Oliver Pooley – Relativity and the Growing Block

Relativity and the Growing Block – Oliver Pooley (Oxford)

Pooley investigates two problems that stand in the way of reconciling relativistic spacetime and the growing block. The first problem concerns the status of simultaneity and the present. A metaphysics of time that does not introduce a preferred simultaneity relation can claim to be more thoroughly relativistic than one that does. A B-theoretic “block universe” model of time can clearly be relativistic in this sense. In other work I have argued that a shrinking tree model that embraces relativism (in Kit Fine’s sense) is also appropriately relativistic. Can an attractive Growing Block view be fashioned along similar lines? I will argue that it cannot.

The second problem concerns the interpretation of spatiotemporal relations that hold of events within the Growing Block. Suppose, as many have, that a global present and a metaphysically preferred simultaneity relation are compatible with letter of relativity. One might then seek to argue that relativistic Growing Block models merely require that the physics and spacetime structure of the ever growing block obeys relativistic laws (Earman). However, the natural interpretation of such models leaves the view of time vulnerable to the “How does I know that it’s Now now?” objection of Bourne and Braddon-Mitchell. A promising response to this objection defends a Growing Block view that is a close cousin of permanentist presentism (e.g., Correia and Rosencrantz). On this view, the (spatio)temporal structure of the “block” is to be given an reductive analysis in terms of primitive tense. I will explore what would seem to be obvious difficulties with recovering relativistic spatiotemporal relations along these lines.

In investigating both these problems, I will seek to make contact with and illuminate some recent proposals by physicists seeking to reconcile relativity and the Growing Block (Ellis, Dowker, Sorkin).

Full paper here.

Because the papers are works in progress, they have been password protected. Please don’t quote or cite without permission. To register for the conference, and get the password, please contact Graeme A Forbes at G.A.Forbes@kent.ac.uk

5 comments

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  1. Peter Forrest

    Thank you Oliver.

    Do you think that quantum theory solves some of the problems Relativity poses for the Growing Block? Let me make a suggestion and then ask a more focused question.

    On something like the Briggs-Forbes theory we can posit many block-universes between which reality is indeterminate. These have, I hold, no privileged direction, being as C-theorists say. There is a hypertime, T, consisting of a totally ordered sequence of moments. At the beginning of hypertime there is maximum indeterminacy, but it gets less as T increases. On this theory, for each T there is a region r(T) is not completely determinate but much more so than the rest of space-time. For T*later than T the region of near determinacy r(T*’) contains r(T) as a proper part. So the near-determinate block grows.

    Now for my question: Can the objections from Relativity to the Growing Block be restated as objections to this Briggs-Forbes-ish proposal?

    Peter

  2. Natalja

    Thanks!

    I’d like to understand tenseless relativism better (p. 9). Does footnote 10 say that unlike Fine’s external relativist, the tenseless relativist doesn’t posit tensed facts (at the fundamental level)? Am I right in thinking that this is an additional, significant difference compared to the view mentioned at the beginning of section 4 according to which there is an absolute way reality is (and was), additional to the rejection of this absoluteness assumption?
    I take it the idea is that the reason T’s should be replaced by t’s is that there is no longer an A-theoretic time in which the truncated blocks persist. Rather, the times that reality is relative to are the original times in the block(s).

    But I’m not sure what exactly differentiates the view from a block view, i.e. what prevents the ‘as of’ locution from being interpreted in a block-friendly manner. As of t2, I was sitting, because as of t2, the universe is such that I am sitting (tenselessly) at t1; block-translation: at t2 it’s true that I was sitting, because I am sitting (tenselessly) at t1.

    Relatedly, I’m not sure why there is any need to treat talk of future growth differently from talk of past growth. Consider one time, and the block that contains it as the latest time. Why is it the case that we can consider only how, as of that time, things are from the perspective of earlier, not later times? Because as of that time, there aren’t any later times. But then as of later times, there are (aren’t there?). And since, in looking to the past perspectives, we use the ‘as of’ device, why not use it in looking forward as well?

  3. Rachael Briggs

    Very rich and interesting paper, Oliver; I particularly enjoyed the exposition of, and solution to, the problem posed by Brad Skow (and also by Kristie Miller in her paper for this volume). The problem is that there are too many entities that seem to be candidate truthmakers for claims about the past (such as “Oliver Pooley wrote a paper.”) One candidate truthmaker is an event that exists in an earlier part of the block (in B-time), at this very moment (in A-time). Another candidate truthmaker is a part of the block as it used to be at an earlier moment of A-time–a moment when Oliver Pooley’s paper-writing abutted the bleeding edge of the block. If the Growing-Block theorist claims that the first thing is the truthmaker, then there’s some problem—perhaps she has trouble accounting for the idea that the block used to be shorter, since there is no past part of the block (in B-time) right now (in A-time). If she instead claims that the second thing is the truthmaker, then she has no justification for committing herself to the concrete past; why doesn’t she switch to presentism, which offers all the same truthmakers without the ontological commitment?

    Part of your solution is to collapse the two different kinds of temporal dimensions by analyzing B-time in terms of A-time. The block is just a hunk of stuff. What makes some of the events in the block earlier is that there used to be (in A-terms) a past time t, such that they are present at t.

    This is ingenious. Does it address the “now now” problem? I’m not sure. I don’t yet know how to say, in your framework, that some event is happening now, as opposed to earlier.

    You might think that the events happening now are just those that are happening, but weren’t happening before, and the objects that exist now are just those that exist, but didn’t exist before. But that doesn’t seem quite right. The week-long jazz festival that is happening now was also happening yesterday; likewise, I exist now, and existed yesterday. A better thing to say would be to say that the events happening now are just those that are happening, and are intrinsically as they never were before, and the objects that exist now are likewise those that exist, but are intrinsically as they never were before. Last year’s jazz festival has undergone some mere Cambridge change since yesterday (it coexists with more things than it used to), but it hasn’t undergone any intrinsic change. This year’s jazz festival has undergone intrinsic change: it’s longer than it ever was before, and has more music than ever. Similarly, Napoleon has undergone some mere Cambridge change since yesterday, but I now have properties I never had before–I’m longer-lived than ever. (There’s going to be a problem if you’re an endurantist and you believe that things can persist for a while without changing intrinsically, but otherwise, it seems to work.)

    Given my proposed account of presentness, I can ask, “how do I know that I’m undergoing intrinsic change, unlike boring, static old Napoleon?” Your answer is that there is no fact of the matter as to whether I am undergoing intrinsic change. I am undergoing intrinsic change relative to my time; Napoleon is undergoing intrinsic change relative to his time; there is no fact of the matter about which of us is undergoing intrinsic change full stop. It also looks like there’s also no fact of the matter about which of us exists full stop. So Pooley has dissolved the “now now” problem, but at a cost–the Growing-Block theorist can’t say that future things are nonexistent full stop, but only that future things are nonexistent now.

  4. Rachael Briggs

    Another worry about my proposed gloss of “happening now”–it interacts oddly with relativity. It looks like events that are lightlike separated from me are going to count as happening now, which seems odd. If I get a message from Alpha Centauri, at the time when I receive the message, its sending counts as absolutely present. That seems odd.

    Equally oddly, events that are spacelike separated from me are not happening now, but will happen in the future–there are times in my future light cone that contain those events in their past light cones.

    One final oddity is that “now now” doesn’t collapse to “now”. Suppose Graeme beams a photon toward me while I’m holding up a mirror, so that the photon is reflected back to a detector in Graeme’s lab. Graeme detects the reflected photon. It looks like the following is true for him, at the time of detection: “the photon is being reflected off Rachael’s mirror now”. And it looks like the following is true for me, at the time of reflection: “Graeme is sending the photon now”. But the following is false for Graeme, at the time of detection: “Graeme is sending the photon now”. Lightlike separation is intransitive. (For similar reasons, so is spacelike separation.)

    This makes me wonder why your Growing-Block theorist doesn’t opt for the view that there is a preferred frame of reference which is not discoverable by any physical means.

  5. Steve Savitt

    On page 2 of your draft there is a long paragraph summarizing the relativistic view of times. I agree completely with what you say in that paragraph.

    In the next paragraph you say

    “Our situated experience, thought and talk, enjoyed and employed within the universe, is completely (and relatively directly) analysable in terms of this picture…”

    I trust that by ‘analysable’ you do not mean “translatable without loss of meaning”. If you meant that, your assertion would probably be incorrect.

    I suppose you mean something more like explainable, rather than analysable. Linguists are one group that try to provide such explanations for our use of tensed language. My tiny exposure to such work convinces me that (1) linguists consider subtleties far beyond any raised in our metaphysical papers but that (2) they may in the end succeed. (I am ever the optimist.) But whether they succeed or not, you have already said that “This [relativistic] picture leaves nothing out spatiotemporally speaking.” I would infer from this that one’s understanding of perspectival language is simply irrelevant to one’s understanding of spacetime.

    I am therefore puzzled by all the attention paid to language. If we were philosophers of language, then of course we would pay attention to language, of which temporal discourse is a part. But since we are philosophers of time, let us pay attention to time.

    From this perspective it is of course important to look at alternative views of time (and/or space) in our best physics, like causal set theory (as you do). It’s also useful to note, given a physical theory like special relativity, that the best way to restate a traditional metaphysical view like the growing block view is Stein’s (as you do). So it’s not as if there is nothing to do if you take the evolving world-picture of physics seriously and are puzzled about time. But, I ask seriously, why should one also be puzzled about language?

    [I know this is about Oliver’s paper, but I suppose I should anticipate an ad hominem response, since I have talked about tensed vs untensed language in varous papers. But I don’t take any of those reflections to help one understand time. I take them only, if correct, to help clear away some obstructions to examining time.]

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