Free Republic

It seems like the most obvious physical fact: The universe has four dimensions--three spanning space and one ticking away time. But the ultimate theory of gravity should explain why the universe is four-dimensional and how those dimensions arose, say researchers trying to unify the theories of quantum mechanics and relativity. Now, calculations in the 24 September PRL [Phys. Rev. Lett.] show that when all possible microscopic contortions of spacetime are added together, a large-scale four-dimensional universe can emerge. For nearly 80 years physicists have struggled to reconcile the prevailing theory of gravity with quantum mechanics. According to Einstein's general theory...