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Does Penrose's Andromeda paradox prove determinism?

  1. Dec 18, 2014 #1
  2. jcsd
  3. Dec 18, 2014 #2

    PAllen

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    No, and see our FAQ:

    https://www.physicsforums.com/threads/what-is-the-pfs-policy-on-lorentz-ether-theory-and-block-universe.772224/ [Broken]

    This question is philosophy more than physics, and not much discussion will be allowed here.
     
    Last edited by a moderator: May 7, 2017
  4. Dec 18, 2014 #3
    I was unsure, but thought, due to the argument/paradox being based entirely of special relativity, specifically relativity of simultaneity that it would be allowed. And also that I am not asking for opinion on determinism/free, it seems to be determinism to me, but I can't see it ever called it, so I'm wondering whether I'm missing something...?
     
  5. Dec 18, 2014 #4

    PAllen

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    If you read and think about the FAQ, then, in philosophy terms, the ontological character of simultaneity in SR subject to interpretation. The philosophic analog of minimalist interpretation is that simultaneity has no reality at all in SR (rather than being something real and frame dependent, it is a frame dependent convention with no reality status). Also, note that block universe and LET would provide radically different 'reality descriptions' of the Andromeda paradox, yet both are indistinguishable by experiment.
     
  6. Dec 18, 2014 #5

    PAllen

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    Well, a trivial, physics based argument that you can't prove determinism from SR is that QFT is the basis of the best theories we have for matter (the standard model). QFT is based on SR yet is non-deterministic.
     
  7. Dec 18, 2014 #6
    I haven't read much on LET, but this is great, thanks!
     
  8. Dec 18, 2014 #7

    PeterDonis

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    To the extent that the argument claims to just be deducing consequences from SR, it is not valid. The key error is in this sentence (from the Penrose quote given in the Wikipedia article):

    "Then they can hark back to that chance encounter, and come to the conclusion that at that time, according to one of them, the decision lay in the uncertain future, while to the other, it lay in the certain past."

    SR, as a theory, does not support the claim that "according to one of them, the decision lay in the uncertain future, while to the other, it lay in the certain past". That is because, in SR, the "certain past" of a given observer at a given event does not include all of spacetime to the past of that observer's surface of simultaneity through that event; it only includes the past light cone of that event. Similarly, the "uncertain future" of a given observer at a given event does not include all of spacetime to the future of that observer's surface of simultaneity through that event; it only includes the future light cone of that event. There is a third region of spacetime, the spacelike separated region, which falls into neither of these categories in SR.

    This is one of the fundamental differences between SR and Newtonian physics; in Newtonian physics, the third region does not exist. And Penrose, in the passage quoted, is erroneously making use of Newtonian intuitions when he uses the terms "uncertain future" and "certain past" to refer to an event that is spacelike separated from the observer. What makes this really surprising is that, in an earlier section of the same book, Penrose actually explains, in detail, the distinction I have just described--he explicitly talks about the third region of spacetime, how it's there in SR and isn't in Newtonian physics, and even gives it a name, "Elsewhere". Then, in the passage quoted, he forgets all of that and goes back to Newtonian assumptions. It's one of the best simple illustrations I've seen of why you can't trust authority; even world-class experts in a field can make simple-minded errors.

    Okay, I'll stop ranting now. ;)
     
  9. Dec 18, 2014 #8

    Hahaha, no it's very helpful, thank you.
     
  10. Dec 18, 2014 #9
    I certainly wouldn't so quickly dismiss the writings of anyone with Penrose's reputation and credentials.
     
  11. Dec 18, 2014 #10

    PeterDonis

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    First of all, I'm not "dismissing" his "writings"; I'm saying that one particular argument he presents in one particular book is wrong--and what's more, he himself, in the same book, explains why it's wrong.

    Second, you're making an argument from authority, even after I've explicitly shown how a world-class authority can make simple-minded errors. If you think the argument I made in my previous post is wrong, then you should give a counter-argument. Of course I can't stop you from just making a judgment that Penrose is more reliable than me, rather than going to the trouble of making a counter-argument; but really, is the argument I made in my post that complicated?
     
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