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Can baseballs truly synchronize clocks ?

  1. Mar 14, 2014 #1


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    Einstein defined truly or absolutely synchronous clocks as follows:
    "The simultaneity of two definite events with reference to one inertial system involves
    the simultaneity of these events in reference to all inertial systems. This is what is meant
    when we say that the time of classical mechanics is absolute. According to the special
    theory of relativity it is otherwise."
    http://hep.fi.infn.it/calvetti/A.Einstein-Relativity.pdf page 83

    Suppose we have a double-armed baseball tossing machine that can toss two baseballs
    equally forcefully in opposite directions. If this machine is placed midway between two
    unstarted-but-set-to-start-on-zero clocks, it seems to me that a couple of machine-tossed
    baseballs would start the clocks at absolutely the same time, thereby absolutely synching them.

    Is there any physical reason why this won't happen? Just wondering….

  2. jcsd
  3. Mar 14, 2014 #2


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    Staff Emeritus
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    Relativity predicts that the baseball tossing mechanism will provide the same synchronization as light-tossing.

    It will be hard to toss baseballs accurately enough to get experimental verification. You can improve accuracy by tossing the baseballs faster and faster. In fact, if you use a particle accelerator to accelerate particles as fast as you can, the particles will be moving essentially at the speed of light - very fast baseballs, in essence.

    The idea is that all fair synchronization, whether it is based on very fast particles, or very accurately tossed lower-speed particles, or light itself, will be equivalent.

    Relativity predicts tha tthe speed of light being the same for all observers and the same in all directions , i.e. isotropy, and also that that limiting speed, c matches the limiting speed of how fast you can toss a baseball and/or elementary particle. A consequence of relativity is that you get different synchronization results for different frames of reference. See "the relativity of simultaneity" , and/or "Einstein's train" there's been a number of recent threads on the concept.

    So the short answer is that you can synchronize clocks with baseballs, but you won't thereby achieve an "absolute" synchronization, you'll get the same relative synchronization that you get with light.
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