The speed of light in a vacuum is measured to be the same in all frames and FROM all frames. If a spacecraft passes an observer at relativistic speed with a beacon flashing inside his cabin that can also be seen by the observer, both the observer and the passenger would measure the speed of the light from that beacon the same. The observer would see the flashes coming faster or slower(time dilation due to speed)and the light would be shifted(toward blue while approaching, then the correct color as it went by and red as it receded. The Doppler effect). The passenger would see no such shift in frequencyIn all cases all parties would measure the speed of light in a vacuum to be the same. Period. This is one of the most tested LAWS of our Universe, nobody will be making a dent in that fact. Farsight Your "bouncing ball" diagrams are demonstrating frequency change, not speed change. In your diagrams motion is vertical and does not vary, while the frequency is horizontal, slowing with gravity, varying with Doppler as well. GrumpyPlease Register or Log in to view the hidden image!