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Is Retrocausality inherently deterministic?

  1. Aug 28, 2015 #1
    I'm a "lurker" of this forum and decided to create an account because I was curious as to whether Retrocausality implies a determinate, or indeterminate view. I'm posting this thread as a derivative from the discussion taking place in the quotes down below from the following thread:

    Last edited: Aug 28, 2015
  2. jcsd
  3. Aug 28, 2015 #2


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    Welcome to PhysicsForums, Hybrid!

    Retrocausality is a component of a number of reasonable and viable interpretations of QM. The existing variations do not have any apparent contradictions with the predictions of standard QM. I could not really call these "deterministic" in the sense that there is still no obvious explanation for outcomes in specific cases.

    However, it does supply a mechanistic - even if "ad hoc" - that is both local and realistic. The "hidden" variables are not independent of the observer. The observer's choice of what to measure is itself a variable participating in an overall context, even though in the future. Those variables are local if you do not constrain the time direction, and that neatly otherwise explains all existing experiments apparently demonstrating non-locality.

    Superdeterminism is a non-scientific explanation for violation of Bell inequalities. Essentially it says: The true value of some testable value is X, but the observed value is inexplicably Y, although other testable values do not deviate from the observed value.

    It fails because it can equally apply to ANY scientific theory or experimental value and therefore provides no useful explanation. c is not c, h is not h, and so forth. You may as well say that electrons are composed of tiny turtles you cannot see. Or that the entire universe, as well as yourself, was created last Thursday. Not very useful, obviously.

    On the other hand, most physical mechanisms are time symmetric anyway, and there is no obvious reason why time should be constrained to what we call the forward direction.
  4. Aug 28, 2015 #3
    Thank you for accurately answering my question, and just to clarify, what I'm taking from this is that Retrocausality is indeterminate, given the probabilistic nature of quantum mechanics?
  5. Aug 28, 2015 #4


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    There are different versions, but yes that is what I would say for all of them. There is still no explanation of why the possible outcomes collapse to a single one, only an explanation of how key things such as the double slit experiment or Bell tests are explained under the interpretation. All of this at a high level, of course.

    Relational Blockworld (RBW) substitutes acausal for indeterminate: "Such acausal, global determination relations do not respect any common cause principle." RBW does not identify with either time symmetric or retrocausal, although its concept of time places it squarely within that class of interpretations. It is one of the more comprehensively explained of the time symmetric interpretations.

  6. Aug 31, 2015 #5
    Considering that backwards in time signals automatically allow FTL signals, I fail to see why anyone would call retrocausality "local".
  7. Aug 31, 2015 #6


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    Any "action" that flows either forward or backward in time is constrained by c. Ergo it is local by definition. It is true that the net effect of a series of such component actions can appear non-local.

    As far as I know: You cannot construct experimental diagrams in which items display non-locality that cannot also be connected by local influences going forward and/or backward in time. Surely that must be suggestive of something.
  8. Sep 11, 2015 #7
    In the Relational Blockworld, is it pretty much all "one" world, where it's retrocausual and anything that can happen does happen and is time symmetric, indeterminate, but within the confines of that one "Universe", and time doesn't exist? No beginning and no end? All events/configurations "always" exist?

    Or is RBW agnostic when it comes to determinism?

    Also is this an accurate description of the RBW, but just looked at in a different light?


    After reading into RBW I find I'm very confused but intrigued, as with all interpretations of quantum mechanics.

  9. Sep 11, 2015 #8


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    I know it's frustrating to hear this, but unless and until any of these questions can be answered, at least in principle, by observation and experiment they are no part of modern science and they're out-of-scope for Physics Forums. RBW has many of the same problems as the block universe interpretation of Minkowski space, a topic that is explicitly off-limits here: https://www.physicsforums.com/threads/what-is-the-pfs-policy-on-lorentz-ether-theory-and-block-universe.772224/ [Broken]

    Anything that starts with "Warning: The central idea in today's post is taken seriously by serious physicists; but it is not experimentally proven and is not taught as standard physics" is not going to be an acceptable source under the PF rules.
    Last edited by a moderator: May 7, 2017
  10. Sep 11, 2015 #9
    Thanks for the reply Nugatory, and while it is a bit frustrating it's also true that it all comes down to interpretation. I'm just trying to in a way figure out where I stand, and was hoping Mr.Chinese would elaborate a bit more on RBW and the questions I was asking above.

    Hehe, I would assume so and maybe I shouldn't have posted that. I just found it a bit interesting while I was searching around for information regarding RBW.
    Last edited by a moderator: May 7, 2017
  11. Sep 11, 2015 #10


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    First, RBW is quite different from the kinds of block world prohibited here, although it does share the words "block world". Second, I think the best way to learn about it is from any of the key papers published by the authors, a couple presented below.

    More importantly, there are "some" physical predictions under RBW different than other interpretations! By Nugatory's definition, I think that would be called science. :smile: These differences involve fairly complex issues at the cosmological scale. There is evidence both in favor and against RBW at this level, and research is ongoing. Obviously, if there had already been a breakthrough, we'd know it. (The extremely short version is that re-calibration of "standard candles" per RBW leads to a fit of one body of data without the need for accelerating expansion of dark energy.)

    W.M. Stuckey, Michael Silberstein, and Timothy McDevitt

    To answer within the context of the OP: The authors do NOT consider RBW deterministic (nor even retrocausal). Rather than indeterministic, they prefer "acausal" or "adynamical". I group RBW with the retrocausal or time-symmetric interpretations because the future is part of the quantum context, a common element of this group. This despite the authors politely and patiently disagreeing (one is a PF member). :smile:
  12. Sep 11, 2015 #11
    Hey thanks for the follow up, and I will read into the arXiv PDF's you linked and look into it further. :smile:
  13. Sep 12, 2015 #12


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    not published in a peer-reviewed journal according to arXiv and not listed in INSPIRE!

    not published in a peer-reviewed journal according to both arXiv and INSPIRE!
    I've nothing to add, and from the abstract I don't think, I want to read these papers ;-).
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