B. H. Manners

Hello,

I know next to nothing about physics and wanted to ask our experts a question. From what I understand all the matter in the universe was all glumped together at one time. I have read that sometimes stars collapse due to the weight of their own mass and form a black hole.

Why did the original "Big Bang" glump of matter not collapse on itself and form a super-duper sized black hole?

Jimmy Higgins

Well, there are three possible ends for a star. How a star dies is based solely on their mass. A star that has a mass that is 2.2 times that of our sun, will eventually collapse into a black hole. The other two options are neutron star and drawf star.

I may be incorrect, however, I believe it is thought that the original composition of the universe "before" the big expansion was a singularity. Therefore, it really couldn't collapse on itself. It was already infitesimally small.

B. H. Manners

I have to admit I am confused even more. The pre-big bang matter was all compacted into a wee bitty shape. Yet, the great mass and gravity was still there. It only seems logical that it would have collapsed in on itself, singularity or not. However, I am physics stupid, so someone come teach me different.

fando

Well, you see, a black hole as we know it is a singularity in the fabric of spacetime. It needs spacetime to be relatively smooth and empty to exist (as compared to the very early universe); It needs General Relativity to describe it. At the begining of the universe, the nature of spacetime was completely different from what we're used to (or what General Relativity says), so it's a stretch to think of singularities in something which can't really accomodate the definition in a way we understand clearly. The entire universe at the time obeyed laws which are as much quantum as they are macroscopically relativistic. The nature of the universe at this time is still being untangled in theories of quantum gravity, so as far as I know, there's no easy way to explain why the universe was able to escape a situation that should intuitively (under General Relativity, that is, at the exclusion of quantum) collapse under its own mass.

In short, the complete explanation of what happened at the very beginning is a modern puzzle that we're just beginning to unravel. At this stage, we can't use just General Relativity to explain the escape from a global singularity: there's something quantum in the excuse. Welcome to the fronteirs of science! ]

My memory is getting rusty, so this post might be rusty too.. beware!

Zentraedi

Well you would have to assume that the initial force of the big bang overwhelmed the confines of gravity. We are still debating whether that very thing will eventually happen. A "closed" universe is such the case. If there is enough mass in the universe its gravity will pull itself back together. It would be pure guess work as to where the initial force of the big bang came from. I would guess from another universe. We may be inside another universe's black hole.

Friar Bellows

My naive answer to your question is that whatever caused the universe to expand in the first place must have been strong enough to overcome the tendency of matter to collapse in on itself. Hopefully, others more qualified and informed will flesh out my answer or shred it to bits. Either would suit me.

I'll also leave for others to point out the pitfalls of using rough analogies (i.e. star vs primordial universe) in physics.

Some links which may be of interest to you:

Frequently Asked Questions in Cosmology

220 FAQs About General Cosmology

180 FAQs About Big Bang Cosmology

and last but not least:

A Ridiculously Short History of Time

eh

It is also quite possible that there was no matter at all in the beginning. The universe could have been empty (except for a cosmological constant) and expanded until our inflation epoch occured. Thus we get a universe that expands without the need for a huge amount of energy to give it a push over gravity.

Mr. Sammi

Somewhere in the poor section of Montréal, I heard a rumor that you need space to have gravitational effects, some one was saying that there was some other interacting force which was in effect at this early period of this Universe, but it was not called gravity at the time... Hearing ALL this I could not tell you, to what time, they were making reference.

[edited to correct the spelling of 'Montréal'. I notice it in your location and it drives me crazy. -Wyz_sub10]

* * *

But in addition to this they were saying, these poor folk in Montréal, that space was created because of the entrophy effect. If I quote them correctly, they said that after the dark energy was resolved into quantum precursors, the loss of energy due to the change caused gaps in the energy field, they claim that things actually began to clump together, or it seemed like some sort of accumulation factor, the change of states, or the movement from one energy form to another energy form, caused this loss of initial statehood, which slowly became the gaps in the Energy Fields - now called space.


I have no idea from where this rumor originated but I strongly believe (during one of my eavesdropping sequences) that it was the man with no hat who was starting these rumors.

An analogy was also spoken of. It was said that a dense sphere, had in effect no space within, and if things become polarised within the sphere, space is created within this sphere. That was all I heard.


Sammi Na Boodie (with black hat over his ears)

Jesse

Is the big bang a black hole?

Note that because the laws of physics are time-symmetric, in theory they should allow "white holes", which would look like black holes in reverse, spewing out matter inexorably instead of pulling it in inexorably. But probably they don't exist for reasons related to the second law of thermodynamics. The Big Bang is not thought to be a white hole in a pre-existing space, but white holes do show that you have to be careful about the idea of "inevitable collapse" in general relativity.

DNAunion

DNAunion: oooh, ooh, oooh....I think I know the answers. The relevant concepts are false vacuum decay and negative pressure.

What, you want me to explain them to you? No can do - I don't understand them.

But at least anyone interested could do some searches and see if they understand it.