I have been reading books recently regarding Supersymmetry and extra dimensions. Specifically they are Supersymmety, Unveiling the Ultimate Laws of Nature by Gordon Kane and Warped Passages, Unraveling the Mysteries of the Universe's Hidden Dimensions by Lisa Randall, which have been instrumental in helping me develop this model of the universe.
I propose that at the moment of the Big Bang all 10 or 11 dimensions were of equal size and all forces are united in one super force. In this model, the number of dimensions that are manifest is directly related to the amount of energy available in the universe.