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Themes > Science > Physics > Elementary particle physics > Elementary particle physics Today > Branes > Branes and other Universes |
Standard particles like photons, quarks and leptons, exist only in three-dimensional subspace, a three-brane. But there are also hidden (hyperspace) dimensions, known as ``the bulk.'' While matter and light stick to the lower dimensonal branes, gravity traverses both branes and bulk. The possibility of superstrings having effects at relatively low energies allows the possibility of hidden dimensions could be around a millimeter across. In these hidden dimensions, the 3 dimensions of our universe would be extremely thin (about 10-millionth of a billionth of a millimeter) but these universes woul exist in other dimensions, which are extremely thin relative to our universe. Such parallel 3-D universes, or three-branes, might contain unusual forms of matter, possibly forming stars, planets, etc. The specific laws of physics would be different, but the laws of gravity would be the same, because gravity can move across the braneworlds Such hidden worlds might explain the problem of the missing mass in the universe, the so-called "dark matter", needed to balance out the expansion of the universe. It is also neeed to explain the behaviour of galaxies. Galaxies spin as though they they are a single unit, not a loose agregation of stars. They also appear to contain matter far beyond their visible edges; occasionally distant stars brighten as though an intervening massive object has ``lensed'' their light by gravitational bending. But critics have pointed out that hidden millimeter-sized dimensions might conflict with observational data about the universe and its past. Many brane scenarios are inconsistent with current estimates of the age of the universe and measurements of the amounts of various chemical elements created in the big bang. It is also hard to reconcile certain brane approaches with a constant strength of gravity in the universe today. But it is too early to say if these objections apply to all versions of the brane approach or just those proposed so far. |
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