Bojowald's popular-level book

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bcrowell
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I bought a copy of Bojowald's new popular-level book on quantum cosmology with LQG, Once Before Time: A Whole Story of the Universe. It was a big disappointment. The style is really hard to plod through; you can really tell that English isn't his native language. The book starts by covering a lot of preliminaries about quantum mechanics and general relativity, and it doesn't do that very well. This first half of the book is in particularly in need of some diagrams. E.g., there is a description of the Bohr model of the atom in words, with no diagram of the circular orbits. Rather than useful scientific diagrams, most of the illustrations in the book are photos of abstract sculptures. Once he gets into the quantum gravity stuff, there are some descriptions of contact with observation, but these are already out of date. He discusses tests of dispersion of the vacuum, which the LQG community has already disowned as a prediction of the theory. He also devotes some space to Smolin's cosmological natural selection, which has recently been falsified by the observation of a high-mass neutron star. Amazingly for a book about LQG, there are absolutely no drawings of spin networks.
 

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marcus
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I'm sorry to hear of the book's apparent shortcomings and of your severe disappointment! I haven't seen the English version, but in 2009 I saw some sample pages of the German original which were offered by Amazon.de (the German amazon). The sample was not enough for me to get a fair impression.

I suppose the English version is a straight translation?---or perhaps some revision occurred as well.

I saw your "one-star" review of the book on Amazon.com, essentially the same as here.
https://www.amazon.com/Once-Before-Time-Whole-Universe/product-reviews/0307272850/ref=dp_db_cm_cr_acr_txt?ie=UTF8&showViewpoints=1

I think Loop cosmology is an interesting field, which should have a clear informative popularization. Eventually it will get a well-written popular treatment, but judging by your reaction this is not yet the book that is needed.
 
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marcus
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One reason I respect Martin Bojowald (whatever may be his deficiencies as a popularizer of quantum cosmology) is that he almost singlehandedly initiated Loop cosmology as a line of research----with his 2001 paper "The Absence of Singularity..."

For a few years, until Ashtekar got busy on it in 2006, Bojowald was the main person working in that area. He developed it, wrote the review papers, recruited younger researchers to be his collaborators, and so on.

Now the field has suddenly gotten away from him in a curious way. Ashtekar and collaborators have radically revised it, and gotten new results. But also starting around 2009 Rovelli has begun to apply the full (spinfoam) LQG to cosmology. Ashtekar has at least one paper about that too.

The original Loop cosmology going back to 2001 was "symmetry reduced". It treated only one or two degrees of freedom, or at most a handful: analogous to the classical Friedmann equation and certain classical Bianchi models.

Now "LQC" includes the idea of progressively relaxing assumptions of homogeneity/isotropy and applying the full LQG---so that Loop cosmology becomes less of a toy model.

The seminal paper on this is 1003.xxxx by Bianchi Rovelli Vidotto. It changes the field. That kind of change makes it hard for the popularizer. I don't see how Bojowald's book, if it was written in 2008 (publ. spring 2009) could possibly be up-to-date. Let alone the problems of shifting over to a second language.
 
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One reason I respect Martin Bojowald (whatever may be his deficiencies as a popularizer of quantum cosmology) is that he almost singlehandedly initiated Loop cosmology as a line of research----with his 2001 paper "The Absence of Singularity..."
I agree, I actually followed his initial presentations about the subject even in 2000 I remember. It was nice, someone with clear mathematical competence trying to find out phenomenology - irrespective of whether it was right or wrong. I just think he should not write popular books yet: the field is too immature and too few results have been obtained and too much doubt still rests upon whether his physical results will remain valid in full LQG. Moreover, he is too young to waste his time on nontechnical 250 page accounts. From the moment, they are sure (a) the singularity washes away (b) the BH puzzle is solved in full LQG and (c) dark matter is explained, then he might think about writing a popular book :smile: At least, I would wait that long ...
 
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marcus
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A fair and generous-spirited assessment---which competing scholars are not always able to give each other's work. This part of what you say rings a bell for me:
...someone with clear mathematical competence trying to find out phenomenology - irrespective of whether it was right or wrong...
One could imagine that this was the whole or main motive for launching LQC, to get a comparison with something in the real world by whatever means possible. And damn the consequences, win or lose, for the theory. To make testing paramount. I have no way to guess what they actually had in mind back in 1999 and 2000 (when you were already watching.) Old Kastrup may have put the idea in Bojowald's head.

If that was their idea then so far back, Kastrup might now be pleased by the general direction shown by Wen Zhao and by Barrau and Grain, because they rather clearly aim at testing win-or-lose.
( https://www.physicsforums.com/showthread.php?p=2979963#post2979963 )
 
  • #6
atyy
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LQC is definitely worth investigating. So is Ashtekar's work on it.

But it should not be taken to mean that LQG is worth investigating, ie. I'm not so sure about Rovelli's stuff. There is no indication that Rovellian LQG is coherent.

Barrett, Freidel, Livine, Oriti are all pulling in a different direction from Rovelli.
 
  • #7
atyy
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He also devotes some space to Smolin's cosmological natural selection, which has recently been falsified by the observation of a high-mass neutron star.
A prediction comes from a mathematically coherent theory, not a bunch of nonsense statements cobbled together, from which the "prediction" is a matter of taste. Is Smolin's theory of the former type?
 
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LQC is definitely worth investigating. So is Ashtekar's work on it.

But it should not be taken to mean that LQG is worth investigating, ie. I'm not so sure about Rovelli's stuff. There is no indication that Rovellian LQG is coherent.

Barrett, Freidel, Livine, Oriti are all pulling in a different direction from Rovelli.
Well, all I wanted to say was that it has to be shown that LQC is an excellent approximation to a coherent theory of quantum gravity, which one would expect to use similar basis states such as spin-networks. That is what I call LQG, it's a hypothetical theory which nobody knows what it really is :smile: I was not giving any judgement of validity about any of the above directions you mention for understandable reasons.
 
  • #9
atyy
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Well, all I wanted to say was that it has to be shown that LQC is an excellent approximation to a coherent theory of quantum gravity, which one would expect to use similar basis states such as spin-networks.
Maybe http://arxiv.org/abs/0907.2994 ?

Then link to to gravity via AdS/CFT ?
 
  • #10
marcus
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Wall Street Journal review of Bojo's book:
http://online.wsj.com/article/SB10001424052748704104104575622591025130892.html
print mode:
http://online.wsj.com/article/SB10001424052748704104104575622591025130892.html#printMode

The WSJ reviewer is Brian Clegg--author of a popular-written book called Before the Big Bang.

==sample excerpt from Clegg's WSJ review==
...are represented by different modes of a single elementary object, the string. The attractive image of vibrating strings, however, hides horrendously complex mathematics, the need for nine or 10 dimensions, equations with billions of solutions (any of which could match reality) and a total absence of predictions that could be tested by experiment to add weight to the theory.

Loop quantum gravity is less well developed but takes a very different approach. In this theory it is not only matter that can be split down to atoms. Space itself, even with no matter present, is atomic. Some of the properties of these atoms of space can best be described mathematically using an extended, one-dimensional loop, hence the term "loop quantum gravity." Once more the math is ferocious, with space constructed from a latticework weave of one-dimensional components; like string theory, loop quantum gravity has yet to make a useful prediction that can be tested.

Although both theories attempt to explain the nature of space, time and the universe, they have emerged from totally different directions. String theory was developed by combining the way particles and forces are described, making use of the powerful influence that symmetry holds in basic physics and regarding space-time as a given. Loop quantum gravity stems from an analysis of the geometry of the universe, building everything, including space-time itself, from scratch.

These two theories, string and loop quantum gravity, produce fundamentally different views of the universe's origins. The existing theory about the big bang (and about black holes) involves singularities—points of collapse where standard physical measures like density become infinite, causing the equations to break down. String theory offers mechanisms to get around the singularity problem of the big bang: Physicists Paul Steinhardt and Neil Turok have proposed an "ekpyrotic" model,...

The biggest benefit of loop quantum gravity is that it doesn't involve these singularities and infinities. It predicts a quantum effect where the gravitational force becomes repulsive in the conditions around the big bang, producing a "big bounce" before a singularity can form. If this were the case, it would be possible in principle for some information to pass through this bounce from a previous incarnation of the universe. Loop quantum gravity offers the tantalizing possibility of a prehistory of everything.

...There is no doubt that Mr. Bojowald will leave many casualties by the roadside—but those who persevere will find undoubted insights into one possible explanation of the universe at its most fundamental and will experience the work of top-level science as close to first-hand as is humanly possible for a nonscientist.
==endquote==

Another favorable review appeared in the Columbus Dispatch:
http://www.dispatch.com/live/content/arts/stories/2010/11/28/back-to-the-future.html?sid=101 [Broken]

So far, in this thread, maybe the most intriguing comment to come up was this by Atyy:

...
Barrett, Freidel, Livine, Oriti are all pulling in a different direction from Rovelli.
Would you like to explain more what you have in mind? In what sense are BFL&O at odds with R?

Are their directions differing trivially like by 5 or 10 degrees? Or are their directions opposed, like 180 degrees off?
 
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  • #11
atyy
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180. Rovelli is going for gravity+matter, the others are going for unification. (Just a guess, of course).
 
  • #12
tom.stoer
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I bought a copy of Bojowald's new popular-level book ... Once Before Time ... It was a big disappointment.
I bought the book already some time ago when it was published in German. I had some e-mail conversations with Martin and I am very much impressed about the "almost physical results" regarding black holes, bing bounce, inflation, CMB etc. that emerged from his (and of course Ashtekar's) LQC. But I have to admit that bcrowell is unfortunately right, I was disappointed, too.

The problem with the book is that it has not so much to say (or that is has not much to say which hasn't been said elsewhere). Bojowald's LQC is fine for one chapter or two, but unfortunately not for a whole book. So there should be a concept for the book far beyond LGC. Unfortunately such a concept is missing.

Compared to writers like Hawking, Smolin, Greene et al. Bojowald is more modest and objective; he is less focussed on in-house advertising. So on the one hand encouraging, other hand, it makes the book a bit bland.
 
  • #13
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Here's my scathing review: http://www.goodreads.com/review/show/132016329

Bojowald argues for a cyclic model because Inflation contains a singularity.
He argues correctly that this requires a real theory of quantum gravity, since the singularity unacceptable.
While this is surely true, he leap frogs from to a conclusion that any better model MUST be cyclic.
That makes no sense.

He also seems very confused about entropy.
He says that the early universe need not have had low entropy.
So his argument goes, gravity is responsible for the low entropy of stars, galaxies, etc.
But he's excluding gravity from his analysis of macro-states, which is a mistake.
Gravity is there, so we'd expect a universe fully of clumps.
The early universe, being free of clumps, is in an unexpected macro-state indeed.

My other complaint with the book is that Bojowald wastes the readers time with mysticism, myth, and other such mumbo-jumbo.
It's plain disrespectful!
 

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