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Would Photon Clocks be possible?

  1. Mar 25, 2013 #1
    My question is as follows:
    A photon clock (two 100% reflective mirrors exactly parallel and photons whizzing in between) actually possible. My question is made assuming we could get the mirrors exactly parallel. So really, I suppose my question is:
    Are 100% reflective mirrors possible to make in reality?
    Thanks all,
  2. jcsd
  3. Mar 25, 2013 #2


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    For the sake of argument, let's assume it's possible to construct such a device. However, I don't see how this device would work as a clock. How do you detect any "ticking" of the clock? A photon always gets absorbed as a whole. So, when you detect the photon, the "clock" is destroyed. By the way, there already are quite accurate atomic clocks.
  4. Mar 25, 2013 #3

    Vanadium 50

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    This is done all the time at radio frequencies. You don't need 100%, just enough so that you can "top off" the wave by adding energy to it.
  5. Mar 25, 2013 #4


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    (It might be better to call this hypothetical device a "light clock" instead of a "photon clock".)

    Whether it's practical to build or one or not is almost the point. We talk about them in our thought experiments because they are drop-dead simple with no distracting mechanical details; time dilation and length contraction are the only ways of affecting their reading.

    As DennisN points out, in real experiments we use physically realizable clocks. These require an enormous amount of time and money and ingenuity to understand and control all the mechanical, electrical, and environmental conditions that can affect their operation. All of this effort, although essential to experimental design, gets in the way of simple explanations of the underlying theory.
  6. Mar 26, 2013 #5


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    Your description is very close to how a laser is built except that as others have pointed out, the photons will not just keep bouncing back and forth between the two mirrors on their own, you have to have some way of rejuvenating them.
  7. Mar 26, 2013 #6
    Perhaps some scheme wherein a cluster of photons is originally projected. Each time one of the mirrors/detectors is encountered by them, some are absorbed/ measured, while others are reflected. Thus we get an attenuating regular measurement until they are gone? And of course more can always be sent out.
  8. Mar 26, 2013 #7
    Surely you do need 100%, as otherwise, each time the photons were reflected some would escape, but as they go so fast, they would all escape extremely quickly? I may be wrong, but thats what I think.

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