time existence at light speed

[James R]

If we put a tiny clock on a photon and let it ride from our galaxy to the next, would its time change?

That's impossible to answer, since we can't put a tiny clock on a photon (or on anything that travels at the speed of light).

Technically, the Lorentz transformations (and therefore time dilation equations etc.) cannot be applied to objects moving at the speed of light, since such objects have no rest frame.

 

[Crunchy Cat]

That's impossible to answer, since we can't put a tiny clock on a photon (or on anything that travels at the speed of light).

Technically, the Lorentz transformations (and therefore time dilation equations etc.) cannot be applied to objects moving at the speed of light, since such objects have no rest frame.

This is quite true. If photons can't have a reference frame, can they still move through time?

 

[James R]

I think I already answered that, above.

 

[Crunchy Cat]

I think I already answered that, above.

The answer you gave implies that photons can't have a reference frame (i.e. it's a meaningless concept). At the same time, my interpretation is that you are saying that we can observe a photon in space-time at points a, b, c, d, etc.

What this means to me (and please do correct me if I am wrong) is that a photon doesn't have an "age" because it simply can't. From our perspective we can say "yep, that photon travelled for 30 days and 30 nights"; however, there is no perspective from the photon. Because of this, it seems we can say that we are moving through space-time and observing a photon from our perspective; however, as the photon cannot have a reference frame it has no perspective. It would seem then a photon is moving through space only and we are observing it from the perspective of space-time. What do you think?

 

[noodler]

Photons travel along geodesics, right?
Because they have no mass, their path or worldline must lie along the observer's nullcone. The photon cannot therefore have a timelike geodesic.

The (boundary of the) future cannot be timelike or spacelike, since if it was we would be able to 'see' it now.

 

[James R]

The answer you gave implies that photons can't have a reference frame (i.e. it's a meaningless concept).

They don't have a rest frame.

At the same time, my interpretation is that you are saying that we can observe a photon in space-time at points a, b, c, d, etc.

That's an obvious truth from your daily life.

What this means to me (and please do correct me if I am wrong) is that a photon doesn't have an "age" because it simply can't. From our perspective we can say "yep, that photon travelled for 30 days and 30 nights"; however, there is no perspective from the photon.

True. However, we can get an idea by imagining a massive object travelling at very close to the speed of light. It's perspective is one in which the universe appears to have practically no length in the direction of travel, and in which time in the outside universe appears to run at a snail's pace (almost stopped).

It would seem then a photon is moving through space only and we are observing it from the perspective of space-time. What do you think?

I can only repeat what I said before: if a photon is here now and over there in a microsecond from now, then it moved in both space and time - obviously.