Big Bang. How did it expand?

[buddyarrows]

Hi, This might be a stupid question but here goes:

What I can’t understand is how the big bang expanded!

As I understand it all the mass of the universe was in a singularity and the four forces where as one so how did or what made it explode?

As I understand it, during the initial expansion the four forces separated into electro, strong, weak and gravity, but why then did gravity as I assume having the same attraction as today and having all that mass in a very close proxminity not overcome the expansion and fall back into a singularity again!

In short how did this "big bang/black hole" explode, as its mass should have held it together as in any other black hole we observe in the universe, does this make sense? Am I missing something?

Hope some one can explain in simple terms.

Thanks

David

[room16]

I apologise for this quote, but tommy cooper comes to mind "Just like that!" lol.

In all honesty i still think it is all speculation. There are plenty of theories and even though its believed that it all comes from a singularity, much like anyone else, its hard to percieve.

There is proof of expansion, but im not even sure if those figures are correct in a sense that as soon as you step off the earth, there are more than one variable in observations on all levels and there are also the unknowns and the known unknowns to contend with.

Although i really enjoy seeing pictures of the deepest depths of space and time, it would be nicer to see more work done to understand those things that are a hell of a lot closer. We are now seeing a boost in this area, thankfully... lets hope it continues.

As for how did it explode, perhaps there were pockets of newly emerging forces that caused an explosion at the speed of light, then eventually when things settled, the dust and particles made suns and so on....gravity may have found its enemy in the heart of a singularity- anti gravity?.

This is all speculation, im that flumuxed by the amount of different so called explinations that it seems just as easy to make up my own lol.

[Doc]

The big bang was not an explosion of matter into space, rather it was an explosion of space itself, and since space and time are interconnected, we really have to say it was an explosion of space and time, or space-time.

So, the big bang wasn’t an explosion of stuff like atoms or molecules, it was an explosion of a place and instance, it was the creation of when and where.

Alot of people think of the Big bang as an explosion. It was not, I like to think of it a the big Expansion...

Almost instantly the universe gets very large, driven on by the vacuum of space it expands, and space and time are created.

[FraserClarke]

Doc is right. Thinking of it as an explosion is the wrong way to go about it. Everything (i.e. everything, not just matter and energy) was created in the big bang. Before that, there was no space, no time, nothing. In fact, the concept of 'before' can't even exist, as there was no time to measure a before by!

Everything after about ~10^-20 seconds or so (that's not '10 to 20 seconds', that is 0.00000000000000000001 seconds), is pretty well explained and the theories basically verified (that's basically why big particle accelerators like LHC etc are built).

*why* it happened in the first place; I *think* that is still pretty much open to theory...

But, to get to your point about forces. Yes, there are four major forces, which control how different types of matter are created. strong is responsible for making things like protons. weak binds atomic nuclei together. electromagentic holds electrons around nuclei to make atoms, and finally gravity holds atoms and molecules together to make stars and galaxies etc.

And that is the order their strengths go in. Gravity is by far (many orders of magnitude) the weakest force out of the four. Just think; a little fridge magnet using electromagnetic force can hold itself up against the gravitational pull of the whole Earth!! The only reason that gravity is so important to us is that it can operate over such huge distances (the entire size of the universe)

So, in the early universe, gravity was there; but it's so weak it has very little effect compared to all the other forces. You have such a massive amount of energy bouncing around, gravity has no hope of stopping the expansion. Not, at least for 10's of billions of years -- and even that looks unlikely now...

(PS - not a particle physicist or cosmologist, so some descriptions may be a bit off...)

[astoc]

I don't think we have a clue at present. I think it may remain beyond the reach of theory. We know it is expanding, we can measure it, but to ask why in my eyes is akin to asking why it's all there in the first place.

I find it comforting, apparently unanswerable questions

John

[ollypenrice]

Let's not forget that the expansion may be a phase applying at the moment but that, as when a ball is thrown into the air, gravity WILL win in the end and the universe will go into Big Crunch nas the ball will reverse its direction. Current observation suggests otherwise but such observations are dependenton serious bits of estimating and cannot, as far as I know, be considered beyond reasonable doubt.

Olly

[themos]

You have such a massive amount of energy bouncing around, gravity has no hope of stopping the expansion.

To me, that is counter-intuitive. Massive amounts of energy in a tiny space(time) should produce enormous gravity. In fact, the earliest era of the universe is called the Planck era because quantum gravity effects are assumed to dominate.

[buddyarrows]

Thanks for all your fascinating answers. Something out of nothing is somehow hard to perceive, and the creation, beauty and wonder of the universe probably will always have it's mystery. I think it was the late great Carl Sagan who said, "whats the point of the universe if there is no one to look at it and wonder".

I know I love looking up on a clear night wondering whats it all about and now I have a little more to wonder about, may be some day we will be able to explain it's mystery.

Clear nights and keep looking.

David:icon_salut:

[FraserClarke]

Let's not forget that the expansion may be a phase applying at the moment but that, as when a ball is thrown into the air, gravity WILL win in the end and the universe will go into Big Crunch nas the ball will reverse its direction.

Gravity does NOT have to win... just as when you throw a ball into the air, it does NOT have to come down again...

An object in a gravitational field has a certain amount of 'gravitational potential energy'. If you give it more kinetic energy than that, it will escape from the gravitational field (it will reach infinity with some positive energy, so will keep going forever). For example, for a ball on the Earth's surface, if you give it 10megajoules of kinetic energy, it will be able to entirely escape the Earth's gravitational field (this is how you define escape velocity BTW -- which is ~11.5km/s from the Earth's surface).

The odd thing is that the Universe is so very close to being balanced with just enough energy for to counteract the expansion. You have to balance this very very closely for a Universe to live for 14 billion years, as we see in our own. A bit more matter, and the Universe collapses very quickly. A bit less matter, and it flys apart very quickly, and you never form stars and galaxies.

Current measurements (WMAP currently having the smallest error) show the Universe is 'flat' (i.e. just enough gravity to counteract the expansion) to ~2% I believe. However, lots of other things start falling down theoretically well before this level, and the Universe has to be flat to <0.001% for current cosmological models (which are really very well tested) to work. Why that is is, I believe, not well understood at present (I could be wrong)

The answer may be something like Sagan's -- it's only because it is so well balanced that we are here to ask the question (more formally known as the "antrhopic principle"); but that is a bit unpalatable to physicists...

[George Jones]

Current measurements (WMAP currently having the smallest error) show the Universe is 'flat' (i.e. just enough gravity to counteract the expansion) to ~2% I believe.

If the cosmological constant/dark energy is non-zero, then spatially flat universes aren't on boundary between expand forever and re-collapse.

Most cosmologists think the data favour a universe that expands forever.

[FraserClarke]

Yes, indeed you are right. There isn't the same link between flat and critical density if you have a cosmological constant.