Hiatus and open thread

I'll be too busy for writing substantial posts during the following two weeks. I may break the rule to post some short notice or other. but major blogging won't return until sometime around June 7th.

Readers, especially those who come regularly but do not comment, are invited to use the comment thread for identifying themselves, saying what they find interesting about this blog, and/or discussing whatever subjects they want to.

Recent Book Buying

Taking advantadge of a "buy 3 for the price of 2" offer at the university bookshop, I have enlarged my book collection by the following six books for the price of four (which was £35). I have read so far the first two of them.


1) Jared Diamond, Collapse. By the author of the best science book I read in 2005, Guns, Germs and Steel, comes this exploration of how and why human societies meet or avoid enviromental collapse. From lots of interesting examples from little-known bits of history (like the Norse settlers in Greenland, the civilization of Easter Island, or the causes leading to the Rwanda genocide) Diamond attempts to derive lessons for our present and future. Not as excellent as GG&S, but still a highly recommended read.

2) Sophia McDougall, Romanitas. How would the world be like today if the Roman empire had not fell? This novel explores this question, presenting a Rome that rules half of the world (with only Japan as a rival superpower) and that combines present-day technology with institutions like slavery and crucifixion. The concept is fascinating, but unfortunately the book spends too little time exploring the society, history, philosophy, etc. of this Roman Empire and presents instead a formulaic thriller about a murder conspiracy that forces the imperial heir to run away and hide with escaped slaves. The plot does not fail to be gripping after some slowness of pace in the opening, but the premise could have been used for something much better.

3) Susanna Clarke, Jonathan Strange and Mr Norrell. A fantasy set in a sort of 19th century Britain in which magic is real. I bought it reasoning that a book to which a Crooked Timber seminar was dedicated cannot fail to be good.

4) Richard Dawkins, The Ancestor's Tale. Dawkins telling the complete and detailed evolutionary story that lead from the origin of life to us? Surely unmissable.

5) Philip Pullman, The Subtle Knife and The Amber Spyglass. When I read Northern Lights a few years ago I was not overly impressed by it. But afterwards I read so much praise for Pullman's trilogy that I gave its first volume a second chance some months ago, and found it more interesting. Interesting enough to buy these other two volumes to see how the parallel universes concept and the anti-religious implications ara developed. Having read C.S. Lewis' Narnia books last year and knowing that Pullman intended to write a sort of atheist response to Narnia was an important factor that added to my curiosity.

Alejandro’s First Law of Blogging

…says that, when there are no thoughts to fill up a post, links take the place of thoughts:


Peter Woit’s post on the priority for the Landscape concept has spawned a fascinating thread which has currently reached its 118th comment. Among the (luckly fewer than usual) crackpot comments, one finds there a deeply technical discussion between Bert Schroer and Urs Schreiber about CFTs and the Maldacena conjecture; a discussion between Lee Smolin and some string theorists on the sociological problems for doing research in non-string theory quantum gravity, and an amusingly childish discussion between Peter and Lubos Motl as to whose blog is read by more academic physicists. By the way, I should thank Peter for putting a link to my "Landscape Chat" post in an update; it has provoked the highest spike in my sitemeter since I started the blog.

John Baez's This Week's Finds, edition 232, explains in a lucid way the wonders of 2+1 gravity coupled to particles, after showing some really cool (in every sense) pictures of neutrino detectors in the South Pole.

José Antonio Ortega Ruiz has a nice collection of links on how to write physics papers.

PZ Myers smacks down a Jewish rabbi who is making a particulary idiotic version of the already by itself idiotic argument that atheists cannot provide a basis for morality in the way religion can. Differences due to upbringing and cultural identification: when I see Chistians acting like bigoted fools, I feel amused if they are powerless and scared if they have power; but when I see Jews acting like bigoted fools, I feel sad.

Richard of Philosophy, et cetera gets into a quarrel with Timothy of Positive Liberty over whether government taxation violates the right to private property. (Round 1, round 2, round 3, round 4.) I am squarely on Richard side’s here: no, it does not. Fortunately I don’t need to make a post arguing in detail why the idea of property as a “fundamental natural right” (or in general the idea of “fundamental natural rights”) is flawed, as Richard has already written a couple of excellent posts explaining it, and of course much better than I could have done.

Actually, I admire so much Richard’s general philosophical acuteness that it saddens me to see him accepting Chalmers’ zombie argument for dualism. I have tried to convince him of his error in the comments to this post, but with little success. We all have our particular blind spots…

This was a couple of weeks ago, but I missed linking to it: the latest historical sporking, this time of the film Spartacus. Not as funny as the previous one, but still worth reading.

My nonintelligent friend, a recent newcomer to the blogger community, has started a singular discussion on how to translate into English a well-known quip in vulgar Spanish relating shortness to sexual endowment.

Science and Religion Redux

Recently there has been quite a lot of discussion around the blogosphere (or at least around the corners of it I visit) about the demarcation or overlapping of science and religion. See Ed Brayton at Dispatches, Tim Sandefur, Jason Kuznicki and again Sandefur at Positive Liberty, and Brandon at Siris.

The issue is of course largely semantic, on what should we understand by "religion". Provisionally we can define as a religious doctrine any one that includes reference to a supernatural realm. (While this may leave out some forms of religion, for example pantheistic ones, it probably reflects quite well the ordinary Western use of the term). It is clear then that a religious claim will always have a metaphysical element, but also that it need not be purely metaphysical. Some religious statements are so (e.g. "God exists"), while some have in addition an ethical content ("Pride is a sin against God") or an empirical content ("God created the world in six days").

Stephen Jay Gould introduced the concept of NOMA (Nonoverlapping Magisteria) for the idea that proper religious claims should not address empirical matters. (The original article can be read here). This seems at first glance to make a nice division, that many people in our cultural climate would endorse: the empirical and testable goes to science, the metaphysical and ethical to religion. But things can't be so simple.

To start with, a way of using NOMA which one sees often, especially by religious people (for example in the context of bioethics), is along the lines of "Science can tell us how to do something, but only religion can tell us if we should do it". The fallacy of the binary division is clear here: it is true that science cannot answer ethical questions, but there is no reason to think that only religion can do so (as opposed to nonreligious ethical philosophy, or even unsystematized moral feelings). The situation is not symmetrical: there is every reason to trust the scientist more than the priest on the question of how a given contraception technique works, but there is no solid reason to trust the priest more than the scientist, the philosopher or the man of the street on the question of whether to use it is moral. This, however, could be said to be a mistake in popular use of NOMA rather than in the principle itself, which should state only that "religion does not deal with empirical matters, only with metaphysical or ethical ones" without saying that only religion can make ethical pronouncements (or metaphysical; there is nonreligious metaphysics, after all).

Another criticism of NOMA, that Jason makes in his post, it that it can be seen as commiting the No True Scotsman fallacy. One can imagine the defender of NOMA, when confronted with a creationist who makes lots of empirical claims based on his religion (about the young age of the Earth, the Flood, etc.), answering: "Your position is not really religious, because true religion is not concerned with empirical matters". This would seem to be a cheap redefinition that goes not only against the popular use of the term, as stated at the beginning of this post, but also against the creationist own subjective religious conviction.

However, Brandon in his post defends NOMA against this charge (though critizizing other aspects of it) saying that what NOMA aims at is clarifying a conceptual confusion. Perhaps in popular use the term "religion" applies to some empirical doctrines; but if we are convinced that there is a deep divergence between empirical and nonempirical claims, and that only science has authority to make the first ones, and that the core and fundamental elements of religion are not empirical, then the NOMA move would not be a cheap redefinition but one that aims at clearing a conceptual confusion and making for a more organized intellectual panorama.

But how true is it that the fundamental elements of religion are not empirical? I would like to think it is true, as it would eliminate all possible conflict between science and religion, and I think it is true of a pure, idealized form of religion. But there is hardly any real-world religious tradition for which this is true. Take Chistianity for example; surely a core element of it is the claim that a man called Jesus lived 2000 years ago, was crucified, and resurrected. What if we found convincing historical evidence that Jesus never existed, or that he existed but did not die in the cross? While I don't think it is likely that this will happen (unlike, for the latter example, the many amazingly guillible people who are taking seriously The Da Vinci Code) it is surely an empirical question to be decided in principle by science. (Even the resurrection is: concievably we could find Jesus' tomb with his remains still there, disproving a literal bodily resurrection.) What about the idea of an inmaterial soul? Suppose science comes to give a complete and convincing explanation of human consciousness that does not involve the spirit; wouldn’t that force a serious reconsideration of some core religious doctrines?

So, while I sympathize with NOMA as stating an ideal for religion, I think it stands in too large contradiction with our central concrete examples of religion to be "true", even in the way Brandon suggests. Insisting on it could be a useful move for making religion evolve in a good direction, but not a clarification of a minor conceptual confusion that does not affect fundamental religious tenets.

My ideal of religion would be one that had only purely trascendental and ethical doctrines, basing them on faith but claiming no rational authority, and tolerating other religious and nonreligious (for example philosophical) views on its subject. Its function would be to provide a way for people to give meaning to their lifes in a trascendental context for those who need to. I personally would not adhere to it; I am too much of a rationalist to be able to just have faith in a non-rationally based idea, and I don’t feel the need of a trascendental meaning for my life. But I would have no quarrel at all with those who embraced it, and could even view them with sympathy.

Sadly, this kind of religion is quite far away from those that have the spotlight in the real world.

Landscape chat

A couple of days ago I met in MSN an old friend from the University of Buenos Aires who is doing his PhD in America, in an area of physics unrelated to string theory or quantum gravity. He asked me for my opinions on the anthropic landscape controversy, and we got into a lively discussion about that. I thought of writing my opinions as a serious post, but finally I decided it would be of interest to quote the relevant part of the raw conversation we had, only translated into English and with a few personal things and jokes edited out. So what follows is NOT a summary of my considered, carefully thought and argued opinions on string theory and the anthropic principle, but rather a verbatim record of an informal chat conversation full of vague, spontaneous, half-baked and imprecise ideas… which will probably be more fun to read.

Friend: what is your position with respect to the concept of “landscape” in string theory?

Alejandro: well, it is clearly a blow to the ambitions some had in ST of attaining a unique possible theory to recover the standard model, but I don’t see it as something that necessarily transforms it into a pseudoscience unconnected with reality, as some extremists say

A: it is more like transforming string theory into something more similar to quantum field theory… a general language in which many “theories” can be written and relations between them be found

F: hmmmm

A: there is still no proof that it has anything to do with the real world, but all theories of quantum gravity are alike in that… and though I have more instinctive simpathy for loop quantum gravity, I must admit that sting theory gives a more solid impression.

F: so?

A: so, I dunno

F: hahahahaha

A: what are people saying in your university?

F: there are people that are betting on the concept of landscape

F: others are completely against
F: there’s quite a fight over that

A: what I think creates more polemic is not the landscape itself but applying to it the anthopic principle

A: that does seem a bit phony to me

A: it may be true that the vacuum in which we live is selected anthropically, but it is not a scientific approach to argue in that way. The anthropic principle requires the assumption that there exist other universes with other vacuum states (that is, that the landscape is a real landscape of existing universes, not only of mathematical solutions to the theory)

F: but why do you think it’s phony?

A: and as the existence of other universes is as unknowable as God’s, to say “the universe is at it is because of anthropic selection” is like saying it is so because of divine creation… both may be true, but they are untestable

F: and so?

A: it may be true, but it is not a part of science, or at least I don’t see how it can be made into one at the moment

A: that doesn’t imply that no testable predictions may come out of string theory… only not by that kind of reasoning

F: I dunno… What it seems to me is that if one accepts the anthropic principle then it ceases to make sense to look for a fundamental explanation of why the universe is as it is and I think that has a huge impact on science

F: I agree that it is not something testable, but that is not important

A: you mean, at a philosophical level, what would it imply if it was true

A: but I don’t know if it is such a big deal

A: it would imply that very basic features of the universe, like the particle spectrum of the standard model, or perhaps the number of dimensions, don’t have anything deep justifying them, allright

A: but from the point of view of sting theory, assuming it to be correct, it could be said that those features precisely cesase to be the really “fundamental” ones that we must understand. The really fundamental features could be those included in string theory itself, beyond its low energy solutions

A: analogy: perhaps a pre-Darwinist biologist tried to find a fundamental explanation to why we have 5 fingers… And now perhaps we say that there is no fundamental explanation, simply the first creature that developed fingers millions of years ago happened to develop 5 instead of 4 or 6, just by chance…

A: but that does not prevent us from having a fundamental explanation of life in terms of genetics and DNA

A: I don’t know if it’s a good analogy, but do you get my idea?

F: yes I do, and I think precisely that is the important thing, that it makes no sense to try to understand why we have five fingers!

F: it says that there are things that it makes no sense to try to understand why they are as they are

F: one could regroup considerably the scientific effort!

A: but precisely, it changes the focus so now that no longer seems to be a fundamental thing… but there are other things that are indeed fundamental and understandable… isn’t that enough for you?

A: did you want to understand eveything everything everything?

F: no, but it seems to me that some people lose perspective of what it is worthy to try to understand and what not

F: and having a theoretical limit may be helpful to use better the efforts

A: (warning, all what I said is assuming string theory, the landscape and the anthropic principle to be correct, things I don’t accept at all to be certain. I’m playing a bit devil’s advocate here)

F: I agree completely with you there

F: but for now string theory seems the only alternative

F: lqg is in much worse shape it seems to me

F: until recently some people were convinced that it was worth to try to find a theory of everything

F: the anthropic principle would allow those efforts to be better used

A: lqg has some deep problems to be solved yet, but it is making progress… I still have hopes in it

F: ok, but maybe it turns out to have the same problem

A: the point is that it is less ambitious… it never tried to be a theory of everything

A: strings was sold as a theory of everything, and now they are discovering that they almost certainly cannot be one

A: unless it redefines what is understood by a theory of everything, as you say

F: dunno… I think that all this anthropic principle business, whether or not it was necessary, is provoking a pause that seems needed to me

F: the strange thig is that it puts man in the center again, we are back to Copernicus!

F: but in a slightly different way

A: it seems to me that despite its name the anthropic universe is more de-centralizing of man… it implies that there are millions of alternative universes and that we are simply in the only one in which we can be

A: the formulations of it as saying “the universe is as it is because we exist” are tricky, I think

F: sure, but they are not necessarily invalid

F: just like the aesthetic concepts are not necessarily valid within physics

A: my personal suspicion, is that there is a huge amount of physics we still don’t understand (like, what we know is just the tip of the iceberg) and so that to realte the physics we are starting to understand just now (like string theory, if it turns out to be correct) to fundamental conclusions about a Theory of Everything or an anthropic explanation by chance of everything will turn out presumptuous

A: I don’t think we have came to the point in which physics can start giving us answers to those fundamental questions

F: I agree completely!

F: but there are many that think (or thought) differently!

F: and that is why the emergence of the anthropic principle is refreshing

F: that is the only advantage I see to it

A: I dunno… I think it may be falling in the sme mistake in a different way

F: what do you mean?

A: like, replacing an explanation of everything from a unique theory, by an explanation of everything by chance

F: wait, I’m not saying that the anthropic principle is correct, I’m saying that the fact that it is considered and discussed implies that people are revising their ideas and they will not dream on reaching the final theory of whatever…

A: yes, well, maybe in that sense it is ok

F: it is something that seems so irrational and yet came out of something so rational that it must make you think there is something beyond worth looking for

F: so… whatever

A: whatever

Book Review: Colleen McCullough, The Song of Troy

You may be surprised at me dedicating a lengthy book review to a work of an author mostly known by a melodramatic uber-bestseller about a forbidden love involving a Catholic priest. While I don’t care too much for The Thorn Birds (although it made for a passable holiday reading once) I absolutely love Colleen McCullough's more recent series of Roman historical novels, collectively called Masters of Rome. That prompted me to buy and read this other historical novel of hers.

The Masters of Rome novels are set in the last decades of the Republic, the age of Caesar and Cicero, a time that I have always found fascinating. My interest was probably born from reading a juvenile biography of Caesar as a child, grew in my teens when I discovered Steven Saylor’s Roma Sub Rosa historical mysteries and developed further with Rex Warner’s excellent novelized biography of Caesar. So when some years ago I discovered by chance at a secondhand bookshop the second title of the Masters of Rome series, I found it to be what I had always dreamt of reading, and I eagarly searched for the other titles till I had read them all. These novels are epic in scope and detail, being each almost one thousand pages long and including lengthy glossaries. They are carefully researched and use practically every piece of information we have about the people of that age, but give life to the characters as no history textbook could. Perhaps their only fault is that the portrait of Caesar, who dominates the story in the last three books, shows him as too flawless and perfect in some respects. But the richness and realism with which the other figures (Marius, Sulla, Cicero, Pompeius, Brutus, and dozens of others) are described, and the powerful progression of political and military conflicts that eventually destroy the Republic, more than compensate for it. The Wikipedia article linked above says McCullough is writing a seventh book to conclude the series. I pray it comes out soon.

Taking a rest from the Roman Novels, she published in 1998 the book I am reviewing now, a novelization of the Troyan War which I have read last week. Giving such an epic subject, I was expecting something with the scale of the Roman series. But I was disappointed in that expectation; the book is less than 500 pages long, and as it tries to tell the whole story starting from the birth of Paris, it inevitably goes a pretty fast pace. In the Roman novels we may have sometimes dozens of pages devoted to a single battle or Senate meeting; here some stories (like Odysseus trying to feign madness to avoid going to the war) are introduced and finished with in three or four pages. This is the first problem with the book: it is at least half too short of what it should be to give the characters and the story the depth they deserve. Of course, not everyone likes 1000-pages long books, and I might be judging only by contrast with the Roman books; so let’s move on.

The story is told from multiple points of view, with successive chapters narrated by Achilles, Odysseus, Agamemnon, Helen, Brise, Hektor, Priam and others. I didn’t like too much this constantly shifting point of view because the characters don't have time to develope a personality beyond some simple basic traits: Odysseus = clever and amoral, Helen = spoiled and sensuous, and so on.

I want to comment on something that made me reflect while and after reading the book: the choices made by the author with regard to the gods and other “mythical” aspects of the story. Deciding on how seriously to take them is a crucial question for someone writing an historical novel based on Greek mythology (or the Bible, for that matter). On one extreme, one could simply include the gods and supernatural events as completely real within the story, just as Homer does; the problem with this is that for a modern reader it could work as Tolkien-esque fantasy, but never as historical novel. It would be a different kind of story, not situated on a real date of the historical past. On the other extreme one could exclude all supernatural aspects of the story and leave only the human ones, rationalizing or directly eliminating from the story all mythical elements; this is perhaps the easiest approach, and it was used in the recent Hollywood movie Troy, which as far as I remember did not include the supernatural at all. An intermediate path, difficult but rewarding if well done, is to create a sort of magical realism athmosphere where the Gods are “felt” as real, and events like fulfilled prophecies and true oracles are common, but the gods do not appear in person and there are no events that are clearly and explicitly supernatural. The reader can then still read the story as historical fiction –but set in a time where mythos seems really true in some sense. Robert Graves was a master of this form, applying it to the Argonauts story (The Golden Fleece) and the Gospels story (King Jesus). Only that the mythology alive in the background of these novels was not any historically accurate one but his own personally created myth of the White Goddess.

But I am digressing, and a discussion Graves’ fascinating and bizarre poetic mythology will have to be left for another post. The point I was arriving to is that McCullough seems to vacillate between the no-nonsense realistic approach and the magical realism one. Oracles and prophecies abound in her book and are always truthful, but the characters act motivated by purely human and worldy causes, and many mythical themes receive explicit mundane rationalizations (e.g. it is said that someone who claims to have a God as father is usually a bastard). This makes the mythical components left in the story seem somehow unreal and fake. Given the amount of rationalizations there are, I was surprised at seeing at the end that the Trojan Horse was kept in the story. In fact, the global traditional plotline is followed pretty accurately -with one major exception. (Spoiler ahead!)

McCullough chooses to describe the quarrel between Agamemnon and Achilles over Brise and the consequent wrath of Achilles deserting the army as just a ruse, a clever plot designed by Odysseus with the connivence of Agamemnon and Achilles. The point is to make the Trojans confident at seeing discord inside the Greek camp, go out of the city and engage the Greeks in battle, so Achilles can suddenly turn back into combat and defeat them. It seemed to me here that McCullough was trying to be too clever by half; it is an original idea but quite contrived and unbelievable, and makes key aspects of the story farcical.

On the other hand, I don’t want to sound too disparaging of the book: the tale is really captivating, and honestly I had difficulty in putting down the book before I had finished it. So perhaps I have been criticizing it to strongly for what it deserves; as a minor historical novel with less aspirations than the Masters of Rome series it does a good job. But overall, I would be much more happy if Ms. McCullough had dedicated the time spent writing The Song of Troy to write instead half of an extra Roman novel.

Best. Paper. Ever.

Here.

Well, perhaps "paper" should be replaced with "undergrad lab report" and "best" should be replaced with "most honest". Or with "funniest". It certainly beats in the last category the report I wrote seven years ago for my first lab course, which I titled "Indiana Joules: Raiders of the Lost Energy". (I swear I'm not making this up. Throw your rotten tomatoes if you want.)

HT: Pharyngula.

Reviewing Quantum Gravity

Last week two leading researchers of the LQG community published papers that review the state of the field from different perspectives and with a different focus:

Abhay Ashtekar: Gravity, Geometry and the Quantum

Lee Smolin: Generic predictions of quantum theories of gravity

Marcus has asked me to make a comment on the second of them, but I will include also the first because it will enable me to sneak in a question that has puzzled me for a while about the results in singularity resolution within Loop Quantum Cosmology. I should start by saying that I am no expert in LQG, not even in the measure a graduate student working directly in it would be; I work in quantum field theory in curved spacetime, not quantum gravity proper. True, I am a member of a research group with an important LQG component, and I have a great interest in the developments made in the theory; but I have not studied it “seriously” (which means: beyond reading several review articles and Rovelli’s Quantum Gravity textbook without following the more technical parts of the math, and assisting to several seminars and to the Loops 05 conference). So my comment on these papers can’t be an “informed critical comment”; it will be more like a “summary plus personal subjective impressions and questions”. I’m not sure if that is what Marcus wanted, but it’s the best I can make. I hope that people with more knowledge than me will jump in and correct any mistakes.

OK, no more disclaimers. Smolin’s paper is focused on generic predictions from background independent quantum theories of spacetime. It starts listing four assumptions these theories are based on: quantum mechanics, background independence (partial, because some structures like dimension and topology may be fixed), discreteness and causality. And here comes my first question: I thought one of the main selling points of LQG was that the discreteness of spacetime is not an assumption of the theory but a natural consequence of a background independent quantization of grvity. In fact, when Smolin lists the theories he has in mind he includes causal sets, dynamical triangulations and consistent discretization models, but not canonical loop quantum gravity proper. The formal description of the theories made later, however, seems appropiate only for the latter, describing Wilson loops, spin networks, and so on. If these feature in causal sets or CDT models, I was not aware of it.

Likewise, the “well studied generic consequences” discussed in Section 3 are three results classically associated with canonical LQG: ultraviolet finiteness due to discreteness, elimination of spacetime singularities (these are discussed at much more length in Ashtekar’s paper) and horizon entropy. I am surprised that Smolin seems to regard the last of these as a settled matter, with the “correct” way of doing the calculation already known as being the one that gives the same Immirizi parameter implied by classical quasinormal modes. That is not the impression I obtained from a seminar we had a couple of months ago. A fourth generic consequence, of which I was not aware of previously, seems to be a natural role for the cosmological constant in the theory; the description of this is intriguing but too sketchy for me to follow, so I guess I’ll have to llok at the 59-pages long referenced paper.

Section 4 mentions briefly the results in recovering a classical spacetime for long distances: Rovelli’s “gravitons from LQG” calculation, Freidel and Levine’s result of DSR as flat limit of 2+1 QG, Loll et al.’s results on the large distance limit of CDTs with 3+1 emergent dimensions, and work using noiseless subsystems techniques. Section 5 is on “Possible new generic consequences”, which are more speculative than those in previous sections. The first is DSR (doubly or deformed special relativity) as classical limit of QG in 3+1 dimensions. Smolin mentions possible experimantal tests of this idea, but downplays a bit what are (in my impression) large technical and conceptual problems to understand fully what DSR means, let alone what it predicts. Next come Smolin’s pet speculation on matter as emergent from geometry (ridiculed by Lubos here; I as a rule take with suspicion anything Lubos says outside from technical areas of string theory, but in this case it does seem to me that, at the least, Smolin’s idea needs quite a lot of more hard working on until we can say that matter as we know it can arise from geometry). Follows a discussion on disordered locality, which excites Smolin becase he hopes it may explain puzzles like dark matter (via some MOND-like model) and the Pioneer anomaly, as he explained in a Loops 05 talk. This seems very optimistic to me; intuitively I would expect non-local effects, if they persist at low energies, to mess up the theory and perhaps make it inconsistent with our present well tested low-energy local physics, instead of magically creating exactly the kind of effect that accounts for the few anomalies we presently cannot explain. Surely, a lot of more work needs to be done here. Finally there is a simple calculation attempting to relate disordered locality to the cosmological power spectrum.

In general, the impression I have is that all the “generic predictions” Smolin discusses in section 5 are at this stage more speculations than predictions, even tentative ones. The strongest generic results of the LQG program seem to me the discretization of spacetime giving finitenesss to the theory and the resolution of singularities. This last issue brings us to Ashetekar’s paper.

This paper starts with a brief revision fo the formal structure of LQG, and then applies it to homogeneous and isotropical cosmology. In Loop Quantum Cosmology, the spacetime is first assumed to have the usual symmetries so there is effectively only one degree of freedom (the scale factor) and then this variable is quantized following an analogous procedure as the degrees of freedom in the compelte theory. One might of course question whether the operations of quantizing and imposing symmetry “commute”, so the results found this way would be preserved for cosmology in the full theory; but leaving that aside, the results found in LQC are indeed impressive. Starting with a semiclassical state approaching a Friedmann clasical solution at late times, with a scalar field added as a non-geometrical degree of freedom, and evolve it backwards towards the Big Bang. What you find is that the matter density increases until reaching approximately 2.5 times the Plack density, and then it bounces and starts to decrease again, approaching another classical (collapsing) universe in the distant past. The singularity is avoided by the effect, at Planckian distances, of what Ashtekar calls an effective repulsive gravitational force arising from the quantisation of the geometry, akin to the effective repulsion between fermions arising from the Pauli principle.

This result is without a doubt important and exciting, especially because similar effects may resolve black hole singularities as well. However, the idea that a bounce from the collapse of a previous classical universe is a realistic scenario for “what happened before the Big Bang” is one that creates a host of problems in my opinion. First, our universe is known to be in an accelerated expansion that will not recollapse to a Big Crunch, quite the opposite; then why did the previous universe collapse? To postulate as "cosmic initial condition" a large classical universe collapsing seems even stranger than a singularity to me. Leaving aside this quasi-metaphysical worry, I see a serious potential problem in the second law of thermodynamics. A realistic collapsing universe would almost certainly be increasing its entropy to a maximum, ending in a very "messy" state with lots of black holes; not the kind of smooth, low entropy state we have at the beginning of our universe. Of course the calculations Ashtekar presents can't address these problems because they restrict to a case with imposed homogeneity. I would be surprised if the apparent mirror symmetry between the collapsing and the expanding phase persists when anisotropy is allowed, as this would seem to be against the Second Law. (You would be right in presuming that my worries about time asymmetry and the low-entropy beginning of the universe were spawned by reading Penrose; see this Physics Musings recent post). A similar question arises if black hole singularities are resolved with a similar bounce: does the black hole transform into a white hole after passing through the Planckian regime? But don't white holes violate the Second Law?

In summary, the elimination of singularities thanks to the loop quantization seems compelling, but the bouncing mechanism puzzles me because in a realistic scenario I don't see how to reconciliate it with the Second Law. Any ideas?

New Links

Three new links are welcome to my blogroll today: Jose Antonio Ortega Ruiz's Physics Musings (reflections on physics gravitational, quantum gravitational, philosophy of, and other) Jessica Henig's Bee Policy (miscellaneous science-related content) and Steve Esser's Guide to Reality (philosphy, mostly of physics and of consciousness).

Via the first of them I also found R.F. Streater's homepage, with a huge collection of physics links. Don't miss his contentious list of lost causes in theoretical physics. And, to continue the physics linkage, you should check Warren Siegel's homepage, which is full of interesting stuff, both serious and fun; not least in the last category is The Official String Blog (featuring comments by "Wrought" and "Bottle"!)

The BAFICI Chronicles

Following my relentless policy of publicizing my friends' blogs, I suggest anyone who reads Spanish and is interested in cinema to go and read the 12-post chronicle my suspicious friend has wrote on the Buenos Aires International Independent Film Festival.

Monkeys on Typewriters!

You probably have all heard once or another the statement that an large number of monkeys typing randomly would eventually write the complete works of Shakespeare. Yesterday for some reason I started wondering about the origin of this statement; I had a vague idea that it was Arthur Stanley Eddington. Looking into Wikipedia, however, I found out that the original quote is from Emile Borel. Eddington repeated the image a few years later and probably contributed to its popularity, although he used "all the books in the British Museum" instead of the works of Shakespeare.

But I wouldn't be writing this post if I hadn't found something more interesting at the Wikipedia article -the experiment has been actually tried! In 2003, at the Paignton Zoo in England. The results after one month of leaving a computer inside the monkeys' cage were not encouraging:

At first, said Phillips, "the lead male got a stone and started bashing the hell out of it.

"Another thing they were interested in was in defecating and urinating all over the keyboard," added Phillips, who runs the university's Institute of Digital Arts and Technologies.

Eventually, monkeys Elmo, Gum, Heather, Holly, Mistletoe and Rowan produced five pages of text, composed primarily of the letter S.

If anything, this proves that 1 Month is much less than Infinity. Perhaps with some more time they would have reached the level of It was the blurst of times....".

You can read the PDF for the full text created by the monkeys here. Photos of the authors are included

Books!

First, I apologize for the lack of posting in the past few days. Attribute it to a combination of unusual blog laziness and the usual connection problems to login to Blogger from home.

In the time that pondering the response of particle detectors in de Sitter space leaves me, I have been reading several books which deserve a notice here:

1) Daniel Dennett, Content and Consciousness.

Writing last week's post on Chalmers and Dennett left me with a strange urge to read this book, Dennett's first published one and the only one I had not read before, excluding his latests Breaking the Spell and Sweet Dreams. So I got it from the university library. It is a less easy, smooth read than his later works –its origin out of a Ph.D. thesis is visible- and some parts of the discussion seem outdated. But it is interesting as foreshadowing the major themes in his future works, and the first chapter, on ontological commitments of mental discourse, makes his position on some fundamental questions more clear and understandable than any more recent statements, while at the same time highlighting both the similarities and the differences with the Rylean approach to philosophy of mind. Dennett compares talk of minds with talk of voices; sentences about voices like "Smith had a high-pitched voice which he has lost, but fortunately it is kept in tapes" cannot be translated into physicalistic language in a way that identifies any physical entity, process or set thereof as "the voice" -and yet we are happy with saying both that voices exist, and that they are not misterious entities which are "left out" of a physicalistic description like Cartesian souls would be. So far this is very much like Ryle on minds, and –I think- also like the most recent version of Putnam with its conceptual relativity + "natural realism". But Dennett adds a twist: in his opinion this peaceful coexistence of body-talk and mind-talk can only go on if we acknowledge that "strictly speaking" it is body talk which is fundamental, and mind-talk is "not referential"; otherwise we would be led inevitably to absurd (from a Rylean standpoint) sentences as "both the body and the mind exist". This is putting Quine on top of Ryle, so to say. It privileges the conceptual frame that integrates with the rest of science in a continuous web as the "true" one, while the other ones are left as being "true with a grain of salt" as Dennett puts it in The Intentional Stance. It is interesting that perhaps Dennett and (the present) Putnam may hold views substantially very similar in philosophy of mind, and seem to say very different things due to a metaphilosophical disgreement: Dennett assumes that the paradigm of true discourse is physical science, while Putnam does not want to privilege one kind of discourse in such a way. It is only this difference what makes Dennett a "materialist" and Putnam not one. The disagreement between Dennett and Chalmers, as we saw, is also ultimately metaphilosophical though in a different way. (I am using "metaphilosophical" as short for "meta-philosophy of mind")


2) Susan Haack, Manifiesto of a Passionate Moderate.

I saw this book on a shelf of the library while I was searching for Dennett’s and borrowed it seduced by the lovely title. It consists in essays against relativistic tendencies in philosophy –the main target being Richard Rorty. Haack describes herself as a pragmatist in Pierce’s tradition, and claims that Rorty's philosophy with its disregard for truth, "pure inquiry", and related concepts is a perversion of Pierce’s insights. There is a deliciously funny "dialogue" between Rorty and Pierce built up entirely with quotes from them, which shows how diametrically opposite are their views on most philosophical subjects. Some of Pierce's quotes, such as a refutation of Kuhnianism avant la lettre, are amazingly prescient, or else they show that there is nothing new under the sun. My favourite essay in the book apart from that one is "Reflections on Relativism: From Momentous Tautology to Seductive Contradiction", which explores the possibility and self-consistency of a middle groud between what Putnam calls "metaphysical realism" and "conceptual relativity" –the possibility of what Haack calls an "innocent realism". This is tangle of philosophical problems which fascinate me -see my old post on Social Constructivism- and on which I might write more shortly. The rest of the essays –attacking feminist epistemology, or cultural relativism, for example- are good, common sensical, and mostly not very deep.


3) Isaac Asimov, Foundation's Edge

A change of genre! Asimov's Foundation series was my favourite piece of literature at the age of 15, and this book was my favourite in the whole series. It was also the only one that I didn't buy, reading it from a library instead, and therefore the only one I hadn't reread since that age. Last week I saw it in a book sale for only £1 and I couldn't resist buying it, even knowing that I was going to be disappointed. And I was, of course. The clash between the First and Second Foundations that fascinated my younger self seems now too contrived. There are many loose threads, not only in intertextual references (mentions to robots, Eternals and other Asimovian creations that are not consistent with the rest of the series) but also within the book itself. The depiction of Second Foundationers as human beings with weaknesses and political rivalry is interesting, as is the alternative between three possible futures presented at the end of the book (although, as many have pointed out, the choice made at the end has disturbing political implications, I think that Asimov was innocent of political allegory and was just trying to write a thrilling story). But the two main characters Trevize and Pelorat are among the worst that Asimov ever created, as is the Gaian Bliss that joins them at the end. But at least this book is not just plain bad as its sequel Foundation and Earth, which keeps this three obnoxious characters, throws away all the interesting Galactic politics and Seldon Plan discussions that define a Foundation book, and gives the characters instead the boring task of finding the lost planet Earth. This book is not a sequel fully worthy of the classic Foundation trilogy, but at least it makes an interesting read for those that have read it and are anxious for more.


And now two brief notices also book-related.The first concerns a book I have not read and always have felt ashamed of not having read: Dante's Comedy. Even not having read it, I found this post and discussion about it at The Valve most interesting. The second concerns the first novel I read in my life (at age 6), Robinson Crusoe. The Little Professor has a collection of links about it.