Is Simultaneity "Real"?

Discussion in 'Physics & Math' started by Mike_Fontenot, Jul 7, 2019.

  1. Mike_Fontenot Registered Senior Member

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    In my paper,

    "Accelerated Observers in Special Relativity", PHYSICS ESSAYS, December 1999, p629

    I gave a proof that (in regards to the well-known twin "paradox"), the current age of the home twin (she), according to the traveler (he), as given by the CADO reference frame (which is completely equivalent to the better-known "co-moving inertial frames montage"), AGREES with what he can determine himself, using ONLY his own elementary observations, combined with his own elementary calculations. I first show how the traveler could do that if he were perpetually inertial. Then, I show how he can do that during his unaccelerated inertial periods. And finally I prove (by using a "counter-factual" argument, combined with a causality argument) that the same result holds even during each instant of his accelerating periods. IF my proof is valid, then it is NOT true, as is commonly believed, that simultaneity conventions are arbitrary and meaningless: there is only ONE valid definition of simultaneity, and simultaneity IS meaningful and "real". All of this is discussed in Section 10 of my webpage,

    https://sites.google.com/site/cadoequation/cado-reference-frame

    and to a greater extent (and more rigorously) in my paper.

    So is my proof valid? No one has ever contacted me (in the 20 years since that paper was published) and told me that they had found a flaw in my proof. And several times over the years, I have looked again carefully at my proof, and I have never spotted an error in it. If anyone reading this believes they have found an error in my proof, I would like to hear from them. Email me at PhysicsFiddler@gmail.com.

    ___________

    Michael L. Fontenot
     
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  3. Neddy Bate Valued Senior Member

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    I haven't looked at your proof, but within the context of SR, simultaneity is not arbitrary or meaningless. It is defined by the Einstein synchronization method of ideal clocks, which is based on the speed of light being a constant.

    Relativity of simultaneity is every bit as important in SR as length contraction and time dilation. For example, the ladder or barn-pole "paradox" would be a real paradox if the relativity of simultaneity were not real. Just because some people have a difficult time with the SR simultaneity convention, does not make it arbitrary or meaningless.
     
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  5. Mike_Fontenot Registered Senior Member

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    I agree with you. But a lot of people don't. I got banned from the Physics Forum about 10 years ago for my blasphemous views. The favored flavor of simultaneity over there is the Dolby and Gull "Radar method", in which the current age of the home twin (she), according to the traveler (he), increases at about half of his ageing rate for the first half or so of the outbound leg, then about twice as fast as his ageing for the second half or so of the outbound leg. That rate continues for about half or so of the inbound leg, and then drops to about half of his ageing rate for the last half or so of the inbound leg. So in the radar method, her age starts increasing faster than his ageing well BEFORE he does his turnaround ... her ageing rate depends on how he will choose to accelerate in the future ... it violates causality. And even more pleasing for many people, she never gets younger (according to him) for any scenario in the Radar method.
     
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  7. DaveC426913 Valued Senior Member

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    Neither of these things are what happens in "standard" relativity, as far as I understand. Are you sure you've got that correct?

    1] Her rate of aging was slower than his for the first half of the outbound journey. But it only speeds up to his rate; she never starts aging faster than him on the outbound leg.

    2] The event that initiates the change in her rate of aging doesn't violate causality; the event that initiates the change in her rate of aging is him starting to decelerate. That causes the rate of recession to decrease.


    Say on the outbound leg, her rate of aging was half (1/2) of his.
    At midpoint, he begins deceleration.
    Her rate of aging increases: from 1/2 to 1 (as he arrives).
    Her rate increased - but it never surpassed his.
     
    Last edited: Jul 9, 2019
  8. Mike_Fontenot Registered Senior Member

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  9. DaveC426913 Valued Senior Member

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    This does address my post. Your hypothesis seems to be dependent on an error in the standard twin paradox.
    If there's no error, but instead you've inteepreted it wrong, then there is no need for an alternate hypothesis.

    To further address some other apparent misinterpretations:
    Instantaneous turnaround requires infinite acceleration.

    Use "arbitrarily high" acceleration. It matters.

    No she does not. This is the same misinterpretation. You are confusing her age with her rate of aging.

    She was aging slower then he (say, at half the rate).
    During his decel to turnaround (which occurs over a non-zero duration), her rate of aging goes from 1/2 to one.
    At the moment where they are at rest relative to each other, she is aging at the same rate as he is, although she is observed to still be younger.
    As his continued acceleration brings them back together, her rate of aging is greater than his, even though for a while she is still younger.
    As he builds to top speed, her rate of aging will increase. She will eventually be observed to be older than he and aging faster than he.
    As he starts his decel at Earth, her rate of aging will slow down to 1, until when he is at rest relative to her her rate of aging is 1.
     
  10. Mike_Fontenot Registered Senior Member

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    I don't think you and I are capable of communicating. I tried. We'll just have to leave it at that.
     
  11. Neddy Bate Valued Senior Member

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    Sorry but this is not correct. As he decelerates, he must consider her rate of aging to go above 1, because she must end up older than the traveling twin once they are both mutually at rest. Remember, she never accelerates at all, so she is not the younger twin.

    She has to be older than him at this point. It is not about what he observes, it is about her current age. She should be about twice his age at this point.

    Think about it from her reference frame. The whole outbound leg, she considers him to be aging at half the rate of herself. When he decelerates at the turnaround point, he is about half her age. Now you have to figure out how to reconcile that with his reference frame. When he is momentarily stopped at the turnaround, they both have to agree on who is older and who is younger.
     
    Last edited: Jul 9, 2019
  12. DaveC426913 Valued Senior Member

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    I can see how not being able to communicate your ideas would cause you frustration.
    But I'm more concerned if you aren't able to understand ideas communicated to you. How could you get misunderstandings corrected?

    We're both trying. I'm showing where (I think) there's some flaws how you're interpreting the twins paradox. Let's first address those, and you may find there's no need for an alternate solution.



    If you're a visual type, here is a diagram that illustrates what happens to her rate of aging and to her age, as observed by him.
    It shows how her rate of aging (purple curve) changes, but her cumulative age never jumps instantaneously (green curve).


    (Notice, by the way, now nicely the green curve is symmetrical across its own length.)

    Please Register or Log in to view the hidden image!

     
    Last edited: Jul 9, 2019
  13. DaveC426913 Valued Senior Member

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    He will observe it to go above 1, but not until his velocity changes direction.

    As long as his velocity is positive (i.e. he is heading away from her), he will observe her rate of aging to be slowed (though rapidly speeding up to "normal").

    What he "considers" it to be is a separate issue.


    Thanks, I should not have made reference to her "actual" age.
    Too bad I can't go back and delete that.
    It just muddies the water.
     
    Last edited: Jul 9, 2019
  14. Neddy Bate Valued Senior Member

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    I don't think you referenced her actual age at all, and if you had, it would not have muddied the waters, because that is what the twin paradox is supposed to be about.

    When he stops at the turnaround point, she must actually be older than him, regardless of what either of them might see with their eyes.
     
  15. DaveC426913 Valued Senior Member

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    It is about their ages when he coordinates their times.

    The OP seems to have started with some trouble interpreting the twin paradox, so it's simpler if we just look at what can be observed. After all, this is the "round trip" experiment we're examining.
     
  16. Neddy Bate Valued Senior Member

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  17. Neddy Bate Valued Senior Member

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    If by "coordinates their times" you mean he calculates what her age would actually be. This is done by considering how much time it would take for light to reach his eyes, and then adding that much time to what his eyes see as her age.

    It is never simpler to consider what can be observed. There is Doppler effect, time delays, etc. The thread is about actual times displayed on two (or more) clocks simultaneously.
     
  18. Neddy Bate Valued Senior Member

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    Now please show me where in your graphs you show that she is older than him at the turnaround?
     
  19. DaveC426913 Valued Senior Member

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    I think you are going to confuse the OP even further.

    While I don't doubt we can go into details, the OP seems to have made several apparent errors in his interpretation (see post 4 and post 6). I think we should get those cleared up first. This whole problem might go away.
     
  20. DaveC426913 Valued Senior Member

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    The chart doesn't illustrate "actual", it illustrates "observed".


    The OP thinks that her age jumps "instantaneously".
    This is based on two flawed assumptions:
    1] That acceleration can be infinite.
    2] That it is her age that's affected, rather than the rate of her aging.

    Note that, for the OP to think she "ages instantaneously by a large amount"*, he must be talking observation.

    *see me call out in post 6.
     
    Last edited: Jul 9, 2019
  21. DaveC426913 Valued Senior Member

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    The chart doesn't illustrate "actual", it illustrates "observed".

    And "observed" is what the OP is talking about.

    Else he would not have said
    "...she instantaneously ages by a very large amount..."
    or "...he finds her to be the older when they are reunited..."


    The OP thinks that her age appears to jump "instantaneously".
    This is based on two flawed assumptions:
    1] That his acceleration can be infinite.
    2] That it is her age that's affected, rather than the rate of her aging.
     
  22. Neddy Bate Valued Senior Member

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    Okay, well that is a separate issue. How are you going to deduce that she is older than him at the turnaround from that?

    Infinite acceleration is just the easiest acceleration profile to use. That way she should be exactly twice his age at turnaround, assuming gamma =2. If you mess around with finite accelerations, you complicate the issue.

    So the issue is that on his outbound journey, he recons she is always half his age, but when he stops at the turnaround, she has to be twice his age. None of this is visual, it is the actual ages of the twins. Your replies do not address this.

    Well if her age goes from half of his age, to twice his age, what do you suppose is changing?

    No, he is talking about infinite acceleration. If you prefer a finite acceleration, just make it over a small enough distance that we can neglect its effects. Her age has to go from half his age to twice his age, as he decels to the turnaround. How does that happen?
     
  23. DaveC426913 Valued Senior Member

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    That is the issue I am talking about with the OP.
    Yours is the separate issue.

    Has the OP asked that?

    Which would be fine if the OP wasn't confused about her age jumping instantaneously.


    Again you're discussing a different aspect. Your beef is not with me.

    I have quoted the OP describing observed phenomena incorrectly. I am correcting that.

    If you want to discuss what he calculates her age to be - you should quote the parts of the OP where he is talking about actual age on Earth when he is away - and then address the OP, rather than me.
     

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