From my understanding objects moving close to the speed of light experience a time distortion in that time moves slower and slower as they get closer to the speed of light. If that is the case shouldn't photons be affected by this as well and cause us to wrongly calculate the age of the universe and distance between stars as we don't take into consideration time distortion?
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$\begingroup$ Electromagnetic waves (photons, if you want) have an invariant that is independent of the coordinate system: the number of wavelengths that fits between any two spacetime points they pass. That's the yardstick and at the same time the clock of photons. $\endgroup$– CuriousOneCommented May 15, 2015 at 7:33
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$\begingroup$ Thank you for the answer. From your reply I understand that the speed of light is constant. But if photons have a moving mass, matter has mass, if the theory says that mass approaching the speed of light will experience time distorsion why wouldn't light particles as well? $\endgroup$– user2835340Commented May 15, 2015 at 10:32
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$\begingroup$ As you say, "if photons have a mass", then you are right. However, photons are massless, which is the only reason the can actually travel at the speed of light. If you imagine a Minkowski diagram, then lightrays are "lightlike", which means that the proper time is zero, which means that if photons were conscious, the would experience "birth" and "death" at the same moment. $\endgroup$– CleverCommented May 15, 2015 at 10:51
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$\begingroup$ Thanks, I think the question can be considered answered by both replies, I was confused by the fact that on several occasions I heard that photons have moving but no stationary mass. $\endgroup$– user2835340Commented May 15, 2015 at 13:26
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$\begingroup$ Photons don't have mass. They have momentum. The confusing part is that in classical mechanics mass and momentum are linked by velocity in a linear way, but in relativity they are not. $\endgroup$– CuriousOneCommented May 15, 2015 at 14:35
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The time dilation (to use the proper term - not distortion) occurs in the frame of reference of the moving object. So only the photon "feels" that time has slowed down. In our reference frame, we simply observe a photon whizzing alone at precisely c. So all our observations that depend on knowing the speed of light remain accurate.
Actually, if you consider the magnitude of the time dilation in the case of a photon:
$t'$ = $t \over \sqrt(1-v^2/c^2)$
as $v \rightarrow c$, the denominator $\rightarrow 0$ so the time dilation is undefined. The photon can then traverse the entire universe in zero time in its reference frame.
