"'Tis well an old age is out, / And time to begin a new"

I thought of putting together a year-in-reading post but was confounded by the apparent length of this year, the sense that events in the psychological far past -- acquisition of Kindle, acquaintance with Cobbett -- really took place this March or April (the Kindle came about Apr. 15, I remember this because when I went home to collect it in the afternoon I found my landlady downstairs and said something about having to file my taxes). And it hasn't been a year that's defined by stuff I've read -- if anything, a year with swaths of mental paralysis cut through it, long intervals of staring at books and not registering a word -- although I discovered Thomas Bernhard [just noticed, and was amused by, his initials being TB] and Teju Cole. (Also: Cobbett, Saintsbury on prose rhythm, Flaubert's Parrot, Vertigo, The Ambassadors, two of Gissing's novels.)

Anyhow, it is a good time for a broader retrospective post, esp. because the year-end coincides with a "natural" break: I have just accepted a postdoc at Harvard, which I'll begin in the fall; while the thesis must still be written, I suppose I'm well into the home stretch. On this front at least, "things have turned out better / than I once expected or ever deserved"; I had multiple good options. Nevertheless, when I think back on the past five years or so the chief impression is one of waste, of time that I could have spent on various kinds of growth but did not, the sense that owing to my laziness I've been coming 

                                              to resemble
The beasts who repeat themselves, or a thing like water
Or stone whose conduct can be predicted,

and that my immediate recourse to these lines -- which I might also have cited for similar reasons five years ago -- is further depressing evidence that they apply to me. But enough of this, it cannot be helped: one is less impressionable than one used to be -- people are -- and attempts to fight this are inherently limited. (One's memory is also less vivid than it used to be: it is appalling to think how little I remember of Proust. What else have I read as a grad student that really sticks in the memory? Lydia Davis, Thomas Browne, Urquhart's Rabelais, Sabbath's Theater, Hollinghurst. Muldoon's recent poetry -- especially this -- and fragments of Geoffrey Hill and Charles Wright. I went through a phase, in 2008 perhaps, when I bought a large amount of contemporary poetry; seems to me now that I only remember the titles of the books. Reading this list, I suspect that one thing I should definitely have read more of is literary criticism and/or philosophy.)

I am glad on the whole that I went to grad school in physics, and a little surprised that I've enjoyed the "work" aspect of it. (I cannot say much in defense of life in central Illinois, though.) I was fortunate to stumble quite blindly into an area -- in a field that I had been drawn to for its difficulty and lack of obvious correspondence with my strengths -- where taste and wide reading mattered as much as analytical ability, and to have an advisor who let me pick my own problems. I was fortunate to pick up the learning on the cheap, by going to talks rather than reading papers -- UIUC being fairly central in my field -- and especially by getting to spend fall 2010 in Santa Barbara where I was deluged with information at workshops and conferences. And I was fortunate, above all, that innumerable things did not go wrong that anyone acquainted with many grad students knows can easily go wrong. (I suppose some of this text will be reused in thesis acknowledgments.)

Which brings us to 2011, which was a strange year. (As a coherent unit it began Dec 18 2010 when I arrived in Chicago without an overcoat.) I had finished the paper that will presumably be most of my thesis in July 2010, and had spent the fall thinking of other things but mostly going to talks and meeting people; meanwhile the advisor decided to move to Atlanta, so when I came back I was in effect in the position of a postdoc without a group. I couldn't at that point have applied for any of the really nice fellowships -- deadlines tend to be Oct/Nov -- so the choices were (a) get a temporary postdoc and apply for fellowships in a year; (b) move to Atlanta; (c) stay on in Urbana and soldier on. Option (c) was the most appealing as it didn't involve moving, but also the most sensible as it turns out: really the imperative was to position myself optimally for the job market this year, and moving/completing thesis were much less useful than getting as much research done and published as I could. (Did not quite meet expectations but didn't fail completely either.) Esp. with the departure of two good friends in the summer and the encroachment on a third of child-rearing duties, I've had a wealth of solitude that I'm afraid I've mostly spent drifting about the internet, tweeting maniacally, and -- esp. in the fall -- inspecting the publication record of everyone who ever got a postdoc I wanted. I do not know if it was the solitude or the anxiety, but I have never had such an infertile year intellectually -- I cannot think of a single good idea.

But that's all over for now, and I can return, I hope, to attacking various things like a shark. I don't know when I'll be defending/moving yet, but it won't be until the summer: long enough to kippleize my surroundings a little further, write two or three papers, fill out some reimbursement forms, and figure out how to format a thesis according to UIUC registrar's specs. For the moment at least, I vaguely look forward to it.

(Previous, similar posts here and here.)

Horse-science

Recent reading has thrown up a cluster of bilaterally related stuff that more thought could perhaps assemble into a complete picture. For now I'll just provide the list.

First, Michael Wood, writing about the future of universities in the LRB:

If we can’t speak the language of our enemies, not only will they not listen to us – they might not listen to us anyway – but they can’t. We need to be saying things they could hear if they would listen. ‘They’, by the way, includes all kinds of people within universities as well as outside them. But what if we can’t speak that language without losing the battle? What if the very language wins the battle by definition? What if we can’t speak of cost-effectiveness because we don’t understand either cost or effect in the way our enemies do?

Amusingly, an article about Michael Polanyi in the same issue suggests what the right language might be:

Michael thought, with few exceptions, that political meddling with a self-organising economy was wrong and destructive. (Nye notes that Michael Polanyi, Hayek and von Mises were all using the notion of ‘spontaneous order’ at that time, and while it has been claimed that Polanyi’s scientifically derived concept had priority, the usage was common in 19th-century European liberal thought.) [...] Scientific research, in its essential nature, is spontaneous, self-directing and self-organising, driven on only by its ‘internal necessities’ [...] Bernal talked of the freedom of necessity, while Polanyi asserted the necessity of freedom. Scientific autonomy had historically been a substantial fact and it had proved its rightness.

In other words, the argument against planning science -- either central or corporate -- is formally the same invisible-hand argument that the right uses to argue against planning the economy, and that "Burkeans" have used for various purposes. (It is trivial to generalize this argument to some aspects of the humanities, certainly the creative arts.) Of course, it would be silly for me to expect anyone on the contemporary right to find this persuasive, but that simply indicates the extent to which ideology is subservient to class warfare in politics (and probably has always been).

The article goes on to describe Polanyi's irrationalist defense of science:

The notion of ‘connoisseurship’ hasn’t often been attached to scientific judgment, but Polanyi repeatedly did just that: ‘Connoisseurship, like skill, can be communicated only by example, not by precept. To become an expert wine-taster, to acquire a knowledge of innumerable different blends of tea or to be trained as a medical diagnostician, you must go through a long course of experience under the guidance of a master.’ And so too to become a scientist.

Science is a vast fiduciary system. Scientists know what they do by finding trustworthy sources and then trusting them. It is also what Polanyi called a polycentric system, in which autonomous and only loosely co-ordinated groups of specialists – mildly sceptical and mainly trusting – periodically keep an eye out for what is going on next door. The coherence and integrity of the body of scientific knowledge arise through these processes of mutual adjustment. Finally, the bases of scientific judgment cannot be completely articulated because the ‘tacit dimension’ is ineliminable. It is not a fly in the formal ointment; it is what makes science science. You would understand that, Polanyi suggested, if you knew what it was to be ‘confronted with the anxious dilemma of a live scientific issue’. The further away you are from the quotidian life of scientific practice, the more you tend to be infatuated with myths of method.

Nye convincingly argues that the major purpose of Polanyi’s anti-rationalist philosophy of science was political and, specifically, that it was meant to counter Communist visions of hierarchical control. The political machinery of Communist planning proceeded through rational and formal method and it presumed rational and formal method in the object of planning. Conceptions of effective method had been devised to celebrate science, but in the middle of the 20th century they were having the unintended consequence of making people think they could command and control scientific inquiry in whatever direction they thought society needed. But you cannot plan and co-ordinate practices that are in their nature self-organising and whose most basic judgments are not formally specifiable. It was not just that a proper understanding of the nature of science was necessary to defend it; a proper understanding of science could contribute to the defence of liberal society as a whole: ‘The world needs science today above all as an example of the good life. Spread out over the planet scientists form even today, though submerged by disaster, the body of a great and good society.’ The fabric of science was political.

(When I hear "the fabric of science" I inevitably think of nylon.)

The bit in bold reminded me instantly of Michael Wood summarizing Auden:

Art can’t redeem the world, and that is why we must be modest about it. But it can show us what redemption would look like, and this is why it matters.

And thence, by a relatively short step, to Auden, in "Streams," writing about the innocent anarchic nature of water, which

    tells of a sort of world, quite other,
  altogether different from this one

with its envies and passports, a polis like that
to which, in the same of scholars everywhere,
   Gaston Paris pledged his allegiance
  as Bismarck's siege-guns came within earshot.

(There is an interesting tension here between the idea of art or science as romantic, spontaneous effusion that is implicit in this line of "spontaneous order" thinking, and the more common idea in Auden that the redemption is hard work, that it is something arrived at by a painful process of discipline. It is hard to think of redemption in non-Arcadian terms. The art/nature contrast and the planning/spontaneity contrast are not quite the same because traditional ways of life or scientific practice, which are spontaneously ordered, quite seamlessly include many very artificially organized activities. Conservatism is on this reading chiefly opposed to glibness -- David Brooks often says or implies this, but of course it is nothing if not glib to conflate this kind of view with the politics of the contemporary right.)

But to return to Polanyi. Shapin doesn't say this but his views on science are reasonably common among theoretical physicists; a good example is Steven Weinberg on scientific beauty in Dreams of a Final Theory:

A physicist who says that a theory is beautiful does not mean quite the same thing that would be meant in saying that a particular painting or a piece of music or poetry is beautiful. It is not merely a personal expression of aesthetic pleasure; it is much closer to what a horse trainer means when he looks at a racehorse and says that it is a beautiful horse. The horse trainer is of course expressing a personal opinion, but it is an opinion about an objective fact [...] that this is the kind of horse that wins races.

And elsewhere, flogging the horse metaphor on PBS:

The horse breeder has seen lots of horses and from experience with horses knows that that's the kind of horse that wins races. [...] So it's an aesthetic sense that's been beaten into us by centuries of interaction with nature.

(Weinberg's thoughts on this topic are stimulating but I disagree with them -- I think a majority of theoretical physicists nowadays would dispute the plausibility of "rigidity" as a criterion -- and I fear that it is ultimately just another example of the depressing trend where very successful people over-generalize from their success.)

I'm not sure how much weight any of these ideas individually bears, but I think they form an interesting strand in the history of 20th century liberalism.

Porcine, peregrine, passerine

(Further adventures in naming and necessity)

1. From the Times archive (1828), a story about "Mr Hogsflesh, the Sapient Pig":

One day last week a man of the name of Hogsflesh, a vender of fish about the streets of Lewes, who, from the singular coincidence of his name and disposition, has obtained the nickname of the Sapient Pig, undertook for a trifling wager to eat a raw rabbit, which he devoured as hungrily as a ploughman would a beef-steak pudding, picking the head and legs in clever style. He is in a short time to eat a cat in the same raw state, for which purpose he has had a tooth drawn, which troubled him when tearing to pieces his raw meal.

2. I was delighted by this term in a PRL that came out today [Bailung et al., PRL 107, 255005 (2011); for solitons see here; cf. peregrine falcons, Peregrine Pickle...]

Peregrine analyzed the [non-linear Schrodinger equation] ... It has been suggested that rogue waves in the ocean are related to what are now called Peregrine solitons. Peregrine solitons have been observed in nonlinear fiber optics experiments [8]. They have also recently been observed in deep water wave experiments performed in a water tank.

3. I was also instantly reminded of Passerine's tanager (more commonly Passerini's but never mind that), a name that borders on tautology (tanagers being by definition passerines). (HT Jenny Davidson.)

4. The Philip Larkin toads trail in Hull (via Calista). It seems to me that there's a crude chiasmus in the fact that Larkin had a toad squatting on him, while Toad of Toad Hall was on a perpetual lark.

Closing tabs

I can scarcely believe I just wasted an entire day reading stuff. "It never rains but pours" I guess...

1. Read Wells Tower's brilliant article about traveling with his dad in Iceland and Greenland. There are no satisfactory options re pagination, but the print version is the least bad. I won't excerpt anything because I can't decide what to, and because you really have no excuse for not reading the whole thing. NB Tower's prose is good but too heavy on obvious special effects. "Under a sky the color of..." appears at least twice, and various natural formations are compared to various kinds of candy, only once to possibly good effect:

Spilling from between a pair of russet crags, the dirty tongue of ice had a roasted look about it, like a charred marshmallow, pallid innards oozing forth.

2. Applied broetry: the Facebook terms of service in bro-speak.

3. Marina Warner on Tracey Emin (LRB). A fine lead-in:

Quilts used to be made from baskets of scraps; old clothes were cut up, the worn and stained bits discarded, the best parts kept for reuse. Every household where a woman lived had such a container – a midden of memories – and when the scraps had become a patchwork quilt, spotting this old dress or that old pair of curtains or that old cushion was part of the pleasure of the bed, a domestic pleasure. The quilt became history, the equivalent of an itinerant storyteller’s painted roll.

4. A nice exhibit on Palladio and his influence in Britain. Architecture is a little outside my usual limits but I have always been fond of Pope's epistle to Burlington on architecture. Exhibit includes some useful information about Burlington and his houses.

5. Fascinating article in Nature News about the search for chimpanzee culture:

Some chimps dance slowly at the beginning of rain showers, others don't; some use long sticks to dig up army ants; others use short sticks. In West Africa, some chimp groups hammer nuts with a stone or a piece of wood to open them. But east of the river Nzo-Sassandra, which cuts across Côte d'Ivoire, only one group has been seen cracking nuts. [...] Deciphering culture in the wild is difficult because researchers must ensure that behavioural differences between groups do not have other causes, such as variation in genetics or environmental conditions. "Why is it all chimps don't do everything? One solution is that there are hidden ecological differences between populations," says primatologist Richard Wrangham at Harvard University in Cambridge, Massachusetts. A behaviour could be linked to any number of variables such as amount of rainfall, the types of tree available, or the kinds of predator in the area, he says.

These influences can be subtle, as researchers found while studying how chimps use sticks to harvest army ants. Chimpanzees in Guinea sometimes use short sticks and sometimes use sticks up to twice as long. No reason for this was obvious until Tatyana Humle, an anthropologist at the University of Kent, UK, found that some ants are more aggressive, with longer legs and larger mandibles; they run up sticks quicker and bite harder⁵. This might explain why chimps elsewhere in Africa also choose tools of varying lengths to get at ants.

But researchers have not been able to find obvious explanations for other variations related to ant harvesting. Chimpanzees in Cote d'Ivoire sweep the ants off their sticks and into their palms before eating; in Guinea, only about 320 kilometres away, the animals stick the ant-laden sticks directly into their mouths. The same type of ant is present in both places.

6. Also in this week's Nature, presumably gated, an article about how the coffee-stain effect (i.e., the ring-like shapes of coffee stains, prev. posts here and here) does not exist for ellipsoidal (M&M shaped) colloidal particles [Nature 476, 308 (2011)]. I don't fully follow the argument but the basic idea is that repulsive interactions among the particles keep the solute from moving outward with the fluid.

7. Seventeenth-century drinking habits revisited, at the Awl. (See here for prev.)

Nor need it seem incredible, that common drunkards should drink thus, for they can disgorge themselves at pleasure, by only putting their finger to their throat, and they will vomit, as if they were so many live whales spewing up the ocean; which done, they can drink afresh.

Re spewing whales see also: ambergris, Simon Armitage. 

The fine structure of stains

I blogged last year about the Chicago group's work on why coffee-stains are ring-shaped, with a sharp outer edge fading as one moves in. A quick reminder:

(In other words, the edge of a droplet is stuck where it is; as the droplet evaporates, more and more of the water must move from the center to the edge, so that most of the water gets to the edge before it evaporates, so most of the evaporation and hence the deposition happens at the edge.)

There's a nice new article in PRL today (ungated) that takes a much closer look at the structure of a stain:

(c) is a blow-up [optical microscope] of the red square in (b) and (d) is a blow-up [electron microscope] of the red square in (c). The solute particles at the outermost edge of the stain are arranged in precise crystalline patterns; as you move further in towards the (relatively sparse) middle of the stain, the particles become randomly distributed. The physics of this turns out to be fairly simple, given what's already known about evaporation. To quote the paper:

The [solute] particle velocity increases dramatically in the last moments of the droplet’s life. We refer to this sudden change in speed as ‘‘rush hour.’’ The particles that arrive early, at a low deposition speed, form an ordered (square or hexagonal) structure. In contrast, particles that arrive during rush hour have a high speed and form a jammed, disordered phase.

[NB you could ask why there's a tendency for things to crystallize at all. In this case I think that's just electrostatic repulsion -- particles would like to be as far from each other as possible, i.e. in a crystal, but might not have any way to get there.] The authors also claim to have a theory of why one sees both hexagonal and square crystals in the ordered region [see part (d)] but I don't have the time right now to follow up that paper trail.

Update Here is the Physics blurb about this.

"It is this deep blankness is the real thing strange"

As the summer of writing papers yields to the fall of trying to find work, one is naturally much troubled by introspection -- which, in my case, is of a self-pitying and/or self-accusing kind that it's probably best not to inflict on others; hence the general hush. A few observations:

• There is much to be said for the theory that procrastination is self-sabotage. I suspect that I'm invested in telling myself that I've underachieved and in making this seem plausible on the merits. (The alternative, that one did one's best but still ended up mediocre, is much more dispiriting.)
• Wasted effort is character-building. (So is putting a lot of effort into something you know you'll never get good at; so are routine tasks that eat up a lot of your time.) I have avoided all of these to a large extent, and the consequent damage is a profound inability to get myself to work hard.
• In my case, part of the problem was that, by managing to avoid all teaching responsibilities, and not (e.g.) having a family to worry about, I managed to keep afloat relative to others -- workwise -- without doing very much. Had I been more driven and less indolent, I would have done more, and perhaps accomplished more; even if that effort had been wasted, I would have accustomed myself to long, concentrated spells of working. It appears to be easier to increase one's time at work than to increase one's efficiency: any obligation that caps work hours is a good thing.
• It is pointless to commit yourself to things that you're not up to -- however much you'd like to be up to them -- on the assumption that commitments really are binding on your future self. Your future self is more slippery than you give it credit for being. Your future self is also quite good at damage control.
• An almost-snowclone: "X's weaknesses are inseparable from his strengths." Depressingly true of most of us, I think. I often wish I were better with details than I am, but I think that if I had (ceteris paribus) that sort of mind I would be subject to the shortcomings of the detail-oriented people I see all about me. (This is partly a numerical thing: for some reason it is rarer to find physicists who are heedless of particulars than to find those who pay too much attention to them.)
• There is no such thing as bad luck. There is unreasonably good luck, and then there is the luck we deserve.

Tomonaga and the bottle

From Freeman Dyson's new NYRB piece on Feynman:

Feynman had looked forward to meeting Sin-Itiro Tomonaga, the Japanese physicist who shared the Nobel Prize with him. Tomonaga had independently made some of the same discoveries as Feynman, five years earlier, in the total isolation of wartime Japan. [...] Feynman and Tomonaga shared three outstanding qualities: emotional toughness, intellectual integrity, and a robust sense of humor.

To Feynman’s dismay, Tomonaga failed to appear in Stockholm. The Ottaviani-Myrick book has Tomonaga explaining what happened:

Although I sent a letter saying that I would be “pleased to attend,” I loathed the thought of going, thinking that the cold would be severe, as the ceremony was to be held in December, and that the inevitable formalities would be tiresome. After I was named a Nobel Prize awardee, many people came to visit, bringing liquor. I had barrels of it. One day, my father’s younger brother, who loved whiskey, happened to stop by and we both began drinking gleefully. We drank a little too much, and then, seizing the opportunity that my wife had gone out shopping, I entered the bathroom to take a bath. There I slipped and fell down, breaking six of my ribs… It was a piece of good luck in that unhappy incident.

After Tomonaga recovered from his injuries, he was invited to England to receive another high honor requiring a formal meeting with royalty. This time he did not slip in the bathtub. He duly appeared at Buckingham Palace to shake hands with the English Queen. The Queen did not know that he had failed to travel to Stockholm. She innocently asked him whether he had enjoyed his meeting with the King of Sweden. Tomonaga was totally flummoxed. He could not bring himself to confess to the Queen that he had got drunk and broken his ribs. He said that he had enjoyed his conversation with the King very much. He remarked afterward that for the rest of his life he would be carrying a double burden of guilt, first for getting drunk, and second for telling a lie to the Queen of England.

Dyson is on paper the obvious choice for a piece about Feynman; as usual there's a lot of recycling, but with an interesting twist. In an old NYRB review of a previous Feynman book, Dyson had categorized Feynman with Einstein and Hawking as physicists who have become "Wise Men" to the public. In the new iteration of this remark, Feynman has provisionally been dropped from the list, the Wise Men are "superstars," but the point is spelled out nicely:

Lesser lights such as Carl Sagan and Neil Tyson and Richard Dawkins have a big public following, but they are not in the same class as Einstein and Hawking. Sagan, Tyson, and Dawkins have fans who understand their message and are excited by their science. Einstein and Hawking have fans who understand almost nothing about science and are excited by their personalities.

(A point worth making is that Einstein and Hawking would arguably have been substantially less revered if they stood for something in the public mind that the public cared about -- evolution, say, or whether the universe had a beginning. Being a polemical figure reduces one's stature. The closest thing to Hawking in recent news was Grisha Perelman, but as a mathematician he is somehow too peripheral. To become the relevant kind of cultural figure one needs to be cartoonish and nonthreatening. Though arguably physics has never been threatening.)

---

A bit of news today that will please many physicists: the journal Physical Review Letters (the Berkeley of the physics publishing hierarchy; the most prestigious journal that also publishes a lot of articles) has switched from a 4-page limit to a word count limit. Objectively this is reasonable and frankly somewhat belated; I believe (or at least hope) that the journals also intend to make articles available as single-column HTML files, it is extremely annoying to read two-column text on a laptop. I have mixed feelings about the new limits: I had just begun to get the hang of maximizing the number of words you could cram into 4pp. by rewriting each paragraph so as to have it end at the end of a line.

"Rhombs, and wedges, and half-moons, and wings"

The line is from Paradise Regained; I found it because I was looking for pentameter lists of nouns. The first search result for "rhombs and wedges," however, is the Tilings Encyclopedia, a repository of Penrose tilings and other aperiodic (mostly substitution) tilings of the plane, such as the (new-to-me) pinwheel patterns of Radin and Conway and others, and their relatives, like this kite-domino tiling:

(The pinwheel tilings have the property that every tile appears at least once in every possible orientation.)

[PS a topic I've been paying some attention to lately is the existence of quasicrystalline, i.e., Penrose-tiling-ish, solutions to certain packing problems, which are interesting as statistical physics. For prev. coverage of this see here and here.]

Clearances

Strange how natural it is to lower one's expectations, to the point that even a late and disappointing end to a project counts as an "accomplishment," at least the mind insists on treating it as such; even successful damage control occasions a degree of self-congratulation. Perhaps basking is just an excuse for laziness. Anyway, a paper that I should have completed two months ago will finally be sent out today (at 3:01 pm, re  which see here); and I've put together a talk for DAMOP, though not the accompanying paper. I'll be in Atlanta tomorrow through Friday and don't expect to blog much. (Email access might also be limited, not sure about this.) A few miscellaneous notes for the time being:

1. I recently discovered the enormous utility of the term "account" in technical physics writing. Unlike most of its synonyms ("description," "explanation," "theory," "claim") it is not standard physics jargon, so has no connotations whatsoever and can be used to refer to other people's work without implying anything at all about it. It is even better than treatment, the only real competitor, which implies that the cited work did something more than (e.g.) hand-waving/speculation. "Account" is especially good when you're citing papers you haven't read beyond the abstract and conclusions. (Physics has accelerated the "deterioration process" of my writing; at this rate I'll soon become entirely unable to start a sentence without "hence" and/or "furthermore.")

2. Speaking of physics jargon I am a big fan of this abstract ("away from the decoupling limit the Hamiltonian constraint is maintained at least up to and including quartic order in nonlinearities, hence excluding the possibility of the Boulware-Deser ghost up to this order").

3. Calista has been doing Spenser, which is great because it means I don't have to. The best find so far is the etymology of the word "blatant," which was apparently a Spenserian coinage. There is a "blatant beast" in the Faerie Queene, a many-tongued monster, which later came to mean babbling (re a person), then clamorous (re a person), and then finally clamorous (re a fact). OED sensibly dismisses the suggestion that "blatant" comes from the Scots for "bleating" (this is Spenser after all) and notes that as it was originally often written "blattant" the a would have been short at first. I assume that there is some connection here with the "couchant lions" etc. in heraldry...

4. Finally a note re Chomskygate and associated matters. (This should be a long post on its own but I don't feel like writing it.) What Chomsky supposedly said:

derided researchers in machine learning who use purely statistical methods to produce behavior that mimics something in the world, but who don't try to understand the meaning of that behavior. Chomsky compared such researchers to scientists who might study the dance made by a bee returning to the hive, and who could produce a statistically based simulation of such a dance without attempting to understand why the bee behaved that way. "That's a notion of [scientific] success that's very novel. I don't know of anything like it in the history of science," said Chomsky. 

See also Language Log. I think there are three issues here that are at least partly separable. (1) Computers and their role in "understanding," e.g., does having a computer-generated "proof" of a theorem in mathematics imply that the theorem is "understood"? (See, e.g., Doron Zeilberger. I don't know these proofs well enough to have an opinion.) (2) Phenomenology and "microfoundations" -- is it OK to base a model on phenomenological observations or should all true explanations be reductions to first principles? Chomsky seems to hold the latter view; I disagree, at least partly on the grounds that there are typically a lot of "first-principles" models that agree on large-scale properties, so that it is misleading at best to say that a first principles model explains patterns seen in large-scale data. It is worth noting, though, that if you hold Chomsky's view on reduction, then it is true that most work in the field is irrelevant: if one wanted to understand underlying principles one would want to construct experiments (or at least clever natural experiments) that isolated certain aspects of linguistic behavior, not try to model the entire thing. (3) "What is science?" This is one of those bad questions like "what is poetry?" A discipline is either a defensible expenditure of intellect and resources or not, just as a piece of writing is either rewarding to read or not. The trouble with a question like "is this science/poetry?" is that it inevitably conflates the Q. of worthwhileness with the unrelated Q. of whether X resembles the members of some predefined set.

5. Andrew O'Hagan, Seamus Heaney, and Karl Miller tour Scotland, Ireland, and Wales. (Why didn't they do Cornwall?) I was amused to learn from the article that Lesmahagow is an actual place in Scotland (cf.) and also by Hugh MacDiarmid's sheep-inspired terms for Scottish weather:

Hugh MacDiarmid had a feeling for the freezing lives of sheep, and he resurrected, or to some extent invented, the words that would capture the rude nature of the Scottish snowstorm, calling it the ‘yowdendrift’, when snow is blown across the fields at speed, or the ‘yow-trummle’, the ewe-tremble, when the shorn animals are seen to shiver and quake as they catch their death.

The Fractal Geometry of Wrinkles

The folds of a curtain tend to grow larger and smoother as you move away from the fixed end; this behavior is generally true of suspended sheets -- they tend to form wrinkles near the fixed ends that turn into larger smoother billows as you move away from the edge. (The picture above, L, is a sheet of two-layer graphene suspended over a trench.) A natural question that this sort of recurring structure brings up is whether, if you took a picture of the region near the surface (i.e., the region with small wrinkles) and blew it up, you'd get something that looked exactly like the region with larger wrinkles -- whether the joints at which wrinkles join and split look the same at all scales, in other words. A nice new paper in PRL ["Wrinkling Hierarchy in Constrained Thin Sheets from Suspended Graphene to Curtains,"  PRL 106, 224301 (2011)] shows that this is indeed the case, and that -- under some weak assumptions -- the average wavelength (crest-crest distance) of the folds scales as the distance from the fixed end as x^(2/3) for light sheets and as x^(1/2) for heavy sheets. ("Light" and "heavy" are defined somewhere in the article...) Here are some of the results:

So wrinkling is one of those "universal" phenomena that people in statistical physics are obsessed with (see prev.) -- as evidence for the anti-reductionist view that you can't really explain macroscopic effects in terms of what things are made of, because (e.g.) every large sheet-like object behaves in much the same way and so the microscopic details don't add anything significant to the story.

Two notes:

(1) The new PRL is closely related to a paper that was featured in Phys. Rev. Focus a couple of months ago on the crumpling of paper. The first author on the crumpling paper was the aptly named Robert Schroll.

(2) The new PRL introduces the semi-charming term "wrinklon" for the site at which a wrinkle forks. (Any clump-like or singular feature is a [blank]-on as per standard naming practice, which I think began with "soliton.") One of the experiments they did to study wrinklons was, I thought, very elegant: they took a plastic sheet, clamped one end of it to a surface with serrations at wavelength lambda, and the other to a surface with serrations at twice the wavelength. (So the folds at one end should be twice as tight as at the other; see figure below.)

This trick allowed them to isolate and study single layers of "wrinklons."

Viscous fingering, venom delivery, and other phenomena

1. Some entertaining PRL titles from Blogger Outage Day:

• Fluid mixing from viscous fingering
• Tears of Venom: Hydrodynamics of Reptilian Envenomation

Abstract of the venom article:

In the majority of venomous snakes, and in many other reptiles, venom is conveyed from the animal’s gland to the prey’s tissue through an open groove on the surface of the teeth and not through a tubular fang. Here we focus on two key aspects of the grooved delivery system: the hydrodynamics of venom as it interacts with the groove geometry, and the efficiency of the tooth-groove-venom complex as the tooth penetrates the prey’s tissue. We show that the surface tension of the venom is the driving force underlying the envenomation dynamics. In so doing, we explain not only the efficacy of the open groove, but also the prevalence of this mechanism among reptiles.

1'. Lovely high-speed video of how hummingbirds drink -- turns out it isn't capillary action after all. (Wired Science via Jeremy)

2. William Barnes was a delatinizer:

He called for the purification of English by removal of Greek, Latin and foreign influences so that it might be better understood by those without a classical education. For example, the word "photograph" (from Greek light+writing) would become "sun-print" (from Saxon). Other terms include "wortlore" (botany), "welkinfire" (meteor) and "nipperlings" (forceps).

3. R.S. Thomas's poem "In Church" is an unusually clear-cut example of the standard use of the linebreak in accentual verse (3 beats to the line here):

These are the hard ribs
Of a body that our prayers have failed
To animate. Shadows advance
From their corners to take possession
Of places light held
For an hour. The bats resume
Their business. The uneasiness of the pews
Ceases. There is no other sound
In the darkness but the sound of a man
Breathing, testing his faith
On emptiness, nailing his questions
One by one to an untenanted cross.

I will have more to say about this anon; I'm just posting the passage now in case I forget how it goes.

From Dallas with Dyspepsia

I am coming around to the view that these APS meetings are generally awful. Some people insist that they're great if treated correctly, but I don't see it, I have been exhausted and irritated ever since we arrived and immediately found out that physicists had overwhelmed all the restaurants near the convention center. The coffee-shop lines have been consistently dire. The meeting itself has been wearying -- I had signed up, unwisely, to give two talks, neither of which I put together until the very last minute -- and there are far fewer talks this year than in prev. years that I feel compelled to go to.

We're staying at the Magnolia, an enormous hotel in downtown Dallas that's notable primarily for its lurching turn-of-the-20th-cent elevators. (They're also really slow.) There are three Englishwomen here who seem to spend most of their time riding the elevators and repeating a few obvious jokes about them. (I wonder if this is a successful pick-up strategy?) As convention centers go this one is exceptionally ugly, and abuts a graveyard with a huge Confederate memorial (Jefferson Davis's marble neck-beard is like a wrinkled goiter), but is otherwise OK. It is adequately provided with restrooms, and the wireless internet is a LOT better than one expects at these things. If only my laptop had a functioning battery... but one is forced to hang out in corners w/ power outlets.

I wonder what the etiquette is re gawking at people's name-tags. Personally I can't help it.

Rationality and other lost causes

I'm writing this in a state of sleep-deprivation and, to some extent, relief; after a week of trying -- stupidly -- to finish up a paper before the APS meeting (in Dallas next week), I have had to resort to plan B/damage control: pad talks and be opaque enough (hopefully!) to avoid getting scooped.

Note that Alan has a new blog (linked, as one might expect, on the right.) In this post he touches on a longstanding disagreement between us on "reasonableness." To be a little reductive, Alan is (like most of my friends) a firm believer in self-improvement, intuition pumps, Science, and the like; I am a nihilistic slob, with considerable sympathy for irrationalism. Part of this is, no doubt, due to differences in temperament (this is the only way I can explain the fact that I'm not a vegetarian), but differences in intellectual history also have something to do with it.

I should distinguish between contemplative and instrumental rationality: the former is about getting facts right, not believing false arguments, etc.; the latter is about getting what one wants, whatever that might be. (The former is a limiting case of the latter.) Given a list of desires and beliefs, instrumental rationality tells you what actions are (in some pretty obviously meaningful sense) "rationally binding." In certain very specific contexts (e.g., a prisoner trying to escape), what one wants is clear, and instrumental rationality is a useful tool.

Perhaps some cases in the historical core material of economics -- purely profit-maximizing regimes of endeavor -- resemble this; however, whether any of it applies to everyday life is much less clear, as it is not evident that people have fixed desires in any meaningful sense. (I wholeheartedly agree with Andrew Gelman's aphorism that "the utility function is the epicycle of social science," which I probably consider to be more broadly true than Gelman does.) In order to adapt instrumental rationality to everyday life, one is forced to do a sort of three-step: (a) assume that a utility function exists, (b) use a combination of survey data, "revealed preference," behavior, and intuition-pumping to figure out what the utility function says, (c) accuse people of being irrational when the "best" utility function doesn't do a good job of predicting their behavior.

Bertrand Russell remarks, re Locke's ethics:

Almost all philosophers, in their ethical systems, first lay down a false doctrine [in context: a false descriptive theory of human motivation], and then argue that wickedness consists in acting in a manner that proves it false, which would be impossible if the doctrine were true. Of this pattern Locke affords an example.

To the extent that (b) is about empirics (revealed preference or survey data), the three-step above clearly falls into this pattern, with (a) as the false doctrine. To the extent that it relies on intuition pumps, these are only as reliable as one's prejudices. Extreme cases can be dismissed on the grounds that they're outside the expected regime of validity of one's moral systems. (Derek Parfit attempts unpersuasively to counter this argument somewhere, I forget his point.) On the other hand, there is no particular reason to expect that true observations about human nature of the kind that come out of neuroscience etc. (which are bound to be statistical) are likely to imply, or "go with," a moral system. In order to make this sort of inference one must bring in a principle of the form "what is 'normal' is 'healthy' and 'good'" -- or some equivalent kind of naturalistic inference even in the individual non-collective sense -- that I find (even in its mild forms like "it cannot be morally binding to be an outlier") both repugnant and not a priori true.

In short, I believe that this line of thinking is unlikely to get anywhere specific, and the standard attempts to work around the skeptical arguments remind me of the epic exercise in flailing that is the Russell/Whitehead Principia Mathematica. This is, perhaps, where differences in training (not to mention the degree of one's interest in self-improvement) come in: Alan would presumably say that one ought to learn philosophy to (a) at least understand the skeptical arguments (self-improvement) and (b) find a systematic framework, however imperfect, to address these questions in. As regards (a) there are lots of causes in physics and math that are understood to be lost causes. I understand many of them very hazily -- it is useful to know enough to realize when a line of inquiry you once thought promising turns out to be equivalent to a lost cause -- but do not have the time to buttress my skepticism. And I think (b) relies on an assumption about conscientiousness being intrinsically worthwhile -- esp. w.r.t. important matters -- that is quite unnatural for a physicist; one does not waste time on problems, no matter how important, that are generally believed to be intractable, unless one starts out with a specific reason to believe the consensus is wrong. If the most elaborate reflection doesn't produce policy that's demonstrably better than dominance reasoning plus coin-flipping -- and the upshot of the skeptical arguments, I think, is that it cannot -- one shouldn't waste time on it. Ideas do not get A's for effort.

---

An especially important example -- pace Kuhn, a paradigmatic one -- of a lost cause is Aristotelian physics. Steven Weinberg (again via Alan) wrote of "the shift (which actually took many centuries) from Aristotle's attempt to give systematic qualitative descriptions of everything in nature to Newton's quantitative explanations of carefully selected phenomena." The primary lesson of this example is that the best way to get a handle on some problem is not always -- or even generally -- to approach it head-on. One is better off explaining something thoroughly and working outwards. The flip side is that one might end up with meteorology, in which the questions "of interest" are intractable and the explicable phenomena (icicle bending!) aren't of much interest. (If I were an economist I would be working on Zipf's law.) Almost all phenomena -- and a fortiori almost all relevant ones -- are in practice impossible to understand from first principles.

There's much more to be said about all of this but I'll restrict myself to a brief note on "ideology" as the term is used in physics. An "ideology" is a widely believed but vague and/or unprovable rule of thumb that can be applied to prove various specific results. It is, in general, a rule about what questions to ask and what kinds of answers to look for. The "renormalization group" idea in physics is an ideology that plays a role that's roughly like that played by evolution in biology: one cannot reduce it to a precise, true, non-vacuous statement, but it guides the field. Ideologies are what Weinberg refers to as the "soft" parts of theories:

There is a "hard" part of modern physical theories ("hard" meaning not difficult, but durable, like bones in paleontology or potsherds in archeology) that usually consists of the equations themselves, together with some understandings about what the symbols mean operationally and about the sorts of phenomena to which they apply. Then there is a "soft" part; it is the vision of reality that we use to explain to ourselves why the equations work. The soft part does change; we no longer believe in Maxwell's ether, and we know that there is more to nature than Newton's particles and forces. ... But after our theories reach their mature forms, their hard parts represent permanent accomplishments.

This distinction exists to some degree outside particle physics -- a great deal has been learned about the lineages of various species, etc., even if the ideology that led to these discoveries turns out to be false. But it's worthwhile to distinguish between the predictions of a theory -- i.e., predictions that come out of the "hard part" -- and those of an ideology, which come from the soft part. The latter cannot be disproved in any straightforward way -- they are just patterns we impose on selected agglomerations of fact -- and change, as
often as not, because the community becomes interested in other problems where the ideology is less useful. (For instance, an ideology in condensed matter physics is -- very roughly -- that any graph of the properties of a large system that exhibits jumps is a sign that there's something "topological" about the system. This ideology has led to a number of fascinating discoveries about the way electrons move in metals; however, it is always possible to have jumps for all sorts of non-topological reasons. A bit of particle physics ideology that was behind Weinberg's Nobel Prize-winning work was the puzzling-to-an-outsider belief that all bosons [particles obeying Bose-Einstein statistics] are gauge bosons.)

As I understand them, both "incentives" and adaptationism are ideologies of this kind. I think ideologies are great as long as one's ultimate objective is to solve specific problems. One should perhaps be more careful, though, when trying to justify specific research programs on the grounds that they might "prove" or "disprove" the ideology; it's (in T.S. Eliot's phrase) like trying to dispel a fog with hand grenades. I.e., a lost cause.

"It would be ok as long as the cans weren't stored upside-down."

I'd shared this preprint unread when it popped up on the arxiv but apparently it's good enough for Nature News, which has a good writeup. I particularly enjoyed the caveats.

The widget-free way to foamy stout

Stouts bubble less readily than lagers or other carbonated drinks when poured because they contain dissolved nitrogen as well as the carbon dioxide that drives the fizz. Adding nitrogen makes the beer less acidic, and gives a longer-lasting head with relatively small bubbles that are behind stouts' smooth, creamy 'mouth feel'.
But the addition also demands the use of the widget [a hollow sphere with a hole in it], which takes in gas and beer as it floats in the canned stout and, when the can is opened and the pressure drops, jets it out again through the hole, helping to create the foam.

The new study suggests that the same result could be achieved by coating part of the can's interior with cellulose fibres. [to increase the rate of bubbling, which is intrinsically low for stout: bubbles nucleate faster on rough surfaces]
[...]
However, [some guy] adds, the bubbles might fill with liquid while the can was in storage. Lee says the coating would be placed in the gap at the top of the can: "It would be ok as long as the cans weren't stored upside-down."

Andrew Alexander, a chemical physicist at the University of Edinburgh, UK, also believes that can coatings would be impractical compared with widgets. "Widgets are genius — they're cheap, work really well, are totally non-toxic and don't mess with the beer," he says. "Would a fibrous coating be cheaper than what is essentially a ping-pong ball with a hole in it? I don't think so."
But Lee says that using widgets slows down the process of canning stout. "Oxygen stuck in the widget can affect the beer's flavour, so you have to pump nitrogen in several times to remove it," he says. "The cellulose coating is an alternative worth investigating."
However, it is likely to be some time before fibre-lined stout cans appear on supermarket shelves. "We've spoken to brewers," says Lee, "but we're not sure if they're interested yet."

Fluid mechanics video dump

Adapted from an email I just wrote Kit, who wanted cool physics videos for a high school math class. These will be familiar to many -- from the feed -- but aren't archived anywhere, so it is perhaps worth collecting the links here.

1. Stephen Morris's fluid-mechanical sewing machine (maple syrup -- not really, but he is Canadian -- dropped onto a moving belt):

2. Stephen Morris, "chemical plumes" (Quicktime) and the "washboard road" effect (i.e., the fact that dirt roads go sinusoidal over time when driven on). Should note in passing that talking to David Grier about washboard road was one of the things that sold me on many-body physics as a prospective graduate student.

3. Sid Nagel's splashing-droplet videos (scroll down). The discovery that water doesn't splash at low atmospheric pressure is remarkable and not something I'd ever have expected. The other stuff on Nagel's website is pretty neat as well. (Either Nagel or someone introducing him described his lab as "where theory comes to die.")

4. The phenomenon of self-propelled Leidenfrost droplets moving uphill (U. of Oregon; see my recent post for context; this youtube video is a decent intro to the Leidenfrost effect).

What are colleges for? etc.

There's been a good deal of talk lately about increasing the educational "productivity" of universities, making college cheaper and more "scalable" in innovative ways, etc. I think this is a lost cause as it is hard to quantify outcomes, or expect the market to do so, partly because the monetary "value" of a college education usually has little to do with the skills one is supposed to have acquired. Most of the college wage premium accrues to people who take up jobs that are not related to material they learned at college. (This is increasingly inevitable as service-sector opportunities fluctuate more rapidly than manufacturing opportunities.) It is possible that the premium has to do with some vague notion that people learn "critical thinking" etc., but this doesn't seem likely. My impression at least is that the primary factors behind the wage premium are: (a) employers assume that people who got into good colleges are smart, (b) working through college and not dropping out demonstrates traits -- e.g., a willingness to do things because one has to, to meet deadlines, etc. -- that are useful, (c) most hirers have been to college, and there's a networking effect. (a) and (c) are difficult to industrialize but it seems unlikely that a college education without either would be sought after.

It seems easier to justify universities starting from the research end. As Sean Carroll has remarked, this is really the only way one (or, more precisely, an intelligent Martian) can make sense of the setup. To put it crudely, the core function of the university is to act as a patronage system for scientists, artists, and other scholars working on things that are arguably valuable but, for various reasons, do not offer a "market-based" livelihood. (In the simplest-to-justify cases, as with medical research, the reasons have to do with the problems of secrecy and/or free-riders in market-based alternatives.) In order to keep its patrons (rich -- and/or, for state schools, powerful -- alumni) loyal and happy the university admits their kids (which gives them "cultural" prestige markers, which include a possibly undeserved reputation for intelligence -- this is partly why elite universities need to admit smart kids!), arranges sports and alumni events, etc. The elite university serves two further purposes: (a) it perpetuates knowledge, and itself, by training academics as well as various people who are in the broad penumbra of the academic world -- editors, certain kinds of journalist, etc., (b) it provides a channel for a few people from disadvantaged backgrounds to leapfrog the various middle classes and land in the elite, or at least impress their existence on the elite. In political-economy terms (b) is important as most decisions are made by elites and the extent to which they are even aware of how the poor live determines the extent to which their policies hurt the poor.

One can also argue that a task like teaching, which -- as Robert Lowell remarked -- "you're always up to, or more or less up to," is a good thing for a creative artist. One doesn't have teacher's block. Cf. Lowell's contemporary Richard Feynman, famously, on the Institute for Advanced Study --

When I was at Princeton in the 1940s I could see what happened to those great minds at the Institute for Advanced Study, who had been specially selected for their tremendous brains and were now given this opportunity to sit in this lovely house by the woods there, with no classes to teach, with no obligations whatsoever. These poor bastards could now sit and think clearly all by themselves, OK? So they don’t get any ideas for a while: They have every opportunity to do something, and they’re not getting any ideas. I believe that in a situation like this a kind of guilt or depression worms inside of you, and you begin to worry about not getting any ideas. And nothing happens. Still no ideas come.
Nothing happens because there’s not enough real activity and challenge: You’re not in contact with the experimental guys. You don’t have to think how to answer questions from the students. Nothing!

[Along these lines there is a wonderfully snide remark in Auden's "Letter to Lord Byron" about the newly financially independent poet of Byron's generation: "he sang and painted and drew dividends / but lost responsibilities and friends." The flip side is that you've got to guard against the complacency that comes from being engrossed in unimportant tasks even as your real agenda languishes. I must admit that my choice of graduate school was not unaffected by a desire to avoid teaching, on the (all-too-plausible) grounds that it would be work and I'd be crap at it.]

I tend to think that these functions are important, and that the modern university is the minimal setup that performs all of them and locks in enough interests to form a sustainable ecosystem. It doesn't scale well because it is so heavily about access, which doesn't scale at all. One is left with two questions: (a) if access is to be rationed, who should get it? (b) what about everyone else? I think the "fairness" aspects of (a) are over-pondered; any conceivable admissions process would be unfair in some respects. (b) is an interesting issue but I don't think one could discuss it in detail without lapsing into futurism. There are motivated, clever, and unlucky people for whom (e.g.) the secondary campuses of state schools offer just about enough by way of resources to get a good education or sustain a decent research program; one supposes, however, that the majority of students are there as a way of getting ahead, which means that they are demonstrating their willingness to do arbitrary tasks to deadlines in a rather expensive way. There must be simpler arrangements... (Of course college is also about access to booze while under 21, which does scale, and this shouldn't be underrated.) Before one thinks of such rearrangements, though, it would be nice if graduate schools were more open to applicants with nontraditional backgrounds.

---

This is really in the spirit of "closing tabs," but re justifying research: last semester I was at a KITP talk on giving talks that was notable mostly for a spirited exchange near the end between Tony Zee and Bill Phillips on how to sell physics (say to the DoD/DoE/Congress). Zee took the line that one should assert that the sciences (and humanities) are what make a civilization worth defending; Phillips objected, reasonably enough, that this wouldn't work with any actual congressmen, and that one had to focus on concrete possibilities. I mostly agree with the destructive half of Phillips's point but I don't think that carving out little bits of academia as "obviously useful" is much of a solution. To some extent it plays into the hands of the large fraction of Congress that is explicitly anti-academic, by setting up their salami tactics for them. It isn't clear to me that we aren't doomed. (See Michael Berube on this.)

I remember Phillips and Zee disagreeing, too, about the utility of structuring talks to make them exciting (which was what the meta-talk was about). There is an ideal of complete spontaneity and informality in many corners of physics -- the ideal talk is a lucid extemporaneous (if blackboard-assisted) lecture delivered in one's bedclothes, and any too-obvious sign of preparation -- fancy slides or pictures, a prepared text (the horror!) -- is vaguely frowned upon, and marks you as possibly an experimentalist. Far worse, though, to come off as making your work sound more interesting than it is, even if that is obviously what everyone wants to do; the most admired talks are the kind described in this post (via Ross McKenzie's blog):

He showed up in the convention center wearing a brightly colored short-sleeved shirt, shorts, and, if I remember correctly, sandals. Not only had he forgotten to dress for Boston's weather, he'd also left his laptop in California. [...] Using hastily prepared, hand-written viewgraphs, he gave one of the best talks of the meeting. Indeed, it's conceivable that in creating his viewgraphs, Heath was forced to focus more on his message than on its presentation.

"Pure content" is a myth, of course, but a widely held one. There is an implied arrogance behind all of this that is pervasive in academia but is perhaps exacerbated by the overwhelming maleness of physics, and that hurts us when we have to deal with the possessors of real power. (This is related to Nozick's notion, in some typically obnoxious essay, that academics have a sense of entitlement that businessmen do not.) I remember saying once that I was a trust fund brat without a trust fund; this is true of all academics, to a degree (ineluctable pun).

Leidenfrost ratchets

This week's flood of recreational physics continues... Nature Physics has a new paper online (gated version here, no arxiv that I could find) on self-propelling Leidenfrost droplets. The Leidenfrost effect is the fact that a droplet [1] of water floats above a really hot skillet on a cushion of steam (generated, say, by the bottom of the droplet boiling -- see this youtube video). As steam is a bad conductor of heat, the floating droplet takes a long time to heat up and boil. It was discovered a few years ago [Linke et al., PRL 96, 154502 (2006), gated supplementary material has video] that droplets placed on "ratchets" -- i.e., surfaces with sawtooth-shaped serrations -- moved at about 10 cm/s "against the grain" of the serrations.

As the new Nature Physics paper says, various explanations are possible:

First, the base of the drop is deformed by the presence of the ratchet below, which induces a modulation of its curvature and consequent Laplace pressure gradients⁴. Second, a wave propagates from the trailing edge to the leading edge of the drop, making the transport of matter possible in the direction of its motion. Third, a Leidenfrost drop is likely to oscillate spontaneously²⁰; for each elementary rebound, part of the kinetic energy can be transferred from the vertical to the horizontal direction because of the slope of the teeth. Fourth, the Marangoni effect related to temperature differences might cause a displacement, as seen in Marangoni-levitating drops heated asymmetrically using a light source²¹. Fifth, as the drop loses material, this gas flow might provoke a motion provided it is made directional (or rectified) by the presence of the teeth.

The fifth explanation differs from the other four in that it doesn't rely on the droplet being fluid -- all the others depend on the deformability of the droplet. So the authors tested this by repeating the experiment with dry ice. Since dry ice sublimates, it too should levitate on a cushion of gas when dropped onto a "skillet" with a sufficient temperature gradient. But it isn't liquid, so it can't, e.g., "modulate its curvature."

In the event, a piece of dry ice propels itself exactly like a droplet of water; this establishes that gas flow is behind the self-propelling. How does this work?

As the gas moves towards the step, that is towards a sudden contraction in the fluid channel, the flow resistance is higher than in the reverse direction²³. As a consequence, the vapour will mainly escape along the smallest slopes of the texture, which propels the Leidenfrost body in the direction shown in Figs 1 and 2 (jet thrust). This interpretation was confirmed by forcing contact between the hot ratchet and a disk of dry ice, thus printing the tooth pattern on the bottom of the disk, and observing a similar motion with this textured disk on a hot flat solid.

In other words most of the evaporated carbon dioxide moves up the gradual ramps, i.e., "with the grain" of the ratchet, so (by Newton's third law) the levitating solid is pushed in the opposite direction.

In addition to the appeal of all simple phenomena that could have been discovered centuries ago, this work is a neat example of the scientific method in action, and esp. of the value of clever controls. This is an aspect of good scientific practice that doesn't get the attention it deserves; the original Freakonomics book is actually the only piece of popular writing about anything where I've seen it covered in any detail.

---
[1] I don't know what the technical difference is between a droplet and a drop. No one ever seems to talk about drops of water in physics.

Recreational physics roundup

I have always enjoyed work on pattern formation on the everyday scale; it is heartening (a word I overuse, perhaps revealingly) to see that there is still so much in front of one's nose that bears closer inspection. (See here and here for previous local coverage.) The past few days have been abnormally rich on this front -- three worthwhile stories! -- and I wanted to blog about them, partly for ease of future reference.

---
Bubbles and memory

There's a new story in Phys. Rev. Focus about hysteresis in soap bubbles. (Like most Focus articles it seems to have been written by a journalist. I also find it irritating that they publish Focus articles a while before the paper comes out, because you've typically forgotten all about the work by the time it's published.) Soap bubbles grown on a triangular-prism-shaped frame form dipyramids that either intersect at a triangle -- for a squat prism -- or are joined by a thin vertical strand of soapy water -- for a skinny prism. For a certain range of aspect ratios both solutions are possible, so as you stretch or contract the sides of the prism, the bubble can take either form depending on which way you were tuning the length (i.e., on the bubble's "past"). This is interesting primarily -- from a physics point of view -- as the most purely geometrical example of hysteresis that I know of: the films try to minimize their area, and in this range the two lowest-area configurations look substantially different.

It is also an excuse to replug a beautiful old paper by the Chicago group on a much more nontrivial example of memory in bubbles -- viz. how air bubbles blown through a nozzle "remember" irregularities in the shape of the nozzle.

---
"Nonideal icicles"

Stephen Morris at the University of Toronto does a lot of beautiful work on pattern formation in systems that are "fluid" in some sense. (My favorite thing on his website is the fluid mechanical sewing machine, but irritatingly that link is broken.) Morris's group has a new paper out in Phys. Rev. E, featured in Physics, on the growth of icicles. They grew large numbers of icicles in their lab and studied how the quality of water, the wind speed, etc. affect the growth of icicles. A result that jumped out at me: lab-grown icicles often have bifurcated tips as in (c) and (d) of the figure, but this seems to happen most often when the fan in the experiment is turned off. The implication is that wind somehow straightens out icicles.

---
Huddles of tetrahedra

This is somewhat older work that Ross McKenzie recently linked to. Here's an NYT piece on the race to find ever-closer packings of regular tetrahedra. I recommend reading the linked Nature article (journal link here, ungated arxiv here), which is pretty accessible. There is some back-story to this: Stanislaw Ulam conjectured a long time ago that it should be possible to pack any kind of convex shape more closely than hard spheres. As far as I know there is no proof of this, but it's plausible and known to be true for lots of shapes including M&M's (another NYT story) and more recently tetrahedra. How tetrahedra pack is of particular interest as there is a theory of glassiness (see an old post here) that depends rather crucially on the fact that you cannot tile three-dimensional space with tetrahedra. The theory is basically that particles in an incipient solid like to clump into tetrahedra (each particle is exactly as far away as it wants to be from every other) but the tetrahedra can't line up, so that on large scales you have a jammed amorphous mess: here is a PRB paper by David Nelson related to this theory. The Nature paper is prima facie a beautiful application of ideas from physics to solve a purely mathematical problem -- a project that's close to the formalist, interdisciplinary lump of matter I sometimes refer to as my heart -- but its really surprising finding is that one of the best ways to put the tetrahedra together is to have them form a quasicrystal. This actually makes it a little surprising that 3D quasicrystals aren't common in nature, unless tetrahedra are a much less central motif than the Kleman-Sadoc-Nelson line of thinking about glasses would suggest.

Roundabout dogs, southern discomforts, etc.

  

[Flickr, Creative Commons, etc.]

Wikipedia has this to say (re roundabout dogs):

The phenomenon consists of anonymous people placing homemade dog sculptures, typically made of wood (or sometimes plastic, metal or textile) in roundabouts (traffic circles). Occurrences were reported all over Sweden, and the phenomenon also spread to other countries, such as Spain after it was mentioned on Spanish television (PuntoDos).^[1] Swedish tabloid paper Expressen even placed one at Piccadilly Circus.

The prophet Muhammad was drawn as a roundabout dog but apparently not installed as one. (The installation would have been ephemeral in any case I suppose.)


*


I'm in Charlottesville, VA. The trip was smooth, except for a distressing encounter with a manic autoflush at O'Hare; I'm being put up at the Marriott, which is nice except that my room is next to the ice machine. Garrulous taxi drivers are a recurring theme in my existence. Last night I did trivia -- which I'm crap at -- with Joe Caissie, an Amherst non-acquaintance and twitter friend, who replied to my tweet saying I was in C'ville and debating whether to explore it before snarking about it. I gave a talk this afternoon; the slides are here, though I'm afraid they pdf'ed the hidden slides as well as the real ones, so the talk seems even less coherent than it was. Heard a horrifying story at lunch about some climate scientist who is being persecuted by Ken Cuccinelli for "fraudulence" because he "cited" a later-shown-to-be-flawed paper of his in his publication list. (I love that if he hadn't cited the paper he would have been fraudulently hiding something.) I am also sad to hear that Jim Webb doesn't intend to run again; his politics and mine aren't identical, but he is one of the few politicians that care about convicts'/prisoners' rights, the one political cause I'm passionate about.

Dinner at Boylan Heights; being an experimental feeder I tried the "green eggs and ham" -- i.e. hamburger on English muffin with ham, a fried egg, and pesto on it -- the pesto was definitely a mistake. On the other hand tater tots are superior to fries as a side. I had just reread The Debt to Pleasure on the flight (having switched it in at the last minute for Seamus Deane's creditable but tedious memoir), and could imagine Tarquin Winot inveighing against the combination. Next to me at the bar was some guy who was talking to some chick, not his girlfriend, about abortions and messed-up mutual friends and the like. At some point he (distinctly) said, "she just sprinkles her pussy-dust all over the situation," a felicitous phrase if only because it reminds me of this appalling old story in The Economist that I've never been able to forget. (You've been warned.) And they agreed that the woman in question was "close-chested," another new expression to me, though apparently not to Google. I'll be here tomorrow, then in Atlanta until Wed., then back in Urbana until March meeting.

Adiabatic quantum computation in Egypt

I am amused by the recent proliferation of things Egypt-related but not Egypt-specific essentially related to the current mess. This is the case, e.g., with Hernando de Soto's [1] WSJ op-ed on property rights in Egypt, and, more benignly, with this old NASA photograph of Cairo and Alexandria that has been circulating about the internet. (Alexandria turns out to be one of those long skinny coastal cities like Santa Barbara.) I suppose there's no harm in using topical excuses to force one's longstanding obsessions down the casual reader's throat, though it's hard to do this in a way that's not misleading. So instead of parodying de Soto with "How Egyptian protesters used the laws of gravity to bring down the regime," I'll just write a physics-y post that I was meaning to anyway and add "in Egypt" the way one adds "in bed" at the end of a fortune cookie.

[NASA photo, Flickr, creative commons, etc.]


What follows really belongs on the defunct physics blog, being a little technical. But it isn't really physics, and has to do, besides, with the work of Dorit Aharonov, another of the squalid scholars.

---

1. Conventional quantum computers are structured like Turing machines. They consist of a (finite) set of internal states (logic gates, etc.) and a "tape" which (at the beginning of the computation) has the input string written on it, say in Arabic numerals. The tape is connected to the machine by a read-write head. At each step of the algorithm one can move the tape back and forth, change the internal state, and/or write on the bit of tape that's under the head. At some point the algorithm stops (assuming the problem is decidable); this happens when the internal state of the machine is the designated "end" state and the answer to the original problem is on the tape. Quantum computers differ from classical computers in that the number of allowed tape configurations is (in principle) much larger, as superpositions are allowed in intermediate steps. The complexity of an algorithm is related to how many steps it takes to process an input string of length N, and in particular how this grows with N (e.g., polynomially/exponentially). The complexity of a problem is the complexity of the asymptotically slowest-growing (at large N) algorithm that can solve it.

The problem with this construction is that, while it is easy to find upper bounds for complexity (just write down an algorithm), it is generally hard to establish lower bounds, because it is hard to make useful statements about all conceivable algorithms, or to rule out the possibility that one is just not being clever enough. Generally in this sort of situation one's instinct is to look for a way of talking about the "space of all problems," which (if one is lucky) has some degree of geometric structure -- so that, e.g., two problems are "near" or "far" in problem space.

2. Adiabatic quantum computation begins with the observation that "satisfiability" problems in computer science [2] can be recast in terms of the physics of magnets. Magnets consist of spins that can either point up or down (i.e., true or false); depending on the details, spins might want either to line up or to point in opposite directions [3]. Depending on the interactions there might be a "good" configuration for the spins (i.e., one in which all pairs of spins that want to line up do so and all pairs that want to point in opposite directions do so) or not. (In the latter case the system is called "frustrated." A simple example of a frustrated system: three spins on a triangle that all want to point in opposite directions. If 1 is up, then 2 and 3 want to point down, but this doesn't work because 2 and 3 want to point in opposite directions. No configuration satisfies all the bonds in Egypt.) The lowest possible energy of a frustrated system is higher than that of an unfrustrated system, so the question of whether a spin system is frustrated reduces to that of what its lowest possible energy ("ground state energy") is. Obviously the question of whether a spin system is frustrated is closely related that of whether a set of statements can be satisfied, if you map the clauses onto spins (T/F = up/down). There are some explicit examples of this mapping in the original paper of Farhi et al.

3. This mapping isn't immediately useful as it just recasts the satisfiability problem in the language of magnetism. This is where the physics comes in. Farhi et al. observed that the quantum mechanical "adiabatic theorem" tells you that, if you change your Hamiltonian (the Hamiltonian of a system is an assignment of an energy to every possible configuration of the system) sufficiently slowly, the ground (lowest-energy) state of the original Hamiltonian goes into the ground state of the final Hamiltonian. How slowly you have to go depends on the energy gap between the ground and the next-lowest-energy (first excited) state all along the path in "Hamiltonian space" that leads from the initial to the final Hamiltonian. The bigger the minimum gap, the faster you can afford to go. Often the minimum gap vanishes in the large-system limit (this is called a quantum phase transition); in this case you have to go arbitrarily slowly as the number of spins increases. The minimum allowed speed might either vanish as a power-law or exponentially with the system size. Alternatively there might be exact "degeneracies" for finite systems in which case the algorithm is doomed.

4. The adiabatic algorithm works like this. You start the system off in some reference "trivial" state, let's say with a Hamiltonian that wants all the spins to point up. (E.g. spins in a strong external field.) Call this H_0. The problem Hamiltonian, which encodes the input -- the logical expression you want to check the satisfiability of -- is called H_1. You turn a hypothetical knob so that at time t, the Hamiltonian is H(t) = t/T H_1 + (1 - t/T) H_0. Or you use a curvier path. Assuming T is large enough, the ground state of H(T) is the answer to your problem. The complexity question becomes one of finding the path with the slowest-growing T(N); in general the slowness comes from segments of the path that are near the phase transitions between the initial and final states; the gaps here are given by the theory of critical slowing down; therefore you have mapped the complexity problem into a problem about phase transitions. To rephrase, what this approach does for you is it maps the space of problems onto the space of quantum Hamiltonians, the structure of which can be understood in terms of renormalization group flows.

5. Satisfiability problems aren't everything. The Aharonov et al. paper establishes that adiabatic quantum computation is equivalent to standard quantum computation. (I haven't read the proof.)

6. Of course, the Hamiltonians of conventional magnetic systems are what they are; you can't implement the adiabatic algorithm as stated, and it isn't likely to be terribly useful as a means of quantum computation. However, one does have a fair amount of control over the Hamiltonians describing cold atomic gases, and there's been a fair amount of work on actually implementing the algorithm. A variant that's been proposed is computation-through-dissipation, which is a clever mashup of the adiabatic algorithm and optical pumping. I'm a little skeptical about the practical prospects for this approach, but it is theoretically interesting because dissipative systems are hard to analyze and it would be nice if one were able to use the mapping in reverse and use computer science results to say something about them.

---
[1] Yes, I considered calling him Hernando de Stoato and posting this on STOATUSblog.
[2] Viz. questions about whether a very long logical string is true on any assignment of truth-values to its constituent particles, which, e.g., A or B is but A and not-A isn't
[3] In a physical system this depends on why the spins are interacting at all; there are various possible mechanisms. In the model one puts this in by hand by assigning an energy penalty to undesired configurations.