2017-07-31 20:12:49 UTC
My reply (Comment #2):
A mathematical concoction obviously – physically this is absurd, to say the least.
There is no expansion of the universe – it is STATIC. Star light slows down as it travels through the space vacuum, an effect caused by a factor equivalent to vacuum friction. For not so distant stars this is expressed as Hubble redshift but beyond a certain distance the star light does not reach us at all (Olbers' paradox).
The idea that vacuum can slow down light is largely discussed, but only in a quantum gravity context:
Sabine Hossenfelder: "It's an old story: Quantum fluctuations of space-time might change the travel-time of light. Light of higher frequencies would be a little faster than that of lower frequencies. Or slower, depending on the sign of an unknown constant. Either way, the spectral colors of light would run apart, or 'disperse' as they say if they don't want you to understand what they say. Such quantum gravitational effects are miniscule, but added up over long distances they can become observable. Gamma ray bursts are therefore ideal to search for evidence of such an energy-dependent speed of light."
That photons lose energy/speed as they travel through vacuum is a dangerous concept so hints in that direction are rare:
Nature: "As waves travel through a medium, they lose energy over time. This dampening effect would also happen to photons traveling through spacetime, the researchers found."
Quote: "Some physicists, however, suggest that there might be one other cosmic factor that could influence the speed of light: quantum vacuum fluctuation. This theory holds that so-called empty spaces in the Universe aren't actually empty – they're teeming with particles that are just constantly changing from existent to non-existent states. Quantum fluctuations, therefore, could slow down the speed of light."