No way out

日期:2017-12-08 01:46:25 作者:蔺钍 阅读:

By Charles Seife IT’S bad news for Star Trek fans. Black holes, which physicists believed could allow future civilisations to tunnel to far-flung regions of the Universe or even to other universes, appear to be useless for such intergalactic travel, Israeli scientists have shown. Einstein’s general theory of relativity describes space and time as a flexible fabric which the gravitational pull of an object can warp. In a black hole—the superdense remains of a collapsed star—the gravity is so enormous that it can be likened to a hole in the fabric of space-time itself. Scientists have speculated that if you could go through the hole in a spaceship, you would jump halfway across the Universe in an instant, or even emerge in another universe. But others argued that a black hole’s gravitational pull is so great that a spaceship would never escape from its grasp. Worst of all, anyone entering a black hole would slam into a “singularity”, a point where the bending of space-time becomes infinite and all matter is torn apart. But several years ago, physicists found a way round this. They speculated that a spinning or an electrically charged black hole might have a stretched-out singularity in the shape of a ring. In theory, a spaceship could fly through the ring without getting shredded. “It allows the observer to fall into a black hole and fly through it, and emerge nobody knows where,” says Nickolay Gnedin, an astrophysicist at the University of Colorado at Boulder. But now Piran and his colleague Shahar Hod have scuppered this idea. They used computers to simulate both how a charged black hole forms from the remains of a star and how the singularity behaves—the first time that a single computer program has simulated these two processes at once. The simulations showed that the formation of a black hole creates a new kind of singularity due to an effect called “mass inflation”. When a traveller moves towards the black hole, the apparent mass of the hole increases to infinity. So in the end, the traveller would indeed be ripped to shreds (Physical Review Letters, vol 81, p 1554). “This singularity goes through the entire system,” says Piran. “It doesn’t leave any hole through which matter may pass.” “It’s quite an amazing piece of work,” says Eric Poisson, an astrophysicist at the University of Guelph,