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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To a photon, there’s no such thing as time. From its point of view, it would be instant. One way of thinking about this is that in special relativity, distances shrink by a factor of sqrt(1-v^2/c^2). That is zero for a photon where v equals c, so from the photon’s point of view, the distance between the Earth and the Sun is zero.
More technically, “age” is a funny concept in relativity. Time is seen differently by different observers. You need to specify both where and when something happened (not just “Alice met Bob at the corner of Main and Elm, but Alice met Bob at the corner of Main and Elm at 4:30 on Friday). If you take two different events at different times and different places, different observers won’t agree on how far apart they are or when they happened, but they will always agree on the difference between distance squared and time multiplied by the speed of light squared (dx^2-c^2 dt^2). Since a photon moves at the speed of light the distance it moves dx in a time dt is just speed times dt, or dx=cdt, so dx^2-c^2 dt^2=0. As far as the universe is concerned, the distance between a photon leaving the sun and that photon hitting the earth is exactly zero. In our frame, that means dx is 93 million miles and dt is 8 minutes, but to the photon dx=0 and dt=0. There’s no “right” answer for the age of the photon, since every frame is valid, but if you ask the photon, you’ll get zero.
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