Speed of light measured in/by a parallel frame moving at c

[San K]

Scenario:

Alice is "sitting" on photon A
Bob is "sitting" on photon B

both are moving in same direction, their paths are parallel to each other.

Per relativity the speed of light is constant

So Alice will measure Bob's speed to be c
and Bob will measure Alice's speed to be c

yet they are both moving at constant velocity c

how is this (paradox?) resolved?

 

[Doc Al]

how is this (paradox?) resolved?

By recognizing that the "rest frame of a photon" makes no sense. (Alice cannot "sit on a photon".)

See: https://www.physicsforums.com/showthread.php?t=511170

 

[1977ub]

If Alice accelerates, trying to catch up with photon A, she finds that it still eludes her, traveling at c.