My question is, is it sensical or non-sensical to use a photon reference frame to observe, using relativity, another photon?

 

If it is sensical, then what is happening in terms of time dilation/length contraction in the following cases...

 

Case A: 2 parallel photons travelling in the same direction separated by some arbitrary small distance say 1 mm. I understand that this would perhaps constitute the same frame of reference for both photons but, photon A would observe photon B to be travelling at c, is this not right? Lorentz transform would give us an undefined (division by 0) answer, is this correct?

 

Case B: 2 minutely diverging photons (coming from same source - may even be entangled) eg. 1 mm apart after 1 second ie having travelled approx. 3x10^8 m

 

Case C: 2 photons diverging at a 60 degree angle from the same source - may even be entangled.

 

Case D: 2 parallel photons (in close proximity) travelling in opposite directions separated by some small distance say 1 mm. Is this the same as case A?

 

Just need things cleared up by the experts. Thanks.

"My question is, is it sensical or non-sensical to use a photon reference frame to observe, using relativity, another photon?"

 

NON

NON

 

Thats a loaded answer...Could you explain a bit more so lay-people such as myself can understand it?

 

I get the original question. I just don't get the answer it was given.

I just noticed Martian's followup.

I had just followed his advice before he gave it.

NON meant nonsensical.

It is impossible to get into the rest frame of a photon.

I didn't read past that.

Now I see that case A shows it is impossible.

The rest makes no sense to me. Sorry

Is is sensical the same as sensible? I'm confused.

It is non-sensical to use a photon rest frame to conduct any observations. This is simply because such a rest frame is undefined, as the four-velocity is indeterminate (0/0) etc.