Insects with cogs

Here’s the initial version of my latest news story for Nature.

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Toothed gears allow young jumping planthoppers to synchronize their legs.

If you’re a young planthopper, leaping a metre in a single bound, you need to push off with both hindlegs perfectly in time or you’ll end up spinning crazily. Researchers in England have discovered that this synchrony is made possible by toothed gears connecting the two legs.

Zoologists Malcolm Burrows and Gregory Sutton of Cambridge University say that this seems to be the first example of rotary motion in nature coupled by toothed gears. They describe their results in Science [1].

Their microscopic images of the hindleg mechanism of the planthopper Issus coleoptratus show that the topmost leg segments, ending in partly circular structures, are connected by a series of tiny intermeshing teeth about 20 micrometres (thousandths of a millimetre) long.

When the insects jump, the two legs rotate together, the cog teeth ensuring that they thrust at exactly the same time. “The gears add an extra level of synchronisation beyond that which can be achieved by the nervous system”, says Burrows.

Planthopper nymphs can take off in just 2 milliseconds, reaching take-off speeds of almost 4 metres per second. For motions this rapid, some mechanical device is needed to keep the legs synchronized and avoid lopsided jumps that lead to spinning along the body axis. The problem doesn’t arise for grasshoppers and fleas: they have legs at the side of the body that push in separate planes rather than counter-rotating in a single plane, and so they can jump one-legged.

Toothed gears have been used in rotating machinery for millenia: Aristotle and Archimedes described them, and they seem to have been used in ancient China much earlier. But like the wheel, this human invention seemed previously to have little value in the natural world.

Now, however, the gear joins the screw-and-nut as a mechanism whose complex shape has been mastered by evolution. In 2011 Alexander Riedel of the State Museum of Natural History in Karlsruhe, Germany and his colleagues reported a screw-and-nut system in the leg joints of a weevil [2].

Riedel considers this new work “significant and exciting”. It adds to the view that “most of the basic components of engineering have been developed in the natural world”, he says. Perhaps gears are not more common, he adds, because there are different ways to achieve the same goal. Honeybees, for example, “couple the movement of both wings to stabilize their flight by using pegs, not as moving gears but more like a Velcro fastener.”

Curiously, the gears are only found in the young nymph insects. When they undergo their final moult, sloughing off their exoskeleton for the last time to reach full adulthood, the gears disappear and instead the legs are synchronized by simpler frictional contact.

Burrows and Sutton aren’t yet sure why this is so, but it might be because of ease of repair. “If a gear breaks it can’t be replaced in adults”, says Burrows. “But in nymphs a repair can be made at the next of several moults.” He also explains that the larger and more rigid adult bodies might make the frictional method work better.

References

1. Burrows, M. & Sutton, G. Science 341, 1254-1256 (2013).
2. van de Kamp, T., Vagovic, P., Baumbach, T. & Riedel, A., Science 333, 52 (2011).

Some additional comments from biomimetics expert Steven Vogel of Duke University:

Interesting business. I can't think of another case of rotary gears at the moment. The closest thing that has yet come to mind is the zipper-like closure once described in (if I recall right) ctenophore mouths.

So many creatures jump without such an obvious mechanical coupling between paired legs that it can't be too difficult to keep from going awry. In any case, some compensation would often be necessary for irregularity in stiffness and level of substratum, etc. One does wonder about whether proprioceptive feedback can work at the short times that would necessarily be involved.

M. Scherge and S.N. Gorb, in their 2000 book, Biological Micro- and Nanotribology, do quite a thorough job. The upshot seems to be that what Burrows describes may be functionally novel, but from a structural point of view it represents (as is so typical of evolutionary innovations) no spectacular discontinuity. They talk about coxal rather than trochanteral segments, one unit more proximal, of course, for whatever that matters.

Synchronizing legs may be no absolute requirement. After all, surfaces are irregular in level, resilience, and so forth, and the legs never push directly at the center of gravity of the insect. So perfect synchrony won't necessarily give a straight trajectory anyway. And some post-launch adjustment may be possible, either inertially or aerodynamically. (Zero-angular-velocity turns, as righting cats, or tail-swinging, as perhaps in jumping rodents that have convergently evolved long tails with hair tufts at their ends.)

Maybe gears such as these come with an odd disability--they really louse things up if they mesh out of register. Or maybe they're tricky to molt and get back into register.

Filleting the gear bottoms is an interesting fillip. For us that's a relatively recent development, I gather. We've made gears for a long time--the antikythera mechanism (100 bce) is a bunch of 'em. Ones that take reasonable torque might be more recent, but are still old - I found some in Agostino Ramelli (1588), unfilleted. And the gears salvaged from a horse ferry (1830) scuttled on Lake Champlain were unfilleted. Odd that no one seemed to have noticed that filleted gears are much, much less prone to getting knocked off, particularly with brittle cast iron.

I take mild issue with Burrow's use of ‘force' for acceleration. It's not only incorrect, but it tends to perpetrate the myth that insects are superstrong, instead of recognizing artifacts of scaling. I wrote an essay about the matter a few years ago; it became chapter 2 in "Glimpses of Creature in their Physical Worlds" (2009). The upshot is that we expect, and find, that acceleration scales (or bumps into a limit line) inversely with length - from jumping cougars down to shooting spores, five orders of magnitude. That keeps the stress on launch materials roughly constant, assuming roughly constant investment in the relevant guns. 200 or 500 g isn't out of line for their size. Good, but not earthshaking.

I'm amused to learn of yet another case of something I once commented on (in "Cats' Paws and Catapults") when trying to inject a note of reality into the hype and hope of biomimetics: "The biomechanic usually recognizes nature's use of some neat device only when the engineer has already provided us with a model. Put another way, biomechanics still studies how, where, and why nature does what engineers do."

Storm in a test tube

Here’s the last of the La Recherche pieces on 'controversies': a short profile of Martin Fleischmann and cold fusion.

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It would be unfair to Martin Fleischmann, who died last year aged 85, if he were remembered solely for his work on ‘cold fusion’ – the alleged discovery with his coworker Stanley Pons in 1989 that nuclear fusion of heavy hydrogen (deuterium), and the consequent release of energy, could be achieved with benchtop chemistry. Before making that controversial claim, Fleischmann enjoyed international repute for his work in electrochemistry. But to many scientists, cold fusion – now rejected by all but a handful of ‘true believers’ – cast doubt on his judgement and even his integrity.

Fleischmann was born in 1927 to a family with Jewish heritage in Czechoslovakia, and came to England as a young boy to escape the Nazis. He conducted his most celebrated work at the University of Southampton, where in 1974 he discovered a technique for monitoring chemical processes at surfaces. This and his later work on ultra-small electrodes made him a respected figure in electrochemistry.

After officially retiring, he conducted his work with Pons at the University of Utah in the late 1980s. They claimed that the electrolysis of lithium deuteroxide using palladium electrodes generated more energy than it consumed, presumably because of fusion of deuterium atoms packed densely into the ‘hydrogen sponge’ of the palladium metal. Their announcement of the results in a press conference – before publication of a paper, accompanied by very scanty evidence, and scooping a similar claim by a team at the nearby Brigham Young University – ensured that cold fusion was controversial from the outset. At the April 1989 meeting of the American Chemical Society, Fleischmann and Pons were welcomed like rock stars for apparently having achieved what physicists had been trying to do for decades: to liberate energy by nuclear fusion.

Things quickly fell apart. Genuine fusion should be accompanied by other telltale signatures, such as the formation of helium and the emission of neutrons with a particular energy. The claim also depended on control experiments using ordinary hydrogen in place of deuterium. Pons and Fleischmann were evasive when asked whether they had done these checks, or what the results were, and the only paper they published on the subject offered no clarification. Several other groups soon reported ‘excess heat’ and other putative fusion signatures, but the claims were never repeatable, and several exhaustive studies failed to find convincing evidence for fusion. The affair ended badly, amidst law suits, recriminations and accusations of fraud.

Fleischmann always maintained that cold fusion was real, albeit perhaps not quite the phenomenon he’d originally thought. The pattern of marginal and irreproducible effects and ad hoc, shifting explanations fits Irving Langmuir’s template of “pathological science”. But even now, some cling to the alluring dream that cold fusion could be an energy source.

Remembering the memory

Here’s my second piece for La Recherche’s special issue in August on scientific controversies – this one on the ‘memory of water’.

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So far, “The Memory of Water” has been used as the title of a play, two movies, a collection of poems and a rock song. When the French immunologist Jacques Benveniste proposed in 1988 that water has a memory, he gave birth to a catchphrase with considerable cultural currency.

But Benveniste, who died in 2004, also ignited a scientific controversy that is still simmering a quarter of a century later. While most physicists and chemists consider Benveniste’s original idea – that water can retain a memory of substances it has dissolved, so that they can display chemical effects even when diluted to vanishing point – to be inconsistent with all we know about the properties of liquid water, Benveniste’s former colleagues and a handful of converts still believe there was something in it.

The claim would be provocative under any circumstances. But the dispute is all the fiercer because Benveniste’s ‘memory of water’ seems to offer an explanation for how homeopathy can work. This ‘alternative’ medical treatment, in which putative remedies are so diluted that active ingredients remain, has a huge following worldwide, and is particularly popular in France. But most medical practitioners consider it to be sheer superstition sustained by ignorance and the placebo effect.

Yet while there seems no good reason to believe that water has a ‘memory’, no one is quite sure how to account for the peculiar results Benveniste reported in 1988. This episode illustrates how hard it is for science to deal with deeply unorthodox findings, especially when they bear on wider cultural issues. In such cases an objective assessment of the data might not be sufficient, and perhaps not even possible, and the business of doing science is revealed for the human endeavour that it is, with all its ambiguities, flaws and pitfalls.

Rise and fall

Benveniste did not set out to ‘discover’ anything about water. As the head of Unit 200 of the French national medical research organization INSERM in Clamart on the edge of Paris, he was respected for his work on allergic responses. In 1987 he and his team spotted something strange while investigating the response of a type of human white blood cell, called basophils, to antibodies. Basophils patrol the bloodstream for foreign particles, and are triggered into releasing histamine – a response called degranulation – when they encounter allergy-inducing substances called allergens. Degranulation begins when allergens attach to antibodies called immunoglobulin E (IgE) anchored to the basophil surface. Benveniste’s team were using a ‘fake allergen’ to initiate this process: another antibody called anti-IgE, produced in non-human animals.

The researchers sometimes found that degranulation happened even when the concentration of anti-IgE was too low to be expected to have any effect. Benveniste and colleagues diluted a solution of anti-IgE gradually and monitored the amount of basophil degranulation. Basic chemistry suggests that the activity of anti-IgE should fall smoothly to zero as its concentration falls. But instead, the activity seemed to rise and fall almost rhythmically as the solution got more dilute. Even stranger, it went on behaving that way when the solution was so dilute that not a single anti-IgE molecule should remain.

That made no sense. How can molecules have an effect if they’re not there? Benveniste considered this finding striking enough to submit to Nature.

The editor of Nature at that time was John Maddox, who often displayed empathy for outsiders and a healthy scepticism of smug scientific consensus. Rather against the wishes of his staff, he insisted on sending the paper for peer review. The referees were puzzled but could find no obvious flaw in Benveniste’s experiments. After they had been replicated in independent laboratories in Canada, Italy and Israel, there seemed to be no option but to publish Benveniste’s paper, which Nature did in June 1988 [E. Davenas et al., Nature 333, 816 (1988)] – accompanied by an editorial from Maddox admitting that “There is no objective explanation of these observations.”

Hope for homeopathy?

The Nature paper caused pandemonium. It was clear at once that Benveniste’s results seemed to be offering scientific validation of homeopathy, the system of medicine introduced in the early nineteenth century by the German physician Samuel Hahnemann, in which the ‘active’ ingredients, already diluted to extinction, are said to get even more potent as they get more dilute.

Advocates swear that some clinical trials support the efficacy of homeopathy, but most medical experts consider there to be no solid evidence that it is effective beyond what would be expected from placebo effects. Even many homeopaths admit that there is no obvious scientific way to account for the effects they claim.

Not, at least, until the memory of water. “Homeopathy finds scientific support”, proclaimed Newsweek after Benveniste’s paper was published.

But how could water do this? The French team evidently had no idea. They suggested that “water could act as a ‘template’ for the [anti-IgE] molecule” – but this made no sense. For one thing, they evidently meant it the other way round: the antibody was acting as a template to imprint some kind of molecular structure on water, which could then act as a surrogate when the antibody was diluted away. But why should a negative imprint of the molecule act like the molecule itself? In any case, the properties of antibodies don’t just depend on their shape, but on the positions of particular chemical groups within the folded-up protein chain. And most of all, water is a liquid: its H2O molecules are constantly on the move in a molecular dance, sticking to one another by weak chemical bonds for typically just a trillionth of a second before separating to form new configurations. Any imprint would be washed away in an instant. If Benveniste and colleagues were right, shouldn’t water show the same behaviour as everything it has ever dissolved, making it sweet, salty, biologically active, toxic?

But data are data. Or are they? That’s what Maddox had begun to wonder. To get to the bottom of the affair, he launched an unprecedented investigation into INSERM Unit 200. Maddox travelled to Clamart to watch Benveniste’s team repeat their measurements before his eyes, accompanied by American biologist Walter Stewart, a ‘fraud-buster’ at the National Institutes of Health who had previously investigated allegations of misconduct in the laboratory of Nobel laureate David Baltimore, and stage magician James Randi, a debunker of pseudoscientific claims like those of the ‘psychic’ Uri Geller. “So now at last confirmation of what I have always suspected”, one correspondent wrote to Nature. “Papers for publication in Nature are referred by the Editor, a magician and his rabbit.”

The Nature team insisting that the researchers carry out a suite of double-blind experiments designed to rule out self-deception or trickery. Their conclusions were damning: “The anti-IgE at conventional dilutions caused degranulation, but at ‘high dilution’ there was no effect”, the investigators wrote [J. Maddox et al., Nature 334, 287 (1988)]. Some runs did seem to show high-dilution activity, but it was neither repeatable nor periodic as dilution increased.

Attempts by other labs to reproduce the results also failed to supported Benveniste’s claims. Although occasionally they did see strange high-dilution effects, it is not at all uncommon to find anomalous results in experiments on biological systems, which are notoriously messy and sensitive to impurities or small changes in conditions. The ‘high-dilution’ claims meet all the criteria for what the American chemist Irving Langmuir called ‘pathological science’ in 1925. For Langmuir, this was the science of “things that aren’t so”: phenomena that are illusory. Langmuir adduced several distinguishing features: the effects always operate at the margins of detectability, for example, and their supporters generally meet criticisms with ad hoc excuses dreamed up on the spur of the moment. His criteria apply equally to some other modern scientific controversies, notably the claim by Russian scientists in the late 1960s to have discovered a new, waxy form of water called polywater, and the claims of ‘cold nuclear fusion’ achieved using benchtop chemistry by Martin Fleischmann and Stanley Pons in Utah in 1989 [coming up next!].

Disappearing act

After Maddox’s investigation, most scientists dismissed the memory of water as a chimera. But Benveniste never recanted. He was sacked from INSERM after ignoring instructions not to pursue the high-dilution work, but he continued it with private funds, having attracted something of a cult following. These studies led him to conclude that water acts as a “vehicle for [biological] information”, carrying the signal that somehow encodes the biomolecule’s activity. Benveniste eventually decided that water can be “programmed” to behave like any biological agent – proteins, bacteria, viruses – by electromagnetic signals that can be recorded and sent down telephone wires. In 1997 he set up a private company, DigiBio, to promote this field of “digital biology”, and it is rumoured that the US Department of Defense funded research on this putative ‘remote transmission’ process.

Such studies continue after his death, and have recently acquired a high-profile supporter: the immunologist Luc Montagnier, who was awarded the 2008 Nobel prize for the co-discovery of the AIDS virus HIV. Montagnier believes that the DNA molecule itself can act as both a transmitter and a receiver of ultralow frequency electromagnetic signals that can broadcast biological effects. He believes that the signals emitted by pathogen DNA could be used to detect infection. He maintains that these emissions do not depend on the amount of DNA in suspensions of pathogens, and are sometimes detectable at very high dilution. They might originate, he says, from quantum effects in the water surrounding the DNA and other biological structures, according to a controversial theory that has also been invoked to explain Benveniste’s experiments [E. Del Guidice et al. Phys. Rev. Lett. 61, 1085 (1988)].

“Benveniste was rejected by everybody, because he was too far ahead”, Montagnier has said [Science 330, 1732 (2010)]. “I think he was mostly right but the problem was that his results weren't 100% reproducible.” In 2010 Montagnier began research on high-dilution DNA at a new research institute at Jiaotong University in Shanghai. “It's not pseudoscience, it's not quackery”, he insists. “These are real phenomena which deserve further study.” He is currently the head of the World Foundation for AIDS Research and Prevention in Paris, but his unorthodox views on water’s ‘memory’ have prompted some leading researchers to question his suitability to head AIDS projects.

Meanwhile, the idea that the undoubtedly unusual molecular structure of water – a source of continued controversy in its own right [see e.g. here and here] – might contrive to produce high-dilution effects still finds a few supporters among physical chemists. Homeopaths have never relinquished the hope that the idea might grant them the scientific vindication they crave: a special issue of the journal Homeopathy in 2007 was devoted to scientific papers alleging to explore water’s ‘memory’, although none provided either clear evidence for its existence or a plausible explanation for its mechanism [see here].

Such efforts remain firmly at the fringes of science. But what must we make of Benveniste’s claims? While inevitably the suspicion of fraud clouds such events, my own view – I joined Nature just after the ‘memory of water’ paper was published, and spoke to Benveniste shortly before his death – is that he fully believed what he said. A charming and charismatic man, he was convinced that he had been condemned by the ‘scientific priesthood’ for heresy. The irony is that he never recognized how his nemesis Maddox shared his maverick inclinations.

The “Galileo” rhetoric that Benveniste deployed is common from those who feel they have been ‘outlawed’ for their controversial scientific claims. But Benveniste never seemed to know how to make his results convincing, other than to pile up more of them. Faced with a puzzling phenomenon, the scientist’s instinct should be to break it down, to seek it in simpler systems that are more easily understood and controlled, and to pinpoint where the anomalies arise. In contrast, Benveniste studied ever more complicated biological systems – bacteria, plants, guinea pigs – until neither he nor anyone else could really tell what was going on. The last talk I saw his team deliver, in 2004, was a riot of graphs and numbers presented in rapid succession, as though any wild idea could be kept in the air so long as no one can pause to examine it.

This, perhaps, is the lesson of the memory of water: when you have a truly weird and remarkable result in science, your first duty is to try to show not why it must be true, but why it cannot be.

The antimony wars

The August issue of La Recherche has the theme of ‘controversies in science’. I wrote several pieces for it – this is the first, on the battle between the Galenists and Paracelsians in the French court in the early 17th century.

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“I am different”, the sixteenth-century Swiss alchemist and physician Paracelsus once wrote, adding “let this not upset you”. But he upset almost everyone who came into contact with him and his ideas, and his vision of science and medicine continued to spark dispute for at least a hundred years after his death in 1541. For Paracelsus wanted to pull up by its roots the entire system of medicine and natural philosophy that originated with the ancient Greeks – particularly Aristotle – and replace it with a system that seemed to many to have more in common with the practices of mountebanks and peasant healers.

Paracelsus – whose splendid full name was Philip Theophrastus Aureolus Bombastus von Hohenheim – had a haphazard career as a doctor, mostly in the German territories but also in Italy, France and, if his own accounts can be believed, as far afield as Sweden, Russia and Egypt. Born in the Swiss village of Einsiedeln, near Zurich, into a noble Swabian family fallen on hard times, he trained in medicine in the German universities and Ferrara in Italy before wandering throughout Europe offering his services. He attended kings and treated peasants, sometimes with a well-filled purse but more often penniless. Time and again his argumentative nature ruined his chances of a stable position: at one time town physician of Basle, he made himself so unpopular with the university faculty and the authorities that he had to flee under cover of darkness to avoid imprisonment.

Paracelsus could be said to have conceived of a Theory of Everything: a system that explained medicine and the human body, alchemy, astrology, religion and the fundamental structure of the cosmos. He provided one of the first versions of what science historians now call the ‘chemical philosophy’: a theory that makes chemical transformation the analogy for all processes. For Paracelsus, every natural phenomenon was essentially an alchemical process. The rising of moisture from the earth and its falling back as rain was the equivalent of distillation and condensation in the alchemist’s flask. Growth of plants and animals from seeds was a kind of alchemy too, and in fact even the Biblical creation of the world was basically an alchemical process: a separation of earth from water. This philosophy seems highly fanciful now, but it was nonetheless rational and mechanistic: it could ascribe natural and comprehensible causes to events.

Although Paracelsus was one of the most influential advocates of these ideas in the early Renaissance, they weren’t entirely his invention (although he characteristically exaggerated his originality). The chemical philosophy was rooted in the tradition known as Neoplatonism, derived from the teachings of Plato but shaped into a kind of mystical philosophy by the third-century Greek philosopher Plotinus. One of the central ideas of Neoplatonism is the correspondence between the macrocosm and the microcosm, so that events that occurred in the heavens and in the natural world have direct analogies within the human body – or with the processes conducted in an alchemist’s flasks and retorts. This correspondence provided the theoretical basis for a belief in astrology, although Paracelsus denied that our destiny is absolutely fixed by our horoscope. He proposed that the macro-micro correspondence led to ‘signatures’ in nature which revealed, for example, the medical uses of plants: those shaped like a kidney could treat renal complaints. These signatures were signs left by God to guide the physician towards the proper use of herbal medicines. They exemplify the symbolic character of the chemical philosophy, which was based on such analogies of form and appearance.

What the chemical philosophy implied for medicine conflicted with the tradition taught to physicians at the universities, which drew on ideas from antiquity, particularly those attributed to the Greek philosopher Hippocrates and the Roman doctor Galen. This classical tradition asserted that our health is governed by four bodily fluids called humours: blood, phlegm, and black and yellow bile. Illness results from an imbalance of the humours, and the doctor’s task was to restore this balance – by drugs, diet or, commonly, by blood-letting.

Academic doctors in the Middle Ages adopted the humoral system as the theoretical basis of their work, but its connection to their working practices was generally rather tenuous. Often they prescribed drugs, made from herbs or minerals and sold by medieval pharmacists called apothecaries. Doctors charged high fees for their services, which only merchants and nobles could afford. They were eminent in society, and often dressed lavishly.

Paracelsus despised all of this. He did not share the doctors’ disdain of manual work, and he hated how they paraded their wealth. Worse still, he considered that the whole foundation of classical medicine, with its doctrine of humours, was mistaken. When he discovered at university that becoming a doctor of medicine was a matter of simply learning and memorizing the books of Galen and Avicenna, he was outraged. He insisted that it was only through experience, not through book-learning, that one could become a true healer.

By bringing an alchemical perspective to the study of life and medicine, Paracelsus helped to unify the sciences. Previously, alchemy had been about the transmutation of metals. But for Paracelsus, its principle purpose was to make medicines. Just as alchemists could mimic the natural transmutation of metals, so could they use alchemical medicines to bring about the natural process of healing. This was possible, in fact, because human biology was itself a kind of alchemy. In one of his most fertile ideas, Paracelsus asserted that there is an alchemist inside each one of us, a kind of principle that he called the archeus, which separates the good from the bad in the food and drink that we ingest. The archeus uses the good matter to make flesh and blood, and the bad is expelled as waste. Paracelsus devised a kind of bio-alchemy, the precursor to modern biochemistry, which indeed now regards nature as a superb chemist that takes molecules apart and puts them back together as the constituents of our cells.

Most of all, Paracelsus argued that medicine should involve the use of specific chemical drugs to treat specific ailments: it was a system of chemotherapy, which had little space for the general-purpose blood-letting treatments prescribed by the humoral theory. This Paracelsian, chemical approach to healing became known in the late sixteenth century as ‘iatrochemistry’, meaning the chemistry of medicine.

Paracelsus was able to publish relatively little of his writings while he was alive, but from around 1560 several publishers scoured Europe for his manuscripts and published compendia of Paracelsian medicine. Once in print, his ideas attracted adherents, and by the last decades of the century Paracelsian medicine was exciting furious debate between traditionalists and progressives. Iatrochemistry found a fairly receptive audience in England, but the disputes they provoked in France were bitter, especially among the conservative medical faculty of the University of Paris.

That differing reception was partly motivated by religion. Paracelsus belonged to no creed, but he was widely identified with the Reformation – he even compared himself to Martin Luther – and so his views found more sympathy from Protestants than Catholics. The religious tensions were especially acute in France when the Huguenot prince of Navarre was crowned Henri IV in 1589. Fears that Henri would create a Huguenot court seemed confirmed when the new king appointed the Swiss doctor Jean Ribit as his premier médicin, and summoned also two other Huguenot doctors with Paracelsian ideas, the Gascon Joseph Duchesne and another Genevan, Theodore Turquet de Mayerne.

In 1603 Jean Riolan, the head of the Paris medical faculty, published an attack on Mayerne and Duchesne, asserting the supremacy of the medicine of Hippocrates and Galen. Although these two Paracelsians sought to defend themselves, they only secured a retraction of this damning charge by agreeing to practice medicine according to the rules of the classical authorities.

But the Paracelsians struck back. Around 1604, Ribit and Mayerne helped a fellow Huguenot and iatrochemist named Jean Béguin set up a pharmaceutical laboratory in Paris to promote chemical medicine. In 1610 Béguin published a textbook laying out the principles of iatrochemistry in a clear, straightforward manner free from the convoluted style and fanciful jargon used by Paracelsus. When this Latin text was translated into French five years later as Les elemens de chymie, it served much the same propagandizing role as Antoine Lavoisier’s Traité élémentaire de chemie did for Lavoisier’s own system of chemistry at the end of the eighteenth century.

But the war between the Galenists and the Paracelsians raged well into the seventeenth century. Things looked bad for the radicals when Henri IV, who had been prevented in 1609 from making Mayerne his new premier médicin, was assassinated the following year. Lacking royal protection, Mayerne took up an earlier offer from James I of England and fled there, where he flourished.

Yet when Riolan’s equally conservative son (also Jean) drew up plans for a royal herb garden in 1618, he did not anticipate that this institution would finally be established 20 years later as the Jardin du Roi by the iatrochemist Gui de la Brosse. In 1647 the Jardin appointed the first French professor of chemistry, a Scotsman named William Davidson, who was an ardent Paracelsian.

Most offensive of all to the Paris medical faculty was Davidson’s support for the medical use of antimony. Ever since the start of the century, Paracelsians and Galenists had been split over whether antimony was a cure or poison (it is in fact quite toxic). Davidson’s claim that “there is no more lofty medicine under heaven” so enraged the faculty that they hounded him from his post in 1651, when the younger Riolan republished his father’s condemnation of Duchense and Mayerne.

Yet it was all too late for the Galenists, for the Jardin du Roi, which became one of the most influential institutions in French chemistry and medicine, continued to support iatrochemistry. The professors there produced a string of successful chemical textbooks, most famously that of Nicolas Lemery, called Cours de chimie, in 1675. These men were sober, practical individuals who helped to strip iatrochemistry of its Paracelsian fantasies and outlandish jargon. They placed chemical medicine, and chemistry itself, on a sound footing, paving the way to Lavoisier’s triumphs.

What was this long and bitter dispute really about? Partly, of course, it was a power struggle: over who had the king’s ear, but also who should dictate the practice (and thus reap the financial rewards) of medicine. But it would be too easy to cast Riolan and his colleagues as outdated reactionaries. After all, they were right about antimony (if for the wrong reasons) – and they were right too to criticize some of the wild excesses of Paracelsus’s ideas. Their opposition forced the iatrochemists to prune those ideas, sorting the good from the bad. Besides, since no kind of medicine was terribly effective in those days, there wasn’t much empirical justification for throwing out the old ways. The dispute is a reminder that introducing new scientific ideas may depend as much on the power of good rhetoric as on the evidence itself. And it shows that in the end a good argument can leave science healthier.

Before it gets too previous, here is an earlier piece for BBC Future.

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It’s time for one of those imagined futures which always miss the mark by a mile – you know, “Imagine setting off for work with your jet-pack…” But here we go anyway: imagine that photographs, newspapers and books speak, that you can play music out of your curtains, that food wrapping calls out “I’m nearly past my sell-by date!” OK, so perhaps it’s all a bit nightmarish rather than utopian, but the point is that some weird and wonderful things would be possible if a loudspeaker could be made as thin, light and flexible as a sheet of paper.

That’s what is envisaged in a study by Andrew Barnard and colleagues at the Pennsylvania State University. They have revisited an idea nearly a hundred years old, and sounding decidedly steampunk: the thermophone or thermoacoustic loudspeaker, in which sound is generated by the effect of a material rapidly oscillating between hot and cold. In 1917 Harold Arnold and I. B. Crandall of the American Telephone and Telegraph Company and Western Electric Company showed that they could create sound by simultaneously passing alternating and direct currents through a very thin platinum foil. This heats up the foil, and the heat is conducted into the air surrounding it, in pulses that are paced by the frequency of the a.c. current.

A sound wave in air corresponds to an oscillation of the air pressure. An ordinary loudspeaker generates those pressure waves via a mechanical vibration of a membrane. But air pressure is also altered when the air gets hotter or cooler. So the thermal oscillations of Arnold and Crandall’s platinum film also generated a sound wave – without any of the cumbersome, heavy electromagnets used to excite vibrations in conventional speakers, or indeed without moving parts at all.

The problem was that the sound wasn’t very loud, however, and the frequency response wasn’t up to reproducing speech. So the idea was shelved for almost a century.

It was revitalized in 2008, when a team in China found that they could extract thermoacoustic sound from a new material: a thin, transparent film made from microscopic tubes called carbon nanotubes (CNTs), aligned parallel to the plane of the film. These tiny tubes, whose walls are one atom thick and made from pure carbon, are highly robust, need very little heat input to warm them up, and are extremely good heat conductors – just what is needed, in other words, to finally put the idea of Arnold and Crandall into practice and create gossamer-thin loudspeakers.

The Chinese team, led by Lin Xiao at Tsinghau University, showed that they could get their CNT films to emit sound. But that’s not the same as making a loudspeaker that will produce good-quality sound over the whole frequency range of human hearing, from a few tens of hertz (oscillations per second) to several thousand. So while the CNT speakers might have valuable applications such as sonar – they work perfectly well underwater – it isn’t yet clear if they can produce hifi-quality sound in your living room.

That’s what Barnard and colleagues have sought to assess. One of the factors determining the loudness of the devices is how efficiently heat can be transferred into the surrounding gas to induce pressure waves. This depends on how much the gas heats up for a given input of heat energy: a property called the heat capacity. A low heat capacity means that only a small energy input can create a big change in temperature, and thus in pressure. So the sound output can be improved by surrounding the CNT film with a gas that has a lower heat capacity than air, such as the inert gases helium, argon or xenon. Xiao’s team has already demonstrated this effect, but Barnard and colleagues now show that it offers perhaps the best avenue for improving the performance of these devices. To transmit the acoustic vibrations of the inert gas to the air beyond, so that we can hear the results, one would separate the gas and air with a flexible membrane.

Another way to improve the sound output is to make the surface area of the film bigger. That can be done without ending up with a carpet-sized device by stacking several sheets in layers. The Pennsylvania group has shown that this works: a four-layer speaker, for example, is significantly louder for the same power input.

All things considered, Barnard and colleagues conclude that “a high power CNT loudspeaker appears to be feasible.” But it won’t be simple: the CNT films will probably need to be enclosed and immersed in xenon, for example, which would pose serious challenges for making robust ‘wearable’ speakers.

And there is already competition. For example, a small start-up British company called Novalia has created an interactive, touch-sensitive printed poster that can generate drum-kit sounds through vibrations of the paper itself. Curiously, that technology uses electrically conducting inks made from a pure-carbon material called graphene, which is basically the same stuff as the walls of carbon nanotubes but flattened into sheets. So one way or another, these forms of ‘nanocarbon’ look destined to make our isles full of noises.

Reference: A. R. Barnard et al., Journal of the Acoustical Society of America 134, EL280 (2013).

Seven Ages of Science

I hope people have been listening to Lisa Jardine’s Seven Ages of Science on BBC Radio 4. It is very nice – a refreshingly personal and idiosyncratic take on the history of science, rather than the usual plod through the usual suspects. I made a few modest contributions to some episodes, plucked from some long but fun conversations.

Why you should appear in your papers

Here’s my latest Crucible column for Chemistry World.

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The strange thing about Einstein’s classic 1905 papers on relativity, quantum theory and Brownian motion is that he is largely absent from them. That’s to say, he hardly ever uses the first person singular to put himself in the reference frame. “We have now derived…”, “We now imagine space to be…” – we and Einstein do it all together. He pops up a little thrillingly at the start of the extraordinarily brief “E=mc2” paper, but quickly vanishes beneath the passive voice and the impersonal “one concludes”.

It wasn’t his intention but this all makes Einstein sound magisterial. Lavoisier was already vacillating 130 years earlier, when he is sometimes “I” and sometimes “we” – calculatedly so, for he’s very much present in person when distinguishing his own discoveries from Priestley and Scheele, but tells us bossily that “we shall presently see what we ought to think” when it comes to choosing amongst them.

I’m left thinking about these questions of voice after reading a paper by ‘science studies’ researchers Daniele Fanelli of the University of Edinburgh and Wolfgang Glänzel of the Catholic University of Leuven (PLOS ONE 8, e66938; 2013). They report that bibliometric analysis of around 29,000 papers ranging across all the sciences from maths and physics to social sciences, as well as some in the humanities, show significant differences in style and content which point to a genuine hierarchy of sciences, along the lines first postulated by the French philosopher Auguste Comte in the 1830s. As we would put it today, physics and maths are the ‘hardest’ sciences, and they become progressively ‘softer’ as we move through chemistry, the life sciences, and the social sciences. The key criterion the authors use for this classification is the degree of consensus in the field, as revealed for example by the number, age and overlap of references.

There’s a lot to discuss in these interesting findings; but one aspect that caught my attention was the authors’ comparison of whether or not papers use personal pronouns. “Scientists aim at making universal claims, and their style of writing tends to be as impersonal as possible”, say Fanelli and Glänzel. “In the humanities, on the other hand, the emphasis tends to be on originality, individuality and argumentation, which makes the use of first person more common.” They found that indeed the ‘harder’ sciences tend to use personal pronouns less often.

The assumption here is that an impersonal, passive voice suggests a universal truth. It really does suggest that – and that’s the whole point. Fanelli and Glänzel’s implication that the passive voice reflects science’s ability to deliver absolute knowledge is a case of science falling for its own tricks. Scientists actively cultivated the impersonal tone as a rhetorical device to persuade and convey authority. This process began with the institutionalization of science in the seventeenth century, and it was a feature of what historian Steven Shapin has called the “literary technology” of that age: a style of writing calculated to sound convincing.

There were good reasons for this, to be sure. Experimental scientists like Robert Boyle wanted to free themselves from the claims of the Renaissance magi to have received deep insights through personal revelation; on the contrary, they’d found stuff out using procedures that anyone (with sufficient care and education) could conduct. So it didn’t matter any more who you were, an attitude encapsulated in Claude Bernard’s remark in 1865 that “Art is I; Science is We.” Or better still, science is “It is shown that…”

Yet the pendulum is swinging. Many books advising how to write scientific papers tend now to recommend the active voice. For example, in Successful Scientific Writing (Cambridge University Press, 1996), Janice Matthews and Robert Matthews say “Many scientists overuse the passive voice. They seem to feel that every sentence must be written in passive terms, and they undergo elaborate contortions to do so.” But the passive voice, the authors say, “often obscures your true meaning and compounds your chances of producing pompous prose.” The American Institute of Physics, American Chemical Society and American Medical Association all recommend the active voice and use of pronouns, although they accept the passive voice for methods sections.

I would go further. If scientists care about precise reporting, they should insist on planting themselves in their papers. Their fallibility, preconceptions and opinions are a part of the picture, and it’s misleading to imply otherwise. For many of the scientists who, during my years as an editor at Nature, balked at writing “I” rather than “We” in their single-author papers, the worry was not that they’d seem less authoritative but rather, too arrogant. But I suspect “I” also seemed disturbingly exposing. Either way, if you did the work, you’ve got to admit to it.

How plastics got under control

Several things to catch up with after the holidays, and here’s the spoddiest first: a leader for Nature Materials celebrating the 50th anniversary of the chemistry Nobel for Ziegler and Natta.

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One could tell the history of the twentieth century through the medium of polymers. In a weird and ramshackle way that is almost what American author Thomas Pynchon attempted in his novel Gravity’s Rainbow, which shows the German cartel IG Farben clandestinely orchestrating the Second World War and making rockets with unnerving, sensory polymer skins. But the truth is scarcely less strange and no less dominated by the agencies of conflict, commerce and politics.

Karl Ziegler, who 50 years ago won the Nobel Prize in Chemistry alongside Italian chemist Giulio Natta for their work on the stereoselective catalysis of alkene polymerization, began his work on polymerization during the Second World War to make synthetic rubber for the German war effort as supplies from the Asian rubber plantations were cut off. When the war ended Ziegler was in Halle, soon to become Russian-occupied territory, and the American authorities encouraged him to take a post at Mülheim to preserve his expertise for the West. It was there in 1953 that he discovered the organometallic compounds, such as triethylaluminium, that would not only catalyse ethylene polymerization at lower temperatures and pressures than the standard industrial process then prevailing but would produce orderly straight-chain molecules without random branching, creating a high-density product with new potential uses.

Natta, working in Milan, was also drawn into synthetic-rubber work during the war, and once he heard about Ziegler’s discovery he realised that it could be used to make ordered polymers from other alkenes. He and his coworkers quickly discovered that ethylaluminium chloride and vanadium tetrachloride would catalyse the formation of polypropylene with a stereoregular isotactic chain structure: all the methyl side-chains on the ‘same’ side, enabling orderly crystalline packing into a solid, high-density form. The Italian chemicals company Montecatini, which funded Natta’s research, immediately developed this process on an industrial scale, and were marketing isotactic polypropylene at Ferrara by 1957 as a bulk plastic, a fibre and a packing film. Natta went on to conduct pioneering work on the synthesis of rubbers by controlled polymerization of butadiene.

Yet the stereoselective polymerization of propylene into a high-density plastic was in fact discovered independently before Ziegler and Natta, by American chemists J. Paul Hogan and Robert Banks working at the Phillips Petroleum Company in Oklahoma. They too were stimulated by the war – but in this case by its termination, which reduced the demand for oil and prompted Phillips to diversify its products. Hogan and Banks began in the early 1950s to look for ways to convert the small alkenes from oil refining into petrol. When they used a catalyst of nickel oxide and chromium oxide to process propylene, they found a solid white crystalline product.

This new, stiff plastic, marketed by Phillips from 1954 as Marlex, owed its commercial success to a craze that swept the United States in the late 1950s: the hula hoop. Demand for this toy consumed the Phillips plant’s entire output, and boosted production to a level that paved the way for more practical uses: industrial tubing, baby bottles and other household products. But the patent application filed by Hogan and Banks was contested by Ziegler’s rival claim, leading to a court battle that lasted three decades. Because of this, and since the American chemists were slow to publish, their discovery was eclipsed by the Ziegler-Natta Nobel – even though chromium catalysts are still widely used.

Even this is not the full extent of the priority dispute, for Alexander Zeltz and Ron Carmody of Standard Oil in Indiana also made a partially crystalline isotactic form of polypropylene in 1950 using a molybdenum catalyst. But there’s more to a discovery than being first: it’s not clear that they knew quite what they had made, and in any case there were complex questions to be addressed about the degree of stereoselectivity created by the different catalysts.

Basic science is here more the beneficiary than the begetter, for the work of Ziegler and Natta pointed the way to approaches to stereoselective formation of carbon-carbon bonds that remain a rich field of science today. Its value has occasionally surfaced in unexpected ways – it was an inadvertent excess of Ziegler-Natta catalyst, for example, that led Hideki Shirakawa to discover the first electrically conducting polymer, a form of polyacetylene, in Tokyo in 1967. The scale of the polyolefin industry, meanwhile, scarcely needs emphasizing: close to 50 million tons of polypropylene alone is produced each year.

One moral of these stories is that true discovery requires that you know what you’ve done, and show it. But they also reveal how the conventional narrative of technological advance, whereby ‘pure’ fundamental science leads to applications, is seldom of much relevance in fields such as materials chemistry. Social and cultural drivers often determine what gets explored – if not necessarily what comes out. And success may be determined by the fickle whims of the market rather than the merit of the product. One might add the lesson that, if you want recognition, publish quickly and get a good lawyer – not perhaps the most edifying moral, but that’s the way of the world.

Appearances matter most in musical performance

This is a long version of the news story I’ve just published with Nature – there is just so much to talk about here.

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Our judgements of quality depend more on how a musician moves than what they sound like.

He’d whip his long hair around as he played, beads of sweat flying into the audience, and women would swoon or throw their clothes onto the stage. No, this isn’t the young Mick Jagger or Jimmy Page but Franz Liszt, sometimes dubbed the first rock star, of whose famously theatrical piano recitals Robert Schumann once said that, if he played behind a screen, “a great deal of poetry would be lost”.

But who cares about the histrionics – it’s the music that matters, right? Not according to a new study which shows that people’s judgements about the quality of a musical performance are influenced more by what they see than by what they hear [1].

These findings by social psychologist Chia-Jung Tsay of University College London, who is also an acclaimed classical pianist, may be embarrassing and even shocking to music lovers. The vast majority of participants in Tsay’s experiments – around 83 percent of both untrained participants and professional musicians – insisted at the outset that sound was their key criterion in assessing video and audio recordings of performances.

Yet it wasn’t. The participants were presented with recordings for the three finalists in each of 10 prestigious international competitions, and were asked to guess the winner. With just sound, or sound plus video, novices and experts both guessed right at about the same level as chance (33 percent of the time), or a little less. But with video alone, the success rate for both rose to about 46-53 percent. The experts did no better than the novices.

In experiments where participants were randomly assigned to receive the silent videos, Tsay says “they expressed much frustration and lack of confidence in their choices, not realizing that they were the ones to best approximate the original decisions.” She would receive comments like “It’s impossible to take seriously without sound” and “This is meaningless since I can't hear [the performer]”

This is a brilliant paper”, says philosopher of music Vincent Bergeron of the University of Ottawa in Canada. “The fact that the judgments of both novice and expert participants are affected in the very same way suggests that the visual channel constitute a powerful and robust factor in the evaluation of musical performances.”

Rethinking performance

The results raise provocative questions about what musical performance really is. Classical audiences in particular might like to claim that they are there to enjoy the exquisite sounds the performers are making – but it seems their assessments are based primarily on what they are seeing.

“As an academic I was delighted to find these counterintuitive results”, says Tsay. “As a classical musician, I was initially somewhat disturbed. It was surprising to find that there is such a wide gap between what we believe matters in the evaluation of music performance and what is actually being used to judge performances.”

But Bergeron isn’t perturbed. He has previously argued that visuals do play a part in how we experience music when we see it performed [2]. “One could plausibly argue that music made for performance, such as classical music, is a visual as well as a sonic art, and that it should also be evaluated on the basis of how it looks”, he says.

Bergeron’s earlier case built partly on the work of Jane Davidson on the University of Western Australia in Crawley, Australia, who also found that judgements of quality depend on sight as well as sound [3]. Music neuropsychologist Daniel Levitin of McGill University in Canada agrees that Tsay’s results might have been anticipated, both because of earlier work on the subject [4,5] and because of what we know about cognition in general.

“In a sense, the visual channel is more primordial than the auditory”, he says. Besides, “there are lots of ways in which our intuitions about our own cognition are wrong”, he says. “The whole field of perception and cognition is full of these, such as visual and auditory illusions.”

But Davidson says that there seem to be nuances in such judgements. For example, in her studies “musicians were still able to differentiate between poorer and better quality musical sound”, she says.

In Davison’s experience, the assessments of non-musicians may rely more on visuals than that of professional musicians. “In my own studies, musicians were able to use sound and vision independently”, she says. “It was only non-musicians who relied mainly on the visual information.”

She adds that some studies, including her own, that lay sound from one performance on top of visuals from another find that, although the visuals dominate perceptions, such tricks “don’t fool experts”.

What kind of messages do we take away from visual information? Tsay was able to rule out the possibility that a performer’s gender, race or attractiveness influence judgements, at least in her experiments, by tests in which she reduced the video data to black-and-white outlines of the performers. Participants still guessed the competition winners correctly with much the same better-than-chance success rate (48 percent) as before.

Tsay thinks that, at least for this kind of music, visual cues carry implications about the degree of passion and motivation that the performer displays. These are qualities that many participants cited as important in their evaluations, and even musical novices can identify them visually. Perhaps they do it even more accurately than the ‘experts’, Tsay says, because they are unencumbered by the sound “that professional musicians unintentionally and non-consciously discard.”

Looking good

One has also to wonder if musicians already unconsciously know that it matters what they look like in performance. Tsay suspects they do. “Many performers do have the intuition that the role of visual information is an important one”, she says. Moreover, having studied at top musical institutions such as the Juillard School in New York, she says “Some teachers at conservatories seem to be quite attuned to the important role that visual information plays in the judgment of music, and they make their students aware of its impact for effective performance.”

Davidson agrees that performers sense the significance of how they look. “Look at the artistry of Judy Garland”, she says. “Every move is integrated into a smooth action plan, as if it were created in the moment, yet it is totally rehearsed and polished as an integrated essential element of her vocal performance.”

“Really good musicians do this too,” she adds. “There are data from Glenn Gould’s career which shows how he moved very differently when only concerned with creating a sound recording rather than when in the recital room.”

The topic is probably an under-researched aspect of musical performance, however. (Musicologist Susan Fast of McMaster University in Hamilton, Canada, has provided a rare analysis of the visual body language cultivated by the rock group Led Zeppelin [6].) “I think the claims of the current paper need some really good social psychological contextualizations and clarifications”, says Davidson.

Whether or not musicians do learn to enhance their “visual merit”, the question is sure to arise: “should they?” Isn’t this a bit like cheating? Is the celebrated Chinese pianist Lang Lang (see above), for example, fooling audiences as he makes great sweeping gestures with his arms, eyes closed and head thrown back in ecstasy?

Perhaps the key question is whether the visual information is reliable – helping us to pick out the most deserving winner, say – or misleading, making us prefer performers who rely on visual flair rather than musical depth. “It is possible that some performances can be ‘trained’ or ‘choreographed’ in a way that may not be authentic or true to the meaning of the musical composition, but may still remain effective as a performance as judged by audiences”, Tsay admits.

“The video is a "bad" signal if it leads to bad outcomes, that is, if we reward musicians in competitions conducted this way and then find that those musicians fail to sustain creative careers”, says Levitin. “I don't know of any study that looks at these outcome measures.”

But one might also argue that a competition is seeking only to identify who is “best” on the day. In which case, what should “best” mean?

“I would say that it depends on one's ontology”, says Bergeron. “Someone who thinks that musical performances are essentially sonic events should recognize that our aesthetic evaluations of musical performances might be systematically mistaken. However, someone who is not prepared to accept that our aesthetic evaluations of musical performances might be systematically mistaken should recognize that musical performances might be visual as well as sonic events.”

In any event, says Bergeron, the fact is that ‘experts’ seem to be swayed by visuals whether they like it or not. “This might be a practical reason to embrace the idea that music made for performance is a visual as well as a sonic art, since it might be psychologically impossible to distinguish, in our experience of performances, those aesthetic qualities that belong to the sound from those that belong to the visual aspects.”

In the end, says Tsay, this comes down to a matter of priorities. “It may be less a question whether the visual channel gives us ‘good’ or ‘bad’ data, and more a question of what we as musicians and audience members believe truly reflects quality”, she says. “This likely changes with time and with changes in technologies and the consumption of music.” After all, in Liszt’s day live performance was the only way audiences would ever hear music. And with the cult of the “artist as expressive genius” firmly established since Beethoven’s day, it made sense for him to perform with flair. Evidently, it still does.

References
1. Tsay, C.-J. Proc. Natl Acad. Sci. USA doi: 10.1073/1221454110.
2. Bergeron, V. & Lopes, D. M. Philos. Phenomenol. Res. 78, 1 (2009).
3. Davidson, J. W. Psychol. Music 21, 103 (1993).
4. Vines, B. et al., Ann. N. Y. Acad. Sci. 1060, 462 (2005)
5. Vines, B. et al., Cognition 101, 80 (2006).
6. Fast, S. In the Houses of the Holy (Oxford University Press, Oxford, 2001).

Bohr's beginnings

Here’s a book review, of sorts (I was asked to write something more like an essay review) just published in New Scientist.

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Love, Literature and the Quantum Atom Finn Aaserud & J. L. Heilbron Oxford University Press, 2013 ISBN 978-0-19-968028-3

Niels Bohr was one of the most profound thinkers among the early pioneers of quantum theory. He was the first truly to recognize and confront the philosophical problems that the theory posed, and the solutions he offered, such as the idea of complementarity and the Copenhagen interpretation, are still debated today. One hundred years ago he devised the first quantum picture of the atom, and he also anticipated quantum effects in biology.

What impresses most about Bohr’s scientific thought is that he could leave consistency to littler minds. Like James Clerk Maxwell, another genuinely deep physicist, he was happy to leave some matters unresolved and to accept contradiction. So what if the Bohr atom violates classical electrodynamics, which says it should decay? So what if wave can be particle? That’s just how things are (or how they seem, which for Bohr was much the same).

Love, Literature and the Quantum Atom is valuable for reminding us of this. But it’s a peculiar beast all the same, bearing signs of having been cobbled together for the Bohr atom centenary. In the first section, Finn Aaserud, director of the Niels Bohr Archive, offers a fresh perspective on Bohr’s early family life through newly released correspondence, especially with his wife Margrethe. Then the science historian John Heilbron, who collaborated with Thomas Kuhn in 1969 on a study of the Bohr atom, supplies a new account of the development of that seminal work in which he considers Bohr’s interests in literature, particularly that of Goethe and Ibsen. Finally the book reprints Bohr’s three-part paper (the so-called “Trilogy”) from 1913, “On the Constitution of Atoms and Molecules”.

To link Bohr’s extra-curricular reading with his science, Heilbron has been set a more or less impossible task. At times he can pursue it only by finding apt quotes from Ibsen’s Peer Gynt or Goethe’s Faust with which to punctuate Bohr’s professional life, irrespective of whether Bohr himself had the words in mind. Heilbron’s account of Bohr’s scientific journey is as insightful and informative as we’d expect from him. But once we get to the equipartition principle and the Balmer series, Goethe doesn’t have much to add.

This experiment fails not because a scientist’s interest in arts and literature can tell us nothing about his or her science, but because it seems Bohr’s cannot. He read widely and thought deeply, but on this showing was addicted to the strain of Germanic-Nordic romanticism that today looks like sentimentality, even chauvinism: great men striving to be great, while their pure-hearted, maidenly lovers pledge placid and dewy-eyed support. Margrethe was in fact Bohr’s staunch and sometimes steely ally, as he knew and appreciated – which is why all his talk of “my little one” who he would (using Ibsen’s words) “lock away as heart’s treasure” makes you realise why modernism and Virginia Woolf were so badly needed.

In a soul as noble as Bohr, this kind of sentiment has its touching aspect. But it’s not hard to see why, for less principled men, these visions of struggle and destiny, of heroes and Vikings, led down darker paths. It’s not too much to suggest that this was a Germanic thing (including Dutch and Danish – as physicist Hendrik Casimir attested, in the Netherlands too the intellectual elite was saturated in Germanic Kultur). There’s no inevitable path from Goethe to Goebbels, but the notion of Bildung – the particularly German character development all professors had to undergo – did breed the sort of patriarchal and patriotic conservatism that, as Heilbron showed in his splendid biography of Max Planck (The Dilemmas of an Upright Man, 1986), made it all but impossible for the traditional academics to muster any resistance to the Nazis.

This is why I’m left with mixed feelings about this glimpse at Bohr’s hinterland. On the one hand it is refreshing to see a great scientist being passionate about a difficult philosopher like Kierkegaard instead of coming up with empty soundbites about philosophy being dead. On the other hand, such an education evidently did little to build a moral framework; those few who, like Bohr and Max von Laue, behaved with something approaching heroism in the face of Hitler did so from some inner reserve of integrity that drew little on their broad education. Their generation was in this respect neither better nor worse than the culturally unsophisticated Feynman or the later generations brought up on Star Trek, Star Wars or Tomb Raider. Whatever it is that makes truly noble and responsible (let alone successful) scientists, it isn’t great art.

Colour for free

I have written up my “history of colour chemistry” talk for publication in the little-known journal Interfaces, produced by the Université Paris Diderot and others. This stems from a conference on colour held at the university in early 2012, which, as the other contributions to this volume indicate, was a very diverse affair. The kind folks in Paris have made this and some of the other articles available online for free as pdfs - you can find it here.

Fuelling physics envy?

Here’s an opinion piece I have just published in Physics World, before it was edited.

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Physics envy might get a fresh stimulus from a new paper which claims to present “bibliometric evidence for a hierarchy of the sciences”. By analysing features such as authorship, mode of expression and range of citations in about 29,000 papers from maths to the social sciences and humanities, bibliometrics experts Daniele Fanelli of the University of Edinburgh and Wolfgang Glänzel of the Catholic University of Leuven say that there are good objective reasons to support the hierarchy that proclaims maths and physics the ‘hardest’ and most solidly grounded of the sciences [1].

The work provides a fascinating glimpse at the stylistic and methodological differences that exist between disciplines. It’s telling us something worth knowing: that fundamental differences in style and content across the sciences are real, so that it might be a mistake to evaluate and manage all the sciences in the same way. What it is not telling us is that physics is the most exemplary or exalted of the sciences.

The authors are mostly scrupulous in avoiding that implication. They suggest that this hierarchy is only to be expected because, progressing from physics to sociology, the complexities of the subject matter – the degrees of freedom, if you like – are increasing. So it is scarcely surprising that the phenomena become harder to interpret and consensus becomes harder to achieve: as Fanelli and Glänzel put it, the data “become less able to speak for themselves.” In this much, they are endorsing the view first espoused in the 1830s by the French philosopher Auguste Comte, who also posited a hierarchy from mathematics to physics, chemistry, biology, psychology and sociology based on the level of complexity involved. Comte was the father of positivism, which asserts that all authoritative knowledge derives from an objective, data-driven, scientific study of the world.

Comte’s hierarchy is typically expressed in terms of the ‘hard’ and ‘soft’ sciences. Fanelli and Glänzel embrace these terms, saying that they “seem to capture an essential feature of science”, and that pretending they do not exist could be a “costly mistake”. The authors don’t deny that all disciplines have cultural and “non-cognitive” components, but say that they seem nevertheless shaped “by objective constraints imposed by the subject matter”.

Before grappling with those assertions, let’s look at what the duo did. They figured that a defining characteristic of a ‘hard’ science is the ability to reach a shared interpretation of phenomena. Consensus might be expected to be reflected in several general features of papers. For example, they will be shorter, since there is less need to justify and explain a study; the references will tend to be more recent (key questions are resolved faster), fewer, less diverse and dominated by tightly focused papers rather than general monographs. But titles might be longer, since the issues addressed will be more precisely defined, and the number of coauthors might be greater, since more researchers share commonly agreed goals and because increased specialization makes collaboration essential. Fanelli and Glänzel analysed these parameters in thousands of papers on the Thomson Reuters’ Web of Science, categorized into disciplines such as physics, chemistry, plant and animal sciences, and psychiatry/psychology, and find that the expected trends are borne out by the data.

So what’s the problem? Let’s start with semantics: ‘hard’ and ‘soft’ are prejudicial terms. It is very difficult to avoid reading them both as “hard-headed/soft-headed”, suggesting that the social sciences are pervaded by woolly thinking, and as “hard/easy”, suggesting that the physical sciences are more intellectually challenging and reinforcing the snooty conviction that the most brilliant scientists choose physics. But arguably (most) questions in physics are in fact the easiest to answer securely because they tend to be the easiest to isolate and interrogate experimentally. Economics is failing to answer our real-world questions not because economists are less able, but because economics is so complex, with few if any universal laws and very patchy data. (There’s another reason too, which I’ll come to shortly.)

Yet more invidious than the ‘hard/soft’ terminology is the whole notion of a hierarchy. By definition, this implies a judgement of status: there’s a top and a bottom. At best it invokes condescension towards those disciplines unlucky enough not to be physics; at worst, we’re invited to feel impatient that these ‘softer’ sciences haven’t yet got themselves physics-ified. Comte certainly felt that all sciences aspire to the condition of physics, and he looked forward to the time when the social sciences reached this stage of higher evolution. It was in Comte’s time that historians of science began to construct the narrative in which the mathematization of nature, as displayed in Newton’s Principia, was the defining achievement of the Scientific Revolution, ignoring the fact that this approach was of no value in, say, zoology, botany, chemistry, geology and medicine. When Immanuel Kant declared that the chemistry of his day was “not science” because it was insufficiently mathematical, he was exposing his limited understanding of what chemistry was about, both then and now.

Not only is mathematization, with its consequent opportunities for reductive subdivision of problems, of limited value in some sciences, but they – the life and social sciences particularly – have a dependence on context and history that offers scant purchase for physics-style universal rules, and means different data sets may tell different stories. When those dependencies are neglected for the sake of simplification, as in mainstream neoclassical economic theory, the result is a model so abstracted and simplistic that no amount of empirical input – not even the near-collapse of the global economy – can make much impression on the ramparts of its ivory towers.

I happen to believe that many sciences, from biology to sociology, can in fact benefit from physics-based ideas. But placing physics at the top of the tree doesn’t help, because it blurs the view of where “physics thinking” is and isn’t appropriate. And presenting science in terms of “consensus deficit” is not just misguided but potentially dangerous. A quest for consensus tacitly accepts Comte’s assumption that all questions can be given a single, scientifically based answer. But many cannot, not just in the humanities but also in history, politics, ethics, the social sciences, economics and beyond. Even in the so-called ‘hard’ sciences, the value of having complementary but not entirely compatible models is under-rated. For some questions about humanity, we may be better served by a diversity of views – including old ones – than by a doomed dream of consensus.

1. D. Fanelli & W. Glänzel, PLoS ONE 8, e66938 (2013).

The transformation of Paris

Here is my previous Under the Radar story for BBC Future – the next should be along very shortly. There’s a bigger story to this stuff – I hope I might get to tell it some time.

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They are what make Paris so distinctive: the grand, wide boulevards that march in straight lines through the city, lined with bustling cafés and tempting patisseries. But this isn’t how Paris looked at the time of the Revolution in the late eighteenth century. The city is one of the most striking examples of rational urban planning, conducted in the middle of the nineteenth century during the ‘Second Empire’ of Napoleon III to ease congestion in the dense network of medieval streets.

It’s not hard to see how the redesign, conducted by Baron Georges-Eugène Haussmann at the emperor’s command, transformed Parisian life. You only have to compare the cityscape today with the narrow, convoluted passageways of the Marais district, one of the few parts of Paris largely untouched by Haussmann’s plans. But what exactly did these so-called ‘Second Empire reforms’ really do to the properties of the road network? How did they alter the way residents navigated the city? Can we be sure that other changes, whether contemporaneous or subsequent, didn’t have equally profound impact?

Until recently, these are questions that will have relied largely on the subjective impressions of urban theorists. After all, we can’t make measurements to compare today’s traffic flow with that from the days of Robespierre. But a new study by a collaboration of mathematical physicists and social historians in France shows that, simply by analysing old and new maps of the city, it’s possible to quantify what effect Haussmann’s plans had on the shape and life of Paris. The results offer a case history of how cities may evolve through a combination of spontaneous self-organization and top-down central planning.

Marc Barthelemy of the CEA Institute of Theoretical Physics in the Parisian suburb of Gif-sur-Yvette and his colleagues have analysed maps of the city road network at six moments in time since the Revolution: 1789, 1826, 1836, 1888, 1999 and 2010. They looked at some basic properties of the networks, such as the numbers of nodes (intersections) and edges (roads between nodes), as well as using more sophisticated concepts from the modern theory of complex networks, such as the quantity called ‘betweenness centrality’ (BC) that measures the importance of individual nodes to the navigability of the network.

The results are revealing. Whether or not Haussmann made a difference depends on what you look at. For example, between 1836 (before the changes) and 1888 (when they were essentially complete), the total number of nodes and their total length both increase very sharply – more or less doubling – while changing rather little thereafter. You might say that Haussmann added a lot of ways of getting from place to place. But this growth is mirrored by a steep rise in the city’s population, suggesting that this factor, rather than planning in itself, drove the increases: they might have happened anyway, albeit not necessarily in the same way.

What’s more, changes in the average BC values of the network also suggest that there was nothing unusual about the Haussmann developments, compared to what came before and after. Rather, the web of streets just got steadily denser, as has been found for some other cities.

A quite different picture emerged, however, when the researchers looked at the spatial patterns of change. When they plotted maps of the nodes with the largest BC values – the intersections that are most important for finding a shortcut between any two other nodes – the results look quite different up to 1836 and after 1888. In the earlier period, most of the high-BC nodes are clustered around the city centre, although between 1826 and 1836 an important traffic channel opened up in the Saint Martin region in the east of Paris, where several large properties owned by the church or aristocrats were sold and divided up to create new houses and roads.

But after Haussmann, the high-BC nodes form a more open, widely spaced system of key channels, somewhat like the vein network of a leaf. In other words, Haussmann’s avenues and boulevards helped to prevent routes becoming funnelled through the congested city centre, and gave Paris space to breathe.

The new roads also altered the typical shape of blocks. It’s been found previously that many urban road networks tend to intersect at right angles, dividing up the space ever more finely into square or rectangular blocks a bit like the crack networks of ceramic glazes. That’s what Paris looked like before the 1850s. But the new boulevards sliced boldly through this grid, creating a wider variety of block shapes, especially triangles and elongated rectangles.

So whether the Second Empire reforms transformed the face of Paris is a subtle question. Some of the changes over the nineteenth century, such as higher street density and increase in intersections, might have happened anyway thanks to the growth in population. In other ways, Haussmann stamped a ‘non-natural’ geometry on the city’s evolving network. Although Haussmann’s plans were criticized both at the time and by later architects, it looks as though they did a pretty good job, making the city centre less congested in a way that Parisians still benefit from today. London, in contrast, missed its chance: the grand new streets proposed by Christopher Wren after the Great Fire in 1666 weren’t built in time to prevent the city’s natural, spontaneous evolution from reasserting itself. All the same, using the tools that Barthelemy and colleagues have developed, it might now be possible to probe Haussmann’s scheme more closely – to ask, for example, how close it came to finding the very best solution to the problems it tackled.

Reference: M. Barthelemy, P. Bordin, H. Berestycki & M. Gribaudi, Nature Scientific Reports 3, 2153 (2013).

Plastic fantastic

Here’s the initial version of a leader I wrote for last week’s Nature.

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The transition from basic science to practical technology is rarely linear. The common view – that promising discoveries need only patience, hard work and money to shape them into commercial products – obtains only rarely. Often there are more factors at play: all kinds of technical, economic and social drivers must coincide for the time to be right. So dazzling forecasts fail and fade, but might then re-emerge when the climate is more clement.

That seems to be happening for organic electronics: the use of polymers and other organic molecules as the active materials in information processing. That traditionally insulating plastics could be made to conduct electricity was discovered serendipitously in the late 1960s by Hideki Shirakawa in Tokyo, in the form of silvery films of polyacetylene. Chemists Alan Heeger and Alan MacDiarmid collaborated with Shirakawa in 1976 to boost the conductivity of this material by doping with iodine, and went on to make a ‘polymer battery’. Other conducting polymers, especially polyaniline, were mooted for all manner of uses, such as antistatic coatings and loudspeaker membranes.

This early work was greeted enthusiastically by some industrial companies, but soon seemed to be leading nowhere fast – the polymers were too unstable and difficult to process, and their properties hard to control and reproduce reliably. That changed in the late 1980s when Richard Friend and coworkers in Cambridge found that poly(para-phenylene vinylene) not only would conduct without doping but could be electrically stimulated to emit light, enabling the fabrication of polymer light-emitting diodes. The attraction was partly that a polymer’s properties, such as emission colour and solubility, can be fine-tuned by altering its chemistry. Using such substances for making lightweight, flexible devices and circuits, via simple printing and coating techniques rather than the high-tech methods needed for inorganic semiconductor electronics, began to seem possible. The genuine potential of the field was acknowledged when the 2000 Nobel prize for chemistry went to Shirakawa, Heeger and MacDiarmid.

The synthesis of gossamer-thin organic electronic circuits reported by Martin Kaltenbrunner in Tokyo and colleagues (Nature 499, 458-463; 2013) is the latest example of the ingenuity driving this field. Their devices elegantly blend new and old materials and techniques. The substrate is a one-micron-thick plastic foil, while organic small molecules provide the semiconductor for the transistors, other organic molecules and alumina constitute the insulating layers, and the electrodes are ultrathin aluminium. The featherweight plastic films, 27 times lighter than office paper, can be crumpled like paper, and on an elastomeric substrate the circuits can be stretched more than twofold, all without impairing the device performance. Adding a pressure-sensitive rubber layer produces a touch-sensing foil which could serve as an electronic skin for robotics, medical protheses and sports applications.

Wearable and flexible electronics and optoelectronics have recently taken great strides, propelled in particular by the work of John Rogers’ group at Illinois (D.-H. Kim et al., Ann. Rev. Biomed. Eng. 14, 113-128 (2012)). Such devices can now be printed on or attached directly to human skin, and can be made from materials that biodegrade safely. Especially when coupled to wireless capability, both for powering the devices and for reporting their sensor activity, the possibilities for in situ monitoring of wound care and tissue repair, brain and heart function, and drug delivery are phenomenal; the challenge will be for medical procedures to keep pace with what the technology can offer. At any event, such applications reinforce the fact that organic electronics should not be seen as a competitor to silicon logic but as complementary, taking information processing into areas that silicon will never reach.

At the risk of inflating another premature bubble, these technologies look potentially transformative – more so, on current showing, than the much heralded graphene. The remark by Kaltenbrunner et al. that their circuits are “both virtually unbreakable and imperceptible” says more than perhaps they might have intended. In this regard the new work continues the trend towards the emergence of a smart environment in which all kinds of functionality are invisibly embedded. What happens when packing film (one possible use of the new foldable circuitry), clothing, money, even flesh and blood, is imbued with the ability to receive, process and send information – when more or less any fabric of daily life can be turned, unseen, into a computing and sensing device? Most narratives currently dwell on fears of surveillance or benefits of round-the-clock medical checks and diagnoses. Both might turn out to be warranted, but past experience (with information technology in particular) should teach us that technologies don’t simply get superimposed on the quotidian, but both shape and are shaped by human behaviour. Whether or not we’ll get what’s good for us, it probably won’t be what we expect.

Radio DNA

Another cat among the pigeons, perhaps… here is my latest Crucible column for Chemistry World.

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It has to rate as one of the most astonishing discoveries of this century, and it came from a Nobel laureate. Yet it was almost entirely ignored. In 2011 Luc Montagnier, who three years earlier was awarded the Nobel Prize in medicine for his co-discovery of the AIDS virus HIV, reported that he and his coworkers could use the polymerase chain reaction (PCR, the conventional method of amplifying strands of DNA) to synthesize DNA sequences of more than 100 base pairs, without any of the target strands present to template the process [1]. All they needed was water. Water, that is, first subjected to very-low-frequency electromagnetic waves emitted and recorded from solutions of DNA encoding the target sequence. In other words, the information in a DNA strand could be transmitted by its electromagnetic emissions and imprinted on water itself.

Maybe you’re now thinking this work was ignored for good reason, namely that it’s utterly implausible. I agree: it doesn’t even begin to make sense given what we know about the molecular ingredients. But the claims were unambiguous. The authors say they took a 104-base-pair fragment of DNA from HIV (and who knows about that better than Montagnier?) and copied it, reproducibly and with at least 98% fidelity, by adding the PCR ingredients to the irradiated water. If you choose to ignore this, are you saying Montagnier is lying?

What you’re actually saying is that science doesn’t always work as it is ‘supposed’ to, by claims being tested and then accepted or rejected depending on the result. Of course, many trivial claims never get replicated (that’s another story), but really big ones – and they don’t come much bigger than this – are immediately interrogated by other labs, right? That’s what happened with cold fusion, however implausible it seemed. True, some results can’t be replicated without highly specialized kit and expertise – no one has rushed to verify the Higgs boson sighting. But Montagnier and colleagues used nothing more than you’d find in most molecular biology labs worldwide.

So what’s going on? What we’re really seeing tested here are the unwritten social codes of science. Montagnier has long been seen as something of a maverick, but in recent years some have accused him of descending into quackery. Since claiming in 2009 that some DNA emits EM signals [2], he has suggested that such signals can be detected in the blood of children with autism and that this justifies treating autism with antibiotics. He has seemed to suggest that HIV can be defeated with diet and supplements, and commended the notorious ‘memory of water’ proposed by French immunologist Jacques Benveniste [3]. Although he is currently the head of the World Foundation for AIDS Research and Prevention in Paris, his unorthodox views have prompted some leading researchers to question his suitability to lead such projects.

But science judges the results, not the person, right? So let’s look at the paper. At face value making a simple claim, it is in fact so peppered with oddness that other researchers probably imagine any attempt at replication will be deeply unrewarding. There are hints that the EM emissions come from a baffling and bloody-minded universe: their strength doesn’t correlate with concentration, they seem to appear in some ranges of dilution and then vanish in others, and there is no rhyme or reason to which organisms or sequences produce them and which don’t. That the authors show the signals not as ordinary graphs but as a screenshot adds to the misgivings.

Then there’s the ‘explanation’. Montagnier has teamed up with Italian physicist Emilio Del Giudice and his colleagues, who in 1988 published a “theory of liquid water based on quantum field theory” [4] which proposed that water molecules can form “coherent domains” about 100 nm in size containing “almost free electrons” that can absorb electromagnetic energy and use it to create self-organized dissipative structures. These coherent domains are, however, a quantum putty to be shaped to order, not a theory to be tested. They haven’t yet been clearly detected, nor have they convincingly explained a single problem in chemical physics, but they have been invoked to account for Benveniste’s results and cold fusion, and now they can explain Montagnier’s findings on the basis that the EM signals from DNA can somehow shape the domains to stand in for the DNA itself in the PCR process.

Make of this what you will; the real issue here is that it all looks puzzling, even prejudiced, to outsiders, who understandably cannot fathom why a startling claim by a distinguished scientist is apparently just being brushed aside. Perhaps it might help to stop pretending that science works as the books say it does. Perhaps also, given that Montagnier says his findings are motivating clinical trials to “test new therapeutics” for HIV in sub-Saharan Africa, it might be wise to subject them to more scrutiny after all.

References
1. L. Montagnier et al., J. Phys. Conf. Ser. 306, 012007 (2011).
2. L. Montagnier et al., Interdiscip. Sci. Comput. Life Sci. 1, 81 (2009).
3. E. Davenas et al., Nature 338, 816 (1988).
4. E. Del Giudice, G. Preparata & G. Vitiello, Phys. Rev. Lett. 61, 1085 (1988).

Maxwell's fridge

I haven’t generally been putting up here the pieces I’ve been writing for Physical Review Focus, as they can tend to be a bit technical. But as I’ve been writing this and that about Maxwell’s demon elsewhere, I thought I’d post this one. The final version is here.

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In 1867 the physicist James Clerk Maxwell described a thought experiment in which the random thermal fluctuations of molecules might be rectified by intelligent manipulation, building up heat that might be used to do useful work. Now in Physical Review Letters a team at the University of Maryland outline a theoretical scheme by which Maxwell’s nimble-fingered ‘demon’ might be constructed in an autonomous device that in effect uses computation to transfer heat from a cold substance to a hotter one, thereby acting as a refrigerator.

Maxwell believed that his demon might oppose the second law of thermodynamics, which stipulates that the entropy of a closed system must always increase in any process of change. Because this law seems to be statistical – an entropy increase, or increase in disorder, is simply the far more likely outcome – the demon might undermine it, for example by physically reversing the usual scrambling of hot and cold molecules and thereby preventing the diffusion of heat.

Most physicists now agree that such a demon wouldn’t defeat the second law, because of an argument developed in the 1960s by Rolf Landauer [1]. He showed that the cogitation needed to perform the selection would have a compensating entropic cost – specifically, the act of resetting the demon’s memory dissipates a certain minimal amount of heat per bit erased.

Despite this understanding, there have been few attempts to postulate an actual physical device that might act as a Maxwell demon. Last year, Christopher Jarzynski and Dibyendu Mandal at Maryland proposed such a ‘minimal model’ of an autonomous device [2]. It consisted of a three-state device (the ‘demon’) that can extract energy from a reservoir of heat and use it to do useful work. The transitions in the demon are linked the writing of bits into a memory register – a tape recording binary information – which moves past the it, according to particular coupling rules.

In collaboration with their colleague Haitao Quan, now at Peking University, Mandal and Jarzynski have now refined their model so that the demon is a two-state device coupled to heat exchange between a hot and a cold reservoir. Again, the operation of the demon is ensured by the coupling rules imposed between its transitions, the reservoirs and the memory, resulting in a mathematically solvable model whose performance depends on the model’s parameters.

The demon can absorb heat from the hot reservoir to reach its excited state, and reverse that process, without altering the memory. But the rules say that energy may only be exchanged with the cold reservoir by coupling to the memory. The demon can absorb heat from the cold reservoir if the incoming bit is a 0, or release it if the bit is a 1. And whenever energy is exchanged with the cold reservoir, the demon reverses the bit, which affects the entropy of the outgoing bit stream. So each 0 allows the chance for energy to move from the cold reservoir into the demon – and potentially then out to the hot reservoir.

The researchers find that the behaviour of the system depends on the temperature gradient and the relative proportions of 1s and 0s in the incoming bit stream. In one range of parameters the device acts as a refrigerator, drawing heat from the cold reservoir colder while imprinting a memory of this operation as 1s in the outgoing bit stream. In another range it acts as an information eraser: lowering the excess of 0s in the bit stream and thus randomizing this ‘information’, while allowing heat transfer from hot to cold.

Jarzynski says that, while the model couples heat flow and information, it doesn’t have Landauer’s condition explicitly built in. Rather, this condition emerges from the dynamics, and so the results provide some support for Landauer’s interpretation.

How might one actually build such a system? “We don’t have a specific physical implementation in mind”, Jarzynski admits, but adds that “we are exploring a fully mechanistic Rube Goldberg-like contraption where the demon and memory are represented by wheels and paddles that rotate about the same axis and interact by bumping into one another.”

Trying to figure out how a physical device might act like Maxwell’s demon is “an important task”, according to Franco Nori of the University of Michigan. “To build such a system in the future would be another story, but this is a very important step in the right direction,” he says.

Although he sees this as “an interesting theoretical model of Maxwell's demon”, Charles Bennett of IBM’s research laboratory in Yorktown Heights, New York, thinks it could be made even simpler. “It’s somewhat unrealistic and unnecessarily complicated to have the tape move at a constant velocity”, he says – the parameter describing the tape speed could be eliminated “by coupling each 0→1 tape transition to a forward step of the tape and each 1→0 transition to a backward step.”

References
1. R. Landauer, IBM J. Res. Dev. 5, 183 (1961).
2. D. Mandal & C. Jarzynski, Proc. Natl Acad. Sci. USA 109, 11641-11645 (2012).