String theory is a revolutionary way of describing the world. It states that all aspects of our universe -- all the particles that make up matter, and all the forces that act on those particles -- are made up of tiny strings of energy. According to string theorists, these imperceptibly tiny strings, or loops, of energy hold the key to understanding and explaining the behavior of the smallest particles and the largest bodies in the universe.

String theory is not so different from many earlier scientific theories. The objective of string theory and earlier theories of physics is what physicists call unification. The goal of unification is to describe unimaginably complex phenomena in the simplest possible terms, and to mathematically connect seemingly disparate physical concepts.

Isaac Newton did exactly this when he developed his theory of gravity, which says that any two objects -- from the smallest to the largest -- exert an attractive force on each other. According to Newton's theory, the strength of this force depends on the mass of the objects and the distance between them. For over two hundred years, Newton's theory of gravity made it possible to unify our understanding of falling objects at the surface of Earth with the attraction between the Sun and planets in our solar system, as well as with many other diverse phenomena.

In the twentieth century, Einstein set out to unify two concepts: his new and revised theory of gravity and electromagnetism. He wanted to prove mathematically that these two forces -- the only ones known at the time -- are governed by one underlying principle. However, shortly after he began this quest, the tide of theoretical physics swung toward quantum mechanics, and Einstein died without seeing the fulfillment of his dream of a unified field theory.

String theory basically takes up where Einstein left off -- but with an even bigger objective: it attempts to attribute the properties of all fundamental particles and forces to the vibrations of strands of energy, called strings. String theory may one day prove to be the "theory of everything" that its proponents suggest, but even if it doesn't, at the very least, according to string theorist Brian Greene, if it is correct, this theory will provide the most solid foundation yet for truly understanding the universe.