Physicists would like to be able to describe everything in the universe with one simple, beautiful theory, just a few basic ideas and equations.

We are partly some way towards achieving this.

Current theories suggest that all matter in the universe is made up of 12 particles, 6 quarks and 6 leptons. And for each of these matter particles, there is a corresponding anti-matter particle, which is the same but in reverse.

The everyday matter we live with is made of just 3 of these; two quarks, up and down, which make up the protons and neutrons which form the nucleus of all atoms; and one of the leptons, the electron. Another of the leptons, the electron anti-neutrino, an anti-matter particle, is involved in beta radioactive decay.

And these particles interact using just 4 forces: the Strong force, which binds quarks to other quarks and holds protons, neutrons and nuclei together; the Electro-Magnetic force, which binds nuclei to electrons and holds atoms, molecules and you and I together; the Weak force, which is involved in Beta Decay and allows neutrinos to interact with matter; and Gravity, which keeps us on the planets and holds planets, stars, Solar Systems, Galaxies and the Universe together.

Unfortunately this is not simply enough. Why are there 2 families of 6 particles? Why are there 4 forces? Why do the particles have the masses that they have? There are too many arbitrary values; it would be much simpler if all these numbers could be derived from a few equations.

Michael Faraday started it all by showing that electricity and magnetism were facets of the same thing. Albert Einstein had a go by showing that space, time, gravity and acceleration are all related. Particle Accelerators have demonstrated that at high enough energies electro-magnetism and the weak force become one, the electro-weak force. And at even higher energies the Strong force and the electro-weak force merge.

It is this unifying of the Strong, Electro-magnetic and Weak forces and the idea that all matter is made up of just 12 particles, which can be grouped into 2 families of 6, each family containing 3 pairs, that is described by Grand Unified Theories or GUTs.

But Physicists want a Theory Of Everything, a TOE. The search for this can be summed up by the attempt to merge Gravity with the other three forces. Unfortunately the two successes of the 20^th century, Quantum Mechanics; which describes the way the 12 particles and the three forces behave; and General Relativity; which describes Gravity; are very different beasts. A TOE would merge these two.

Some work has been done towards this though. Quantum Theories of Gravity and Super-Symmetric String theories are a move towards a TOE and may even have a bearing on Human (and Animal) Consciousness.

But don't imagine that a TOE is just around the corner. At the end on the 19^th century Physicists thought they were close to a Theory of Everything, once they had dealt with a couple of issues, "two dark clouds on the horizon" as Ernest Rutherford termed them. One was the Photo-Electric effect, which was a foundation for Quantum Mechanics, and the other was the orbit of Mercury, which was a foundation of General Relativity. And both of these generated more questions than they did answers!