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: 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...
GABRIELE VENEZIANO (CERN): We accidentally discovered string theory.
NARRATOR: ...the humble beginnings of a revolutionary idea.
LEONARD SUSSKIND (Stanford University): I was completely convinced it was going to say, "Susskind is the next Einstein."
JOSEPH LYKKEN (Fermilab): This seemed crazy to people.
LEONARD SUSSKIND: I was depressed, I was unhappy. The result was I went home and got drunk.
NARRATOR: Obsession drives scientists to pursue the Holy Grail of physics, but are they ready for what they discover? Step into the bizarre world of the Elegant Universe right now.
BRIAN GREENE: It's a little known secret but for more than half a century a dark cloud has been looming over modern science. Here's the problem: our understanding of the universe is based on two separate theories. One is Einstein's general theory of relativity?ªthat's a way of understanding the biggest things in the universe, things like stars and galaxies. But the littlest things in the universe, atoms and subatomic particles, play by an entirely different set of rules called, "quantum mechanics."
These two sets of rules are each incredibly accurate in their own domain but whenever we try to combine them, to solve some of the deepest mysteries in the universe, disaster strikes.
Take the beginning of the universe, the "big bang." At that instant a tiny nugget erupted violently. Over the next 14 billion years the universe expanded and cooled into the stars, galaxies and planets we see today. But if we run the cosmic film in reverse, everything that's now rushing apart comes back together, so the universe gets smaller, hotter and denser as we head back to the beginning of time.
As we reach the big bang, when the universe was both enormously heavy and incredibly tiny, our projector jams. Our two laws of physics, when combined, break down.
But what if we could unite quantum mechanics and general relativity and see the cosmic film in its entirety?
Well, a new set of ideas called "string theory" may be able to do that.
And if it's right, it would be one of the biggest blockbusters in the history of science. Someday, string theory may be able to explain all of nature, from the tiniest bits of matter to the farthest reaches of the cosmos, using just one single ingredient: tiny vibrating strands of energy called strings.
But why do we have to rewrite the laws of physics to accomplish this? Why does it matter if the two laws that we have are incompatible? Well, you can think of it like this. Imagine you lived in a city ruled not by one set of traffic laws, but by two separate sets of laws that conflicted with each other. As you can see it would be pretty confusing.
To understand this place, you'd need to find a way to put those two conflicting sets of laws together into one all-encompassing set that makes sense.
MICHAEL DUFF (University of Michigan): We work on the assumption that there is a theory out there, and it's our job, if we're sufficiently smart and sufficiently industrious, to figure out what it is.
STEVEN WEINBERG (University of Texas at Austin): We don't have a guarantee?ªit isn't written in the stars that we're going to succeed?ªbut in the end we hope we will have a single theory that governs everything.
BRIAN GREENE: But before we can find that theory, we need to take a fantastic journey to see why the two sets of laws we have conflict with each other. And the first stop on this strange trip is the realm of very large objects.
To describe the universe on large scales we use one set of laws, Einstein's general theory of relativity, and that's a theory of how gravity works. General relativity pictures space as sort of like a trampoline, a smooth fabric that heavy objects like stars and planets can warp and stretch.
Now, according to the theory, these warps and curves create what we feel as gravity. That is, the gravitational pull that keeps the earth in orbit around the sun is really nothing more than our planet following the curves and contours that the sun creates in the spatial fabric.
But the smooth, gently curving image of space predicted by the laws of general relativity is not the whole story. To understand the universe on extremely small scales, we have to use our other set of laws, quantum
mechanics. And as we'll see, quantum mechanics paints a picture of space so drastically different from general relativity that you'd think they were describing two completely separate universes.
To see the conflict between general relativity and quantum mechanics we need to shrink way, way, way down in size. And as we leave the world of large objects behind and approach the microscopic realm, the familiar picture of space in which everything behaves predictably begins to be replaced by a world with a structure that is far less certain.
And if we keep shrinking, getting billions and billion of times smaller than even the tiniest bits of matter?ªatoms and the tiny particles inside of them?ªthe laws of the very small, quantum mechanics, say that the fabric of space becomes bumpy and chaotic. Eventually we reach a world so turbulent that it defies common sense.
Down here, space and time are so twisted and distorted that the conventional ideas of left and right, up and down, even before and after, break down. There's no way to tell for certain that I'm here, or here or both places at once. Or maybe I arrived here before I arrived here.
In the quantum world you just can't pin everything down. It's an inherently wild and frenetic place.
WALTER H.G. LEWIN (Massachusetts Institute of Technology): The laws in the quantum world are very different from the laws that we are used to. And is that surprising? Why should the world of the very small, at an atomic level, why should that world obey the same kind of rules and laws that we are used to in our world, with apples and oranges and walking around on the street? Why would that world behave the same way?
BRIAN GREENE: The fluctuating jittery picture of space and time predicted by quantum mechanics is in direct conflict with the smooth, orderly, geometric model of space and time described by general relativity. But we think that everything, from the frantic dance of subatomic particles to the majestic swirl of galaxies, should be explained by just one grand physical principle, one master equation.
If we can find that equation, how the universe really works at every time and place will at last be revealed. You see, what we need is a theory that can cope with the very tiny and the very massive, one that embraces both quantum mechanics and general relativity, and never breaks down, ever.
For physicists, finding a theory that unites general relativity and quantum mechanics is the Holy Grail, because that framework would give us a single mathematical theory that describes all the forces that rule our universe. General relativity describes the most familiar of those forces: gravity. But quantum mechanics describes three other forces: the strong nuclear force that's responsible for gluing protons and neutrons together inside of atoms; electromagnetism, which produces light, electricity and magnetic attraction; and the weak nuclear force: that's the force responsible for radioactive decay.
Albert Einstein spent the last 30 years of his life searching for a way to describe the forces of nature in a single theory, and now string theory may fulfill his dream of unification.
For centuries, scientists have pictured the fundamental ingredients of nature?ªatoms and the smaller particles inside of them?ªas tiny balls or points. But string theory proclaims that at the heart of every bit of matter is a tiny, vibrating strand of energy called a string. And a new breed of scientist believes these miniscule strings are the key to uniting the world of the large and the world of the small in a single theory.
JOSEPH LYKKEN: The idea that a scientific theory that we already have in our hands could answer the most basic questions is extremely seductive.
S. JAMES GATES, JR.: For about 2,000 years, all of our physics essentially has been based on...essentially we were talking about billiard balls. The very idea of the string is such a paradigm shift, because instead of billiard balls, you have to use little strands of spaghetti.
BRIAN GREENE: But not everyone is enamored of this new theory. So far no experiment has been devised that can prove these tiny strings exist.
SHELDON LEE GLASHOW (Boston University): And let me put it bluntly. There are physicists and there are string theorists. It is a new discipline, a new?ªyou may call it a tumor?ªyou can call it what you will, but they have focused on questions which experiment cannot address. They will deny that, these string theorists, but it's a kind of physics which is not yet testable, it does not make predictions that have anything to do with experiments that can be done in the laboratory or with observations that could be made in space or from telescopes. And I was brought up to believe, and I still believe, that physics is an
experimental science. It deals with the results to experiments, or in the case of astronomy, observations.
BRIAN GREENE: From the start, many scientists thought string theory was simply too far out. And frankly, the strange way the theory evolved?ªin a series of twists, turns and accidents?ªonly made it seem more unlikely.
In the late 1960s a young Italian physicist, named Gabriele Veneziano, was searching for a set of equations that would explain the strong nuclear force, the extremely powerful glue that holds the nucleus of every atom together binding protons to neutrons. As the story goes, he happened on a dusty book on the history of mathematics, and in it he found a 200-year old equation, first written down by a Swiss mathematician, Leonhard Euler. Veneziano was amazed to discover that Euler's equations, long thought to be nothing more than a mathematical curiosity, seemed to describe the strong force.
He quickly published a paper and was famous ever after for this "accidental" discovery.
GABRIELE VENEZIANO (CERN): I see occasionally, written in books, that, uh, that this model was invented by chance or was, uh, found in the math book, and, uh, this makes me feel pretty bad. What is true is that the function was the outcome of a long year of work, and we accidentally discovered string theory.
BRIAN GREENE: However it was discovered, Euler's equation, which miraculously explained the strong force, took on a life of its own. This was the birth of string theory. Passed from colleague to colleague, Euler's equation ended up on the chalkboard in front of a young American physicist, Leonard Susskind.
LEONARD SUSSKIND: To this day I remember the formula. The formula was... and I looked at it, and I said, "This is so simple even I can figure out what this is."
BRIAN GREENE: Susskind retreated to his attic to investigate. He understood that this ancient formula described the strong force mathematically, but beneath the abstract symbols he had caught a glimpse of something new.
LEONARD SUSSKIND: And I fiddled with it, I monkeyed with it. I sat in my attic, I think for two months on and off. But the first thing I could
see in it, it was describing some kind of particles which had internal structure which could vibrate, which could do things, which wasn't just a point particle. And I began to realize that what was being described here was a string, an elastic string, like a rubber band, or like a rubber band cut in half. And this rubber band could not only stretch and contract, but wiggle. And marvel of marvels, it exactly agreed with this formula.
I was pretty sure at that time that I was the only one in the world who knew this.
BRIAN GREENE: Susskind wrote up his discovery introducing the revolutionary idea of strings. But before his paper could be published it had to be reviewed by a panel of experts.
LEONARD SUSSKIND: I was completely convinced that when it came back it was going to say, "Susskind is the next Einstein," or maybe even, "the next Newton." And it came back saying, "this paper's not very good, probably shouldn't be published."
I was truly knocked off my chair. I was depressed, I was unhappy. I was saddened by it. It made me a nervous wreck, and the result was I went home and got drunk.
BRIAN GREENE: As Susskind drowned his sorrows over the rejection of his far out idea, it appeared string theory was dead.
Meanwhile, mainstream science was embracing particles as points, not strings. For decades, physicists had been exploring the behavior of microscopic particles by smashing them together at high speeds and studying those collisions. In the showers of particles produced, they were discovering that nature is far richer than they thought.
SHELDON LEE GLASHOW: Once a month there'd be a discovery of a new particle: the Rho meson, the Omega particle, the B particle, the B1 particle, the B2 particle, Phi, Omega...more letters were used than exist in most alphabets. It was a population explosion of particles.
STEVEN WEINBERG: It was a time when graduate students would run through the halls of a physics building saying they discovered another particle, and it fit the theories. And it was all so exciting.
BRIAN GREENE: And in this zoo of new particles, scientists weren't just discovering building blocks of matter. Leaving string theory in the
dust, physicists made a startling and strange prediction: that the forces of nature can also be explained by particles.
Now, this is a really weird idea, but it's kind of like a game of catch in which the players like me and me are particles of matter. And the ball we're throwing back and forth is a particle of force. It's called a messenger particle.
For example, in the case of magnetism, the electromagnetic force?ªthis ball?ªwould be a photon. The more of these messenger particles or photons that are exchanged between us, the stronger the magnetic attraction. And scientists predicted that it's this exchange of messenger particles that creates what we feel as force. Experiments confirmed these predictions with the discovery of the messenger particles for electromagnetism, the strong force and the weak force.
And using these newly discovered particles scientists were closing in on Einstein's dream of unifying the forces. Particle physicists reasoned that if we rewind the cosmic film to the moments just after the big bang, some 14 billion years ago when the universe was trillions of degrees hotter, the messenger particles for electromagnetism and the weak force would have been indistinguishable. Just as cubes of ice melt into water in the hot sun, experiments show that as we rewind to the extremely hot conditions of the Big Bang, the weak and electromagnetic forces meld together and unite into a single force called "the electroweak."
And physicists believe that if you roll the cosmic film back even further, the electroweak would unite with the strong force in one grand "super-force." Although that has yet to be proven, quantum mechanics was able to explain how three of the forces operate on the subatomic level.
SHELDON LEE GLASHOW: And all of a sudden we had a consistent theory of elementary particle physics, which allows us to describe all of the interactions?ªweak, strong and electromagnetic?ªin the same language. It all made sense, and it's all in the textbooks.
STEVEN WEINBERG: Everything was converging toward a simple picture of the known particles and forces, a picture which eventually became known as the "Standard Model." I think I gave it that name.
BRIAN GREENE: The inventors of the Standard Model, both the name and the theory, were the toasts of the scientific community, receiving Nobel
Prize after Nobel Prize. But behind the fanfare was a glaring omission. Although the standard model explained three of the forces that rule the world of the very small, it did not include the most familiar force, gravity.
Overshadowed by the Standard Model, string theory became a backwater of physics.
GABRIELE VENEZIANO: Most people in our community lost, completely, interest in string theory. They said, "Okay, that was a very nice elegant thing but had nothing to do with nature."
S. JAMES GATES, JR.: It's not taken seriously by much of the community, but the early pioneers of string theory are convinced that they can smell reality and continue to pursue the idea.
BRIAN GREENE: But the more these diehards delved into string theory the more problems they found.
JOSEPH LYKKEN: Early string theory had a number of problems. One was that it predicted a particle which we know is unphysical. It's what's called a "tachyon," a particle that travels faster than light.
JOHN H. SCHWARZ (California Institute of Technology): There was this discovery that the theory requires ten dimensions, which is very disturbing, of course, since it's obvious that that's more than there are.
CUMRUN VAFA (Harvard University): It had this massless particle which was not seen in experiments.
MICHAEL B. GREEN: So these theories didn't seem to make sense.
JOSEPH LYKKEN: This seemed crazy to people.
CUMRUN VAFA: Basically, string theory was not getting off the ground.
JOSEPH LYKKEN: People threw up their hands and said, "This can't be right."
BRIAN GREENE: By 1973, only a few young physicists were still wrestling with the obscure equations of string theory. One was John Schwarz, who was busy tackling string theory's numerous problems, among them a mysterious massless particle predicted by the theory but never seen
in nature, and an assortment of anomalies or mathematical inconsistencies.
JOHN H. SCHWARZ: We spent a long time trying to fiddle with the theory. We tried all sorts of ways of making the dimension be four, getting rid of these massless particles and the tachyons and so on, but it was always ugly and unconvincing.
BRIAN GREENE: For four years, Schwarz tried to tame the unruly equations of string theory, changing, adjusting, combining and recombining them in different ways. But nothing worked. On the verge of abandoning string theory, Schwarz had a brainstorm: perhaps his equations were describing gravity. But that meant reconsidering the size of these tiny strands of energy.
JOHN H. SCHWARZ: We weren't thinking about gravity up 'til that point. But as soon as we suggested that maybe we should be dealing with a theory of gravity, we had to radically change our view of how big these strings were.
BRIAN GREENE: By supposing that strings were a hundred billion billion times smaller than an atom, one of the theory's vices became a virtue.
The mysterious particle John Schwarz had been trying to get rid of now appeared to be a graviton, the long sought after particle believed to transmit gravity at the quantum level.
String theory had produced the piece of the puzzle missing from the standard model. Schwarz submitted for publication his groundbreaking new theory describing how gravity works in the subatomic world.
JOHN H. SCHWARZ: It seemed very obvious to us that it was right. But there was really no reaction in the community whatsoever.
BRIAN GREENE: Once again string theory fell on deaf ears. But Schwarz would not be deterred. He had glimpsed the Holy Grail. If strings described gravity at the quantum level, they must be the key to unifying the four forces. He was joined in this quest by one of the only other scientists willing to risk his career on strings, Michael Green.
MICHAEL B. GREEN (University of Cambridge): In a sense, I think, we had a quiet confidence that the string theory was obviously correct, and it didn't matter much if people didn't see it at that point. They would see it down the line.