1. Subscribersonhouse
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    28 Mar '16 11:22
    http://phys.org/news/2016-03-image-hubble-cosmic-kaleidoscope.html#nRlv

    My question is, if entire clusters of galaxies are attracted to each other as in this image, apparently almost 200 TRILLION times the mass of our sun, will the expansion of the universe win out and pull these galaxies apart eventually or can the local group locally counteract the expansion of the entire universe?
  2. Cape Town
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    28 Mar '16 12:04
    Originally posted by sonhouse
    http://phys.org/news/2016-03-image-hubble-cosmic-kaleidoscope.html#nRlv

    My question is, if entire clusters of galaxies are attracted to each other as in this image, apparently almost 200 TRILLION times the mass of our sun, will the expansion of the universe win out and pull these galaxies apart eventually or can the local group locally counteract the expansion of the entire universe?
    At present, local gravity is winning. However it is currently believed that the universe's expansion is accelerating and will continue to do so and thus even atoms will eventually be ripped apart. It is not about counteracting the expansion of the 'entire universe' but rather counteracting the expansion of local spacetime. Once local space time is expanding faster than light, it becomes impossible for anything to stay together.
  3. Subscribersonhouse
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    28 Mar '16 12:25
    Originally posted by twhitehead
    At present, local gravity is winning. However it is currently believed that the universe's expansion is accelerating and will continue to do so and thus even atoms will eventually be ripped apart. It is not about counteracting the expansion of the 'entire universe' but rather counteracting the expansion of local spacetime. Once local space time is expanding faster than light, it becomes impossible for anything to stay together.
    I thought the expansion was universal, that is, expanding everywhere already faster than c. Are you saying the expansion is variable?
  4. Cape Town
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    28 Mar '16 13:52
    Originally posted by sonhouse
    I thought the expansion was universal, that is, expanding everywhere already faster than c. Are you saying the expansion is variable?
    I am sure we have discussed this before. Speed is relative between two points. You cannot put a 'speed' figure on expansion. To say 'space is expanding faster than c' is incoherent. Currently the expansion of space is:
    74.3 plus or minus 2.1 kilometers (46.2 plus or minus 1.3 miles) per second per megaparsec (a megaparsec is roughly 3 million light-years).

    http://www.space.com/17884-universe-expansion-speed-hubble-constant.html

    If the expansion continues to accelerate, the moment the expansion as measure between two sides of a galaxy cluster exceeds c, then the cluster is almost certain to disperse (its a little more complicated than that).
    At a much later date, the expansion over a distance of one nanometre will exceed c. At that point molecules start to get ripped apart.
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    28 Mar '16 14:444 edits
    Originally posted by twhitehead
    At present, local gravity is winning. However it is currently believed that the universe's expansion is accelerating and will continue to do so and thus even atoms will eventually be ripped apart. ....
    Actually, although it is currently believed that the universe's expansion is currently accelerating, that 'great rip' theory that predicts the eventual ripping up of everything (even atoms) is far from yet considered to be a scientific fact and many if not most physicist and cosmologists think it is probability false and even just a bit fanciful. Personally I have no opinion on its validity.
  6. Cape Town
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    28 Mar '16 15:43
    Originally posted by humy
    Actually, although it is currently believed that the universe's expansion is currently accelerating, that 'great rip' theory that predicts the eventual ripping up of everything (even atoms) is far from yet considered to be a scientific fact and many if not most physicist and cosmologists think it is probability false and even just a bit fanciful. Personally I have no opinion on its validity.
    Yes, I should not have implied it was 'fact'. It is one hypothesis amongst many.
  7. Standard memberapathist
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    28 Mar '16 20:39
    Originally posted by twhitehead
    ... You cannot put a 'speed' figure on expansion. ...At a much later date, the expansion over a distance of one nanometre will exceed c. ...
    hmm
  8. Subscribersonhouse
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    28 Mar '16 21:091 edit
    Originally posted by twhitehead
    I am sure we have discussed this before. Speed is relative between two points. You cannot put a 'speed' figure on expansion. To say 'space is expanding faster than c' is incoherent. Currently the expansion of space is:
    [quote]74.3 plus or minus 2.1 kilometers (46.2 plus or minus 1.3 miles) per second per megaparsec (a megaparsec is roughly 3 million ligh ...[text shortened]... er a distance of one nanometre will exceed c. At that point molecules start to get ripped apart.
    Of course that is assuming the present accelerated expansion will continue unabated.

    Right now we don't know what is causing the acceleration so there could also be some kind of correction a billion or 10 billion years from now.

    Anyway, it is no cause for panic since not only will humans be extinct but our entire solar system will be extinct🙂

    Here is my pet theory of the acceleration:

    Our universe in some multi-dimensional way is surrounded by sister universes like foam where one bubble (our universe) is totally surrounded by other bubble universes.

    So the mass of all those bubble universes will tend to pull at our universe gravitationally, normal gravitation, no need for any esoteric physics in that case.

    So in that scenario, our universe may be destined to just blob up together with another bunch of universes like how foam in water tends to combine into larger bubbles and that could go on for quadrillions of trillions of years and we may never even notice the transitions.

    You heard it first here.

    And maybe last🙂
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