String theory is an active research framework in particle physics that attempts to reconcile quantum mechanics and general relativity. It is a contender for a theory of everything (TOE), a self-contained mathematical model that describes all fundamental forces and forms of matter.
String theory is currently the best candidate for a unified theory of all forces and all forms of matter in nature. As such, it has become a focal point for physical and philosophical discussions.
But despite its extraordinary popularity among some of the smartest people on the planet, string theory hasn't been embraced by everyone--and now, nearly 30 years after it made its initial splash, some of the doubters are becoming more vocal.
Pythagoras could be called the first known string theorist. Pythagoras, an excellent lyre player, figured out the first known string physics -- the harmonic relationship. Pythagoras realized that vibrating Lyre strings of equal tensions but different lengths would produce harmonious notes (i.e. middle C and high C) if the ratio of the lengths of the two strings were a whole number.
Surprisingly, strings and black holes have been found to be inextricably intertwined, and the understanding of one is giving new insights into the other.
String theory is at this moment the most promising theory that unifies all particles and forces in nature, including gravity, in a way consistent with the laws of quantum mechanics and relativity. String theory answers fundamental questions about the symmetries of nature, the quantum behaviour of black holes, the existence and breaking of supersymmetry, and the quantum treatment of singularities.
Just as a particle has an intrinsic mass, a string would have an intrinsic tension. Just as a particle is subject to the laws of special relativity, a string would also be relativistic. Finally, one would have to devise a "quantum mechanics" of strings in analogy with that for point particles.
In the standard model of particle physics, particles are considered to be points moving through space, tracing out a line called the World Line. To take into account the different interactions observed in Nature one has to provide particles with more degrees of freedom than only their position and velocity, such as mass, electric charge, color (which is the "charge" associated with the strong interaction) or spin.
string theory, in particle physics, a theory that attempts to merge quantum mechanics with Albert Einstein’s general theory of relativity. The name string theory comes from the modeling of subatomic particles as tiny one-dimensional “stringlike” entities rather than the more conventional approach in which they are modeled as zero-dimensional point particles. The theory envisions that a string undergoing a particular mode of vibration corresponds to a particle with definite properties such as mass and charge.
In String Theory, the myriad of particle types is replaced by a single fundamental building block, a `string'. These strings can be closed, like loops, or open, like a hair. As the string moves through time it traces out a tube or a sheet, according to whether it is closed or open. Furthermore, the string is free to vibrate, and different vibrational modes of the string represent the different particle types, since different modes are seen as different masses or spins.
One mode of vibration, or `note', makes the string appear as an electron, another as a photon. There is even a mode describing the graviton, the particle carrying the force of gravity, which is an important reason why String Theory has received so much attention.
The discovery of string theory as a potential unified theory was something of an accident. In a context unrelated to the unification of forces, researchers in the 1970's wondered what theory one might be able to write down to describe a fundamental quantum string -- an object with a finite spatial extent, which could not be described in terms of deeper constituents. It was certainly an interesting new mathematical problem in a physical context.