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Reference frames

  1. May 2, 2013 #1
    What is the criteria to see the latest state of some object which exists after all the previous states in other reference frames? For instance, one observer may see a plane coming off the airport as 'present', other may see 'its flying' as present, but what is the criteria of those reference frames so we can see the 'latest' event?
  2. jcsd
  3. May 2, 2013 #2


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    Different reference frames have no bearing on what any observer sees, measures or observes. They only affect the coordinates that are applied to different events. The observers have to wait for the light to propagate from those events to wherever they are and by that time all frames preserve the timing of what the observers see. You're never going to understand this until you decide to learn about the Lorentz Transformation process which is very simple.
  4. May 2, 2013 #3


    Staff: Mentor

    It's not a matter of reference frames, it's a matter of where you are relative to the object. To be sure you see the "latest" state of the object, you need to be co-located with the object, so there is no time delay for light signals to get from the object to you. That's true regardless of what reference frame you use.
  5. May 2, 2013 #4
    As an additional insight, the above replies reflect the fact that all reference frames see the speed of light as 'c'. In other words, if you are stationary with respect to an object and I am 'rocketing' right past you, that is, at high speed, I'll see the event at the same time as you if we are the same distance from the object.

    Another way to think about it is in a police radar observation: The cop may be sitting idle, you may be approaching her position at 80 mph...but you see each other at the same moment...nobody gets a 'preview' peek. As noted in the above comments, the closer you become, the more 'current' your observations of each other.
  6. May 2, 2013 #5


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    Isn't what you are saying here is that at the moment that two observers are colocated, all frames will agree that whatever one sees, the other sees at the same time?

    I'm not sure what you are trying to say here but it doesn't seem to be merely another way to think about your first comment because these observers are not colocated. Can you elaborate?
  7. May 3, 2013 #6

    you interpret, I think, correctly the simple examples I posted...nothing esoteric was intended.

    From the wording of the OP question, I assumed the OP is asking a basic question.

    In the first, I was trying to give an basic example for the OP how two collocated observers see everything at the same time even in relative motion; in the second, that they see each other in the same 'latest state' when in relative motion. [Of course they see almost everything else at different times....]
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