The Tired Photon Theory

British cosmologist E Arthur Milne posited that the expansion of space time was merely an illusion. Caltech astronomer Fritz Zwicky proposed that light waves could be interacting with matter, setting up a sort of gravitational drag. The more a light wave traveled, the more a lost energy, shifting its wavelength toward the red end of the spectrum. This could explain why the nebula furthest out displayed the largest red shifts.