Quick and dirty Big Bang question

[andy_d]

Prescisely what force was responsible for the expansion of the universe? As in, what force is it that gravity has fighting against this whole time in the big tug of war to decide the fate of the universe.

I'm aware that the inflationary model calls on the power of vacuum energy for it's accelerated expansion, but what about the more traditional model?

[JB01]

In the original Big Bang model, there is no force causing expansion and against which gravity is fighting. Matter is simply assumed to be flying apart ballistically, with gravity gradually working against its outward inertia to slow the expansion. If there were no gravity in this model, the universe would continue to expand at a constant rate simply because objects travel at constant velocity unless acted upon by some external force (Newton's 1st law).

Because of recent observations that indicate that the expansion of the universe is actually accelerating, however, it is now believed that there is some outwardly directed force causing the expansion; acceleration requires force to be applied. The nature of this expansion force is still an unsolved problem, as far as I know, but the name of a major candidate theory is "dark energy".

[andy_d]

That's what seemed odd to me. Expansion is a pretty critical part of the whole Big Bang concept, yet I couldn't find anywhere what was considered to have imparted the momentum to all that matter, and the picture of the early universe is a confusing mishmash of matter, radiation, and exotic forces. I can't say i'm terribly impressed with the idea that it is simply assumed to be already expanding.

I can't help feeling, intuitively, that we're missing some pretty humungous pieces of the jigsaw. Mind you, we're also missing most of the mass of the universe, so maybe that shouldn't come as a surprise :D

[Shadowy Man]

I can't say i'm terribly impressed with the idea that it is simply assumed to be already expanding.


I think that is the case in the traditional Big Bang Theory. The universe was once hot and dense and has been expanding since then.

To understand the expansion you need to get into Inflationary Theory, a much newer theory that has a lot of support due to its predictions being observed in the cosmic background radiation. I highly recommend picking up Alan Guth's book entitled The Inflationary Universe.

[joedad]

I can't help feeling, intuitively, that we're missing some pretty humungous pieces of the jigsaw. Mind you, we're also missing most of the mass of the universe, so maybe that shouldn't come as a surprise :DI'll second that.

Does Dark matter/energy push or pull? Is the Universe being pulled apart or pushed apart? What is the source of the accelerating expansion? Is the source internal or external to the Universe? Lots of wonderful questions.

[Shadowy Man]

Does Dark matter/energy push or pull?

Dark matter pulls. I.e. it attracts matter through gravity.

Is the Universe being pulled apart or pushed apart? What is the source of the accelerating expansion?

Currently unknown.

Is the source internal or external to the Universe?

How would you even formulate a theory in which the source is external to the Universe? What does that even mean?

[Jesse]

That's what seemed odd to me. Expansion is a pretty critical part of the whole Big Bang concept, yet I couldn't find anywhere what was considered to have imparted the momentum to all that matter, and the picture of the early universe is a confusing mishmash of matter, radiation, and exotic forces. I can't say i'm terribly impressed with the idea that it is simply assumed to be already expanding.D

The laws of physics are time-symmetric, which means they work the same backwards as forwards--thus, if the universe had enough mass to collapse back into a big crunch (http://en.wikipedia.org/wiki/Big_Crunch), however you choose to explain the fact that the matter would be rushing together at the end of the universe should also serve just as well as an explanation for why it was rushing apart at the beginning. Basically, I think the technical answer would just be that this type of universe is a valid solution to the equations of general relativity. In a similar way, a "white hole" which spews matter outward from a singularity of infinite density is just as valid a solution to these equations as a black hole, although physicists generally don't expect to see white holes in our universe for reasons relating to the thermodynamic arrow of time (http://www.voidspace.org.uk/science/h.shtml).

You may find this older thread helpful:

Why didn't the Big Bang suck? (http://www.iidb.org/vbb/showthread.php?t=67799)

[JB01]

Dark matter pulls. I.e. it attracts matter through gravity.

Correct, but dark energy pushes, at least some of the time. These are two different ad hoc hypotheses invented to solve two different problems, and should not be confused with each other.

[V-Bird]

What is caused and is still causing the expansion of the Universe is the void itself.

It is not a 'Big Bang' like an explosion, it is more accurately described as the 'Big Disintegration'

Imagine if you can a true, total void, such total emptiness is the only 100% vacuum ever, a true nothing is in itself utterly useless it is neither large or small.

For whatever reason there was a movement in this nothing, I can speculate on this and even produce some VERY warped maths to NEARLY prove it, but as yet, not quite.

What you must now contemplate is something that really is the first and continuing paradox.

Movement is energy.

So compared to '0' even the smallest amount of energy is an infinite multiplication, this is a truly horrendous paradox, the '0' was quite happy being exactly bvgger all.

This is the first true paradox.

'0' to 0.0... followed by as many noughts as you wish, so long as there is a '1' on the end of it means infinite expansion.

Now, to see this another way is that in nothing if something appears the nothing no longer exists, we have something!

The second paradox is even more astounding.

The '0' merely enclosed this tiny something, forming the perfect utter vacuum around it, and tore it to pieces, but in so doing, like the many headed monsters of legend, just increased its size, the zero fought with the something, this tumult can only be imagined.

In a very short time there has to have been some kind of equilibrium, the maths go this way.

For a tiny instant there was a moment when there would have been a ball of seething coalescing energy paused, it can collapse and be extinguished or can continue with the expansion.

Now this I think happened many times, with the '0' collapsing existance and it forming again, maybe this happened for millenia of our time, but what had to happen was for the ball to become inconsistent in structure.

I'll explain what I mean... if the first expansion produced a ball that was perfectly evenly textured [like a 'Creamed Soup'] then it would collapse back, if the consistency was like a Minestone, then the next phase could proceed.

It is impossible to know if the partial expansion happened just the once or millions of times... it is of no real consequence.

The Universe happened, so the latter consistency also must have happened at some point.

What happened next is what we see now, the ever expanding Universe into that '0'.

That is the 3rd ongoing paradox...

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This is only a theory, as will all such explanations of the start will be, make of this one what you will.

Regards,

V.