Is Last Thursdayism possible?

Last Thursdayism is the idea that all of us and the world around us just came into existence last Thursday. We have what appear to be memories of a past that pre-dates last Thursday because when we came into existence, our brains were formed in such a way as to contain those false memories.

Last Thursdayism isn't actually a belief a certain segment of the population believes in. It's mainly just used as a thought experiment to illustrate certain points. I've invoked it to illustrate how it's possible to know some things without being able to prove them. I can't prove that anything happened before last Thursday, but I'm nevertheless justified in thinking it did. However fallible my memory may be, it still justifies me in believing certain things about the past.

Last Thursdaism can't be disproved by some appeal to evidence because the world would look exactly the same whether it's true or false. Our memories would be exactly the same, too.

This thought experiment rests on the mere possibility of Last Thursdaism. A person might object to Last Thursdaism on the basis of something else they know by intuition--it's impossible for something to come from nothing. If it's impossible for something to come from nothing, then Last Thursdaism isn't possible.

Does this undermine the thought experiment? I don't think it does. First, I think Last Thursdaism can be offered as a logical possibility. Creation out of nothing isn't a logical impossibility. It's more of a metaphysical impossibility. So Last Thursdaism can be logically possible without being metaphysically possible.

Second, it depends on what you're using Last Thursdaism to illustrate. I use it to illustrate the fact that we can know some things without having to prove them. A person might object to my illustration by saying, "We know there's a past because creation out of nothing is impossible, so things couldn't have just popped into being fully formed." But the reality is that we all know there's a past, and our intuition about creation out of nothing has nothing to do with it. We don't reason from that intuition to our belief in the past. That makes the impossibility of creation out of nothing irrelevant to the illustration.

Third, as I've said in some previous posts, I don't think thought experiments necessarily have to describe possible states of affairs in order to do some work for us. Even if we grant that Last Thursdaism isn't possible (whether physically, logically, or metaphysically doesn't matter), we can imagine it being possible, and we can use that imaginary state of affairs to illustrate our point. It's similar to how Aristotle imagined a state of affairs in which the law of non-contradiction didn't hold in order to illustrate why we all know it does. His scenario wasn't possible, but it gets the point across.