Distance between fast moving objects

  • Thread starter Chuck37
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  • #26
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EDIT: This by the way is what GPS has to do all the time so that distances and times that our receivers display on the ground will be correct.
I'm not familiar with any relativistic stuff required on the receiver end besides Sagnac, at least for normal receivers. Jets and satellites might require something extra. What are you referring to?
 
  • #27
ghwellsjr
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I'm not familiar with any relativistic stuff required on the receiver end besides Sagnac, at least for normal receivers. Jets and satellites might require something extra. What are you referring to?
I didn't say GPS receivers have to do relatvisitic stuff, it's done in the satellites. In your example of the satellite communicating to the guy on the ground, one or the other of them has to do a transformation of the data. It doesn't matter which one. As I said in post #17, you, in the jet or satellite, and the guy on the ground have to have prior agreement on which frames to use to communicate meaningful information and then I said you, in the jet or satellite, could transform the distances into another rest frame (in this case, the ground rest frame) in a meaningful way. That is what GPS satellites do. Their clocks actually run at a different rate than ground clocks do and they make an adjustment to compensate.

By the way, we have only been discussing Special Relativity but in actuallity, clocks at different elevations on the earth run at different rates due to the effects of General Relativity and so we use what is called Coordinated Time to take this into account and that is what GPS compensates for. If you actually had an atomic clock on the earth and you received a GPS signal that also provided time information, they wouldn't necessarily match.
 

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