The Grand Unified Theory is a vision of a physics theory that can combine three of the four fundamental forces into one single equation. The four forces are the Strong Nuclear Force, the Weak Nuclear Force, the Electro-Magnetic Force, and the Gravitational Force. The EM and Weak forces were initially thought to be two separate forces until scientists discovered one theory (the Electro Weak theory) to explain both of them and then went on to observe this unified force in action (much like Maxwell unified the electric and magnetic forces into the Electro-Magnetic Force).

Apparently M-Theory is making some progress towards a TOE (Theory Of Everything);

A unified field theory may lie beyond our current means of scientifically understanding and describing the universe. A fundamentally new approach and outlook on the universe may be required for an understanding of the link between the four fundamental forces in quantum theory. This is where the theory formerly known as Super Strings (now M-Theory) comes in.

In essence, the Grand Unified theory retains classical premises and in doing so can combine three of the four forces. While the TOE alters classical premises and attempts to unify all four forces. I am no expert at M-theory but it uses extra dimensions which help the model but detach from classical intuitions.

I have my own theory for everything, which is far simpler than M-theory. The only assumption needed is the speed of light is the ground state of the universe; lowest potential. The speed of light is the same in all references, therefore the same analysis applies to all reference, with each seeing the very same ground state.

If you look at gravity, the mass contracts space-time, therefore gravity, via mass, moves space-time in the general direction of the speed of light reference, where space-time contracts all the way to a point. This limit only happens with black holes.

All the other forces, release energy or photons, at the speed of light. These force reflect partial conversion back to C. All roads lead to Rome.

If you were on a speed of light reference, the universe would appear contracted to a point. What that means you will not be able to see energy unless it has infinite wavelength. Any wavelength smaller than infinite would define a fraction of this point universe, which cannot happen, due to the definition of a point; fraction of a point does not exist. Therefore, the universal red shift is simply energy expanding wavelength, toward infinite wavelength, so it can be seen; lower potential with C. Lowering potential with the C ground state will clump mass, reduce force potential for the release of energy at C, and cause the universe to red shift that energy.

In this model, we can start before classical time=0, since if the speed of light is the ground state, then time begins before there is any deviation away from the C ground state; before the singularity.