In
physics, a
string is a physical object that appears in
string theory and related subjects. Unlike
elementary particles, which are zero-dimensional or point-like by definition, strings are one-dimensional extended objects. Theories in which the fundamental objects are strings rather than point particles automatically have many properties that some physicists expect to hold in a fundamental theory of physics. Most notably, a theory of strings that evolve and interact according to the rules of
quantum mechanics will automatically describe
quantum gravity.