In a recent paper, I offered my readers the following thought experiment:
"You are in the kitchen one day with your spouse and, suddenly, everything around you freezes. Your spouse stops moving, the clock stops ticking, the crickets stop chirping, but you continue to move normally. Suddenly, a man walks into the room. He explains to you that he is a time-traveler from the future. He takes you on several time-traveling trips with him and convinces you beyond any doubt that he has the power of time travel he claims to have. When you finally return to the kitchen, he informs you that when he leaves and time begins to move normally for everyone else again, he needs you to kill your spouse. If you do not, he explains, he will travel five years into the past and kill your spouse himself."
The purpose of this thought experiment was to probe my readers' intuitions on this story, with an eye towards making an argument about the unreliability of our intuitions when we are confronted with temporally abnormal situations.
After reading the paper, someone objected that I should not have used this thought experiment because it is not metaphysically possible. When I heard this, I was rather surprised, not because I disagreed about the possibility of this example (though I don't think it is metaphysically impossible as it stands; it is just metaphysically impossible on the most natural reading of it), but because I don't tend to think that it always matters whether or not thought experiments are metaphysically possible. Of course, if the goal of the thought experiment is, for instance, to find out what we should or should not do in a given situation, it is pretty silly to offer a situation that could never happen. But given that the end goal here was somewhat tangential to the intuitions themselves, the question of possibility never occurred to me.
Anyway, the point of this post is to find out what everyone else thinks. Should our thought experiments always be metaphysically possible? If not, is it always preferable that they be so? If not, should I still have used one in this particular instance? Inquiring minds want to know.