Năstase, Horaţiu [UNESP]2020-12-122020-12-122019-01-01Fundamental Theories of Physics, v. 197, p. 201-211.2365-64250168-1222http://hdl.handle.net/11449/200468In this chapter we will finally start describing string theory. String theory is a theory of relativistic strings. That means, it is not like violin strings, or cosmic strings, which are essentially non-relativistic and as a result can have compression modes, along the string. Also, unlike them, they represent an idealization, and have zero thickness, i.e., they are truly one-dimensional, and moreover their endpoints will move at the speed of light. But like them, will be characterized by a certain string tension, or energy per unit length, T.201-211engCapítulo de livro10.1007/978-3-030-15077-8_172-s2.0-85085177405