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I Time Dilation (Clock specific)

  1. Feb 22, 2017 #1
    Hi, I went ahead and read through all the similar discussions and none are on this particular topic so I'll go ahead and shoot. I did find this topic as well, but my question is pretty simple.

    I think I understand how time dilation works, I read through the explanation here, this jives with the explanation provided in this World Science Festival panel in this video (it starts at around 11:30 if the link didn't work). This is the light clock thought experiment where it shows why a light particle in the moving clock is bouncing slower than the one in the stationary clock. This makes sense to me, and I wondered if the Hafele-Keating experiments which use a cesium beam atomic clocks work on the same basic principle described?
  2. jcsd
  3. Feb 22, 2017 #2


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    Why would they behave any differently?
  4. Feb 22, 2017 #3


    Staff: Mentor

    Hi Maaruk, welcome to PF, and thank you for taking the time to dig around a bit and come with a thoughtful question!

    So the hypothetical clock which is a pulse of light bouncing back and forth is called a light clock. It is primarily meant to be an easy to analyze teaching tool. As far as I know there is not any such clock built that actually works that way. However, assuming that the principle of relativity is true then if a light clock slows down in a reference frame then so must all other comoving clocks.

    Edit: I just had a thought that you could consider the microwave cavity to be a kind of mirror arrangement
  5. Feb 22, 2017 #4
    From the description of the atomic clock used in the H-K experiment it wasn't clear to me whether the cesium clock uses the same metronomic principle as the light clock.

    Thank you for the welcome.

    I definitely appreciated how easy the light clock concept was to understand, and why movement would affect its measurement of time. I just wasn't clear on whether the atomic clock in the H-K experiment operates with roughly the same principle and something very similar to the light clock thought experiment is happening in the H-K experiment. Maybe more clearly, are the mechanisms of the light clock and the cesium clock roughly the same? I think I see what you are saying about the microwave cavity, I read through 5 different descriptions of the cesium clock and I still wasn't sure so I thought I would find someplace to ask :biggrin:
  6. Feb 22, 2017 #5


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    Cesium clocks are not light clocks, but they have been compared to light clocks in various reference frames: They are equivalent.
  7. Feb 22, 2017 #6
    Thanks guys, very helpful. Asking accurate questions is very helpful, and I know sometimes I do not ask accurate questions. Plus it doesn't help that I am usually a mess of terminology but I generally know what I mean by something. Thanks again.
  8. Feb 22, 2017 #7


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    Your first thread here is exemplary -- Welcome to the PF. :smile:
  9. Feb 22, 2017 #8


    Staff: Mentor

    As mfb says, they are definitely not the same. For the light clock, the point is that you can use the second postulate to analyze how the clock rate changes with speed and then you use the first postulate to extend that analysis to atomic clocks (or any other kind)
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