What is the Black Hole Bounce Theory and How Can it Be Tested?

[marcus]

Smolin has presented a testable theory which
offers a possible explanation for some parameters in the Standard Model
and in Cosmology.

In his recent paper he presents a handful of empirical tests which
could shoot down the theory---that is, the theory is falsifiable: it
makes predictions which can be tested with available tools and which
if found not to be the case would invalidate the theory.

The theory is fairly complicated and depends, among other things, on the idea that our universe is the result of a black hole bounce.
According to Loop Quantum Gravity and allied approaches (Smolin cites personal communication from Martin Bojowald, but there is also the recent paper of Modesto) when the classical model black hole is quantized the singularity disappears and spacetime extends, forming another universe inaccessible to us from which we can receive no news. In a certain sense the new spacetime ballooning out from the BH "bounce" or quantum ex-singularity is actually in the future from the standpoint of everything in our spacetime (until and if the hole evaporates, upon which causal relation ceases totally).

If universes are typically created from a black hole bounce, then certain postdictions can be made about the parameters of the Standard Model as well as some observational predictions. The reasoning is rigorous but subtle---best to read Smolin's latest article "Scientific Alternatives to the Anthropic Principle":

See in particular pages 30-31 "Successes of the theory"
also section 6.2 answering previous criticisms
also 6.3 "Why a single heavy pulsar would refute the theory"
and 6.4 "How observations of the CMB could refute the theory."
and 6.5 "How early star formation could refute the theory."


Some sources:

"The fate of black hole singularities and the parameters of the standard models of particle physics and cosmology"
Smolin
http://arxiv.org/gr-qc/9404011

"Disappearance of the Black Hole Singularity in Quantum Gravity"
Modesto
http://arxiv.org/gr-qc/0407097

"Scientific Alternatives to the Anthropic Principle"
Smolin
http://arxiv.org/hep-th/0407213

 

[sol2]

This seems awful familiar to me. Turok's and Steinhardt's homepage are listed in link as well. I am not forgeting the essence of the thread started Marcus.


http://physicsweb.org/objects/news/6/4/21/020421.gif

Theories of 'bouncing' or cyclic universes, however, do not predict a beginning or an end of time, and therefore do not need to explain them. Early advocates of a cyclic model thought that the universe must shrink into a singularity - a point of infinite density and temperature - before exploding in a new big bang. But this idea proved too difficult to explain, and most theorists rejected the concept of a cyclic universe.

Now Steinhardt and Turok say that - according to 'M-theory' - the universe need not pass through a singularity between a big crunch and a big bang. Supported by most cosmologists, M-theory says that space-time has eleven dimensions, of which we perceive four: three in space and one in time. Our four-dimensional 'brane' - short for membrane - is moving among the remaining dimensions or branes, which are hidden at very small or very large length scales.

http://physicsweb.org/article/news/6/4/21

Who thought of these issues, or does everyone get a swing at it from a different perspective?

 

[setAI]

awesome stuff!


___________________________

/:set\AI transmedia laboratories

http://setai-transmedia.com

 

[marcus]

awesome stuff!


___________________________

/:set\AI transmedia laboratories

http://setai-transmedia.com

I agree
and for me the overall most impressive thing
is where Smolin says that finding even one pulsar above some mass
would refute the theory.

he has a specific model in mind, in other words, that is falsifiable and has some explanatory power.

If universes really do bud
thru black holes
and if the parameters are like genes (constants of nature can change
slightly as they go thru into the bud)

then genes that lead to rapid reproduction (lots of black holes) will
swamp the alternatives

so evolution would fine-tune certain physical constants---those that govern star formation and gravitational collapse---and he lists some of them and what the effect of varying a bit either way would be on reproductive rate

so the prediction is that your typical U will be a good black- hole-maker
and he says some things which if we could find them would show that
ours is sub-optimal---unlikely according to this theory---which would
discredit the theory.

It predicts something that can be looked out for---hence not pure daydreaming.

so I'm impressed---cant say I want to believe the theory or disbelieve it---but it gets my attention more than any of the other "multiverse" stories.

 

[marcus]

the real nuts and bolts multiverse

It is an idea whose time has come I'd say.
the key connection is what has been done in Loop Gravity
getting rid of the BB singularity at the start
and getting rid of the BH singularity so that a seamless JOINT
can be made between the two models

I don't know any other theory of gravity or theory of spacetime
where you can weld the beginning of a universe onto the bottom of a black hole----maybe you do and if so please give me a link!

The links here are Modesto 2004 and Bojowald 2001, I'll fetch them later.

The key logical step is to make it falsifiable. Make it predict something that is already practical to check.
Smolin has found the only way so far to do this AFAIK----have a testable multiverse. It depends critically on the role of black holes and this
seamless connection of the two spacetimes. have to go, more later

 

[marcus]

the usual (non-predictive) multiverse story

Except for Smolin's the usual multiverse story I've been hearing is not predictive and is invoked to solve some difficulty in string theory or in someone's inflation scenario.

Like so-and-so's inflation scenario requires a very unlikely and finely-tuned scalar field ('inflaton') and no one can say how that could have happened. So we picture ourselves as a rare fortunate bubble, one of the few bubbles where a quantum hiccup gave just the right inflaton, or we say that somehow a good inflaton got started and has been passed along and we are one of an eternal sequence of inflations----the main thing is the guy is telling you this because his model requires an unlikely bit of luck that he can't give you an ordinary scientific explanation for.

Or like there are 10¹⁰⁰ possible distinct string theories and none has been found that has the right cosmological constant or dark energy density-----traditionally one would want a theory to explain why the CC has to be what it is----but we give up on that, say, and imagine a "landscape" of different string theories and imagine that one of them (that we don't know how to find mathematically) has the right CC----maybe there's a multiverse out there and we live in one of the rare inhabitable bubbles.

What Smolin is doing is quite different. He is not trying to duck some problem with LQG (not trying to solve a crisis of too many vacuum or an unexplained inflaton)----LQG gives him a multiverse and he starts right away using it to make predictions which can be tested.

If black holes don't have a singularity in them and the spacetime extends to form a new expanding region with similar (but not identical) fundamental constants then there's an evolutionary situation in which those sets of constants will win out that promote plentiful star formation and lots of collapsing to form black holes. The holiest universes will produce the most babies.

So the prediction is not that parameters like ours are rare (as in some string multiverse stories----we are one in a jillion because that's the only one allowing "intelligent" life-forms----no no no! Universes with parameters like ours are extremely common! that is what the prediction says. Our physical constants are common because they accelerate the production of black holes

Sound crazy? OK shoot it down. Find an example, Smolin challenges you, of just one physical constant which, if you made it a few percent different either way, would cause more black holes to form.

Anyway, that's my take on it---let's hear some others' perspectives. I think Smolin's multiverse story is unique in that it is not a cop-out---not invoked to cover some theoretical embarrassment----and rather than dodging refutation, it courts it: this being the test of meaningful science.

 

[marcus]

So many papers have come out eliminating the Big Bang "singularity" that I have lost count
Bojowald was the first, in 2001, but since then quite a few authors have confirmed the result and extended it to broader assumptions and used different methods to get the result and so on.

What should the ex-singularity be called?

In English, more and more frequently people are calling it a "bounce".

that has the appeal of alliteration (which is favored in English at least in USofA) people can easily switch from "Big Bang" to "Big Bounce"

Objectively I don't know if bounce is quite right. It is a crossover or transition from contraction to expansion. A reversal.
A German journalist has called it a "turning inside out"
which in English would technically be called an "eversion" that is what you do to a sock when you turn it inside out: you evert the sock.

In fact in the quantum geometry model of the ex-singularity the volume element is turned inside out---I find this puzzling---at the moment of reversal.

In a popular series of articles about Loop Quantum Cosmology and the new vision of the big bang---quantum bounce in place of classical singularity---Rudy Vaas called it
"Der Umgesteulpte Urknall"

knall is bang, Urknall is primordial bang
stuelpe is something you turn inside out, like a cuff on pantsleg or shirtsleeve
Umgestuelpte means, so I am told, "turned-inside-out"

a lot of the progress in Loop Quantum Cosmology is being made in Germany these days, so maybe they have journalistic language rights on
a piece of the action.