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Bill Angel

Is there a problem reconciling the properties of a black hole with the properties of the "big bang"?

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Here's a question related to the findings about black holes.
The image released yesterday is of a black hole with a mass of 6.5 billion suns.
That is apparently a mass sufficient to ensure that nothing, neither energy nor mass, can escape the black hole's gravitational pull.
When the universe came into existence the total mass created was far greater than that of 6.5 billion suns. And the mass was concentrated in a volume as small or smaller than the volume of a black hole. So how could this mass overcome its mutual gravitational attraction to fly apart and create what we presently observe as the universe? There seems to be something of a conceptual contradiction here. A black hole is supposed to be a region of space that represents a singularity in which the laws of physics and SpaceTime are unknown. But the moment that the “Big Bang” occurs, a moment when the total density of mass is greater than what it would be in a black hole, is supposed to be a moment where the properties of SpaceTime and the laws of physics are both knowable and are the same as what we presently observe in the universe. 

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2 minutes ago, Bill Angel said:

That is apparently a mass sufficient to ensure that nothing, neither energy nor mass, can escape the black hole's gravitational pull.

Note that a black hole can have any mass. The key point is that the mass must be in a volume smaller than the Schwarzschild radius. So, for example, if the Earth was crushed down to be about 1.5cm across, it would turn into a black hole.

6 minutes ago, Bill Angel said:

When the universe came into existence the total mass created was far greater than that of 6.5 billion suns. And the mass was concentrated in a volume as small or smaller than the volume of a black hole. So how could this mass overcome its mutual gravitational attraction to fly apart and create what we presently observe as the universe?

The difference here (I think, and I may be wrong!) is that a black hole is what you get when have a concentration of mass surrounded by (largely) empty space so there is nothing to stop it collapsing to form a black hole.

However, the early universe was denser but it was also uniformly full of matter. So it was all being pulled on in all directions so there was nothing to make it collapse. (Sort of)

Also, it was expanding. For reasons we don't know. Maybe the result of bouncing back from an earlier collapse.

But, anyway, the concepts of the Big Bang and black holes an't be inconsistent as they are both solutions to the equations of GR, under different conditions.

 

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3 hours ago, Bill Angel said:

Here's a question related to the findings about black holes.
The image released yesterday is of a black hole with a mass of 6.5 billion suns.
That is apparently a mass sufficient to ensure that nothing, neither energy nor mass, can escape the black hole's gravitational pull.
When the universe came into existence the total mass created was far greater than that of 6.5 billion suns. And the mass was concentrated in a volume as small or smaller than the volume of a black hole. So how could this mass overcome its mutual gravitational attraction to fly apart and create what we presently observe as the universe? There seems to be something of a conceptual contradiction here. A black hole is supposed to be a region of space that represents a singularity in which the laws of physics and SpaceTime are unknown. But the moment that the “Big Bang” occurs, a moment when the total density of mass is greater than what it would be in a black hole, is supposed to be a moment where the properties of SpaceTime and the laws of physics are both knowable and are the same as what we presently observe in the universe. 

The BB was an evolution of space and time [as we know them] from t+10-43 seconds. Matter came later.  The BB and GR [or is that GR and the BB :P] are compatible and go together like a hand in a glove. 

To supplement Strange's excellent answer I found this......

http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/universe.html

Why did the universe not collapse and form a black hole at the beginning?

Sometimes people find it hard to understand why the Big Bang is not a black hole.  After all, the density of matter in the first fraction of a second was much higher than that found in any star, and dense matter is supposed to curve spacetime strongly.  At sufficient density there must be matter contained within a region smaller than the Schwarzschild radius for its mass.  Nevertheless, the Big Bang manages to avoid being trapped inside a black hole of its own making and paradoxically the space near the singularity is actually flat rather than curving tightly.  How can this be?

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 even when spacetime is not.  Spacetime's curvature can come from the temporal parts of the spacetime metric which measures the deceleration of the expansion of the universe.  So the total curvature of spacetime 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

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