String_theory. The Elegant Universe: Series ... The Elegant Universe: Part 3 PBS Airdate: November 4, 2003 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—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, 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—that 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. S. BRIAN GREENE:The atmosphere was electric. S. S. What is string theory?" Pull a loose thread on a cartoon garment and what happens? That's right, the character's sweater completely unravels, leaving only a pile of string and some animated nudity. That's cartoon physics for you, but it's also a lot like the very serious business of superstring theory. Break everything down to its simplest form and all you have is a pile of incredibly tiny bits of string. Particle physicists define elementary particles or fundamental particles as the smallest building blocks in the universe. In other words, particles such as leptons and quarks have no substructure. That's not the case for string theorists, who think we need to venture deeper (or smaller) than our current technology allows.
Superstring theories take this idea and build the entire universe from the bottom up. As you probably guessed, superstring theory is still developing, meaning that physicists continue to work out kinks in the individual string theories. Brian Greene: Making sense of string theory. What is String Theory ? We live in a wonderfully complex universe, and we are curious about it by nature. Time and again we have wondered--- why are we here? Where did we and the world come from? What is the world made of? It is our privilege to live in a time when enormous progress has been made towards finding some of the answers. String theory is our most recent attempt to answer the last (and part of the second) question. So, what is the world made of? Our current knowledge about the subatomic composition of the universe is summarized in what is known as the Standard Model of particle physics. There are four fundamental forces in the universe: gravity, electromagnetism, and the weak and strong nuclear forces.
The behavior of all of these particles and forces is described with impeccable precision by the Standard Model, with one notable exception: gravity. In the last few decades, string theory has emerged as the most promising candidate for a microscopic theory of gravity. String theory. String theory was first studied in the late 1960s[3] as a theory of the strong nuclear force before being abandoned in favor of the theory of quantum chromodynamics. Subsequently, it was realized that the very properties that made string theory unsuitable as a theory of nuclear physics made it a promising candidate for a quantum theory of gravity. Five consistent versions of string theory were developed until it was realized in the mid-1990s that they were different limits of a conjectured single 11-dimensional theory now known as M-theory.[4] Many theoretical physicists, including Stephen Hawking, Edward Witten and Juan Maldacena, believe that string theory is a step towards the correct fundamental description of nature: it accommodates a consistent combination of quantum field theory and general relativity, agrees with insights in quantum gravity (such as the holographic principle and black hole thermodynamics) and has passed many non-trivial checks of its internal consistency.
The Official String Theory Web Site.