Presentism and Relativity

Familiarly, presentism faces an objection from special relativity. According to special relativity, so the objection goes, there is no such thing as absolute simultaneity: events that are simultaneous according to some reference frame are not simultaneous according to another. As a result, what counts as the present is different from one reference frame to another. If presentism is true, then, what exists must vary from one reference frame to another. But this is uncomfortable. Let us spell this argument out in a bit more detail.

1) There is no such thing as absolute simultaneity. (Premise from special relativity.)
2) Only the present time exists. (Premise from presentism.)
3) Only presently existing things exist, and only presently occurring events are occurring. (From 2.)
4) The present time is the time that includes all and only what is simultaneous with your reading of this . (Analytic of ‘the present time’.)
5) What is simultaneous with this utterance varies from one reference frame to another. (From 1.)
6) What things exist, and what events are occurring, varies from one reference frame to another. (From 3, 4 and 5.)

Presentism looks unacceptable then insofar as special relativity and what we might call ontological absolutism – the claim that what things exist, and what events are occurring, is absolute and not relative to anything; a fortiori it is not relative to a reference frame – are both acceptable.

What does the presentist need to do to meet this objection? A sufficient condition for meeting it, presumably, is that they give some reason for privileging one reference frame over any other; for in that case they can claim simply that what exists is what is simultaneous with your reading of this according to the privileged reference frame. What is simultaneous with your reading of this according to non-privileged reference frames is neither here nor there: there is no pressure to think these things exist unless they are simultaneous with your reading of this according to the unique privileged reference frame.

But how can the presentist have a reason for thinking that one reference frame is privileged (without resorting to claiming that God smiles upon one and not the others)? What could ground the privileged status of one reference frame over another, given that the physical facts don’t appear to distinguish between them?

I hear that question as a question about truthmakers. What we need is a truthmaker for the claim that some reference frame is privileged. If there is some ontological ground for distinguishing one reference frame from the others – some thing or things that mark to pick out one reference frame – then we can, without being arbitrary, take that reference frame to be the privileged one: the one that reveals what there is. So what might the truthmaker be for the fact that some reference frame is the privileged one?

Remember that, for the presentist, to exist is to be present. So consider all the events that exist – they are all and only the presently occurring events. So surely the privileged reference frame is just that one according to which exactly these events are simultaneous. In that case the truthmaker for the fact that this is the privileged reference frame is just what makes it true that those events exist – namely, those events.

So the thought is this. Everyone in this debate agrees that there is a unique set, S, which is the set of the existing entities. (That just follows from the assumption of ontological absolutism, and if you reject that then there is no problem in the first place.) This lets us single out a unique reference frame: the unique reference frame according to which exactly the members of S are simultaneous. And so, if we’ve got good reason to think that everything that exists is present then we’ve got good reason to think that this frame is the privileged reference frame. Since everything in S exists then everything in S is present; so they had better be simultaneous; so the reference frame that says they are simultaneous (and that nothing outwith S is simultaneous with any of them) is obviously the privileged one.

I imagine that seems way too quick. But ask yourself what the demand against the presentist is. It’s not that they must be able to discover what is present. The preceding remarks do not help the presentist do that. It may be in principle impossible for the presentist to know what exists because it is in principle impossible for them to know if their reference frame is the privileged one. But the objection against the presentist wasn’t epistemic, it was ontological. The objection wasn’t that discovering what is present, and hence what exists according to the presentist, is made difficult because there is no absolute simultaneity; the objection was that there is no absolute fact of the matter as to what is present, and hence no absolute fact of the matter as to what exists according to the presentist, because there is no absolute simultaneity. That is what I think is answered by the preceding remarks: insofar as we have reason to think that there is an absolute fact of the matter as to what exists, the presentist has reason to think that there is an absolute fact of the matter as to what is present, since granting the presentist that there is a unique set of existing entities allows them to uniquely specify a reference frame – the reference frame according to which they are all only the present things. What other reference frame could be a candidate for being privileged, given that the presentist thinks that to exist is to be present?

(And the epistemic objection doesn’t seem too worrying to me in any case. It seems to reduce to: you can’t know what exists, because you can’t know if you’re in the privileged reference frame. But why is that any better than any of the myriad sceptical challenges that aim to undermine your knowledge by showing that there are empirically equivalent possibilities where you get it wrong?)

I think the objection against the presentist has seemed more forceful than it is due to the assumption that the presentist should be able to pick out a unique reference frame independently of picking out the class of existing entities. But why hold that assumption? It’s not as if those entities exist in virtue of that reference frame being privileged. If that were the case then it may well be objectionably circular to presuppose their existence in an explanation of why that reference frame is privileged. But existence facts are, plausibly, brute: when it is true that a exists it is true solely in virtue of a. So the existence of the members of S can be taken for granted in any metaphysical explanation we choose to give – indeed, if the truthmaker theorist is right, all explanation comes to a halt when, and only when, we reach propositions concerning what the members of S are.

The members of S don’t exist because they are all present according to the privileged reference frame; rather, it is that reference frame that is privileged because it is the one according to which all and only the members of S are present. All of us, presentist and non-presentist alike, have to simply accept as brute the existence of some entities. For the non-presentist, accepting a set of things whose existence is brute does not serve to privileged one reference frame, but that is precisely because they don’t accept that to exist is to be present. For the presentist, however, these entities must be present, because everything is present, and so it follows immediately that only a reference frame according to which all and only these things are simultaneous is one that gets things right. Since we are sure of at least one thing that it is present – namely the reading of this sentence – and since there is a unique reference frame according to which that event is simultaneous with exactly the members of S, we know that that reference frame is the privileged one.

The argument from relativity might have force against other versions of the A-theory – such as the moving spotlight or growing block views – that postulate a privileged present without saying that what it is to exist is to be present. Such views require a privileged frame of reference but can’t say that it is the frame of reference according to which all the existing things co-exist: that frame of reference would get things wrong since both views admit the existence of past entities as well as present ones. And so they need another answer as to what grounds the privileged status of the reference frame that gets things right, and it’s not clear what they can say. But presentism, I think, faces no problem: and so this is one reason to think that presentism is the best version of the A-theory available.

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10 responses to “Presentism and Relativity

  1. Hi Ross, that’s a really nice point. So I wonder whether this means that all it takes for presentism to be true is that there is some frame of reference such that everything which exists is simultaneous with the present moment according to that frame of reference? Call that condition (A).According to you, the truth of (A) will suffice to privilege the frame of reference which makes (A) true, which means that everything which exists is present, and so presentism is true. But that makes it seem that really the presentist is committed to a second claim on top of (A): that if (A) is true, then the frame which makes (A) true is privileged as present – call that claim (B). Now I’m tempted to say that it’s fruitless to argue for or against (B); I for one wouldn’t see much point in resisting (B) if I bought into (A). But I’m also unsure what philosophical arguments could be put forward for or against (A), or indeed for the necessity of (A). Maybe you’re thinking that we could give a general argument for A-theory, and then use the argument from relativity to rule out the other versions of A-theory. That would be a way of arguing for the combination of (A) and (B) without arguing for either individually. That feels fishy to me, but I can’t quite put my finger on why.

  2. A sufficient condition for meeting it, presumably, is that they give some reason for privileging one reference frame over any other; for in that case they can claim simply that what exists is what is simultaneous with your reading of this according to the privileged reference frame.Won’t ‘x is present’ be indexed to the frame of reference of the utterer of that proposition? It sounds like ‘x is present’, which is already indexed to the world in which it is uttered should be indexed to the world-frame pair (w, F). So which reference frame gets privileged will depend on who is speaking. But in ordinary discussion, we simply won’t make that distinction. We’ll talk ontologically pass one another a bit, but not enough to matter. What did I miss?

  3. (5) in the argument is what sounds false.5) What is simultaneous with this utterance varies from one reference frame to another.(5) seems false for the same reason that (5′) is false.5. What is nearby Smith varies from one location to another.What’s nearby Smith is the table, and that’s true no matter what your location happens to be. What is simultaneous Smith’s with uttered sentence S is the table. That should be true at any reference frame, no?

  4. Hi Ross, I like the gist of this post – it’s something I’ve thought myself on occasion. My only worry is this – doesn’t it just push the problem back a step further? Instead of wondering about why one frame gets privileged, we now have the new worry of why the objects which are simultaneous to each other in one frame exist rather than those which are simultaneous in another. We still have a kind of worry of how to pick out a privileged reference frame, it’s just transformed a bit. But isn’t it still the same basic worry, just in presentist terms? Or am I missing something?

  5. Hi Daniel (Nolan, Elstein, a.n. other?),I have a modest and a more ambitious claim. The modest one is just: one who already takes herself to have reason to be a presentist shouldn’t be moved to abandon presentism on hearing the objection from STR, because she has the resources to answer it. The more ambitious one is the (allegedly) fishy one: one who already takes herself to have reason to be an A-theorist should be a presentist, because then she will have resources to answer the STR objection that she wouldn’t otherwise have. What I definitely don’t think is that any of this gives anyone any reason to be either an A-theorist or a presentist.Hi Mike,I take it that the A-theorist wants to say that sentences like (5), or ‘x is present’, are ambiguous. There is, to be sure, the relative notion of ‘simultaneous’, which gives rise to a relative notion of presentness’. On the relative notion, ‘x is present’ will indeed be indexed to the F of R of the utterer. (I reject the claim that it’s already indexed to a world, incidentally, because I am not a Lewisian realist – no one else should think that claims are world-indexed.) But the A-theorist should also admit a non-relative notion: x is present simpliciter. I take it that if she can’t earn the right to say that, it’s game over for A-theory.(5) is just true given the relative reading of ‘simultaneous’ – unless what you have in mind is something like the following: what we judge as simultaneous according to a reference frame depends on what is simultaneous according to our frame of reference. So (5) would come out false because, essentially, ‘simultaneous with’ is rigid across frames of reference. Is that what you have in mind?But certainly, I agree that (5) is false on the absolute understanding of ‘simultaneous’ (whereby x and y are simultaneous iff they are both present simpliciter). The challenge which I was trying to answer is that the B-theorist doesn’t think the A-theorist can reject (5) in this way because she doesn’t think there’s an absolute notion of presentness or simultaneity.Hi Ian,I guess it doesn’t seem like the same worry to me. Partly because I don’t think that there is a worry here. As I’m thinking about it, once you’ve got to facts about what there is, your work in giving metaphysical explanations is done. If you ask me why the things in my ontology exist, you’re asking me to explain the brute facts.Now I guess you could object to stopping here, and insist that even facts about what there is demand metaphysical explanation. That would be an anti-truthmaker-theory-esque objection. But at the very least, that sounds like a very different kind of objection to the STR objection, and doesn’t seem to have anything in particular to do with the A-theory/B-theory debate.

  6. I actually agree with your more ambitious claim – that presentism might have an advantage over other versions of the A-series here – but disagree with your more modest claim that a presentist has nothing to fear from STR. The problem I have is with the following:And the epistemic objection doesn’t seem too worrying to me in any case. It seems to reduce to: you can’t know what exists, because you can’t know if you’re in the privileged reference frame. But why is that any better than any of the myriad sceptical challenges that aim to undermine your knowledge by showing that there are empirically equivalent possibilities where you get it wrong?This rejection of the epistemic objection seems much too quick to me. There’s a big difference between the underdetermination of theory by data in standard sceptical scenarios, and the underdetermination of the privileged frame by possible observations. The problem for the presentist who takes the ‘unidentifiable preferred frame’ line is that best theory tells us that there is no reliable method by which we could come to true beliefs about what is present and what is actual. But this contrasts with our normal view of the world whereby we do have a candidate reliable method (observation using the senses) which is capable of telling us about at least some present and existent objects. Without such a method, it seems that not only can we definitely not know which frame is the preferred one, but also that we know that we can’t know which frame is preferred.I think this matters – the notions of ‘present objects’ and of ‘existing objects’ just couldn’t play the cognitive role they do for us if their reference was unknowable. Without knowability, how do you have rational relevance? Any good account of our use of the concept of the present must be able to explain why presenthood matters to us, and this task seems impossible if we do not know what is present, and know that we do not know what is present.

  7. Totally fair points Al. I wasn’t really trying to address the epistemic problem here, only the metaphysical one, so I’m happy if I’ve done that: but you’re definitely right, the epistemic one shouldn’t be dismissed as quickly as I dismissed it.

  8. Pardon the intrusion – but I came across this post looking for an article and I wanted to make a brief comment. Presentism faces many potential obstacles from relativity, most of which depend on whether or not we live in a background free universe (or some other more exotic model. Yet I think that the issue of simultaneity may be a pseudo-problem. The assumption that Presentism requires a preferred frame of reference seems to accept that a 4D space-time manifold imposes physical reality on observables rather than the other way around.Basically, if you look at it from the viewpoint that relativistic space-time is defined by the set of events between particles that “exist”, and that spacetime “events” are not defined for particles that do not “exist”, a different model emerges. A hint at the possibility of constructing this model is found in the fact that it can be argued that the bundle of worldlines that is “you” grows longer until the day you die, and then has a fixed length. While it is mathematically difficult, I think it is possible to identify a subset of all worldliness, including yours, that are expanding – increasing in length – without identifying the “simultaneous” points on any 2 worldlines. To me that sub-set of expanding worldlines represents a relativistic physical reality without invoking the fundamental question of simultaneity. What is real becomes a kind of block universe defined by the relativistic relationships of particles that “exist”. If this is correct you have a Presentism that comfortably fits inside Einstein’s relativity, at least within GR.At the heart of all this is the issue of fundamental temporality, which is addressed in Carlo Rovelli’s extensive body of works – including “Physics Meets Philosophy at the Planck Scale”,http://xxx.lanl.gov/abs/gr-qc/9903045, and “A note on the foundation of relativistic mechanics. II: Covariant hamiltonian general relativity to field theory” (http://xxx.lanl.gov/abs/gr-qc/0202079).

  9. Hi Ross,There appear to be two major definitions of presentism (although I am not sure if either appeal):a) The doctrine that only the present is realb) The view that only present objects exist.Some may see these as being equivalent, whereas I do not. I totally agree with (a) but disagree with (b). Why? Because I don't believe that objects are real. I believe that they are mental constructs. Existence is one concept, separation is another. The act of objectifying, of isolating and naming, is something that we learn very early – it is part of our rudimentary language socialisation. However, it is cultural, it is paradigmatic and belongs to the dominant discourse, especially the philosopher’s discourse. This is also so for what may be called ‘events’ and their ‘reference frames’. Like your particles of a cat (another blog), how is it possible to demarcate what is cat from what is not? If one considers the particles to be, say, electrons, then they are (a) – for want of a better term – in motion, and (b) unable to be isolated.I would like to see some evidence for the existence of separate objects, that does not rely upon the concept of time, or that separate ‘times’ exist.Special relativity is, likely, an absurdism. It is dependent upon the impossible concept of separating observer and the observed and the whole. (Hence the uncertainty principle.) – Sanatan Saraswati

  10. This solution seems like a pretty modest solution to avoiding the problems posed by relativity. Personally, I accept the theory of relativity (and have an appreciation for the science), but I myself do not accept that change does not exist, contrary to some others. To do so, in my opinion, is to underestimate our conscious experience, as having changing experiences is integral to the way we experience the world (indeed, I wouldn't be experiencing the world the way I do if it were not for that). This, I think, is enough to vindicate the "A-series" over the "B-series" as defined.So I would accept the physics is true (even going so far as to adopt a block-universe ontology if it calls for it), but I believe that there has to be room somewhere in reality for our fleeting conscious experience. Perhaps there is a hidden undetectable frame somewhere, as you say, or perhaps a detectable frame does exist, but physicists just did not discover it yet with their current understanding(a theory that unifies QM and GR is still up for grabs, but I wouldn't hold my breath on the issue). Or maybe, if there is a block universe, that the time of this block universe is distinct from the time in which we attribute to our conscious experience, as described here:http://fqxi.org/community/forum/topic/259.These are just some of the options available, but I do not subscribe to any in particular. But essentially I accept that our conscious experience is dynamic and I leave it open for how to reconcile our conscious experience with reality.

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