STR and the Metaphysics of Time

The Special Theory of Relativity (STR) is one of the most well-confirmed theories in modern physics, or so I've been told by those I trust. It's also widely regarded by metaphysicians as being of utmost significance for the metaphysics of time. In particular, it's widely thought to have dealt a death blow to the tensed (A-theory) of time. The reason is that all versions of the A-theory of time require the postulation of an absolute, objective 'now', whereas STR only acknowledges simultaneity relative to an inertial reference frame. I say that STR doesn't 'acknowledge' absolute simultaneity here because I think that's the accurate way to put it, but many would endorse the stronger claim that STR positively rules out any such thing as an absolute, objective 'now'.

In a paper written about three decades ago, Hilary Putnam famously declared that STR had decisively settled the metaphysical debate between the A-theory and the tenseless (B-theory) of time in favor of the latter. More recently, in his 2001 book Four-Dimensionalism, Ted Sider has argued that the A-theory requires an objectionable 'scientific revisionism' regarding STR and is therefore to be rejected. Similar sentiments from B-theorists like Putnam and Sider can easily be multiplied. Furthermore, many major proponents of the A-theory like Dean Zimmerman admit that objections based on STR have kept them awake at night (Dean makes this admission in his contribution to a forthcoming book on debated questions in metaphysics).

I beg to differ with such sentiments. As I see it, few if any major metaphysical questions have been settled by advancements in science. The reason is that major metaphysical questions address issues at a deeper level than sciences like physics and biology are equipped to handle. In particular, I don't think that STR has any significance for the debate between tensed and tenseless theories of time. Pace Sider, I claim that A-theorists can embrace STR without any objectionable revisionism.

Here's how I see matters. Like Newton before him and like many others since, Einstein assumed that the 't' variable in his equations denoted time - not just time as it can it principle be measured by observers like us (empirical time), but time itself (metaphysical time). Newton had no particular need to distinguish between the two, though he certainly could have had he wanted to. Einstein, however, defines 'simultaneity' in broadly epistemic terms (recall his famous thought-experiment on how two observers, one on a swiftly moving train, the other standing beside the train tracks, would ascertain the timing of a lightning-strike at the front of the train). Given the fact that epistemological and metaphysical questions are distinct, Einstein therefore had a good reason for distinguishing empirical time from metaphysical time. But he didn't. He wrote as if his equations had metaphysical, and not just empirical, significance. And countless scientists and philosophers have just gone along with him in that. But why should anyone who appreciates the epistemology/metaphysics distinction grant STR such metaphysical significance? Why can't the A-theorist simply say that STR gives us an accurate description of empirical time but says nothing about the metaphysical time with which the A-theory is concerned? As far as I can see, that's a wholly respectable position to take. In philosophy of science terms, it amounts to opting for an instrumentalist, as opposed to a realist, interpretation of STR, at least as far as its references to 'time' are concerned.

One reason for thinking that this is the right approach to take is that the finite speed of light seems to be a metaphysically contingent fact. It is easy to imagine light, or some other type of signal, going faster and faster until, in the limit, transmission is instantaneous, in which case even on Einstein's verificationist epistemological criteria, we'd have to admit absolute simultaneity. Now how do we know that no such instantaneous signals exist? The only reason for thinking that they don't would have to be that if such signals did exist, then they ought to be detectable by us, but they aren't, etc. But why accept that? Why think that the limitations of our finite minds define the limits of reality? Furthermore, it seems at least possible that a being like God, one who is simultaneously present to and aware of the entire universe, exists. If so, then such a being's God's-eye view would provide a privileged reference frame that could be identified with the absolute, objective 'now' of a tensed metaphysical time. Of course, that reference frame wouldn't be of any use to physicists, but so what? Why should we expect specialists on matters physical to have anything particularly important to say about matters meta-physical? (Those who endorse scientific materialism - the view that the physical world is all there is - might suppose we have a reason for expecting this, but scientific materialism is a metaphysical thesis, not one that can itself be established by the deliverances of physics.)