Sean Carroll On The Mysteries Of Time It's easy to find a dictionary definition of "time." But ask a group of theoretical physicists and the answer isn't as clear. Sean Carroll of CalTech discusses the mysteries of time in his book, From Eternity to Here: The Quest for the Ultimate Theory of Time.
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Sean Carroll On The Mysteries Of Time

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Sean Carroll On The Mysteries Of Time

Sean Carroll On The Mysteries Of Time

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IRA FLATOW, host:

Talking about the 21st century, we like to think that we know lots about lots of things medicine. We know about lots of things about computers, maybe the physics of "Lost." But what we really don't know very much about is our universe and the parts that make it up - time, space, matter, energy. But our spot, right here in our solar system, right here in our galaxy, is good enough for scientists to reckon that the universe is about 13.7 billion years old -we've got that down; that it's expanding - we've sort of taken care of that in the last 100 years.

And we have a theory that says it started with a big bang, or did it? Could anything have existed before the big bang? Well, that's one of the mysteries of modern physics and cosmology and one of the topics in my next guest's new book, a sort of guide book to what we know about time and the universe.

Sean Caroll is the author of "From Eternity to Here: The Quest for the Ultimate Theory of Time." He's also a theoretical physicist at CalTech in Pasadena. He joins us from NPR West.

Welcome back to SCIENCE FRIDAY.

Dr. SEAN CAROLL (Author, " From Eternity to Here: The Quest for the Ultimate Theory of Time"): Hi, Ira.

FLATOW: Just small things that you think about, I think.

Dr. CAROLL: Yeah. You know, just musings on an afternoon, right, the origin of the universe...

(Soundbite of laughter)

Dr. CAROLL: ...the nature of space and time.

FLATOW: Well, it seems like we know so little about all of these stuff.

Dr. CAROLL: Well, I don't know - I don't think that's right actually. We know a lot. Of course, as scientists, we immediately gravitate to the boundary between what we know and what we don't know. So...

FLATOW: Yeah.

Dr. CAROLL: ...I certainly don't want to give the impression that does - of not too much we know, since, from Isaac Newton to Ludwig Boltzmann to Albert Einstein, we've learned a tremendous amount about how time works.

FLATOW: Well, let me put a parameter on that, 'cause you're right, it's unfair to say we don't know anything with. If we don't know what 96 percent of the universe is made out of, that's not a whole lot, is it?

Dr. CAROLL: Are you kidding? That means we know what four percent of the universe is made out of.

(Soundbite of laughter)

Dr. CAROLL: That's pretty awesome. A hundred years ago, we didnt know anything.

FLATOW: Well, that's true. That's the old saying that 99 percent of all the scientists who ever lived, their - are alive today.

Dr. CAROLL: That's right. And we even know something about that 96 percent, so we're getting there. I think we're making progress.

FLATOW: What is it about time that fascinates so many people? I mean, there's so much fiction, nonfiction, that has been written about time and it's still going on. And you write a lot about it in your book.

Dr. CAROLL: Yeah. I think that time is a great way to connect the very every day, the Monday and pieces of our lives to the biggest questions we can possibly ask ourselves.

In the book, I talked about how the features of time in your kitchen, the fact that there's an arrow of time that says you can do certain things and you can never undo them. You can turn an egg into an omelet. You can't turn an omelet into an egg. You can mix milk into your coffee but not unmixed it.

So, we know a little bit about how that works. And it goes back to the 19th century. But what we don't know is why it is like that. Why we live in a universe where there's things you can do but not undo. So, just really a moment reflection on stirring milk into your coffee leads you to ask questions about the Big Bang.

FLATOW: Talking with Sean Caroll, author of "From Eternity to Here: The Quest for the Ultimate Theory of Time," on SCIENCE FRIDAY from NPR.

I'm Ira Flatow. Our number is 1-800-989-8255. You can also send us - thank you - a Twitter. Our tweet is...

(Soundbite of laughter)

FLATOW: ...@scifri at S-C-I-F-R-I. Are you saying that the - there is no reason why time could not be running in the opposite direction?

Dr. CAROLL: Well, the surprise is that there is a direction at all. If you fly out into space and you're in a space suit far away from the Earth or any other planets or anything, you wouldn't be able to tell the difference between any of the directions in space - up, down, left, right and so forth. And Einstein told us a long time ago, that time and space are closely related to each other. They're both just different aspects of one big thing called space time.

So, why is it that time has such a pronounced direction from past to future? So, yeah, you could easily imagine different universes where there was no direction or even universe as part of our universe where time loose in the opposite direction.

FLATOW: And why does time run at the speed that it runs?

Dr. CAROLL: Well, I don't think it's easy to talk about the speed of time. You know, we feel time passing...

FLATOW: Right.

Dr. CAROLL: ...because our bodies are made of clocks. We have our heartbeat pulsing away. We have our breath and our essential nervous system. And we have other clocks. We have atomic clocks and pendulums lying around. And we don't always match up very well because our biology is not very accurate. You know, we get adrenalin rushes and things go faster or slower, psychologically.

But time itself passes at one second per second, and that's not going to change. You can change the total amount of time that passes by taking some weird path through space time, but time itself moves at the same rate.

FLATOW: But one of Einstein's great theories of gravity was that he was saying that time can change.

Dr. CAROLL: That's right. And that's, sort of, just like space can change. If you travel from a starting point to an ending point, if you go on a straight line, it will take you less distance than if you go in a curve line. And that's really all Einstein is saying, but he says the same thing is true for time. If you take a curvy path through space time, it will actually take you less time elapsed, as far as you're concerned, to get to where you're going than if you just take the direct route or just stay still as you possibly can.

FLATOW: Question from Second Life from Laura Geino(ph) who says is there any evidence of more than just the one-time dimension?

Dr. CAROLL: There is no evidence of that, for sure. In fact, physicists, being the naturally curious creatures that they are, have certainly asked the question: why is there one direction of time rather than zero or two or 28? And so far, there's no absolutely agreed upon answer except that when we try to change things, physics doesn't work as well.

You know, the rules breakdown. It's very hard to come up with the consistent scenario. So, it looks like one dimension of time is what works, but I can't say that we won't understand that deeper at some future time.

FLATOW: Why - what started this questioning of time? Where does it go back to, I mean, in the relative history of last 100 or so years?

Dr. CAROLL: Well, yeah, I think I actually - I have to go back to 140 years if that's okay.

FLATOW: Yeah. That's okay.

Dr. CARROLL: It was really the 1800s where we started talking about entropy, you know? Entropy is this concept of disorderliness. And that is what really what controls the arrow of time. The fact that things become more disorderly as things go on is behind everything in terms of how we experience time. And it was really in the 1870s that Boltzmann and Maxwell and Gibbs, and some of the great under-recognized heroes of 19th century physics, began to understand how entropy worked. And they immediately ran into this problem of the early universe.

Why was it so weird? Why was the - even though they didnt know about the Bing Bang or general relativity or quantum mechanics, they were asking about the origin of the universe and why it had such a low entropy, and they couldnt come up with any good explanations.

FLATOW: Mm-hmm. Talking with Sean Carroll, author of "From Eternity to Here: The Quest for the Ultimate Theory of Time."

We'll take a break and come back with your questions. Our number: 1-800-989-8255. You can tweet us @scifri, at S-C-I-F-R-I, or in Second Life. And stay with us. We'll be right back after this short break.

I'm Ira Flatow. And this is SCIENCE FRIDAY from NPR.

(Soundbite of music)

You're listening to SCIENCE FRIDAY from NPR. I'm Ira Flatow.

We're talking with Sean Carroll, author of "From Eternity to Here: The Quest for the Ultimate Theory of Time." He's also theoretical physicist at CalTech out there in Pasadena, California. Our number: 1-800-989-8255.

Let's go to Robert(ph) in Burlington, Vermont. Hi, Robert.

ROBERT (Caller): Hi. Say, I have a question about, I guess, creation and the fact that we think that we know that when the Big Bang happened, it was it wasnt that there was this time - there was a clock that was already ticking and that there was also this big space as a vacuum. And then this Big Bang happened at a certain time and expanded into the space. It's that space and time were also created at the time of the Big Bang. Is that correct?

Dr. CARROLL: Yeah. I would like to spread the word that we don't actually know that. It is true that my close personal friends, other physicists and cosmologists will tell you that we know that, but they're just exaggerating a little bit. It's possible that that's true. It's possible that what we know of as the Big Bang was the beginning of time itself, and there was nothing before that. But the alternative is also possible. It's possible that what we know of as the Big Bang was just a phase the universe went through.

And the problem is that we have a theory, Einstein's general theory of relativity that predicts, unambiguously, that there was a Big Bang, but it also predicts that it itself breaks down at the Bing Bang. General relativity isnt up to the task of correctly describing what happens then. So it's an open question.

And in fact, in my book, I push the idea that we should take very seriously the idea that the Big Bang was not the beginning. It helps us understand some things about our universe if we ask whether or not the Big Bang was just part of a much bigger picture.

FLATOW: So what came before the Big Bang?

Dr. CARROLL: Another universe that didnt have an arrow of time out of which our universe was created. So we're the baby universe and that's the parent universe.

FLATOW: Could it be that we - there are lots of universes around?

Dr. CARROLL: It could be. I mean, basically, if there's more than one, there's likely to be an infinite number. Those are the two natural numbers for there to be, and that's absolutely possible. And physicists right now are struggling with this philosophy question of how we deal with the idea that there could be many universes out there. Is that a scientific idea? How would we ever test it? What implications does it have for the universe we see?

FLATOW: Yeah, you know, because it's great dinner conversation between us and everybody else tonight. But there's no really good way of testing out these theories.

Dr. CARROLL: There's not a good way right now, but were - the people who work on these ideas are incorrigible optimists.

(Soundbite of laughter)

Dr. CARROLL: Do you think that if we push the theory...

FLATOW: Yeah.

Dr. CARROLL: ...forward better and better, and we keep collecting data from any number of different sources, we'll be able to put together a comprehensive picture which is testable. Even if we can't see the actual universes very far away, the framework that predicts they exist will somehow be able to test. That's the hope.

FLATOW: And theories like string theory are beginning to fall by the wayside.

Dr. CARROLL: Oh, no. Not at all. String theory is part of this bigger picture. I mean, we need to bring together what we know about gravity from Einstein, what we know about quantum mechanics. We still know exactly how that's going to happen. But string theory is still the leading candidate for doing that. So it might be a huge help in putting this picture together.

FLATOW: Mm-hmm. 1-800-989-8255. Let's go to Peter(ph) in Grants Pass, Oregon. One of my favorite places. Hi, Peter.

PETER (Caller): Hi there. A question. It would seem that the majority of the cosmological models depends upon an assumption that - I would like to know how it is justified. And that is that light, whether considered as a continuous electromagnetic radiation or as a quantum, that it is steady in its characteristics over time.

How do we justify - how do we argue against the fact that there might be a decay in quanta over a period of time, either by, you know, large energy splits or by just abrasion that could easily be interpreted as red shifts, and would completely change, if we really understood it, if its - which shift the whole concept of the Hubble concept.

FLATOW: Let me get - a good question. How do we know that Einstein set time to be - set light to be constant? How do we know it doesnt change?

Dr. CARROLL: Well, we do our best to explore the different possibilities. We certainly - there are physicists who have contemplated the idea of what are called tired light models of the universe, where light just sort of loses energy gradually as it moves through a non-expanding universe.

That's kind of a hard idea to make work, you know? Energy is not conservative. That's true. And the alternative, the actual prediction of general relativity and what we know about electromagnetism has been tested many, many different ways.

It's not just that we see galaxies moving away from us. It's that, that, you know, they take longer amounts of time for different things to happen just like relativity predicts. And the whole picture predicts things about the element abundances in the early universe and the cosmic microwave background.

So, our basic picture of the Big Bang in the last 13.7 billion years is really, really well established and fits the data very well.

FLATOW: Of course, Einstein took gravity and made it a geometrical object that...

Dr. CARROLL: That's right. Yeah.

FLATOW: And yet, we have all the other forces that are quantum particles. They're not geometry. They're little particles and waves. And we haven't been able to reconcile those two yet. Do you think we're going to be doing that anytime soon?

Dr. CARROLL: We will. I can't give you a date when it's going to happen...

(Soundbite of laughter)

Dr. CARROLL: ...but nature does it, the universe does it. There exists both quantum mechanics and the other forces of nature. So, you know, it's a big puzzle. And in some sense, we have no right to expect this is an easy problem. There's a natural energy at which quantum mechanics and gravity both become important at the same time. But that energy is well above what we're able to actually reproduce here on earth in a particle accelerator. So we're going on our thoughts right now. We don't really have much experimental guidance.

FLATOW: Hi, George in New Jersey. Hi. Welcome to SCIENCE FRIDAY.

GEORGE (Caller): Hi. Thank you. I teach high school physics. And one of the first questions I like to ask my kids in the beginning of the year is what's time?

FLATOW: What is time?

Dr. CARROLL: Well, chapter one of my book...

(Soundbite of laughter)

Dr. CARROLL: ...tells exactly what's going on and...

FLATOW: I didn't put them up to this. No.

Dr. CARROLL: It does. It's a great question, because there's not one answer. There's different answers. You know, we invent the word time, you know, we put it to different uses, and it gets confusing. So one simple answer is that time is what clocks measure. We live in a world where things that happen - there are - there exists things that happen over and over again at a repetitive, predictable rate. Every time the earth moves around the sun, it revolves around its axis 365-and-one-quarter times. That's one definition of time.

Another is that time is a coordinate on the universe. It's a label. If you want to say, I'm going to listen to SCIENCE FRIDAY, when is that? You say, okay, that is at 12 p.m. Eastern - Pacific time at a certain place in the universe. And finally, time is this medium through which we move. Time is what gives meaning to our ideas of change and experience and memory. And so we talk about traveling through time or experiencing time or the flow of time, and all of these are separate, but closely related meanings. It's not that one is right and one is wrong. They're all there.

FLATOW: We have a question coming in from Second Life, from DareX(ph) in there who wants to know: Isn't space still expanding faster than the speed of light?

Dr. CARROLL: Well, space is expanding, but it doesn't have a speed. If you think about what it means to say that space expanding, it means if you look at different galaxies, galaxies or other far away objects are moving away from us, but they don't move at a constant speed. Nearby galaxies move us - move away from us relatively gradually. Very far away galaxies move away very quickly. And very, very far away galaxies would appear to be moving faster than the speed of light if we can see them, and we can't. But that's okay. There's rule against that. What Einstein really says is that two objects cannot pass by each other faster than the speed of light. That says nothing about what a galaxy many billions of light years away should be doing.

FLATOW: So the universe is getting bigger?

Dr. CARROLL: Yes, it is.

FLATOW: And so, there is some boundary to it.

Dr. CARROLL: No, there's not.

(Soundbite of laughter)

Dr. CARROLL: The universe is getting bigger, which means that if you pick some far away galaxy, there's more and more space, more and more distance between us and that galaxy, as time goes on. But that says nothing at all that how big space is. If you take all of the integers from, you know, zero to one, two, three, and minus one, minus two, minus three, multiple them all by two, they all move apart from each other. But there's still an infinite number of them. That was a never an obstacle. So we don't know whether the universe is finite in extent or goes on forever. My guess is it goes on forever.

FLATOW: So what people think about is definitions of time, universe, space, expansion, have a slightly different meaning to scientists who think in those terms?

Dr. CARROLL: Absolutely. So one of the things I did for writing my book was I walked around and asked people what they mean or what they think that the word time means to them. And you get very different answers, from physicists and from non-physicists. And so part of the challenge there was to connect these different things.

Regular nonscientists think of time as something that controls their motion through life or through the universe, whereas scientists tend to think of it as a way to measure things, something that clocks measure or something that you can measure in some other way.

FLATOW: Hmm. How do we know that we here on planet Earth, we're not just a random fluctuation of energy like we hear about, you know, maybe at the creation of the universe?

Dr. CARROLL: Well, we think that we're not. This is a great story that I talk about a lot in the book, because it's really kind of mindboggling. If you go back to the 18th century, in the 1890s - the 19th century, the 1890s, Boltzmann was confronted with this question. Boltzmann is the Austrian physicist who really figured out how entropy works, but he was stuck with this problem of why the entropy of the early universe must have been so small.

And his guess was, well, what if the entropy of the whole universe is very large, that it's just like a box of gas, and all the gases spread smoothly, uniformly to the box? But if you wait long enough, the box - well, the gas will just fluctuate into some very unlikely configuration. It will all be one side of the box or something like that. And Boltzmann suggested maybe our universe is like that. Maybe our universe is just a random fluctuation out of the chaos around it.

And the problem is it doesn't work. It's a very, very clever and provocative idea, but you can plug in the numbers. We know well enough to make predictions out of this theory. And the predictions are that it's much easier to make one person than to make a whole galaxy, much less 100 billion galaxies that we see in our universe. So with overwhelming probability, if that kind of scenario was right, we would exist all by ourselves as lonely observers floating in an otherwise cold and desolate universe. We would not be surrounded by 100 billion stars in our galaxy, 100 billion galaxies in our universe.

FLATOW: But it is possible that our universe, our whole universe, not just us on Earth, could have popped out of a fluctuation...

Dr. CARROLL: It is possible.

FLATOW: ...a quantum fluctuation.

Dr. CARROLL: That's right. And I discuss this a lot in the book, because it's possible only under certain circumstances. It's not possible that we fluctuated around some what physicists call equilibrium, some situation that was just staying there forever and ever and ever, because it's easier to have small fluctuations and big fluctuations, and our early universe is a very, very, very big fluctuation.

But it is possible if there is no static, fixed equilibrium once-and-for-all at-rest configuration the universe can be in. If we have a restless universe that is always looking for ways to get bigger and have more entropy, then it can sit there for billions and billions and billions of years relatively quietly, and then give birth to another part of universe in this flash of light that we call the Big Bang.

FLATOW: This is SCIENCE FRIDAY from NPR.

I'm Ira Flatow talking with Sean Caroll, author of, "From Eternity to Here: The Quest for the Ultimate Theory of Time." Sean, I'm wondering about how you spend your time. I mean, do you sit there thinking big thoughts with a pencil, a piece of paper, or...

Dr. CAROLL: Well, that is my day job, yes.

(Soundbite of laughter)

Dr. CAROLL: That's not the only thing that I do, but I'm a theoretical physicist, so I dont look through telescopes or build equipment, and I don't even do computer stimulations. I leave that to my graduate students. And I sit there, you know, in Starbucks or at the wine bar with a pencil and paper and I, you know, draw pictures and draw equations and try to see how to fit different ideas together. Happily, you know, it's actually a very social occupation where we work together and we bounce ideas off each other. So that's a lot of the fun.

FLATOW: So you have to leave it, though, to the experimentalist to come up to -with some way of coming up with an experiment that would prove what youre saying.

Dr. CAROLL: Basically, yes. I mean...

(Soundbite of laughter)

Dr. CAROLL: ...nobody wants me building anything...

(Soundbite of laughter)

Dr. CAROLL: ...especially large, expensive pieces of equipment. That would not be a good way for the world to...

FLATOW: Uh-huh.

Dr. CAROLL: ...spend its resources. But - so physics is very specialized. We have people who are experimentalists, observers, theorists. And I would certainly try to think of new ways to analyze data that they have collected, or try to suggest new ways they could collect data to test an idea, buy they're going to be the ones that are actually...

FLATOW: Yeah.

Dr. CAROLL: ...collecting the data and doing the job well.

FLATOW: One of the things they've come up with is the Large Hadron Collider, which might finally - it's now working.

Dr. CAROLL: It is.

FLATOW: Is there something that you would hope to see come out of there? They talk about the Higgs boson. Is that something youre interested in? And why are we so interested in that?

Dr. CAROLL: We would love to see the Higgs boson. There's a long laundry list of things we would love to see: Super symmetry, extra dimensions, technicolor and all these wonderful words for hypothetical things that particle physicists have suggested. And it's not just a forlorn hope. We really are, with the Large Hadron Collider, looking into a regime where new things should happen. We can't guarantee, because that's why you do experiments. You don't know what the answers are.

We have every reason to believe that we're looking into a new place in the universe where we should see new things. My personal hope is that we see something that nobody has predicted yet, an absolute surprise that will really shake us in terms of how we think about things, and that would put us on a new direction.

FLATOW: And what would that be?

Dr. CAROLL: I dont know.

(Soundbite of laughter)

Dr. CAROLL: I would love to learn something about space and time. That's what I would like to learn. I was learning...

FLATOW: Well, when I talk to other physicists - and maybe you share this view -they would love nothing better to not see something, not to see the Higgs boson, because then that would send them back to your, you know, your wine bar.

Dr. CAROLL: Well, you know, when you go to a wine bar, you don't let to go empty handed. And so a couple of new particles of forces of nature or phenomena that we have not yet anticipated are a huge help. That's the problem. You can't understand the universe just sitting in the wine bar with your empty piece of paper. You need clues. You need experiments to knock you out of your dogmatic slumbers and say, oh, I didn't think of that. Otherwise, we never would have thought of relativity or quantum mechanics, or any of these great ideas.

FLATOW: Mm-hmm. So youre unlike them. You'd like to see the Higgs boson pop out somewhere.

Dr. CAROLL: Among other things. I mean, I certainly don't want to see nothing. That would be the real disaster. I want to see something. I want to see lots of things. I want to see the Higgs boson and other things, let's put it that way.

FLATOW: Mm-hmm. And what - give me one other thing that we might understand.

Dr. CAROLL: Well, the easiest example that we're really hopeful about is super symmetry, which is basically a new symmetry of nature that mixes together matter particles with force particles. You know, we have things...

FLATOW: Hmm.

Dr. CAROLL: ...like electrons and protons that make up stuff. And we have things like photons and gluons that hold that stuff together. Super symmetry actually relates those, and it's very, very plausible that that kind of new, deep feature of space and time will show up at the LHC.

FLATOW: Mm-hmm. Well, I wish us all very - oh, you - luck in finding that stuff.

Dr. CAROLL: Thanks. I'm not looking. But I'm cheering them on. I think it's a very, very exciting - it's very - it's great and fun to talk to the experimenters at the LHC these days, because they're finally on the right track. They're sort of vibrating with excitement. So I'm looking forward to the next few years.

FLATOW: I think we all are. Sean Caroll, thank you for taking time to be with us today.

Dr. CAROLL: Thanks, Ira.

FLATOW: Have a good weekend. Sean Caroll is author of, "From Eternity to Here: The Quest for the Ultimate Theory of Time." Everything you want to tell about time is right here in this book. And take - you might take some time to read it.

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