>Motivation: Can there be in-universe traversable wormholes which can never be time machines? There was a paper(?) that noted that specific configurations of w

>Motivation: Can there be in-universe traversable wormholes which can never be time machines? There was a paper(?) that noted that specific configurations of wormholes (basically tree shaped, no loops) do not allow time travel. I think it or another paper postulated some mechanism for wormholes collapsing if they violate that property.