According to the Unruh effect, an accelerating observer will find himself surrounded by a "warm bath" of particles (see http://en.wikipedia.org/wiki/Unruh_effect ). Now consider two observers,A and B, one accelerating (B) and the other (A) in constant motion (or rest). Let the accelerated observer now shine a beam of light away from him. This beam of light can now be scattered by the particles surrounding him (which exist only to him and not to A). This means that the observer A will see some strange deviations of the light leaving the accelerated observer (even when the effect would be very small). This would look even more strange, considering the fact that A sees no particles at all (from which the light could scatter). To observer A, it would appear that the light is scattered by the vacuum itself. I was wondering whether such effects could also have implications for the observation of other stars, galaxies, the cosmic background, etc. Does anyone know of such considerations being taking into account in cosmology ?