Sachs-Wolfe effect in a Dark Energy universe?

In summary, the integrated Sachs-Wolfe effect is a phenomenon that occurs when a photon travels through a changing gravitational potential due to spacetime expansion. This can result in a blueshift when the photon enters a gravitational well and a redshift when it exits. While dark energy is not the cause of expansion, it can contribute to accelerated expansion. However, the integrated Sachs-Wolfe effect can still occur even in a universe with only one galaxy, as long as there is some spatial variation in density. If there are no other gravity wells besides our own, then the effect would not be observed.
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TL;DR Summary
Sachs-Wolfe effect in Dark Energy universe?
The integrated Sachs-Wolfe effect occurs when a photon goes through a gravitational potential that changes due to spacetime expansion (presumably caused by dark energy). For that reason, a photon going through a gravitational well would gain energy (blueshift) when entering and it would lose energy (redshift) when exiting it. If the universe expands, the well becomes "less deep" and therefore, the photon gets more energy and becomes blueshifted.

However, would this effect still occur if we had a photon traveling in a universe with only one galaxy (the Milky Way) and the rest of it dominated by Dark Energy (that is, the Universe once the expansion separates all non-gravitationally bounded structures to us)?
 
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Suekdccia said:
The integrated Sachs-Wolfe effect occurs when a photon goes through a gravitational potential that changes due to spacetime expansion
Yes.

Suekdccia said:
(presumably caused by dark energy)
No. Dark energy is not the cause of expansion. It's only the cause of accelerated expansion. But you don't need accelerated expansion to have a nonzero integrated Sachs-Wolfe effect. All you need is some spatial variation in density.

Suekdccia said:
would this effect still occur if we had a photon traveling in a universe with only one galaxy (the Milky Way) and the rest of it dominated by Dark Energy (that is, the Universe once the expansion separates all non-gravitationally bounded structures to us)?
If you postulate that there are no other gravity wells except the one we are in, then no, we would no longer observe any Sachs-Wolfe effect, just a (small) blueshift from photons falling into our gravity well.
 
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