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I Block universe discussion

  1. Jul 10, 2017 #1
    Einstein said, "The distinction between past, present and future is only an illusion, even if a stubborn one."

    That's my problem--that illusion is so vivid and stubborn.

    Paul Davies said in his book "About Time": There is only one rational conclusion to draw from the relative nature of simultaneity; events in the past and future have to be every bit as real as events in the present.
     
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  3. Jul 10, 2017 #2

    jbriggs444

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    If you decide that by the force of pure reason you can tell how things must be, that is a clue that you have departed from science into philosophy.
     
  4. Jul 10, 2017 #3
    But, he didn't decide just by the force of pure reason. He decided based on measurements and observations culminating in the relative nature of simultaneity.

    I like your comments, jbriggs444. And your avatar is by far my favorite on the forum.
     
  5. Jul 10, 2017 #4

    PeterDonis

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    This is a common unjustified claim in pop science books. Read this Insights article:

    https://www.physicsforums.com/insights/block-universe-refuting-common-argument/
     
  6. Jul 11, 2017 #5
    Peter, does an expert such as Einstein, Roger Penrose or Paul Davies lose his stature and authority in physics as soon as he writes a book for the general public? Or, maybe you're suggesting that he alters the true description of the physics for public consumption? I was quite impressed with Roger Penrose's book (also read it years ago). I still look forward to reading your article. Thanks for your contributions to the forum.
     
    Last edited: Jul 11, 2017
  7. Jul 11, 2017 #6
    I found this interesting quote about Einstein and block universe:
    Karl Popper about Einstein:
    << The main topic of our conversation was indeterminism. I tried to persuade him to give up his determinism, which amounted to the view that the world was a four-dimensional Parmenidean block universe in which change was a human illusion, or very nearly so. (He agreed that this had been his view, and while discussing it I called him "Parmenides".)... >> (Karl Popper, Unended Quest: An Intellectual Autobiography.Routledge Classics. Routledge. pp.148–150).
     
  8. Jul 11, 2017 #7

    PeterDonis

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    No, because they never had any in the first place in the sense you mean. Science does not work on "stature and authority". Nobody should be believed or their arguments accepted without examination simply because they are a famous physicist. That goes just as much for their peer-reviewed science as for their pop science. Even famous physicists sometimes get things wrong, so you have to check what they say. That was part of the reason I wrote that Insights article--to show that even someone as smart as Roger Penrose can make mistakes.

    I don't think that's the case with the particular argument I refuted in the Insights article. I think it was an honest mistake. But an honest mistake is still a mistake.

    I do think a lot of pop science books leave things out, and the authors aren't always very careful to say what they are leaving out, or why, or how it affects what they keep in. Feynman, in one of his pop science books (I think it was QED, but I'm not sure), at least said that he was being careful to mention all the stuff he was leaving out (and did a pretty good job of keeping that promise). But many, if not most, authors aren't as careful as that.
     
  9. Jul 12, 2017 #8
    Peter, I gave it another go. Correct me if I'm wrong, but you don't seem to accept that special relativity is about 4D objects and 4D universe. In previous posts in this thread I agreed with Dale , JBriggs ... that special relatvity is all about 4D objects and 4D universe. 4D means units that include past, present and future. And I found it very interesting and agreed with them that "3D section" (3D world of simultaneous events) should be replaced by 4D slice out of the full 4D object/universe.

    Obviously, if you don't accept special relativity is about 4D objects/4D universe, then you can never understand, nor accept Block Universe, nor slices through 4D Block Universe.... Is this what I read in your article?
     
  10. Jul 12, 2017 #9

    jbriggs444

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    Please do not put words into our collective mouths.
     
  11. Jul 12, 2017 #10

    Dale

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    @Ebeb note that I do not "accept Block Universe". I use the Block Universe interpretation when it suits my needs and I use LET instead when it suits my needs. I don't accept or reject either.

    Instead, I pay attention to which parts of each interpretation are physical (experimentally measurable) and which parts are philosophical. I use the most convenient philosophical tools as needed, but work hard to keep the experimentally measurable stuff in the forefront. I am not 100% successful, but I work at it.
     
  12. Jul 12, 2017 #11

    PeterDonis

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    I made no such general statement in the article; I specifically said that I was only refuting one particular argument, the argument that relativity of simultaneity implies that the 4D "block universe" model must be true.

    No. See above.
     
  13. Jul 13, 2017 #12

    Dale

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    I have no problem calling the universe an object and therefore it is physically 4D. Certainly, it has been measured to have nonzero extension in the time dimension.

    However, the Block Universe goes further and asserts that the future is also fixed. I have no physical measurements that support that claim. I don't object to it, but in the absence of measurements of the future, it is in my "not physical" category.
     
  14. Jul 13, 2017 #13
    Allow me to try once more understand what you guys have in mind.

    Do you have physical measurement that a present world exists?
    You cannot measure a present world, because 'present world' is based on simultaneity, and because simultaneity is a mathematical relative thing, you have to consider 'present world' non-existent. This means there is nothing existing 'now' at a distance from an observer. And because you don't accept the full life of a remote object exists out there, there is simply nothing out there to be observed/measured.
    Only the present 'now' event of an observer does definitely 'exist now' for him.
    This is even more confusing, because you would definitely reject we are solipsists.
    Yes, I guess you will find the above a total mess, but the posts I read in this thread won't help either.
    It's sad, but there seems to be no way we can or will understand each other... Very weird because for decades now I do understand perfectly what Einstein, Penrose, Davies, ... tell me in their writings. But that too I got wrong, isn't it?
     
  15. Jul 13, 2017 #14

    PeterDonis

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    No. Our physical measurements can only tell us about our past light cone. We don't physically measure 3-D worlds. (This is all discussed in my Insights article.)
     
  16. Jul 13, 2017 #15

    PeterDonis

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    That's right--because our direct observations tell us that all the events in our past light cone exist, so what exists is certainly not limited to our present moment, i.e., to a single event. And those events in the past light cone include all kinds of evidence of the existence of objects other than ourselves. (This is also discussed in my Insights article.)
     
  17. Jul 13, 2017 #16

    PAllen

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    There are things far away from me that I detect from my past light cone. I readily infer their history continues beyond my last observation. However, which point in such unobserved future of the object corresponds to my present moment is not part of physics, it is the composition of convention and extrapolation. Even in my past light cone, the correspondence between events in the distant object's history and events in my past is a matter of convention, not physics. Even in SR, there is more than one convention in common use, while in GR, one hardly even bothers with the notion of distant now because of the plethora of choices with no basis for preferring any.
     
  18. Jul 13, 2017 #17
    PeterDonis, just trying to make sure I understand the Premise 2 that you are concerned about in your article on Block Universe. Is it that the Block Universe should not be accepted because it has not been verified with observations not available within our light cones? Should it be accepted if events outside of our light cone could demonstrate the same conclusions as presented by Penrose in his paradox?
     
  19. Jul 13, 2017 #18

    PeterDonis

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    My argument is not that the block universe "should not be accepted". It is that the specific argument I described in the article is incorrect, because its second premise is not required by SR.

    It is impossible for us to have knowledge of events outside our past light cone, so this suggestion is meaningless.
     
  20. Jul 13, 2017 #19
    Sorry to belabor the point, but what do you mean by "...its second premise is not required by SR"? Do you mean that SR does not require relativity of simultaneity for events outside of our light cones, therefore the Block Universe theory is also not required by SR outside of our light cones? Would you then be saying that SR theory is not validated for events outside of our light cones?
     
  21. Jul 13, 2017 #20

    PeterDonis

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    The second premise is "3D worlds are real at every event". That premise is not required by SR.

    How can it be, since, as I said before, it is impossible for us to have knowledge of events outside our past light cone?
     
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