### Chapter 6: Nothing but Music: The Essentials of Superstring
Theory

The standard model, which describes the elementary particles
of the universe as amorphous, zero-dimensional points, is not comprehensive
because it ignores gravity. Superstring theory, on the other hand,
describes the most basic ingredients of matter as Planck-length
strings that vibrate perpetually, like tiny rubber bands.

Before explaining why only string theory can resolve the
conflict between general relativity and quantum mechanics, Greene
supplies a brief history of the origins of string theory. In 1968,
theoretical physicist Gabriele Veneziano was trying to understand
the strong nuclear force when he made a startling discovery. Veneziano
found that a 200-year-old formula created by Swiss mathematician
Leonhard Euler (the *Euler beta function*) perfectly
matched modern data on the strong force. Veneziano applied the Euler
beta function to the strong force, but no one could explain why
it worked.

Two years later, Yochiro Nambu, Holger Nielsen, and Leonard Susskind
unveiled the physics beneath Euler’s strictly theoretical formula.
By representing nuclear forces as vibrating, one-dimensional strings,
these physicists showed how Euler’s function accurately described
those forces. But even after physicists understood the physical
explanation for Veneziano’s insight, the string description of the
strong force made many predictions that directly contradicted experimental
findings. The scientific community soon lost interest in string
theory, and the standard model, with its particles and fields, remained
unthreatened.

Then, in 1974, John Schwarz and Joel Scherk studied the
messenger-like patterns of string vibration and found that their
properties exactly matched those of the gravitational force’s hypothetical
messenger particle. Schwarz and Scherk argued that string theory
had failed to catch on because physicists had underestimated its
scope.

But the enthusiasm faded fast, for string theory’s conflicts
with quantum mechanics remained unresolved. Then, in 1984, Schwarz and
Michael Green declared that string theory was capable of explaining
all four forces and all matter as well. String theory, they said,
was not a strong force theory, but a *quantum* theory
that also included gravity. Shwarz’s and Green’s reinterpretation
marked the first-ever quantum mechanical theory of the gravitational
force.

In 1984, Brian Greene started graduate school at Oxford
University. The reaction to Schwarz’s and Green’s discovery was
to influence the direction of his research for the next two decades.
Greene came to believe that particle physics had no future: only
string theory, he believed, could explain all properties of the
microworld. String theory can make numeric predictions that the
standard model, which is too flexible to explain the properties
of elementary particles, can only assume.