Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Was the entire universe a Black Hole for many years?

  1. Apr 17, 2004 #1
    I read that the determining factor of a Black Hole being created is when the mass of an object divided by its radius exceeds a critical point. If the number is more then this critical point then it is a Black Hole; if the number is less then this critical point then it is not a Black Hole.

    Also, I read that if you replay the expansion of the universe in reverse, it leads to an extreme amount of mass in a small amount of space and eventually leads to the Big Bang theory.

    My question is, if the only determining factor of Black Hole creation is mass divided by its radius exceeding a critical value, then it seems like the entire universe would have been a Black Hole for many of years after the Big Bang? And would remain a Black Hole until the universe had enough time to expand large enough until you could divide the mass of the universe by its radius and not end up with a number that is less than the critical value needed to be a Black Hole?

    Was the entire universe a Black Hole for many years?
  2. jcsd
  3. Apr 17, 2004 #2


    User Avatar

    What you're talking about is the Schwarzchild radius, the radius that light cannot escape.

    I also wonder about this, since is the universe started as a very dense, small object, how did stuff fly out? It must've been very massive to contain all of our universe's energy too.
  4. Apr 17, 2004 #3


    User Avatar
    Science Advisor

    This is indeed one of the sticking points of cosmology, and it may be more troublesome than you realise. You see, objects within a black hole cannot move outward away from the center. This would seem to indicate that if the universe ever were a black hole, it still would be. It could not have "expand large enough until you could divide the mass of the universe by its radius and not end up with a number that is less than the critical value needed to be a Black Hole", because it could not expand at all.

    Cosmologists are trying to reconcile this with the Big Bang model, and there are hopes that the Theory of Everything (which should unite QM with GR) will show some means by which this expansion is possible. One possible solution that has been put forward is the "inflation" model, which would have the universe existing in this black hole state for a very short time. In this model, the reason things could move away from the center is that everything in the universe was moving faster than light, but for a very short period of time (something like 10-35 seconds).

    Which is about the amount of time I have right now, so I'll post more later :biggrin:.
  5. Apr 17, 2004 #4


    User Avatar
    Homework Helper
    Gold Member

    Why do all Cosmologists assume that the universe started at one point, or atleast a very small point.

    It makes sense to make this assumption because the universe is expanding, and things like the critical density.

    If they believe in virtual particles, wouldn't it make sense to believe in virtual energy. Something that repays itself in forms of matter. Is it possible to think that at one time the universe was contracting, and all of the sudden large amounts of virtual energy makes its way into our universe. This might be very rare, but then again, with infinite time(if it exist) everything is possible. With all this virtual energy coming in all at once, it might have stimulated expansion. As we wait for the sudden change in virtual particles, that will draw energy towards it (to repay "loan"), the universe will continue to expand.

    Of course, virtual particles is predicted from the Quantum/Uncertainty Principle. I am not aware about virtual energy.

    Again, this type of universe creates more questions than answers.
  6. Apr 18, 2004 #5


    User Avatar
    Science Advisor

    I should also take a second to mention M-theory; that branch of QM which unifies the other five superstring theories into a single model. The details are not terribly important for the current discussion, but only one feature of the theory. M-theory was arrived at by showing that the other string theories were looking at the same equations from different perspectives. This meant that the "blind spot" in one theory could be covered by switching to another. As one set of numbers goes toward infinity in one theory, another theory sees those same numbers getting smaller (metaphor: as the number of shapes a string could take approaches infinity and becomes impossible to calculate, the number of shapes it cannot take becomes smaller and more easy to manage).

    On of the results of this strategy shows that, below a certain critical value (a very very small value), there is no mathematical difference between contraction and expansion. This of course does not help explain why the expansion could contiue through the sizes in between this very small value and the Schwartschild Radius of the primal black hole, but it's a start.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook