Why Does Our Universe Have Three Dimensions? : Discovery News: The result was two separate space-times: the unfurled three-dimensional one that we inhabit, and a six-dimensional one that contracted as violently as ours expanded, shrinking into a tiny Planckian ball. As our universe expanded and cooled, the four forces split off one by one, beginning with gravity. Everything we see around us today is a mere shard of the original shattered nine-dimensional universe.