Why didn't the big bang just become a black hole?

[WannabeNewton]

The assumptions of homogeneity and isotropy mentioned above by both Mordred and bapowell have explicit mathematical formulations. It might help to look at the mathematical descriptions to get a feel for what homogeneity and isotropy are so that you don't mistake them for much stronger statements as bapowell pointed out above.

 

[brianhurren]

there is no 'outside' of the universe. The Universe is a container, a big room if you like, that contains everything. If it contains everything then it must also contain itself. If it contains everything including itself then there can't be an outside.

as for what is it expanding into, probably not expanding into anything, its just part of its bendy stretchy nature.

 

[yamex5]

I don't understand why this debate always renews every year. Instead of speculating about why the big bang did not become a black hole, why doesn't someone first show that the big bang conforms to the Schwarzschild solution? The Friedmann-Robertson-Walker model, on which the big bang cosmology is based, lacks the symmetries of a black hole spacetime. So why would the big bang form a black hole?

For the more ignorant among us (and I admit to being one!), it is hard to understand why all the energy arising from the big bang (I am assuming that there was no matter in the initial fraction of a second) did not have the gravitational effect of not allowing any energy to escape.
However, this was answered by antiphon earlier, clarifying that if the energy/mass is distributed evenly across the entire universe, then there is no way for a black hole to form.

 

[Drakkith]

For the more ignorant among us (and I admit to being one!), it is hard to understand why all the energy arising from the big bang (I am assuming that there was no matter in the initial fraction of a second) did not have the gravitational effect of not allowing any energy to escape.

There is no point where our models say that energy was created by the big bang. At the point in time where our models break down, matter and energy already existed in the form of massive, exotic particles and high energy EM radiation. It's important to remember that in modern cosmology, the big bang is not a single event, but a process of expansion. Our models predict that the universe was once very dense and very hot and expanded from there. They do not predict a creation event.

 

[yamex5]

There is no point where our models say that energy was created by the big bang. At the point in time where our models break down, matter and energy already existed in the form of massive, exotic particles and high energy EM radiation. It's important to remember that in modern cosmology, the big bang is not a single event, but a process of expansion. Our models predict that the universe was once very dense and very hot and expanded from there. They do not predict a creation event.

Okay, I see what you're saying. But it doesn't change the fundamental question posed here, namely, why doesn't the concentration of matter and energy just collapse into a black hole?
So now the question is, if there was clumping, why didn't all of the early universe collapse into a black hole?
Is it possible that the expansion of the universe was so quick that the universe could not collapse?
Or do we just not know?

Thanks!

 

[PeterDonis]

Is it possible that the expansion of the universe was so quick that the universe could not collapse?

The quick answer is yes, that's why the universe didn't collapse at the start--it was expanding too fast.

But there's more to it than that. Even if the universe had collapsed at the start, it wouldn't have been a black hole, because a black hole is a region of spacetime that can't send light signals to infinity, i.e., to a region very far away outside the hole. But if we're talking about the whole universe, there is no "outside", so there is no "infinity" to send light signals to, so there's no meaning to the term "black hole" when applied to the whole universe. The concept doesn't make sense.