Bosonic string theory

In 1969 and in 1970, Yoichiro Nambu, Holger Bech Nielsen and Leonard Susskind are going to recognize that the dual resonance model, could have a description as a spacetime theory of strings. Susskind, Nambu and Nielsen are going to reveal the unknown physics that lurked behind Veneziano's discovery. The idea was that nuclear forces, could be represented, as vibrating, 1-dimensional strings. Indeed, this was the proposal that the Veneziano model was a theory of strings, thus, is considered to be the birth of string theory. 

Susskind thought of the Veneziano amplitude and began to visualize elastic strings. The string was stretched out between two quarks and it could vibrate. These strings could have different patterns of vibration. Susskind proposed that Veneziano's S-matrix formula described two rubber bands on a collision course. 

Yoichiro Nambu, who is a bit older than Leonard Susskind, had been doing the same calculations in Chicago. Nambu was born in Japan, and after World War II, came to the University of Chicago. Nambu, had for some time, been one of the most eminent theoretical physicists in the world. Nambu had a reputation as one who saw things long before everyone else. Nambu was, renowned for his quiet, well-mannered, but always penetrating style. Nambu lets the merit of his work speak for itself. We can also say that it was clearly Nambu who wrote down the basic equations of string theory. Nambu wanted to make sense of the hundreds of hadron particles that were being discovered, that could, of course, not be fundamental. Nambu thought that this was indicative of some kind of underlying structure. Nambu's idea was that the hadron consisted of some sort of vibrating string. Each mode of string vibration corresponded to a kind of subatomic particle. This was quite the seminal insight, that the Euler Beta function found by Veneziano and Suzuki could be explained by vibrating strings. 

Holger Nielsen, a physicist from Denmark, was also thinking about similar ideas. However, he had a different angle on the elastic strings.

This was the earliest version of string theory, that had a considerable number of problems: The theory only contained bosons in its spectrum. These are the particles that mediate fundamental interactions as excitations of their corresponding fields, that have an integer value spin. However, if string theory were to be a consistent theory of nature, it would also have to include fermions, these are the matter particles with a ½ integer value spin. There was also the presence of a particle called a tachyon. This is a hypothetical particle that moves faster than the speed of light. Of course, this is not allowed by special relativity, thus, this was an inconsistency with the theory. The theory came about in the late 1960s and is 26 dimensional. It was shown by Claud Lovelace that these earliest versions of string theory had problems, unless, they were formulated in 26 dimensions. 

This was the original version of string theory, developed in the late 1960s and it was known as bosonic string theory. Let us recall that there are two kinds of subatomic particles: fermions, which have a spin of ½ integer, which are typically matter particles, like the quarks and electron, and bosons, which have an integer value spin of 1, like the photon. Bosons are typically messenger particles. Supersymmetry, is a kind of symmetry that posits a relationship between these two families of particles. However, supersymmetry had yet to be incorporated into string theory at this time and thus the theory only contained bosonic patterns of vibration. If string theory were to be a theory of everything, it would have to be able to account for both bosonic and fermionic vibrations.