# A quick Big Bang question



## Quokka (May 14, 2007)

Hey all, I've a question about the big bang and expansion that Im having trouble finding a clear answer to.

Lets asume that the big bang happened (my question doesn't go anywhere without it  ), the universe explodes outwards and begins expanding, something that is still happening today.

My question is why isn't the universe expanding outwards as if everything was riding on the film of a bubble, leaving a hollow core behind?

I know there has been interactions between matter/forces ever since but has that really occured to the extent that enough matter was directed backwards allowing the universe to appear as a constant total? 

Wouldn't the initial forces have been great enough to atleast ensure that the point of origin appeared as a less dense space?


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## gully_foyle (May 14, 2007)

Hi Quokka,

My lay understanding is that it is expanding more or less equally in every direction. It is not expanding outward as such. When you hear the balloon analogy, in which dots are drawn on the balloon and inflation of the balloon represents expansion of the universe, what that means is that the surface of the balloon is expanding and the distance between the points are expanding evenly. The surface is the universe. It does not mean that the universe is being hollowed out like a balloon.

Hmm, not explaining things very well hey? 

Imagine the balloon was filled with points. As the balloon expands those points move away from each other evenly, so the density of the points is constant throughout the balloon. So it is with our universe. What happens in alternate universes, and even parallel universes, is the realm of science fiction. That's why we read it.

The big bang is an unfortunate term. It implies an explosion. It is better to think of it as rapid expansion or inflation.

Useful authors on the subject would be Stephen Hawking and Stephen Weinberg who has a book called _The First Three Minutes.

_That the universe expands is a given, but that it is expanding from a single point is still up for grabs. I'm not sure that the Steady State theory is completely dead yet. Not that I'm a big bang skeptic.


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## Quokka (May 14, 2007)

Thanks Gully, I made sure of stating the big bang as a premise as I know there are alternatives. Personally I like the idea of a big bang(s) cycle no understanding at all to back that up it just feels more logical than a steady state or single event. Although i think at the moment the science is currently leaning towards everything just moving further apart and cooling.

Your reply does help as did just writing the question out. Like you said I think expansion creates a better image than explosion.

Also it wasn't just a case of matter moving out to fill a void but actually space-time/ the universe itself expanding? or is that wrong?

It had been bugging me how a universe can be constant in all directions and yet have started from a single point.


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## j d worthington (May 14, 2007)

A few things to note: the actual origin of the material (whether it came from a singularity, from another universe, or from something else) still remains theoretical, as we've only been able to reconstruct within a few microseconds following the initial burst. However, in that interval, there were no particles as we recognize them; rather we had the stuff that would become such. And, as this was dispersed and became matter as we understand it, it formed clouds, clumps which attracted other matter to it, in conflict with both forces that repelled, and dark matter (and dark energy) which played a part in both slowing down and speeding up dispersion in certain pockets within the whole.

As those clouds condensed, they formed stars and protoplanetary discs, which in turn intensified gravitational tugs on nearer matter, including other stars, planets, planetary debris, comets, etc. And, as various stars (and star systems) are approaching each other, that also makes a difference -- not to mention the black holes, and super-black holes, which also caused (and continue to cause) fluctuations in how the matter is distributed. In fact, there is evidence we may have many minute black holes within our solar system, from what I understand... this is something that they're doing quite a bit of research on, as well.

Put all this together, and it wasn't a smooth movement out from any particular point -- even if you discount the idea of multiple big bangs, which still remains a possibility, and which would throw even more mind-boggling twists into the mix. Rather, it began as such, but quickly was distorted into something else in portions where matter was more dense, to take other patterns. That's a very crude way of putting it, and not at all accurate... but about the closest I can approximate it from my understanding, without getting into a tremendously long discussion on the subject -- and certainly in 'way over my head! 

You might try the following:

Big Bang - Wikipedia, the free encyclopedia

Big Bang nucleosynthesis - Wikipedia, the free encyclopedia

Cosmic inflation - Wikipedia, the free encyclopedia

And some of the other articles you can link to through these, as well as various reference works they provide.


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## gully_foyle (May 14, 2007)

Quokka said:


> Personally I like the idea of a big bang(s) cycle no understanding at all to back that up it just feels more logical than a steady state or single event. Although i think at the moment the science is currently leaning towards everything just moving further apart and cooling.



Actually alot of the theory has been leaning towards cyclic universe creation, and that fortunately this version of the universe had the right ingredients for "life". And that possibly, because this universe was "configured" correctly, it's the only one that won't collapse in upon itself and will just keep expanding.

The person to read up on for cyclic universes is Lee Smolin. I read his _The Life of the Cosmos_, and it aint no easy read, but worth it.

Then there is the steady state theory, championed by Fred Hoyle, which says that the universe has always been and will always been, and that expansion is a natural state. That the creation of vacuum, which contains energy which creates matter, is kind of spontaneous. 

But Fred Hoyle is best remembered here for his Sci Fi. If you have not read _The Black Cloud_ then please go find a copy. It is classic english SF, lots of guys in cardigans smoking pipes and trying to deduce the nature of whatever is threatening earth.


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## Quokka (May 15, 2007)

Thanks Gully, I'll have to have a look at _The Black Cloud _I havent read it yet and sometimes its nice to read about scientists in cardigans without the guns and aliens and breaking down doors. It was one of the things I enjoyed about Benfield's _Timescape_ as well.


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## Tillane (May 20, 2007)

Or, if you want the 11:30pm, slightly unhinged and entirely lay version - or just want a laugh at my expense - here's something I wrote on my blog a while back...

_ I was reading Paul Davies book _The Mind Of God_ last night, and an odd thought came to me. Now, before I explain this, I should point out that my brain tends to work in odd ways - particularly after 11pm.

Anyway. One part of Davies' book deals with the theory of the creation of the universe, and more particularly with the divide between the cyclical universe theory and the big bang theory. One major bone of contention is expansion - the universe is expanding, but the big bang theory doesn't really explain __why.  And I got thinking about black holes.

Now, stay with me on this. The universe (as we know it) is around 13 billion years old. That means that, at the furthest ends of the universe, the stars are 13 billion years old. Which, to my (uneducated) mind, means that an awful lot of the stars at the furthest reaches of the universe will have collapsed into black holes. Actually, it means that most of the stars at the furthest reaches of the universe will now be black holes. And the rest will have been __swallowed up by the black holes.

Still with me? Okay. So. If there are so many black holes near the edge of the universe (and I use this term loosely. I have no real clue whether or not there actually __is an edge of the universe.), and these black holes are pulling matter towards themselves, then maybe - just maybe - these black holes are the reason for the expansion of the universe. Maybe there are enough of them out there to cause the matter in the universe to rush toward them, making us - nearer the centre of the universe - think that the universe is expanding, when in fact it's rushing toward oblivion.

So, the theory. Expansion is caused by a preponderance of black holes at the edge of the universe. Here's another theory. Say these theoretical black holes swallow up enough matter that the universe - while still seeming to __expand from our POV - actually starts to contract? In other words, what happens when the black holes swallow so much matter that they begin to move toward each other? Maybe the universe contracts until the black holes start to affect __each other. Maybe the universe is left with little other than black holes, which pull towards each other and merge into one, single, spinning singularity of matter and time. What would we call this - a meta-black hole? An ultra black hole? Who knows? In any case, we're left with a single spinning singularity with infinite mass (and time), occupying an almost immeasurably small space. A space where gravity (having reached breaking point) collapses. What do we have here? Do we have a big bang?

Oh, I think we do.  And there's more.  From this big bang, maybe we create __our universe - or a very close facsimile of it. A universe ruled by the same laws, which will expand and contract and die in the same way. Do we have a cyclical universe? Oh, I think we __do!

Told you my brain works in odd ways.
_


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## chrispenycate (May 21, 2007)

May I? Firstly, a sphere of black holes aroun a central point woud give a net gravitational effect of zero. Secondly, taking any particular point as the centre from wich everything started, and from which everything is diverging at a rate proportional to its distance from the point, with a sharp cutoff when at the speed of light times the age of the universe (this side universe, the other outer dark) is misleading; the space in which the universe is contained is expanding, so any chosen point will be the "centre" from which everything came, and will have a largely homogenous distribution of matter around it. No "edges" required.
Now. if we could observe thirteen billion light years away, in all probability there would be fewer stars and black holes in those regions, not because "now" (as far as the concept of "now" can be stretched, which isn't that far) there's any difference, but because the light's taken so long to get to us that it's coming from a time before the star-making process was developed; it takes _time_ for those dust clouds to coalesce, to collapse, time that the it of universe we're talking about observing hadn't yet had when the light set out.
Now, taking the law of conservation of momentum (which has not, as far as I know, been rescinded despite Newton being out of favour) if thoseblack holes have enough mass to pull all the matter and energy out from the centre, they've got too much for the additional mass to make an appreciable difference. 
And, if gravity propagates at light speed, they would have had to be out there at least thirteen billion years before the big bang.
Furthermore, if their existence were to cause a collapse, it would be of the matter (and energy) within the universe, not the spacetime; so you'd be left with an empty universe, not an "all the dimensions rolled up into an infinitessimally small space" cosmegg. 

Lndeed, your hypothesis is beginning to look like a black colander, I fear.


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## Tillane (May 22, 2007)

chrispenycate said:


> Indeed, your hypothesis is beginning to look like a black colander, I fear.


I suspected as much. Well, it _was_ late when I came up with it.  I'd have been more surprised if it had stacked up...


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## Spartan27 (Sep 21, 2007)

Quokka said:


> Hey all, I've a question about the big bang and expansion that Im having trouble finding a clear answer to.
> 
> Lets asume that the big bang happened (my question doesn't go anywhere without it  ), the universe explodes outwards and begins expanding, something that is still happening today.
> 
> ...


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## Spartan27 (Sep 21, 2007)

chrispenycate said:


> May I? *Firstly, a sphere of black holes aroun a central point woud give a net gravitational effect of zero.* Secondly, taking any particular point as the centre from wich everything started, and from which everything is diverging at a rate proportional to its distance from the point, with a sharp cutoff when at the speed of light times the age of the universe (this side universe, the other outer dark) is misleading; the space in which the universe is contained is expanding, so any chosen point will be the "centre" from which everything came, and will have a largely homogenous distribution of matter around it. No "edges" required.
> Now. if we could observe thirteen billion light years away, in all probability there would be fewer stars and black holes in those regions, not because "now" (as far as the concept of "now" can be stretched, which isn't that far) there's any difference, but because the light's taken so long to get to us that it's coming from a time before the star-making process was developed; it takes _time_ for those dust clouds to coalesce, to collapse, time that the it of universe we're talking about observing hadn't yet had when the light set out.
> Now, taking the law of conservation of momentum (which has not, as far as I know, been rescinded despite Newton being out of favour) if thoseblack holes have enough mass to pull all the matter and energy out from the centre, they've got too much for the additional mass to make an appreciable difference.
> And, if gravity propagates at light speed, they would have had to be out there at least thirteen billion years before the big bang.
> ...


 
Crispy..actually it would be much much less than zero...


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