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Message: <blockquote data-quote="freyar" data-source="post: 6041141" data-attributes="member: 40227">The difficulty is that the effects of the overall expansion of the universe (whether the accelerating kind or a more mundane decelerating kind) do not just "add" with the effects of the matter in the galaxy on gravity.  (We say the equations of general relativity are "nonlinear" because the results are not additive.)  So, while I don't have the exact solutions to the equations at hand in this case, what you do expect to happen is that the gravitational attraction of the matter in the galaxy to "win" over the expansion of the universe, so the space inside the galaxy shouldn't stretch.  In other words, the galaxy is "gravitationally bound," so the distance across the galaxy shouldn't be increased by the overall expansion of the universe.  That will only affect distances between objects that aren't bound together.  Another point to make is that, even if the expansion of the universe were happening in our galaxy, it would be a very small effect.  The expansion is only noticeable on very large distance scales (for example, the expansion rate between our Milky Way and Andromeda, the closest large galaxy, is quite slow).What's interesting is when you get borderline cases, like galaxies that are gravitationally attracted to each other but also being swept apart by the expansion of the universe.  Then there is a legitimate competition between the two effects.I hope this doesn't muddy the picture, but cosmology is a big and sometimes complicated subject.</blockquote>

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