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?ªin 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...it all started with an apple.
BRIAN GREENE: The triumph of Newton's equations come from the quest to understand the planets and the stars.
NARRATOR: And we've come a long way since.
BRIAN GREENE: Einstein gave the world a new picture for what the force of gravity actually is.
NARRATOR: Where he left off, string theorists now dare to go. But how close are they to fulfilling Einstein's dream? Watch The Elegant Universe right now.
BRIAN GREENE: Fifty years ago, this house was the scene of one of the greatest mysteries of modern science, a mystery so profound that today thousands of scientists on the cutting edge of physics are still trying to solve it.
Albert Einstein spent his last two decades in this modest home in Princeton, New Jersey. And in his second floor study Einstein relentlessly sought a single theory so powerful it would describe all the workings of the universe. Even as he neared the end of his life Einstein kept a notepad close at hand, furiously trying to come up with the equations for what would come to be known as the "Theory of Everything."
Convinced he was on the verge of the most important discovery in the history of science, Einstein ran out of time, his dream unfulfilled.
Now, almost a half century later, Einstein's goal of
unification?ªcombining all the laws of the universe in one, all-encompassing theory?ªhas become the Holy Grail of modern physics. And we think we may at last achieve Einstein's dream with a new and radical set of ideas called "string theory."
But if this revolutionary theory is right, we're in for quite a shock. String theory says we may be living in a universe where reality meets science fiction?ªa universe of eleven dimensions with parallel universes right next door?ªan elegant universe composed entirely of the music of strings.
But for all its ambition, the basic idea of string theory is surprisingly simple. It says that everything in the universe, from the tiniest particle to the most distant star is made from one kind of
ingredient?ªunimaginably small vibrating strands of energy called strings.
Just as the strings of a cello can give rise to a rich variety of musical notes, the tiny strings in string theory vibrate in a multitude of different ways making up all the constituents of nature. In other words, the universe is like a grand cosmic symphony resonating with all the various notes these tiny vibrating strands of energy can play.
String theory is still in its infancy, but it's already revealing a radically new picture of the universe, one that is both strange and beautiful. But what makes us think we can understand all the complexity of the universe, let alone reduce it to a single "Theory of Everything?"
We have R mu nu, minus a half g mu nu R?ªyou remember how this goes?ªequals eight Pi G T mu nu...comes from varying the Einstein-Hilbert action, and we get the field equations and this term. You remember what this is called?
No that's the scalar curvature. This is the ricci tensor. Have you been studying this at all?
No matter how hard you try, you can't teach physics to a dog. Their brains just aren't wired to grasp it. But what about us? How do we know that we're wired to comprehend the deepest laws of the universe? Well, physicists today are confident that we are, and we're picking up where Einstein left off in his quest for unification.
Unification would be the formulation of a law that describes, perhaps, everything in the known universe from one single idea, one master equation. And we think that there might be this master equation, because throughout the course of the last 200 years or so, our understanding of the universe has given us a variety of explanations that are all pointing towards one spot. They seem to all be converging on one nugget of an idea that we're still trying to find.
STEVEN WEINBERG (University of Texas at Austin): Unification is where it's at. Unification is what we're trying to accomplish. The whole aim of fundamental physics is to see more and more of the world's phenomena in terms of fewer and fewer and simpler and simpler principles.
MICHAEL B. GREEN (University of Cambridge): We feel, as physicists,
that if we can explain a wide number of phenomena in a very simple manner, that that's somehow progress. There is almost an emotional aspect to the way in which the great theories in physics sort of encompass a wide variety of apparently different physical phenomena. So this idea that we should be aiming to unify our understanding is inherent, essentially, to the whole way in which this kind of science progresses.
BRIAN GREENE: And long before Einstein, the quest for unification began with the most famous accident in the history of science. As the story goes, one day in 1665, a young man was sitting under a tree when, all of a sudden, he saw an apple fall from above. And with the fall of that apple, Isaac Newton revolutionized our picture of the universe.
In an audacious proposal for his time, Newton proclaimed that the force pulling apples to the ground and the force keeping the moon in orbit around the earth were actually one and the same. In one fell swoop, Newton unified the heavens and the earth in a single theory he called gravity.
STEVEN WEINBERG: The unification of the celestial with the terrestrial?ªthat the same laws that govern the planets in their motions govern the tides and the falling of fruit here on earth?ªit was a fantastic unification of our picture of nature.
BRIAN GREENE: Gravity was the first force to be understood scientifically, though three more would eventually follow. And, although Newton discovered his law of gravity more than 300 years ago, his equations describing this force make such accurate predictions that we still make use of them today. In fact scientists needed nothing more than Newton's equations to plot the course of a rocket that landed men on the moon.
Yet there was a problem. While his laws described the strength of gravity with great accuracy, Newton was harboring an embarrassing secret: he had no idea how gravity actually works.
For nearly 250 years, scientists were content to look the other way when confronted with this mystery. But in the early 1900s, an unknown clerk working in the Swiss patent office would change all that. While reviewing patent applications, Albert Einstein was also pondering the behavior of light. And little did Einstein know that his musings on light would lead him to solve Newton's mystery of what gravity is.
At the age of 26, Einstein made a startling discovery: that the velocity
of light is a kind of cosmic speed limit, a speed that nothing in the universe can exceed. But no sooner had the young Einstein published this idea than he found himself squaring off with the father of gravity.
The trouble was, the idea that nothing can go faster than the speed of light flew in the face of Newton's picture of gravity. To understand this conflict, we have to run a few experiments. And to begin with, let's create a cosmic catastrophe.
Imagine that all of a sudden, and without any warning, the sun vaporizes and completely disappears. Now, let's replay that catastrophe and see what effect it would have on the planets according to Newton.
Newton's theory predicts that with the destruction of the sun, the planets would immediately fly out of their orbits careening off into space. In other words, Newton thought that gravity was a force that acts instantaneously across any distance. And so we would immediately feel the effect of the sun's destruction.
But Einstein saw a big problem with Newton's theory, a problem that arose from his work with light. Einstein knew light doesn't travel instantaneously. In fact, it takes eight minutes for the sun's rays to travel the 93 million miles to the earth. And since he had shown that nothing, not even gravity, can travel faster than light, how could the earth be released from orbit before the darkness resulting from the sun's disappearance reached our eyes?
To the young upstart from the Swiss patent office anything outrunning light was impossible, and that meant the 250-year old Newtonian picture of gravity was wrong.
S. JAMES GATES, JR.: If Newton is wrong, then why do the planets stay up? Because remember, the triumph of Newton's equations come from the quest to understand the planets and the stars, and particularly the problem of why the planets have the orbits that they do. And with Newton's equations you could calculate the way that the planets would move. Einstein's got to resolve this dilemma.
BRIAN GREENE: In his late twenties, Einstein had to come up with a new picture of the universe in which gravity does not exceed the cosmic speed limit. Still working his day job in the patent office, Einstein embarked on a solitary quest to solve this mystery. After nearly ten years of wracking his brain he found the answer in a new kind of unification.
PETER GALISON (Harvard University): Einstein came to think of the three dimensions of space and the single dimension of time as bound together in a single fabric of "space-time." It was his hope that by understanding the geometry of this four-dimensional fabric of space-time, that he could simply talk about things moving along surfaces in this space-time fabric.
BRIAN GREENE: Like the surface of a trampoline, this unified fabric is warped and stretched by heavy objects like planets and stars. And it's this warping or curving of space-time that creates what we feel as gravity.
A planet like the earth is kept in orbit, not because the sun reaches out and instantaneously grabs hold of it, as in Newton's theory, but simply because it follows curves in the spatial fabric caused by the sun's presence. So, with this new understanding of gravity, let's rerun the cosmic catastrophe. Let's see what happens now if the sun disappears.
The gravitational disturbance that results will form a wave that travels across the spatial fabric in much the same way that a pebble dropped into a pond makes ripples that travel across the surface of the water. So we wouldn't feel a change in our orbit around the sun until this wave reached the earth.
What's more, Einstein calculated that these ripples of gravity travel at exactly the speed of light. And so, with this new approach, Einstein resolved the conflict with Newton over how fast gravity travels. And more than that, Einstein gave the world a new picture for what the force of gravity actually is: it's warps and curves in the fabric of space and time.
Einstein called this new picture of gravity "General Relativity," and within a few short years Albert Einstein became a household name.
S. JAMES GATES, JR.: Einstein was like a rock star in his day. He was one of the most widely known and recognizable figures alive. He and perhaps Charlie Chaplin were the reigning kings of the popular media.
MARCIA BARTUSIAK (Author): People followed his work. And they were anticipating...because of this wonderful thing he had done with general relativity, this recasting the laws of gravity out of his head...there was a thought he could do it again, and they, you know, people want to be in on that.
BRIAN GREENE: Despite all that he had achieved Einstein wasn't satisfied. He immediately set his sights on an even grander goal, the unification of his new picture of gravity with the only other force known at the time, electromagnetism.
Now electromagnetism is a force that had itself been unified only a few decades earlier. In the mid-1800s, electricity and magnetism were sparking scientists' interest. These two forces seemed to share a curious relationship that inventors like Samuel Morse were taking advantage of in newfangled devices, such as the telegraph.
An electrical pulse sent through a telegraph wire to a magnet thousands of miles away produced the familiar dots and dashes of Morse code that allowed messages to be transmitted across the continent in a fraction of a second. Although the telegraph was a sensation, the fundamental science driving it remained something of a mystery.
But to a Scottish scientist named James Clark Maxwell, the relationship between electricity and magnetism was so obvious in nature that it demanded unification.
If you've ever been on top of a mountain during a thunderstorm you'll get the idea of how electricity and magnetism are closely related. When a stream of electrically charged particles flows, like in a bolt of lightning, it creates a magnetic field. And you can see evidence of this on a compass.
Obsessed with this relationship, the Scot was determined to explain the connection between electricity and magnetism in the language of mathematics. Casting new light on the subject, Maxwell devised a set of four elegant mathematical equations that unified electricity and magnetism in a single force called "electromagnetism." And like Isaac Newton's before him, Maxwell's unification took science a step closer to cracking the code of the universe.
JOSEPH POLCHINSKI (University of California, Santa Barbara): That was really the remarkable thing, that these different phenomena were really connected in this way. And it's another example of diverse phenomena coming from a single underlying building block or a single underlying principle.
WALTER H.G. LEWIN (Massachusetts Institute of Technology): Imagine that everything that you can think of which has to do with electricity and
magnetism can all be written in four very simple equations. Isn't that incredible? Isn't that amazing? I call that elegant.
PETER GALISON: Einstein thought that this was one of the triumphant moments of all of physics and admired Maxwell hugely for what he had done.
BRIAN GREENE: About 50 years after Maxwell unified electricity and magnetism, Einstein was confident that if he could unify his new theory of gravity with Maxwell's electromagnetism, he'd be able to formulate a master equation that could describe everything, the entire universe.
S. JAMES GATES, JR.: Einstein clearly believes that the universe has an overall grand and beautiful pattern to the way that it works. So to answer your question, why was he looking for the unification? I think the answer is simply that Einstein is one of those physicists who really wants to know the mind of God, which means the entire picture.
BRIAN GREENE: Today, this is the goal of string theory: to unify our understanding of everything from the birth of the universe to the majestic swirl of galaxies in just one set of principles, one master equation. Newton had unified the heavens and the earth in a theory of gravity. Maxwell had unified electricity and magnetism. Einstein reasoned all that remained to build a "Theory of Everything"?ªa single theory that could encompass all the laws of the universe?ªwas to merge his new picture of gravity with electromagnetism.
AMANDA PEET: He certainly had motivation. Probably one of them might have been aesthetics, or this quest to simplify. Another one might have been just the physical fact that it seems like the speed of gravity is equal to the speed of light. So if they both go at the same speed, then maybe that's an indication of some underlying symmetry.
BRIAN GREENE: But as Einstein began trying to unite gravity and electromagnetism he would find that the difference in strength between these two forces would outweigh their similarities.
Let me show you what I mean. We tend to think that gravity is a powerful force. After all, it's the force that, right now, is anchoring me to this ledge. But compared to electromagnetism, it's actually terribly feeble. In fact, there's a simple little test to show this. Imagine that I was to leap from this rather tall building. Actually, let's not just imagine it. Let's do it. You'll see what I mean.
Now, of course, I really should have been flattened. But the important question is: what kept me from crashing through the sidewalk and hurtling right down to the center of the earth? Well, strange as it sounds, the answer is electromagnetism.
Everything we can see, from you and me to the sidewalk, is made of tiny bits of matter called atoms. And the outer shell of every atom contains a negative electrical charge. So when my atoms collide with the atoms in the cement these electrical charges repel each other with such strength that just a little piece of sidewalk can resist the entire Earth's gravity and stop me from falling. In fact the electromagnetic force is billions and billions of times stronger than gravity.
NIMA ARKANI-HAMED (Harvard University): That seems a little strange, because gravity keeps our feet to the ground, it keeps the earth going around the sun. But, in actual fact, it manages to do that only because it acts on huge enormous conglomerates of matter, you know?ªyou, me, the earth, the sun?ªbut really at the level of individual atoms, gravity is a really incredibly feeble tiny force.
BRIAN GREENE: It would be an uphill battle for Einstein to unify these two forces of wildly different strengths. And to make matters worse, barely had he begun before sweeping changes in the world of physics would leave him behind.
STEVEN WEINBERG: Einstein had achieved so much in the years up to about 1920, that he naturally expected that he could go on by playing the same theoretical games and go on achieving great things. And he couldn't. Nature revealed itself in other ways in the 1920s and 1930s, and the particular tricks and tools that Einstein had at his disposal had been so fabulously successful, just weren't applicable anymore.
BRIAN GREENE: You see, in the 1920s a group of young scientists stole the spotlight from Einstein when they came up with an outlandish new way of thinking about physics.
Their vision of the universe was so strange, it makes science fiction look tame, and it turned Einstein's quest for unification on its head. Led by Danish physicist Niels Bohr, these scientists were uncovering an entirely new realm of the universe.
Atoms, long thought to be the smallest constituents of nature, were found to consist of even smaller particles: the now-familiar nucleus of protons and neutrons orbited by electrons. And the theories of
Einstein and Maxwell were useless at explaining the bizarre way these tiny bits of matter interact with each other inside the atom.
PETER GALISON: There was a tremendous mystery about how to account for all this, how to account for what was happening to the nucleus as the atom began to be pried apart in different ways. And the old theories were totally inadequate to the task of explaining them. Gravity was irrelevant. It was far too weak. And electricity and magnetism was not sufficient.
BRIAN GREENE: Without a theory to explain this strange new world, these scientists were lost in an unfamiliar atomic territory looking for any recognizable landmarks.
Then, in the late 1920s, all that changed. During those years, physicists developed a new theory called "quantum mechanics," and it was able to describe the microscopic realm with great success. But here's the thing: quantum mechanics was so radical a theory that it completely shattered all previous ways of looking at the universe.
Einstein's theories demand that the universe is orderly and predictable, but Niels Bohr disagreed. He and his colleagues proclaimed that at the scale of atoms and particles, the world is a game of chance. At the atomic or quantum level, uncertainty rules. The best you can do, according to quantum mechanics, is predict the chance or probability of one outcome or another. And this strange idea opened the door to an unsettling new picture of reality.
It was so unsettling that if the bizarre features of quantum mechanics were noticeable in our everyday world, like they are here in the Quantum Caf??, you might think you'd lost your mind.
WALTER H.G. LEWIN: The laws in the quantum world are very different from the laws that we are used to. Our daily experiences are totally different from anything that you would see in the quantum world. The quantum world is crazy. It's probably the best way to put it: it's a crazy world.
BRIAN GREENE: For nearly 80 years, quantum mechanics has successfully claimed that the strange and bizarre are typical of how our universe actually behaves on extremely small scales. At the scale of everyday life, we don't directly experience the weirdness of quantum mechanics. But here in the Quantum Caf??, big, everyday things sometimes behave as if they were microscopically tiny. And no matter how many times I