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Why haven't we had another big bang?


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Assuming that the big bang theory is correct and that our current universe was formed 13.7 billion years ago, then why haven't we had another one in all that time? If one big bang was feasible why hasn't there been another one, either within our curent perceived universe, or in the empty space that this one is expanding in to?

Edited by Gilps
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...but why are we still waiting? Our universe is expanding in to something - dark matter? Why have we not had another bang in that dark matter? The conditions for a big bang cannot be impossible to achieve as we have already had one, so why not another?

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Assuming that the big bang theory is correct and that our current universe was formed 13.7 billion years ago, then why haven't we had another one in all that time? If one big bang was feasible why hasn't there been another one, either within our curent perceived universe, or in the empty space that this one is expanding in to?

Maybe there has been one. How would we know?

D

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Assuming that the big bang theory is correct and that our current universe was formed 13.7 billion years ago, then why haven't we had another one in all that time?

The "big bang" theory doesn't tell us what caused the big bang, it just says that conditions in earlier times were different and then quantifies that difference.

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Our universe is expanding in to something - dark matter?

No, it's not.

As far as we know, all of space and time came into being at the moment of the big bang.

Don't think of it as an explosion in a conventional sense....the big bang happened everywhere, not at some specific location which it's now expanding away from.

It isn't expanding into empty space....it contains all of space.

What is happening is that the distances between the objects in the universe are getting larger (on a big scale) as space itself expands between them.

Rob

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...but why are we still waiting? Our universe is expanding in to something - dark matter?

That's a misconception. The big bang is an expansion of space itself, so the universe is simply expanding, but not "into" something; it's not particles moving to a place that was empty, it's the space between particles itself that expands. As a result, should some part of the universe far from us somehow "bang", we wouldn't see it directly in the rest of the space, it would be a growing bubble that pushes just some points in our space straddling it apart.

But we won't have a new big bang because the initial conditions aren't ripe for it in the part of the universe that we see (exactly because the big bang happened).

There are models where very far from us the universe is still inflating, by the way, i.e. that we live in a bubble that keeps on growing because of inflation happening at the edge of the ever larger bubble (but again, it's not our bubble moving into new territory, it's space itself at the edge that expands, i.e. bubbles up itself). What we see of the universe is only a really small part if the inflation theory is correct, so all these hypotheses are really untestable (they only make sense to make an otherwise testable theory more simple and elegant).

There are hypotheses that this part of the universe may encounter another phase transition (something that could then cause another "bang") once it's empty enough (if the expansion indeed does keep accelerating). There are even more elegant cyclical models, like that of Penrose (conformal cyclical universe) which reformulates an existing universe that is ever expanding into a universe from another eon that "bangs": the remote future of this universe would become the pre-big bang state of another "simply" by applying quite a bit of rescaling. But it's far from a theory yet.

Edited by sixela
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Like a balloon blowing up - it is the material itself that is stretching (expanding) but from the perspective of the balloon surface (2 dimensional) it is not expanding into anything else 2 dimensional, it is the whole 2 dimensions that are expanding

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Like a balloon blowing up - it is the material itself that is stretching (expanding) but from the perspective of the balloon surface (2 dimensional) it is not expanding into anything else 2 dimensional, it is the whole 2 dimensions that are expanding

but a balloon has an inside and an outside. I'm assuming our universe is like a balloon and ever expanding, but in to what? And why hasn't there been another big bang in that other "what"?

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No, it's not.

As far as we know, all of space and time came into being at the moment of the big bang.

Don't think of it as an explosion in a conventional sense....the big bang happened everywhere, not at some specific location which it's now expanding away from.

It isn't expanding into empty space....it contains all of space.

What is happening is that the distances between the objects in the universe are getting larger (on a big scale) as space itself expands between them.

Rob

This is the bit that I struggle with. If there was nothing there before the bang, and everything came in to being at the point of the bang, then how can you have had a bang from nothing. I understand some of the theory behind the processes that took place at the moment of the bang, but there still must have been something there to go bang in the first place.

And if those pieces necessary for the bang were there then, why have we not had another since?

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If there was nothing there before the bang, and everything came in to being at the point of the bang, then how can you have had a bang from nothing.

Nobody knows. The laws that work usually don't work before a certain point in the past.

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The trouble is not being able to see outside the dimensions we understand within our own universe. Until we can remove that horizon all we can do really is speculate and test theories within the limits of our understanding.

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but a balloon has an inside and an outside.

But the surface of the balloon doesn't (OK, because of the limitations of experiment, it always will have a thickness, but think of the very outer surface of material, with a thickness of zero). From the perspective of an organism living in that 2 dimensional world, the surface is not expanding "into" anything (from his perspective there is no third dimension into which it can expand). His universe is just stretching - in all directions - in two dimensions.

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This is the bit that I struggle with. If there was nothing there before the bang, and everything came in to being at the point of the bang, then how can you have had a bang from nothing.

First of all, it's not a given you can define something "before" the bang; as Olly said time itself is only shaped by the big bang, even though there are some formulations in which "before the bang" actually has a meaning.

Just to give one example, Penrose's conformal cyclical cosmology definitely has a "before" but that before is actually the extremely thin universe in a previous aeon before all particles are causally disconnected. Note that *at* the big bangs in that theory, it still doesn't make sense to talk about time, that one state of the universe (which you can express as the completely disconnected end state of the previous aeon or the big-bang state of the next) is one in which essentially time has no meaning.

but there still must have been something there to go bang in the first place.
You won't solve the ontological problem with cosmology, I'm afraid. Logically, the most "sensible" thing to exist is absolute nothingness (which includes the absence of physical laws that can create something out of the absolute nothingness) but that is "unfortunately" an easily falsifiable hypothesis. There *is* something.
And if those pieces necessary for the bang were there then, why have we not had another since?
Because those "pieces" are in another state. You can burn yourself with boiling water, but wait for long enough for it to cool down and it's going to be a lot harder, especially if you can no longer boil it.

The big bang really is irreversible, at least if our current view of the universe with accelerating expansion is true: the universe has cooled since its start and that has changed what particles exist and even how forces manifest themselves, and more recently dark energy has won over baryonic and dark matter; the more it expands, the more dark energy wins and stacks the cards against the rest and rips the universe apart.

Interestingly, even if you accept a universe that will rip itself apart after a long agony of heat death there are:

1) cyclical models where you don't have to have a start; just as a few examples,

a) that of Penrose mentioned above and

:o those of others, where e.g. a universe that has disconnected patches of empty space sees patches contract again and "bang", each universe begetting a colossal amount of new universes, in a genealogic tree that has no end whether you zoom in or out

c) models in which sufficiently stretched space and vacuum goes into a state change that creates something interesting once more

2) and others where we are just a bubble in a timeless substrate that hasn't undergone a bang and inflation (in which even after our part of the universe has ripped itself so much apart that no particles can interact, essentially stopping the clock here, there are other very remote parts that are always interesting and teeming with physics after having created their space and time).

Even though you have an entire zoo of models that don't need a beginning (not that they're necessarily right), it still doesn't fix the problem of explaining why there's something rather than absolutely nothing.

Not even having physical laws that create all of the universe from "nothing" (as in no space, time or matter) will, because those physical laws will still be something more than philosophical nothingness.

Answering that question is metaphysics, and even though many will believe something in preference to another as a matter of belief or even aesthetical preference, it won't be possible to turn these into theories: we can only observe what is in our observable universe.

Edited by sixela
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but a balloon has an inside and an outside. I'm assuming our universe is like a balloon and ever expanding, but in to what?

That's where the balloon analogy breaks down. As others have said, the analogy works only if you consider we're flatlanders living on the balloon surface and able to "look" only along the balloon surface (the only way for them to see it's a curved surface is indirect, e.g. by realising that large triangles appear to have a sum of the angles that is different from 180°, while small triangles have angles that do add up to 180°).

There isn't anything "outside" of the balloon at all, or "inside" for that matter. Everything that is is just the surface.

It's hard to picture the three dimensional analogy, I know.

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Assuming that the big bang theory is correct and that our current universe was formed 13.7 billion years ago, then why haven't we had another one in all that time? If one big bang was feasible why hasn't there been another one, either within our curent perceived universe, or in the empty space that this one is expanding in to?

maybe theres a big bang every 14 billion years,this could be the millionth time its happened!:o

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but a balloon has an inside and an outside. I'm assuming our universe is like a balloon and ever expanding, but in to what?

I think its helpful to think that the universe does not have an edge and just keeps going. The way I think of the universe is a infinently large piece of rubber with 1cm squares all over. At the big bang the squares were all 1cm still, and 14bn years later the 1cm squares are now 3cm big. Also I my head this is why we get red-shift because the light waves have been stretched by the expanding universe.

But this is the model of the universe from my head, by no means fact! :o

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Hi Gilps, I am straying towards a possible scenario were the universe just starts all over again, ie another BB. Not that I am qualified to give reasons why I think that but surely it could be possible, if it eventually ends up having nothing within it, no atoms?, matter?, then that is sort of the same as coming from nothing :o

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Because 13.7 billion years is a very, very, very, very short time on the time scales that these things work on.

Add say 1000 0's to the time we have already had and another might occur.

Who said our big bang was the first and only one?

You need to think in slightly longer timescales.

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Hi Gilps, I am straying towards a possible scenario were the universe just starts all over again, ie another BB. Not that I am qualified to give reasons why I think that but surely it could be possible, if it eventually ends up having nothing within it, no atoms?, matter?, then that is sort of the same as coming from nothing :o

That sounds like the theory in place before it was discovered that the universe is expanding too fast to collapse back in.

Perhaps there has been successive big bangs but we can't see them because they are within the event horizons of black holes.

Edited by haitch
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That sounds like the theory in place before it was discovered that the universe is expanding too fast to collapse back in.

Perhaps there has been successive big bangs but we can't see them because they are within the event horizons of black holes.

Yes if only we could travel through one :o

thing is, I think BC said on WOTU even they would disappear so what happens at the other end?

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