Didn't Einstein postulate that we are traveling at c through time? Is it not true that to travel in any of the other three (spatial) dimensions we need to take away from speed c as nothing can go faster than c? And if photons travel at c, that means that they take away all of their "traveling through the temporal dimension" time in order to use it in their "traveling through the spatial dimensions" time? So then a photon does not experience the flow of time.



*Does that mean it only moves in three dimensions?!!*



Also, what are some materials that can slow photons down, how, and why can’t they be slowed down enough to be stopped? Why is c still considered constant if light can be slowed down?



But anyway, that’s going off track. Since a photon does not experience time, it does not age. However, we CAN say for how long it has existed (the example with astronomers estimating the “ages” of photons given by reilly).



I think that there is a clear distinction between physical age and the time for which something has existed. This stems mainly from the difference in reference frames. For example, if you could go in a rocket ship at something like 99.9999% c, and die in the process (el oh el), your death certificate would not take into account the fact that you had barely aged for the time you had traveled at nearly c, even if it equaled out to hundreds of “Earth years”. This is because only the time for which you have existed, in the Earth reference frame, is acknowledged.



Photons do not age, but we find it convenient to say for how long they existed. Something does not have to age in order to exist in a temporal dimension.



- Alisa