On Oct 26, 4:22?pm, YBM <ybm...@nooos.fr> wrote:
> rbwinn a ?crit :
> 
>> A beam of light enters the arm of an interferometer at where S'
>> represents the frame of reference of the interferometer, and S 
>> represents a frame of reference at rest relative to the 
>> interferometer, with the interferometer moving at a velocity of v
>> relative to S.
> 
> Wait a minute : here is what you wrote :
> 
> "S' represents the frame of reference of the interferometer"
> 
> "S represents a frame of reference at rest relative to the 
> interferometer"
> 
> "the interferometer moving at a velocity of v relative to S."
> 
> So the interferometer is at the same time at rest in S and moving
> at v relative to S !

How would the interferometer be at rest in S?  It is moving with a
velocity of v relative to S.