"This leads to the prediction of vacuum friction: The quantum vacuum can act in a manner reminiscent of a viscous fluid."
"...explains Liberati. "If spacetime is a kind of fluid, then we must also take into account its viscosity and other dissipative effects, which had never been considered in detail". Liberati and Maccione catalogued these effects and showed that viscosity tends to rapidly dissipate photons and other particles along their path, "And yet we can see photons travelling from astrophysical objects located millions of light years away!" he continues. "If spacetime is a fluid, then according to our calculations it must necessarily be a superfluid. This means that its viscosity value is extremely low, close to zero"." https://phys.org/news/2014-04-liquid-spacetime-slippery-superfluid.html
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." http://www.nature.com/news/superfluid-spacetime-points-to-unification-of-physics-1.15437
"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."
Photons are slowed down by vacuum friction – is this the cause of the Hubble redshift, in a STATIC universe? In Einstein's schizophrenic world "slowed light" is never associated with the Hubble redshift. The discussion always goes to a red herring – loop quantum gravity and "energy-dependent speed of light":
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." http://backreaction.blogspot.fr/2017/01/what-burst-fresh-attempt-to-see-space.html
Any thought transition from "slowed light" to "Hubble redshift" is prevented by crimestop:
"Crimestop means the faculty of stopping short, as though by instinct, at the threshold of any dangerous thought. It includes the power of not grasping analogies, of failing to perceive logical errors, of misunderstanding the simplest arguments if they are inimical to Ingsoc, and of being bored or repelled by any train of thought which is capable of leading in a heretical direction. Crimestop, in short, means protective stupidity." http://ebooks.adelaide.edu.au/o/orwell/george/o79n/chapter2.9.html