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time travel

time travel

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time travel

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  1. time travel the grandfather paradox i

  2. If time travel is possible, then one can commit grampatricide before one’s father is conceived. • One cannot commit grampatricide before one’s father is conceived. • [So] Time travel is not possible. the grandfather paradox

  3. If time travel is possible, then one can commit retro-suicide. • One cannot commit retro-suicide. • [So] Time travel is not possible. the retro-suicide paradox

  4. If time travel is possible, then one can change the past. • One cannot change the past. • [So] Time travel is not possible. the altered past paradox

  5. The Law of Non-Contradiction: For any proposition P, it is not the case that (P & not-P). the altered past paradox

  6. The Change Principle: Necessarily, for any X, X changes only if there is some property P such that one of X’s temporal parts has P and one of X’s temporal parts lacks P. the altered past paradox

  7. If time travel is possible, then one can change the past. • One cannot change the past. • [So] Time travel is not possible. the altered past paradox

  8. Tim can kill Grandfather. • Tim cannot kill Grandfather. lewis’s puzzle

  9. The Compossibility Principle: A sentence of the form “A can X” is true in context C iffA’s Xing is compossible with the facts that are relevant in context C. lewis’s puzzle

  10. Tim can kill Grandfather. • Tim cannot kill Grandfather. lewis’s puzzle

  11. Tim’s killing Grandfather is compossible with the R facts. • Tim’s killing Grandfather is not compossible with the R+ facts. lewis’s puzzle