CLAIMS that time travel is impossible in principle have been shown to be in error by an Israeli researcher. Amos Ori, of the Technion-Israel Institute of Technology, in Haifa, has found a flaw in the argument put forward recently by Stephen Hawking, of Cambridge University, claiming to rule out any possibility of time travel.
This is the latest twist in a story that began in the late 1980s, when Kip Thorne and colleagues at the California Institute of Technology suggested that although there might be considerable practical difficulties in constructing a time machine, there is nothing in the laws of physics as understood at present to forbid this. Other researchers tried to find flaws in the arguments of the CalTech team, and pointed in particular to problems in satisfying a requirement known as the "weak energy condition", which says that any real observer should always measure energy distributions that are positive. This rules out some kinds of theoretical time machines, which involve travelling through black holes held open by negative energy stuff.
There are also problems with time machines that involve so-called singularities, points where space and time are crushed out of existence and the laws of physics break down. But Ori has found mathematical descriptions, within the framework of the general theory of relativity, of spacetimes which loop back upon themselves in time, but in which no singularity appears early enough to interfere with the time travel, and the weak energy condition is satisfied (Physical Review Letters, vol 71 p 2517).
"At present," he says, "one should not completely rule out the possibility of constructing a time machine from materials with positive energy densities."
0 တဟက:
Post a Comment