cross-posted from: https://lemmy.ml/post/19504984
It’s all relative
2 points
Which is achieved by spacetime dilation which can in turn stretch or compress the light waves.
2 points
While it is true that space time dilation can cause red/blueshift, that is a distinct from the doppler effect which is the primary effect here.
(dilation plays only a small role: without time dilation our answer going from 700nm to 350nm would be 0.5c instead of the 0.6c calculated below)
