String Theory: A Brief Overview. General relativity and quantum mechanics take different approaches at looking at how the universe works. Many physicists feel that there must be a method that unites the two. One contender for such a universal theory is superstring theory, or string theory, for short. Let's take a brief overview of this complex perspective. One string, no particles Children in elementary school learn about the existence of protons, neutrons, and electrons, basic subatomic particles that create all matter as we know it. Scientists have studied how these particles move and interact with one another, but the process has raised a number of conflicts. According to string theory, these subatomic particles do not exist. How do strings replace point-like particles? Limiting the dimensions of the universe Einstein's theory of relativity opened up the universe to a multitude of dimensions, because there was no limit on how it functioned.
We only experience four dimensions. Searching for evidence Further reading: Brian Greene: Making sense of string theory. String field theory. The principal advantages of the formalism are that it allows the computation of off-shell amplitudes and, when a classical action is available, gives non-perturbative information that cannot be seen directly from the standard genus expansion of string scattering. In particular, following the work of Ashoke Sen,[1] it has been useful in the study of tachyon condensation on unstable D-branes. It has also had applications to topological string theory,[2] non-commutative geometry,[3] and strings in low dimensions.[4] String field theories come in a number of varieties depending on which type of string is second quantized: Open string field theories describe the scattering of open strings, closed string field theories describe closed strings, while open-closed string field theories include both open and closed strings.
Light-cone string field theory[edit] and two vertices for splitting and joining strings, which can be used to glue three propagators together, where , and , gauge field . And . The . 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.
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. 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.