Nature of Time Dilation and Length Contraction

Discussion in 'Physics & Math' started by Prosoothus, Apr 4, 2006.

  1. MacM Registered Senior Member

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    How can you ignore that his statement is simply false? It is not what is indicated by the physical system of GPS.
     
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  3. DaleSpam TANSTAAFL Registered Senior Member

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    What is false about it? And how is it inconsistent with GPS?

    -Dale
     
    Last edited: May 9, 2006
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  5. MacM Registered Senior Member

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    Maybe we are not looking at the same post.

    [post=1043741]Here[/post] it is:

    ******************* Extract ************************

    *************************************************

    If that were true then any prelaunch calibration would upset the balance because true time dilation due to velocity would be non-existant on average.

    Perhaps I am misreading his scenario. If they are in circular orbits in opposite directions at a common radius then perhaps he would be right but that doesn't fit the original post by 2Inquisitive.

    Also GPS would not use relative velocity between such clocks but would use the local common preferred rest frame as a referance for each clock.
     
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  7. 2inquisitive The Devil is in the details Registered Senior Member

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    Pete, Dale, ALL clocks in the GPS system are synchronized and beat at the same rate at all times. An 'average' rate of beat would give erroneous results, both in time dissemination and triangulation results on Earth. Any suggestions that the satellite clocks are not precisely synchronized with Earth clocks in both time interval (beat rate) and precise time (GPS-UTC) is pseudoscience.
     
  8. DaleSpam TANSTAAFL Registered Senior Member

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    That is what he is describing. For example, if 2 satellites were in 2 different GPS orbital planes then they could be close enough to each other twice per orbit that they could compare clocks "locally". Each time they got close they would find that their clocks were synchronized, but as they separated they would lose synchronization.

    Obviously such occasional synchronization is insufficient for GPS. They need to be synchronized during the whole orbit, not just when they are near each other. And they don't need to be synchronized at all in any of the satellites' various rest frames, but just in some standard inertial frame.


    The synchronization could be done in any inertial reference frame. The ECI frame is "prefered" in terms of computational convenience only.

    -Dale
     
  9. DaleSpam TANSTAAFL Registered Senior Member

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    Yes, you are right. That is why I made the comment to MacM that:
    -Dale
     
  10. 2inquisitive The Devil is in the details Registered Senior Member

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    DaleSpam:
    This has been brought up repeatedly, the newer generation of GPS satellites can synchronized themselves autonomously with no intervention, 'signals' or anything else, from the ground for up to 180 days. You could blow up ALL the ground control stations, and the GPS recievers belonging to the military and private citizens would still work correctly for a minimum of 180 days.

    DakeSpam:
    Name and describe this other inertial reference frame that is not Earth-centered.
     
  11. DaleSpam TANSTAAFL Registered Senior Member

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    Cool! Trust the military to put something like that in as a design requirement.

    On a tangentially related topic: I wonder what kind of local GPS-denial techniques they have now that they have gotten rid of that deliberate error signal.


    You could use one where the north pole was at the center instead of the center of the earth. Or where the center of the earth was at (1569,23,-86764)km. You could have the earth be stationary or move at an arbitrary constant velocity. Any such frame would be related to the ECI frame through a Lorentz transform.

    All of the timing and synchronizations results would work exactly the same, but the computations would be less convenient due to the bigger numbers. The ECI is used for computational convenience, not any deeper reason.

    -Dale
     
  12. Pete It's not rocket surgery Registered Senior Member

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    The transient relativity-induced time discrepancies are not large enough to affect the system, as far as I can tell. Relativity affect are only an issue between ground-clocks and satellite clocks because the difference is accumulated, not transient.
     
  13. Pete It's not rocket surgery Registered Senior Member

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    Hi Mac,
    In the post to which you responded, A and B were two satellite clocks. 2inq changed the scenario from the earlier one in which A was a ground-clock.
     
  14. MacM Registered Senior Member

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    10,104
    Thanks for the clarification.
     
  15. MacM Registered Senior Member

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    Well, no. GPS satellites do not all orbit around the equator or a plane orthogonal to the earths axis.

    The center of the earth is the only referance which is common to all satellites.

    BTW clocks at the equator and the pole have the same tick rate.

    No again. Where v1 is a surface clock at the equator and v2 is a GPS orbiting clock and v3 = v2 - v1 (relative velocity of clocks) the SR calculation yields only -5.8us/day.

    The correct figure is -7.2us/day based on the absolute velocity of orbit using the local preferred common rest frame the ECI.
     
  16. 2inquisitive The Devil is in the details Registered Senior Member

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    It has been a while since I read the techniques, but the GPS satellites broadcast on two frequencies, of course. One is the 'civilian band' in which the deliberate errors were introduced. In case of national emergency, the errors can be reintroduced or they could stop broadcasting on that frequency altogether if the emergency were severe enough. But there is still Russia's GLONASS system and the European union has already launched the first of their satellites for their upcomming system. The military uses a precision band that is denied to regular citizens. It is much more precise than the normal band and requires authorization to obtain the recievers that can decode the signals, such as science experiments. I have read they can change this code to one only the military can read, or the militaries of allied nations could be given the new code.
    The satellites would then be in huge ellipital orbits, according to those coordinates. Satellites move at different velocities at different points in an ellipital orbit, synchronization could not be done. The satellites all travel at the same velocity relative to the Earth-centered coordinates only.
     
  17. DaleSpam TANSTAAFL Registered Senior Member

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    So?


    What are you talking about? None of the satellites pass through the center of the earth. What makes one point not on any orbit different from any other point not on any orbit?


    Yes, and my socks are a nice cotton-poly blend.


    It's only prefered for computational convenience. You really need to learn to do the Lorentz transform, you keep sounding like an idiot. If you are trying to synchronize clocks in a given inertial frame then obviously the important velocity is the velocity relative to that frame, not to some other frame. Your v3 would be the wrong velocity (even if you used the correct formula). This would be blatantly apparent even to you if you knew how to do the math.

    -Dale
     
  18. DaleSpam TANSTAAFL Registered Senior Member

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    No, the orbits would still be circular in the pole-centered coordinates. In fact, the orbits would be circular in any un-boosted (relative to the ECI) inertial frame.

    Perhaps it would be easier to think of the orbit as a helical worldline in spacetime. Moving the center to the pole (or to any other point) would simply shift the helix. A boost would simply be a rotation of the helix. In any case the helical path can still be calculated just fine as can the proper time and the coordinate time at any point along the helix.

    -Dale
     
  19. MacM Registered Senior Member

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    10,104
    So a polar orbit would not have a Keplarian orbit referance the pole, only the center of earth.

    What? Where does this come from. Certainly not from anything I posted.

    I really, really, hope this comment means you disagree that clocks at the equator and poles of earth have a common tick rate.

    You apparently fail to realize that v3 is the relative velocity between the clocks if you were using SR.

    Considering the magnitude of correctly posted calculations I won't even respond to this false innuendo.
     
    Last edited: May 10, 2006
  20. James R Just this guy, you know? Staff Member

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    Dalespam:

    I led MacM through the basics of the GPS system about a year or so ago. And now you're justing doing what I did all over again. Trust me - with MacM it is a complete waste of time. A year from now, he will still be making all the same false claims.

    In five years or so on this board, he still hasn't grasped the concept of a reference frame yet, so his chances of understanding the GPS system are so close to zero as to make any attempt to explain it to him a complete waste of time.

    Nevertheless, if you want to keep trying, I wish you all the best.
     
  21. Pete It's not rocket surgery Registered Senior Member

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    Cue blast of vitriol from Mac.
     
  22. MacM Registered Senior Member

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    You lying sack of crap. When I first posted GPS information you didn't seem to know anything about it. 2Inquisitive gave you some quick courses and nothing, NOTHING, I have said has ever been demonstated invalid by you.

    You infact have flip flopped from GPS proves SR to GPS doesn't use SR. You have flipped from orbit is not inertial since it is an accelerated frame to it is inertial since it is in free-fall.

    Get real all this is available for readers to research back through.
     
  23. MacM Registered Senior Member

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    Seek and you shall receive.

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