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Aug 23, 2013 at 8:24 comment added pmnev @ Ben McKay: Thanks a lot, I beleive Luo-Stong's theorem answers my question.
Aug 22, 2013 at 17:33 comment added Ben McKay Tilla Weinstein's book discusses the Luo-Stong theorem, which apparently gives both necessary conditions and sufficient conditions, and she gives an explicit counterexample.
Aug 22, 2013 at 17:27 comment added Ben McKay Maybe the answer is in Tilla Weinstein's book An Introduction to Lorentz Surfaces.
Aug 22, 2013 at 17:25 comment added pmnev @Misha On a general Lorentzian disk one also cannot have a closed null-curve, if there were one, we would have a simply connected domain (the interior of the null-curve) with a non-vanishing vector field tangent to the boundary, which would contradict the hairy ball theorem. Concerning null-curves asymptotically approaching one another, I would expect that this is impossible on a disk too; that was a part of the question. On a cylinder, as opposed to the disk, one can have these effects, as e.g. in Misner space.
Aug 22, 2013 at 17:24 comment added Ben McKay Sorry, I didn't read the question carefully enough.
Aug 22, 2013 at 16:30 comment added Misha @pmnev: Null-curves on the discs is Minkowski plane is never recurrent, for instance; also, one null-curve cannot be asymptotic to another one. However, I would like to see an example of nontrivial dynamics on symply-connected Lorentzian surfaces as there might be some topological obstructions.
Aug 22, 2013 at 14:46 comment added pmnev Right, I understand that, but I did not ask whether all Lorentzian metrics on a disk are conformal to Minkowski metric on a standard disk. In terms of this dynamical system, my question is whether one arising from given Lorentzian metric on a disk can be realized on some closed curve (boundary of a domain) in Minkowski plane.
Aug 22, 2013 at 14:05 history answered Ben McKay CC BY-SA 3.0