THE Universe might yet collapse in a devastating 鈥渂ig crunch鈥�. Physicists have shown that even though its growth is speeding up, it could still start to implode by the time it鈥檚 only twice its current age.
鈥淎 few years ago, nobody would even think seriously about the end of the world within the next 10 to 20 billion years, especially since we learned that the Universe鈥檚 expansion is accelerating,鈥� says Andrei Linde of Stanford University. 鈥淣ow we see it is a real possibility.鈥�
In 1998, astronomers studying distant supernovae found evidence that the expansion of the Universe is getting faster. This suggests that some kind of 鈥渄ark energy鈥� is pushing space apart.
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Most theories of dark energy propose that the Universe鈥檚 accelerating expansion is driven by a cosmos-wide repulsive 鈥渟calar field鈥� that has a uniform magnitude right across space. A similar energy field is thought to have made the Universe expand incredibly quickly just after the big bang, a period known as inflation. Last month, Linde won the Dirac medal for his role in developing this theory.
快猫短视频s have assumed that the repulsion of the field will drop as the Universe grows, eventually falling to zero. Though this would slow the rate of expansion of the Universe, it would never actually stop expanding.
But Linde says this assumption could be wrong. He and his colleagues have shown that according to some theories of supergravity, which try to describe gravity within the context of quantum theory, the dark energy from a scalar field will do more than simply reach zero 鈥� it will become negative and possibly even plunge as far as minus infinity. This would slow the rate of expansion of the Universe and then put it into reverse, causing space and time to collapse to a point in a big crunch.
Linde and his colleagues calculate that the typical time for the Universe to start this collapse would be in 10 to 20 billion years from now. Its current age is about 14 billion years.
鈥淭his was the greatest surprise,鈥� says Linde. 鈥淲e might be in the middle of the life cycle of the Universe, not at the beginning.鈥� His team鈥檚 report is at .
With both collapse and indefinite expansion possible, we seem to be further than ever from predicting the fate of our Universe. But Linde says observations of supernovae, the leftover radiation from the big bang and galaxy distributions should help resolve the issue by pinning down the densities of dark energy and matter at different times in the past.
鈥淚t was never easy to look into the future, but it is possible and we should not miss our chance,鈥� says Linde. 鈥淲e may be unable to change our fate, but we surely want to know it.鈥�
England鈥檚 Astronomer Royal, Martin Rees of Cambridge University, is keeping an open mind. He agrees that a future collapse is possible. 鈥淪ince we have no idea what the dark energy is, such scenarios cannot be ruled out,鈥� he says. 鈥淏ut ultra-long-range forecasts are all exceedingly speculative.鈥�