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I would like to know if the trajectory of our galaxy has been calculated because it is usually said that the cosmos is emptying due to the expansion of the universe but at the same time there is a region of space that we are traveling to along with many other galaxies in the Laniakea supercluster. Space is expanding in all directions and getting faster and faster but due to the proximity to the Great Attractor, will the Milky Way end up joining together in a sea of galaxies or will it be left alone with Andromeda and satellite galaxies?

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There is a recent paper (Shaya, E., Tully, R. B., Pomarède, D., & Peel, A. (2022). Galaxy flows within 8,000 km/s from Numerical Action methods. arXiv preprint arXiv:2201.12315, more material ) that addresses this, and has some nice animations. In particular, this video shows an extrapolation of galactic cluster trajectories 10 billion years into the future.

Note that most parts show locations in co-moving coordinates that expand with the universe (much more convenient for examination), but about a minute in there is a demonstration how the distances actually scale when the expansion is plotted.

In particular, it turns out that while the Local Cluster is moving towards the Virgo cluster and the core of Laniakea with the Great Attractor, the speed is not enough to catch up with them. The end result is that we will be isolated.

enter image description here

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In the long run, the expansion of space will win out over any gravitational attraction our galaxy feels towards the Great Attractor.

First off, we are not gravitationally bound to the Great Attractor. Even if the universe was not expanding, the fact that we are not gravitationally bound implies that we would eventually leave the gravitational influence of the Great Attractor (though that would likely take billions upon billions of years).

Secondly, the expansion of the universe will one day become so dominant that even the closest clusters (what's left of them anyway) will succumb to the expansion of the universe. Nothing that isn't gravitationally bound will be able to fight that expansion. The expansion will win out in the end. At least, that's what current observations and theory tell us we can expect...

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  • $\begingroup$ How does your last few sentences work? This is only true if $w<-1$? $\endgroup$
    – ProfRob
    Feb 14, 2022 at 19:53
  • $\begingroup$ @ProfRob Unless I'm much mistaken, it is the general consensus that that is how things will turn out under (debatable) reasonable assumptions. E.g. this source or this one. $\endgroup$
    – zephyr
    Feb 14, 2022 at 20:35
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    $\begingroup$ Neither source says that the expansion would have an influence on our Galaxy, or any other gravitationally bound system. That would require phantom energy with $w < -1$. $\endgroup$
    – ProfRob
    Feb 14, 2022 at 21:48
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I was under the impression that the coined "great attractor" was more like a force that is attracting the universe within on itself leading to the theorized big crunch of the universe. And that it is the force opposing the expansion of the universe? Or is it the void that seems to surround the universe?

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