Subtitles section Play video Print subtitles 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 -- from 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, bestselling author and physicist. BRIAN GREENE 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 -- that our understanding of the universe is based on two sets of laws, that don't agree? 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 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. 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... it all started with an apple. S. JAMES GATES, JR. 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. THE ELEGANT UNIVERSE Hosted By Brian Green Einstein's Dream A Theory of Everything? 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 -- combining all the laws of the universe in one, all-encompassing theory -- has 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 -- a universe of eleven dimensions with parallel universes right next door -- an 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 -- unimaginably 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 -- you remember how this goes -- equals 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? DOG BARKS: Vau, vau! 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 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 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. Newton's Embarrassing Secret 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 -- that the same laws that govern the planets in their motions govern the tides and the falling of fruit here on earth -- it 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.