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Slow clocks on moving body is an illusion?

  1. Nov 13, 2009 #1

    I chanced upon https://www.physicsforums.com/showthread.php?t=321935 and read Doc AI's reply basically saying: if 2 bodies moving near speed of light relative to each other, the clocks on the other body will appear slower on either body.

    And I think this should theoretically mean the slowness is only an effect of observation (as an inability to observe to great accuracaries due to some unknown limitations of observation devices such as the eye etc.) and not in reality happening. Is this correct or wrong?

    Or has it been experimentally shown that a moving body really has all processes slowed down. e.g. a slowed chemical reaction? I really don't think this is the case because if Doc AI is correct, the people carrying out the experiment are the ones moving with respect to the experiement itself!

    Or even weirder, is to say that sending one single object to the past/future is relativitiscally equivalent to sending the rest of the universe to the future/past. Perhaps we are already phasing in and out of the 4th dimension without knowing.
  2. jcsd
  3. Nov 13, 2009 #2


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    Science Advisor

  4. Nov 13, 2009 #3
    Particles that decay really *do* decay at a much slower rate if they are moving quickly. This is an effect that people really have measured in the laboratory.

    That said, this *is* a function of how we are doing the observing. It's not a limitation of our measuring equipment... it's a function of the difference in speed between the particle and us. If you could travel at the same speed as the particles, you'd measure the same rates of decay as for particles that seem stationary.
  5. Nov 13, 2009 #4
    Alright, I'll try to read more first.
    And yes, my bad, I totally missed the first sticky.
    Any case, thanks =)
  6. Nov 13, 2009 #5

    Doc Al

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    Note that I did not use the word "appear" in my response.

    If you mean due to some observational error or optical illusion, then that is wrong. Once you correct for light travel times, etc., then the measured rate of a moving clock will really be slower than the identical clock at rest.

    What relativity predicts is that moving clocks (and any process that behaves like a clock) will be measured as running slowly according to the observer's clocks. (It is a bit sloppy to say that clocks "really" slow down, since you must specify according to who.) That is definitely what relativity predicts, and time dilation has been confirmed in every test so far.
    I'm not sure what you mean. You have one set of folks, with their clocks and measuring devices, making observations of a moving clock. So sure, the observers are moving with respect to the observed!

    :bugeye: :confused:
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