Deriving Dimensions

From: Sam Wormley (swormley1_at_mchsi.com)
Date: 09/29/04 

Date: Wed, 29 Sep 2004 03:40:06 GMT

Ref: http://focus.aps.org/story/v14/st13

Phys. Rev. Lett. 93, 131301
(issue of 24 September 2004)
        
Deriving Dimensions

   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 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 of relativity, mass
   and energy warp spacetime. The undulations then affect the
   trajectories of passing objects, producing the effects we
   call gravity. In Einstein's theory, spacetime is a stretchy,
   dynamical entity.

   However, the precise state of any dynamical thing remains
   uncertain, according to quantum mechanics. So at lengths of
   about 10-35 meters, spacetime can no longer be smooth, but
   must be roiling and frothy. That "quantum foam" bedevils
   researchers trying to concoct a quantum theory of gravity
   because in it concepts such as "ahead" and "behind" or
   "sooner" and "later" can loose their meaning. And no one has
   explained how the four-dimensional spacetime we take for
   granted emerges from the fantastical foam. Researchers have
   attempted to generate familiar four-dimensional spacetime by
   adding up all the possible configurations of the foam, thus
   borrowing a page from quantum mechanics, in which theorists
   assume that a particle travels between two points by taking
   every conceivable path at once. But these calculations have
   produced spacetimes that have either just two dimensions, or
   infinitely many.

See: http://focus.aps.org/story/v14/st13

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