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Photon in time versus photon not so much-ish in time

  1. Apr 19, 2010 #1
    Okay, second question I have to ask, again, hopefully not stupid. First, I've been perusing the forums and see the common question asked again and again, what's it like for a photon "experiencing" reality, and I totally agree or understand the standard answers: the math breaks down, we don't/can't know, the frame is invalid, but an electron moving at .99c would see such and such. The proper time for a photon is null and it travels through no space to arrive at its destination. So it has this null, or completely unextended, aspect. But within spacetime it's an energy/momentum transmitter, and acts as a carrier wave for information. Maybe this is a meaningless question, or perhaps my characterization is inaccurate, but does anybody have a good explanation for how this dual aspect works?

    Again, thanks for any help.

  2. jcsd
  3. Apr 19, 2010 #2
    It's a good questin. Part of the thinking about it should be "how long is a photon"? The answer is that it depends on the definiteness of it's energy. Most of us think a photon has a definite specific exact energy h*f. But this is only true for a photon that is extremely long in space. By the uncertainty relation it's possible to emit a photon over a very short period of time so that there is great uncertainty about it's energy. It's a "white photon". This white photon would have a very short spatial extent.

    Back to your question, whether a photon has a very narrow energy or whether it is "white", it travels at c and doesn't experience time. To a photon there is no difference between traveling a millimeter or traveling 10 billion light years. You are right about null proper time but it has extent and that extent is embedded within a travel distance. Two circularly polarized photons of 300 MHz are sent into space. One hits the moon and twisted 402 million times. The other is still going and will twist uncounted times before it hits something distant but no proper time elapsed for either. It's difficult to imagine how this looks in the photons frame.
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