Discussion:
If the Universe Is Expanding, Then Why Aren't We?
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Pentcho Valev
2017-07-31 20:12:49 UTC
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Sabine Hossenfelder: "The solution of general relativity that describes the expanding universe solves Einstein's equations on average; it is good only on very large distances. But the solutions that describe galaxies are different – and just don't expand. It's not that galaxies expand unnoticeably, they don't expand at all. The full solution, then, is both the cosmic and the local solutions stitched together: expanding space between non-expanding galaxies. (Though these solutions are usually only dealt with by computer simulations due to their mathematical complexity.)" http://scienceblogs.com/startswithabang/2017/07/28/if-the-universe-is-expanding-then-why-arent-we-synopsis/

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."

Pentcho Valev
Pentcho Valev
2017-08-02 16:04:19 UTC
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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."
https://www.sciencealert.com/how-much-do-we-really-know-about-the-speed-of-light?perpetual=yes&limitstart=1

Photons are slowed down because vacuum exerts a force equivalent to friction:

"Vacuum has friction after all. In quantum mechanics, the uncertainty principle says we can never be sure that an apparent vacuum is truly empty. Instead, space is fizzing with photons that are constantly popping into and out of existence before they can be measured directly. Even though they appear only fleetingly, these "virtual" photons exert the same electromagnetic forces on the objects they encounter as normal photons do."
https://www.newscientist.com/article/mg20927994.100-vacuum-has-friction-after-all

"This leads to the prediction of vacuum friction: The quantum vacuum can act in a manner reminiscent of a viscous fluid."
http://philpapers.org/rec/DAVQVN

"So how can a vacuum carry force? One of the first things we learn in classical physics is that in a perfect vacuum - a place entirely devoid of matter - friction can't exist, because empty space can't exert a force on objects traveling through it. But, in recent years, quantum physicists have shown that vacuums are actually filled by tiny electromagnetic fluctuations that can interfere with the activity of photons - particles of light - and produce a measurable force on objects."
http://www.businessinsider.com/casimir-effect-vacuum-space-nanoparticles-2017-4

Vacuum friction slows down photons coming from distant stars - so the Hubble redshift is produced, in a STATIC universe. Assume that, as the photon travels through space (in a STATIC universe), it bumps into vacuum constituents and as a result loses speed in much the same way that a golf ball loses speed due to the resistance of the air. On this hypothesis the resistive force (Fr) is proportional to the speed of the photon (V):

Fr = - KV

That is, the speed of light decreases with time in accordance with the equation:

dV/dt = - K'V

Clearly, at the end of a very long journey of photons (coming from a very distant object), the contribution to the redshift is much smaller than the contribution at the beginning of the journey. Light coming from nearer objects is less subject to this effect, that is, the increase of the redshift with distance is closer to LINEAR for short distances. For distant light sources we have:

f' = f(exp(-kt))

where f is the initial and f' the measured (redshifted) frequency. For short distances the following approximations can be made:

f' = f(exp(-kt)) ~ f(1-kt) ~ f - kd/λ

where d is the distance between the light source and the observer and λ is the wavelength.

The approximate equation, f' = f - kd/λ, is only valid for short distances and corresponds to the Hubble law.

The original equation, f' = f(exp(-kt)), shows that, at the end of a very long journey (in a STATIC universe), photons redshift much less vigorously than at the beginning of the journey. It can be shown that this provides an alternative explanation of the observations that brought the 2011 Nobel Prize for Physics to Saul Perlmutter, Adam Riess and Brian Schmidt.

Pentcho Valev

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