392: Understanding the Biggest Ideas in the Universe Without Being a Physicist
“On the philosophy side, you can get away with not confronting our best current theories of reality. … On the physics side, you can just be perfectly happy getting a good enough answer from a calculation to make a prediction, even though some of the assumptions that went into that calculation are completely nonsensical. And this kind of problem really lurks in a lot of areas of fundamental physics today.”
This week we welcome back theoretical physicist and philosopher Sean Carroll to talk about how his most recent book, The Biggest Ideas in the Universe: Space, Time, and Motion, attempts to bridge the gap between how scientists talk about physics and how they usually go about explaining it to non-scientists. The goal is to help you understand what physicists are talking about—equations and all—without needing to know much more than some algebra.
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[This transcript was produced by a computer and may contain errors.]
Intro:
You and Betty and the Nancies and Bills and Joes and Janes will find in the study of science a richer, more rewarding life.
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Indre Viskontas:
Hey, welcome to Inquiring Minds. I'm Indre Viskontas. This is a podcast that explores the space where science and society collide. We want to find out what's true, what's left to discover, and why it matters.
It's always a good day when I get a new book from one of my favorite physicists, Sean Carroll, sent to my house. If you don't know Sean or his work, you're in for a treat. Sean Carroll is the Homewood Professor of Natural Philosophy at Johns Hopkins and Fractal Faculty at the Santa Fe Institute. He's also host of the Mindscape podcast and author of several books, including one of my favorites called The Big Picture. He's received awards from the National Science Foundation, NASA, the American Institute of Physics, and many others. And now he's promised us a trilogy of books to help those of us who are not professional physicists take a deeper dive into the biggest ideas in the universe.
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Sean Carroll, welcome back to Inquiring Minds.
Sean Carroll:
Thanks so much for having me back. It's great to be here.
Indre Viskontas:
It's always so good to talk to you. So you're promising us a trilogy.
Sean Carroll:
That's right. [laughs]
Indre Viskontas:
So for listeners who don't know about this exciting trilogy, tell us a little bit about sort of why you decided to break it up into three books. What is it?
Sean Carroll:
Well, I'll tell you the true story. I mean, the fake story would be something about, you know, I don't know, literary merit or something. But this project started during the pandemic when I decided that what I would try to do, I don't have any ability as a theoretical physicist to cure COVID or make the epidemic spread any more slowly. So I said, at least I can keep people entertained by making some YouTube videos explaining concepts in physics. And as often happens with what I try to do, it got out of hand and it grew. And the gimmick was that I could try to explain basic ideas in physics, but I would use the equations. I would not assume you knew the equations. I would teach them to you, teach you what calculus is, what a matrix is, all that stuff, what an imaginary number is, but then put them to work. And the reason you can do it is because you don't have to solve the equations as someone who is playing along. And after this is all done, it turned into a large number of videos. And I thought it would make a good book. And I really wanted to write like an opus, like a thousand page book with all the physics in it. And my publisher came back and said, we love this idea, except we also love the idea of very short books. How would you like to divide it into seven volumes? And I said, no, I'm just not going to do that. That's not going to happen. So we compromised on three. That's the reason why there are three.
Indre Viskontas:
Well, I mean, it makes a lot of sense, as you say, from a literary perspective and sort of fits the whole idea of a story. And also, I feel like although I would love to have that thousand page opus on my shelf, I find it more tractable to read one book at a time.
Sean Carroll:
Yeah. Look, you're a book author. We know that we like to kvetch a little bit about our publishers sometimes, but they also know what they're doing sometimes. And I would not reject their advice out of hand just because it wasn't what I thought of the first time. And I do think the material falls pretty cleanly into three separate sections. The first book that just came out is about classical physics from Aristotle, basically up to Einstein. The second book will be about quantum mechanics and particle physics. The third book will be about complexity and emergence. So these are all related, but pretty separate topics. So the three volumes, that should be fine.
Indre Viskontas:
Yeah, I have to say, like the emergence and complexity one is the one I'm most looking forward to.
Sean Carroll:
Hang in there.
Indre Viskontas:
Yeah, I really do feel like we're on book one. You got to read book one and then the payoff comes in book three.
Sean Carroll:
Exactly.
Indre Viskontas:
So one thing I want to kind of gloss over a little bit, I think this is a really important point. The difference between understanding an equation and having to solve it. Tell us more about that.
Sean Carroll:
Yeah, the equations that we look at in physics, whether it's Einstein's equation or the Schrodinger equation or whatever, if you're a professional physicist or if you're a student studying to be a professional physicist, you get to be told what the equation says. But that's the easy part. And the hard part is, okay, applying it to different situations. Solve the equations for a spinning black hole or for an electron in a helium atom or whatever. And that's why the memories of most young physics students are mostly of doing problem sets, pulling all-nighters with their friends or doing take-home exams and all those things. It's all about solving the equations. And what I realized was, if you're aiming at an audience that does not intend on eventually being professional physicists, but just wants to know the material, there is a happy medium where you can go beyond just hand waving and metaphors and so forth and do some of the equations, but not fret about ever solving them. You just want to know what they mean. You just want to know what the ideas are. And that's what I'm aiming to do in these books. We'll see if it works.
Indre Viskontas:
I also want to underscore this other part of it that you talk about where a lot of us who aren't physicists professionally love the metaphors, love understanding things through the analogies. And you've written books using that. So why is that not enough, in your opinion?
Sean Carroll:
Look, it is enough for some people, depending on what you want. I'm a huge believer in a vast, diverse, pluralistic ecosystem of talking about these things. Look, I'm active on Twitter. You can't explain quantum field theory on Twitter, really, or Einstein's equation. I've done my best. But it's possible to get some understanding using metaphors and pictures and things like that. But the problem with metaphors and words is that usually they convey some aspects of the reality, but not all of them. And it's very difficult as the recipient of the analogy to really appreciate which parts are supposed to be conveyed and which parts are not. So, for example, a classic example is we try to explain the expanding universe by imagining a balloon that we're blowing up. And in many ways, that tells you a little bit about the expanding universe. But then you have to say, but there's nothing inside the balloon. That doesn't count. The balloon is not expanding into anything. And people are like, well. You can tell them that, but they don't really believe it. And they're like, well, are galaxies expanding? If I draw dots on the balloon, the dots expand along with the balloon. And you have to say, no, no, no, they're not really expanding because that's not part of the analogy that I was supposed to try to convey. So the equations and this is really sort of the payoff of the book. And when I give talks about it and things like that, the equations can surprise us. The equations know more than we do. They're smarter than we are. And they're right. They're the actual theory. And so if you can get that little bit of extra understanding, you're less likely to be confused by the words.
Indre Viskontas:
So now we get a sense of sort of what the payoff is for doing the work in terms of understanding these equations a little bit better. And I do want to get into a few of them, or at least some of the general concepts, because I think it's really hard to talk about equations without seeing what they are. But there are things we can sort of talk around them that are really important. But one of the things that I wanted to ask right from the beginning is that our last guest was Temple Grandin. And she just wrote a book called Visual Thinking, in which she lays out sort of the different ways in which people can think, right, sort of how we think. And one of them that she was describing that I thought was exactly relevant to how you're thinking about or how you're presenting this information in the book is she distinguishes object visualizers, so people who like literally see pictures, from people who are more sort of visual spatial oriented, where like algebra is easy for them. But for the object visualizers, algebra can be very difficult. And then there's, of course, the majority of us who are kind of verbal thinkers who think in language. What are you?
Sean Carroll:
I've never actually heard that distinction that you just mentioned from Temple Grandin. So I'm going to have to think about it a little bit. There's a related distinction among mathematicians where they distinguish between being an algebraist and being a geometer. So it's the algebraists who are happy with equations and the geometers are happy with pictures. Within that distinction, I'm much more of a geometer. I'm actually much happier with the pictures than with the equations. But, you know, none of these distinctions are hard and fast, right?
Indre Viskontas:
Right, it’s a spectrum.
Sean Carroll:
So certainly sometimes as a newly minted philosopher myself, I talk to fellow philosophers and sometimes my feeling is just like, just give me some equations. Like you're saying a bunch of things. It would be so much easier if you gave me equations. So I do have those moments as well.
Indre Viskontas:
Yeah. And so I think one of the reasons I want to bring this up is because I think that for some people who are reading your book, I think different thinking styles will get different things out of the book and will approach the book in different ways and this whole sort of idea of equations. And so, you know, I guess that would be something that I wondered if you thought about, like whether, you know, as you mentioned right off the top, that not everybody needs to go deep into equations. And so I guess, you know, do you have any advice for people who traditionally have found equations frightening? Like, what was, I mean, I guess, or sort of what was your writing strategy to make them more tractable for people for whom they are intimidating?
Sean Carroll:
Yeah, good. Let me, I definitely want to answer that. That's a crucial question. But it reminds me of a related fact that I also want to get on the table, which is that the end of my book, it’s not a long book. It's pretty short, 250 pages, something like that, big font and etc. But we do Einstein's equation for general relativity. And most, let's put it this way, very few people who get an undergraduate bachelor's degree in physics and even a lot of people who get a PhD in physics never get that far, never get to Einstein's equation for general relativity. They're learning other things and general relativity is sort of used by specialists. And so even people who are really into the equations, because if we have this paradigm that we're teaching you to solve all the equations and make a living out of it, there's so many things, so much work you have to do that you just have to go slowly. And so with this approach in The Biggest Ideas, we can go very fast, much faster than undergraduate physics education would. So even if you're into it, this kind of approach pays off. But you're asking about the people who are not into it so much. And surely I do try in the book to deploy bunches of different strategies. There's a lot of figures in the book, as well as a lot of equations, work hard on those. Shout out to Jason Torchinsky, my friend who is usually an auto writer. He writes about cars, but he's also a wonderful scientific illustrator. And I also tell stories. I tell stories. There's some jokes in there and the footnotes. I love digging into the history of this field because it is just amazing. And every time I write a new book and I focus in on some particular historical event, I learn something about some figures that I had never heard before. My favorite for this book was Carolyn of Anspach, who was a princess in Prussia. And she was back in the days of Newton and Leibniz in the 17th century. And she was actually tutored by Leibniz. But then she married the Prince of Wales, the heir to the British throne. So she moved to England and fell under the spell of Newton. And Leibniz was really upset by this. And he would write to her and say, like, don't fall for what Newton is telling you. But she was very smart. She did some of the very first controlled medical trials that she arranged and things like that. And she mischievously sort of set Newton and Leibniz against each other, writing letters back and forth. And their correspondence, it's called the Clark-Leibniz correspondence because it was actually Samuel Clark who was listening to what Newton said and then writing letters. This is one of the foundational texts in philosophy of science. And it's really Carolyn's fault that it ever happened. But you never hear her name. So I do hope that telling some of those stories humanizes the process along the way.
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Indre Viskontas:
OK, so now we sort of laid out sort of why people should read this book, given them a bit of a tantalizing like there's stuff in there that is going to make you feel so happy if you're annoyed with the film Gravity and various other things. But now I want to talk a little bit about some of the sort of nuts and bolts. And in particular, like one of the things that I the other you haven't mentioned this, but one of the things I like about the book is that you also talk about why physicists talk like physicists. And one of them is the spherical cow.
Sean Carroll:
Mhmm. [laughs]
Indre Viskontas:
So tell us the not very funny spherical cow joke, just so that I don't set up too high expectations.
Sean Carroll:
So the dairy. Yeah, please don't don't let them think that—there's a much funnier joke in the end of the book. The dairy farmer wants to improve their dairy productivity milk output. And for some reason, they go to the local university and go into the physics department rather than the biology department, I suppose, or the agriculture department. And they ask physicists, you know, how do I, what do I do? And the theoretical physicist who happened to be listening, you know, goes away and comes back and says, OK, I have it. I have a theory for how to improve your milk output and then starts with: first assume a spherical cow. That's it. That's the joke. There's really no more. I can't make it better. I tried to make it better, but it's not supposed to be funny. What it's supposed to do is to illustrate a method of thinking that both makes fun of physicists, but also works really well if you're a physicist. You know, it won't work if you're trying to improve the dairy output of a dairy farm to assume that the cows are spherical. I mean, cows are intrinsically not spherical. That's important for what it is to be a cow. Once you've made that approximation, you're probably too far away from the reality of dairy farming to be of much help. But there are situations in physics where you make kind of that big of an assumption, a simplification, and it really is helpful. You know, ignore air resistance, right? Thinking there are only two particles in the universe, thinking the universe is perfectly smooth everywhere. Like these are all crazily wrong approximations, but they're really, really good at giving you physical insight. So I coined the term “the spherical cow philosophy” because again and again in physics, you can actually make progress by simplifying in exactly the right way. And the reason why people like Galileo or Einstein are geniuses is because they just had a sense for what parts of a problem were the important ones and which parts you could throw away. So you're right. I mean, part of the book is not just here's a bunch of thoughts and equations, but I want to give you some insight into how physicists think. So at the end, when we do talk about Einstein's equation, I don't just tell it to you. I say, well, look, you might have guessed this. Here's why that doesn't work. Here's another guess. Here's why that doesn't work. More or less tracing the reasoning that Einstein himself undoubtedly went through.
Indre Viskontas:
So one of the spherical cows that I really enjoyed learning about and helped me understand this is the oscillator. So tell us a little bit about oscillations. And, you know, as a neuroscientist, this is something I think is really important for us to understand because neural oscillations are sort of one of the big frontiers now that we’re trying to understand what they mean in terms of how they relate to, you know, brain and behavior and sort of how our minds work. So tell us a little bit about like, let's define what an oscillator is and kind of what are some of the main physics things that we need to know if we want to understand this a little bit more deeply.
Sean Carroll:
Yeah, it's funny because the phrase “simple harmonic oscillator” means nothing to most people. But any physicist will just laugh when you say that out loud because simple harmonic oscillators are ubiquitous. They are literally everywhere around us. I mean, the basic idea is you push something and there's a force that pushes it back in the direction where it started from. But then it comes back and it overshoots. So it goes past where it started from and then it gets forced back again. Voila, you have an oscillator. And obviously there's a million different examples lying around. The simplest possible one is probably a pendulum. You have a pendulum and poke it a little bit or, you know, anything falling, a chandelier suspended from a string. Or for that matter, in the world of music, plucking the string on a musical instrument, right, they vibrate back and forth and that therefore it's an oscillator. But of course, all of these oscillators are a little bit different. For the pendulum, it will eventually slow down, right? It will eventually lose energy and stop. Likewise for the violin string or whatever, you know, the different violin strings made of different materials will sound a little bit different. So there are details, there are complications. But if you do the spherical cow thing, if you simplify it and say, imagine that there's no air resistance, that we've poked our oscillator, our pendulum, just a little bit, that the violin string is absolutely pure and there's nothing that is making it go off note or whatever, then it turns out that the mathematical description of the violin string and the pendulum is exactly the same. And in fact, when you eventually get in book two to quantum field theory and you say, well, the universe is made of fields and those fields, guess what? You can poke them and they vibrate and they obey the same exact equations. So sometimes in the world, in the universe, you poke something and it moves. And basically, there's a set of things that can happen. Either it's unstable and just keeps moving forever. Like you push a ball down a hill or there's friction and it stops or it oscillates. There you go. There's not a lot of different possibilities. And so it turns out that many, many things in nature from quantum fields to pendulums, what's inside whatever clock you use. If you have a mechanical watch, there's a little spring that bounces back and forth. If it's an electrical quartz watch, there's a little crystal that vibrates back and forth. And like you say, in the brain, in your body, lots of different parts of you are just jangling oscillators back and forth. So that's a great example of a very, very simple system that just keeps showing up. And one of the things that I can do in the book, because you have a little bit of equations under your belt by that point, is show you in the mathematical detail why this particular set of equations is so applicable over and over again.
Indre Viskontas:
And you do something similar too when you talk about sort of our conception of space. And so I think that this is something that also kind of I think for a lot of people, conceptualizing space and understanding how to work with the physics of space can be a barrier into moving on further. So can you give us a little bit of sort of like the fundamentals of how we should think about the physics of space?
Sean Carroll:
Yeah. Well, you know, look, it's a really good question. And it's one of the things that I enjoyed about the chance to write the book is that even, you know, there's lots of books without equations that will tell you about general relativity and special relativity and Einstein's equations, stuff like that. But mostly they don't take the time to start with what is space, what is time, what is motion. Right. And even though my book is short, I get to do that. And I talk a little about the philosophical background and so forth. Again, Newton and Leibniz argued over what space is. There's a picture of space, which is probably pretty intuitive to most of us today, in which space is a thing. Space is an arena. Space is a container in which things are located. So you have space. And by space, we don't mean the final frontier. We don't mean outer space. We mean literally the three dimensional world around us with things at different locations. And the question is, is that three dimensional world a separate thing in addition to the things in it, which is what Newton would have said. Leibniz would have said the only things that are real are the things, not space. But if you told me this thing is a certain number of centimeters away from this other thing, and you told me that list of distances for literally every set of things in the universe, space is basically a bookkeeping device. It's the relationship between all the things. And so to this day, in highfalutin questions about quantum gravity and the emergence of the universe, people argue over whether space is a substance or a relation. And you won't ever read about that in physics textbooks, but I thought it lets the reader in on why physicists think about things in certain ways, if you know what the alternatives are.
Indre Viskontas:
And to me, I thought it was really interesting too to find out that now you have a foot in each department, physics and philosophy. And there seem to be some characteristics of the conversations I overhear amongst physicists that are similar to the conversations I hear from philosophers, but coming from very different backgrounds or foundations. So I wonder if you could talk a little bit about that. What is it like? When you talk to your philosophy colleagues, how is that different from when you talk about your theoretical physics colleagues?
Sean Carroll:
It's a fascinating question. It's really, really interesting to me. Someone should write a book about this, not me. But both physics and philosophy in their different ways, parts of them, not the whole parts, but parts of these two fields are devoted to figuring out the ultimate questions. What is the universe made of? How does it work? Why is it there? Where did it start? All of these questions, right? The way they do it is pretty different. And what's interesting is there is an overlap. So when I first discovered philosophy when I was an undergraduate, I knew that there was philosophy of physics, but mostly it was how are theories invented and how do we decide? And what is science and what is not science? They were methodological questions. I didn't know that there's a whole extra group of philosophers who are doing what is called foundations of physics. And they're really asking questions about the universe. They're not asking questions about science. They're saying what happens when a quantum measurement occurs? What does it mean to have a singularity? Why is the past different from the future? Things like that. And those are big questions that philosophy has to say something about, and so does physics. But the interesting thing is in the history of academia, we have decided that these are two different fields. Philosophy and physics are not even in the same school, right? There's the humanities or arts and sciences, I guess arts and humanities and then there's the natural sciences. Usually a different dean is in charge of both departments, right? And so therefore the philosophers end up talking to other philosophers and the physicists end up talking to other physicists. And so even though they are motivated by very similar questions, they don't talk to each other nearly as much as they could. So I'm very happy that here at Johns Hopkins we're actually devoted to overcoming that barrier a little bit. We started a new forum on natural philosophy, borrowing the terminology back from Isaac Newton and Galileo, philosophy that is really informed by dialogue with nature, by experiment and observation and trying to move forward. So I do think that even though both sides are used to talking to other people in other ways, the philosophers are much more likely to be talking about the nature of rationality. The physicists are much more likely to do a scattering calculation. There is still more than enough overlap for them to get together and converse.
Indre Viskontas:
To me, what's kind of fascinating too is that you have over the last, you're right, that a couple hundred years ago the philosopher and the physicist, especially the theoretical physicist, was often the same person. And then as academia sort of created these separate departments, they sort of went in very separate directions in some ways, I think, at least in terms of who wins the argument. What makes a good philosophical argument versus a good theoretical physics argument? And so I wonder if you have any thoughts about how to bring those two fields closer together so that we do get to some higher truth about some of these big questions.
Sean Carroll:
Yeah, you know, I'm teaching a course right now on topics in the philosophy of physics. And so I'm forced to systematically go through and read what other people say and look at the big questions rather than just do your own research. And I got to say, as fascinating as these questions are, and as brilliant as some of the people are who talk about them, there's a lot of silly things that are being said in the academic literature about these very important questions. And you can see why for different reasons. On the philosophy side, you can get away with not confronting our best current theories of reality. You can sort of work in a tradition where there's certain questions that are considered to be interesting and certain words that are considered to be meaningful and just stay in that tradition and sort of never get shaken out of your dogmatic slumbers by a new discovery or something like that, right? On the physics side, you can just be perfectly happy getting a good enough answer from a calculation to make a prediction, even though some of the assumptions that went into that calculation are completely nonsensical. And this kind of problem really lurks in a lot of areas of fundamental physics today. And the thing about physics is we're not done. We don't have all the answers. So the fact that we're not being careful even in the answers we think we have I think is like an obvious room for improvement situation because maybe thinking about these foundations and making sure we get the arguments right will improve our understanding of the emergence of space-time and quantum gravity and the origin of the universe and the nature of time and all of these questions that even physicists think are perfectly respectable ones to think about.
Indre Viskontas:
Well, if anyone can draw these two fields closer together and actually get some answers to some of these big questions, it's you. So I'm glad that that is on your shoulders.
Sean Carroll:
Thank you very much.
Indre Viskontas:
So I want to remind our listeners that Sean Carroll's new book The Biggest Ideas in the Universe: Space, Time, and Motion, Part 1, I should say, The Biggest Ideas in the Universe, Part 1, is now available at booksellers everywhere. And Sean, do not pull a George R. R. Martin on us. Book 3 better come out before the HBO series.
Sean Carroll:
[laughs] If I have an HBO series, I might just resign so that makes perfect sense. So you should tell the people at HBO not to sign me up for a multi-season deal.
Indre Viskontas:
Okay, great, great. Well, thanks so much for coming back on Inquiring Minds and chatting with us about your book.
Sean Carroll:
Thanks, Indre. Anytime you want me, I'm here. Thanks.
Indre Viskontas:
So that's it for another episode. Thanks for listening. And if you want to hear more, don't forget to subscribe. If you'd like to get an ad-free version of the show, consider supporting us at patreon.com/inquiringminds. I want to especially thank David Noel, Herring Cheng, Sean Johnson, Jordan Miller, Kyle Rejala, Michael Galkul, Eric Clark, Yuxi Lin, Clark Lindgren, Joelle, Stefan Meyer-Aewald, Dale Lemaster, and Charles Blyle. Inquiring Minds is produced by Adam Isaak. And I'm your host, Indre Viskontas. See you next time.
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