I've been rereading Sider's argument against presentism in Four-Dimensionalism (4-Dism). This time around, I've been struck by the weight Sider places on a certain type of verificationist claim. I provide three examples, with commentary. First:
The main problem with [saving "a single "hyperplane" of simultaneity relative to some frame of reference"] is that it is scientifically revisionary, for it in essence recognizes a distinguished relation of simultaneity. (Sider, 4-Dism, p. 47)
Sider also knocks the notion of "absolute position" on the following grounds:
The problem is that there is no empirical basis for assuming that absolute comparisons of position make any sense. (Sider, 4-Dism, p. 28)
Finally:
The point, then, is that the physical considerations in Newton's rotating bucket thought-experiment do not support that claim that cross-time comparisons of position are meaningful, since Minkowski and neo-Newtonian space-times account for the thought-experiment (and are physically adequate in other ways as well). (Sider, 4-Dism, p. 31)
I'm not at all sympathetic to these types of argument. In the first place (and taking Sider's points in reverse order), cross-time comparisons of position are clearly meaningful. I take myself to know what people mean when they make such comparisons. Now if I was a verificationist, I might not think that such comparisons were meaningful (on the assumption that there is no method of empirically verifying the truth of such comparisons, which I'll grant). But nobody should be endorsing verificationism these days. So what's going on? Perhaps the thought is that such comparisons aren't "empirically meaningful" in the sense that they can't be verified empirically. But that's not to object to them unless one thinks that investigation of the nature or structure of space and time is a task for scientists only. I don't see why I should buy that latter claim, nor have I ever seen an argument for it. I'm open to hearing them, though.
Sider's second claim concerns whether "absolute comparisons of positions make any sense". Here he says we have no "empirical basis for assuming" that they do make sense. Let's suppose he's right about that. Does that show that they don't make sense? Does that show that we have no reason to think they make sense? Again, of course not. I suspect one would endorse such a position only if one was in the grip of a philosophical theory according to which cross-time comparisons of position can't make sense unless there is empirical evidence available that can support such comparisons. But I'm not in the grip of such a theory, and I know of no good reason to endorse such a theory. Where is the defense of this odd theory?
Lastly, I'll grant that to privilege a hyperplane of simultaneity is revisionary, in some sense of "scientifically revisionary". It's "revisionary" in this sense: most scientists don't privilege (or think there is any good scientific reason to privilege) any such particular hyperplane. But scientific reasons, again, aren't the only reasons there are. And as far as I can see, there is zero scientific evidence that rules out privileging such a hyperplane. In other words, the scientific evidence we have supports SR, but not a version of SR that entails that there is no such privileged hyperplane. If I'm right about what our current empirical evidence shows, then the fact that most scientists don't endorse a privileged hyperplane is, while revisionary in a certain sense, not revisionary in any philosophically interesting sense. One should only care about being "scientifically revisionary" in the interesting sense when the best scientific evidence we have shows or provides support for the claim that one's revisions are false. But since this is not the case, the appeal to being "scientifically revisionary" is empty.
None of this is to say that Sider doesn't present some powerful arguments against presentism. Indeed, 4-Dism contains the best presentation of the arguments presentists like myself have to face. Many of these arguments are powerful. But where the arguments turn upon considerations like the one's above, I'm not convinced. There they seem to sacrifice philosophy on the altar of science. But I'm open to being possibly enlightened.
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