The year 1984 is marked by many as the start of “the first superstring revolution.” The major finding that sparked the revolution was the proof that string theory contained no anomalies, unlike many of the quantum gravity theories, including supergravity, studied during the 1970s.
For nearly a decade, John Schwarz had been working on showing that superstring theory could be a quantum theory of gravity. His major partner in this, Joel Scherk, had died in 1980, a tragic blow to the cause. By 1983, Schwarz was working with Michael Green, one of the few individuals who had been persuaded to work on string theory during that time.
Typically, two major problems arose in theories of quantum gravity: anomalies and infinities. Neither is a good sign for a scientific theory.
Infinities occur when values, such as energy, probability, or curvature, begin increasing rapidly to an infinite value.
Anomalies are cases where quantum mechanical processes can violate a symmetry that is supposed to be preserved.
Superstring theory was actually pretty good at avoiding infinities.
One simplification that allows you to understand, in very general terms, how superstring theory avoids infinities is that the distance value never quite reaches zero. Dividing by zero (or a value that can get arbitrarily close to zero) is the mathematical operation that results in an infinity. Because the strings have a tiny bit of length (I call it L), the distance never gets smaller than L, and so the gravitational force is obtained by dividing by a number that never gets smaller than L2. This means that the gravitational force will never explode up to infinity, as happens when the distance approaches zero without a limit.
String theory also had no anomalies (at least under certain specific conditions), as Schwarz and Green proved in 1984. They showed that certain 10-dimensional versions of superstring theory had exactly the constraints needed to cancel out all anomalies.
This changed the whole landscape of theoretical physics. For a decade, superstring theory had been ignored while every other method of creating a quantum theory of gravity collapsed in upon itself under infinities and anomalies. Now this discarded theory had risen from the ashes like a mathematical phoenix — both finite and anomaly free.
Theorists began to think that superstring theory had the potential to unify all the forces of nature under one simple set of physical laws with an elegant model in which everything consisted of different energy levels of vibrating strings. It was the ideal that had eluded Einstein: a fundamental theory of all natural law that explained all observed phenomena.
