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B Big bang vs Black hole

  1. Aug 15, 2015 #1
    Dear PF Forum,
    I have read a link about big bang time line. Started from time zero, then Baryogenesis, lepto genesis, planck time then on...
    I try to make a simple calculation here with Schwarzschild calculator.
    The mass of the universe is: 1053Kg.
    Schwarzschild radius: 1.486 x 1026
    So at T+20 minutes after big bag, the radius of the universe is: 1.8 x 107Km
    All these mass is packed at that radius, defintely below Schwarzshild Radius.
    How can all that mass continued to spread out much less for millions of year.
    What triggered that expansion?

    And if I imagine what sphere is 20 minutes light year with that mass compared to Neutron Star.
    A 2 solar mass neutron star is about 10 km in diameter, this is very roughly.
    In 20 minutes light speed, the sphere could be packed by... (1.8 x 107/5)3 = 4.66 x 1019 neutron stars.
    And the number of stars in the universe if a galaxy has roughly 100 billions stars in 100 billions galaxy is 1022. So the sphere is much denser than neutron star?
  2. jcsd
  3. Aug 15, 2015 #2
    With regard to the expanding Universe, I think the various inflation theories attempt to address this.
    They propose that in the very earliest stages, meaning the first few trillionths or less of a second, the Universe was not only expanding, but did so at a phenomenally faster rate.
    In that scenario you can't just make a simple linear extrapolation. of size over time.

    Inflation is not fringe stuff:
    The mechanism responsible for inflation is not known, the basic picture makes a number of predictions that have been confirmed by observation. The hypothetical field thought to be responsible for inflation is called the inflaton.

    Last edited by a moderator: Aug 15, 2015
  4. Aug 15, 2015 #3


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    You may have noticed the Schwarzschild radius of a black hole with the mass of the universe is about the same as the size of the observable universe- which should tell you something is very wrong. We can safely say observations suggest we do not reside inside the event horizon of a universe mass black hole. Our universe is expanding, not collapsing. So what's up with that? Our universe underwent some rather astonishing changes in a short amount of time billions of years ago- about 14 billion years ago by the math. From an unimaginably compact, dense and hot state it rapidly expanded into an unimaginable huge, diffuse and rather leisurely expanding state. We can and do observe the universe back to when it was about 400,000 years old, and perceive it was expanding at an ever increasing rate the further back we look. We are still exploring the laws of physics that ruled the early universe, but, it's a little like trying to figure out chess by studying middle game positions from matches played centuries ago. We mostly have just educated guesses about the initial position, sequence of moves and how the rules may or may not have changed over time. We can rest assured that some of these guesses are, as Wolfgang Pauli might say, 'not even wrong'.
  5. Aug 15, 2015 #4
    Dear Chronos, I calculate the Schwarzshild radius for our universe using this link: http://hyperphysics.phy-astr.gsu.edu/hbase/astro/blkhol.html
    And I plug in the mass of the universe: https://en.wikipedia.org/wiki/Universe
    The Schwarzshild radius is: 1.483755 x 1026 metres. I divide it by 300 million, I came up with this number: 4.94585 x 1017
    Then I divide it by 60 x 60 x 24 x 365, I have: 15,683,192,319 years. So the Schwarzchild radius for the mass of the Universe 1053 (according to Wikipedia) is 15.6 gly.
    The universe is about 13.8 billions light years old. But the observable universe is 46 gly in radius.
    I think with this mass (1053), we are not living in a black hole.
    Either wiki is wrong, the Schwarzshild calculator is wrong, or I made a mistake in my "calculation".

    "If" the universe has a centre.
    That is enough for me to fullfill my curiousity. Thanks.
  6. Aug 16, 2015 #5


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    Yes, but, you may wish to reconsider equating the age of the observable universe with the schwarzschild radius of a universe mass black hole.
  7. Aug 16, 2015 #6
    1. The schwarzschild radius of a universe mass black hole is: 1.483755 x 1026m
    2. It is 15,683,192,319 light years
    3. The age of the universe is: 13.8 billions years.
    4. The radius of the observable universe is: 46 gly.
    What do you mean equating the age of the observable universe? Can you kindly explain?

    Btw number 1 and 2 I calculate it using schwarzschild calculator base on the known mass of the universe and calculate it with spread sheet help.
    Number 3 and 4, I read it from various sources.
  8. Aug 16, 2015 #7


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  9. Aug 20, 2015 #8


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    We have a FAQ about this:

    https://www.physicsforums.com/threads/is-the-universe-a-black-hole.506992/ [Broken]
    Last edited by a moderator: May 7, 2017
  10. Aug 23, 2015 #9
    If you believe in the Big Bang, here is a simple mental exercise to try.

    Legend has it that the Universe is expanding, so if you run time back in your mind, it will contract.

    So as you do that, the Universe gets smaller and smaller, and the space between everything gets smaller too.

    Then things come together and we start getting black holes, and as the Universe gets still smaller, they all come together until all there is, is one big black hole.

    A couple of rules on black holes: They are stable, in their way. They only grow by the addition of more material, and all the material in the Universe is already in that black hole. And finally, they do not expand.

    So, that is the end of the Universe, even before it began.
  11. Aug 23, 2015 #10
    Perhaps I should read the FAQ, this forum has it, see bcrockwell reply. Perhaps the mathematic model is different in big bang. So it's not a black hole.
    Btw, what do you mean by "the end of the universe before it began"?
  12. Aug 23, 2015 #11
    Well there are the cyclic universe models, although these are less popular than they used to be.
    In that case you would have the collapse of a previous state of the Universe prior to what we call the big bang and the expansion of the universe into the one we see today.
    There is no evidence for the cyclic model though, it's just there among possibilities which haven't been discounted.
    Nobody at this time can confidently proclaim the state the universe was in prior to the big bang, neither what it's eventual end will be.
  13. Aug 25, 2015 #12
    The Big Bang wss not a black hole
  14. Aug 25, 2015 #13


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    A concise summary of the thread.
  15. Aug 25, 2015 #14


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    And a good note on which to close it.
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