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Hubble's Law says that galaxies are moving away from Earth at speeds proportional to their distance. The resolution of Olbers' Paradox is that the universe is of finite age.

However, Hubble's observations of farther galaxies are of then younger galaxies. As with Olbers' Paradox, we are now seeing those galaxies as they were and not as they are. Farther younger galaxies had greater accelerations. Older closer galaxies now (or closer to now) have lower accelerations. Galaxies are negative accelerating.

Yet whenever Hubble's observation of farther galaxies with greater accelerations is brought up it's as hand wavy evidence of an expanding universe (but ignoring their age). Still, if nearer galaxies are accelerating less and we can see negative acceleration, isn't this evidence of energy dissipation? Yes, I know that energy isn't conserved on observable universe scales. I'm just wondering if this is the evidence. Moreover, if galaxies are negative accelerating and energy is dissipating then what's the evidence for dark energy (the 2011 Nobel Physics Prize notwithstanding)?

Olsonist
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1 Answers1

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It's not usually interpreted this way. The galaxies are largely stationary, but the space between them is expanding. This naturally leads to galaxies further away exhibiting greater recession velocities (which is not acceleration - from their point of view, they are stationary; they definitely don't feel a force due to $F = ma$).

The more commonly-cited "evidence" that energy is not conserved in cosmology is that distant objects exhibit redshift, which (because of quantum mechanics $E = hf$) suggests that the light is losing energy as it travels.

But perhaps the strongest evidence comes from theoretical considerations. Energy conservation is supposed to come with time-translation symmetry, but in General Relativity and especially cosmology, time-translation symmetry is not present, and Noether's theorem breaks down. As a result, the question "is energy dissipating?" is itself not well-posed.

Allure
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