Superstring theorist Brian Greene and his idea of an infinite number of universes + Interview

Alexander Fabry ..........Extra dimensions are old news. The newest mind-bending descriptions of reality dreamed up by the world’s smartest physicists, and explained by superstar superstring theorist Brian Greene in his latest book The Hidden Reality, include untold numbers of extra universes. A million universes isn’t cool. You know what’s cool? Ten to the 500th power universes. Greene was already an important string theorist when his enormously successful first book—The Elegant Universe—catapulted him into the firmament of popular physics with the other stars of the genre, Carl Sagan and Stephen Hawking.

Selling more than a million copies, the book was for many people a first close encounter with the deeply weird world of superstring theory. In that volume, and in his later gig hosting a PBS miniseries based on the bestseller, Greene introduced quantum mechanics and Einstein’s theories of special and general relativity before heading off into the multi-dimensional realms of Calabi-Yau manifolds and super-symmetric string theory. In his new book, Greene takes us down the rabbit hole yet again, this time setting a course for the terra incognita of parallel universes, hidden worlds, alternate realities, holographic projections, and multiverse simulations. Greene likes to drop you into the middle of the action first and then explain the backstory (and sometimes it does feel like a full-scale intellectual invasion is happening), but he has an elegant knack for anticipating questions and immediately dealing with any confusion or objections.
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Greene describes nine different theories which imply that we are living in a vast multiverse. He’s pretty confident that some of them are true, but less sanguine about others (chances are small that we’re living in a vast simulation with other universes running as parallel processes on some higher-order cosmic computer). One important takeaway, though, is what he calls the “Copernican pattern”: over the past 500 years, each new cosmological discovery has removed us from being in a privileged position in the universe. First, we realized that the sun, not the earth, was the center of the solar system; then we discovered that our sun is just an ordinary star in the Milky Way, and that our galaxy is just an ordinary galaxy among about 80 billion or so that are visible. Greene takes this further: what we call our universe is only one piece of an unbelievably vast multiverse.

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Excerpt from Brian Greene's new book 'The Hidden Reality'

Chapter 1

The Bounds of Reality

On Parallel Worlds

If, when I was growing up, my room had been adorned with only a single mirror, my childhood daydreams might have been very different. But it had two. And each morning when I opened the closet to get my clothes, the one built into its door aligned with the one on the wall, creating a seemingly endless series of reflections of anything situated between them. It was mesmerizing. I delighted in seeing image after image populating the parallel glass planes, extending back as far as the eye could discern. All the reflections seemed to move in unison - but that, I knew, was a mere limitation of human perception; at a young age I had learned of light's finite speed. So in my mind's eye, I would watch the light's round-trip journeys. The bob of my head, the sweep of my arm silently echoed between the mirrors, each reflected image nudging the next. Sometimes I would imagine an irreverent me way down the line who refused to fall into place, disrupting the steady progression and creating a new reality that informed the ones that followed. During lulls at school, I would sometimes think about the light I had shed that morning, still endlessly bouncing between the mirrors, and I'd join one of my reflected selves, entering an imaginary parallel world constructed of light and driven by fantasy. It was a safe way to break the rules.

To be sure, reflected images don't have minds of their own. But these youthful flights of fancy, with their imagined parallel realities, resonate with an increasingly prominent theme in modern science - the possibility of worlds lying beyond the one we know. This book is an exploration of such possibilities, a considered journey through the science of parallel universes.

Universe and Universes

There was a time when "universe" meant "all there is." Everything. The whole shebang. The notion of more than one universe, more than one everything, would seemingly be a contradiction in terms. Yet a range of theoretical developments has gradually qualified the interpretation of "universe." To a physicist, the word's meaning now largely depends on context. Sometimes "universe" still connotes absolutely everything. Sometimes it refers only to those parts of everything that someone such as you or I could, in principle, have access to. Sometimes it's applied to separate realms, ones that are partly or fully, temporarily or permanently, inaccessible to us; in this sense, the word relegates ours to membership in a large, perhaps infinitely large, collection.

With its hegemony diminished, "universe" has given way to other terms introduced to capture the wider canvas on which the totality of reality may be painted. Parallel worlds or parallel universes or multiple universes or alternate universes or the metaverse, megaverse, or multiverse - they're all synonymous and they're all among the words used to embrace not just our universe but a spectrum of others that may be out there.

You'll notice that the terms are somewhat vague. What exactly constitutes a world or a universe? What criteria distinguish realms that are distinct parts of a single universe from those classified as universes of their own? Perhaps someday our understanding of multiple universes will mature sufficiently for us to have precise answers to these questions. For now, we'll use the approach famously applied by Justice Potter Stewart in attempting to define pornography. While the U.S. Supreme Court wrestled mightily to delineate a standard, Stewart declared simply and forthrightly, "I know it when I see it."

In the end, labeling one realm or another a parallel universe is merely a question of language. What matters, what's at the heart of the subject, is whether there exist realms that challenge convention by suggesting that what we've long thought to be the universe is only one component of a far grander, perhaps far stranger, and mostly hidden reality.

During the last half century, science has provided ample ways in which this possibility might be realized.
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Varieties of Parallel Universes

A striking fact (it's in part what propelled me to write this book) is that many of the major developments in fundamental theoretical physics - relativistic physics, quantum physics, cosmological physics, unified physics, computational physics - have led us to consider one or another variety of parallel universe. Indeed, the chapters that follow trace a narrative arc through nine variations on the multiverse theme. Each envisions our universe as part of an unexpectedly larger whole, but the complexion of that whole and the nature of the member universes differ sharply among them. In some, the parallel universes are separated from us by enormous stretches of space or time; in others, they're hovering millimeters away; in others still, the very notion of their location proves parochial, devoid of meaning. A similar range of possibility is manifest in the laws governing the parallel universes. In some, the laws are the same as in ours; in others, they appear different but have shared a heritage; in others still, the laws are of a form and structure unlike anything we've ever encountered. It's at once humbling and stirring to imagine just how expansive reality may be.

Some of the earliest scientific forays into parallel worlds were initiated in the 1950s by researchers puzzling over aspects of quantum mechanics, a theory developed to explain phenomena taking place in the microscopic realm of atoms and subatomic particles. Quantum mechanics broke the mold of the previous framework, classical mechanics, by establishing that the predictions of science are necessarily probabilistic. We can predict the odds of attaining one outcome, we can predict the odds of another, but we generally can't predict which will actually happen. This well-known departure from hundreds of years of scientific thought is surprising enough. But there's a more confounding aspect of quantum theory that receives less attention. After decades of closely studying quantum mechanics, and after having accumulated a wealth of data confirming its probabilistic predictions, no one has been able to explain why only one of the many possible outcomes in any given situation actually happens. When we do experiments, when we examine the world, we all agree that we encounter a single definite reality. Yet, more than a century after the quantum revolution began, there is no consensus among the world's physicists as to how this basic fact is compatible with the theory's mathematical expression.

"The Hidden Reality" - an Interview with Brian Greene

Todd Miller ................ As I type this, I am aware that, somewhere in the cosmos, another me may be typing an introduction to his interview with the Brian Greene of his respective universe. In-fact, there may be an infinite number of us, typing away - perhaps in precisely the same way - perhaps slightly differently. The math suggests that we are not alone, and our universes may not be alone either.

Parallel universes and the theories that predict their existence are the subjects of Brian Greene's latest book, The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos. Greene is a professor of physics and mathematics at Columbia University, and is recognized for a number of groundbreaking discoveries in his field of superstring theory. His previous books include The Fabric of the Cosmos and The Elegant Universe, a finalist for the Pulitzer Prize and the inspiration for the companion Emmy and Peabody award-winning NOVA series "The Elegant Universe."

Todd: Can you talk about when you first knew you wanted to be a physicist?

Brian: Sure. I was a teenager, and I had one of those moments - I think most teenagers do - where you begin to wonder why am I here. What's it all about? What's the point of it all, that kinda thing.

The immediate next thought for me was that since we humans have been around for a while, people must have been thinking about these very questions for, in some sense, hundreds or thousands of years. So if people have been thinking about this for thousands of years, if there were an answer, we would have it.

The fact that we didn't have an answer led me to suspect that maybe the attempt to find an answer is misguided at some level. Maybe what we really need to be doing is trying to understand the question better. Not why am I here, but how is it that I'm here? How is it that there is a universe? How is it that a universe could give rise to the stars and galaxies, planets and people that we see?

That really led me to sort of shift my focus to trying to understand in some sense the nature of reality rather than trying to answer sort of the more perplexing questions of existence. Of course physics is a subject that focuses on those very questions of the true nature of reality.

Todd: Is it fair to say that there was a philosophical path that drove you to science?

Brian: I think you could probably say that. It certainly went hand in hand, I should say, with a certain joy that I found in doing mathematical calculations that I can trace that back to many years even before when I was quite young, and my dad taught me the very basic operations of arithmetic.

I was five years old or so, and he just set me going, and I recall I'd spend many a weekend multiplying these huge numbers together. I had big sheets of construction paper just sort of for the joy of seeing how the numbers would fit together and combine into new patterns of numbers.

I had already a scientific mathematical orientation, which naturally melded with, if you will, the philosophical interest to set me on a direction that I've been on ever since.

Todd: Can we talk about parallel universes?

Brian: Sure.

Todd: Let me try to reality check this with you. As I understand it, the various theories that describe how everything works, including general relativity, quantum mechanics and string theory, all allow for the possibilities of parallel universes, right?

Brian: That's right.

Todd: So far, so good. In some of these universes, you and I might be having this conversation maybe in exactly the same way and maybe a bit differently.

Brian: Right.

Todd: Am I correct in understanding that the pathways to the various parallel universes through these theories are different? For example, with general relativity, as I understand it, parallel universes can happen because the theory allows for an infinite universe, but there's only a finite way that stuff can be organized, so sooner or later our universe is bound to repeat.

Brian: Yep, all right on target.

Todd: This could be a really short interview.

Brian: I can fill in any details if you like.

Todd: This is actually an elaborate run up to a big question that I hope you can help me with. To continue a bit further down this road, in quantum mechanics, as I understand it, the path to parallel universes is that the fact that an action potentially has multiple outcomes means that you need multiple universes to park all of those outcomes, right?

Brian: That's correct, too.

Todd: So if you have 1,000 different possible outcomes, you need 1,000 different universes.

Brian: In one particular approach to quantum mechanics, which is the one that comes from that guy who I described, Hugh Everett, who initiated that idea in the late '50s and people have been developing ever since.

There are other approaches to quantum physics which do not require every outcome to happen. There are other approaches to quantum mechanics which attempt to say only one really happens, and those approaches try to introduce new mathematics to make that happen, to bridge from the range of possibilities to only one unique outcome.

That approach isn't convincing too many of us. It's a possibility, but as I described in the book, even the Many Worlds approach to quantum mechanics is not convincing too many people. I'm pretty out front - if you have read that chapter - on explaining its potential weaknesses, its Achilles heels.

The bottom line is as of today we do not know how to navigate from the fuzzy, hazy, probabilistic description of reality that comes from the basic laws of quantum physics. How do you navigate from that to the definite reality that we see when we look around or that we see in our detectors when we do an experiment? We see one definite outcome.

The Many Worlds approach is one proposal for how to bridge that gap, and as you say, if it's correct, then every outcome would happen and every outcome would need to be parked in its own universe.

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Todd: In string theory we have yet another way to get to multiple universes, right? You have a braneworld within which our universe resides, and you can potentially have multiple brane worlds, right?

Brian: That's exactly right. One of the big developments in the late '90s through to today is that string theory is not only a theory that contains strings. It also contains these membrane-like objects which we call branes because they can have not only two dimensions - your typical image of a membrane - but they can have three dimensions, which we call a three-brane, co-opting the brane part of membrane and changing the number in front to indicate how many dimensions the brane has.

When you study the math of these membranes, you find that we very well could be living on and in one of these three branes, one of these slabs, if you will, with other slabs, other universes out there. That is a direct consequence of the mathematics of these entities.

Todd: Branes can be infinite, right?

Brian: Yes.

Todd: So here's my big question: can you have a multiverse on a single brane?

Brian: Absolutely. As you say, if a brane is infinite, then all of the discussion that is in, I guess Chapter 2 of the book, about what happens if there's infinite space, would apply, as you're saying, to that brane. You could have a variety of different universes coming from the different branes, and on each of those branes there could be a variety of different universes coming from the infinite expanse.

Todd: It turns my head completely inside out and backwards, but in a good way.

Brian: Everything you're saying is right on target.

Todd: Can we talk a little about where string theory came from?

Brian: Yep.

Todd: I understand that for a long time physicists used general relativity to study big things like stars and quantum mechanics to study small things like subatomic particles, but when a situation called for the study of a big thing in a small place like the Big Bang, the two theories just couldn't work together, right?

Brian: Yep, that's exactly right. The math fell apart. The math of quantum mechanics and the math of general relativity , when they confront one another they are ferocious antagonists and the equations don't work.

Todd: Was it the prediction of black holes that first forced the issue to call out for some way to reconcile general relativity and quantum mechanics?

Brian: Is it the first? It's a good historical question, which I don't know if it was the first time that people really started to worry about this. Certainly by the late '40s and early '50s there was definitely a recognition that the need to put gravity and quantum mechanics together was a significant one.

I'm pretty certain if you were to speak to a historian of physics that you would find that even before those concrete examples that I like to use in order to help the reader ground the need for putting gravity and quantum mechanics together in a real world, real universe context, the Big Bang or black holes, people realize that once quantum mechanics came on line in the 1920s and 1930s, quantum mechanics really ultimately speaking to a framework that should apply to everything. It should apply to every force of nature.

Even if one wasn't thinking about black holes and the Big Bang and just thinking quantum mechanically, you'd want to try to bring general relativity into this framework so that you would have a complete theory, not one that was segregated. When it comes to black holes and the Big Bang, sure, now it becomes more concrete, but I think even theoretically people knew this was an issue.

Todd: I'm getting the sense from your book and also the NOVA series that things are trendy in physics like anything else and, for a while, unification and the theory of everything just wasn't really in vogue. Einstein tried to do it, and it didn't work out. Physicists latched onto quantum mechanics and charged off in that direction, right?

Brian: Yep, that's exactly right. It is the case, as you say, like in many other fields there are areas in physics that are hot for a period of time and everybody wants to work on it, and then they may go cool for a while. I think that's the nature of human exploration.

The thing is, certain problems don't attract attention at a given moment in time in a given historical episode, not only because they're out of fashion, but also because they're just so hard and nobody has any good ideas that it just doesn't seem fruitful to pursue it further.

That's really the case with Einstein and the unified theory. Everybody knew that that was an important goal. Nobody had any really good ideas on how to pursue it, and that's why Einstein was kinda left out in the cold when he was pursuing the unified theory.

What happened in the '60s and '70s was that finally some ideas came on line. Once there are ideas, people were game to try to make progress. It was not so much a fad issue as opposed to nobody could figure out what to do back in Einstein's time.

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Todd: I guess if Einstein can't do it, then who can?

Brian: Well, that certainly is intimidating. If Einstein were here today, he would be in the thick of it, and it would make perfect sense that now that we have some concrete tools to make progress, he'd no longer be alone in this journey.

Todd: Since we're on an Einstein thread, I'd like to pursue this a bit. I've got a question about the cosmological constant. My probably oversimplified understanding is that the cosmological constant was a fudge factor that Einstein introduced into his general theory of relativity because he disagreed with what his math was telling him, which was that the universe was expanding. Had he trusted his math, he would have predicted the expanding universe a decade before Hubble observed it, right?

Brian: Yep.

Todd: Can you talk a bit more about the story with the cosmological constant and why the story doesn't really end there?

Brian: Sure. Einstein spent ten long years trying to figure out how the force of gravity works. Newton had given us an equation for gravity in the late 1600s that is very good at making predictions about how the planet should move, how the moon should move, all under the influence of gravity, but Newton left out a big part of the story, which is how is gravity transmitted from place to place. How does the sun transmit gravity across the emptiness of space, the 93 million miles that separates us? How does gravity get from there to here?

Einstein tries to fix this problem and in so doing doesn't just fill in a gap in the Newtonian picture. He comes to a whole new version of gravity, his general theory of relativity, this monumental new view of space and time, or space in time, warp, and curve to communicate the force of gravity.

That's great, triumphant, but then he sits down and applies this new mathematical theory of gravity, not to the earth, the sun, the galaxy, but to the whole thing, the universe, the observable universe and comes to what he considered a very unpalatable conclusion, which is that math shows that the universe can't stand still. The universe has to be either expanding or contracting.

That was so at odds with what everybody thought. You look up in the sky and it looks on the larger scale, but nothing's moving. Nothing's changing. He was very distraught that his ten-year-long odyssey led to a theory that made a prediction that seemed blatantly wrong.

He went back to the math and reconsidered his equations a little bit more fully and found that there was a way in which you could easily modify the equations so that they would no longer imply that the universe was expanding or contracting.

This modification as you describe is called the cosmological constant. It's one more term in the equations. What does it do? Well, if you want a static situation - the example I use in the book is if you have a tug of war and you want it to be static, you need both sides to have equal but opposite pull, equal but opposite forces that will cancel each other.

The goal for Einstein in seeking a static universe was to counterbalance the attractive pull of gravity. Gravity pulls inward. That's the force that's most relevant in the largest scales of the cosmos. If it pulls inward, to balance it, you need a force to push it outward, and that's what the cosmological constant does. It's an outward-pushing version of gravity that can counterbalance the usual inward attractive pull of gravity giving rise to a static universe.

With this mathematical realization, Einstein was a pretty happy camper. All of a sudden his theory was not in conflict with what everyone believed to be the case about the universe, that it's static, eternal, unchanging.

Ten years later, Edwin Hubble and his coworkers, through their astronomical observations, showed that the universe is expanding. It's not static. There's no need to balance gravity because the universe is not balanced. It's actually dynamic and changing.

Einstein is reported to have said that this was a blunder to have modified the equations, and he tossed the cosmological constant into the garbage can. You're right. The story does not stop there because 80 years later, teams of astronomers are measuring the expansion of space to try to figure out the degree to which the expansion is slowing down over time.

Everyone knew that since gravity is attractive it pulls things together and the expansion should slow over time like when you throw a ball up in the air. It goes up, but goes up slower and slower because gravity pulls it back.

Shockingly they find that the universe is not slowing down in its expansion. It is speeding up. If it's speeding up, that means you need an outward push, something that goes the opposite to gravity and that is exactly what the cosmological constant is able to do. It acts opposite to gravity.

The astronomers brought back in the cosmological constant, not finely adjusted to exactly cancel attractive gravity, but having a value that would overwhelm attractive gravity giving rise to an outward push that can explain the observations of a universe that's not just expanding but speeding up in its expansion. That's the story.

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Todd: So there are not one, but potentially three stupendous discoveries or predictions that come out of the general theory of relativity. There's the first that we know and love. There's the second, which had he left the cosmological constant out, he would have predicted the expanding universe a decade before it was observed. And had he left it in, he would have discovered that the universe is expanding more rapidly.

Brian: That's right.

Todd: In "The Elegant Universe" NOVA series, there's a scene where Leonard Susskind talks about staring at his string equation and seeing a vibrating string. I'm astounded by the way physicists can see the universe in math. Is there a way for you to describe to a layperson how a Leonard Susskind sees vibrating strings in math or how Veneziano recognized the strong force in a 200-year-old formula?

Brian: Well, I think there's two parts to the answer. The more general answer is what physicists do is try to find patterns, patterns in data or patterns in their equations. In essence what we try to do is line up the patterns in our mathematics with the patterns that we observe.

All mathematics is is a language that is well tuned, finely honed, to describe patterns; be it patterns in a star, which has five points that are regularly arranged, be it patterns in numbers like 2, 4, 6, 8, 10 that follow very regular progression. Math is very good at being able to describe those kinds of patterns.

What Leonard, for instance, is saying in that specific example is when you look at the mathematical equations that he was writing on his blackboard, he could see certain patterns imbedded in the mathematics. Those patterns were very directly describable in terms of a string as it vibrates because as a string vibrates, there are very definite patterns.

If you just think of a violin string, it can sort of vibrate where the whole string goes up and down in unison, or it can vibrate a little bit more actively where half goes up while the other half goes down and they're vibrating sort of side by side if you know what I'm saying where the left side is going up while the right is down, the right is up, the left is down.

You can do a more complicated version of that where you've got the middle of the string is going down and the two sides are going up and vice versa.

All those patterns, those very simple pictures of how a string can vibrate, translate into mathematical quantities. Leonard could see those mathematical quantities in the mathematical equation. He said, "Oh wow, those mathematical quantities are falling right into the pattern that I'm familiar with from looking at a vibrating filament, therefore this math is probably describing a vibrating filament."

Todd: So much of this is about recognizing the patterns in the math.

Brian: Completely. That's exactly what it is. For instance, when a string vibrates, you know that there's a main tone - like a violin string has a C - but then there are overtones, and that's what gives a violin its richness of timbre. A piano, when you play a C, there are different overtones, but again it's all coming from a vibrating string, and the possible ways in which that vibrating string can be shaped.

What Leonard could see in the mathematical equations were all the overtones, and because he could see the overtones, he could see the different representations mathematically of the shape of a vibrating string, he concluded that the math must be describing that kind of an object.

Todd: Did I read somewhere that you studied piano somewhere along the line in your career?

Brian: Yeah, not much, but yes I did.

Todd: Do you think that might have anything to do with your attraction to string theory?

Brian: No, none whatsoever, I don't think. I will say that music as we're all familiar with, again, is another way that pattern gets represented. What makes a Beethoven symphony spectacular, what makes a Brahms rhapsody spectacular is that the patterns are wondrous. The patterns of the notes are both wondrous, appealing, moving, emotive. Again, all you do with your ear is sense the patterns of the notes.

In a way, mathematics is just a different way of representing those kinds of patterns. It represents it in a way that, for reasons that we are still baffled by, the patterns that math is very good at describing seem to emerge in nature in very natural ways. That's why math is so good at describing the natural world.

Todd: Math is the language of nature?

Brian: It's a language of pattern, which for reasons that we don't know appears to be the language of nature. It's not impossible that one day we'll find a better language for describing nature that's not mathematical. It's not impossible. I describe that a little bit toward the end of the book.
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Todd: Do I understand correctly that one of the attractions of physicists to string theory is its elegance as compared with something like the standard model?

Brian: Yes, that certainly is an appealing quality.

Todd: My limited understanding is the standard model potentially you have to update it as new particles are discovered. String theory potentially you can use the same elegant formula as is to describe everything.

Brian: Yes, if string theory is right. String theory could be wrong. It has not been experimentally confirmed, and that's important to underscore. What leaves people dissatisfied with the standard model is that it's an enormously long equation which has within it 57 distinct particle species. Each one you have to input into the mathematics its mass, its charge, its properties, and the nuclear forces. It just feels ungainly.

We can't help but think that there's got to be a more compact - a more compact and a more efficient, more effective, more unified description of the particles of nature that doesn't feel like you're simply adding particle upon particle upon particle every time you find a new one in an experiment.

As you say, string theory is a theory that, at least on paper, has the capacity to do just that. If string theory is right - it's a big "if" - then different particles are different string vibrations. You don't really have to update the theory if you find new particles. If the theory's right, then every particle you find will be corresponding to some particular vibrational pattern of the string.

Todd: By comparison, how long is the actual string formula?

Brian: The first thing I should say is many of us believe we've yet to really find the full string equation. We believe that we have approximate equations, but whether that is the full equation, we're not sure.

The candidate equations that we have for the mathematics of string theory comfortably fit on a single line of a piece of paper. In analyzing those equations you have to do an enormous amount of complex calculation that then takes pages and pages and pages and fills thousands of journal pages even as we speak here today. The starting point is a pretty simple equation, much simpler than the equation of the standard model.

Todd: So potentially there's one equation that fits neatly on one line that potentially describes everything.

Brian: That's right.

Todd:You talked about proving or testing the string theory. In your NOVA series, some of your colleagues said that if you can't test it in the way that we test normal theories, it's not science, it's philosophy. Can you talk about testing string theory and about gravitons and sparticles?

Brian: First of all, they're absolutely right in the sense of there's no reason to believe string theory is right until you experimentally confirm it. There's just no way around it. Nothing I've ever said or really anything my colleagues would say would ever disagree with that.

The question then is: are there ways in which you can test string theory? String theory is a huge challenge to test because, as we're saying, it really comes into its own in pretty extreme realms, the Big Bang, black holes, and so forth.

There are potential indirect tests that wouldn't prove the theory right, but if they gave positive outcomes would be pretty convincing - circumstantial evidence I should say - that we're heading in the right direction.

Some of the examples that you mentioned are right on target. They're a class of particles that string theory suggests should be in existence. They're called supersymmetric particles or sparticles for short.

They are partners to the known particles that no one has ever seen. We believe we haven't seen them because they're heavier than their known counterparts, particles like selectrons, which is a supersymmetric electron, a partner to electrons, squarks, partners of quarks, and so forth. The large Hadron Collider is looking for these supersymmetric particles, these sparticles. If they're found, it would be enormously exciting.

There's other possibilities of detecting extra dimensions through these missing energy signals that we were talking about where particles slam into each other and some debris is kicked out. It carries away energy, and if you have a missing energy signal, it would suggest that there are other dimensions out there beyond the ones that we know about here.

I've been working myself on the possibility of testing the string theory through astronomical observations. It's possible that string theory could have left imprints in the microwave background radiation, this heat left over from the Big Bang. We're looking for patterns in that heat temperature variations from one point in the sky to the other which if they fit a certain pattern would again be indirect evidence that a string theory is correct.

That's the best we can do today; try to amass a number of different experimental results that all point toward string theory being right. But there's no way that we can definitively at this moment make any statement one way or the other.

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Todd: I've got a question about practical applications. I understand that it's challenging or impossible to project practical applications of theoretical physics, but I seized on an example in your book. Can you talk about the role that general relativity plays in today's GPS?

Brian: The way the GPS system works is there are satellites in orbit around the earth. Those satellites need to be able to determine your position with great precision so that the little map in your GPS system in your car places you at the location that you're really residing at.

For those satellites to be able to do their job correctly they need very, very precise timing signals. They're basically bouncing light signals between you and the satellite to determine exactly where you are. The satellite measures tiny time differences between emission and absorption of the signals that are being sent back and forth.

General relativity tells us that because the satellite is in motion and because it is experiencing less gravity than it would if it was on the earth's surface, general relativity says that time on the satellite elapses at a different rate than it would otherwise.

If you don't take into account that effect of gravity and motion on time, the satellites will make a mistake. They will get your position wrong because their timing will be out of sync. That is a very concrete way in which the general theory of relativity affects something that we do use in our everyday lives.

Todd: If we don't factor general relativity into these clocks, if I'm driving from Las Vegas to L.A., I could end up in the Pacific Ocean.

Brian: That's exactly right. Very quickly these GPS systems would become completely inaccurate if they didn't take these corrections into account.

Todd: I have arrived at my last question, which is, in the course of your career what has surprised you most about the universe.

Brian: What has surprised me most about the universe? Well, I'll give you two answers. The most concrete one, the most shocking result that we found is in fact this accelerated expansion of space that we were talking about before - completely unexpected.

Most of us when we first encountered it said "come on, that can't possibly be true," and yet experiment after experiment is confirming that is true.

Speaking from a more global perspective, the most wondrous thing about science - maybe it's not the most surprising as of now because we're getting used to it - but the fact that mathematics is so good at describing things that are out there.

When I was - I think it was ninth grade - and I was taking my first physics class, the teacher gave us this problem, some simple problem of a ball that was attached to a piece of chewing gum that itself was attached to the ceiling, and someone lets the ball swing by the chewing gum. The goal was to figure out how the ball would move.

When I sat down and did those calculations, at the end of it, I got up from my desk, and I ran down to the hall to my father and said, "Can you believe it? Look at this formula." This mathematics that I just calculated on this piece of paper would really describe how that ball would swing. How powerful is that? I didn't get up and do the experiment. All I did was calculate. Math describes the world. That, to me, is still the most wondrous thing about all that we do in theoretical physics.

Todd: Everything potentially can be rendered into math.

Brian: So far that seems to be the case.

Todd: Another good reason for kids in the US to study and get their math and science scores up.

Brian: Yep, without a doubt.

Coast To Coast AM: Multiverse & Parallel Worlds 2-10-2011

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