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  • 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.