Michael Duff: Einstein didn't explain everything. We need a...

Quantum theory deals with the very small: atoms, subatomic particles and the forces between them. General relativity deals with the very large: stars, galaxies and gravity, the driving force of the cosmos as a whole. The dilemma is that on the microscopic scale, Einstein's theory fails to comply with the quantum rules that govern the behaviour of the elementary particles. On the macroscopic scale, black holes are threatening the very foundations of quantum mechanics. Something big has to give. This augurs a new scientific revolution.

Some believe that this revolution is already under way because of "superstrings". As their name suggests, superstrings are one-dimensional string-like objects. Just like violin strings, they can vibrate, and each mode of vibration, each note if you like, corresponds to a different elementary particle.