One of the strangest features of string theory is that it requires more than the three spatial dimensions that we see directly in the world around us. That sounds like science fiction, but it is an indisputable outcome of the mathematics of string theory.

The funny thing is, I sometimes get the impression that some people outside of the field think that there's some element of security that we have in working on a theory that hasn't made any predictions that can be proven false. In a sense, we're working on something unfalsifiable.

The full name of string theory is really superstring theory. The 'super' stands for this feature called supersymmetry, which, without getting into any details, predicts that for every known particle in the world, there should be a partner particle, the so-called supersymmetric partner.

Brian Greene Quotes