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.)
Hi again,
I’m not sure what I think about these issues myself – it’s not clear to me really how damaging STR is to presentism.
I do wonder, though, what you mean exactly by this distinction between ’empirical time’ and ‘metaphysical time’. I guess you could say something like that it’s a distinction between ‘time as experienced’ and ‘time as it is in itself’ but that wouldn’t really be any clearer – it’s not as if there were two times and we experience or theorize about one and not the other. Maybe all you really meant by using such terminology was that STR is empirically adequate but its theoretical structure doesn’t (or we don’t have any reason to think that it does) correspond to anything in reality (and thus take an antirealist position concerning STR). If that’s what you mean, that makes better sense.
In any case, I can see opponents saying some things like the following (I don’t know if any of this is very plausible since I don’t enough about these debates, but see what you think):
It’s ad hoc to consider STR in an antirealist fashion but not other scientific theories (assuming this is true) when STR has lots and lots of confirmation – its one of our best. And reality really being how STR says it is is the best explanation for the experimental evidence we’ve seen and the fulfillment of STR’s predictions, etc. such as relativity effects like time dilation and so on.
In addition, I think (maybe) a lot of the reasoning behind STR has historically had to do with Einstein and others’ belief that physics is the same in every frame. You could argue from this to the realist truth of STR in this way (I’m probably messing this up a bit but here it goes): There’s at least in some places no material medium in space for light to be transmitted through and yet it transmits through such spaces all the same. But if light had a velocity of 0 then it would be a kind of standing electromagnetic field. But those sorts of thing physically require a material medium to be grounded in. So, as a part of physics, light can’t have a velocity of 0. But since physics has to hold exactly the same in each frame, there can be no frame in which light has a velocity of 0. What you need to get to STR exactly now is that light has the same constant speed in every frame, but I think you might be able to argue in a tight way from the non-zero claim to that in some way. But even if you couldn’t do something formal, STR would greatly simplify and explain systematically the non-zeroness of light velocity. But then you pretty quickly get STR mathematically out of all that. And even if we left off those extra arguments, it’s very likely (perhaps – I can’t remember the math around all these issues) that the non-zeroness of light’s velocity in all frames may produce relativistic consequences anyways.
One could here, on your side, appeal to considerations from other parts of physics like quantum mechanics to argue for a privileged foliation of spacetime, but it’s not clear in that case that this can help the presentist (though it may be more help to the eternalist A-theorist, though that’s not crystal clear either) since you’ve still got a picture with all these NON-privileged foliations lurking about too. Though maybe the presentist can deal with all this too.
I’m not sure that any of that is accurate at all, but it’s something to chew on.
Anyway, thanks for a great blog. I discovered it a little while back and have been enjoying it.
Almost forgot, I wanted to comment on this:
“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.”
I’m not sure how such a being’s God’s-eye view would provide a privileged reference frame. For one thing the force of ‘simultaneously’ is unclear here. If you mean absolutely simultaneous, that seems question-begging whereas if you mean simultaneous relative to a certain frame then it’s unclear what could decide the reference frame unless it is that being’s reference frame in which case that being would have to be traveling through spacetime on a certain trajectory. But then it couldn’t obviously be simultaneously present to the entire universe since the universe on STR is a fourdimensional manifold enompassing absolutely non-simultaneous regions (but maybe I’m misunderstanding ‘present to’ here). So I guess none of that was clear to me (and maybe nothing I’ve just said is very clear either!).
In any case, even if you did have a privileged reference frame, you couldn’t identify that with an absolute now since a reference frame isn’t a time but is more like a set of coordinate axes extending through spacetime. So it’s just not the right sort of thing to that sort of work all on its own.
Hi Ian,
Thanks for your comments. Let me try to address some of them.
(1). Empirical time vs. metaphysical time. As I understand STR, it makes accurate predictions about the observable rates of physical processes and about the observable sequencing of physical events in relation to different reference frames. Thus, STR may predict that I, in my reference frame, will observe three events, A, B, C, in that order separated by 1 sec, whereas you, in your reference frame, may observe the sequence as ACB with a 1 sec gap between A and C, and a 2 sec gap between C and B. This is the kind of thing that I mean by ’empirical time’ – the observable rates and sequences of physical processes and events as measured under normal physical constraints.
As for ‘metaphysical time’, by this I mean the actual rates and sequences of processes and events (whether physical or not) as it would be measured by a hypothetical ‘ideal’ observer, one not subject to any physical constraints (finite speed of light, etc.).
As far as I can see, STR is only concerned with empirical time and has nothing whatsoever to say about metaphysical time. Thus, if when the A-theorist claims that there is an objective, absolute ‘now’ he is talking about metaphysical time, then there is no clash with STR.
(2) Ad hocness. You worry that it may be ad hoc to single out STR for an instrumentalist reading while holding to a realist interpretation of other scientific theories. That’s a legitimate concern, but I think it’s one that is fairly easily met. All the A-theorist needs is some kind of independent reason for positing metaphysical time. For example, a theistic A-theorist has an independent commitment to the existence of an ideal observer not subject to physical constraints (i.e., God).
(3) God’s-eye view. You wonder how bringing in a God’s-eye view could establish a privileged reference frame. I take it for granted that, for a being like God, simultaneity means ‘absolute simultaneity’. You think this is question-begging, but how so? The point of my post was to argue that STR does nothing to rule out an A-theory of time. It’s not question-begging if, in the interests of making that case, I help myself to an A-theory of time.
(4) Finally, you write “even if you did have a privileged reference frame, you couldn’t identify that with an absolute now.”
Good point. What’s needed is not just a privileged reference frame, but something that singles out a particular time as ‘now’. For moving spotlighters this is the spotlight. For growing blockers, this is the leading edge of reality, the point at which new event accrue. For presentists, this is simply the real.
Would the distinction be like that between absolute and relational time? Time exists as an absolute, allowing change etc., and then there is time as measured by clocks, which might change their speeds (relative to absolute time) for various physical reasons (?) If so, this reminds me of 10-dimensional superstrings. I don’t know much about them either, but it seems that physicists are simply regarding varying physical magnitudes as extra dimensions because that makes the maths simpler (like regarding colours as extra dimensions), which would not be much of a threat to a belief that space-time was really (3 + 1)-dimensional (?)
Hi Enigman,
No, my ’empirical’/’metaphysical’ distinction cuts across the ‘absolute’/’relational’ distinction.
An absolutist view of time takes it to be analogous to a container within which events take place. Thus, time is something in addition to events. A relationalist view of time says denies that time is anything over and above (or under and beneath) events.
By ’empirical’ time I mean the sequencing of events as measurable by beings limited to finite transmission speeds. By ‘metaphysical’ time I mean the sequencing of events as measureable by beings unlimited by finite transmission speeds.
STR, I claim, tells us a lot about empirical time, but it can’t rule out metaphysical time, which is what A-theorists are concerned with. When physicists and A-theorists use the same word ‘time’ for both, they talk past each other.
Hi Alan,
Thanks for the replies! I think you’ve addressed most of the concerns, but I’m still wondering what you think of the scientific concern I mentioned about the speed of light in inertial frames. Do you think that would be a problem for presentism?