5th dimension - Kaluza-Klein Theory

Kaluza-Klein theories show how you can get Electro-Magnetism from Einstein's General Relativity (gravity) if you assume an extra (5th) dimension which is a circle. A particle moving around this circle (i.e. with momentum in the 5th dimension) appears to a 4-dimensional observer (us) to have electric charge. It is quantized because the circle has a finite size. When you note that the (8) is a circle (O) we can move towards figuring things out. http://en.wikipedia.org/wiki/Kaluza-Klein_theory