# Idea of universe

1. Mar 25, 2015

### Shu Sheng

Is it possible that the universe started with a collapsing supermassive black hole that released what it absorbed after eating the entire universe? If so , could it be possible that this an infinite cycle of death and birth of universes?

2. Mar 25, 2015

### Chronos

The process by which the entire energy content of the universe could end up in a single black hole is not easily explained by physics as currently known.

3. Mar 25, 2015

### elusiveshame

Wasn't that one of Hawkings earlier theories that he disproved with his later theory?

4. Mar 25, 2015

### marcus

Maybe I'm wrong, but that part sounds to me like a round-about way of describing the observer's experience of a classic "big crunch",

in a spatially finite universe running according to the standard LambdaCDM model, that just happens to be contracting rather than expanding.

What would be the observational difference for people living in a galaxy within the event horizon of an extremely large BH and people in a galaxy that formed part of a collapsing Friedmann universe?
that part is harder to imagine. Why would a contracting universe reach a maximum density and then re-expand? How could there be an "infinite cycle"?
Why would an expanding universe like ours (especially with our cosmological curvature constant Lambda) ever start contracting?

Let's not worry about "infinite cycle" for now, and try to understand a ONE-TIME occurrence of what you are talking about. Imagine that there is a contracting universe---never mind how it got to be there or how it came about. How would a contracting universe reach a maximum density and start to re-expand looking like the familiar LambdaCDM universe that we see? What would be the observational consequences, that astronomers could look for, to test the idea?

Shu Sheng, I would suggest you read the paper called "LambdaCDM bounce" by Yi-Fu Cai and Edward Wilson-Ewing. As I recall it was posted on arXiv.org in December 2014. It is the top hit when you google "LambdaCDM bounce".

At this time, with our limited physical knowledge, don't try to think about "infinite cycle". Just try to imagine clearly how there could have been a bounce at the start of the expansion of the universe we now see expanding. If it happened, shouldn't there be some detectable traces of it?
Yi-Fu Cai and Ed W-E have been thinking about that.

I will google for you and get the url, in case you want to check this out.
http://arxiv.org/pdf/1412.2914.pdf
This is for the short summary:
http://arxiv.org/abs/1412.2914

Last edited: Mar 25, 2015
5. Mar 25, 2015

### wabbit

I have been wondering about that. In other words, what is the difference between the Schwarzchild metric and a suitably chosen FLRW metric (perhaps a flat one if the asymptotic flatness of the BH is a reliable hint)? Is there a change of coordinates (with time a function of r for the BH I suppose) that would show the two metrics as asymptotic near their respective singularity? Or at least coordinates that would allow to quantify the difference? (Thinking of a white hole vs expanding universe here, but this should be the same for BH and contracting).

Last edited: Mar 25, 2015
6. Mar 25, 2015

### marcus

I don't see the Schw. metric as applicable to a BH that "eats the entire universe", as Shu Sheng says. You need a BH model where the event horizon extends to infinity. In Shu Sheng's picture there is no "outside" that does not get gobbled up. So all space must be within the EH.
Need a slightly different model. If I correctly understand what he is imagining.

Last edited: Mar 25, 2015
7. Mar 25, 2015

### wabbit

Hmm maybe not the whole universe, but asymptotic near t=0(FLRW)/r=0(WH).
Also in such a change of coordinates I wouldn't be surprised to see some kind of correspondence between BH horizon and cosmological horizon, if the region of the coordinate change extends that far - but this is secondary, I was primarily considering the situation you mentionned, i.e. inside the horizon (e.g. $r\leq r_0<r_H$ WH, $t\leq t_0$ FLRW, or rather both time-reversed).

Also as to outside, in the BH the outside is r>r0, this would correspond to something like t>t0 in FLRW (and at some point the metrics will diverge anyway, assuming they can be made similar in a region).

Maybe such a similarity region is small - it needs to match scalar spacetime curvature for instance and I suppose these behave quite differently as one approches t=0 in FLRW vs r=0 in BH.

Last edited: Mar 25, 2015
8. Mar 25, 2015

### rootone

Essentially it is one idea amongst many that have been considered by serious scientists.
However there isn't any particular reason to favour this model over other ideas, and certainly there isn't observational evidence in favour of it.

9. Mar 25, 2015

### marcus

Yi-fu Cai and Ed Wilson-Ewing examine the observational evidence. Currently it appears to favor a version of their LambdaCDM bounce scenario (which does not require hypothesizing an "inflation" field or a "multiverse") which has a slower speed of sound in Dark Matter over versions of their model assuming a higher speed of sound.

They go through and consider quite a lot of different kinds of observational evidence, as I recall, to check consistency with their model.

Their paper is December 2014. There seems to be observational data which is applicable to this kind of thing. I mean non-inflation/non-multiverse modeling of the start of expansion. The situation may have changed since the last time you examined it.

10. Mar 25, 2015

### rootone

Noted, I wasn't aware of this work.
Will take a look.