What is String Theory ?

In 1915 Einstein further unified space, time, and gravitation with his general theory of relativity, showing that warps and curves in space and time are responsible for the force of gravity.

The behavior of all of these particles and forces is described with impeccable precision by the Standard Model, with one notable exception: gravity.

These were monumental achievements, but Einstein dreamed of an even grander unification.

He envisioned one powerful framework that would account for space, time, and all of nature’s forces—something he called a unified theory.

Our current knowledge about the subatomic composition of the universe is summarized in what is known as the Standard Model of particle physics. It describes both the fundamental building blocks out of which the world is made, and the forces through which these blocks interact. There are twelve basic building blocks

For the last three decades of his life, Einstein relentlessly pursued this vision. Although from time to time rumours spread that he had succeeded, closer scrutiny always dashed such hopes.

For technical reasons, the gravitational force, the most familiar in our every day lives, has proven very difficult to describe microscopically. This has been for many years one of the most important problems in theoretical physics-- to formulate a quantum theory of gravity.

Most of Einstein’s contemporaries considered the search for a unified theory to be a hopeless, if not misguided, quest.

Six of these are quarks--- they go by the interesting names of up, down, charm, strange, bottom and top. (A proton, for instance, is made of two up quarks and one down quark.) The other six are leptons--- these include the electron and its two heavier siblings, the muon and the tauon, as well as three neutrinos.

The essential idea behind string theory is this: all of the different 'fundamental ' particles of the Standard Model are really just different manifestations of one basic object: a string.

A string can do something aside from moving--- it can oscillate in different ways. If it oscillates a certain way, then from a distance, unable to tell it is really a string, we see an electron.

Predictions And Theoretical Difficulties of String theory

String theory was an intuitively attractive proposal, but by the mid-1970s more-refined measurements of the strong force had deviated from its predictions, leading most researchers to conclude that string theory had no relevance to the physical universe, no matter how elegant the mathematical theory.

In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings.

This is mostly due to the fact that string theory is still under development. We know bits and pieces of it, but we do not yet see the whole picture, and we are therefore unable to make definite predictions.

Nevertheless, a small number of physicists continued to pursue string theory.

In string theory, one of the many vibrational states of the string corresponds to the graviton, a quantum mechanical particle that carries gravitational force. Thus string theory is a theory of quantum gravity.

In 1974 John Schwarz of the California Institute of Technology and Joel Scherk of the École Normale Supérieure and, independently, Tamiaki Yoneya of Hokkaido University came to a radical conclusion.

They suggested that one of the supposedly failed predictions of string theory—the existence of a particular massless particle that no experiment studying the strong force had ever encountered—was actually evidence of the very unification Einstein had anticipated.

String theory is a broad and varied subject that attempts to address a number of deep questions of fundamental physics.

. String theory has been applied to a variety of problems in black hole physics, early universe cosmology, nuclear physics, and condensed matter physics, and it has stimulated a number of major developments in pure mathematics.

One of the goals of Physics is to find a single theory that unites all of the four forces of nature. These are; electromagnetism, gravity, and the strong and weak nuclear forces. The first two are familiar. Electromagnetism is the force that holds a fridge magnet to a refrigerator while gravity is trying to pull it off towards the earth.

The Official String Theory Website: An excellent introductory site for the nonspecialist, including RealAudio interviews with leading string theorists, and a tour of the Big Bang.

Although no one had succeeded in merging general relativity and quantum mechanics, preliminary work had established that such a union would require precisely the massless particle predicted by string theory.

A few physicists argued that string theory, by having this particle built into its fundamental structure, had united the laws of the large (general relativity) and the laws of the small (quantum mechanics).

Rather than merely being a description of the strong force, these physicists contended, string theory required reinterpretation as a critical step toward Einstein’s unified theory.