In the early part of this century, physicists Theodore Kaluza and Oskar Klein discovered that if you look at the equations for general relativity written in terms of a 5-dimensional space time and not the familiar 4-dimensional one, you end up with two sets of equations. The first set are identical to the equations for gravity for a 4-dimensional spacetime. The second set is a collection of equations which can be easily cast to look like Maxwell's equations for electromagnetism. This caused some excitement because it LOOKED like adding a dimension allowed you to unify gravity and light, mathematically. In some sense, light appeared as a by-product of spacetime having this additional space-like dimension. However, the scale of this dimension was microscopic and even by Kaluza-Klein's estimation, being orders of magnitude smaller than the nucleus of an atom.
Today, the 'Kaluza Klein' approach to unification appears even in the most advanced theories involving what are called 'super strings'. Other theoreticians are not as convinced that adding a dimension or two is really that necessary, and believe that super string theory will eventually be expressed purely in terms of a 4-dimensional spacetime.