So time is relative, speed will altere the “perception” of time… Right?. If you travel at almost C you “age slower”. And photons travel for around 8 minutes before hitting earth.
So… How this combine together? Is 8 minutes for us a lifetime for that photon or the other way around? Is this even applicable to something without mass?
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For the photon, no time would have passed at all. What that means in practice is that photons can’t change as they travel. The photons we receive are exactly the same as the ones that were sent.
Here’s another example. Back in the 80’s, it was thought that neutrinos were massless, and traveled at the speed of light. Neutrinos are extremely light particles that are emitted from some nuclear reactions – and they come in three “favours”.
Also, back in the 80’s, careful measurements had been done of the number of neutrinos coming from the sun, and the figure was only about 1/3 of what it should have been.
There were a few ideas proposed to explain that. One was that the sun had switched off and we would all freeze to death within 10000 years or so, but another was that some of the neutrinos from the sun were transmuting into the other forms, and we were only detecting the 1/3 that stayed in their original form. However, if neutrinos were traveling at c, that couldn’t happen – **if, for the neutrino, no time had passed, then it couldn’t transmute**, since change needs a passage of time, and for objects at c, no time passes.
Since then, we have confirmed that, in fact, neutrinos do have mass, and don’t travel at c, and so time does pass for them on their journey to us from the sun, so we aren’t doomed to an icy future. This was very exciting for the physics world, and probably won (or will win) someone a Nobel Prize.
However, for light itself, we know it travels at c, and therefore no time passes for the photons as they cross the 8 light-minutes between the sun and us. (For them, it also seems like no distance has been traversed).
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