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Recently I've read that the expansion of the Universe as observed is not exactly uniform as proposed by Hubble. Therefore is it possible that instead of space expanding in all directions all matter is falling toward some distant barycentre? Galaxies already closer to it than our own would be accelerating faster and thus we'd observe them redshift. At the same time, our galaxy would be accelerating faster than galaxies which are farther away than us from the "universal centre of mass" which should also result in observing them move away from us. Assuming we have only seen a small part of Universe and in particular only space on one side of the supposed centre so far, all galaxies except the ones on the same sphere around the distant centre as ours would look redshifted to us. For example when looking at this map of galaxy redshifts one can see a big purple arc which could be due to galaxies having the same distance as we do from the centre.

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  • $\begingroup$ There is no center of the universe. $\endgroup$ – Kyle Kanos Jun 21 '15 at 14:17
  • $\begingroup$ Your comment Recently I've read that the expansion of the Universe as observed is not exactly uniform as proposed by Hubble. is a bit unclear to me. Have you a link to the source, please? $\endgroup$ – user81619 Jun 21 '15 at 14:34
  • $\begingroup$ Sure, I should have included the link in the original post. Here's the article I was referring to: universetoday.com/19509/the-universe-is-not-expanding-uniformly $\endgroup$ – Ardath Jun 21 '15 at 14:41
  • $\begingroup$ Dear future close-reviewers: I've given this a bit of an overhaul to hopefully clarify what's being asked. And to Ardath, please let me know if I've changed the intention of your question (though I think I mostly edited language). $\endgroup$ – Kyle Oman Jun 22 '15 at 22:47
  • $\begingroup$ Thanks for editing (I'm still learning English), you didn't change the intention of my question, though now I feel that a simple image might be helpful in showing other users what I meant imgur.com/3x28tXW $\endgroup$ – Ardath Jun 22 '15 at 23:31
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Is it possible that universe is not expanding but instead being dragged into singularity?

No. We see galactic redshift every where we look, the galaxies are moving apart like the raisin-cake analogy. There is no overall gravitational field in the universe. You may have heard about "the big crunch" but I'm afraid it's popscience. The universe didn't contract when it was small and dense, and it isn't contracting now. Au contraire, the expansion is increasing.

Therefore is it possible that instead of space expanding in all directions all matter is falling into some distant barycentre?

No. As above. Note that the universetoday article dates from 2008. When you look up something more recent such as the Wikipedia dark flow article what you see is this: "In 2013, data from the Planck spacecraft showed no evidence of 'dark flow'".

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The scientific paper linked in the article you read is saying that it seems that there's a clustering of mass beyond the reach of current all-sky galaxy redshift surveys that is pulling the local volume more to one side. Such clusterings are possible in the framework of the standard $\Lambda$CDM cosmology, but a clustering large enough to explain the data is only likely at about the 2% level (assuming WMAP-5 parameters, which incidentally are a bit out of date, the article you read is 7 years old). This sort of thing is vaguely worrying to cosmologists, but there is enough uncertainty in the methodology that it's not very worrying. Still, it will be worth following up with deeper all-sky galaxy redshift surveys to find out what's going on.

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Is it possible that universe is not expanding but instead being dragged into singularity?

Yes. That possibility is called the Big Rip. 'dragged into a singularity' can happen even while 'expanding', so they are not contradictory. It would occur if the rate of cosmic acceleration is exponential. In the Big Rip scenario, there is a finite time in the future where all the metric components will become singular. And there doesn't need to be any special center or frame of reference for this to occur. The Big Rip is a space-like singularity.

Although I'm not sure what happens with pre-existing black holes on a Big Rip scenario, I suspect the space-like singularity of the Big Rip melds with the black hole singularities

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    $\begingroup$ I suppose you could argue along similar lines for a Big Crunch. $\endgroup$ – Kyle Oman Jun 22 '15 at 18:54

protected by Qmechanic May 9 '16 at 18:05

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