The Grandfather Paradox

The Grandfather Paradox is one of the better known problems in philosophy. It can be very briefly summarised as follows: if time travel is possible, then it should be possible to go back in time and kill your own grandfather before he has children. But, then you would not be there to kill him, therefore you wouldn’t kill him. So on and so forth, you get the picture.

This seems like a problem for the idea of time travel. However, clearly, it’s not. The events of the past have already been established and cannot change. Your grandfather has had children, and one of those had you. It seems impossible to think otherwise.

However, intuitively we want to believe that if time travel was possible, we could, at least hypothetically kill our own grandfather. Imagine time travel is possible and imagine someone who wants to kill their own grandfather.

David Lewis’ response to the problem is one I’m most familiar with, and he puts it beautifully. The time traveller can kill the grandfather, and he at the same time cannot. The time traveller might have everything necessary to kill the grandfather. In every way imaginable he is free to do so. He can kill his grandfather. However, the time traveller exists. Grandfather somehow will get out of the attempt alive. We know that because the past has already occurred and it is impossible to change it. In that sense, the time traveller cannot kill his grandfather.

Therefore, the seemingly contradictory statement that the time traveller can and cannot kill grandfather, is not actually a contradiction, as the can and cannot refer to different things.

This argument and example are roughly the same as that David Lewis gives in his article titled The Paradoxes of Time Travel. I consider it the most convincing solution to the problem posed by the Grandfather Paradox.


~ by majorshake on September 27, 2011.

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