STRING THEORY - 1
Everything stems from Gabriele Veneziano, who, studying hadrons, particles like protons and neutrons, notes in 1968 that their spin, their rotation, although it is a concept of rotation different from the one of macroscopic objects, is never greater than a certain multiple of the root of their energy. To explain this relationship, he tries to use a 200-years-old formula made by Leonhard Euler, which provided information on the strong interaction, one of the four fundamental forces of the Universe that holds together quarks inside protons and neutrons or protons and neutrons themselves inside the nucleus of an atom.
Gabriele Veneziano
In 1970 an explanation is attempted by another team by representing this interaction as composed of one-dimension vibrating strings, but it is contradicted by experiences. In 1974, however, a model of vibrating strings is developed to matches exactly with the gravitons, hypothetical particles that would be the cause of gravity.
This leads to the Bosonic String Theory, according to which each string vibrates in a different way, and each one would correspond to a particle. At the time, both types of string are still considered: the open one, a string with a starting point and an endpoint, and the closed one, a ring-like string. Lately studies are focusing mainly on the second type.
The problem with this theory is that it solely considers bosons, particles that cause the four fundamental forces or have an even number of fermions, while it ignores the other half of the particles that make up the Universe, the fermions itself, that always have a mass (an example is an electron). Theories that try to include fermions through supersymmetry, a concept according to which for every fermion and boson there is a boson and a fermion of equal mass, are the Superstrings Theories.
As studies continued, several scientists in the 1980s recognize in the String Theory a possibility to describe all elementary particles and their interactions: thus between 1984 and 1986, the First Superstring Revolution happens right after the cancellation of some anomalies and the discovery of the heterotic string, a mixture of bosonic and superstring.
In the 90s the Second Superstring Revolution follows with Edward Witten's M-Theory: through it, scientists recognize that the different superstring theories represent just various edges of an unknown eleven-dimensional theory, and for this reason, the M of the name does not stand for anything specific (some hypothesize mystery and magic) since the theory is not yet fully understood.
PIC CREDITS
Gabriele Veneziano - Betsythedevine