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dotancohen is offline
Jun17-11, 07:46 AM
P: 106
I am trying to understand the implications of a fixed speed of light, mostly to explain it to my nieces and daughters.

The distance to Aldebaran is 65 light years. I understand that means that it's distance is equal to the distance that light would travel in a vacuum in 65 years. But how much time passes for the photon? Did it experience 65 years of travel? Assuming that a hypothetical massless clock were traveling with the photon, would that clock have registered 65 years?

Also, people like to say that the light that we are seeing left Aldebaran 65 years ago. I understand that this is incorrect, rather, that the light left now (in our frame of reference). Does that imply that the photon felt the time pass between Aldebaran and here instantly? Id est, a massless clock on that photon would have measured no time at all?

And if that photon were to glint in my daughter's eye and bounce back towards Aldebaran, how much time would have passed on Aldebaran between the photon's departure and it's return? Due to the motion of celestial objects, would the photon have to travel a different path (i.e., be bounce back at an angle!=0 degrees) or would reflecting it back in the direction that we see Aldebaran get it back home?

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