Relaxing to Three Dimensions

We propose a new selection principle for distinguishing among possible vacuathat we call the "relaxation principle". The idea is that the universe willnaturally select among possible vacua through its cosmological evolution, andthe configuration with the biggest filling fraction is the likeliest. We applythis idea to the question of the number of dimensions of space. We show thatunder conventional (but higher-dimensional) FRW evolution, a universe filledwith equal numbers of branes and antibranes will naturally come to be dominatedby 3-branes and 7-branes. We show why this might help explain the number ofdimensions that are experienced in our visible universe.Comment: 4 pages; minor improvements, references adde