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

[bapowell]

Well everyone has a different viewing of things and I respect yours. Me personally can see that the Big Bang tries to explain how the universe banged into existence. The singularity is part of this theory to me. But it's how I'm taught. I do agree though that yes physics does break down when it come to a singularity but it doesn't completely vanish. But it doesn't make any sense to me to say that there was no singularity at all. If there was no singularity then how did it come into existence? It certainly didn't come from nothing. That I'm positive of.

Right. Who's saying it came from nothing? The point is that nobody knows what happened *at* the big bang, because all of our physical theories cannot be applied there. Our theories only become operative at the Planck time, $t \gtrsim 10^{-44}$ sec. The idea is that we need a quantum theory of gravity -- an understanding of how spacetime behaves and evolves at high enough energies that quantum mechanics becomes important. We don't currently have such a theory, but the expectation is that it will "resolve" the initial singularity, in the sense that it will replace the singularity with a smooth, finite spacetime solution. So, yes, physics in principle does have something to say about the initial moment of the big bang, but we don't currently know exactly what that something is yet. And that's OK -- that's how science works. We're still working on it and we don't have the answer yet. You can choose to believe whatever you want about the origin of the universe, but be careful to draw the line between physics and philosophy, and between facts and speculation.

 

[mannygonzales1]

And I think I've drawn that line pretty good. Not even close to perfect but I do believe in this 'singularity' very much so.

 

[Mordred]

Here is one of the better big bang reviews and descriptives in terms of its current evolution.


http://arxiv.org/abs/1304.4446

believe what you like however its not shared in real cosmology

 

[mannygonzales1]

Oh, so sorry professor.(:

 

[bapowell]

Oh, so sorry professor.(:

I'm sorry if you have a misconception, but this is a forum where we discuss accepted scientific theories. We've tried to convey that modern cosmology does not interpret the existence of singularities as physical elements. You can "believe" in singularities all you like, and you can imagine whatever you want regarding the origin of the universe, but you are not doing science then.

 

[Mordred]

Lol trust me I am far from a professor lol.

Seriously though, this thread has as gently as possible shown that the BB models do not start from some super particle, as well as the misconceptions regarding the term singularity. None of the various inflation based models have ever described it in terms of some infinitely dense etc.
The article I posted is equivelent to an extremely well written FAQ directly related to the hot big bang model. Far better than a great deal many I have read.

Edit not to limit the article to a FAQ

 

[brianhurren]

being both finite and infinite

This is where it gets a bit confusing.. if the universe was once the size of a marble, how is it infinite? lol Unless it has something to do with that video game analogy where you move off the left side of the screen and reappear on the right side, making spacetime like a sphere though space itself isn't. ohh.. my head hurts

funny you should menchan that.I was just thinking this same thing the other day. How can something be both finite and infinite at the same time. then I thought, it could be finite in 4D but infinite in 3D. Consider this suppose you have got a 3D cube and a 2D wall. the cube is finite and the wall is infinite. Suppose you want to cover the wall completely with squares from the cube. You would slice the cube up into infinitesimally thin slices and cover the wall. So the cube projected or flattened out onto the wall could be infinite as seen from the 2d wall and would be finite as seen from inside the 3D cube. Notice how the points of the cube map onto the points on the wall 1 to 1. for every point in the cube there is a point on the wall. they both have the same degree of infiniteness. So there points could both be labelled with transfinite number Aleph null or Aleph zero.
Another question might be how big is the cube, the cube could be any size you like, but not zero. if it was zero it would be a single point and would not map 1:1 with points on the wall. so the degree of infinity needs to be conserved. (go on...beat that Doctor Who!)
don't know if this has anything to do with big bang...I was trying to answer how can something be finite and infinite at same time.

marijuana isn't a gateway drug ----maths is.

 

[bapowell]

It's not nearly as complicated as all that. When people speak of the universe being the size of a marble, they are talking about either: the observable universe or the entire universe. If they are talking about the observable universe, they are referring to the region of the universe that was observable at the time soon after the big bang -- essentially a causal ball with radius determined by the distance that light had traveled since the big bang. This makes no claims regarding the size of *the* universe -- it could well be infinite. If, however, they are referring to the entire universe, well then of course the universe is finite if the marble is finite.

 

[DrWafflez Jr.]

What is the cosmological scale?

 

[DrWafflez Jr.]

I'm new at this

 

[bapowell]

What is the cosmological scale?

Can you say in what context you heard this term? The phrase "on cosmological scales" essentially means "on large enough scales where homogeneity and isotropy are good approximations".

 

[DrWafflez Jr.]

I saw it on the eleventh post on this topic

 

[Mordred]

http://en.wikipedia.org/wiki/Cosmological_principle

The cosmological principle is usually stated formally as 'Viewed on a sufficiently large scale, the properties of the Universe are the same for all observers.' This amounts to the strongly philosophical statement that the part of the Universe which we can see is a fair sample, and that the same physical laws apply throughout. In essence, this in a sense says that the Universe is knowable and is playing fair with scientists.

the two terms that describe this is homogeneous: no preferred location one place is the same as another.

and Isotropic no preferred direction, no matter where you look its the same.

If you look at the universe from Earth, a large enough scale where this would hold true would be larger than 100 Mpc. (Mega parsecs.) This size averages out large scale structures such as galaxy clusters. So in this case the cosmological scale would be >100 Mpc

 

[DrWafflez Jr.]

http://en.wikipedia.org/wiki/Cosmological_principle

The cosmological principle is usually stated formally as 'Viewed on a sufficiently large scale, the properties of the Universe are the same for all observers.' This amounts to the strongly philosophical statement that the part of the Universe which we can see is a fair sample, and that the same physical laws apply throughout. In essence, this in a sense says that the Universe is knowable and is playing fair with scientists.

Does that mean the cosmological principle says that the laws that we perceive in our viewable universe is the same in the parts we can't see?

 

[bapowell]

Does that mean the cosmological principle says that the laws that we perceive in our viewable universe is the same in the parts we can't see?

The principle is primarily concerned with the large-scale distribution of matter in the universe -- essentially, how the universe "looks" to observers placed throughout it. It is an assumption of the principle that the universe appears homogeneous and isotropic on large scales, independent of the location of the observer. It is an assumption, because obviously we have no empirical data regarding the distribution of matter outside the observable universe.

But to say that cosmological principle suggests that all the laws of physics are the same I think is going rather beyond what the intent of the principle is. The cosmological principle is a statement about the distribution of matter and energy in the universe, and so has implications only for those laws most directly affecting the distribution of matter and energy.

 

[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.