Friday, June 1, 2018

special relativity - Does light itself experience time dilation?


This seems weird for me. Every time I see light, I will think, "Hey, that light travels from the past far away from us!"


Correct me if there is misconception.



Answer



In special relativity, time dilation is determined by the Lorentz factor $$\gamma=\frac{1}{\sqrt{1-v^2/c^2}}$$ Say the photon travels some time $T$ in our frame of reference. It is obviously travelling at the speed of light. We see that the Lorentz factor diverges as we go to the speed of light. Thus, in order for the photon's time in our frame to remain finite, its proper time must tend to zero. This is the colloquial "time stops at the speed of light."


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