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B Why didn't the Universe end up in a huge black hole?

  1. Jul 28, 2017 #1
    Since in the beginning of the universe all matter was concentrated in a ridiculously small space, how didn't the whole universe just ended up as a huge black hole right after the gravitational force appeared?

    Only solution I can think of is that space itself was expanding faster than matter could gather together, and that this process continued long enough to prevent everything from collapsing.

    But still, given the fact that galaxies hold matter together today while the universe is expanding, it is hard to think that matter couldn't just "resist" the expansion back then as it does now.
     
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  3. Jul 28, 2017 #2

    phinds

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    This question has been answered here dozens of times. I suggest a forum search.
     
  4. Jul 28, 2017 #3
    That part is COMPLETELY not true... If Universe is infinite, it was also infinite back then.
     
    Last edited: Jul 28, 2017
  5. Jul 28, 2017 #4
    I have wondered about the question in the op also, and tried forum searches and internet searches. All I come up with are endless threads about weather or not the universe is a black hole, I don't think that's the question here. I'm not sure exactly how to ask the question, or if there is even a rational answer. But I'll try anyway:

    The density of a stellar mass black hole is something like 6x10^18 kg/m3. I don't know if that changes with size of the black hole. The question is, at some point in the early universe, was the density ever greater than that? And if so why wasn't it a black hole? There is a huge gap in my knowledge here and I suspect there is something fundamental that I am missing. Any thoughts would be appreciated, or links to a thread or papers that might help fill in the missing pieces. Apologies if this is not what the op was asking.
     
  6. Jul 28, 2017 #5

    phinds

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    Yes, the density in the early universe was incredibly high BUT ... for one thing, it was pretty much uniform so there was no center for anything to coalesce around and for the other thing, the inflationary pressure was WAY stronger than gravity anyway.
     
  7. Jul 28, 2017 #6

    phinds

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    And in addition to this, even if it was finite it was unbounded so there still was no center for anything to coalesce on.
     
  8. Jul 28, 2017 #7
    I did a search but didn't find it. This "uniformity" perfectly preventing any concentration is strange for me, since the CMB itself shows clearly signs of energy concentration in the early universe.

    As for the inflation, that makes a lot of sense.

    As a matter of fact I found this video about the subject:

     
  9. Jul 28, 2017 #8

    phinds

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    Sure. 1 part in 100,000
     
  10. Jul 29, 2017 #9

    bapowell

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    Can you elaborate? The CMB is consistent with a highly uniform universe on cosmological scales.
     
  11. Jul 29, 2017 #10
    As phinds pointed out, the extreme inflationary pressure of the early universe would have prevented its gravitational collapse:

    Gravitational collapse occurs when an object's internal pressure is insufficient to resist the object's own gravity. For stars this usually occurs either because a star has too little "fuel" left to maintain its temperature through stellar nucleosynthesis, or because a star that would have been stable receives extra matter in a way that does not raise its core temperature. In either case the star's temperature is no longer high enough to prevent it from collapsing under its own weight.​
     
  12. Jul 30, 2017 #11

    Bandersnatch

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    However, you don't need anything to collapse, or even be very dense, to form a black hole. The event horizon forms if there's enough mass contained in some region of space, but the more mass there is, the less dense it can be.
     
  13. Jul 30, 2017 #12

    phinds

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    Yes, but this only works if the mass is NOT uniformly distributed along with other mass. That is, think of a 3D lattice of 10x10x10 Earth sized bodies, each 1 million miles from the next neighbor but with nothing else around. Clearly, this will collapse into a BH. Now think of the same lattice extended to infinity in all directions. No BH will form because there is no center. This is the point I made in post #5.
     
  14. Jul 30, 2017 #13

    Bandersnatch

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    And I wasn't correcting you. :smile:

    I kinda wanted to engage you about the role of 'inflationary pressure' in the context of the question, but seeing how I don't feel I'm on sufficiently solid footing to even formulate the question correctly, I decided against it.
     
  15. Jul 30, 2017 #14

    bapowell

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    Are you talking about the observable universe? We have no idea whether the universe, of which our observable patch is but one part, is infinite, finite, or bounded in any way.
     
  16. Jul 30, 2017 #15
    yes sorry, i suppose in part I was talking about the observable universe. you can disregard that bit :)
     
  17. Jul 30, 2017 #16

    PeterDonis

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    Because it was expanding rapidly.

    And if that mass is not expanding rapidly. This qualification isn't often discussed, because black hole formation is normally discussed in the context of the collapse of a static object like a star. But the qualification is still a valid one.
     
  18. Jul 30, 2017 #17

    PeterDonis

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    The OP question has been answered, and speculative posts are not allowed. Thread closed.
     
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