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Comment by ben_w

4 days ago

"A" universe, but not "the" (i.e. our) universe.

Specifically: https://en.wikipedia.org/wiki/Gödel_metric

It's specifically a universe where time travel definitely happens.

From the paper:

> Finally, we stress again that our main results are valid in an arbitrary background spacetime (including charged Kerr black holes [51, section 12.3]), provided that the CTC of interest is the orbit of a periodic one-parameter family of symmetries of the metric. This happens in all axisymmetric models whose rotation Killing field becomes timelike somewhere.