Whoever wrote that either hasn't read Hawking's paper, or completely misunderstood it. Even the abstract makes it clear that an energy 'back-reaction' would counteract the formation of a loop back in time (a closed time-like curve). Basically, the more curved spacetime becomes, the greater the resistance to further curvature. He concludes that, 'The laws of physics do not allow the appearance of closed timelike curves'.
Of course, Hawking may be wrong - but his paper doesn't support the claim made about it.
It has been suggested that an advanced civilization might have the technology to warp spacetime so that closed timelike curves would appear, allowing travel into the past. This paper examines this possibility in the case that the causality violations appear in a finite region of spacetime without curvature singularities. There will be a Cauchy horizon that is compactly generated and that in general contains one or more closed null geodesics which will be incomplete. One can define geometrical quantities that measure the Lorentz boost and area increase on going round these closed null geodesics. If the causality violation developed from a noncompact initial surface, the averaged weak energy condition must be violated on the Cauchy horizon. This shows that one cannot create closed timelike curves with finite lengths of cosmic string. Even if violations of the weak energy condition are allowed by quantum theory, the expectation value of the energy-momentum tensor would get very large if timelike curves become almost closed. It seems the back reaction would prevent closed timelike curves from appearing. These results strongly support the chronology protection conjecture: The laws of physics do not allow the appearance of closed timelike curves.
Of course, Hawking may be wrong - but his paper doesn't support the claim made about it.
Last edited:
Upvote
0