The Smallest Ideas in the Universe with Sean Carroll

What is the nature of quantum physics? Neil deGrasse Tyson and comedian Chuck Nice get quantum, exploring Schrodinger’s Cat, electrons, Hilbert Space, and the biggest ideas in the universe (in the smallest particles) with theoretical physicist Sean Carroll.

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

• 0:00Neil deGrasse Tyson?

  Chuck, my brain is exhausted.

• 0:01Chuck Nice?

  Yeah, I gotta tell you, first of all, I don't even know if I'm here right now. I'm not sure what field I'm in. I don't know if I exist.

• 0:09Neil deGrasse Tyson?

  This is what happens when you spend time with theoretical physicist Sean Carroll, and we just did.

• 0:14Chuck Nice?

  Yes, we did.

• 0:14Neil deGrasse Tyson?

  He took us into the quantum realm.

• 0:16Chuck Nice?

  Yeah.

• 0:17Neil deGrasse Tyson?

  Which apparently was not even, barely contained in the universe itself.

• 0:20Chuck Nice?

  Exactly, right. So, when you do this, don't even think.

• 0:24Neil deGrasse Tyson?

  It's not real.

• 0:25Chuck Nice?

  You don't even know. You don't even know what you're doing there, okay?

• 0:29Neil deGrasse Tyson?

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

• 0:42Neil deGrasse Tyson?

  This is StarTalk. Neil deGrasse Tyson here, your personal astrophysicist. Got with me Chuck, nice Chuck.

• 0:50Chuck Nice?

  Hey, Neil.

• 0:50Neil deGrasse Tyson?

  Hey.

• 0:51Chuck Nice?

  What's happening?

• 0:51Neil deGrasse Tyson?

  All right, what are you holding in your hand here?

• 0:53Chuck Nice?

  Holding a book.

• 0:54Neil deGrasse Tyson?

  Oh, okay.

• 0:54Chuck Nice?

  A book that I, you know, that I picked up off of the coffee table.

• 1:01Neil deGrasse Tyson?

  The biggest ideas in the universe. Well, that's what this episode is gonna be about.

• 1:05Chuck Nice?

  Yes.

• 1:05Neil deGrasse Tyson?

  But I know some big ideas.

• 1:08Chuck Nice?

  Right.

• 1:08Neil deGrasse Tyson?

  But I don't know the biggest ideas. There's a "the" in the front of this title.

• 1:12Chuck Nice?

  Right.

• 1:12Neil deGrasse Tyson?

  And...

• 1:13Chuck Nice?

  Like the qualifier.

• 1:14Neil deGrasse Tyson?

  Yeah, so...

• 1:18Neil deGrasse Tyson?

  This is written by the one and only Sean Carroll. Sean, welcome to my office.

• 1:22Sean Carroll?

  Thank you so much. New York, your office, these are the best places, most exciting places.

• 1:27Neil deGrasse Tyson?

  We have corresponded and emailed and talked, and we have never been in the same space.

• 1:33Sean Carroll?

  No, I think we did in LA once, right? I think so. I think briefly, very, very briefly. But yeah, many phone calls, many emails.

• 1:40Neil deGrasse Tyson?

  Delighted to have a meaningful exchange with you at this point.

• 1:43Sean Carroll?

  Right, with microphones in front of us. Cameras trained. Meaningful.

• 1:47Chuck Nice?

  Exactly.

• 1:48Neil deGrasse Tyson?

  Okay, so just before we delve in... Which Sean Carroll are you?

• 1:53Sean Carroll?

  I'm the physicist one.

• 1:54Neil deGrasse Tyson?

  The physicist Sean Carroll?

• 1:56Sean Carroll?

  Yes.

• 1:56Neil deGrasse Tyson?

  And the other Sean Carroll is who?

• 1:58Sean Carroll?

  My evil twin. He has beards. You know which one is the evil twin.

• 2:02Neil deGrasse Tyson?

  But is it like that? Is it a?

• 2:04Sean Carroll?

  It's not quite as evil. It's more like bushy Santa Claus. It doesn't really look like, but he's a very accomplished biologist, also writes books. You should buy those too.

• 2:13Neil deGrasse Tyson?

  Okay, nice. All right. Very good. So Sean Carroll, let me get your bio going here. The Homewood Professor of Natural Philosophy.

• 2:21Sean Carroll?

  Ooh.

• 2:21Neil deGrasse Tyson?

  That's very retro.

• 2:22Sean Carroll?

  It is.

• 2:23Neil deGrasse Tyson?

  Oh man, just like Newton.

• 2:25Sean Carroll?

  I was gonna say, yeah.

• 2:26Neil deGrasse Tyson?

  Good bike had some title like that. Natural Philosophy at the Johns Hopkins University down in Baltimore, which is the home of the headquarters of the Hubble Space Telescope.

• 2:36Sean Carroll?

  Oh.

• 2:37Neil deGrasse Tyson?

  The Space Telescope Science Institute is right there.

• 2:39Sean Carroll?

  Cool.

• 2:40Neil deGrasse Tyson?

  And you're also on the faculty at the Santa Fe Institute, but you're only on a visiting faculty. So they got really cute here fractal faculty.

• 2:49Sean Carroll?

  Yeah, pretty cute.

• 2:49Neil deGrasse Tyson?

  And you get cuter than, you can't get cuter than that.

• 2:52Sean Carroll?

  No, you can't. I mean, unless there are a bunch of Sean Carrolls who are tinier and look exactly like Sean Carroll.

• 2:58Neil deGrasse Tyson?

  Oh, to continue the fractal. Right. Move on in.

• 3:03Sean Carroll?

  Sean Carroll at all scales. Right, exactly. Frightening.

• 3:06Neil deGrasse Tyson?

  And your research area is quantum physics, spacetime, cosmology, emergence. I love emergence. Maybe we can hit on that. Entropy. I've seen a lot of that lately. Can you do something about entropy? If you can't do anything about it, I have nothing for us.

• 3:21Sean Carroll?

  I can increase it.

• 3:24Neil deGrasse Tyson?

  We can do that without you.

• 3:27Neil deGrasse Tyson?

  Dark energy, symmetry and origins of the universe. You're all in. You got a podcast of your own. Mindscape. I think I've been on that. Have I been on that podcast?

• 3:37Sean Carroll?

  Oh, not yet.

• 3:38Neil deGrasse Tyson?

  Not yet. Okay.

• 3:39Sean Carroll?

  We'll see.

• 3:41Neil deGrasse Tyson?

  It's in my inbox. Maybe I haven't gotten to it yet.

• 3:45Neil deGrasse Tyson?

  And this latest book of the biggest ideas in the universe, the second in a trilogy. This one, Quanta and Fields.

• 3:53Chuck Nice?

  Quanta, wouldn't that be the smallest idea in the universe? Oh.

• 3:58Sean Carroll?

  Smallest thing can be the biggest idea.

• 4:00Chuck Nice?

  Oh, oh, oh, dear. Oh, snap.

• 4:07Neil deGrasse Tyson?

  You gotta put Chuck in his place early, otherwise he'll just run red circles all over you. Yeah, he got you on that one.

• 4:14Chuck Nice?

  Yeah, that's true.

• 4:15Neil deGrasse Tyson?

  He got you. So if this is a trilogy, the first big ideas book was what?

• 4:19Sean Carroll?

  It was called Space, Time and Motion, which is like publisher speak for classical physics.

• 4:24Neil deGrasse Tyson?

  Regular, ordinary armchair physics.

• 4:26Sean Carroll?

  Isaac Newton physics.

• 4:28Neil deGrasse Tyson?

  Yeah, Isaac Newton physics.

• 4:29Sean Carroll?

  And Albert Einstein for that, man. He was the star.

• 4:31Chuck Nice?

  Isn't it funny? At this point, Albert Einstein is the old physics. Classical physics.

• 4:36Neil deGrasse Tyson?

  Now we're going Quanta and Fields, two very big ideas.

• 4:39Chuck Nice?

  Yeah.

• 4:39Neil deGrasse Tyson?

  And can we get a hint in what?

• 4:42Sean Carroll?

  You'll be happy to hear it's Complexity and Emergence is volume three. That's gonna be, it's basically appetizer main course dessert here. So the third one's gonna be fun.

• 4:51Neil deGrasse Tyson?

  Okay, very good. You're an active research scientist, you publish books, you're active on social media. So this is great just to see kindred soul out there.

• 5:01Sean Carroll?

  It's very tiring, isn't it? Why do we do this? Close idea was this.

• 5:07Neil deGrasse Tyson?

  Let's go out and have a drink, we'll talk about it.

• 5:09Chuck Nice?

  In service to the universe.

• 5:11Neil deGrasse Tyson?

  We are servants of cosmic curiosity that permeates within us all. We know that the idea of fields as my memory of the history of physics began with Michael Faraday. Is that correct? Or does it go farther back than that?

• 5:24Sean Carroll?

  That would be fine if you gave it to Faraday. I mean, he certainly played a huge role in figuring out that.

• 5:29Neil deGrasse Tyson?

  Mid 19th century.

• 5:30Sean Carroll?

  Mid 19th century, electricity, magnetism, both had fields associated with them. Technically, no one ever mentions this, but our old friend Pierre-Simon Laplace, circa 1800, realized that, you know, Isaac Newton had this idea of gravity, the inverse square law, and Newton was very puzzled, like you have the earth here, you have the moon over there, there's a gravitational force, how does the moon know? What the gravitational force is.

• 5:58Neil deGrasse Tyson?

  It is nothing between them.

• 5:59Sean Carroll?

  Nothing between them, action at a distance, right? And Laplace figured out you could rewrite Newton's theory of gravity in terms of a gravitational field. So I kind of give him credit. Wow, look at that.

• 6:12Neil deGrasse Tyson?

  So in my high school, I had a friend who, his name was Frank Larisse. We just learned about some of these great French physicists, mathematicians, Lagrange, Laplace. And then over lunch, one day says, there will be the Larisse equation. This was just a fun little dream state that we all occupied in high school. Okay, so fields, why are fields real or are they just a convenience? Because by the way, you are partially in the department of philosophy there.

• 6:47Sean Carroll?

  Yeah.

• 6:48Neil deGrasse Tyson?

  So I get to ask you philosophically leaning questions.

• 6:51Sean Carroll?

  I'm not allowed to say that's a philosophy question and ignore it. I actually have to answer those questions.

• 6:55Neil deGrasse Tyson?

  You actually have to answer it.

• 6:56Sean Carroll?

  That's my job.

• 6:56Neil deGrasse Tyson?

  Good, all right.

• 6:57Sean Carroll?

  Yeah, so the story that we tell in the book is if you were 1895, right? If you were just before the turn to the 20th century, you would have thought that matter, tables and chairs, was made of particles.

• 7:10Neil deGrasse Tyson?

  Right.

• 7:10Sean Carroll?

  Stuff. We knew about electrons, you knew about atoms. And you would have thought that the forces between the atom were mediated by fields, spatial field, the electric field, the magnetic field. And one of the great triumphs of quantum physics in the 20s and 30s was it said, it's all fields. Electricity, magnetism are fields, but so are electrons and quarks and neutrinos. And they vibrate in different ways and through the miracle of quantum mechanics, when you look at those vibrating fields, they appear to us as particles. The particles come out of the field.

• 7:42Neil deGrasse Tyson?

  Is this an early variant of what would later be string theory? Where they're saying particles are vibrations in the strings?

• 7:49Sean Carroll?

  Well, particles are vibrations in the fields, and that's absolutely accurate in the regimes we're talking about here. Is there something deeper that they could be vibrations of, strings, et cetera? That's a speculative idea, very, very promising.

• 8:01Neil deGrasse Tyson?

  On a much smaller scale.

• 8:03Sean Carroll?

  Yeah, much smaller. We don't need to know for predicting what's going to come out of the Large Hadron Collider.

• 8:07Neil deGrasse Tyson?

  Okay, so let me ask you a blunt question, which sounds stupid, but I think it's a meaningful question. Do electrons exist?

• 8:16Neil deGrasse Tyson?

  As, as, as.

• 8:17Chuck Nice?

  Now wait, is that, is that a science or a philosophical question?

• 8:21Neil deGrasse Tyson?

  Well, well, because.

• 8:22Sean Carroll?

  Natural philosophy.

• 8:24Neil deGrasse Tyson?

  As I understand it, we have never measured the size of the electron. It is smaller than the smallest capacity we have ever conjured to measure its size.

• 8:34Sean Carroll?

  Okay, I gotta ask you a preliminary question. How truthful do you want me to be?

• 8:40Chuck Nice?

  I love it.

• 8:42Neil deGrasse Tyson?

  Okay, give me, give me what you say in the back room, in, in the back room with the cigars.

• 8:46Chuck Nice?

  No, first lie to me.

• 8:50Chuck Nice?

  Then tell me the truth.

• 8:52Sean Carroll?

  The lie is.

• 8:53Neil deGrasse Tyson?

  Yes.

• 8:54Sean Carroll?

  What is real is the electron field. And little vibrations in those electron fields show up in our detectors as particles. So it's not that we haven't measured the size of the electron, it's that there is no such thing as the size of the electron. The electron is a vibration in a field. It can have different vibrational wavelengths.

• 9:12Chuck Nice?

  But so, and it shows up as the particle?

• 9:15Sean Carroll?

  Yes, that's right.

• 9:16Chuck Nice?

  Oh my god.

• 9:17Sean Carroll?

  Yeah, that's right.

• 9:17Neil deGrasse Tyson?

  I mean, it comes to the party that way, but otherwise it's not.

• 9:20Sean Carroll?

  Yeah, yeah.

• 9:21Chuck Nice?

  Okay, that is so trippy. That is so freaky, man.

• 9:25Neil deGrasse Tyson?

  Wait, wait, wait, wait.

• 9:26Sean Carroll?

  Well, you and Einstein both were bothered by this.

• 9:28Chuck Nice?

  I am very bothered by this.

• 9:30Neil deGrasse Tyson?

  So you cannot measure the electron in its wave state to be a particle? Because the act of measuring it turns it into the particle.

• 9:40Sean Carroll?

  The way that we usually measure things, you say, where is it? And you get a little track in your particle detector, because you keep asking where it is, and you always get a definite answer to the question, where is it? But when you're not asking that question, it's spread out all over the place.

• 9:55Neil deGrasse Tyson?

  Okay, is that a lie or the truth?

• 9:56Sean Carroll?

  That's really a lie. I haven't even gotten to the truth yet.

• 9:58Neil deGrasse Tyson?

  Okay, okay, now, now give me the truth.

• 9:59Sean Carroll?

  Okay, when quantum mechanics came along in the 1920s, we realized that instead of an electron.

• 10:04Neil deGrasse Tyson?

  Let us celebrate, we're in the centennial.

• 10:06Chuck Nice?

  We're very close.

• 10:07Neil deGrasse Tyson?

  Of this, of the, of the discovery of quantum physics. The centennial decade.

• 10:11Sean Carroll?

  The quantum year, yeah.

• 10:12Neil deGrasse Tyson?

  Yeah, yeah, the centennial decade, and, and that was a watershed decade. Where Hubble discovers that the Milky Way is not alone among galaxies in the universe, and he discovers the universe is expanding. And I'm just saying, we gotta tip our hat to the 1920s.

• 10:27Chuck Nice?

  Yeah.

• 10:28Neil deGrasse Tyson?

  The roaring 20s.

• 10:29Sean Carroll?

  We live in shame that we can't live up to that anymore.

• 10:31Neil deGrasse Tyson?

  I know. I think about that all the time.

• 10:33Sean Carroll?

  Yeah, it was too bad.

• 10:34Chuck Nice?

  Yeah, well, I mean, let's be honest, they weren't working with much to start with.

• 10:38Sean Carroll?

  Low hanging fruit.

• 10:40Chuck Nice?

  Yeah, low hanging. You guys are building on top of everything that they've actually discovered, you know.

• 10:44Sean Carroll?

  Oh, yeah, absolutely. Yeah. All right, we're building up to the truth here. So you realize in the 1920s that you thought the electron was a little particle. In fact, you should describe it in quantum mechanics by a wave function. If you ever took chemistry, if you ever saw those pictures of the orbitals of electrons, et cetera, that's the wave function of the electron.

• 11:02Chuck Nice?

  Mm-hmm.

• 11:03Sean Carroll?

  Soon thereafter, you realize, no, actually, you should be doing field theory, quantum field theory. And so there is a field that the electron is a vibration in. And you're asking what really exists? Well, there's a wave function of that field. So there's like fieldiness on top of fieldiness. And finally, you say that, okay, what if you have like different fields, different particles? Do they each have a wave function? No. There is one wave function for the whole kit and caboodle of them, the wave function of the universe. That's what's real, the wave function of the universe.

• 11:37Neil deGrasse Tyson?

  You know, he's been smoking something.

• 11:39Chuck Nice?

  That's crazy.

• 11:40Neil deGrasse Tyson?

  You know, where was he before this? Where were they? Are you just talking this? Or is this hypothesized, soon to be experimentally verified?

• 11:51Sean Carroll?

  I encourage all of the listeners out there to check out my paper entitled Reality-

• 11:56Neil deGrasse Tyson?

  This would be your research paper.

• 11:57Sean Carroll?

  Research paper called Reality as a Vector in Hilbert Space.

• 12:01Neil deGrasse Tyson?

  Okay.

• 12:02Sean Carroll?

  That's what reality is. So, look, first, let me explain. Not everyone agrees with the true thing I just said. So there's disagreement because of this fact that physicists-

• 12:12Neil deGrasse Tyson?

  It's your personal truth.

• 12:13Sean Carroll?

  Can't agree on what quantum mechanics really said. So we have this idea that everyone uses in quantum mechanics, Hilbert space, which is the space of all possible imaginable quantum states of the universe. And someone like me, who is a purist and extremist about this, says, we have all possible quantum states, the actual universe is one of them, and it changes with time. Other people will say, "No, that's not reality. That's just a tool we use to describe predictions, to make predictions for experiments." Other people will say, "That's part of reality, but there's other parts as well." We don't have a consensus on this.

• 12:50Neil deGrasse Tyson?

  Okay, I like the absence of consensus. Yeah, exactly. It wakes you up in the morning.

• 12:56Neil deGrasse Tyson?

  All things sounds very political.

• 13:02Neil deGrasse Tyson?

  All right, so how do you square all the successful predictions of quantum physics with any intuitive understanding of what's going on? Because I've said many times, and I'm happy to say it again, the universe is under no obligation to make sense to us. So, once you accept that, why try to make sense of it? And jump through hoops and brain twists just to say, "Well, it's gotta be this, or it's gotta be that." But it calculates and it works. Move on.

• 13:32Sean Carroll?

  The universe is under no obligation to make sense, but remarkably, it keeps making sense. Once we really let ourselves listen to what the universe is trying to tell us, the universe seems to be intelligible. It's not deeply ineffably mysterious. And it's a give and take. It's not like our intuition just maps on to reality. Reality is like, "Nope, your intuition was a little bit off there. Try to update." And if you're open-minded about it, and you buy the right books, very updatable. You can absolutely get there, is what I'm saying.

• 14:19Speaker 03

  I'm Ali Khan Hemraj, and I support StarTalk on Patreon. This is StarTalk with Neil deGrasse Tyson.

• 14:34Neil deGrasse Tyson?

  I'm reminded of the charming illustrated book series by George Gamow. Mr. Tompkins in, I guess, Wonderland, or, and what he would do is, he's a physicist, famous physicist, mid 20th century. Lived only, died only 20 years ago or so, but he, yeah, George Gamow, he was one of the original predictors of the temperature of the universe.

• 15:02Sean Carroll?

  I hear the Big Bang Theory.

• 15:03Neil deGrasse Tyson?

  Yeah, if the universe began as an explosion with the Big Bang, could you measure that? And then he was on a paper that, okay, so what temperature did he get for it? It was like, uh...

• 15:13Sean Carroll?

  He was in a factor of 10, yeah.

• 15:15Neil deGrasse Tyson?

  No, was it a factor of 10?

• 15:17Sean Carroll?

  Within a factor of 10.

• 15:19Neil deGrasse Tyson?

  I think it was like 5 degrees. He said, "The universe is 5 degrees," and the universe turned out to be 3 degrees.

• 15:26Sean Carroll?

  Oh, okay.

• 15:27Neil deGrasse Tyson?

  Okay, so Rich Gott, okay, friend of the show, has said, "That's like predicting that a 50-foot flying saucer will land on the White House lawn, but a 30-foot flying saucer..."

• 15:41Sean Carroll?

  That's pretty wild, yeah.

• 15:43Neil deGrasse Tyson?

  Right? Yeah, it's not even that the numbers are different, it's that it's a prediction at all that would come true.

• 15:50Sean Carroll?

  But the story you're telling right here is exactly why this crazy talk about Hilbert spaces and quantum fields has some plausibility, because we have some data in front of us, we try to explain it, we invent an equation that explains it, and then we extrapolate that equation to wild places that it's never been before, and it comes back telling us, "Yeah, that's what I said, that's what I said was gonna happen, and the Big Bang is an example, quantum field theory is another example."

• 16:17Neil deGrasse Tyson?

  But Mark Twain did this first, you know, the Mark Twain-ism?

• 16:20Sean Carroll?

  Yeah.

• 16:21Neil deGrasse Tyson?

  Yeah, so he had read that there was some research paper about the rate at which the Mississippi River is depositing silt in the Delta, and so it's growing in this direction, and then he says, "Oh, that means, you know, 30 million years ago, the Mississippi River ended in Canada." And then he says, "The great thing about science, there's such wholesale conclusions drawn from a trifling investment of fact."

• 16:51Sean Carroll?

  Ooh.

• 16:53Sean Carroll?

  And that's brilliant.

• 16:54Neil deGrasse Tyson?

  Yeah, that's Mark Twain.

• 16:55Sean Carroll?

  Beautiful.

• 16:55Neil deGrasse Tyson?

  Doing it. In Mr. Tompkins and Wonderland, what made it entertaining, especially if you're a budding scientist, is it changes the values of the physical constants in an ordinary world.

• 17:06Sean Carroll?

  Okay.

• 17:06Neil deGrasse Tyson?

  So, and then you get to see what happens in an ordinary way. Otherwise, these phenomena are inaccessible to us. And one of them, he said, all right, 60 miles an hour is the speed of light. And now you're driving down the street, what do you see? And then another one, I think he changed Planck's constant.

• 17:23Sean Carroll?

  Yeah, sure.

• 17:23Neil deGrasse Tyson?

  And so, could you just give me a handle?

• 17:27Sean Carroll?

  Oh, cool.

• 17:28Neil deGrasse Tyson?

  On things that would happen if Planck's constant were macroscopic. Like, if I walked through the doorway, I would like diffract, right? Wouldn't I?

• 17:38Sean Carroll?

  Yeah, you would diffract, and we wouldn't be able to know exactly that you had a position and velocity at the same time, right? You know, the old joke about Werner Heisenberg being pulled over, and the cop says, you know how fast you were going? And Heisenberg says, no, but I know exactly where I am. Because you can't know, according to the Heisenberg uncertainty principle, both your velocity and position at the same time.

• 17:58Neil deGrasse Tyson?

  That's your rock at physics, constantly.

• 18:03Neil deGrasse Tyson?

  I was gonna say, who wrote that? Can I try that out? I don't know.

• 18:08Sean Carroll?

  That's the uncertainty principle. No one would pin you down. In quantum mechanics, you're fundamentally not a set of particles. You're a set of waves. If the Planck constant, which sort of sets the scale for quantum physics, were much bigger, macroscopic, then we would all be these kind of undulating waves moving through the universe, interfering with each other, and becoming entangled, and then measuring things. And you don't want to live there. It's not, no place to be, really.

• 18:34Neil deGrasse Tyson?

  And so, you mentioned entangled. That's been a buzz phrase.

• 18:38Sean Carroll?

  Everybody loves it.

• 18:39Neil deGrasse Tyson?

  Everybody loves.

• 18:39Sean Carroll?

  It's one of the biggest hits.

• 18:41Neil deGrasse Tyson?

  Hearing about.

• 18:42Sean Carroll?

  It's one of the biggest hits right now. Entanglement.

• 18:44Neil deGrasse Tyson?

  Entanglement. So, one of the goals is, what's the farthest particle?

• 18:53Neil deGrasse Tyson?

  That you can entangle on the premise that maybe that'll be useful one day. And from all the news articles, I've seen China leads the world

• 19:00Chuck Nice?

  Uh oh.

• 19:00Neil deGrasse Tyson?

  In entangled particle distances. So, so what do you have to do?

• 19:06Chuck Nice?

  Oh, no, no, I'm sorry, uh, cause I'm, I'm just losing something right here. I'm missing something. If something is entangled, what difference would it make about the distance? I'm missing that.

• 19:18Neil deGrasse Tyson?

  Who knows? I'm saying in science, you just push the envelope if you've never pushed it before.

• 19:23Chuck Nice?

  I got you.

• 19:23Neil deGrasse Tyson?

  One day are they, we heard in Congress, it just, did you hear in Congress? China is, is going to land something on the far side of the moon and Congress wants to know why? How come we're not landing something on the far side of it? This is an entire conversation in Congress.

• 19:38Chuck Nice?

  Right, right.

• 19:39Sean Carroll?

  Now, but Chuck is completely right about entanglement. It doesn't matter how far away things are, but the problem with two entangled particles, which we haven't even defined what that means, but you have a very sophisticated audience. So they know what this means is that as soon as you measure one of them, the entanglement breaks. So it's not that they get further apart, it's just that as you bring them further apart, the chances that one of them bumps into something gets bigger and bigger.

• 20:01Neil deGrasse Tyson?

  And so therefore, so that's what makes this distance record meaningful

• 20:06Chuck Nice?

  I got you.

• 20:07Neil deGrasse Tyson?

  As a, as a record. So one of them was they entangled particles between orbit and earth's surface. And another one was they entangled particles inside a fiber optic, uh, uh, network.

• 20:20Chuck Nice?

  Okay.

• 20:21Neil deGrasse Tyson?

  Fifty kilometers, which was about, which is about city size. And so then the suspicion is with entangled particles, you might be able to make a secure internet, undecodable, un, un-

• 20:34Chuck Nice?

  Unhackable, unhackable. You can't, you can't, it doesn't, encryption wouldn't make a difference at that point.

• 20:39Neil deGrasse Tyson?

  Right. Cause it's instantly, so is this, is this a pipe dream?

• 20:43Sean Carroll?

  Well, it's very hard because once you get beyond a few particles, it becomes harder and harder and harder to remain all of them being entangled with each other. And that's ultimately what you need. But it's a technology problem. It's not like you're violating the laws of physics. So we're setting our best engineers on it, trying to build quantum computers, etc.

• 21:01Neil deGrasse Tyson?

  Get a bridge, engineers, you fix it.

• 21:02Sean Carroll?

  Yeah, you do that. Yeah, we've shown it's conceivable. What do you want from us?

• 21:07Neil deGrasse Tyson?

  Yeah, what more do you need?

• 21:08Chuck Nice?

  The math works.

• 21:09Neil deGrasse Tyson?

  Yeah.

• 21:10Chuck Nice?

  All right, Johnson?

• 21:10Neil deGrasse Tyson?

  There's no law of physics against it.

• 21:12Sean Carroll?

  Exactly.

• 21:14Neil deGrasse Tyson?

  You know, the engineers who said we will never fly faster than sound did not get that from a physicist.

• 21:19Sean Carroll?

  That's right.

• 21:20Neil deGrasse Tyson?

  Okay. Because we, rifle bullets went faster than sound. The crack of a whip is faster than sound. You know, we had that. So, but, so back to this. Can you foresee a value with 50-kilometer quantum entangled network? The size of a city?

• 21:39Sean Carroll?

  You know, mostly that's just showing off. I think it's much more important technologically to have a thousand or a million quantum entangled things very close to each other. Then you can manipulate them, build a computer doo there.

• 21:53Neil deGrasse Tyson?

  Isn't that what goes on in a quantum chip? Isn't there a lot of entangled?

• 21:57Sean Carroll?

  We would like it to be. We don't, it's very, very hard because literally any photon that bumps into them messes things up. That's why you need to push it down to absolute zero or very, very close.

• 22:08Neil deGrasse Tyson?

  Oh, I had not fully appreciated that.

• 22:10Sean Carroll?

  Yeah.

• 22:10Neil deGrasse Tyson?

  The photos I saw, most of that was just

• 22:12Sean Carroll?

  Refrigerators.

• 22:13Neil deGrasse Tyson?

  The door. Yeah, the freezer compartment. Just to have the little bitty thing in the middle.

• 22:19Sean Carroll?

  Otherwise, because like you and I radiating our infrared all over the place would totally decohere those quantum bits.

• 22:26Neil deGrasse Tyson?

  That would be the opposite of coherent.

• 22:28Chuck Nice?

  Which, which is what this conversation makes me feel like.

• 22:31Neil deGrasse Tyson?

  Are you decoherent?

• 22:33Chuck Nice?

  I'm decoherent.

• 22:37Neil deGrasse Tyson?

  Catch us up on entangled particles.

• 22:39Sean Carroll?

  Well, this is part of this fact that we said before that there's not a separate quantum wave function for every individual thing in the universe. There's only one wave function for all of them at once. And what the wave function tells us is the probability of observing something. So if you have two particles, and let's say they have positions, you don't know where it is. In fact, literally, when something like the Higgs boson decays. It goes into an electron and a positron, the anti-elect. And you say, well, what direction are they going in? And the answer is they're both going in all directions. Their wave functions are coming out sort of in a spherical pattern. But then when you observe one of them.

• 23:15Chuck Nice?

  That's where it is.

• 23:16Sean Carroll?

  That's where it is, and momentum is conserved. So now you know the other one is going in exactly. So you know where the other one is without having detected it yet. That's entanglement.

• 23:27Neil deGrasse Tyson?

  So what entangles them?

• 23:28Sean Carroll?

  The rules of physics.

• 23:30Chuck Nice?

  Okay, that doesn't. That's not, stop it.

• 23:33Neil deGrasse Tyson?

  That's just the end of the interview.

• 23:34Chuck Nice?

  You can't do that.

• 23:38Chuck Nice?

  That's my mother saying because I said so. That's what the, Mom, why can't I have ice cream for breakfast? Because I said so. That's why.

• 23:46Neil deGrasse Tyson?

  What law of physics prescribes this?

• 23:48Sean Carroll?

  Quantum mechanics. That's the nature of quantum mechanics. It's sort of that this is how science works. You sort of conjecture an idea, then you say, is that right or not? And so in quantum mechanics, the fundamental way things work is that the state of the universe is a vector in Hilbert space, which means that the combined state of every particle in the universe and every field and every everything is described by one single mathematical object. And in fact, I don't like the word entanglement because it kind of, it makes it hard to update your intuition. It makes it sound like what really exists are these two particles. And you measure one, then you're like, why did the other one change?

• 24:30Sean Carroll?

  If you just accept that what exists is the combined quantum state of everything in the universe, then it's no surprise at all that when you look at a little bit of it, it affects the rest.

• 24:39Neil deGrasse Tyson?

  Okay, but.

• 24:39Chuck Nice?

  Interesting.

• 24:40Neil deGrasse Tyson?

  Can I just take two random particles?

• 24:43Chuck Nice?

  Okay, that's, I gotta admit, that makes a lot of sense.

• 24:48Neil deGrasse Tyson?

  Can I take two random particles that were not born together and entangle them?

• 24:54Sean Carroll?

  Sure.

• 24:54Chuck Nice?

  Okay.

• 24:55Sean Carroll?

  Yeah. Entanglement happens whenever you have two objects that are not entangled, but they interact with each other in different ways depending on different parts of their wave function. Let me just give you a down-to-earth example. Schrodinger's cat. You've heard about this, Schrödinger, who apparently didn't like cats, goes to a great amount of thought experiment effort to put a cat in a superposition.

• 25:19Neil deGrasse Tyson?

  That would have never worked with Schrödinger's dog.

• 25:21Sean Carroll?

  No.

• 25:22Neil deGrasse Tyson?

  That would not have flown.

• 25:23Sean Carroll?

  Schrödinger's daughter said that he didn't like cats.

• 25:26Neil deGrasse Tyson?

  Right, okay.

• 25:26Sean Carroll?

  That's why he picked the cat. So it's in a superposition of alive and dead. I'm a cat person, but in my version, they're a superposition of awake and asleep.

• 25:35Neil deGrasse Tyson?

  Oh.

• 25:35Sean Carroll?

  It's very sweet. You don't have to kill the cat.

• 25:37Chuck Nice?

  You don't have to kill it.

• 25:38Neil deGrasse Tyson?

  I didn't know you didn't have to kill the cat.

• 25:39Sean Carroll?

  The point is, you don't have to kill the cat, but the point is there are different places in the box, okay? And what that means is that everything in the box, the air, the light, you know, everything moving around in the background interacts differently with the awake cat running around, trying to get out, and the asleep cat just snoring peacefully on the ground. And so the environment, as we say, entangles with the cat right away, because it interacts with it, but interacts with it differently depending on different parts of the wave function.

• 26:10Neil deGrasse Tyson?

  I don't know that that's more clear to me. So you're asleep and awake cat. But we declared that without actually sticking asleep and awake cat in the box. I mean, we're just asserting that.

• 26:24Chuck Nice?

  Could the cat just be drowsy?

• 26:27Neil deGrasse Tyson?

  In between.

• 26:29Sean Carroll?

  No, this is, this is.

• 26:30Chuck Nice?

  I'm in and out.

• 26:31Sean Carroll?

  This is Schrödinger's whole point. This is why he set up in the, in the experiment, there's a radioactive substance. Thought experiment? He didn't do it.

• 26:38Neil deGrasse Tyson?

  Just to be clear.

• 26:39Sean Carroll?

  So radioactivity, and there's a Geiger counter, and the Geiger counter will click when it detects a radioactive decay.

• 26:45Neil deGrasse Tyson?

  And radioactivity, you have no idea which particle is going to decay.

• 26:50Sean Carroll?

  Okay.

• 26:50Neil deGrasse Tyson?

  Just statistically, you know very accurately what fraction of them will. But the fact that you don't know creates a brilliant, beautiful, random number, in a sense.

• 27:00Sean Carroll?

  Yeah.

• 27:01Neil deGrasse Tyson?

  Okay? So if you needed a random thing, you get a decaying set of particles, and you can build, you can draw randomness from that, that is, that's as good a random as we can produce.

• 27:12Sean Carroll?

  Hundred percent random, as far as we know, right?

• 27:13Neil deGrasse Tyson?

  Yeah, as far as we know, okay.

• 27:14Sean Carroll?

  Nothing better. And this is, you know, the 1930s, when Schrödinger was very unhappy with the state of quantum mechanics. He was not bragging about quantum mechanics. He was saying, surely you don't believe this. And he says, when we say this particle has a probability of decaying, what quantum mechanics actually says is there's a wave function for the particle. And it is in a superposition of I have decayed and I have not decayed.

• 27:39Chuck Nice?

  Uh huh.

• 27:40Sean Carroll?

  And the part of it that has decayed sets off the Geiger counter. Now, the Geiger counter is in a superposition of I have clicked and I have not clicked. And the Geiger counter in the part that clicks knocks over a hammer, breaks a vial full of sleeping gas. And the cat goes to sleep. So the cat goes into a superposition of being awake and being asleep. That's the whole point of the sort of Rube Goldberg gizmo that Schrodinger builds in there.

• 28:09Chuck Nice?

  But how does that help anything? Like?

• 28:12Sean Carroll?

  Well, Schrodinger is trying to say, in the way that we thought of quantum mechanics back then, there was these giant debates between Bohr and Einstein about what quantum mechanics really means.

• 28:22Chuck Nice?

  Niels Bohr.

• 28:22Sean Carroll?

  And Niels Bohr would have said, look, when you open the box and look, the cat suddenly changes from being in a superposition of awake and asleep to being one or the other.

• 28:32Chuck Nice?

  Okay.

• 28:32Sean Carroll?

  And Schrodinger is like, come on.

• 28:34Chuck Nice?

  Right.

• 28:35Sean Carroll?

  You think that when I look at it, it changes like that?

• 28:37Chuck Nice?

  I got you. I got you. So his thing is that superposition exists at all times, everywhere, no matter what. It has nothing to do with the fact that I looked at it. It's in that superposition. You just gotta accept that.

• 28:52Sean Carroll?

  Should have said that. He blinked. He lost courage at the last second.

• 28:56Chuck Nice?

  Oh.

• 28:57Sean Carroll?

  And it was a decade and a half later, or two decades later, a graduate student at Princeton named Hugh Everett said exactly those words. He said, just believe what the formula is telling you. And what the formula tells you is, when you look at it, guess what? You enter into a superposition.

• 29:14Chuck Nice?

  Right.

• 29:15Sean Carroll?

  There's a part of you that has seen the cat awake and a part of you that has seen the cat asleep. And Hugh Everett says, that's because both of those possibilities exist just in two separate worlds.

• 29:27Chuck Nice?

  Because what we're dealing with is a probability in the first place. So that always exists. It doesn't change because you observed it. Exactly. It's still the same.

• 29:36Neil deGrasse Tyson?

  Well, you just mentioned in that world, I have some memory that I haven't heard about lately, but that...

• 29:44Neil deGrasse Tyson?

  It was a Copenhagen interpretation.

• 29:48Sean Carroll?

  Yeah, that was Niels Bohr.

• 29:49Neil deGrasse Tyson?

  Niels Bohr is Danish.

• 29:50Sean Carroll?

  Okay.

• 29:51Neil deGrasse Tyson?

  And so they credited, I guess, the city. But it was really a Bohr interpretation, not a Copenhagen.

• 29:58Sean Carroll?

  Well, he had his people who would come into his institute and hang around and go out, you know, spreading the gospel of Bohr.

• 30:04Neil deGrasse Tyson?

  Oh, gosh.

• 30:04Sean Carroll?

  So this was the idea. Heisenberg, Pauli, there's a bunch.

• 30:09Neil deGrasse Tyson?

  There's a bunch, okay. So can you catch us up on the many worlds interpretation?

• 30:14Sean Carroll?

  Right, so the Copenhagen interpretation really frustrated people like Einstein and Schrodinger because it seemed to give up on arguably the single most crucial feature of science, which is realism about the physical world. You know, before quantum mechanics came along, you knew there was a real world out there, even if you didn't know exactly what it was doing.

• 30:35Neil deGrasse Tyson?

  You could touch it, poke it, measure it.

• 30:36Sean Carroll?

  And Bohr and his friends seemed to be saying that before you open the box and look at the cat, there is no fact of the matter about what the cat is. And Einstein and Schrodinger said, you know, even if you don't know what the fact of the matter is, there should be some. And so Everett sort of lives up to the dreams of Einstein and Schrodinger and says, yes, there is a reality there, but sadly for you, the reality is there's many different worlds and they don't interact with each other. So Everett is just saying that in this world of superposition that quantum mechanics always describe, you should just take them all seriously. They're all actually there. It's not just a mathematical trick.

• 31:18Chuck Nice?

  That is really, really tough.

• 31:23Sean Carroll?

  I get it.

• 31:23Chuck Nice?

  That is rough.

• 31:24Neil deGrasse Tyson?

  All right, you got the sleepy cat, you got the awake, the sleep cat, you got the awake cat. Is there a world where I open the box and I see the awake cat as a different world?

• 31:37Neil deGrasse Tyson?

  From the one in which I opened the box and it's asleep?

• 31:40Sean Carroll?

  There is, there are, there will be two worlds and it happens long before you open the box. Because as soon as the other stuff in the box, as soon as the photons and atoms and everything become entangled with the cat, boom, there's two worlds.

• 31:53Neil deGrasse Tyson?

  So where are those two worlds? Or is that the wrong question?

• 31:56Sean Carroll?

  That's the wrong question. I see that you quickly got it. As soon as you asked it, you knew.

• 31:59Neil deGrasse Tyson?

  No, I knew, but...

• 32:00Sean Carroll?

  The worlds are not located in space. Space is located in each world. He knows it, Chuck gets it. He gets it.

• 32:08Neil deGrasse Tyson?

  Chuck, I need you, Chuck. Chuck, I need you for this.

• 32:11Sean Carroll?

  I don't believe in anything anymore. It's over. No, there is no God. Oh, no. I mean, that's also true. But okay, that's a whole nother podcast.

• 32:22Chuck Nice?

  Wow. That is so cool. I mean, that is really, really freaky trippy cool.

• 32:28Sean Carroll?

  And many, many people believe this. Not everyone does, so it's a, it's a something we don't have a consensus on right now.

• 32:34Neil deGrasse Tyson?

  Do the people who don't believe it have a better explanation?

• 32:35Chuck Nice?

  Yeah, I was gonna say, if you don't believe that, then you gotta go back to what we were just talking about, which is the Niels Bohr. Now, you're actually, I'm sorry, that sounds more like magic. That doesn't, that sounds like magic to me. Like, I opened it up, or I looked at it, or because I looked at the electron, that's when it is where it is and became what it became. Why would that be? Why, I mean, why would that ever be?

• 33:02Neil deGrasse Tyson?

  I have to clear something up here.

• 33:03Chuck Nice?

  Go ahead, please.

• 33:04Neil deGrasse Tyson?

  Just before...

• 33:04Chuck Nice?

  Help me out.

• 33:05Neil deGrasse Tyson?

  Okay. Let me just clear something up.

• 33:07Chuck Nice?

  Go ahead.

• 33:08Neil deGrasse Tyson?

  In physics, we talk about the observer.

• 33:11Chuck Nice?

  Uh huh.

• 33:11Neil deGrasse Tyson?

  Okay? On many levels.

• 33:14Chuck Nice?

  Okay.

• 33:15Neil deGrasse Tyson?

  In quantum physics, the observer is not simply some conscious entity looking at it.

• 33:20Chuck Nice?

  Right, I understand that.

• 33:21Neil deGrasse Tyson?

  If you wanna make a measurement, you have to like shine light on it. You have to interact with it in some way. And what happened over the years, over the decades, is like the, there was like a new age movement that was convinced, after hearing this kind of vocabulary, started saying, oh, it's our consciousness that's affecting the outcome.

• 33:42Neil deGrasse Tyson?

  Look at it. It's your, your brain energy going into the thing. Yeah, that's like some quantum field of dreams stuff right there, man. That's crazy. That's crazy. So do you get a lot of this new age folks coming back to you?

• 33:56Sean Carroll?

  Absolutely respectable physicists who said exactly things like that.

• 33:59Neil deGrasse Tyson?

  No.

• 33:59Sean Carroll?

  Who really, oh yeah.

• 34:00Neil deGrasse Tyson?

  No.

• 34:01Sean Carroll?

  Ignar, Howley, yeah, they actually, oh yeah. Oh yeah.

• 34:06Neil deGrasse Tyson?

  Okay, but they're all dead now.

• 34:07Sean Carroll?

  Quantum mechanics is forcing you to make some hard decisions about how reality works. And so they're all freaky one way or the other. Either there's many, many worlds, or you bring it into existence by looking at it, or there is no reality. And none of them are exactly what we grew up thinking.

• 34:39Neil deGrasse Tyson?

  Quantum physics, uh, is, you'd agree, is the most successful idea of the universe we've ever had.

• 34:46Sean Carroll?

  Yes.

• 34:46Neil deGrasse Tyson?

  Yes. Nothing comes close. So I can exist in my macroscopic state because the quantum averages of me make me a physical object. That's fair, probably to say that, okay? I see what you're saying. I got you. So I can still be described by quantum physics, that's just not as convenient as Newtonian physics.

• 35:08Sean Carroll?

  And all the light in the room is constantly measuring you and localizing you.

• 35:13Neil deGrasse Tyson?

  Okay. Yes, exactly. Exactly. Okay. So now, are you here?

• 35:17Sean Carroll?

  At the moment.

• 35:18Neil deGrasse Tyson?

  You're here right now. Okay. So if all the quantum phenomenon average out into my macroscopic state, is there any quantum manifestation in the large-scale universe?

• 35:33Sean Carroll?

  Oh yeah, sure. Um, our favorite has to be the microwave background, the cosmic microwave background, right? And we don't know this for sure, but you look at the relic radiation from the Big Bang, okay? Big Bang, 14 billion years ago, was hot and dense and glowing. About 300 and some hundred thousand, 380, I think, hundred thousand years after the Big Bang, it became transparent. And so we see the relic radiation from the Big Bang. And for reasons we don't completely understand, it's super duper smooth. It's almost exactly the same temperature of radiation from place to place. But it's not exactly the same.

• 36:12Neil deGrasse Tyson?

  Direction, you can look in this direction.

• 36:14Sean Carroll?

  Every.

• 36:14Neil deGrasse Tyson?

  Opposite direction.

• 36:15Sean Carroll?

  Coming to you everywhere.

• 36:16Neil deGrasse Tyson?

  Two completely opposite directions.

• 36:18Sean Carroll?

  Right. And we have.

• 36:19Neil deGrasse Tyson?

  The temperature in this office is nowhere near that stable.

• 36:23Sean Carroll?

  Right, right.

• 36:24Neil deGrasse Tyson?

  In this corner, it's like two degrees higher, three, five degrees. And what's it's.

• 36:28Sean Carroll?

  So you're saying for the. One part in a hundred thousand.

• 36:31Neil deGrasse Tyson?

  One part in a hundred thousand difference in temperature from this side of the universe to that side of it.

• 36:36Sean Carroll?

  And it's that uniform all the way across. Yeah, that's right. Insane.

• 36:39Neil deGrasse Tyson?

  It's insane.

• 36:40Sean Carroll?

  That's insane.

• 36:41Neil deGrasse Tyson?

  And my office can't.

• 36:42Sean Carroll?

  Wow, but that, that really does kind of say.

• 36:46Neil deGrasse Tyson?

  Forces your hand.

• 36:46Sean Carroll?

  That you know, that all of that, that the big bang happened and that, you know, it came from this one thing. It had to come from the one thing because that's how, that's the only way as it spreads out that you can get that kind of uniformity. Is that it comes from this one thing. That's right. And the best theory that we have for why it's so uniform is called inflation. Okay. You might have heard before, the universe expands at some super fast rate very, very early on. And it's very much like stretching your sheet on your bed and smoothing it out, right? It wants to smooth it out, but something gets in the way, quantum mechanics. So quantum mechanics says you're trying to smooth out the universe the best you can. But when you measure it, there'll be little ripple.

• 37:27Sean Carroll?

  And we think that those tiny variations in temperature, one part in a hundred thousand, come from the quantum mechanical uncertainty in the state of the universe at early times. And of course, those grow into planets and stars and galaxies.

• 37:42Neil deGrasse Tyson?

  The quantum is, it has left its paw print in the picture of the early universe.

• 37:48Sean Carroll?

  Right. Oh, man.

• 37:50Neil deGrasse Tyson?

  Another way is, am I right to say that had it been completely smooth, it's not clear that we would have made galaxies.

• 37:56Sean Carroll?

  I was gonna say, would we even be here?

• 37:58Neil deGrasse Tyson?

  Exactly.

• 37:58Sean Carroll?

  Would we even be here?

• 37:59Neil deGrasse Tyson?

  These fluctuations give us the seeds on which you collapse matter.

• 38:03Sean Carroll?

  Yeah.

• 38:03Neil deGrasse Tyson?

  All right.

• 38:04Sean Carroll?

  That is so nutty. Let me bring up one other important manifestation of quantum mechanics.

• 38:09Neil deGrasse Tyson?

  Understand it better.

• 38:10Sean Carroll?

  Hopefully it will.

• 38:12Neil deGrasse Tyson?

  Not if it regresses.

• 38:13Sean Carroll?

  The chair is solid. That's all because of quantum mechanics. You know, you've seen the picture, the cartoon of an atom, right? Little nucleus in the middle, electrons orbiting around like it's a solar system. That can't be right because if you get a bunch of atoms together and they're all little solar systems, they would just squish together. It's not right, that picture, because the electrons are not little point particles moving in orbits. They're wave functions that have a size. They take up space. And the reason why the chair can be solid is because the wave functions of electrons in the atoms take up space and don't want to overlap, and therefore matter has extent.

• 38:52Neil deGrasse Tyson?

  One of my favorite stories was, was it from the book Night Thoughts of a Classical Physicist?

• 38:57Sean Carroll?

  Oh, yeah, Louis.

• 38:58Neil deGrasse Tyson?

  But to be said.

• 38:59Sean Carroll?

  Oh, no, that's not Louis.

• 39:00Neil deGrasse Tyson?

  Or, no, no, maybe, no, I'm misremembering. Either it was fictionalized in that novel, or I'm remembering it as a memoir from Ernest Rutherford, who first showed how empty the atom is.

• 39:13Sean Carroll?

  Mm-hmm.

• 39:13Neil deGrasse Tyson?

  By passing, was it neutrons or?

• 39:17Sean Carroll?

  Alpha particles.

• 39:17Neil deGrasse Tyson?

  Alpha particles, okay. So he's got, he's got helium nuclei, and he has a very thin sheet of gold, because you can hammer gold very, very thin. And so he wants to get like the fewest width atoms of gold soil that he can possibly bit. And then he starts firing particles through it, and like nearly all of them just go straight through, untouched, undiverted, nothing. And then he alone, at that moment, realized how empty matter was.

• 39:48Sean Carroll?

  Mm-hmm.

• 39:49Neil deGrasse Tyson?

  And this is the story what I hear, that the next morning he woke up, he was afraid to step on the ground, out of fear he would fall through the floor. Is this just a Pocker full?

• 39:59Sean Carroll?

  The last part you might have made up. I don't know about that one. But the story you can read about in my new book, Quantum and Fields, where I explain this. But the idea that it's empty, you know, I don't like it when people say that, because what Rutherford really figured out.

• 40:15Neil deGrasse Tyson?

  It's because you're a field guy.

• 40:16Sean Carroll?

  Is that, well, the fields are, they matter. But what he really figured out is that most of the mass is at the center in the nucleus, right? And so it's not just that they mostly pass through that's important. Also, very occasionally, one ricochets right back at you. So it's not just that the gold is sort of spread out and diffuse. There's some oomph there right at the middle in the nucleus of the atom.

• 40:37Neil deGrasse Tyson?

  Just while we're like fired up here, what's, what's the latest thinking on dark matter, dark energy? Where we, where should we see future advances?

• 40:46Sean Carroll?

  These are, you know, these are the-

• 40:47Neil deGrasse Tyson?

  We're just looking for a dark matter particle. Is that, are you all in on the particle thing? You got some other exotic?

• 40:52Sean Carroll?

  I'm happy for it to be a particle. You know, I've proposed theories where it's not a particle, but they're not very good, these theories. The dark matter is probably kind of a particle. We haven't found it yet, and I would say that, you know, we, we had a chance of having found it already. The experiments are pretty good, but it wasn't like a 99% chance. It was like a 50% chance it would have found it already. So the fact that we haven't found it already is not yet cause for concern.

• 41:16Neil deGrasse Tyson?

  Okay.

• 41:17Sean Carroll?

  Um, the dark energy is interesting. Again, I've written papers about different possibilities for that, but the simplest one is the best Einstein's idea, that there's energy in empty space. It's just a fact of the matter. Every cubic centimeter of space has 100 millionth of an erg of energy inherent in space itself.

• 41:37Neil deGrasse Tyson?

  Erg is a unit of energy.

• 41:38Sean Carroll?

  Pushing the universe apart. And so we don't know. In fact, there was a provocative recent result from the dark energy spectroscopic instrument, which claimed that maybe the dark energy is declining very slowly.

• 41:52Neil deGrasse Tyson?

  A DESI, dark energy spectrum.

• 41:54Sean Carroll?

  But there's like three different experiments whose nickname is DESI. So I actually like to use all the words.

• 41:59Neil deGrasse Tyson?

  Okay.

• 41:59Sean Carroll?

  This one says-

• 42:00Neil deGrasse Tyson?

  DESI Lu, DESI Lu is a, that's a different one. Yeah, yeah.

• 42:04Sean Carroll?

  So we don't know. That'll be very, very fascinating and exciting.

• 42:07Neil deGrasse Tyson?

  That the, that the dark matter field is changing.

• 42:09Sean Carroll?

  Dark energy field is slowly declining with time.

• 42:12Neil deGrasse Tyson?

  Declining. Now, is that allowed if the Einstein's cosmological constant, which was our first indication that there might be this thing such as dark energy working opposite gravity? That is identically a constant, the way it comes out of the equation.

• 42:26Sean Carroll?

  That's right. So if this is true, then the cosmological constant is not the dark energy. Dark energy is something else. The cosmological constant, the vacuum energy, uh, which are equivalent, that was a candidate. That's one possible thing the dark energy could be.

• 42:37Neil deGrasse Tyson?

  Yeah.

• 42:38Sean Carroll?

  The simplest, most basic thing.

• 42:39Neil deGrasse Tyson?

  I didn't appreciate that.

• 42:40Sean Carroll?

  Yeah.

• 42:40Neil deGrasse Tyson?

  And it's a leading candidate because it comes out of the, we're using the equation anyway, and it was already there.

• 42:45Sean Carroll?

  That's right.

• 42:45Neil deGrasse Tyson?

  And, and then-

• 42:46Sean Carroll?

  Everything else is, is a little bit more delicate, a little more fragile, hard to figure out, but cosmological constant is pretty easy to put in there.

• 42:55Chuck Nice?

  This has been exhausting.

• 42:58Neil deGrasse Tyson?

  One last thing, just as a teaser for your next book.

• 43:01Sean Carroll?

  Yeah.

• 43:02Neil deGrasse Tyson?

  When I think of emergence, I assume you mean it in the tree of life. There are life forms that have features that cannot be deduced from their biological form. Like flocking birds, right?

• 43:18Sean Carroll?

  Yeah.

• 43:18Neil deGrasse Tyson?

  You can't analyze anything about a bird that we know of that will tell you that they should flock with other birds.

• 43:24Sean Carroll?

  Right. So you will not be surprised to learn that there's a lot of philosophical controversy about these concepts. But basically, yes. You know, the point is, we can, as you said before, we can get through the day talking about people and tables and chairs without knowing that they're made of atoms or quantum fields, right? So there's different levels of description that all seem to work. They have to be consistent with each other. But you don't need to know about your quantum fields to get through the day or balance your stock portfolio. Just go through, yeah. Emergence, there we are.

• 43:57Chuck Nice?

  There you go.

• 43:57Neil deGrasse Tyson?

  Emergence.

• 43:58Sean Carroll?

  Consciousness, free will.

• 43:59Chuck Nice?

  Yeah.

• 44:00Sean Carroll?

  All part of that.

• 44:01Chuck Nice?

  All part of emergence.

• 44:02Neil deGrasse Tyson?

  Yeah, the more I think about free will, the less I think we have it. It's, I've not reversed in this vector direction I'm headed about.

• 44:13Sean Carroll?

  That's some momentum.

• 44:14Chuck Nice?

  Yeah, it makes sense. I mean, what if you stripped away everything? Would you then have free will? So if you don't have free will, then what you're talking about is there has to be an influence put upon you.

• 44:24Neil deGrasse Tyson?

  No, no, I'm going to take whoever said it, you'll know. I don't think we have free will, but what choice do I have? Somebody said that, who said that?

• 44:34Sean Carroll?

  That's funny. I don't know that one. There's a philosopher joke, like, you know, you walk into the restaurant and they say, what do you want? And I'll have whatever the universe says I'm going to have. Like, I have no choice about what it's going to be. But I don't think that's the right way to talk. I think I do have the ability to make choices.

• 44:48Neil deGrasse Tyson?

  Well, I've heard you on other podcasts give, for me... What was most resonant account of free will that I can think of while others were spouting off all manner of things. So I felt very in your club. Good. I got your back on this one. Good. So we don't have time for that here, but I, other.

• 45:08Sean Carroll?

  Oh man, you can't leave me hanging like that.

• 45:11Neil deGrasse Tyson?

  There's another book coming out. Oh, okay.

• 45:13Sean Carroll?

  We gotta bring him back.

• 45:14Neil deGrasse Tyson?

  That'll be good. Bring him back. He used to be in California. He's now just down the street in Baltimore. A seller. Right, yeah.

• 45:20Chuck Nice?

  We'll train right away.

• 45:21Neil deGrasse Tyson?

  We can totally do that.

• 45:22Chuck Nice?

  But are you gonna make that trip? I mean, seriously.

• 45:25Neil deGrasse Tyson?

  I'm literally here right now.

• 45:28Neil deGrasse Tyson?

  Where are you?

• 45:28Sean Carroll?

  I was gonna say, how would I know?

• 45:31Neil deGrasse Tyson?

  His vibrational energy is here. It's a probability. Otherwise, don't know. Sean, delight to have you in my office here at the Hayden Planetarium, the American Museum of Natural History. Thanks for making the trip. You're on a book tour right now. Yep. So good luck with that. Sometimes you need a little bit of that. Mm. And keep the physics coming. I will do that. Absolutely. Thanks for having me on. It's always great. There's surely an unlimited appetite for the cool stuff. Lots of cool stuff, big ideas. All right. Chuck, always gonna have you, man.

• 45:57Chuck Nice?

  Always a pleasure.

• 45:58Neil deGrasse Tyson?

  All right. This has been the latest update on the moving frontier of the universe through the lens of theoretical physicist Sean Carroll. I'm Neil deGrasse Tyson, your personal astrophysicist. As always, keep looking up.