Let w be a world where there is only one finite being, George. George has always existed in w. Moreover, each day for George has been just like the previous. Each day, George is mildly happy overall—except he has a minor itch that he can't scratch. Let us suppose that the laws of nature in w are such that they allow one deviation from the endless cycle of repetition from day to day—the itch can disappear (and only in one way, at one particular time of day). After the itch disappears, each day will be mildly happy, and indeed happier than before, and each day, except the first post-itch day, will be just like the previous for George (George won't remember how many days it has been he has lost the itch), forever. Here is an intuition:
- It is better for George to have his itch disappear tomorrow than to have his itch disappear in a billion years.
But not all theories of time can do justice to this intuition. If time is relational (which also, I think, would imply that the B-theory holds), and we tell the details of the story right, then the world where the itch disappears today if the same as the world where the itch disappears in a billion years—both are worlds where there is an itch for an infinite number of years, and then there is no itch for another infinite number of years. Therefore, either time is not relational or else no situation like the above is possible. But the only good reason to think that no situation like the above is possible is if one thinks that there cannot be indiscernibles or one thinks that it is impossible to have existed for an infinite amount of time. Thus, either time is not relational or there cannot be indiscernible times or it is impossible to have existed for an infinite amount of time. Since I think time is relational, I conclude that either there cannot be indiscernible times or it is impossible to have existed for an infinite amount of time.
It's also not clear that presentism fits with (1). In both of the scenarios mentioned in (1), there is a present itch, and the future does not exist. So why should one of the scenarios be better than the other? If this argument, which I am less sure of, is right, then either presentism is false or it is impossible to have existed for an infinite amount of time.
It would be nice to do better than just getting disjunctive conclusions. For that, we'd need other arguments to rule out of more disjuncts.