In this paper : Light is Heavy the following is claimed: "the speed of light appears to be equal for all observers" How can this be true if astronomers rely on the doppler shift to determine if an electromagnetic source is moving away or closer to the earth? How does this tie in with velocity = frequency * wavelength? Is it not because the velocity 'aka speed in a straight line' changes that the wavelength, or frequency changes? hence, the velocity is changed if you are travelling toward or away from a source, resulting in a change of wavelength? Or is it that the velocity remains constant, but the wavelength changes?