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The mysterious cosmic presence called dark energy, which is accelerating the expansion of the universe, might be lurking in hidden dimensions of space. The idea would explain how these dimensions remain stable - a big problem for the unified scheme of physics called string theory... quantum vibrations in the vacuum of space (called vacuum energy or the cosmological constant) that could produce repulsive gravity... should either possess a ridiculously high energy density - 122 orders of magnitude larger than are observed - or cancel out to exactly zero. To make them almost-but-not-quite cancel, in agreement with astronomical observations, means fudging...

For a long time, Itzhak Bars has been studying time. More than a decade ago, the USC College physicist began pondering the role time plays in the basic laws of physics — the equations describing matter, gravity and the other forces of nature.Those laws are exquisitely accurate. Einstein mastered gravity with his theory of general relativity, and the equations of quantum theory capture every nuance of matter and other forces, from the attractive power of magnets to the subatomic glue that holds an atom’s nucleus together. But the laws can’t be complete. Einstein’s theory of gravity and quantum theory don’t...

ASPEN, Colo. - They all laughed 20 years ago. It was then that a physicist named John Schwarz jumped up on the stage during a cabaret at the physics center here and began babbling about having discovered a theory that could explain everything. By prearrangement men in white suits swooped in and carried away Dr. Schwarz, then a little-known researcher at the California Institute of Technology. Only a few of the laughing audience members knew that Dr. Schwarz was not entirely joking. He and his collaborator, Dr. Michael Green, now at Cambridge University, had just finished a calculation that would...

The purpose of FreeRepublic.com's multiple message boards is to limit the topics for each board to particular topics. Posting the same message on all the boards defeats the purpose of multiple-boards for special topics. It is very annoying to see the same message on every bulletin board. PLEASE! DO THE READERS A FAVOR. STOP CROSS-POSTING YOUR MESSAGES!

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...