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For ever and ever

For ever and ever

作者:钱烛  时间:2019-03-08 02:14:06  人气:

By Marcus Chown THE Universe is likely to expand for all eternity. Not only that but the expansion is actually speeding up. This was the conclusion announced in March by astronomers who studied explosions of stars in distant galaxies. Two teams, led by Saul Perlmutter of the Lawrence Berkeley Laboratory in California and Alex Filippenko of the University of California at Berkeley, observed scores of distant “Type Ia” supernovae, in which one star in a binary pair explodes. The teams found they are about 15 per cent fainter than they ought to be. They believe the Universe’s expansion has speeded up while the light from the supernovae was en route to Earth, forcing the light to travel a greater distance. The only way this could have happened is if empty space somehow opposes gravity. This “anti-gravity” effect is represented in Einstein’s equations of general relativity by a term called the cosmological constant. But there is no theory which predicts how big the effect should be. Quantum theory could explain it only if the effect were about 10100 times greater than the teams have observed. Nevertheless, cosmologists have welcomed the result. “I wouldn’t bet my car on it yet, but I think it deserves to be taken seriously,” says Max Tegmark of the Institute for Advanced Study in Princeton. But some astronomers wonder if distant supernovae appear dimmer than expected because supernovae in the past were not as bright as they are now. No one has yet come up with a simple theory that makes early supernovae dimmer in a way that mimics the effects of a cosmological constant, however. If the cosmological constant is real, the Universe won’t collapse in a “big crunch”, but continue to expand for ever, becoming ever more barren as the stars die. In the words of T. S. Eliot, the Universe will end “not with a bang but a whimper”. More on these topics: