String theory attempts to combine two different theories – Quantum Theory and General Relativity – to create one ultimate theory of the universe.
Quantum Mechanics is a mathematical machine that predicts the behaviors of microscopic particles.
General Relativity was proposed by Einstein. It is the combination of space and time into what Einstein called spacetime. The theory states that rather than matter moving through a passive space-time continuum, that the presence of matter should distort space-time. Spacetime can be warped by forces from massive bodies such as planets.
String Theory postulates that subatomic particles such as quarks and electrons are not points of energy or matter, but are one-dimensional strings. String theory, if true, proves that everything in the universe is actually made up of tiny strings that are constantly vibrating or oscillating. The vibration of the string determines the charge and mass of the greater particle.
Superstring Theories take this idea and build the entire universe from the bottom up. And yes, it’s as challenging a task as it sounds. That’s why we speak of String Theories in the plural, because there are several different String Theories that attempt to make it all work. Oh, and at least 10 dimensions are called for, too, just for all the math involved. Physicists propose that any dimensions beyond time and visible space are folded up and out of sight.
As you probably guessed, Superstring Theory is still developing, meaning that physicists continue to work out kinks in the individual String Theories. Eventually they’re aiming to fulfill Einstein’s unrealized goal of unifying General Relativity with Quantum Theory. That’s why string theory also is sometimes called a Theory of Everything (ToE), because it could serve someday as a foundation for all future scientific discovery and innovation.