Gravity + E-Magnetism + Weak Force + Strong Force = Superforce?

According to string theory, when the universe was infinitely dense and hot there was only one force which was a combination of all forces (gravity, E-Magnetism, weak force, strong force) What would the matter in the time before the big bang be like? Why would extreme temperatures cause all the forces to combine into one? Why wasn't the matter evenly dispersed throughout the universe? I want answers people!