Can the Twin Paradox be simplified?

Discussion in 'Physics & Math' started by timewarp, Nov 20, 2011.

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  1. Tach Banned Banned

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    How do you get them to resynch? Do you do the calculations by using the geodesic deviation in order to account for the acceleration at liftoff? What metric do you use for calculating the connection coefficients: Schwarzschild, Kerr? Something else?


    What you "maintain" is irrelevant, what you can "prove" is what is relevant. Turns out that having identical acceleration profiles is irrelevant, the twins aging differential is not a function of acceleration EVEN if they have DIFFERENT acceleration profiles. You, too can prove that but it requires that you write down a fairly involved formalism. Which one are you using, geodesic deviation, hyperbolic motion , Rindler coordinates?

    No, you don't need to refine the setup anymore, I just gave you a generalization to arbitrary acceleration profiles, all you have to do is put the above in a mathematical formalism. Which one are you using?
     
    Last edited: Dec 16, 2011
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  3. OnlyMe Valued Senior Member

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    I phrased this in terms of both proper time and time dilation, to be certain that my meaning was intact and I do recognize that it is at least a bit awkward. But at least here we are in agreement.

    Again the phrasing is not as clean as it could have been.

    My intent was to ask.., if the conclusions within the standard construction of the twin paradox hypothetical, once established, can be applied to a traveling twin who does not return home, as we agreed above.., can those conclusions then be applied in practice, to a twin or an observer who sets off from the Earth and never returns?

    Granted the calculations would not be even practical, too many variables... And the result would not be totally consistent with the hypothetical... But would a real observer age slower, than the stay at home observer, if they never return home?

    And Tach, this is an honest question. I can say that I am not sure myself that it would apply in the same global way, as it does within the hypothetical.., in practice.
     
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  5. Trippy ALEA IACTA EST Staff Member

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    I'm aware of that, and you're aware of that.

    I'm not disputing that, remember?

    This thought experiment wasn't for your edification. It was intended as a point of discussion with other participants in the thread.
     
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  7. OnlyMe Valued Senior Member

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    I think that you have been consistent on the issue, that even in the ideal case I suggested, involving only acceleration for the traveling twin, the age difference when reunited, is explained only by the difference in relative velocity and not the acceleration. I believe that you were at least implying that this proves that acceleration plays no part in any difference in their age when reunited.

    That at least has been my impression. Things do get confused or confusing on occasion.
     
  8. Tach Banned Banned

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    So, how do you do your calculations? what method are you using? I asked several times, no answer.
     
  9. Trippy ALEA IACTA EST Staff Member

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    That is precisely what I have been consistently trying to say.

    Part of good experimental design is to change as few things as possible, because it makes establishing and demonstrating a causal mechanism easier.

    If both twins have been (or have to a good approximation been) subjected to the same acceleration field throughout the entirety of the experiment, then the only difference between them that can have acted as a causal mechanism is their relative velocity.
     
  10. OnlyMe Valued Senior Member

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    I don't believe that we have any evidence that the two situations are equivalent, except under the conditions defined within hypothetical thought experiments. In practice there are conditions and interactions which are by design excluded from the environment of the hypothetical.

    While you are correct in your description of what is observed to occur in the lab, those observations are not confined to the construction of a hypothetical. How a shift in the lab's frame of reference, involving similar velocities exceeds any evidence we can draw from either experience or experiment, with the technologies and practical limitations, we are constrained to at classical scales.

    In other words, I don't know. But I am still thinking about it....
     
  11. RJBeery Natural Philosopher Valued Senior Member

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    I find these mental exercises interesting, but I still consider there to be an elephant in the room. Namely, the unambiguous time dilation differential between the body residing on a mass and one residing outside the gravitational influence of said mass. Alternatively, the constantly-accelerating rocket with a clock in the nose and tail. In either case I find it difficult to attribute time dilation to relative velocity, even if we try to make the claim that these are special scenarios in which relative velocity is not well defined...

    Analogy: I say it takes bread to make a sandwich, you say it takes jam. You guys are busy trying to make 5 sandwiches from jam, bologna, and 2 slices of bread so we can conclude it was the jam; in the meantime...I hand you a bread sandwich.

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  12. Trippy ALEA IACTA EST Staff Member

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    Gravity is equivalent to acceleration.
    Acceleration is the integral of velocity.

    It's still there, it's just harder to see.

    From where I'm sitting, your sandwich analogy is very deeply flawed.
     
  13. RJBeery Natural Philosopher Valued Senior Member

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    "Very deeply flawed" is quite harsh. The analogy is decent. We're descending into semantics, now, and you're resting your definition of relative velocity on top of the EEP; it's an additional degree of separation, when every definition I've ever seen involves a change in distance over time, having nothing to do with acceleration.

    I'm not sure it gets you much anyway, because if you're defining relative velocity as that which is caused by acceleration, then acceleration CAUSES time dilation via that same additional degree of separation.
     
  14. Tach Banned Banned

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    That's incorrect, if the twins are subjected to different acceleration profiles and the difference in the total elapsed time is function of their relative speed only, this is proof sufficient that their aging does not depend on acceleration.
     
  15. OnlyMe Valued Senior Member

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    Tach, I do not see the difference in what Trippy is saying and what you are saying???

    Both of these statements reduce to the samething, any difference in aging is due to velocity not acceleration!

    They are just said in different ways.
     
  16. Tach Banned Banned

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    You think so? Too bad.
     
    Last edited: Dec 17, 2011
  17. Tach Banned Banned

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    That's really too bad since countless of mainstream scientists don't find this difficult at all. Is this one of those cases "it must be wrong because it offends my intuition"?
     
  18. OnlyMe Valued Senior Member

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    You must have put a great deal of thought into such a profound out of context comment!
     
  19. Trippy ALEA IACTA EST Staff Member

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    No I'm not.

    First off, I simply pointed out the relationship between them.
    Velocity is still the change in displacement over time (remember, speed and distance are scalars, displacement and velocity are vectors - facts that Tach needs to reacquiant himself with to understand spinning wheels and doppler shift).

    My point was that while acceleration is the derivative of velocity, velocity is the integral acceleration. You can't have acceleration without first having velocity.

    I then leaned on the EEP to show that acceleration and gravity were equivalent.

    In other words, what I was saying, is that time dialation exists inside a gravity well, because gravity is equivalent to acceleration, acceleration is the derivative of velocity, and velocity causes time dialation. It's a bit clumsy as descriptions go.

    And in the experiment i'm leaning on the EEP to remove acceleration as a difference between the frames.
     
  20. Trippy ALEA IACTA EST Staff Member

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    That's wholy irrelevant, and I wasn't claiming otherwise.

    Once again, you have failed to grasp the whole point of the experiment I initially proposed.

    Look, one more time.

    RJ Beery's complaint is that you can't have two reference frames in motion relative to each other without first accelerating one of those reference frames. I'm eliminating acceleration as a variable by making it a constant, and making it equal and equivalent in both frames.

    Do you understand yet?
     
  21. Trippy ALEA IACTA EST Staff Member

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    Clearly the well reasoned critique of a highly intelligent mind (note the sarcasm dripping from that).

    Tach has repeatedly demonstrated that he is incapable of recognizing equivalent solutions to the same problem expressed mathmatically or in prose.
     
  22. Tach Banned Banned

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    If the acceleration profiles are the same, as you mistakenly consider, then they cancel out, so only someone totally incompetent in experimental physics would conclude that this is equivalent to the acceleration playing no role in the differential aging of the twins. While the correct conclusion is all along that applying identical acceleration profiles results in the acceleration effects canceling each other or , more probably, the experiment being totally brain dead.

    On the other hand, using different acceleration profiles and observing no effect on the differential aging of the twins , mainstream scientists would correctly conclude that acceleration indeed doesn't play any role. This is very simple, basic experimental physics, I wonder how you could miss. On the other hand, I am not wondering anymore.

    The solutions are of course, not equivalent. Only someone ignorant in experimental physics would claim such a thing. If you really and truly want to prove that acceleration has no role, you really need to impart non-equal accelerations to the twins. Get it yet? If you do what you did, any fool will point out that the equal accelerations cancel out, so you've proven nothing.
     
    Last edited: Dec 17, 2011
  23. Trippy ALEA IACTA EST Staff Member

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    Take a moment to re-read what you've just said.

    You have just demonstrated you haven't understood what I have said.

    You've just described a different approach to the same problem - a second way to prove the point, so to speak.

    The question is: "What is the role of acceleration in time dialation".

    There are two ways we can approach this:
    First, we can accelerate two identical twins at the same rate to different speeds, and prove a difference in proper times exist. This is the approach I took.

    Or, we can accelerate two identical twins at different rates to the same velocity and prove that no difference exists, which is the approach that you just proposed.

    The reason I took the first approach over the second approach, is because the second approach introduces an assymetry in the experiment that my proposed setup for the first version does not.
     
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