Ask Lemmy

First of all, talking about a photon's experience is weird because when moving at the the speed of light, the transformation equations associated with changing the frame of reference start having infinities appearing within them which makes it impossible to mathematically define things like time elapsed or distance travelled.

Secondly it is a little confusing to talk about of frames of reference but I will try my best to explain.

Assume there are two balls(A and B) in an empty region of spacing moving away from each other at speed of 1m/s. Since there are refrences in the background, we have no idea of both the balls are moving or ball A is the only one moving or ball B is the only one moving. From ball A's perspective, it would seem like ball B is moving away from it while it is stationary. Vice versa for ball B which thinks A is moving while it is stationary. Now let us say that the balls have a way to measure the time elapsed and distance travelled. Now when ball A sees that 10 seconds have passed and that ball B has travelled 10m. To verify this it measures the reading shown by ball B. To its surprise it finds out the reading from B's instruments show that only 8 seconds have and that B travelled only 8m. This is the time dialation and length contraction that happens in special relativity. Till now everything is fine but interesting things start to happen when you switch perspectives. In the frame of reference of B, it measures that 10 seconds has passed and that A has moved 10m in that duration. When it tries to verify these measurements from A's instruments, it finds out that they show that only 8sec have passed and that A has only travelled 8m. Now we are in trouble as these measurements seem incompatible. Not only are the instruments not agreeing with each, other, the instruments don't even agree with themselves depending on the frame. This is eventually resolved by the realisation that the order of events is not the same for all frames. In A's, frame, it seems to B that started measuring late by 2s while from B's frame it seems A started measurements later. Adding this 2 second delay in both frames solves all the measurement inconsistency issues.(The numbers used are random. If you actually calculate the difference in measurements coming from a relative velocity of 1m/s, the differences will be exceeding small)

Now that a basic understanding is out of the way, let us discuss the case of the photon. From our frame of reference, the photon is moving at the speed of light, we can measure with our instruments for how long the photon moved and what was the distance it moved but when we measure using the photon's instruments we see that the clock always shows the same time and no time has lapsed. From the photon's frame, it seems like it is stationary and everything else is moving at the speed of(which is obviously not true. Weird things happen when we try talk of moving at the speed of light beacuse of the infinities I aluded to before) and so while it clock is ticking, the clocks of the world around it seem stopped. So in conclusion while it valid to say that photons experience no time, it is only because we can't go to the photon's frame of reference because physics and math fail us that point.

Sorry for the incredibly long reply.

I think the point I was trying to make was that the lifetime of the photon is nonzero to us, from our perspective, but zero to the photon, from its perspective. All of its energy is in its velocity.

Remember in Interstellar when they slingshot around the black hole and it cost them like 80 years or whatever? The time around them went by faster as a result. Well a photon going at c would see time around it going by at max time speed as well, so it would arrive at its destination immediately after it departed. (From its perspective.)

That's how I understand it.