String theory is a type of high-energy theoretical physics, practiced largely by particle physicists. It’s a *quantum field theory* that describes the particles and forces in our universe based on the way that special extra dimensions within the theory are wrapped up into a very small size (a process called *compactification*).

This is the power of string theory — to use the fundamental strings, and the way extra dimensions are compactified, to provide a geometric description of all the particles and forces known to modern physics.

Among the forces needed to be described is, of course, gravity. Because string theory is a quantum field theory, this means that string theory would be a quantum theory of gravity, known as *quantum gravity*. The established theory of gravity, general relativity, has a fluid, dynamic space-time, and one aspect of string theory that’s still being worked on is getting this sort of a space-time to emerge out of the theory.

The major achievements of string theory are concepts you can’t see, unless you know how to interpret the physics equations. String theory uses no experiments that provide new insights, but it has revealed profound mathematical relationships within the equations, which lead physicists to believe that they must be true.

These properties and relationships are called by jargon such as various symmetries and dualities, the cancellation of anomalies, and the explanation of black hole entropy.

In recent years, there has been much public controversy over string theory, waged across headlines and the Internet. These issues come down to fundamental questions about how science should be pursued. String theorists believe that their methods are sound, while the critics believe that they are, at best, questionable. Time and experimental evidence will tell which side has made the better argument.