04 May '06 21:41>
Suppose like the other light problem here, you have a spacecraft going extremely close to C and ahead of the craft is a 100% reflective mirror with the shiny side facing the spacecraft. A laser beam of some wavelength, say 500 NM (somewhere around green I think) and it shoots to the mirror ahead and there is also a mirror on the spacecraft aiming to the other one. The 500 Nm would be blue shifted up to some shorter wavelength and make its way to the mirror. The mirror then shoots it back but this time the wavelenght would be downconverted in the red. So is it back to 500 NM? And if the wave is upconverted to a higher frequency, isn't that adding energy to the beam that wasn't there before? Where does that energy come from?