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Hubble measured the velocity of galaxies relative to Earth and determined that the galaxies were moving away from Earth. Speed increased with distance to Earth. This correlates well with the Big Bang theory, which was launched in the first half of the twentieth century. In the second half of the twentieth century, superclusters are discovered. For example, the Virgo Supercluster which is part of the bigger Laniakea Supercluster.

The movement of the galaxies inside the Laniakea and Perseus-Pisces Superclusters has now been mapped. It turns out that they move in all directions, both towards and away from Earth and The Milky Way. I'm having a hard time reconciling this with The Big Bang theory. If the gravity from The Great Attractor or the distant Vela Supercluster, ("Peculiar velocity") overrides The Hubble's flow, then Hubble would not be able to demonstrate that all galaxies were moving away from each other.

Should we look at the expansion of the universe in a bigger perspective, that it is the Superclusters, and not the individual galaxies that are moving apart? But what was it then that Hubbel saw? Did he observed galaxies beyond the Laniakea and Vela superclusters?

The Video is only 4:10 and illustrates the galactic movements within the supercluster.

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    $\begingroup$ Relative to the center of the supercluster is not the same as relative to earth. And probably the red shift due to distance is subtracted and only the residuals looked at $\endgroup$
    – planetmaker
    Commented Dec 16, 2023 at 23:48
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    $\begingroup$ Please provide references to measurements that show galaxies in the Laniakea supercluster are moving towards us. $\endgroup$
    – ProfRob
    Commented Dec 17, 2023 at 0:38
  • $\begingroup$ While the galaxies you mentioned might not actually be moving toward us, your premis still holds, in that there are galaxies moving towards each other. Hubble's observation is intended to be interpreted at a larger scale, in general galaxies move away from each other based on their distance. $\endgroup$
    – Greg Miller
    Commented Dec 17, 2023 at 17:36

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The peculiar velocity of a galaxy does not override the Hubble flow. Rather, it is relative to the Hubble flow. Hubble (and others after him) looked at the redshifts of individual galaxies and compared them to distances measured by the brightnesses of stars or supernovas whose intrinsic brightnesses were known by other means. With a scatterplot you can see a strong linear relationship, and that's where he derived his law. Some nearby galaxies were actually blueshifted, and at all distances the redshifts differ from the predicted values by various amounts. Those differences are the peculiar velocities.

The video actually tried to convey this with the phrase "By discounting cosmic expansion, the team worked out..." around 1:30. So, some galaxies are being pulled towards us by gravity, but they are still receding from us, just not as fast as they would be if there were not that pull.

It is as if all the galaxies are ants walking on an expanding rubber tablecloth. The cosmologists did their calculations as if the tablecloth-stretcher were turned off.

There must be a farthest galaxy that is actually blueshifted relative to us, but I don't know how far it is.

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  • $\begingroup$ So. In real life - the tablecloth is streching faster then the ants can walk? Resulting that they will never reach their goal; The Great Attractor? $\endgroup$
    – Peter
    Commented Dec 17, 2023 at 20:04
  • $\begingroup$ Likewise. Will the whole 3D model in the video be stretched out in all directions if the cosmologists do the same calculations again many years later? $\endgroup$
    – Peter
    Commented Dec 17, 2023 at 20:17
  • $\begingroup$ My guess would be that "farthest galaxy that is actually blueshifted" would be something in the Virgo Cluster (distance $\sim 15$ Mpc), since there are some of those that are blueshifted. $\endgroup$
    – Peter Erwin
    Commented Dec 17, 2023 at 22:08
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    $\begingroup$ This paper lists 65 Virgo Cluster galaxies with blueshifts; I think they say 7 of them have surface-brightness-fluctuation distances, all $\sim 17.5$ Mpc. $\endgroup$
    – Peter Erwin
    Commented Dec 17, 2023 at 22:16
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    $\begingroup$ @Peter I think the answer is basically Yes to both your questions. I mean, there's a lot of random motion, so the overall shape won't remain exactly the same for billions of years. And you wouldn't be able to tell in a video (or hologram or whatever they use in the future) because it would be scaled to whatever level is convenient. $\endgroup$
    – Mark Foskey
    Commented Dec 18, 2023 at 0:30

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