On the trolley a couple of days ago Toph and I were discussing the problem of what happens if you travel back in time and murder your parents before you are born. I rather thoughtlessly said she should try it and see, then decided to withdraw the suggestion.
“Maybe we can find a less bloody way to figure this out,” I said, and suggested the following variation:
On Monday, make a peanut butter sandwich and put it on a plate in the refrigerator.
On Wednesday, open the fridge.
If the sandwich is there, eat it, and then get in your time machine, return to Tuesday and eat the sandwich on Tuesday. But if there is nothing but a plate with crumbs, go do something else.
Much simpler, fewer complications.