String (physics)

String (physics)

A string is a hypothetical vibrating one-dimensional sub-atomic structure and one of the main objects of study in string theory, a branch of theoretical physics. There are different string theories, many of which are unified by M-theory. A string is an object with a one-dimensional spatial extent, unlike an elementary particle which is zero-dimensional, or point-like. Quarks and electrons are thought to be made of strings.

By postulating this one-dimensional structure, many desirable features of a more fundamental theory of physics automatically emerge. Most notably, almost any theory of strings consistent with quantum mechanics must also contain quantum gravity, which had not been described consistently prior to string theory.

The characteristic length scale of strings is thought to be on the order of the Planck length, the scale at which the effects of quantum gravity are believed to become significant:

m

On much larger length scales, such as the scales visible in physics laboratories, such objects would be indistinguishable from zero-dimensional point particles. However, the vibrational modes and structure of the tiny string would be manifested as different elementary particles in the standard model of quantum field theory. For example, one state of the string would be associated with a photon, and another state with a quark. This unifying feature of string theory is among its greatest strengths, however no known solution of string theory exactly reproduces the particle content of the standard model.

Propagating in spacetime, strings sweep out a two-dimensional surface, called a worldsheet, analogous to the one-dimensional worldline traced out by a point particle.