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Yael Loewenstein (Houston/Cambridge) “Against the Standard Solution to the Grandfather Paradox (And How Not to Understand Time-Indexed Modals in Contexts with Backwards Causation)”
12 June 2019, 4:30 pm – 6:00 pm
Abstract: 1000 time travellers travel back in time, each with the intention of killing his or her own infant self. Do they succeed? We start with the assumption that there is no branching time. If the possibility of backwards time travel is not to lead to logical contradiction, every time traveller must fail for some reason or another: perhaps one slips on a banana peel, another kills the wrong child, etc. Although a logically consistent story can be told in which each time traveller fails, it is seemingly inexplicable that something will go wrong for each one.
For a time, this inexplicability objection was thought to provide powerful evidence that there is something incoherent about the possibility of backwards time travel in a universe without branching time. Following David Lewis (1976), however, there is now near-consensus in the literature that the objection has no bite: there is nothing anomalous or inexplicable about the fact that something will go wrong in each case. For as Jenann Ismael (2003) puts it, “…it is built into the description of the class of cases that we are considering…that they are failures, in the same way it is built into the description of the class of cases in which I don’t get ahold of my mom on the telephone that they are unsuccessful…And just as in the case of my failed attempts at mom-calling, there are diverse and unrelated explanations of the individual failures, but nothing spooky or coincidental about the fact that all founder.”
I will argue that although the failure to commit auto infanticide is indeed already built into the description of the class of cases being considered, the example differs from Ismael’s example, and others like it, in a crucial respect. Attending to this difference helps to pinpoint what makes the grandfather paradox so troublesome for the possibility of backwards time travel, and where the inexplicability (still) lurks.