/sci/ - Science & Math

>>11086559
for example this image in that wikipedia page
The text below the image says:
Left: Observer at rest measures time 2L/c between co-local events of light signal generation at A and arrival at A.
Right: Events according to an observer moving to the left of the setup: bottom mirror A when signal is generated at time t'=0, top mirror B when signal gets reflected at time t'=D/c, bottom mirror A when signal returns at time t'=2D/c

why is the light pulse ange modified? It should not matter which direction the observer moves, the mirrors will always reflect the light perpendicular to the surface