Physicists say universe evolution favored three and seven dimensions

Physicists who work with a concept called string theory envision our universe as an eerie place with at least nine spatial dimensions, six of them hidden from us, perhaps curled up in some way so they are undetectable. The big question is why we experience the universe in only three spatial dimensions instead of four, or six, or nine.
Two theoretical researchers from the University of Washington and Harvard University think they might have found the answer. They believe the way our universe started and then diluted as it expanded -- what they call the relaxation principle -- favored formation of three- and seven-dimensional realities. The one we happen to experience has three dimensions.

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