Time travel and grandfather paradox:

Earman suggests in his 1995 paper that physical possibility should be considered similarly with the laws of nature (i.e. logical possibility). Does this mean that it when David Lewis says Tom can humanly kill his grandfather (compossibile with the facts that he is a good marksman and has good aim etc.) implicitly assumes that it is also logically possible to kill his grandfather (thereby creating the contradiction).

This sounds like the same argument Vranas makes: https://onlinelibrary.wiley.com/doi/full/10.1111/j.1468-0114.2009.01353.x#

Would a solution suggesting that Earman and Vranas have intensional context in their mode of reasoning overcome this challenge to Lewis' contextualised 'can' vs 'cannot' solution to the grandfather paradox.

  • This question is unclear. Providing a description of "Lewis's solution", and of how you consider Earman and Vranas "challenge" Lewis's solution would help. Then state more clearly what you are asking about their "challenge".
    – Dcleve
    Dec 13, 2018 at 15:42

1 Answer 1


Earman and Vranas seem to want to protect the timeline. If Tom wanders out of a wormhole time-tunnel and meets his earlier self they are two distinct people. The timelines are blown.

  • Earman suggests (rightly) that physical possibility requires logical possibility since logical possibility is weaker than physical possibility. Hence, this challenges Lewis' solution which says that there is an equivocation (not contradiction) between 'can' versus 'cannot'.
    – Maths
    Dec 11, 2018 at 17:57
  • While Earman's response challenges Lewis' solution, it reaches the same conclusion that the past cannot be changed. Is this the right track? Would really appreciate everyone's thoughts. Thank you.
    – Maths
    Dec 11, 2018 at 17:58
  • How about if you shift from physical to mental. Quantum-entangled, time-tunnel telepathy. If you urge your grandfather to not date your grandmother and he does so, you disappear and your message becomes a dream. Dec 11, 2018 at 19:29

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