Speed of light won't solve the problem.  You have to use velocity of
light.  Einstein said that velocity of light was a constant.  The great
scientist made a mistake when he said this that scientists ever since
have copied.
  If you take a set of coordinates, a photon traveling in the +x
direction has a velocity of c=186,000 miles per second relative to the
set of coordinates.  A photon traveling in the -x direction has a
velocity of -c= -186,000 miles per second.  Since -186,000 does not
equal +186,000 we have just proven that the velocity of light is not a
constant.  What does seem to be a constant is the ability of scientists
to believe that -186,000 = +186,000.  I hope that this will help you.

Robert B. Winn