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I Why did the singularity expand?

  1. Aug 5, 2016 #1
    The singularity before the big bang, was it anything like the singularities in the universe today? Did it have a black hole around it, with an event horizon?

    And what caused the singularity to expand? Why did it expand when the singularities in our universe don't do anything besides suck stuff in?
     
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  3. Aug 5, 2016 #2

    PeterDonis

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    Is not part of the actual model of the universe that is used in cosmology. It's an artifact of an idealized model, not something that actually existed.

    We also don't know that there are any singularities in the universe today. Classical GR predicts their existence, for example at the centers of black holes, but classical GR is expected to break down when spacetime curvature gets strong enough, which it will inside a black hole before the singularity in the classical model would be reached. So we won't know for sure whether there actually are singularities inside black holes until we have a theory of quantum gravity that tells us what happens in regimes where classical GR breaks down.
     
  4. Aug 5, 2016 #3
    Just say for a moment that singularities do exist. What would cause the singularity in the big bang to expand when the singularities inside black holes don't seem to have any inclination to do much of anything? Wouldn't it require some outside force?
     
  5. Aug 6, 2016 #4

    Fervent Freyja

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  6. Aug 6, 2016 #5

    PeroK

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    Mathematically, no process/mapping can expand a point into a volume. Your question is based on a misunderstanding of the relationship between a mathematical model and the physical reality.
     
  7. Aug 6, 2016 #6

    haushofer

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    But they don't.

    Your question is akin to "how could orcs become humans in Darwin's theory of evolution", and on the answer "orcs don't exist in reality" you respond "but suppose for a moment they do exist".

    Well, if they do exist, the theory doesn't explain it.
     
  8. Aug 6, 2016 #7
    Hi Aaronk,

    The singularity of the Big Bang was nothing of the sort of the one's today. No Event Horizont nor a Black Hole around it. There was no space around it. In fact, the explosion of the singularity was not an explosion in space but an explosion of space.

    And well, why did it explode, actually we don't know. There is some theory that says that before the Big Bang our cosmos was actually a perfect ten dimensional universe, a world where interdimensional travel was possible. However, this ten dimensional world was unstable, and eventually it "cracked" in two, creating two separate universes: a four- and a six-dimensional universe. The universe
    in which we live was born in that cosmic cataclysm. Or four-dimensional universe expanded explosively, while our twin six-dimensional universe contracted violently, until it shrank to almost infinitesimal size. This would explain the origin of the Big Bang. If correct, this theory demonstrates that the rapid expansion of the universe was just a rather minor aftershock of a much greater cataclysmic event, the cracking of space and time itself. The energy that drives the observed expansion of the
    universe is then found in the collapse of ten-dimensional space and time.
    According to the theory, the distant stars and galaxies are receding from us at astronomical speeds because of the original collapse of ten-dimensional space and time.

    Hope I helped :)
     
  9. Aug 6, 2016 #8
    Yes, very much so. What you said about the first four dimensions separating from the other six, is there a name for that hypothesis? How many physicists believe that really happened?

    One question, though. My understanding of gravity is that it's a byproduct of mass bending the space-time fabric, the more massive the object the more it bends space, therefore the more gravity it has. So how could a singularity have gravity if it were not inside space?
     
  10. Aug 6, 2016 #9
    It's called String Theory.
    Easy: the singularity of the Big Bang (not of a Black Hole) did not have gravity. In fact since the Big Bang to the Cosmic Inflation, the 4 forces, in where there is the force of gravity, were unified in 1, because the temperature of the universe was very big. So in the Big Bang, gravity did not exist as we know today; we don't know if the unified force was kind of space-time bend or of the exchange of quanta.

    Anyway, as said before, the singularity is not proven to be real, and it's physical properties usually end in paradoxes. For answering many questions about the singularity, first we need to know the "Theory of Everything".
     
    Last edited: Aug 6, 2016
  11. Aug 6, 2016 #10
    It's called String Theory.

    That sound you hear is the sound of me slapping my forehead.

    Easy: the singularity of the Big Bang (not of a Black Hole) did not have gravity. In fact since the Big Bang to the Cosmic Inflation, the 4 forces, in where there is the force of gravity, were unified in 1, because the temperature of the universe was very big. So in the Big Bang, gravity did not exist as we know today; we don't know if the unified force was kind of space-time bend or of the exchange of quanta.

    Anyway, as said before, the singularity is not proven to be real, and it's physical properties usually end in paradoxes. For answering many questions about the singularity, first we need to know the "Theory of Everything".

    I'm completely okay with paradoxes. The existence of anything is a paradox if I understand the current line of thought correctly. Am I correct in assuming that the physics community is in disagreement regarding the existence of singularities? All the documentaries speak about them as if they were a fact, yet one person just compared them to orcs???

    So, these hypothetical singularities, how are the ones in black holes, if they exist, related to the singularity at the big bang? Could it be said that they're simply different degrees of the same thing, with the singularity at the big bang being the granddaddy of all black holes?

    Let's say hypothetically that the entire universe were to eventually get sucked into black holes, so that the only thing left in space were massive black holes wandering the cosmos. Then they start swallowing each other, until there's only one giant black hole left. Would that massive black hole then swallow space and time itself, and if so, would that in any way resemble the singularity some people think existed at the big bang?
     
  12. Aug 6, 2016 #11
    That would not be the case. A black hole absorbes matter and light not space nor time. Why in your hypothetical case the black hole would start doing so?

    Anyway if the big black hole started to do that, the remaining singularity would be exactly as the Big Bang's one. But remember that looking a Big Bang's singularity is looking an entire universe; nothing of the sort of a black hole.

    Said that, we don't know if anything talked would happen. A singularity is part of a mathematical model unproven to be real.
     
    Last edited: Aug 6, 2016
  13. Aug 6, 2016 #12
    If this "black hole apocalypse" were to happen, once you got down to the last black hole, could gravity become so strong that the fundamental forces recombined? And if so, could that cause a collapse of time and space?
     
  14. Aug 6, 2016 #13
    Gravity is the weakest of the 4 forces. It's impossible that the forces would recombine by the strength of gravity.

    Anyway, that hypothetical black hole would not exist as there's not a reason for which it would start to absorb space and time.
     
  15. Aug 6, 2016 #14

    PeterDonis

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    In other words, we're working within the idealized classical GR models that have singularities.

    In the idealized classical GR model of a universe with an initial singularity, the singularity doesn't expand. It's not actually part of the spacetime at all. It's just an abstract limit that can be taken. The expansion in the model is not due to some property that the singularity has; it's a property of the spacetime as a whole.

    The same goes for the singularity at the center of an idealized classical GR black hole; it's not really part of the spacetime, just an abstract limit that can be taken, and the fact that things fall into it rather than expanding out of it is not due to some property that the singularity has, it's a property of the spacetime as a whole.
     
  16. Aug 6, 2016 #15

    PeterDonis

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    In the idealized classical GR model with an initial singularity, this is not correct; "gravity" exists everywhere in this model.

    In models where quantum effects are taken into account, there is no initial singularity, so your statement is meaningless.

    AFAIK there is no model, even an idealized one, in which this is the case.

    AFAIK nobody has any models, even speculative models, in which this happens.

    The forces "recombining" has nothing to do with the strength of any of them. It has to do with the energy density present.
     
  17. Aug 6, 2016 #16

    PeterDonis

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    The OP's original question has been answered, and the thread is degenerating into unfounded speculation. Thread closed.
     
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