[thedoc (OP)]

Paul Hicks asked the Naked Scientists:
   According to Portuguese scientists this week gravity is the most important thing in our universe, pulling everything back to where the big bang started from. Is it not possible that when it does eventually all go back to the same place it started from, that is what caused the big bang and that this cycle that has happened infinite times before. A bit like a bat with a ball on a piece of elastic
What do you think?

[syhprum]

Until recently it was believed that the rate of expansion of the universe was increasing which would mean that the "big bang" was an one off event and the universe would end in an infinitly diluted state.
The concesus of opinion has now changed but it is still in doubt as to whether or not the expansion will cease and reverse leading to a big crunch.
 

[Semaphore]

I recall an article in SciAm which argued exactly that, and moved on to some possible tests which could be made to prove it. It was some time ago, though.

[Janus]

This is known as the oscillating universe model.  It's been proposed before. If I remember right, The problem was that even if the universe were to collapse back to the "Big Crunch" it would not be in the same state as it was during the initiation of the Big Bang and incapable of precipitating a new one.  To use the ball on an elastic string analogy, it would as if the ball ages and deteriorates on both the out bound and return trips to the point that it no longer is in any shape to bounce back out again.

[geordief]

This is known as the oscillating universe model.  It's been proposed before. If I remember right, The problem was that even if the universe were to collapse back to the "Big Crunch" it would not be in the same state as it was during the initiation of the Big Bang and incapable of precipitating a new one.  To use the ball on an elastic string analogy, it would as if the ball ages and deteriorates on both the out bound and return trips to the point that it no longer is in any shape to bounce back out again.

So ,it would be a "soggy mess" ?

Would/could  there not  similar agglomerations in the "vicinity" that would coalesce with this failed  aggregation  and eventually ,statistically some kind of a rebound  would happen?

Could ,perhaps some of the proponents of the oscillating universe have been arguing against a universe identical to the last being formed by these oscillations? Some people may be  fixated on these "identical universes" ,perhaps.

[Ethos_]

When speculating about the so-called "Big Crunch", I think it is a mistake to assume that the cosmos is finite to begin with. If instead, the cosmos is infinite and our observed Big Bang is really only a local "White hole" event, then maybe we can start speculating about what the mass limit might be for black holes.

Just consider the possibility that if the cosmos is in fact infinite, other big bangs may be occurring all the time but are too far outside our observational parameter. Maybe the truth is: Our "Big Bang" really isn't all that big when one considers the possibility of an infinite cosmos.

[alancalverd]

I remember discussing the oscillating universe around 50 years ago with a fellow undergraduate who is now a professor of astronomy, but until a few minutes ago I couldn't get it to oscillate properly. Thanks to all here for the stimulus.

The trick is to allow gravitation to collapse all the mass "indefinitely". Now thanks to Heisenberg, Pauli and Schrodinger, that can't actually happen: if all the stuff was in one place we would know its position absolutely, and as it would all be at the bottom of a very deep potential well, time would stand still so we would know its momentum too: the more it collapses, the  more that quantum indeterminacy says it can't collapse any further. So the bounce is inherent.

And it doesn't need to all collapse to a single point. Quantum indeterminacy sets a limit to the minimum size of any collapsing black hole, so little bits of the universe can be bouncing at any time.

Back in the days of my misspent youth some satirists proposed a rapprochement between Ryle and Hoyle, called the "Steady Bang Theory". Well, here it is. More of a disorganised quasicontinuous firework display.

As The Boss has just called me to dinner, the calculation of the Schwarzchild radius is left as an exercise to the reader. You may assume pi = 22/7, m(p) = m(n) = 1800 x m(e)  and c = 300,000 km/sec for the purposes of this exercise.

[jeffreyH]

I remember discussing the oscillating universe around 50 years ago with a fellow undergraduate who is now a professor of astronomy, but until a few minutes ago I couldn't get it to oscillate properly. Thanks to all here for the stimulus.

The trick is to allow gravitation to collapse all the mass "indefinitely". Now thanks to Heisenberg, Pauli and Schrodinger, that can't actually happen: if all the stuff was in one place we would know its position absolutely, and as it would all be at the bottom of a very deep potential well, time would stand still so we would know its momentum too: the more it collapses, the  more that quantum indeterminacy says it can't collapse any further. So the bounce is inherent.

And it doesn't need to all collapse to a single point. Quantum indeterminacy sets a limit to the minimum size of any collapsing black hole, so little bits of the universe can be bouncing at any time.

Back in the days of my misspent youth some satirists proposed a rapprochement between Ryle and Hoyle, called the "Steady Bang Theory". Well, here it is. More of a disorganised quasicontinuous firework display.

As The Boss has just called me to dinner, the calculation of the Schwarzchild radius is left as an exercise to the reader. You may assume pi = 22/7, m(p) = m(n) = 1800 x m(e)  and c = 300,000 km/sec for the purposes of this exercise.

Now you're just being silly.

[alancalverd]

Or very perceptive, if you ignore my last paragraph. It's a bit like Hawking's "black holes and baby universes" but invoking a quantum limit to the density of a black hole.

[jeffreyH]

How would you test the hypothesis? What initiates your bounce? I get your point about indeterminacy.

Timescales? Why don't we see bouncing black holes?

[alancalverd]

The bounce happens when the last bit of space dust gets sucked into the critically infinitesimal black hole.

Imagine that we have concentrated so much stuff into such a small space that all the quantum numbers are occupied. Problem is that the mass still has a negative gravitational potential, so it will slurp up any passing atom or galaxy, but there are no available quantum states within the event horizon, so it all has to disperse and start again. I haven't thought through the timescale of the event yet, but wouldn't it be fun if Dark Matter turned out to be a dust of tiny black holes sucking the universe inwards?

[Semaphore]

The bounce happens when the last bit of space dust gets sucked into the critically infinitesimal black hole.

Imagine that we have concentrated so much stuff into such a small space that all the quantum numbers are occupied. Problem is that the mass still has a negative gravitational potential, so it will slurp up any passing atom or galaxy, but there are no available quantum states within the event horizon, so it all has to disperse and start again. I haven't thought through the timescale of the event yet, but wouldn't it be fun if Dark Matter turned out to be a dust of tiny black holes sucking the universe inwards?

Dark matter or dark energy?

[alancalverd]

E = mc^2!

[Ethos_]

E = mc^2!

This is the reason we all appreciate Alan here at TNS. Always direct, accurate, and efficient with his answers. Bravo my friend..................

[jeffreyH]

The bounce happens when the last bit of space dust gets sucked into the critically infinitesimal black hole.

Imagine that we have concentrated so much stuff into such a small space that all the quantum numbers are occupied. Problem is that the mass still has a negative gravitational potential, so it will slurp up any passing atom or galaxy, but there are no available quantum states within the event horizon, so it all has to disperse and start again. I haven't thought through the timescale of the event yet, but wouldn't it be fun if Dark Matter turned out to be a dust of tiny black holes sucking the universe inwards?

What would be the maximum number of possible quantum states and how can you define that within a volume of space? Tiny black holes? Really? Wouldn't they just eat everything up? How can they sustain themselves? Hawking radiation?? I think you are onto a winner here!

[jeffreyH]

I have no idea if the following is relevant but I'll post it anyway.

https://en.m.wikipedia.org/wiki/Fidelity_of_quantum_states

[zx16]

When speculating about the so-called "Big Crunch", I think it is a mistake to assume that the cosmos is finite to begin with. If instead, the cosmos is infinite and our observed Big Bang is really only a local "White hole" event, then maybe we can start speculating about what the mass limit might be for black holes.

Just consider the possibility that if the cosmos is in fact infinite, other big bangs may be occurring all the time but are too far outside our observational parameter. Maybe the truth is: Our "Big Bang" really isn't all that big when one considers the possibility of an infinite cosmos.

I think you're right. An eternal, infinite "Steady-State" Cosmos, is far more plausible than the currently fashionable "Big-Bang" hypothesis.
The chief weakness of the Big Bang hypothesis seems to be this:

It supposes that at a certain time in the past, 13.7 billion years ago or whatever, ALL the vast spread of matter in the Universe - billions of planets, stars, galaxies - was somehow concentrated into a single microscopically tiny "point".

Doesn't the absurdity of such an idea reveal itself as soon as it's written!  I can sort of believe that an individual star could shrink into a "Black Hole"  (though such a Black Hole would still have a certain diameter)

But that the entire Universe should once have been a microscopic pin-point - pull the other one!

[alancalverd]

What would be the maximum number of possible quantum states and how can you define that within a volume of space?

Schrodinger and Pauli give us an  insight into the filling of electron orbitals, and we have similar models to describe the stability of nuclei, so in principle I think we can at least say that there must be a maximum density for a black hole of any given dimension.

Imagine for instance that we have the core of a neutron star, consisting of n neutrons bound by gravitation. If we add one more neutron the mass has increased by a factor of 1/n but the volume only by 1/n^3, so eventually there will be a deficit of available quantum numbers within the core volume, but no limit on the ability of the core to attract more neutrons.

Adding one more neutron to a relatively large but sparsely populated nucleus such as U235 precipitates fission. Now if we remove all the electrical charges and consider a highly compressed lump of zillions of neutrons, what happens when that becomes unstable?     

[Ethos_]

Schrodinger and Pauli give us an  insight into the filling of electron orbitals, and we have similar models to describe the stability of nuclei, so in principle I think we can at least say that there must be a maximum density for a black hole of any given dimension.

This is an interesting thought Alan, one that had not occurred to me before reading your observations.

Imagine for instance that we have the core of a neutron star, consisting of n neutrons bound by gravitation. If we add one more neutron the mass has increased by a factor of 1/n but the volume only by 1/n^3, so eventually there will be a deficit of available quantum numbers within the core volume, but no limit on the ability of the core to attract more neutrons.

 

This scenario is one I've wondered about for some time. I have a book by Harrison and Wheeler regarding their computations for reaching this critical mass density. In the case of a neutron star, when it reaches approx. 3X10^54 barons per cubic centimeter, if I remember correctly, the neutron star will collapse to form a black hole.

Concerning a black hole that reaches this speculated limit for quantum number availability, there might also be a point where greater density is disallowed. If I may be allowed to think aloud regarding this question, I would hazard a guess that this mass density might be reached before the total mass of our observable universe could be absorbed. If this turns out to be true, this scenario raises many questions about whether the universe is infinite or finite.

 

[evan_au]

consider a highly compressed lump of zillions of neutrons, what happens when that becomes unstable?

It is thought that in the center of a large neutron star, the pressure may exceed the capacity of neutron quantum levels to resist the pressure.

Under these conditions, the neutrons could hypothetically be crushed to an even denser soup of quarks, in a liquid or superfluid state.

However, the conditions under which this phase transition might occur are unknown. The LHC is able to produce a short-lived quark-gluon plasma at very high temperatures, but this does not provide many clues to what happen in the much cooler and gravitationally-bound conditions inside a neutron star.

See: https://en.wikipedia.org/wiki/Quark_star