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That one bothers me a lot. If time is collapsed to an instant for the photon, and it experiences it's own end of lifetime, what should happen if photon is never going to be absorbed? Especially interesting in the context of constant expansion of the universe driven by dark energy, which allows more space to appear before photon's path, allowing it to move infinite time until time is not relevant anymore.

Update: Sorry, I don't think that this question is asked and answered in the linked one. The question is not about how photon perceives time (which I think was not answered in the related link), but about the paradox. If there is no paradox, then I would appreciate input on why (so for photon time is not one instant?). Link to a Feymann's interpretation of EM transaction is a good one, but it does not explain why photon should have a consumer in any way.

Qmechanic
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Askar Kalykov
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2 Answers2

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Physics has no answer for you.

To consider what a photon "experiences" you would have to conduct your experiments in the rest frame of the photon. If special relativity represents nature faithfully, the photon has no rest frame. So the question cannot be addressed with the theories we have today. How fast can a unicorn run?

garyp
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Photons are massless and they do not have a rest frame, so it would not be correct to say that we know anything about whether photons experience time or how they experience it. You can see phrases like "photons do not experience time" or as you say "photons experience time in an instant" and you get confused.

Now you are correct about expanding space, and that in our universe, where space expansion is real, a photon emitted somewhere might travel through expanding space without being absorbed for a long long time.

It is very interesting to learn about Richard Feynman's view, where he explains this view of yours about the photons absorption, and he describes it as a two way interaction, where there is a target atom, that emits its own photon in the future, that travels backwards in time. In this view, emission and absorption have to happen together, no matter how far apart they are in space and time.

This advanced photon travels back in time and "just happens" to arrive at the source at the exact instant when the regular photon is emitted, causing the emitting atom to be kicked backwards a tiny bit.

Can a photon get emitted without a receiver?

Árpád Szendrei
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