in, we are the shadows of another dimension where we're constantly losing stuff?

• 27:08Neil deGrasse Tyson?

  That's where the socks went, in the dryer.

• 27:11Jordan Klepper?

  Where are my keys? Well, how much time do you have? It's, it's a long explanation.

• 27:17Neil deGrasse Tyson?

  Yeah, keys and socks, I think. The dryer is the portal.

• 27:21Jordan Klepper?

  That's what, that's what it is.

• 27:23Neil deGrasse Tyson?

  Right, that's where you lose your stuff. Okay, so Jordan, next question.

• 27:26Jordan Klepper?

  Next question is from William Warren. William says, "Hello, Dr. Anderson, Dr. Tyson. This is William Warren from Abington, Maryland. If extra spatial dimensions really exist but are curled up too small for us to see, is there any realistic experiment that could reveal them within our lifetimes? Or are they likely to remain forever beyond our ability to test? Thank you so much."

• 27:48Neil deGrasse Tyson?

  Yeah, Laura, why don't you just uncurl them? I mean, come on now. What are you waiting for?

• 27:54Speaker 03

  So it may not be that they are actually all that small. So we were talking a minute ago about how we might lose matter and energy into extra dimensions if they were big. But physicists are actually doing experiments in our lifetime, who knows how they'll go, to try and probe what they call large extra dimensions. And the large is kind of funny to non-physicists because we don't mean large, like the scale of this room. We still mean like, you know, 10 to the negative 19 meters. But there are actually experiments of things like the LHC where people are doing these atom smashing experiments and then trying to see, are there any deficits in energy or outputs from these processes? So is it the case that you could really be seeping some things into extra dimensions? Another use of those extra dimensions that people have considered is, you know,

• 28:39Speaker 03

  if some forces in nature interact with the extra dimensions and some don't, that could explain why gravity is weaker than the other forces, for example. For example, if, you know, gravity could seep into those other directions, it's sort of diluted compared to the rest of the forces. So there are lots of, of potential experiments that could, in our lifetimes, shed light on those scales. In string theory, I'd say the, the best bet is actually going to be not that, but a more indirect argument either for or against string theory based on the predictions it makes. I think it's very possible that we could prove that, you know, string theory is just straight up wrong based on the fact that it just can't get things right about our universe that we already see.

• 29:17Neil deGrasse Tyson?

  So she's, she just slipped something in there that I need some pause. You just said gravity is the weakest force. How weak is it?

• 29:29Speaker 03

  I'm very weak compared to the others.

• 29:31Neil deGrasse Tyson?

  How weak is it?

• 29:34Speaker 03

  Uh, weak, um, many orders of magnitude weaker than the other forces.

• 29:38Neil deGrasse Tyson?

  It is forty orders of magnitude weaker.

• 29:41Jordan Klepper?

  Yeah. Oh, that's like nothing.

• 29:43Neil deGrasse Tyson?

  Then electromagnet, let me, I, I got one for you. Ready? And I think I verified this arithmetically. If you went to the top of a rocket that we launch into space and removed all the electrons from the top one cubic centimeter and put them at the bottom of the launch pad, that leaves a net positive charge in that cubic centimeter. And you have negative charges down there. What do negatives and positive charges want to do? What they want to do?

• 30:11Jordan Klepper?

  What they want to do? I mean, they just want to hang out.

• 30:13Neil deGrasse Tyson?

  Together.

• 30:14Jordan Klepper?

  They want to be together. They love to bond.

• 30:16Neil deGrasse Tyson?

  Their force of attraction is large enough to prevent the rocket from launching.

• 30:23Speaker 03

  It's amazing.

• 30:24Jordan Klepper?

  That is amazing.

• 30:24Neil deGrasse Tyson?

  Yes. Yes.

• 30:26Speaker 03

  So gravity is really freaking weak.

• 30:30Jordan Klepper?

  You guys are dogging gravity. I mean, come on, gravity is worked.

• 30:35Neil deGrasse Tyson?

  Gravity's so weak, I can reach down.

• 30:37Jordan Klepper?

  How weak is it?

• 30:38Neil deGrasse Tyson?

  And I could just pick this up. I have the entire Earth pulling on this and I can just pick it up just by bending over.

• 30:46Speaker 03

  It's actually a really good thing for like all the stuff in our, our universe, right? Cause you couldn't have things like tables and chairs and people. Um, they're all held up by electrical interactions if that wasn't true, right? If gravity was stronger, we'd all just get like pancaked.

• 30:58Neil deGrasse Tyson?

  Yeah. Well, yeah. Well, the table wouldn't hold, the table's held together by electromagnetic forces. You're held together by electromagnetic force. The cup is held together by, and gravity does not collapse it into a pile of goo.

• 31:11Jordan Klepper?

  Gravity is much stronger than you guys give it credit for.

• 31:13Neil deGrasse Tyson?

  No, it's not.

• 31:15Jordan Klepper?

  In high school, I wanted to dunk a basketball and I will tell you, I tried my hardest over and over again, and gravity thwarted me every single day of high school.

• 31:24Neil deGrasse Tyson?

  Is that right? How big are your hands?

• 31:26Jordan Klepper?

  I have, I have big hands. It's, it has nothing to do with my physics. It had, it's gravity. Those are big hands. Could you, okay, is, are you able to, could you ever dunk a basketball?

• 31:34Neil deGrasse Tyson?

  When I was in ninth grade, I could palm a basketball and dunk the ball.

• 31:37Jordan Klepper?

  And why couldn't you now?

• 31:38Neil deGrasse Tyson?

  I didn't say I couldn't now, but I said when I, this is when I first did it. I, I can't now.

• 31:42Jordan Klepper?

  Because of gravity.

• 31:43Speaker 03

  I can't now either.

• 31:44Jordan Klepper?

  Because of gravity, Neil.

• 31:45Neil deGrasse Tyson?

  Okay. So I'm curious about this, that you can lose strength leaking into other dimensions. And I'd heard, and I, I don't know why, cause I didn't take these graduate physics classes. I heard that electromagnetic forces are contained within our universe, but gravitational forces can leak out and be felt by a, by an adjacent parallel universe. Is that true?

• 32:13Speaker 03

  Or at least extra dimensions. Yeah. So the, the, the sort of theoretical framework we're describing isn't necessarily string theory. It could exist outside of string theory. And that's a proposal for maybe why gravity is weaker, why the hierarchy problem is it's called in, in particle physics, you know, that separation of scales between gravity and the other forces exists.

• 32:32Neil deGrasse Tyson?

  Could what we call dark matter be ordinary matter in an adjacent universe, but its gravity is spilling out into our universe? And we're saying, oh, we have a magical force here. It's dark matter, when it's just regular matter spilling into our universe.

• 32:49Speaker 03

  It's a fair question and we don't know what dark matter is. So, you know, all, all bets are on the table at this point. I think there's a lot of proposals for this, but no one is sort of universally agreed upon in terms of, you know, what would be the definitive answer? Like yes, for sure. This works. So if you can see one of these, these large extra dimensions in an experiment, that would be for sure a great confirmation. The other way you can try and do it is to ask a question like you just did and say, is there some signature, either in terms of particles or forces or, or interactions that we would see? If, you know, that, that explanation is right, right? Gravity is weak because it's leaking into another dimension. What else would we see in an experiment? What would be the consequences of that prediction? And if you could make, you know, concrete predictions that you can then

• 33:33Speaker 03

  go test, then, then you're up and running.

• 33:35Neil deGrasse Tyson?

  All right. I'll get right on that. Okay.

• 33:37Speaker 03

  And, and yeah, spoiler alert, it hasn't happened yet. So this is still an open question.

• 33:41Neil deGrasse Tyson?

  All right. Give me some more.

• 33:42Jordan Klepper?

  This is what we got. We got from Jay Valiano. Dear Dr. Anderson, is it possible to explain the consistency test D minus 10 equals zero in layman's terms? And how come some theories speak of 11 dimensions if the formula is 10? Thank you and kind regards from Holland.

• 33:59Neil deGrasse Tyson?

  Oh, I like Holland.

• 34:00Speaker 03

  So, um, first off, nobody, when they were first trying to understand string theory, wanted extra dimensions. They would have been very happy if we could just keep our three spatial and one time like dimension. But the origin, let's start with the, the D equals 10 in string theory. So string theory is this idea that you can, you know, you can put it on a T-shirt. It's very concise to say that all matter, energy in the universe are these little vibrating strings, right? Sounds really great. But then you try and say quantum mechanically, what would that mean, right? Like if I have these little quantum mechanical strings, how would they move? How would they behave? Could they be consistent? And it turns out that theories, before you look at the sort of smallest quantum mechanical distance scales, they make promises.

• 34:41Speaker 03

  So some of those promises might be things like electric charge should be conserved. It should not be created or destroyed, right? In, in interactions. Quantum mechanically, now you have this probabilistic theory where all sorts of, you know, uncertainties and possibilities and sort of quantum weirdness takes over. And those classical promises can get broken. So you could have, you know, the conservation of electric charge is being violated quantum mechanically. And it turns out that when that happens, it's called an anomaly in quantum field theory. These anomalies goof up the, the bookkeeping of your theory. So it's like a bank where, you know, you're, you're having pluses and minuses, adding up all the tallies. And if you don't keep the math right, if all the, the numbers don't add up, then it's not just that the

• 35:25Speaker 03

  theory is going to make a bad prediction. It's that the theory just doesn't even make sense. It's not consistent. It's not a useful tool for the things that you wanted it to do. So when people started studying these string theories 40 years ago, um, they tried to consider these quantum anomalies and ask whether they were really fatal, whether they were going to, you know, sort of kill this whole line of research. And what they found is that all of this quantum uncertainty, this sort of wiggling and violation of these, these principles that we think should hold magically cancels out when you have 10 dimensions. Uh, these quantum anomalies cancel exactly. So the theory becomes really robust and really rigid. It starts making all these, you know, sort of theoretical structure and predictions at that point. And then you could ask questions. You can say, well, what does this predict? What does

• 36:08Speaker 03

  it mean? Can it work? And we're still trying to figure that out, but at least you have a mathematically internally consistent theory at that point. So that's where the D equals 10 comes from.

• 36:18Neil deGrasse Tyson?

  I love the phrase quantum anomaly. It just, just feels cool.

• 36:22Jordan Klepper?

  It feels like a Kendrick Lamar line. It's just playful. It's fun. It's specific.

• 36:28Neil deGrasse Tyson?

  Yeah. Yeah. Yeah. All of the above.

• 36:30Jordan Klepper?

  Uh, I want to stay on this side of the, the earth, uh, near Holland. This is from northern Sweden.

• 36:36Neil deGrasse Tyson?

  Okay.

• 36:36Jordan Klepper?

  I think that's, I think that's near Holland.

• 36:38Neil deGrasse Tyson?

  You're, you're American, so you have no clue.

• 36:41Jordan Klepper?

  I'm going to say it's close. This is from Frederick Johansson. Why is it so difficult to access the higher dimensions? Do you think we'll ever get to see or manipulate them in any way? And people really want to know.

• 36:52Speaker 03

  Yeah.

• 36:53Jordan Klepper?

  People, people want to see, are, are we actually going to see this effect? Are we going to be able to prove it in our lifetimes? What do you, what do you say to Frederick?

• 37:00Neil deGrasse Tyson?

  Let me give another lead into that. Um, we're familiar with the story, the book Flatland by Edwin Abbott. I think that was published back at the turn of the previous century around there. And it chronicled the encounter between people who lived in a flat universe, these squares and triangles and other shapes. And then they encounter a three dimensional shape and they like freak out and don't know how to explain it and what, and there's a hierarchy of how many sides you have is a, is a measure of how aristocratic you are. Of course they had to throw that in there as well. My question is, if you're a square in Flatland,

• 37:38Neil deGrasse Tyson?

  what's preventing you from finding that direction perpendicular to your flat universe to just get a peak at three dimensions? What's stopping us in three dimensions from finding that portal to get a peak at fourth dimension? Why are you preventing us from doing that?

• 38:00Speaker 03

  That's a really good question. And, you know, you're exactly right. So in the Flatland analogy, if you just had two dimensions and there's a third just sitting there, yeah, your, your little 2D, you know, flat people could just pop out of that universe up into a three dimensional space. And indeed, if you let things go, right? You just let them, you know, move, have kinetic energy, bounce into each other, have collisions. If you have large extra dimensions, you would do that. You would see them, you would move into them. You'd, you know, you, you can't prevent or, you know, force things into to other, um, a restricted set of dimensions without a lot of effort. The, the catch with the extra dimensions as they're arising in string theory is this notion of scale again. So imagine that, you know, we are three dimensional beings. Um, imagine that, you know, you're, you're walking on a rope, right?

• 38:46Speaker 03

  And you can walk down the length of a rope, tight rope balancing. If I say, can you walk around, you know, the radial direction or the, you know, the circular direction of the rope, you know, rope compared to our feet, right? Is really hard. We, we can't really resolve in terms of our motion, that extra two dimensional surface of the rope. If you imagine zooming that even further, you know, if you look from very, very far away, that rope looks essentially one dimensional. So the problem is just all the interactions that we're measuring are on such a big scale that they couldn't access these extra directions, um, that we're talking about that would be wrapped up around our existing universe.

• 39:21Neil deGrasse Tyson?

  Okay. So she, she weaseled out of that one too. Did you hear that? You hear that weaseling? You're saying we can't get to those other dimensions because they're so tiny. But if they were big, are you then allowing us to say that they would come into view and we can step into them?

• 39:39Speaker 03

  Yeah. And as I mentioned before, like people, you know, they, they actually think that, you know, maybe these extra dimensions are big enough that we could see them in particle physics experiments.

• 39:48Neil deGrasse Tyson?

  So that's all it has to do with. How big the dimension is.

• 39:51Jordan Klepper?

  Do we have certainty on the size of the dimensions or?

• 39:54Speaker 03

  We have, we know that they can't be bigger than certain energy scales. So the experiments at the LHC, for example, are probing around like, you know, up to a few TEV of energy or roughly about, you know, 10 to the negative 19 meters. So we know that they're not bigger than that, or we would have seen them already.

• 40:10Neil deGrasse Tyson?

  So a TEV, just to, just to catch us up here. So an EV is not an electric vehicle.

• 40:17Jordan Klepper?

  It's not.

• 40:18Neil deGrasse Tyson?

  No, no, not in this kind. It's an electron volt, which is a unit of energy. And it's the energy, I, I haven't done this since like physics 102, but it's.

• 40:30Jordan Klepper?

  I like that even as you're being humble about it. It's not Physics 101. It's Physics 102, just to be clear. I skipped 101.

• 40:39Neil deGrasse Tyson?

  So, it's the energy it takes to move an electron, which has a charge, across a potential difference of one volt. That's an electron volt. Did I get that right?

• 40:50Speaker 03

  I think so.

• 40:51Neil deGrasse Tyson?

  All right, yeah, I remembered it. Okay. So, that's helpful when you're talking about particles, because it's native to their world, right? And so, a Terra electron volt is 10 to the 12 of these things. So...

• 41:05Jordan Klepper?

  That's a big number.

• 41:06Neil deGrasse Tyson?

  That's a big number. And that's the energetics of our particle accelerators today. Yeah.

• 41:11Speaker 03

  Man. Again, thinking about these different wavelengths of light and what you can see, just using photons as an example, you know, you think about radio waves, right? Like, how big does a radio tower have to be in order to make radio waves? Like, it has to be the size of a building, roughly, like, tens of meters. That's, you know, the length scale that you're probing if you were to bounce radio waves off things. And, you know, the grading on your microwave has to be millimeter-sized to keep all the microwaves inside your microwave box. And now we're talking about distant scales of less than 10 to the negative 19. Those are really energetic things, photons, particles, whatever, that you need to be able to probe that low. So, it's hard. There are ways, as I mentioned, though, indirectly, to try and either prove or disprove the theory. And lots of clever theorists are trying to conjecture or come up with sort of no-go results that could

• 41:57Speaker 03

  prove string theory wrong in other ways. So, could we see extra dimensions in our lifetime? Maybe. And people are looking. That would be great if we do. And even if we don't, we might be able to decide some of the merits of this in other ways.

• 42:10Neil deGrasse Tyson?

  I just like the idea you can make a dimension big enough to then just say, "I want to visit that."

• 42:15Jordan Klepper?

  I mean, you'd want to.

• 42:16Neil deGrasse Tyson?

  You'd want to. And it's got to be completely mind-blowing. Like, a square looking at a cube for the first time, that's got to be mind-blowing.

• 42:23Jordan Klepper?

  God, yes. And how disappointing from the other direction.

• 42:27Neil deGrasse Tyson?

  Is that all I am, a square?

• 42:28Jordan Klepper?

  Yeah, a cube looking at a square is like, oh, okay.

• 42:32Neil deGrasse Tyson?

  Well, you do that all the time, looking at your shadow.

• 42:34Jordan Klepper?

  You're right. I'm always disappointed.

• 42:37Speaker 03

  There are great animations online, by the way, of three-dimensional shadows of four-dimensional stuff. Definitely worth checking out.

• 42:42Neil deGrasse Tyson?

  Oh, I've got to find them.

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• 44:55Speaker 07

  This is Ken the Nerd Neck Zabera from Michigan, and I support StarTalk on Patreon. This is StarTalk Radio with Neil deGrasse Tyson.

• 45:10Neil deGrasse Tyson?

  Give me a couple more here.

• 45:11Jordan Klepper?

  Okay, Trippney Salo says, "Hi there, Neil and the gang. This is Salo from the Philippines. String theory says there are hidden extra dimensions curled up all around us, but holography?"

• 45:25Neil deGrasse Tyson?

  Holography? That's right. Is the holographic universe? Is that the...

• 45:29Jordan Klepper?

  That's, yeah, well, but holography?

• 45:31Neil deGrasse Tyson?

  It's not holography.

• 45:32Jordan Klepper?

  Holography?

• 45:33Neil deGrasse Tyson?

  Yeah.

• 45:34Jordan Klepper?

  Yeah. We'll fix it and edit. Edit around this. Make me look smart.

• 45:38Neil deGrasse Tyson?

  Fix it and post.

• 45:39Jordan Klepper?

  All right, yes. "It suggests our entire universe is just a projection from a flat 2D boundary. Is it possible that both of these theories are actually right? Are those extra dimensions just part of that projection? More power to the show, and I hope you can visit your Filipino fans soon."

• 45:54Neil deGrasse Tyson?

  Oh, very nice. I've actually never been to the Philippines, but I'll put that on the list.

• 45:59Jordan Klepper?

  You got a friend there.

• 46:00Neil deGrasse Tyson?

  Yeah, yeah.

• 46:01Speaker 03

  So, I don't know that we are sure about, you know, whether we're living in a holographic universe or on the surface of a black hole. But the underlying physical idea that I think is really exciting is that things like gravity or things like gauge theories, which describe things like electromagnetism, seem to be very deeply related in their structure in ways that no one had anticipated, you know, many decades ago. And so, one utility in a physical theory is that if you can simplify things, if you can come up with a really simple framework that could make a lot of cool predictions, that's useful. So, one of the things that's really neat about the holographic principle is if you take, for example, our, you know, three-dimensional universe or four-dimensional spacetime, if you said that all the dynamics or things that are moving in

• 46:46Speaker 03

  our, you know, core universe, if that could be simplified to something that's happening on the boundary of our universe, if we could describe it that way, that'd be really powerful. And there are, in fact, people that are trying to answer exactly that question, independent from string theory. There's a whole program known as celestial holography, which sounds really cool, talking about the celestial sphere at infinity in our universe and how all the information of things like gravitation in our universe might be encoded on that boundary. So, it's a theoretical tool, but it might be a very useful one long-term.

• 47:15Neil deGrasse Tyson?

  Yeah, but you saying, "I'm alive on the boundary of my own universe."

• 47:20Speaker 03

  Or, I guess the angle I was pushing it on is, we can get information about everything in the universe from its boundary, and that might be simpler. It might, you know, show us a sort of hidden core of things or an organizing principle that might help us solve problems we couldn't have solved otherwise.

• 47:35Neil deGrasse Tyson?

  That's wacky stuff.

• 47:37Jordan Klepper?

  I was gonna say, it sounds philosophical and poetic, that it's on the boundaries are the only ways in which to see sort of what we are existing within.

• 47:46Speaker 03

  That does sound good.

• 47:46Jordan Klepper?

  Also a Kendrick Lamar line.

• 47:50Neil deGrasse Tyson?

  It's very zen of you.

• 47:51Jordan Klepper?

  It is. Maybe it's more Alan Watts, yeah. This is from Farouk. "Greetings, this is Farouk from Queens, New York. The question has been on my mind for the past couple of years regarding the nature of time. If time is measured by the displacement of atoms, but those atoms stop moving, does time still exist as a fundamental property?"

• 48:11Neil deGrasse Tyson?

  Can I take a stab at this?

• 48:12Speaker 03

  Please.

• 48:13Neil deGrasse Tyson?

  And you clean up my mess? So, I think there are two ways you can reckon time. Maybe many, but two that are, I think of when I think about that question. One of them is, in your own sort of world, you can sequence events.

• 48:31Neil deGrasse Tyson?

  Now, this is not for every observer, but for you, you can sequence events to know what happened before or what. Okay? So, that's, in a sense, a time. You have a before and an after. But I can tell you this: if you have no thing that repeats itself, then you have no way to measure the passage of time.

• 48:52Jordan Klepper?

  Wait, explain that to me.

• 48:54Neil deGrasse Tyson?

  Earth rotates once a day, and it keeps doing it. Earth goes around the Sun once a year, and it keeps doing it.

• 48:59Jordan Klepper?

  We need the...

• 49:00Neil deGrasse Tyson?

  We have a day and a year, okay? We got a clock. We got atoms that vibrate. Everything is repeating. The measurement of time is embedded in repeated phenomenon. So, if you go to a world where nothing repeats, there would be no measurement of time. Doesn't mean there isn't time still existing, but you couldn't measure it in any meaningful way. Are we good with that, Laura?

• 49:24Speaker 03

  Yeah. No, I think you're saying that you agree with the questioner, which I think I would too, yeah. In a totally static universe, that isn't a really meaningful question, right? If nothing's moving, if nothing's evolving, then, yeah, you don't really talk about time.

• 49:38Neil deGrasse Tyson?

  Well, okay, so, let's get, take it another layer in. If nothing's moving, everything is static. All I said was that you can't measure time. But you said, "Time won't matter," which is surely true, because everything is the same at all times. If nothing changes, what do you care what time it is?

• 49:58Jordan Klepper?

  But you still experience time.

• 49:59Neil deGrasse Tyson?

  That's what I'm asking. So, is there still a reckoning of time if there's nothing to measure it?

• 50:06Speaker 03

  I mean, I think if nothing is changing literally, then even the measurement or perception of time doesn't mean much, right? One thing that we do know for our universe about time is that time, as you were alluding to in your answer, you were saying, you know, an individual person experiences time. We have a before and after. But there is no universal clock for our universe. We know that in special relativity, all across the universe, in gravitational fields, in different parts of the universe, people are going to measure time differently. Time is going to tick differently. So, then you can say, "Yeah, like, what does that mean if this is a thing that's changing everywhere, right? What do we mean by, you know, this sort of fundamental notion of time?" And there, what we know is that it's not just time, but it's particular combinations of space and time

• 50:50Speaker 03

  that the entire universe has to agree on. So, it may not be pure time, but there is something that everybody has to agree on for universes that do have things moving. And that's given to us by special relativity.

• 51:04Jordan Klepper?

  I love that. I do. Time ticks differently. What?

• 51:10Neil deGrasse Tyson?

  And if nothing changes, you'd really have to ask, "Why do you give a shit about time at all?" I mean, think about it.

• 51:16Jordan Klepper?

  It's like maybe work on changing some shit, okay? "Oh, you're worried about time? I don't know. Why don't you clean up your mess? It's been like this forever."

• 51:24Neil deGrasse Tyson?

  And then you break the symmetry of the universe, and then time begins.

• 51:27Jordan Klepper?

  Now you got your time. Are you happy?

• 51:29Neil deGrasse Tyson?

  Because you cleaned your room.

• 51:31Jordan Klepper?

  This is from David DeLeon. Greetings and salutations, Dr. Tyson and Dr. Anderson. David DeLeon, oh, he gives us a little, oh, wow, we have a lot of info. David DeLeon, raised in Florida, writing out of Indiana. It may just be my own ignorance, but we as humans talk about dimensions in multiple ways. More often than not, I assume it is the physical. The physical three: length, width, height, essentially representing up, down, left, right, forward, and back. Would it not be the most logical that the fourth dimension would be out and in, or quantum and cosmic? I often like imagining zooming out or in at unprecedented distances and winding up

• 52:12Jordan Klepper?

  in a scene similar to that where the zooming started, like a universe in quarks. Any thoughts? Again, thank you for all that you do. Big fan of all knowledge and interpretations of life.

• 52:23Speaker 03

  That's a good question. I would say it's a little different, but the sort of zooming out picture that the question is alluding to is a real thing in physics, and it matters a lot. And this has to do with several things. So the first is whether you expect all of the physics, let's be broad about it, to be the same at every distance scale or not, right? So if you were to say, you know, I measure something here in my little part of the universe to be this big, and now if we just, you know, scaled it up arbitrarily small or big, should all the laws of physics be the same? And we think that that isn't actually a symmetry of the laws of physics as we understand it. We think that the structure is different at different energy scales. That symmetry, if you had a scale where like length didn't matter like that, you could

• 53:06Speaker 03

  zoom in and out, up and down, and everything was the same. That's called a conformal symmetry in theoretical physics. And some things do use it in a really powerful way. So actually, these string world sheets that we mentioned before, these little one-dimensional strings that are vibrating through space, those have a conformal symmetry. You should be able to like scale that world sheet up and down, and it doesn't change how that world sheet behaves, which is really neat. But other physics, like the physics of the strong interactions and quarks, really does seem to be behaving on a different energy scale than gravitation. And this gets studied in things like quantum field theory a lot, where you try and say, if I'm writing down a physical theory, what regime of scales and sizes and energies should it be valid for?

• 53:47Neil deGrasse Tyson?

  So it's just to be clear, it's not that the laws of physics are different, it's that they manifest in different ways.

• 53:53Speaker 03

  Well, the way that you describe them, the systems of equations and the descriptions that you have do change with those different scales.

• 53:59Neil deGrasse Tyson?

  Okay, so we're not, we're not just zoomable?

• 54:01Speaker 03

  Yeah. Although, as we mentioned, string world sheets are, which is kind of cool. So some stuff is, some stuff isn't.

• 54:06Jordan Klepper?

  We still like to be. It's still, it's still a fun idea. Thank you for putting it out there. Dear Dr. Tyson and Laura, this is Jonas William from NYC, just down the road. My question for you is since string theory dualities are so hard to calculate in smooth space, could we use the sign vectors of oriented matroids, matroids, to build a pixelated discrete model of spacetime, which stripping away the smooth geometry naturally solve the infinite singularities of quantum gravity?

• 54:39Speaker 03

  That's a great question, and lots of people-

• 54:41Neil deGrasse Tyson?

  I can't help that one.

• 54:42Speaker 03

  -are actually thinking about that. So people have hoped that there was some sort of fundamental little unit or building block, like, like, you know, building up a big tiled floor by having lots of little tiles that you fit together, maybe you could tile your way to a complete picture of spacetime. And there are several different types of physics that are exploring that. So things like loop quantum gravity or something called causal dynamical triangulations try and do exactly that. They try and build quantum gravity through discretizing spacetime. And I'm not an expert on either one of these fields. These are not string theory, but they're, they're different things that people are, are exploring. And I think, you know, it's a perfectly fair question. Does that solve the problem of quantum gravity? I would say the jury's still out. We haven't decided, but more power to people for asking the idea.

• 55:26Speaker 03

  And who knows, maybe Jonas, you could figure that out, too.

• 55:29Jordan Klepper?

  Wow. Even Neil's like, I don't, I don't know, this is... Let's see if we have one final big question that we can sink our teeth into here, all right? Keith from New York City. Dr. Anderson, is it necessarily true that dimensions are something that objectively exist in nature? Or are dimensions simply an organizing principle that we puny humans use to make sense of the universe? Are they features of reality? Or could they be emergent useful descriptions that arise from something deeper? Is it even possible that dimensions are not real in any sense, but are instead conceptual tools, much as we use imaginary constructs, orbital model of the atom, imaginary numbers in physics and math? Thanks.

• 56:12Speaker 03

  That's a great question. I would say, yeah. I mean, most of the way that we describe the universe is a construct. So could dimensions just be a construct? Yeah. You know, certainly things move, and we can see the degrees of freedom of how things move in our universe. And so that's where we, you know, you see that you can move forward, backwards, side to side, up and down, and those are different. But labeling them as dimensions, labeling them as different, that's just a tool for how we try and describe physics and make predictions. Just like things like, you know, a force, when you say something pushes on something else, that's a construct, too. Turns out a very useful one. But, you know, we don't measure forces, we just measure accelerations. So, yeah, I would say it could be viewed as, as a construct, but one that we think we can get a lot of mileage from.

• 56:59Neil deGrasse Tyson?

  Because that reminds me, in some branches of quantum physics, that we don't understand, we just like the hidden variables hypothesis. It's like, they just assert it because it's, it allows you to think classically about the problem, whether or not it's actually true. But there have been occasions in the past where people just, it pulled something out of their ass to just kind of account for it, and it turned out to be true. There are a couple of occasions such as that.

• 57:28Speaker 03

  And some things where no matter how many hidden variables you have, you still can't get it right, like in quantum mechanics. They can actually, you know, there's theorems that say, no matter how many extra degrees of freedom you have, could you erase that quantum weirdness, that uncertainty, the, you know, the probabilistic nature of quantum mechanics? And the answer is no. You could have an infinite number of hidden variables, degrees of freedom, doesn't help.

• 57:49Neil deGrasse Tyson?

  Fundamental to it. Well.

• 57:53Jordan Klepper?

  I think, I think we, I think we learned some stuff here today.

• 57:55Speaker 03

  These were great questions. Your audience is, is really-

• 57:58Neil deGrasse Tyson?

  No, they're my people. We got good people here.

• 58:00Jordan Klepper?

  And global. This is, this is an international crew here.

• 58:03Neil deGrasse Tyson?

  Yeah.

• 58:04Jordan Klepper?

  People want to know, you know?

• 58:06Neil deGrasse Tyson?

  Inquiring minds want to know.

• 58:08Speaker 03

  Absolutely.

• 58:09Neil deGrasse Tyson?

  Inquiring Patreon members want to know. So where can we keep, keep in touch with your work? Do you have a website or?

• 58:16Speaker 03

  I have a website. I am not on social media, which is a bit embarrassing, a little bit of a let it.

• 58:21Jordan Klepper?

  That is a dimension you don't need to explore. I think you have enough on your plate.

• 58:26Speaker 03

  I'm a little bit occupied otherwise right now.

• 58:28Jordan Klepper?

  Yeah.

• 58:29Neil deGrasse Tyson?

  Okay, it's not social media, but you have a website. Which is it?

• 58:32Speaker 03

  At Virginia Tech. You just search my name and physics, you'll probably find me.

• 58:35Neil deGrasse Tyson?

  All right. Well, Laura, thank you.

• 58:38Speaker 03

  Thank you.

• 58:39Neil deGrasse Tyson?

  For sharing your cosmic expertise with us, living completely in the gaps of my knowledge.

• 58:44Speaker 03

  Well, thank you so much for having me. This was, was a great pleasure, and yeah, I think your, your, your audience members are awesome. So I'm delighted to have a chance to chat.

• 58:53Neil deGrasse Tyson?

  And we think so, too. All right, dude.

• 58:57Jordan Klepper?

  Yeah, thank you.

• 58:58Neil deGrasse Tyson?

  Good to have you always.

• 58:59Jordan Klepper?

  Always good.

• 58:59Neil deGrasse Tyson?

  This has been another episode of StarTalk. I'm Neil deGrasse Tyson, as always, bidding you to keep looking up.

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