What is the Big Bounce and what evidence and arguments are used to support it? Or counter it.

[MSC]

The Big Bounce - Quantamagazine

Quote

In a cyclic universe, periods of expansion alternate with periods of contraction. The universe has no beginning and no end.

I don't know if I'm understanding this correctly. Is there no upper limit to how large the universe can bounce up to or is the image misleading? Is matter a fixed finite or is more created at each bounce? 

If I view it as a series of warping bubbles moving through this multiversal vacuum space, at what point is everything so spread out that it just pops? If expansion is stretching everything further apart, how can another contraction take place if there is no force great enough to overcome expansion and pull everything inwards again for a bounce? 

Another thing I don't understand due to the image, does the universe have some form of directionality in its expansions and contractions? How and why?

Sorry if these seem like stupid questions. I'm sure someone here can help me understand. 

[mathematic]

Any description beyond current expansion from the big bang is pure speculation.

[MigL]

Biggest problem with all versions of cyclic cosmologies is the fact that entropy has to be 'reset' to the low initial state.
One mechanism proposed by R Penrose with Conformal Cyclic Cosmology is that all particles have to eventually decay.
And while a proton decay is possible ( even with other theories ) after more than 10³² years, the decay of fundamental fermions is a lot tougher to come to grips with.

https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology

Edited November 19, 2020 by MigL

[MSC]

16 hours ago, MigL said:

Biggest problem with all versions of cyclic cosmologies is the fact that entropy has to be 'reset' to the low initial state.
One mechanism proposed by R Penrose with Conformal Cyclic Cosmology is that all particles have to eventually decay.
And while a proton decay is possible ( even with other theories ) after more than 10³² years, the decay of fundamental fermions is a lot tougher to come to grips with.

https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology

Thanks for the response! How are you keeping MigL? 

I don't understand how particle decay of protons or fermions relates, admittedly. 

Isn't that only a problem with indefinite and infinite cyclical cosmology? There could very well be bounces without an entropic reset, how many possible bounces there are might be something with a hard limit. It could even be that the limit has already been reached and that is why expansion seems like it will overcome any ability for a contraction to take place again.

Why cyclical cosmology seems relevant to me; there are black holes and voids that are described as potentially being older than the big bang. Not to mention Methuselah, if the margin for error on that approximate age calculation falls before the big bang. 

All that being said, maybe I'm not reading from the right sources but would be interested to hear your thoughts.

 

[MigL]

i'm keeping well, MSC.
Hope you and yours are, as well.

I don't understand CCC very well, especially the requirement/attribute for the past conformal boundary of one FLRW space-time attaching to the future conformal boundary of another.
But I do think that entropy does need to be reset to a low value, such that the universe can 'evolve'.
It could not start at a high value since there would be no free energy for processes.

7 hours ago, MSC said:

there are black holes and voids that are described as potentially being older than the big bang.

I have not seen this information, but it seems, if true, that our notions of the Big Bang, and its duration, would be impacted.
Could you please post the source, as I'm inclined to dismiss it as either untrue, or bad calculations.

As for Methuselah, the jury is still out, but its age is calculated as 14.5 billion years +/- 800 million years, which means it may well be only 13.7 billion years old. It is a metal poor star with 250 times less metallicity than the Sun, indicating it probably formed, shortly after the recombination event ( cause of CMB radiation ), from the available Hydrogen, Helium and sprinkle of Lithium.

[MSC]

Evidence of hawking points

Sorry I misspoke before, beyond SMBHs in the early universe and explaining how they grew to such a size so quickly; there is also evidence of blackhole evaporation in the CMB.

Which to me presents a bit of a dilemma. If the universe is a little under 14billion years old, and it takes 10^64 years for a regular sized blackhole to evaporate, how can we explain the potential evidence of black hole evaporation in the CMB without throwing out the age of the universe?

As for the voids, I double checked what I meant there and withdraw that completely. I was thinking of the bootes void and I remembered watching a documentary of some kind that probably put a bit of woo science in there for dramatic effect. It cited that the universe wasn't or isn't old enough for the bootes void to have formed to the size it is, but having double checked that myself before replying I think it might be a load of BS. 

 

[MigL]

Small Black Holes ( smaller than stellar sized ) are very 'hot' and evaporate very quickly.
If there is evidence of BH evaporation in the CMB, that would be evidence for primordial BHs, and, would be big news.

54 minutes ago, MSC said:

there is also evidence of blackhole evaporation in the CMB

I don't know of any evidence for primordial BHs, their evaporation, or CMB evidence.
So maybe include links for your assertions.

[MSC]

31 minutes ago, MigL said:

Small Black Holes ( smaller than stellar sized ) are very 'hot' and evaporate very quickly.
If there is evidence of BH evaporation in the CMB, that would be evidence for primordial BHs, and, would be big news.

I don't know of any evidence for primordial BHs, their evaporation, or CMB evidence.
So maybe include links for your assertions.

There is a link in my last, about hawking points.

[MigL]

You provided a google search ) result page , not a specific link.

If I take the 2nd ( same as 4th ) result in that google search ...

https://arxiv.org/abs/1909.09672

I get the following

"We investigate recent claims for a detection of "Hawking points" (positions on the sky with unusually large temperature gradients between rings) in the cosmic microwave background (CMB) temperature maps at the 99.98% confidence level. We find that, after marginalization over the size of the rings, an excess is detected in Planck satellite maps at only an 87% confidence level (i.e., little more than 1σ  ). Therefore, we conclude that there is no statistically significant evidence for the presence of Hawking points in the CMB."

So, of the links you provided, the 1st one claims 'apparent' evidence, while the second de-bunks it.
I would think that, at best, you could claim there need to be further observations/investigations into the matter.
Certainly NOT claim there is evidence.

[MSC]

58 minutes ago, MigL said:

You provided a google search ) result page , not a specific link.

If I take the 2nd ( same as 4th ) result in that google search ...

https://arxiv.org/abs/1909.09672

I get the following

"We investigate recent claims for a detection of "Hawking points" (positions on the sky with unusually large temperature gradients between rings) in the cosmic microwave background (CMB) temperature maps at the 99.98% confidence level. We find that, after marginalization over the size of the rings, an excess is detected in Planck satellite maps at only an 87% confidence level (i.e., little more than 1σ  ). Therefore, we conclude that there is no statistically significant evidence for the presence of Hawking points in the CMB."

So, of the links you provided, the 1st one claims 'apparent' evidence, while the second de-bunks it.
I would think that, at best, you could claim there need to be further observations/investigations into the matter.
Certainly NOT claim there is evidence.

Fair enough. I didn't actually understand the part about the confidence level at all. I saw 87% and didn't understand the second figure so I couldn't really draw agreement or disagreement with that, as it reads like there is a high confidence level for the evidence of hawking points that falls short of 100% confidence.

To the inexperienced of us, what exactly does the debunking article say? As it's conclusion seems confusing to me. Is it debunked or is it saying there is currently no way to be 100% certain that those hot patches are hawking points?

The problems I see with CCC, if the universe does have evolutionary phases that would appear cyclical, that does not mean there is no end point where entropy can be reset to a low entropy universal structure. There could have been many bounces before, even if it is impossible for another contraction to occur in this phase due to expansion. 

This is why my questions in my OP were directed more at the image used to represent the theory. It shows a CCC universe getting larger after each contraction. Which seems really strange to me. I can understand how a big crunch contraction can happen in universes where there is far less expansion at work, that does not appear to be this one however. 

So if there is a cyclical universe as has been described by Penrose, can it really be an indefinite infinite one or would that universe also reach a point where it cannot contract anymore and suffers a heat death?

To be very clear as well, I'm not claiming with 100% certainty that this is evidence, I'm just repeating back how it is presented elsewhere and I'm just trying to understand. This is all hypothetical and I don't have access to the same resources as you. I can only repeat what is said in science news outlets and what I can get from free resources. I already pay out of pocket for access to philosophy and ethics publications. So if I say something is evidence, it's not me saying it is that, I'm asking you if they are right to call it evidence. 

If it makes it at all easier to have an open discussion, what I'm really asking is how would a CCC universe exist and is it impossible for such a thing to exist? Whether that is this universe or not.