Took me ages to find the reference and paragraph
No mystery he is talking about about a moving reference frame.
I have a torch and a person passes me at half the speed of light as they are 1 sec away from me I turn my light on when do I they see the light.
So lets follow the story my light beam takes off and takes 1 second to reach where the person was but they have moved 0.5 light seconds away in that time. My light beam will take 0.25 sec to close that distance but they have again move 0.125 light seconds away.
The solution is
Observer position = 1 light second + 0.5C * time
Chasing beam position = C * time.
When does Observer position = Chasing beam position when
1 light second + 0.5C * time = C * time
rearanging
1 light second = C * time - 0.5C time
1 light second = 0.5C time
time = 2 seconds.
Now Einstein is indeed talking about a static reference frame K like we have in the above.
Note in the above example the speed of light is still c when measured by any of us. It's just the closure speed of the photon appears to be c-v because of the static reference frame (K in Einsteins case).
The person moving, the person turning on the beam and me as a static observer would still agree the speed of light is c.
At no point is he saying the speed of light is c-v its the closure speed that is c-v.
In modern science speak we use the term "separation velocity".
Last edited by Orac; 11/30/11 04:32 PM.
