ok, I'm not an expert on relativity althought I was in to it some 10 years ago. however, now there is a question keeping me awake. first of al, the question is: IF light is fastest form we know, does it go with the same speed everywhere? is it constant? and if so, and maybe more importantly, does it have the same speed no matter what the source is? i.o.w. can it be slowed down? reason why I ask this is the following:

whe learn that light takes time to travel from A to B. depending on the speed of A an B relative 'to each other', we know if B is is getting closer, going faster or staying at the same distance from A. Simpel relativity theorie.

ok now, imagine A an B in a concord plane. My speed is altered wether in the plane or outside. if A is in the plane and B outside, time will alter. imagine A and B outside the plane, they live at same speed, inside the plane also.

but then I started asking the question: "imagine A and B moving at the speed of light (or almost) could they still see each other?

here's the image:

A and B go from left tot right at the speed of light:

-----------> A ----------> B --------------->

Does A see B? with twice the speed of light? and does it mean that B doesn't see A at all?