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A paper with the same title as this thread has appeared in the journal Classical and Quantum Gravity (Tippett and Tsang, Class. Quant Grav. 34 (2017) 095006. The doi is 10.1088/1361-6382/aa6549). It describes a geometry in General Relativity that "...is a box which allows those within it to travel backwards and forwards through time and space, as interpreted by an external observer."
The geometry is similar to those proposed by Alcubierre and Krasnikov for what Krasnikov calls Hyperfast travel. This is a method of FTL travel that does not depend upon accelerating a spacecraft to superluminal velocities. The geometry of spacetime does all the work. Tippett and Tsang show how to adapt this idea to time travel. The paper is short and not especially technical, as these things go (e.g., Matt Visser's derivation of the Slater Determinant for the path integral description of a traversable wormhole...not pretty!). It also appears to me on first reading to be entirely plausible, by the somewhat elastic standards of plausibility one must needs use in discussions of time machine physics.
My only complaint about the paper is that the authors, for whatever reason, have not made an ArXiv preprint version of it available. The journal article remains behind a paywall. I can, however, recommend it to anyone with an interest in time machine physics, whether literary, philosophical, or professional.
The geometry is similar to those proposed by Alcubierre and Krasnikov for what Krasnikov calls Hyperfast travel. This is a method of FTL travel that does not depend upon accelerating a spacecraft to superluminal velocities. The geometry of spacetime does all the work. Tippett and Tsang show how to adapt this idea to time travel. The paper is short and not especially technical, as these things go (e.g., Matt Visser's derivation of the Slater Determinant for the path integral description of a traversable wormhole...not pretty!). It also appears to me on first reading to be entirely plausible, by the somewhat elastic standards of plausibility one must needs use in discussions of time machine physics.
My only complaint about the paper is that the authors, for whatever reason, have not made an ArXiv preprint version of it available. The journal article remains behind a paywall. I can, however, recommend it to anyone with an interest in time machine physics, whether literary, philosophical, or professional.
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