One of the key signatures of strings that "fell out" of the team's analysis is known as the string spectrum. Discovered by Italian theoretical physicist Gabriele Veneziano of the European Organization for Nuclear Research (CERN) in the late 1960s, the spectrum is an infinite tower, or ladder, of particles, in which the masses and spins increase in discrete steps.

Other researchers later came to realize that Veneziano's tower of particles corresponds to a harmonic series of a vibrating string. If you pluck a violin string, you'll get a series of notes representing the fundamental note and overtones that follow a similar pattern.

String theory was born, but it was not until 1974 that Caltech's John Schwarz, the Harold Brown Professor of Theoretical Physics, Emeritus, and his colleague Jol Scherk, a French physicist, realized that the theory included gravity, thereby forming the first connection between string theory and general relativity.