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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It doesn’t really make sense to ask “how much time has passed from the perspective of a photon”, because we can’t build something called a “[reference frame](https://en.wikipedia.org/wiki/Frame_of_reference)” for the photon.
Whenever we talk about special relativistic time dilation we must do so by comparing the rate that time is passing in two different reference frames. If I am moving along with you, we are in the same reference frame, but if we are moving relative to each other, then we are different ones. You can think of a reference frame as being a way of describing the universe from your perspective, and when we talk about time dilation or length contraction we have to have two reference frames to compare together. Time always passes normally and distances are always the same in your own reference frame: you won’t see your own clocks ticking slow or fast or your own rulers changing length, but you will see that your clocks disagree with those of someone who is moving relative to you and that you and that same person will disagree on how long your rulers are.
Time dilation and length contraction can be thought of as consequences of one basic fact about the universe: all observers, no matter how they are moving, will agree on how fast light is moving. If you’re moving away from me at 100 mph and you shine a laser at me, you will measure the light leaving the laser as moving at c. I will measure the light from your laser as moving at c as well, not c-100 mph. In order to agree on how fast light is moving while we are moving relative to each other, we must disagree on how fast our clocks are ticking and how long our rulers are.
But if we were, hypothetically, to be moving relative to each other *at* c, we would encounter a paradox: light moving parallel to that reference frame would have to be both moving at c (as it must be in all valid reference frames) and be stationary at the same time. This is a contradiction, so we cannot construct a reference frame for the photon, and without a reference frame it doesn’t really make sense to talk about time dilation or length contraction.
What we *can* say, however, is that as something moves arbitrarily close to c that the time it would see pass while traveling between two points would get arbitrarily close to zero and the distance between those points would as well. People often make the slight error of thinking that because the limit goes to zero here that the answer is that it *is* zero when v = c, but it’s more precise to say that the limit approaches zero as v approaches c, but does not exist *at* v = c. Sort of like how 1/x gets arbitrarily large as x approaches 0 from the positive side, but 1/x does not actually exist when x = 0.
It doesn’t really make sense to ask “how much time has passed from the perspective of a photon”, because we can’t build something called a “[reference frame](https://en.wikipedia.org/wiki/Frame_of_reference)” for the photon.
Whenever we talk about special relativistic time dilation we must do so by comparing the rate that time is passing in two different reference frames. If I am moving along with you, we are in the same reference frame, but if we are moving relative to each other, then we are different ones. You can think of a reference frame as being a way of describing the universe from your perspective, and when we talk about time dilation or length contraction we have to have two reference frames to compare together. Time always passes normally and distances are always the same in your own reference frame: you won’t see your own clocks ticking slow or fast or your own rulers changing length, but you will see that your clocks disagree with those of someone who is moving relative to you and that you and that same person will disagree on how long your rulers are.
Time dilation and length contraction can be thought of as consequences of one basic fact about the universe: all observers, no matter how they are moving, will agree on how fast light is moving. If you’re moving away from me at 100 mph and you shine a laser at me, you will measure the light leaving the laser as moving at c. I will measure the light from your laser as moving at c as well, not c-100 mph. In order to agree on how fast light is moving while we are moving relative to each other, we must disagree on how fast our clocks are ticking and how long our rulers are.
But if we were, hypothetically, to be moving relative to each other *at* c, we would encounter a paradox: light moving parallel to that reference frame would have to be both moving at c (as it must be in all valid reference frames) and be stationary at the same time. This is a contradiction, so we cannot construct a reference frame for the photon, and without a reference frame it doesn’t really make sense to talk about time dilation or length contraction.
What we *can* say, however, is that as something moves arbitrarily close to c that the time it would see pass while traveling between two points would get arbitrarily close to zero and the distance between those points would as well. People often make the slight error of thinking that because the limit goes to zero here that the answer is that it *is* zero when v = c, but it’s more precise to say that the limit approaches zero as v approaches c, but does not exist *at* v = c. Sort of like how 1/x gets arbitrarily large as x approaches 0 from the positive side, but 1/x does not actually exist when x = 0.
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