Physicist Sean Carroll Finds Meaning in the Chaos of the Cosmos

17:10 minutes

Does the Big Bang mark the beginning of the universe or the end of our current scientific knowledge? Is human consciousness purely an emergent property of the laws of physics and science at work? Physicist Sean Carroll ponders the big philosophical questions that guide physics and the human experience.

Segment Guests

Sean Carroll

Dr. Sean Carroll is the author of The Biggest Ideas in the Universe: Space, Time, and Motion, and is the Homewood Professor of Natural Philosophy at Johns Hopkins University in Baltimore, Maryland.

Heard on the Air

Read an excerpt from Sean Carroll’s new book, The Big Picture.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. There are certain questions that keep science geeks lying awake at night, like what happened before the Big Bang? Can we ever come up with one unified model for physics? And when will we finally find those darn gravitational waves? Of course, that last question, at least, was finally put to rest earlier this year. Physics fans can sleep a little easier.

But the question still remains, what does it all mean? When you strip away the math and the equations, what does any of this tell us about where we came from? Does the cosmos reveal anything about human nature? My next guest tackles these big questions in his new book, “The Big Picture– On the Origins of Life, Meaning, and the Universe Itself,” Sean Carroll.

You should know him by now. He’s been on Science Friday quite a number of times. He’s a theoretical physicist at the California Institute of Technology, author of the new book, “The Big Picture.” Welcome back, Sean.

SEAN CARROLL: Thanks, Ira.

IRA FLATOW: Why did you decide to write this book?

SEAN CARROLL: Well, in some senses, this is a book that I’ve been contemplating writing for my whole life, or at least for quite a fraction of it. I’ve always been one who believed that physics is fun, the big questions of the ultimate nature of reality are fun. But it also is the same universe that we’re talking about when we do philosophy or biology or neuroscience. All these things have to fit together somehow, and so this is my opportunity to see how that happens.

IRA FLATOW: You coined a term called poetic naturalism, that’s your perspective on how physics, science, humanities, nature, everything comes together. Is that what you’re talking about here, poetic naturalism?

SEAN CARROLL: Yeah. Naturalism is the idea that there’s one world, the natural world, and poetic reminds us that there are many ways of talking about the natural world. So even though the world is made of particles and forces at the deep level of physics, it’s OK to talk about tables and chairs as real, existing things, even though they’re made of atoms. And in the same way, it’s OK to talk about human beings making choices and judging things right and wrong.

IRA FLATOW: When you talk about where we all come from, people have a religious bent to that. Did you include religion in this category?

SEAN CARROLL: Well, I talk about it. I’m personally not religious, so I try to put forward naturalism as an alternative to where you can really understand and think about questions of meaningfulness from a naturalistic perspective. And I’m very happy if that’s a conversation with people who come from other perspectives.

IRA FLATOW: One of the first ideas you learned about in physics class is the Big Bang, and you say that the Big Bang is, most likely, not even a real event.

SEAN CARROLL: Well, what I say is that we don’t have any idea what happened at this purported moment of the Big Bang. Cosmologists, including some of my best friends and even including me, sometimes exaggerate a little bit about what it means. We say the Big Bang was the beginning of the universe, talking about what happened before the Big Bang is like talking about what was north of the North Pole.

But all of that is not something we understand. These are just hypotheses. These are speculations. It’s very possible there was something before the Big Bang. So we should be a little bit humble where we’re saying, what exactly was it that went on that moment.

IRA FLATOW: Fred Hoyles created that term, didn’t he, many years ago.

SEAN CARROLL: He did. He was trying to make fun of the Big Bang idea. Of course, the Big Bang model, which is really what Hoyle was making fun of, is the general idea that the universe has been expanding from a hot, dense, early state. And that’s 100% true. That we’ve established as correct. But the Big Bang event, the moment, the singularity at the beginning is something we don’t understand.

IRA FLATOW: So it’s sort of a time, a reference time that we can use.

SEAN CARROLL: Exactly. It’s sort of the time at which we no longer understand what the universe was doing.

IRA FLATOW: I’m not laughing at you.


IRA FLATOW: But isn’t that what we think physics and physicists are all about, is understanding what was going on then?

SEAN CARROLL: It is, but our understanding on the basis of data and observations does stretch back to one second after the Big Bang, and we’re now 13.8 billion years after the Big Bang. So we’ve got a lot of it covered. That first second, we’re still working on.

IRA FLATOW: Is physics, then, in trouble, because we don’t know what happened then at that moment? Or are a lot of other things that are going on in the universe, like dark energy? Do we need new physics, new understanding?

SEAN CARROLL: Physics is not in trouble because there are still interesting physics questions to be asked. Physics would be in trouble if we were done. That would be bad for the physics department. We would all change into engineering or biology departments. So physics is as healthy as you could imagine it being.

IRA FLATOW: Our number, 844-724-8255. You can also tweet us @scifri, S-C-I-F-R-I. If you’re just joining us, we’re talking with Sean Carroll, author of “The Big Picture– On the Origins of Life, Meaning, and the Universe Itself.” Just the title, Sean, is like–

SEAN CARROLL: It’s outrageous, isn’t it? Outlandish. How dare anyone write all of these things? So I hurry to point out that even though I’m writing about these topics, I do not actually say how life began, how the universe began, or what the meaning of life is. I talk about how to talk about them. We don’t know the answers to these questions yet.

IRA FLATOW: Do we need input from all different places, from all different ideas about life to understand this?

SEAN CARROLL: Yeah, I think they all fit together, and thinking about how they fit together is illuminating and informative. I’m very quick to say, if you want to be a good biologist, you don’t need to study particle physics. That’s not really very helpful. On the other hand, if your theory of biology is somehow incompatible with what we know about particle physics, then that’s a problem.

IRA FLATOW: There’s an idea called core theory. It has gravity tacked on to the standard model. Can you explain that a little bit?

SEAN CARROLL: Yeah, again, if you listen to popular explanations of physics, you’ll often hear it pointed out that we don’t yet have a complete theory of quantum gravity. That the rules of quantum mechanics, which are so successful in the microscopic realm of atoms and particles, haven’t yet been extended to include gravity.

On the other hand, what that really means is that we don’t understand everything about quantum gravity. We don’t understand the Big Bang or black holes, but we do actually understand quantum gravity in weak gravitational fields, which includes the entire solar system, for that matter. So there’s no problem in doing quantum gravity and including gravity in our best theories of physics here in our everyday lives.

IRA FLATOW: Let’s go to the phones. Some interesting questions. Let’s go to Gainesville, Florida. Hi, Joe. Welcome to Science Friday. Joe, are you there?

JOE: Yes.

IRA FLATOW: Hi, go ahead.

JOE: Yes, I’d like to ask, what does time play into this scenario, and how does infinity and our own mortality make us think about physics?

IRA FLATOW: All right. Time.

SEAN CARROLL: Well, we don’t have nearly enough time to answer these questions. Time is important. It certainly exists and plays a role in our everyday lives and the evolution of the universe. We don’t necessarily understand what it is at a fundamental level. You mentioned infinity. One of the things we don’t know is whether the universe lasts for an infinite amount of time or a finite amount of time.

But you also mention our mortality. One of the things we do understand is our lives last for a finite amount of time. The average human lifetime is three billion heartbeats, and that’s not such a big number. I think we should take every one of those heartbeats to be a very special thing.

IRA FLATOW: I could swear I remember in a past conversation you telling me that physicists don’t believe there is such a thing as time.

SEAN CARROLL: No, I never said that. I’m certain that I never said that. People say it all the time, and I make fun of them for saying that. So I think there is time. Otherwise, how would I have known when to be here for this interview?

IRA FLATOW: We were talking a little bit earlier about spooky action at a distance, which is another hair-curling idea. And the fact that, how can you have two entangled particles knowing each other as what they’re doing, and that’s because there’s no distance or time between them, in some other dimension.

SEAN CARROLL: We don’t know. These are great questions that we’re thinking about right now. I mean, time exists, there’s no question about that. But the question is, does it exist in the same way that electrons exist, that they’re really part of the fundamental ingredients of reality, or does it exist like tables and chairs exist, that they’re sort of useful approximations in certain regimes.

IRA FLATOW: Physicist John Wheeler, I remember meeting him many years ago when I was a young journalist, talking about quantum mechanics, and he said that the reason that the universe exists is because we are here to observe it.

SEAN CARROLL: Well, you know, it’s a free country. People can say whatever they want, but–

IRA FLATOW: It’s the anthropic principle, I think it was at that time.

SEAN CARROLL: I think I actually have a position that is even less popular than that one, which is that there’s no such thing as the reason the universe exists. I think that reasons why certain things are true or false are always relative to some context. The reason why I was tired this morning is because I didn’t have my cup of coffee. But the universe, if the universe is everything, then there’s no context in which we find it, and we might need to be able to accept the idea that there isn’t any such thing as the reason why the universe exists.

IRA FLATOW: It just happens to be here.

SEAN CARROLL: Yeah, it’s just the kind of thing that happens now and again, the universe.

IRA FLATOW: Is physics really coming up with larger ideas about the natural universe, or is it really just mapping out our own brain and consciousness?

SEAN CARROLL: Well, yeah, that’s a dichotomy that people sometimes put forward. Idealism versus realism. Is the world a physical thing that is out there, or is it all just a projection of some ideas or some thoughts. Honestly, I’ve tried, I’ve spent time. I cannot wrap my brain, personally, around what it would mean for the universe to just be a thought or an idea. For me as a physicist who makes up theories and compares them against the data, I’d like to think the real world actually exists.

IRA FLATOW: And do you think that’s we’re going to be able to unite gravity and all the other forces and come up with a–

SEAN CARROLL: Oh, yeah. There’s no question. It will happen, hopefully sooner rather than later. We’re working on it.

IRA FLATOW: And what’s your opinion on string theory? Has it run its course, and is core theory going to take its place?

SEAN CARROLL: Oh no, the core theory is sort of the pedestrian part of quantum field theory, the part that we already understand, the part that has been established. Whereas string theory is much more ambitious. It tries to answer that question I said we don’t have the answer to, which is, what is the complete theory of quantum gravity. I think that it’s very possible that string theory is not the complete theory, but will help us get there by giving us some pointers, some hints as to what direction to move in.

IRA FLATOW: You’ve really been very ambitious, as you say, in writing this book. You’ve reached into all different areas– biology, metaphysics, chemistry– that really, I’m sure you had to go study up on. Were you a little hesitant to branch out?

SEAN CARROLL: I was. It was enormous fun doing the research for this book, because I got to knock on people’s doors, and brilliant people– MacArthur Prize winners, Nobel Prize winners– were happy to talk to me. And I’m not an expert on chemistry, biology, neuroscience, philosophy, any of these things. But then again, I think that probably nobody is an expert, in the world, on all these things all at once, so why not me, is one way to look at it.

IRA FLATOW: OK. Let’s go to phones. Let’s see if we can go to Jeff in Plano, Texas. Hi, Jeff. Welcome to Science Friday.

JEFF: Good afternoon. Thank you. Good talking to you, Sean and Ira. Sean, I was wondering if you’ve ever heard of– and I’m probably getting this wrong– but Roger Penrose, who I’m sure you’re familiar with, once stated something about the human mind and its unique ability to be conscious thought was what gave structure to the universe, I guess you could say. Not in the grand scale structure of galaxies, but it gave the existence to the universe. Do you have more information on that, or is that something you’re aware of?

SEAN CARROLL: I’m aware of ideas like this. For a long time, one of the things that we don’t understand in physics is the deep-down rules of quantum mechanics. We know that quantum mechanics works at the microscopic level. We can put it to use, we can make predictions, but there’s still the question of what is it fundamentally saying? And for a long time, people were really taking seriously the possibility that there was some deep connection between quantum mechanics and consciousness. Because part of the textbook rules of quantum mechanics put a special emphasis on what happens when an observation occurs.

Now increasingly, over the years, that has become less and less popular. We’ve figured out how to deal with quantum mechanics in more traditional ways that make no special reference to the human observer. But there are still a few holdouts, like Roger Penrose, probably the most respectable and famous among them, who really think that you need consciousness to explain quantum mechanics, and vice versa, quantum mechanics to explain consciousness.

I think it’s probably not the way to go. It’s certainly declining in popularity, rather than gaining. But as long as you don’t know the answers, all options are on the table.

IRA FLATOW: I’m Ira Flatow. This is Science Friday from PRI, Public Radio International. In case you just joined us, we’re talking with John Carroll, author of this great big new book, “The Big Picture– On the Origins of Life, Meaning, and the Universe Itself.” It’s going to take a few more than a couple of days to read this book, and then you’re going to want to read it again, because there are a lot of interesting ideas in here. What was the most difficult part about writing this book for you, Sean?

SEAN CARROLL: Oh, that’s a very good question. I think there’s two obvious answers. One is that there’s chemistry in the book, and I don’t know anything about chemistry. I mean, I know more about biology than I know about chemistry, and so now I know what an ATP molecule is, and what a fatty bilipid is and things like that. So–

IRA FLATOW: You’re ahead of me.

SEAN CARROLL: Yeah, that was fun, and I don’t know if I’ll still remember it a year from now, but I knew it when I was writing the book. But the other was, there are people I disagree with about deep issues about the nature of reality, and I wanted to give them a fair shake in the book. I wanted to represent their own views fairly, rather than just caricaturing what they believe. So I put a decent amount of effort into being fair and getting straight how people would’ve put forward their own views, and even if I disagree with them, I hope they won’t think that I’m just making straw men out of their positions.

IRA FLATOW: Physicist Frank Wilczek, a very famous Nobel Prize winning physicist, talking about the core theory, said that in the future, rather than talking about physics in terms of energy, someday the laws of physics will be rewritten in terms of information and its transformation. Is everything just information?

SEAN CARROLL: Well, everything is the universe. Everything is the stuff the universe is. But maybe the best way to talk about the universe is in terms of its information contained in different little parts of it. In particular, if you really believe that quantum mechanics is the right underlying theory of the world, there’s this wonderful, burgeoning, growing field of quantum information, where we really describe different parts of the universe in terms of how much information about one part is reflected in what’s going on in some other part. That’s the miracle of entanglement and the spooky action at a distance.

I’m actually working on finishing a paper right now, where we use ideas from quantum information and mutual information between different parts of the universe to model quantum gravity in a simple way. So yeah, I think that’s one of the possible ways things can go. Of course, we’ll have to see how it happens.

IRA FLATOW: Is the quantum limited? Is there something beyond quantum physics? Is it a subset of something we haven’t discovered yet?

SEAN CARROLL: Well, I don’t know. That would be great. I mean, that’s the kind of exciting possibility that it’s thrilling to think about. But right now, there’s literally no indication from any experiment, whether thought experiment or real experiment, that something like that must be true. So we’re free to think about it, but as long as nature’s giving us zero guidance in that direction, the safe bet is just to still work within the quantum mechanical framework.

IRA FLATOW: Well, it’s a safe bet you’re going to like the book that Sean has written, “The Big Picture– On the Origins of Life, Meaning, and the Universe Itself.” Sean Carroll, research professor in the Department of Physics at California Institute, Caltech, of Technology. Welcome and thanks for coming on today.

SEAN CARROLL: Always great to be here, Ira. Thanks.

IRA FLATOW: We have an excerpt of your book on our website at ScienceFriday.com/bigpicture.

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