NARRATOR: Now, on NOVA, take a thrill ride into a world stranger than science fiction, where you play the game by breaking some rules, where a new view of the universe pushes you beyond the limits of your wildest imagination. This is the world of "string theory," a way of describing every force and all matter from an atom to earth, to the end of the galaxies?ªfrom the birth of time to its final tick, in a single theory, a "Theory of Everything." Our guide to this brave new world is Brian Greene, the bestselling author and physicist.
BRIAN GREENE (Columbia University): And no matter how many times I come here, I never seem to get used to it.
NARRATOR: Can he help us solve the greatest puzzle of modern physics?ªthat our understanding of the universe is based on two sets of laws that don't agree?
NARRATOR: Resolving that contradiction eluded even Einstein, who made it his final quest. After decades, we may finally be on the verge of a breakthrough. The solution is strings, tiny bits of energy vibrating like the strings on a cello, a cosmic symphony at the heart of all reality. But it comes at a price: parallel universes and 11 dimensions, most of which you've never seen.
BRIAN GREENE: We really may live in a universe with more dimensions than meet the eye.
AMANDA PEET (University of Toronto): People who have said that there were extra dimensions of space have been labeled crackpots, or people who are bananas.
NARRATOR: A mirage of science and mathematics or the ultimate theory of everything?
S. JAMES GATES, JR. (University of Maryland): If string theory fails to provide a testable prediction, then nobody should believe it.
SHELDON LEE GLASHOW (Boston University): Is that a theory of physics, or a philosophy?
BRIAN GREENE: One thing that is certain is that string theory is already showing us that the universe may be a lot stranger than any of us ever imagined.
NARRATOR: Coming up tonight, the undeniable pull of strings.
BRIAN GREENE:The atmosphere was electric. String theory goes through a revolution of its own...
MICHAEL DUFF (University of Michigan): Five different string theories...
BRIAN GREENE: ...and reveals the new shape of things to come.
SAVAS DIMOPOULOS (Stanford University): Perhaps we live on a three-dimensional membrane.
BRIAN GREENE: Our universe might be like a slice of bread.
BRIAN GREENE: We're trapped on just a tiny slice of the higher dimensional universe.
ALAN GUTH (Massachusetts Institute of Technology): That's actually a problem.
NARRATOR: Watch the Elegant Universe right now.
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BRIAN GREENE: Imagine that we were able to control space or control time. The kinds of things that we'd be able to do would be amazing. I might be able to go from here...to here...to here...to here...and over to here in only an instant.
Now, we all think that this kind of trip would be impossible. And it probably is. But in the last few years, our ideas about the true nature of space and time have been going through some changes. And things that used to seem like science fiction are looking not-so-far-fetched.
It's all thanks to a revolution in physics called "string theory," which is offering a whole new perspective on the inner workings of the universe.
JOSEPH LYKKEN (Fermilab): String theory holds out the promise that we can really understand questions of why the universe is the way it is at the most fundamental level.
DAVID GROSS (University of California, Santa Barbara): String theory is really the Wild West of physics.
MICHAEL B. GREEN (University of Cambridge): This is an area of theoretical physics which is so radically different from anything that's been before.
BRIAN GREENE: This radical new theory starts with a simple premise: that everything in the universe, the Earth, these buildings, even forces like gravity and electricity, are made up of incredibly tiny, vibrating strands of energy called "strings."
And small as they are, strings are changing everything we thought we knew about the universe, especially our ideas about the nature of space.
To see how, let's first shrink all of space to a more manageable size. Imagine that the whole universe consisted of nothing more than my hometown, Manhattan. So now, just one borough of New York City makes up the entire fabric of space.
And just for kicks, let's also imagine that I'm the CEO of a large corporation with offices on Wall Street. And because time is money, I need to find the quickest route from my apartment, here in upper Manhattan to my offices in lower Manhattan.
Now, we all know that the shortest distance between two points is a straight line, but even if there's no traffic?ªa bit of a stretch even in our imaginary Manhattan?ªit'll still take us some amount of time to get there. By going faster and faster, we can reduce the travel time. But because nothing can go faster than the speed of light, there is a definite limit to how much time we can cut from our journey.
This Manhattan Universe fits with an old, classical vision of space, basically a flat grid that's static and unchanging. But when Albert Einstein looked at the fabric of space, he saw something completely different. He said that space wasn't static; it could warp and stretch.
And there could even be unusual structures of space called "wormholes." A wormhole is a bridge or tunnel that can link distant regions of space, in effect, a cosmic shortcut. In this kind of universe, my commute would be a New Yorker's dream.
But there's a hitch: to create a wormhole, you've got to rip or tear a hole in the fabric of space. But can the fabric of space really rip? Can this first step toward forming a wormhole actually happen? Well, you can't answer these questions on an empty stomach.
Turns out that by looking at my breakfast?ªcoffee and a doughnut?ªwe can get a pretty good sense of what string theory says about whether the fabric of space can tear.
Imagine that space is shaped like this doughnut. You might think that it would be very different from a region of space shaped like this coffee cup. But there's a precise sense in which the shape of the doughnut and the coffee cup are actually the same, just a little disguised. You see, they both have one hole. In the doughnut it's in the middle and in the coffee cup it's in the handle. That means we can change the doughnut into the shape of a coffee cup and back again without having to rip or tear the dough at all.
Okay, but suppose you want to change the shape of this doughnut into a very different shape, a shape with no holes. The only way to do that is to tear the doughnut like this and then re-shape it.
Unfortunately, according to Einstein's laws, this is impossible. They say that space can stretch and warp, but it cannot rip. Wormholes might exist somewhere fully formed, but you could not rip space to create a new one, over Manhattan or anywhere else. In other words, I can't
take a wormhole to work.
But now string theory is giving us a whole new perspective on space, and it's showing us that Einstein wasn't always right. To see how, let's take a much closer look at the spatial fabric.
If we could shrink down to about a millionth of a billionth of our normal size, we'd enter the world of quantum mechanics, the laws that control how atoms behave. It's the world of light and electricity and everything else that operates at the smallest of scales. Here, the fabric of space is random and chaotic. Rips and tears might be commonplace. But if they were, what would stop a rip in the fabric of space from creating a cosmic catastrophe?
Well, this is where the power of strings comes in. Strings calm the chaos. And as a single string dances through space, it sweeps out a tube. The tube can act like a bubble that surrounds the tear, a protective shield with profound implications. Strings actually make it possible for space to rip.
Which means that space is far more dynamic and changeable than even Albert Einstein thought. So does that mean that wormholes are possible? Will I ever be able to take a stroll on Everest, grab a baguette in Paris and still make it back to New York in time for my morning meeting?
It would be kind of cool, though it's still a very distant possibility.
But one thing that is certain is that string theory is already showing us that the universe may be a lot stranger than any of us ever imagined. For example, string theory says we're surrounded by hidden dimensions, mysterious places beyond the familiar three-dimensional space we know.
AMANDA PEET: People who've said that there were extra dimensions of space, have been labeled as, you know, crackpots or people who are bananas. I mean, what, do you think there are extra dimensions? Well, string theory really predicts it.
BRIAN GREENE: What we think of as our universe could just be one small part of something much bigger.
SAVAS DIMOPOULOS: Perhaps we live on a membrane, a three-dimensional membrane that floats inside higher dimensional space.
BRIAN GREENE: There could be entire worlds right next to us, but
NIMA ARKANI-HAMED (Harvard University): These other worlds would, in a very literal sense, be, be parallel universes. This isn't a particularly exotic or, or strange notion.
BRIAN GREENE: No wonder physics students are lining up to explore the strange world of string theory.
SHELDON LEE GLASHOW: String theory is very active. Things are happening. There are a lot of people doing it. Most of the young kids, given the choice, at a ratio of something like ten to one, they will go into string theory.
BRIAN GREENE: But strings weren't always this popular. The pioneers of string theory struggled for years, working alone on an idea that nobody else believed in. Here's the gist of it: for decades, physicists believed that the tiniest bits inside an atom were point particles. Flying around the outside were the electrons, and inside were protons and neutrons which were made up of quarks. But string theory says that what we thought were indivisible particles are actually tiny, vibrating strings.
BURT OVRUT (University of Pennsylvania): It's nothing really mystical. It's a really tiny string. It either closes in to its little circle or it has end points, but it's just a little string.
BRIAN GREENE: In the 1980s, the idea caught on, and people started jumping on the string bandwagon.
MICHAEL B. GREEN: Well, the fact that suddenly all these other people were working in the field had its advantages and its disadvantages. It was wonderful to see how rapidly the subject could develop now, because so many people were working on it.
BRIAN GREENE: One of the great attractions of strings is their versatility. Just as the strings on a cello can vibrate at different frequencies, making all the individual musical notes, in the same way, the tiny strings of string theory vibrate and dance in different patterns, creating all the fundamental particles of nature. If this view is right, then put them all together and we get the grand and beautiful symphony that is our universe.
What's really exciting about this is that it offers an amazing
possibility. If we could only master the rhythms of strings, then we'd stand a good chance of explaining all the matter and all the forces of nature, from the tiniest subatomic particles to the galaxies of outer space. This is the potential of string theory, to be a unified "Theory of Everything."
But, at first sight, in our enthusiasm for this idea, we seem to have gone too far. Because we didn't produce just one string theory, or even two?ªwe somehow managed to come up with five.
MICHAEL DUFF (University of Michigan): Five different string theories, each competing for the title of the Theory of Everything.
BURT OVRUT: And if there's going to be a "The Fundamental Theory of Nature," there ought to be one of them.
AMANDA PEET: I suppose a number of string theorists thought, "Ah, that's fantastic. That's wonderful. And maybe one of these will end up being the right theory of the world." And yet, there must have been a little nagging voice at the back of the head that said, "Well, why are there five?"
BRIAN GREENE: With five competing players, the stage of string theory was looking a little crowded. The five theories had many things in common. For example, they all involved vibrating strings, but their mathematical details appeared to be quite different. Frankly, it was embarrassing. How could this unified Theory of Everything come in five different flavors?
This was a case where more was definitely less. But then something remarkable happened. This is Ed Witten. He's widely regarded as one of the world's greatest living physicists, perhaps even Einstein's successor.
MICHAEL B. GREEN: Ed Witten is a very special person in the field. He clearly has a grasp, particularly of the underlying mathematical principles, which is far greater than most other people.
JOSEPH POLCHINSKI (University of California, Santa Barbara): Well, you know, we all think we're very smart; he's so much smarter than the rest of us.
BRIAN GREENE: In 1995, string theorists from all over the world gathered at the University of Southern California for their annual conference.
Ed Witten showed up at Strings 95 and rocked their world.
EDWARD WITTEN (Institute for Advanced Study): I was really trying to think of something that would be significant for the occasion. And actually, since five string theories was too many, I thought I would try to get rid of some of them.
BRIAN GREENE: To solve the problem, Witten constructed a spectacular new way of looking at string theory.
JOSEPH POLCHINSKI: Ed announced that he had thought about it, and moreover, he had solved it. He was going to tell us the solution to every string theory in every dimension, which was an enormous claim, but coming from Ed it was not so surprising.
BRIAN GREENE: The atmosphere was electric because, all of a sudden, string theory, which had been going through a kind of doldrums, was given an incredible boost, a shot in the arm.
LEONARD SUSSKIND (Stanford University): Ed Witten gave his famous lecture. And he said a couple of words that got me interested...and for the rest of the lecture...I got hooked up on the first few words that he said, and completely missed the point of his lecture.
NATHAN SEIBERG (Institute for Advanced Study): I remember I had to give the talk after him, and I was kind of embarrassed to.
JOSEPH LYKKEN: Ed Witten just blew everybody away.
BRIAN GREENE: Ed Witten blew everybody away because he provided a completely new perspective on string theory. From this point of view, we could see that there weren't really five different theories. Like reflections in a wall of mirrors, what we thought were five theories turned out to be just five different ways of looking at the same thing. String theory was unified at last.
Witten's work sparked a breakthrough so revolutionary that it was given it's own name, "M-theory," although no one really knows what the M stands for.
S. JAMES GATES, JR.: Aah, what is the M for?
BURT OVRUT: M-theory.
STEVEN WEINBERG (University of Texas at Austin): M-theory.
DAVID GROSS: M-theory.
JOSEPH LYKKEN: M-theory.
GARY HOROWITZ (Institute for Advanced Study): The M-theory.
STEVEN WEINBERG: M-theory is a theory...
BURT OVRUT: I don't actually know what the M stands for.
STEVEN WEINBERG: Well, the M has...
BURT OVRUT: I've heard many descriptions.
STEVEN WEINBERG: Mystery theory, magic theory...
JOSEPH LYKKEN: It's the Mother theory.
STEVEN WEINBERG: Matrix theory.
LEONARD SUSSKIND: Monstrous theory? I don't know what it...I don't know what Ed meant.
EDWARD WITTEN: M stands for magic, mystery or matrix, according to taste.
SHELDON LEE GLASHOW: I suspect that the "M" is an upside down "W" for "Witten."
EDWARD WITTEN: Some cynics have occasionally suggested that M may also stand for "murky," because our level of understanding of the theory is, in fact, so primitive. Maybe I shouldn't have told you that one.
BRIAN GREENE: Whatever the name, it was a bombshell. Suddenly everything was different.
JOSEPH LYKKEN: There was a lot of panic, if you like, realizing that big things were happening, and all of us not wanting to get left behind in this new revolution of string theory.
BRIAN GREENE: After Witten's talk, there was renewed hope that this one theory could be the theory to explain everything in the universe.
But there was also a price to pay.
Before M-theory, strings seemed to operate in a world with 10 dimensions. These included one dimension of time, the three familiar space dimensions, as well as six extra dimensions, curled up so tiny that they're completely invisible.
GARY HOROWITZ: Well, we think these extra dimensions exist because they come out of the equations of string theory. Strings need to move in more than three dimensions. And that was a shock to everybody, but then we learned to live with it.
BRIAN GREENE: But M-theory would go even further, demanding yet another spatial dimension, bringing the grand total to 11 dimensions.
BURT OVRUT: We know that there would have to be 11 dimensions for this theory to make sense. So there must be 11 dimensions. We only see three plus one of them. How is that possible?
BRIAN GREENE: For most of us, it's virtually impossible to picture the extra, higher dimensions: I can't. And it's not surprising. Our brains evolved sensing just the three spatial dimensions of everyday experience. So how can we get a feel for them?
One way is to go to the movies.
THEATER BRIAN GREENE: We're all familiar with the real world having three spatial dimensions. That is, anywhere I go, I can move left-right, back-forth, or up-down.
MOVIE SCREEN BRIAN (on screen): But in the movies, things are a bit different. Even though the characters on a movie screen look three-dimensional, they actually are stuck in just two dimensions. There is no back-forth on a movie screen, that's just an optical illusion.
To really move in the back-forth dimension, I'd have to step out of the screen. And sometimes moving into a higher dimension can be a useful thing to do.
MOVIE SCREEN BRIAN GREENE (in theater): So dimensions all have to do with the independent directions in which you can move. They're sometimes called "degrees of freedom."