110 likes | 267 Views
time travel. the grandfather paradox i. 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.
E N D
time travel the grandfather paradox i
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
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
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
The Law of Non-Contradiction: For any proposition P, it is not the case that (P & not-P). the altered past paradox
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
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
Tim can kill Grandfather. • Tim cannot kill Grandfather. lewis’s puzzle
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
Tim can kill Grandfather. • Tim cannot kill Grandfather. lewis’s puzzle
Tim’s killing Grandfather is compossible with the R facts. • Tim’s killing Grandfather is not compossible with the R+ facts. lewis’s puzzle