Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Simultaneity: Train and Lightning Thought Experiment

  1. Nov 30, 2017 #41

    Nugatory

    User Avatar

    Staff: Mentor

    However, if you're thinking about it that way you're setting yourself up for future confusion. When you say "the IF which roughly contains the earth and the star", you seem to be suggesting that there might be an inertial frame (or non-inertial frame, for that matter) that does not "contain" the earth and the star. That's not right, because everything is always in all frames always - there's no such thing as being in one frame and not another.

    There is such a thing as being at rest in one frame and not another, but that doesn't change any of the physics. In particular, the basic principle that the time something happened is the time at which it could be observed minus the light travel time between the event and the point of observation works in all inertial frames. Whether the source or the observer is at rest in the frame is irrelevant.
     
  2. Dec 1, 2017 #42
    I meant the IF in which the earth and the star are basically at rest. In this frame, the star explodes and the time it takes for that light to reach earth is 4 Y. In a different IF - traveling .999c, arriving at the star as it explodes, then passing the earth - the time between explosion and seeing on earth is miniscule.
     
  3. Dec 1, 2017 #43

    Nugatory

    User Avatar

    Staff: Mentor

    As is the distance between the two events.
     
  4. Dec 1, 2017 #44

    Mister T

    User Avatar
    Science Advisor

    Yes, your meaning was clear from the context. That's usually referred to as the rest frame of those objects.

    I think the point @Nugatory makes is that using the language one way signals an understanding, but using it another way signals, if not a misconception, then at least a warning that it might lead to a misconception.

    And calculations done using that frame would also involve the delay due to light travel time.
     
  5. Dec 8, 2017 #45
    OK. How about I back-peddle by a few steps and instead request the following assumption: The two clocks on the moving train are synchronized only after the train has reached its constant velocity. The sense I get is that it can be agreed that one or more valid procedures exist by which these two clocks can be synchronized to each other, in the IF of the moving train. Yes?
     
  6. Dec 8, 2017 #46

    Mister T

    User Avatar
    Science Advisor

    Yes, assuming you mean rest frame of the moving train when you say IF of the moving train.

    But then they won't be synchronized in the rest frame of the platform. That's the point.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Simultaneity: Train and Lightning Thought Experiment
Loading...