Why wasn’t the whole universe a black hole around the time of the big bang?

[knock_knock]

A black hole, according to my crude understanding, exists whenever you get enough mass in a small enough space. Then gravity gets so strong that nothing, not even light, can escape (except for a little bit of radiation due to quantum effects). I’ve even heard that it’s possible that the Earth could be inside a giant black hole, it’s just that we’re so far from its center that we don’t even notice. So, I was wondering: if all the matter in the universe were close enough together to make one big black hole, then how big would that black hole be?

Then I realized that all the matter in the universe actually was packed into a small space right after the big bang. Does it make sense to think of the newborn universe as a black hole? Why or why not? Why didn’t the whole universe act like a black hole then? Does it have anything to do with the laws of physics being different under those high energy conditions? Does it have anything to do with dark energy?

[Peanuthead]

If there was a big bang in a black hole and no one was there to hear it would it still create a universe?

[Sergio]

Perhaps the Universe is a gigantic black hole. What theory predicts about black holes is that matter or energy can’t pass outside of the events horizon, but there is no way to know what happens inside the events horizon.
The radius of the events horizon depends on the mass of the object. The massive ones having greater radiuses and being less dense.
We do not know what is the mass of the Universe, because we have no means to evaluate the mass of the dark matter, but if the Universe is massive enough, it’s events hhorizon may be of the order of 20 billion light-years, about the size cientists think the Universe is.

[Sergio]

Perhaps the Universe is a gigantic black hole. What theory predicts about black holes is that matter or energy can’t pass outside of the events horizon, but there is no way to know what happens inside the events horizon.
The radius of the events horizon depends on the mass of the object. The massive ones having greater radiuses and being less dense.
We do not know what is the mass of the Universe, because we have no means to evaluate the mass of the dark matter, but if the Universe is massive enough, it’s events hhorizon may be of the order of 20 billion light-years, about the size cientists think the Universe is.

[rsa]

Check this out and see if it helps: http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/universe.html

The short answer is that the big bang gets away with it because it is expanding rapidly near the beginning and the rate of expansion is slowing down. Space can be flat while space-time is not. The curvature can come from the temporal parts of the space-time metric which measures the deceleration of the expansion of the universe. So the total curvature of space-time is related to the density of matter but there is a contribution to curvature from the expansion as well as from any curvature of space. The Schwarzschild solution of the gravitational equations is static and demonstrates the limits placed on a static spherical body before it must collapse to a black hole. The Schwarzschild limit does not apply to rapidly expanding matter.

Read the link for more details.

[Waenara]

The Master Speaks: What would happen if you were swallowed by a black hole?

Possibility number three (you may want to sit down for this) is as follows. For reasons that I confess are not entirely clear to me, when a black hole grows to enormous mass, it becomes less dense.

If our entire galaxy collapsed into an ebony aperture (I am getting tired of typing black hole), said BH would be about ten billion light years across, with the average density of a thin gas. If we take this to its logical conclusion, it is possible that the known universe is itself a black hole, with us living in it.

Wherefore, it seems to me, the obvious question is: how the hell do we get out of here? The casual attitude of our public officials toward this baleful possibility is nothing short of scandalous.

[bonzer]

A recent Comments thread about problems with that passage from Cecil’s column.

[Chronos]

If the Universe ever was a black hole, then it still is. This is essentially equivalent to a closed universe, i.e., one that will eventually fall back together in a Big Crunch. The Big Crunch singularity is equivalent to the singularity in the center of a black hole: Inside a black hole, r is a timelike coordinate (and t is a spacelike coordinate), so the center of a black hole is always in the future of anything inside the hole, just like the Big Crunch is in the future of anything in a closed universe.

Recent observations have shown that our Universe is not, in fact, closed, so we’re probably not inside a black hole. But it’s not an absurd idea.