[thedoc (OP)]

My understanding of the big bang, is that we started off with one large mass which contained all material.
This then exploded outwards and is still expanding.

Is there a point in the future where the expansion will stop and everything will start returning to one large mass and in so doing start another Big Bang?

If this is the case, are we sure that our Big Bang was the first and only one, and it not part of a repeating cycle?
   
Asked by Bob


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[chapter podcast=1001362 track=16.05.17/Naked_Scientists_Show_16.05.17_1005178.mp3]  ...or Listen to the Answer[/chapter] or [download as MP3]

[stacyjones]

I think the notion of a Big Bang is incorrect. I think our Universe is part of an ongoing process. It's the Big Ongoing.

Our visible Universe is a larger version of what is represented by the blue lines in the following.



'Supermassive Black Holes Transport Matter into Cosmic Voids, Astronomers Say'
sci-news.com/astronomy/supermassive-black-holes-matter-cosmic-voids-03658.html

“Some of the matter falling towards the holes is converted into energy. This energy is delivered to the surrounding gas, and leads to large outflows of matter, which stretch for hundreds of thousands of light years from the black holes, reaching far beyond the extent of their host galaxies,” the astronomers explained.

At the scale of our Universe the energy referred to above is dark energy. A Universal black hole is powering our visible Universe causing the galaxy clusters to accelerate away from us.

[evan_au]

Is there a point in the future where the expansion will stop and everything will start returning to one large mass and in so doing start another Big Bang?

Einstein's General Relativity predicted that gravity should slow the expansion of the universe. Whether gravity would actually reverse the expansion of the universe depends on the average density of the universe.

Many scientists (including Einstein) considered that a cyclic universe was possible.

However, the discovery of Dark Energy suggests that the expansion of the universe is accelerating, not decelerating. So Einstein's view of a gravity-driven cyclic universe now seems less likely.

But there are several other (more modern) hypotheses that may result in a cyclic universe, including speculation about the possibility of additional unseen dimensions.

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

[EnemyTortoise15]

I realize this is an old topic but no one discussed Thermal Fluctuations or the Poincaré recurrence theorem.

The Heat Death theory says the universe will eventually burn out, becoming nothing but black holes and eventually even they will evaporate due to Hawking radiation. This is due to the 2nd law of thermodynamics, which means that entropy can only increase causing all matter to eventually run out of energy.  When the universe is in this state it's called being in equilibrium.
Thermal Fluctuations occur during equilibrium,  despite its static state, random variances occur and eventually get bigger and bigger.
This bring me to Poincaré recurrence theorem which states that systems can return to their original state after a certain amount of time, in this case billions of years. If our universe were to do this after its end, another Big Bang theoretically could occur. Knowing this, it's easy to imagine our Big Bang was not the first. This could actually lead to the idea that time didn't have a beginning nor will it have an end, assuming the Big Bang just continues to repeat itself.

More than one Big Bang could help explain the cosmological constant too, also known as dark energy or the force that keep out universe expanding. Currently it's explained with the Anthropic Principle which states the energy differs in different areas of the universe which explains why matter isn't equally dispersed throughout. Many scientist think this is an "easy" way out of a problem they can't solve.
Multiple Big Bangs however,  could explain this without the values changing throughout the universe. With multiple locations for Big Bangs, matter would, quite obviously, not be evenly spread.

[PmbPhy]

At the present time it is not known whether there have been more than one Big Bangs. In fact it may never be possible to know such a thing. Being theoretically possible in no way implies that such a thing happened. E.g. while its theoretically possible that Tom Hanks had bacon for breakfast today it by no means can be taken that he actually did.