Why should our big bang be the only one?

[marcus]

Why should "our" big bang be the only one?

Loop quantum gravity has made significant progress at exploring the classical big bang and black hole singularities.
Both circumstances are non-singular when LQG is used to model them: what was formerly a singularity in the classical model is removed by quantizing, and the two regimes look rather similar

see bojowald et al
http://arxiv.org/abs/gr-qc/0503020
http://arxiv.org/abs/gr-qc/0503041
and references therein

this carries the copernican revolution further by suggesting
why should "our" bigbang be the only one?"

Earlier astronomers looked at the stars and were able to ask "why should our sun be special? the sun resembles a star, so why shouldn't these other stars that we see have planets orbiting them too?"

Now it becomes possible to look around and see a lot of black holes and ask "why should our bigbang be special? the big bang resembles a black hole (looked at in LQG from the other time direction), so why shouldn't these black holes that we see be big bangs starting other branches of time?"

In my view this is a major thrust of Loop Quantum Gravity right now. Increasing numbers of LQG people are working on studying the big bang ex-singularity, and some key people have moved over to study the black hole ex-singularity (which is at a much earlier stage of understanding)

Black hole ex-singularity research is now, in 2005, the way big bang ex-singularity research was in 2001, with the very first Bojowald paper that removed the singularity in the very simplest case.

To me, this is at the guts of what is going on in LQG. And it is in this light that I see a very beautiful new Quantum Gravity paper by Rafael Sorkin (a senior QG guru at Smolin and Rovelli alma mater Syracuse, and also parttime at Smolin's Perimeter). This paper is a thoughtful one: deep and simple.

It just came out 5 April05

http://arxiv.org/hep-th/0504037

This paper, as I see it, goes a certain ways towards clearing up Roger Penrose thermodynamic objection to identifying black hole with big bang.
Penrose thermodynamic objection is: "what happens to all the entropy?"

As I read Sorkin, he says the entropy gets stuck on the screen door (the event horizon) and immediately inside, time starts flowing coherently in a new direction, which we, from our perspective, picture as down the hole.
Time makes a fresh clean start, with huge negative entropy. All the old crud is there plastered on the windshield for us to look at as it gradually fades out of existence.

Sorkin also has good things to say about unitarity and non-unitarity, and the "information paradox".

For me this is an exciting paper, maybe it will be for some others.

 

[wolram]

http://xxx.sf.nchc.gov.tw/abs/astro-ph/0504034
Recent developments in the study of primordial black holes (PBHs) will be reviewed, with particular emphasis on their formation and evaporation. PBHs could provide a unique probe of the early Universe, gravitational collapse, high energy physics and quantum gravity. Indeed their study may place interesting constraints on the physics relevant to these areas even if they never formed. In the "early Universe" context, particularly useful constraints can be placed on inflationary scenarios, especially if evaporating PBHs leave stable Planck-mass relicts. In the "gravitational collapse" context, the existence of PBHs could provide a unique test of the sort of critical phenomena discovered in recent numerical calculations. In the "high energy physics" context, information may come from gamma-ray bursts (if a subset of these are generated by PBH explosions) or from cosmic rays (if some of these derive from evaporating PBHs). In the "quantum gravity" context, the formation and evaporation of small black holes could lead to observable signatures in cosmic ray events and accelerator experiments, providing there are extra dimensions and providing the quantum gravity scale is around a TeV.
May be going of at a tanget, but this may have some interest.

 

[marcus]

hi wolram, I think that, as you suspect, primordial black holes are periferally connected with Sorkin's paper, at least tangentially.
the paper's main impact, for me anyway, is on LQG.
Sorkin makes it seem as if the "spinfoam" or path integral direction in LQG is more promising than the "canonical" version. Although the two are closely connected they do differ and the path integral approach has been getting more emphasis for the past few years.

his thesis #9 (necessity of a spacetime approach) bears this out

have to go and do some errands, back later

 

[wolram]

Marcus i hope you have some insight into this, i must confess i am in the
wilderness, it gets more difficult as time goes by rather then easier, i hope
for everything and get nothing, power to you.

 

[marcus]

Marcus i hope you have some insight into this, i must confess i am in the
wilderness, it gets more difficult as time goes by rather then easier, i hope
for everything and get nothing, power to you.

where do you feel best, as regards wilderness, wolram? where do you want to be?
some people are happiest deep in the wilderness as aware as they can possibly be of all the uncertainty and myriad conflicting possibilities, and others are happier with a simplified picture of the progress of events

if you really want to simplify-down your picture, I guess I could help.
It really just means tuning out the noise and minor distractions and focussing on major developments.

I can show you by example how to get focus, but in the end what you see as major as opposed to minor depends on your own judgment
(and it is always possible that at heart you do not want a simplified view but value a chaotic state of mind)

 

[wolram]

By MARCUS

if you really want to simplify-down your picture, I guess I could help.
It really just means tuning out the noise and minor distractions and focussing on major developments
Thankyou for you offer Marcus, I am trying to keep an open mind, but find
it almost impossible as intuition always kicks in, may be i am just to skeptical
and want a black and white picture, but even that is ambiguous, what is
"black", and what is "white", for now i must be happy with what's on offer,
an look for people such as your good self to guide the way.

 

[wolram]

If you have time could you give a little more on this,

Sorkin makes it seem as if the "spinfoam" or path integral direction in LQG is more promising than the "canonical" version. Although the two are closely connected they do differ and the path integral approach has been getting more emphasis for the past few years.

I do understand the word spinfoam, but not its use as a building block, or
tool to aid understanding other systems.

 

[marcus]

... I am trying to keep an open mind, but find
it almost impossible as intuition always kicks in, may be i am just too skeptical and want a black and white picture, but even that is ambiguous,...

in ecclesiastes (one of the more realistic parts of the bible) it says there is a time and season for various things and in particular sometimes it is good to gather stones together and sometimes it is better to scatter them (dont ask me to make sense of that, just read it for your self)

anyway there is a time for being openminded and for questioning and for challenging everything and finding all the possible contradicitons between the different ideas and for listening carefully even to what is distracting noise, to catch the slightest clue that might be in it.

there is a time for that and it seems to me you have a knack for it, you have been skeptical and questioning and openminded for a couple of years at least

maybe now you should gather things together and be selective and tune out the distractions and, so to speak, "build your world-system".

if you believe ecclesiastes (not to say that you should) then there is a time for both scattering and gathering your attention, and people may individually even go thru cycles.

this is something you must do for yourself but others may be able to coach you, or show by example how THEY focus their picture, or give you some encouragement. but most of the work (and the risk-taking) can only be done by you

any kind of selectivity or focus involves the risk that you will focus on the wrong picture and time will prove you wrong-----you just have to be willing to take that risk, have a little faith in yourself and your hunches, construct a coherent picture of how science is developing, what the trends are, and put aside worries that you might be wrong. If your picture eventually turns out wrong, so what? just do the best you can

you have gone thru a two or three years of openminded unfocused broadgauge research, and I (for one) think you have pretty good intuition and common sense, so if you want to narrow it down to a "wolram-picture"----it it is really time now for you to do that---then I think the result might be interesting to see.

I will write you some kind of "how I focus my picture of scientific progress" post. maybe it will help, or show you something by example

 

[wolram]

What a lovely warm and encouraging post Marcus thankyou, from now on
i intend to be less scatter brained, and focus on certain subjects.

 

[marcus]

1. know and make use of your biases

when you plane or carve a piece of wood you go with the grain, so it doesn't rile things up. know your own biases and work with them

example: I have a bias away from particle physics and towards astronomy.
(I actually realize that accelerator research is important and can produce significant results, but I de-emphasize it)

2. pick out a few big points that stand out, that you would like to see resolved

examples I do not like: some people focus on questions like the Origin of Life, are there Intelligent Aliens we can communicate with?, how will the Universe end? How can humans travel faster than light so they can colonize and make Star Trek come true? Well I am being unfair, but the big features of scientific progress, the big puzzles, are different for different people.

examples I personally like: I like the Big Bang and Black Holes.
(I also like Gammaray Bursts, but that fits in somehow with the two others)

In other words I am fascinated by puzzles posed by 1915 theory of GR.

3. construct a simplified picture of scientific progress at this stage of history, minimize distractions, minimize the importance of what doesn't interest you.

example: People have been doing particle research for 100 years, since JJ Thompson deflected a beam of electrons and found the electron charge to mass ratio. they build bigger and bigger accelerators. but the main strokes have been drawn and its finer details now. electrons quarks neutrinos etc are not going to go away. they are just going to refine the numbers a few more percentage points. the particle questions are getting more academic

example: the dark energy question just involves a small percentage variation in expansion. OK focus on the main fact, the expansion. maybe it is accelerating a tiny percentage

understand that these are BIASES. I am not going to spend my whole life being narrowminded! but I need a home base.

example: The most important direction that science is going is to understand conditions at the BB and inside the BH. these are two incredible things that 1915 GR predicted and the history of 20th century is that
1. GR gets checked more and more stringently
2. we "see" the BB and BH more and more, and they get realer and realer for us as time goes on and evidence builds up

example: the most important thing science could do in my lifetime is understand what goes on in Black Holes and Big Bangs. As an added bonus it would be really great if it turned out that they are the same phenomenon.

 

[marcus]

...
i intend to be less scatter brained, and focus on certain subjects.

that sounds like a good idea
now I am undecided as to whether or not to erase post #10 which contains hints by example
I think the best would be for you to focus and be selective by yourself in accordance with your own inclinations, and not to be influenced.
this post #10 is not offered as a recipe
but more as a somewhat exaggerated caricature of my own mental housekeeping. if you will accept it as not a suggestion or prescription for you, but as an example of how someone else goes about it, then I will leave it up for a while

 

[wolram]

Marcus post 10 is most welcome and informative.
I am not sure if BHs will give up much information, or at least until we
can get up close an see if hawking radiation is real.
as for the BB I am also not sure how much nearer to the beginning
we can go with the technology we have to date.
I do believe that something that is detectable and testable is out
there, it is just a case of finding it, what could it be, is it at a mico
or macro scale, is it a entwined with gravity, is it something to do
with entangled states? well the words "new science", keep popping
up in the literature, so may be something new is just around the corner,
this is where i will be looking.

very best.

 

[marcus]

as a "by the way" let's remember Giordano Bruno 1548-1600
here is an exerpt of the Wiki article on him:

"...In 1584, Bruno published two important philosophical dialogues, in which he argued against the planetary spheres. (Two years later, Rothmann did the same in 1586, as did Tycho Brahe in 1587.) Bruno's infinite universe was filled with a substance -- a "pure air", aether, or spiritus -- that offered no resistance to the heavenly bodies which, in Bruno's view, rather than being fixed, moved under their own impetus. Most dramatically, he completely abandoned the idea of a hierarchical universe. The Earth was just one more heavenly body, as was the Sun. ...

Bruno also affirmed that the universe was homogeneous, made up everywhere of the four elements (water, earth, fire, and air), rather than having the stars be composed of a separate quintessence. Essentially, the same physical laws would operate everywhere, although the use of that term is anachronistic. Space and time were both conceived as infinite. There was no room in his stable and permanent universe for the Christian notions of divine Creation and Last Judgement.

Under this model, the Sun was simply one more star, and the stars all suns, each with its own planets. ...

Bruno's cosmology is marked by infinitude, homogeneity, and isotropy, with planetary systems distributed evenly throughout. Matter follows an active animistic principle: it is intelligent and discontinuous in structure, made up of discrete atoms. This animism (and a corresponding disdain for mathematics as a means to understanding) is the most dramatic respect in which Bruno's cosmology differs from what today passes for a common-sense picture of the universe..."

so from Wiki one gets the impression that Bruno had a hodgepodge of ideas some of which would be considered oddball today and others (which were way ahead of their time) would be accepted as common sense today.

he was burnt alive in Rome on 17 February 1600

http://en.wikipedia.org/wiki/Giordano_Bruno

 

[wolram]

he was burnt alive in Rome on 17 February 1600

Im glad we have moved on since then as i may be feeling the heat.

Marcus i actual understand most of the last of the papers you linked to,
somewhere near the bottom it seems he is not bothered about information
loss, if that is what he is saying it must be controversial, although i see
no problem.

 

[setAI]

he was burnt alive in Rome on 17 February 1600

Im glad we have moved on since then as i may be feeling the heat.

I hate to break it to you- but int the 1950s right here in the good ol' US-of-A Willhelm Reich was thrown into prison [where he died] and had all his books burned because of his orgone research- who knew that building aluminum foil wrapped tubes was such an offence

 

[marcus]

... he is not bothered about information
loss, if that is what he is saying it must be controversial, although i see
no problem.

Neither do I. It is controversial though. I can't explain why it is that theoretical physicists are so devoted (on the whole) to zero information loss. this is at the root of the famous "black hole information paradox" which seems greatly overblown to me. why are they not prepared (most of them) to contemplate even a very very slow very slight fading of information? maybe someone else can clarify this conventional insistence of the majority

what I see is a few perfectly good physicists (as far as i can tell) going public with their doubts (Gambini and Pullin did this last year) and saying maybe information is not absolutely preserved and can decay at least on the timescale of the evaporation of a macroscopic black hole

for the zero-loss fanatic, I believe "information" means the definiteness of some quantum state which, if information is lost, turns into a weighted sum or mixture of states. A (pure) quantum state is a vector of length exactly one in an imagined "space" of states. a mathematical map is called "unitary" if it transforms vectors of length one into other vectors of length one. in conventional QM the time-evolution operator is always assumed to be unitary----the process of evolving to the next minute or the next day preserves length of the object (a vector) representing our knowledge.

if it is slightly nonunitary then the operator can transform a vector of length one into a mix of vectors, maybe almost purely one but with a tiny bit of another added in, like a trace ppm impurity.
if the passage of time corresponds to a slightly nonunitary operator, then gradually over a long time a pure state can become incoherent or mixed. So it is no longer a definite pure state and information has been lost.

this would make the mathematics slightly messier, but Gambini and Pullin say that it is how the real world operates and you have to accept it.
they are in the minority. So, I think, is Rafael Sorkin. But we will see.
Somebody named "nonunitary" used to come to PF. I wonder what his idea about this is.

Dont worry about the technicalities. I am glad you were able to get something out of Sorkin's paper.

 

[marcus]

I hate to break it to you- but int the 1950s right here in the good ol' US-of-A Willhelm Reich was thrown into prison [where he died] and had all his books burned because of his orgone research- who knew that building aluminum foil wrapped tubes was such an offence

[for decency sake I have deleted some comments about the persecution of the psychoanalyst and sex therapist Wilhelm Reich]
Really! in America today it is perfectly all right to say whatever comes into your head about the origin of the universe. Don't give wolram the impression that we are barbarians.

[EDIT sorry about the jocular tone very sad what happened to Reich
http://en.wikipedia.org/wiki/Wilhelm_Reich
see Wiki for details, he had these machines to collect orgasm-energy from the universe, accumulate it, and infuse it into his patients or followers, they did involve aluminum foil, as setAI reminds us, Wiki has a photograph of a foil-lined "orgone box" which the patient would sit inside in order to be charged up with orgastic energy. Norman Mailer got the treatment along with several other famous people. amazing.]

 

[Kea]

Cheers to setAI

...which you simply did not do in the Fifties...

I think this may have been the point.

 

[marcus]

I think this may have been the point.

Sorry about the jocular tone, it was sad what happened to Reich.

He died in his sleep, of a heart attack, while in federal prison.
He was 60 years old.
However the contraptions he built to collect sexual energy from the universe and conduct it into his patients have achieved for him a kind of lasting fame. I expect it didnt help, with the Food and Drugs Administration (FDA), that he also claimed that sitting inside an orgone box could cure cancer.

 

[marcus]

I was reading the PhD thesis of Tamara Davis and on page 97 came across a nice quote from Eddington and a parallel one from Einstein.

Davis thesis is good BTW. The first section "Expanding Confusion" was apparently adapted by Davis and Lineweaver for their Scientific American article. It has material for at least another interesting article

Eddington, in The Nature of the Physical World, Maxmillan: New York (1948), p. 74, “The law that entropy always increases – the second law of thermodynamics – holds I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the Universe is in disagreement with Maxwell’s equations - then so much worse for Maxwell equations. If it is found to be contradicted by observation - well these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics, I can give you no hope; there is nothing for it but to collapse in deepest humiliation.”

Einstein, quoted in Thermodynamics in Einstein’s Universe by M. J. Klein, Science, 157, (1967) p 509, “[A law] is more impressive the greater the simplicity of its premises, the more different are the kinds of things it relates, and the more extended its range of applicability. Therefore, the deep impression which classical thermodynamics made on me. It is the only physical theory of universal content, which I am convinced, that within the framework of applicability of its basic concepts will never be overthrown.”

Here is a link to Davis thesis
http://arxiv.org/astro-ph/0402278
Fundamental Aspects of the Expansion of the Universe and Cosmic Horizons

 

[marcus]

the word "gingerly" comes to mind in connection with the latest Ashtekar paper

He and Bojowald seem to be bending over backwards to avoid addressing the possibility that a black hole with matter could continue to a big bang like expansion, allowing time to fork and form two infinite futures

I think there is a deep issue, almost an instinct, in how Ashtekar is behaving. He does not want LQG (which is partly his brainchild) to be perceived as boxed in and forced to violate the 2nd Law or some other article of faith.

He is at pains to argue, in the latest paper, that a black hole can form (temporarily concealing information) and then evaporate, and yield up its sequestered information to observers far in the future, all within the LQG context.

maybe the information needed to reconstruct the past does NOT reside in the black hole interior, and is never released. maybe the information resides in the flattened slowed images on the event horizon which gradually fade out. so maybe the information in the stuff that fell in really is lost (at least to us) although it may take a while to fade out.

as a mere observer, I can't argue with the researchers (it would be comic to try) but my feeling is that the latest A&B paper is "defensive". they don't want adversaries to be able to point an accusatory finger and say that the LQG framework leads inescapably to a confrontation with some universally accepted principle.

but since I have not such a stake in the game, I can contemplate that possibility. Maybe LQG will appear to violate the Second Law at the point where the classical singularity is removed. Perhaps it will violate unitarity or predict the loss of information needed to reconstruct the past. If it turns out that LQG contradicts some cherished principle then maybe that will discredit LQG. It could prove LQG wrong, or it could prove the principle does not apply in this case. I want to consider the possibility that, for example, the sign of the entropy might flip at the "bounce", if that is meaningful to imagine, and that the bounce gives time a fresh start.

so the A&B paper that just posted, which though cautious belongs in this context, leaves me unsatisfied and waiting for the one they say will come out next.

here is a link to more about the A&B paper
https://www.physicsforums.com/showthread.php?p=521630#post521630