Thursday, April 23, 2015

The moral challenge of invisibility

Here is an extended version of my latest piece for Nature News. There are of course more details about lots of the things discussed here in my book Invisible.


Experiments that give subjects the illusion of having an invisible body might reveal how we respond to the ensuing temptations.

We’ve all had those moments of social embarrassment: you’ve just said or done the dumbest thing, everyone is looking at you, and you wish you could just – well, vanish. But what if you really could? Would that help?

Apparently it would. Using a virtual-reality headset and a calculated confusion of the senses, neuroscientists at the Karolinska Institute in Stockholm, Sweden, have been able to give people the illusion that their body is invisible [1]. The subjects feel someone stroking their body with a brush, but when they look down all they see is the brush moving through thin air. This is enough, they testify, to give them the sensation that their entire body cannot be seen. It feels, many say, not only invisible but hollow – a weird dematerialization of their physical person.

And according to both the testaments of the subjects and objective measurement of their physiological response to stress as revealed by their heartbeat rate, this sensation of invisibility reduces their anxiety in social settings, for example if they can see an audience of “serious-looking strangers” seated and watching them.

Why would you want to know what it’s like to have an invisible body? One potential reason is that the technique could be used to treat social anxiety disorder, in which people are acutely susceptible to stress in situations such as having to deliver a presentation or perform before an audience. This is a very common disorder, affecting an estimated one in ten people at some point during their life. They sweat, shake, blush and hear their heart thumping away. Aside from prescribing anti-anxiety medication, this condition is generally treated with cognitive behavioural therapy, which attempts to condition the subjects by degrees to stay calm in a socially stressful setting.

Virtual reality has already shown its value in such treatment. But what if, say the Stockholm team, led by Henrik Ehrsson, you could “give” a patient an invisible body and then gradually make them more visible in stages? The illusion that they create is, after all, a matter of degree: subjects said that they experienced varying depths of visibility, depending on the conditions.

The illusion is also related to studies of how a sense of “body ownership” is triggered by visual and tactile stimuli. In 1998, psychologists Matthew Botvinick and Jonathan Cohen showed that when people see a rubber hand being brushed at the same time as their own hand, out of sight, experiences the same sensation, they feel that the rubber hand is part of their body [2]. Ehrsson and colleagues recently showed that this “rubber hand” illusion can even be invoked for an “invisible hand”, when subjects see the sensation that they feel applied to empty space [3]. That’s what inspired them to carry out the present study, and the results could also cast light on the “phantom body” illusion experienced by some people with paralysis due to spinal-cord injuries, in which they feel they have a body that is out of alignment with their real one.

So, plenty of potential clinical applications. But the research touches on something far deeper, for notions of personal invisibility feature in many of our myths, legends and stories, from Plato’s telling of the myth of Gyges in his Republic to H. G. Wells’ Invisible Man, J. R. R. Tolkien’s The Lord of the Rings and Harry Potter. Invisibility there has other connotations. Gyges is a shepherd of Lydia who discovers a ring of invisibility by chance, and uses it to seduce the queen, kill the king, and make himself ruler. The moral, says Plato’s narrator Glaucon, is that
“No man can be imagined to be of such an iron nature that he would stand fast in justice. No man would keep his hands off what was not his own when he could safely take what he liked out of the market, or go into houses and lie with anyone at his pleasure, or kill or release from prison whom he would, and in all respects be like a God among men.”

Wells seems to have intended his novel to be an updating of the Gyges story, demonstrating the corrupting temptations of invisibility and its severance of personal responsibility. He took great pains to make his invisibility scientifically plausible by the standards of the time, and interestingly he anticipated that an inability to see one’s limbs would confuse the coordination: his invisible man initially can barely walk. Ehrsson’s coauthor Arvid Guterstam says this is something they can now test, but he doesn’t anticipate such an effect. “We are already very used to moving our limbs without directly looking at them, when they are occluded or in the dark”, he says, “so guiding our limbs through space without direct visual feedback shouldn’t be a major issue.” We wouldn’t, it seems, become like David McCallum’s Invisible Man in the 1970s television serial of that name, forever blundering into potted plants – an exigency forced on him, the series producer Robert O’Neill admitted, by the challenge of convincing an audience that an invisible person was actually there.

But would invisibility also confuse our morals? This is where the new work could get really interesting, because the researchers want to examine this “Gyges effect”. “We are planning to expose participants to a number of moral dilemmas under the illusion that they are invisible”, says Guterstam, “and compare their responses to a context in which they perceive having a normal physical body.” I anticipate the worst here, not least because the Gyges effect seems already to operate in internet trolling [4].

One thing is for sure: we should take with a big pinch of salt the authors’ suggestion that there is “the emerging prospect of invisibility cloaking of an entire human body being made possible by modern materials science”. This alludes to recent work on so-called metamaterial invisibility cloaks [5,6]. But not only is that work very far from achieving full cloaking in the visible spectrum (let alone in a wearable suit), but there is good reason to suspect that it will stay that way for the foreseeable future. The hiding of a cat and fish that Ehrsson and colleagues mention [7] sounds impressive but is in the end a kind of high-tech version of the Victorian stage magician’s trick of using mirrors (and probably smoke) to make half a woman’s body vanish.

There are other technologies afoot for making “invisibility cloaks” for humans, generally involving a kind of adaptive camouflage in which the background is either projected onto highly reflective clothing [8] or captured with “onboard” cameras and displayed on wearable LED screens [9]. The first offers a compromised and static illusion – if you want to appear transparent while you give your presentation, you’d do just as well to stand in front of the projector. The second is another speculative and remote (albeit fun) idea that is in any event undermined by the laws of optics [10]. So fear not – no one is going to become a real-life Gyges any time soon.

1. Guterstam, A., Abdulkarim, Z. & Ehrsson, H. H., Sci. Rep. 5, 9831 (2015). (here)
2. Botvinick, M. & Cohen, J., Nature 391, 756 
(1998). (here)
3. Guterstam, A., Gentile, G. & Ehrsson, H. H. J. Cogn. Neurosci. 25, 1078–1099 (2013).
4. Hardaker, C. Guardian 3 August 2013. (here)
5. Schurig, D., Mock, J. J., Justice, B. J., Cummer, S. A., Pendry, J. B., Starr, A. F. & Smith, D. R., Science 314, 977-980 (2006).
6. Leonhardt U.&. Philbin, T. G., Geometry and Light: The Science of Invisibility. Dover, Mineola, 2010.
7. Chen, H. et al., preprint (2013).
8. Tachi, S. Proc. 5th Virtual Reality Int. Conf. (VRIC2003), 69/1-69/9 (Laval Virtual, France, 2003). (here)
9. Zambonelli, F. & Mamei, M. Pervasive Computing 1(4), 62-70 (2002) (here).
10. See comments by M. Hebert in ref. 8.

Monday, April 20, 2015

Goebbels: the gift that keeps on giving?

The story about demands (on my publisher) for royalties for quoting Goebbels raises fascinating issues. It is all the more complex because of the fact that the claim on behalf of Goebbels’ estate is being pursued by the daughter of Hjalmar Schacht, Hitler’s Economic Minister, who is a lawyer.

I considered Schacht’s story briefly in my book Serving the Reich; a more detailed account is given in Eric Kurlander’s excellent Living With Hitler. Schacht offers an interesting case study of the complexities of anti-Semitism during the Nazi regime. He was in many respects a liberal, and although he became a supporter of the Nazis and President of the Reichsbank, he lost his influence after a disagreement with Hitler in 1937 (“You simply do not conform to the general National Socialist framework”, Hitler told him two years later) and eventually became a member of the German Resistance. He was imprisoned after the failed assassination plot of June 1944 and sent to Dachau, but survived.

Schacht seems to have been instinctively averse to racial hatred, and was frequently reprimanded by Party officials for speaking out against attacks on Jews and their property. He argued against some anti-Semitic measures on the grounds that they would weaken Germany domestically and isolate it abroad. Put on trial at Nuremberg, Schacht claimed that he had served in the government “to prevent the worst excesses of Hitler’s policies”, although some historians argue that he aided the Holocaust by expropriating Jewish property. He was acquitted at the trials, and later became an adviser to developing countries on economic development.

Schacht’s trajectory shows how unwise it is to attempt to label individuals as Nazi or not, or as pro-/anti-Semite. As I pointed out in my book, few scientists actually served, as Schacht did, in the Nazi administration; but few, too, spoke out publicly against the regime and actively opposed it, as Schacht did. Does this make them better or worse than him?

Either way, the fact that Schacht’s daughter and Goebbels’ family apparently think it is right that the family should get royalties for quoting him – in preference, indeed, to donating such proceeds to a Holocaust charity – should not shock us as much as it might. It’s a reminder that the legacy of the Nazi regime did not vanish either with Hitler’s death or with the fading of his generation. It is of a part with the widespread sense in Germany after the war that the case was now closed and that only the ardent Nazis had questions to answer.

Remember that the postwar trials were notoriously ineffectual, not just because it was extremely difficult and time-consuming thoroughly to investigate any allegation (let alone to prove it) but because many who supported the regime had little difficulty in obtaining the so-called Persilscheine or whitewash certificates of clearance. The most vociferous Nazis in the universities were dismissed without compensation, while others who had doubtless helped the regime were eased into early retirement. Hardly any of the scientists were incriminated. Pascual Jordan, for example, a Party member whose enthusiasm for National Socialism was such that its ideology even seeped into his physics, was issued a whitewash certificate by Werner Heisenberg, who attested that he had “never reckoned with the possibility that [Jordan] could be a [true] National Socialist” (rather inviting the question of what it would take to convince Heisenberg of that). Niels Bohr was less obliging: he replied to Jordan’s request for a letter of exoneration by sending the physicist a list of Bohr’s friends and relatives who had died in the camps.

The ‘denazification’ of German science was actively obstructed even by those who had had no sympathy with the National Socialists. The prevailing attitude was one of resentment at the intrusiveness of the occupying Allied authorities, which led to a closing of ranks and a feeling of solidarity between the most unlikely of bedfellows. Even relatively blameless individuals refused to condemn those who had been clearly implicated in the Nazi regime. Others drew an invidious parallel between the rooting out of Nazis after the war and the persecution of ‘non-Aryans’ before it. For Otto Hahn, denazification involved “attacks against the science of our nation”.

These prevarications and evasions during ‘denazification’ meant that it quickly became impossible to construct a clear picture of how the nazification of German society had proceeded. And it’s German historians who say this. Klaus Hentschel, for instance, has said that “It was one of the most depressing experiences I ever had as a historian to see reflected in the documents how very soon after 1945 the chance of coming to grips with the National Socialist regime was allowed to slip away, thus missing the opportunity to make a frank assessment of the facilitating conditions the regime had set.”

The prevailing attitude was not guilt or remorse, but self-pity and resentment at the indignities suffered in a defeated nation. Visiting Germany in 1947, Richard Courant, the mathematician who had been forced out of Göttingen in 1933, despairingly described its residents as “absolutely bitter, negative, accusing, discouraged and aggressive.” Hartmut Paul Kallmann, the postwar director of the former Kaiser Wilhelm Institute for Physical Chemistry in Berlin, who as a ‘non-Aryan’ had been dismissed under Fritz Haber’s directorship in 1933 and had worked for IG Farben during the war, wrote to the emigré Michael Polányi in 1946 saying that “the tough momentary situation [here] is deplored much more than the evil of the past 10 years… The masses still don’t know what a salvation the destruction of the Nazis was to the whole world and to Germany as well.” “It is a difficult problem with the Germans”, Margrethe Bohr told Lise Meitner two years later, “very difficult to come to a deep understanding with them, as they are always first of all sorry for themselves.” In 1947 the president of the polytechnic at Darmstadt complained that for some student “it seemed that the only thing the Nazis had done wrong was to lose the war.”

I think such sentiments still prevail in some quarters. From a certain generation of Germans, I have heard comments in response to my book even from evident anti-Nazis to the effect that “well of course you have no idea how hard it was for us.” In fact I have no doubts how hard it was for them. But such comments are offered as a shield against deeper reflection about the moral fallout. Sometimes it’s worse than that. Even for raising the question that folks like Heisenberg and Debye might have had questions to answer, I was called by one party a “cockroach” – and I can’t imagine for a moment that the similarity with the language used by the Nazis to dehumanize Easter Europeans and Jews could have been lost on that person. (This is not, let me stress, a specifically German response – I’m pretty sure that, as Ian Kershaw has intimated, what we saw in Germany before and after the war could have happened anywhere, mutatis mutandis. We are certainly not free from such language in Britain today, as we have sadly discovered recently.)

So no, there is really nothing so strange or surprising about the Schacht/Goebbels response. I am proud that Bodley Head is standing up to it.

Tuesday, April 14, 2015

Condensed-matter physics gets its hands dirty

Here is the original version of my leader for Nature Materials, which I want to put up here to acknowledge the insightful input from Bob Cava and Bertram Batlogg - N Mat's leader style doesn't permit direct quotes, so I had to paraphrase their words.


Is condensed-matter physics becoming more materials-oriented? Or is this just a new wrinkle in an old tradition?

Condensed-matter physics is becoming increasingly oriented towards materials science and engineering. That’s the conclusion reached by two Harvard physicists, Michael Shulman and Marc Warner, after analyzing the statistics of abstracts for the main annual (March) meeting of the American Physical Society since 2007. They enumerated key words used in abstracts to identify trends over the past eight years, and say that during this time the words that are increasing in popularity are often ones associated with specific types of material system, such as “layer”, “thin”, “organic”, “oxide” and indeed “material”. In contrast, words or (word fragments) with generally declining popularity include “superconduct” and “flux” (as well as, oddly, “science”).

What should we make of this? Probably not too much. As the authors are the first to point out, the analysis is preliminary and its timespan limited. It would be good to see it extended over a longer period and expanded to include, say, words in the abstracts of publications in Physical Review Letters, not to mention paying more attention to soft matter rather than primarily solid-state. The present results also paint a slightly confusing picture, taken at face value: condensed-matter physics (CMP) as a whole has been expanding if one judges from the gradual rise in the total number of abstracts submitted to CMP sessions of the March meeting, yet the “condensed matter” section of the preprint server arxiv has made up a shrinking proportion of the total during that time. There are various possible explanations for the discrepancy.

All the same, if it is qualitatively true that CMP has become more materials-focused, it’s worth asking why. Are established researchers in the field are altering the direction of their work away from abstract theoretical questions – what is the origin of high-temperature superconductivity, to take one obvious former preoccupation of theorists – and towards applications of particular materials systems? Or does that reflect a change in the interests of young researchers entering the field? Robert Cava of Princeton University doubts that it’s merely the latter, since old hands enjoy fresh challenges: “For old-timers like me, new areas are a way to use your stored knowledge to have insights that the youngsters miss.”

It is tempting to infer that researchers are just following the money: in this increasingly goal-oriented scientific climate, there may be better funding prospects for a project that can promise concrete applications at the end of the line. But might not the trend instead reflect the internal dynamics of the research community, so that funding follows areas deemed “hot” for other reasons? It’s almost sure to be a bit of both, as the example of graphene shows: there are high hopes for applications in electronics and composites, but much of the interest has come from the fundamental physics that this one-dimensional system seems to offer. More data on the dynamics and trends of funding priorities might help to separate cause and effect.

In any event, Bertram Batlogg at ETH in Zurich says that practical applications of the materials it studies has always been “in the best tradition of CMP”. Given the enormous contributions that the field has made to society – underpinning the technologies of smart phones and solar energy, say – it’s only natural that researchers should have an eye on ensuring that this tradition continues.

Shulman and Warner found that, in comparison to subjects such as atomic, molecular and optical physics, CMP changes fast: the statistics of key words are more volatile. Cava agrees that this is a feature of the field. “Occasionally, say once every 5-10 years, a subject comes up that is so new that many people work on it, because physicists are intrinsically enthusiastic and interested in new science.” He cites the case of pnictide superconductivity, which enjoyed its greatest popularity just before the period of this analysis. Superconductivity is now seeing another little surge of interest owing to topological superconductors.

“I believe that all fields have a natural life cycle”, says Cava. “They naturally go up in activity and then back down as people have had a chance to see what they can contribute and then move on to other new areas.” Shulman and Warner wonder if this cycle is shorter in CMP than elsewhere, perhaps because it can be stimulated by the discovery of a new material system (carbon nanotubes, say, or magnetic multilayers) but also because it can be hard to get at the high-lying fruits for many of these systems owing to the complexities of the many-body interactions they present – that, at least, seems to be what has kept a general theory of high-temperature superconductivity out of reach. What’s more, high-temperature superconductivity showed that there is a very low entry barrier for studying exciting new materials if they are relatively easy to synthesize: any lab well equipped with instrumentation can quickly and easily switch direction and still hope to make a useful contribution.

Might there also be a life cycle for CMP as a whole? The APS division was created only in 1978, from what was formerly the Division of Solid State Physics. Yet Shulman and Warner wonder if it still presents the kind of exciting challenges of 20-30 years ago. No one would claim, however, that the most demanding questions are all answered: perhaps some of them will need to await new techniques or new theoretical methods better able to accommodate complexity. And like chemistry, to some extent CMP creates its own subject: our inventiveness (or serendipity) with new materials systems prompts new questions. As Cava says, “to explore the complexity of the physics people have to think about and perform experiments on real materials. Each material has a different balance of the competing forces that give rise to the complexity of condensed matter physics, so each new material is an opportunity to learn new physics.”

Saturday, April 04, 2015

This explains everything

Prospect preferred that I keep my short review of Steven Weinberg’s book To Explain the World behind the paywall. But he’s obliged by inviting further comment with his piece in the Guardian today, in which he talks both about the history of science and popular science writing. On both, his remarks are useful insofar as they encapsulate the worst of what drives me to despair when some (most definitely not all) scientists talk about these things.

The first thing to say is that Weinberg’s view of the history of science is not down to ignorance. It’s important to say this because that’s what it looks like. But no, Weinberg does not write Whiggish history because he doesn’t know what historians of science do these days, but specifically because he does know and disapproves of it. Yes, this high-energy physicist believes that historians don’t really know how to write history. It is hard to know why he nonetheless expresses “enormous respect for professional historians of science, from whom I have learned so much” – unless he means (as I suspect) that he is grateful to them for having dug all the facts out of the archive, but that he doesn’t believe they can be trusted to know what to do with them. Because Weinberg seems to have learned nothing from historians of science about how to be a historian.

If your view is that science was just kind of blundering around and dragging its feet until Newton’s Principia, then it’s perhaps not surprising if you conclude that the use of mathematics in science by ancients such as Plato and the Pythagoreans was “childish”. Again we have to understand that, while a remark like this coming from an undergraduate would simply indicate ignorance, from Weinberg it conveys something else. I am quite sure that he knows how incendiary such a claim is. But I fear that, in making it, he comes across like Jim Watson, evidently thinking that by saying the “outrageous” he is revealing himself as a bold and outspoken thinker whereas in fact he just sounds silly.

Talking of which… listen to this remark about science commentators and popularizers: “Ironically, as writers they were so much more popular than professional scientists that in many cases it is their comments on scientific research rather than reports of the research itself that were copies and recopied.” When you realise Weinberg is here writing about “the ancient world”, you see how anachronistic his whole perspective is. Those guys were kind of like, well, like Steven Weinberg, only in togas and sandals and doing really crappy maths.

His book is full of this sort of stuff. The generally uncritical reception it has got – with the splendid exception of Steven Shapin’s review in the WSJ – has left me rather depressed about how little general understanding there seems to be of what the history of science is about. So I can only imagine how professionals must feel; as one has said to me, “it's shocking that this sort of thing gets published by a major house”.

If Weinberg genuinely believes that pretty much the entire discipline has got things wrong, you’d think he would make the effort to explain why. But all he does in his book is shrug and say “I don’t buy it.” And all this stems from a total misunderstanding of what the historians are up to. Weinberg seems totally hung up on the idea that they are a nest of arch-relativists, convinced that the science we have today is no more valid than that of Aristotle or Roger Bacon, just a different story for different times. This says more about Weinberg than it does about the history of science. I think you’d have to look very hard to find a historian who truly believes that the theory of general relativity is no better than Newtonian gravity (and presumably therefore that it’s up to us whether or not to adjust our GPS satellite systems to take Einstein’s theory into account). As Weinberg puts it in his article (and now things really do get childish), “I argue with those historians who try to judge each era’s scientific work according to the standards of that era rather than of our own, as if science were not cumulative and progressive, as if its history could be written like the history of fashion.” In other words, he is not really interested in understanding why people once thought the way they did, but just whether they were “right” or “wrong”. A study of phlogiston theory would hold no interest for him, because it was wrong. Why think about wrong ideas? Well, as a scientist, he certainly has the luxury of not doing so. But then please, please don’t try to write history. The reason – one reason – to be interested in such things is that you have an interest in the history of ideas. Weinberg shows no curiosity about ideas that can’t be directly connected to ones we deem to be valid today. Someone with that view is going to be able only to convey a very limited picture of science to the general public.

Which brings me to science communication. Given Weinberg’s dismissive attitude to professional historians, I suppose it should come as no great surprise to discover his view of professional science writers. Like Richard Dawkins selecting The Oxford Book of Modern Science Writing, he only has eyes for fellow scientists who try to popularize what they do. It is essential that such people exist, and the best of them (like Dawkins and E. O. Wilson) have produced much of the best science writing. But the fact that, in an article on writing about science for the general public, Weinberg fails even to acknowledge the existence of people who do this professionally gives us a pretty fair picture of what he thinks about science communication. We have to assume that, like history, this is not something that need be done by specialists – it is best left to scientists themselves, since only they really understand science. They can, you know, just “take time off from their own research” to knock it out.

Like Weinberg? Well, The First Three Minutes is deservedly a classic. But it is helpful that Weinberg starts his piece by saying that “It is mathematics above all that present an obstacle to communication between professional scientist and the general public”, because it tells us from the outset that we needn’t take too seriously his thoughts on science communication. I am quite sure I am not alone when I say that, having written about science (particularly physical science) for more than 20 years, I have almost never found myself frustrated, in wishing to convey an idea or concept, by the fact that I cannot tell it in maths. Indeed, a wish to do so is almost invariably a good sign that the underlying ideas are not properly understood by the author. If scientists cannot communicate a concept without falling back on maths, they don’t truly grasp what it is they are trying to talk about. It is a failure of the communicator, not of the audience.

But even putting that aside, Weinberg’s insistent refrain about the role of maths in science betrays his extreme parochialism. This is reflected in To Explain the World, which is not about the history of science but about the history of physics, particularly celestial and terrestrial mechanics. He still takes the view, popular a century ago but long discarded by historians of science, that no science has really grown up until it becomes thoroughly mathematical. I’m not even sure that there are many physicists who still cling to this absurd notion. It reveals a total lack of understanding of chemistry, materials science, evolutionary biology and cell biology, to name just a few areas. Of course, mathematical and quantitative models are important in all these areas. But they don’t define them in the same way as they do most of physics. Weinberg’s is the kind of thinking that says chemistry only became a proper science (and at the same time, an obsolete one) when quantum theory explained the structure of the atom and the nature of the chemical bond. And that, to use a popular physics slogan, is not even wrong.

This sort of parochialism is reflected in Weinberg’s list of “13 best science books for the general reader”. Only one of them is by a professional science writer (Timothy Ferris, who certainly deserves that place), and nine of them are about physics – and cosmological, nuclear or fundamental physics at that. No chemistry; no surprise. The shortage of women in Weinberg’s list is not because, as he tells us, “women were not welcome in science through most of its history”, but because he does not seem interested in the work of the many excellent science writers who happen to be female. Because they aren’t real scientists, you see. And so there is no room for the likes of Georgina Ferry, Elizabeth Kolbert, Margaret Wertheim, Dava Sobel, Deborah Blum, Gabrielle Walker... Instead, we get Lisa Randall – not, I suspect, because she is a particularly gifted communicator of science (sadly she is not), but because she works in theoretical physics. (If he’d wanted to limit himself to that, he could at least have chosen Janna Levin, who really can write well.)

The great thing about writing books, Weinberg says, is that it has given him “the opportunity of leaving for a while the ivory tower of theoretical physics research, and making contact with the world outside.” He should do it more often.

Thursday, April 02, 2015

Looking for the science vote

Very interesting to see in Nature the changes in British readers’ voting intentions from 2010 to the forthcoming UK election in May. In a nutshell: once a Tory, always a Tory but there’s a big leaching from the middle/left parties to “Don’t know”, plus a substantial boost to the Greens from the same source. I don’t know how representative this of the population as a whole, but it unsettles me to see such a big uncommitted block, and this is why.

I fully support Jenny Rohn and Stephen Curry’s initiative to get science firmly on the political agenda (Science is Vital), but I’m concerned that it not become a call to vote simply on the basis of who you think will do the best job for science (which I'm sure is not Jenny and Stephen's intention). I have heard that kind of single-issue politics already from one or two prominent voices of science, and it troubles me deeply. While obviously wanting everyone to vote the way I do (and accepting that some will think I’m deluded in that choice), I feel that voters ought ideally be making up their minds in the basis of which party will try to create the fairest, most tolerant, egalitarian, responsible and healthy society, and not simply which party is going to perform best on a single issue – even one as important as science. If I felt that the party closest to my political sympathies was failing to do enough for science, I would lobby them to do better, and not switch allegiances on those grounds alone. After all, none of the major parties is likely to deny the importance of science, even if they won’t all back up their words with actions to the same degree. And without wishing to sound too melodramatic, it was by telling themselves that they were doing what was "best for German science" that many German scientists were able to salve their consciences during the Nazi regime.

Thursday, March 19, 2015

The Saga of the Sunstones

In the Dark Ages, the Vikings set out in their longships to slaughter, rape, pillage, and conduct sophisticated measurements in optical physics. That, at least, has been the version of horrible history presented recently by some experimental physicists, who have demonstrated that the complex optical properties of the mineral calcite or Iceland spar can be used to deduce the position of the sun – often a crucial indicator of compass directions – on overcast days or after sunset. The idea has prompted visions of Norse raiders and explorers peering into their “sunstones” to find their way on the open sea.

The trouble is that nearly all historians and archaeologists who study ancient navigation methods reject the idea. Some say that at best the fancy new experiments and calculations prove nothing. Historian Alun Salt, who works for UNESCO’s Astronomy and World Heritage Initiative, calls the recent papers “ahistorical” and doubts that the work will have any effect “on any wider research on navigation or Viking history”. Others argue that the sunstone theory was examined and ruled out years ago anyway. “What really surprises me and other Scandinavian scholars about the recent sunstone research is that it is billed as news”, says Martin Rundkvist, a specialist in the archaeology of early medieval Sweden.

This debate doesn’t just bear on the unresolved question of how the Vikings managed to cross the Atlantic and reach Newfoundland without even a compass to guide them. It also goes to the heart of what experimental science can and can’t contribute to an understanding of the past. Is history best left to historians and archaeologists, or can “outsiders” from the natural sciences have a voice too?

What a saga

The sunstone hypothesis certainly isn’t new. It stems largely from a passage in a thirteenth-century manuscript called St Olaf’s Saga, in which the Icelandic hero Sigurd tells King Olaf II Haraldsson of Norway where the sun is on a cloudy day. Olaf checks Sigurd’s claim using a mysterious sólarsteinn or sunstone:
Olaf grabbed a Sunstone, looked at the sky and saw from where the light came, from which he guessed the position of the invisible Sun.

An even more suggestive reference appears in another thirteenth-century record of a Viking saga, called Hrafns Saga, which gives a few more clues about how the stone was used:
the weather was sick and stormy… The King looked about and saw no blue sky… then the King took the Sunstone and held it up, and then he saw where the Sun beamed from the stone.

In 1967 Danish archaeologist Thorkild Ramskou suggested that this sunstone might have been a mineral such as the aluminosilicate cordierite, which is dichroic: as light passes through, rays of different polarization are transmitted by different amounts, depending on the orientation of its crystal planes (and thus its macroscopic facets) relative to the plane of polarization. This makes cordierite capable of transmitting or blocking polarized rays selectively – which is how normal polarizing filters work. (Ramskou also suggested that the mineral calcite, a form of calcium carbonate, would work as a sunstone, based on the fact that calcite is birefringent: rays with different polarizations are refracted to different degrees depending on the orientation with respect to the crystal planes. But that’s not enough, because calcite is completely transparent: changing its orientation makes no difference to how much polarized light passes through. You need dichroism for this idea to work, not birefringence.)

Because sunlight becomes naturally polarized as it is scattered in the atmosphere, if cordierite is held up to sunlight and rotated it turns darker, becoming most opaque when the crystal planes are at right angles to the direction of the sun’s rays. Even if the sun itself is obscured by mist or clouds and its diffuse light arrives from all directions, the most intense of the polarized rays still come straight from the hidden sun. So if a piece of dichroic mineral is held up to the sky and rotated, the pattern of darkening and lightening can be used to deduce, from the orientation of the crystal’s facets (which reveal the orientation of the planes of atoms), the direction of the sun in the horizontal plane, called its azimuth. If you know the time of day, then this angle can be used to calculate where north lies.

Ramskou pointed out that polarizing materials were once used in a so-called Twilight Compass by Scandinavian air pilots who flew over the north pole. Their ordinary compasses would have been useless then, but the Twilight Compass allowed them to get their bearings from the sun. So maybe the Vikings did the same out on the open sea? Might they have chanced upon this handy property of calcite, found in abundance on Iceland? Perhaps all Viking ships set sail with a sunstone to hand, so that even on overcast or foggy days when the sun wasn’t visible they could still locate it and find their bearings.

The idea has been discussed for years among historians of Viking navigation. But only recently has it been put to the test. In 1994, astronomer Curt Roslund and ophthalmologist Claes Beekman of Gothenburg University showed that the pattern of darkening produced by a dichroic mineral in diffuse sunlight is too weak to give a reliable indication of the sun’s location. They added that such a fancy way to find the hidden sun seems to be unnecessary for navigation anyway, because it’s possible to locate the sun quite accurately with the naked eye when it is behind clouds from the bright edges of the cloud tops and the rays that emanate from behind the cloud. The sunstone idea, they said, “has no scientific basis”.

That was merely the opening sally of a seesawing debate. In 2005, Gabór Horváth at the Loránd Eötvös University in Budapest, a specialist in animal vision, and his colleagues tested subjects using photographs of partly cloudy skies in which the sun was obscured, and found that they couldn’t after all make a reasonably accurate deduction of where the sun was. Two years later Horváth and collaborators measured the amount and patterns of polarization of sunlight in cloudy and foggy skies and concluded that both are after all adequate for the “polarizer” sunstones to work in cloudy skies, but not necessarily in foggy skies. All this seemed enough to rehabilitate the plausibility of the sunstone hypothesis. But would it work in practice?

Double vision

Optical physicists Guy Ropars and Albert Le Floch at the University of Rennes had been working for decades on light polarization effects in lasers. In the 1990s they came across the sunstone idea and the objections of Roslund and Beekman. While Horváth’s studies seemed to show that it wasn’t after all as simple as they had supposed to find the sun behind clouds, Ropars and Le Floch agreed with their concern that the simple darkening of a dichroic crystal due to polarization effects is too weak to do that job either. The two physicists also pointed out that Ramskou’s suggestion of using birefringent calcite this way won’t work. But, they said, calcite has another property that presents a quite different way of using it as a sunstone.

When a calcite crystal is oriented so that a polarized ray strikes at right angles to the main facet of the rhombohedral crystals, but at exactly 45 degrees to the optical axis of the crystal – at the so-called isotropy point – it turns out that the light in the rays at this position are completely depolarized. As a result, it’s possible to find the azimuth of a hidden sun by exploiting the sensitivity of the naked eye to polarized light. When polarized white light falls on our eye’s fovea, we can see a pattern in which two yellowish blobs fan out from a central focus within a bluish background. This pattern, called Haidinger’s brushes, is most easily seen by looking at a white sheet of paper illuminated with white polarized light, and rotating the filter. We can see it too on a patch of blue sky overhead when the sun is near (or below) the horizon by rotating our head. By placing a calcite crystal in the line of the polarized rays oriented to its isotropy point relative to the sun’s azimuth, the polarization is removed and Haidinger’s brushes vanish. Comparing the two views by moving the crystal rapidly in and out of the line of sight, the researchers found that the sun’s azimuth can be estimated to within five degrees.

Haidinger’s brushes: an exaggerated view.

But it’s a rather cumbersome method, relies on there being at least a high patch of unobstructed sky, and would be very tricky on board a pitching ship. There is, however, a better alternative.

Because calcite is birefringent, when a narrow and partially polarized light ray passes through it, the ray is split in two, an effect strikingly evident with laser beams. One ray behaves as it would if just travelling through glass, but the other is deviated by an amount that depends on the thickness of the crystal and the angle of incidence. This is the origin of the characteristic double images seen through birefringent materials. And whereas Roslund and Beekman had argued that changes in brightness for a dichroic substance rotated in dim, partially polarized light are likely to be too faint to distinguish, the contrast between the split-beam intensities as calcite is rotated are much stronger and easier to spot. “The sensitivity of the system is then increased by a factor of about 100”, Ropars explains. At the isotropy point, the two rays will have exactly the same brightness, regardless of how polarized the light is. This means that, if we can accurately judge this position of equal brightness, the orientation of the crystal at that point can again be used to figure out the azimuth from which the most intense rays are coming.

Double images and split laser beams in calcite, due to birefringence.

The human eye happens to be extremely well attuned to comparing brightness contrasts of fairly low-level lighting. So the researchers’ tests using partially polarized light shone through a calcite crystal showed that, under ideal conditions, the direction of the light rays could be estimated to within 1 degree even for low overall light intensities, equivalent to a sun below the horizon at twilight. The method, they say, will work even up to the point where the first stars appear in the sky.

Showing all this is the lab is one thing, but can it be turned into a navigational instrument? Ropars, Albert Le Floch and their coworkers have already made one. They call it the Viking Sunstone Compass.

It’s a rather beautiful wooden cylinder with a hole in the top, through which light falls from the zenith of the sky onto a calcite crystal attached to a rotating pivot turned by a little handle on the lid. There’s a gap in the side through which the observer looks at the two bright spots projected from the crystal. “You simply rotate the crystal to equalize the intensities of the beams”, says Ropars. A pointer on the lid then indicates the orientation of the crystal and the azimuth of the sun, from which north can be deduced by taking into account the time of day. Ropars says that, even though of course the Vikings lacked good chronometers, they seem to have known about sundials. What’s more, studies have shown that people’s internal body clocks (their circadian rhythm) can enable us to estimate the time of day to within about a quarter of an hour.

The Viking Sunstone Compass made by researchers at the University of Rennes. Note the double bright spots in the cavity.

But never mind Vikings – the Rennes team could probably make a mint by marketing these elegant devices as a luxury item for sailors. Ropars says that a US company is now hoping to commercialize the device based on their prototype.

All at sea

When the findings were reported, they spawned a flurry of excited news headlines, many claiming that the mysteries of Viking navigation had finally been solved. It’s not surprising, for the image of brawny Vikings making use of such a brainy method is irresistible. But what, in the end, did the experiments really tell us about history?

There’s nothing in principle that might have prevented the ancient Greeks from developing steam power or microscopes. We are sure that they didn’t because there is absolutely no evidence for it. So an experiment demonstrating that, say, ancient Greek glass-making methods allow one to make the little glass-bead microscope lenses used by Antoni van Leeuwenhoek in the seventeenth century is historically meaningless. What, then, can we conclude about Viking sunstones?

Because the Viking voyages between the ninth and eleventh centuries were so extensive – they sailed to the Caspian Sea, across the Mediterranean to Constantinople, and over the Atlantic to North America – there is a pile of archaeological and historical research on how on earth they did it. The prevailing view is that, in the Dark and Middle Ages, as much sailing as possible was done in sight of land, so that landmarks could guide the way. But of course you can’t cross the Atlantic that way. So if no land was in sight, sailors used environmental signposts: the stars (the Vikings knew how to find north from the Pole Star), the sun and moon, winds and ocean currents. They also relied on the oral reports of previous voyagers to know how long it should take to get to particular places.

What if none of these clues was available? What did they do if becalmed in the open sea on a cloudy day? Well, then they admitted that they were lost – as they put it, hafvilla, “wayward at sea”. The written records indicate that under such circumstances they would convene to discuss the problem, relying on the instincts of the most experienced sailors to set a course.

However, some archaeologists and historians, like Ramskou, have argued that they could also have used navigational instruments. The problem is that there is precious little evidence for it. The Scandinavian coast is dotted with Viking ship finds, some of them wrecks and others buried to hold the dead in graves. But not one has provided any artifacts that could be navigational tools. Nevertheless, the archaeological record is not entirely barren. In 1948 a Viking-age wooden half-disk carved with sun-like serrations was unearthed under the ruins of a monastery at Uunartoq in Greenland. It was interpreted by the archaeologist Carl Sølver as a navigational sundial, an idea endorsed by Ramskou in the 1960s. More recently another apparent wooden sundial was found at the Viking site on the island of Wolin, off the coast of Poland in the Baltic. A rectangular metal object inscribed in Latin, found at Canterbury and tentatively dated to the eleventh century, has also been interpreted as a sundial, while a tenth-century object from Menzlin in Germany might be a nautical weather-vane.

A Viking ship grave at Oseberg in Norway, and the Uunartoq Viking sundial.

So the “instrumental school” of Viking navigation has a few tenuous sources. But no sunstones. That hasn’t previously deterred the theory’s champions. One of them was Leif Karlsen, an amateur historian whose 2003 book Secrets of the Viking Navigators announced his convictions in its subtitle: “How the Vikings used their amazing sunstones and other techniques to cross the open ocean”. One problem with such a bold claim is that the sunstone hypothesis had already been carefully examined in 1975 by the archaeologist Uwe Schnall, who argued that not only is there no evidence for it but there is no clear need either. “Since then, to my knowledge, no research has contradicted this conclusion”, says Willem Mörzer Bruyns, a retired curator of navigation at the Netherlands Maritime Museum in Amsterdam.

In making his case, however, Karlsen presented a new exhibit. In 2002, just as his book was being completed, archaeologists discovered a calcite crystal in the remains of a shipwreck offshore from the Channel Island of Alderney. It has been made misty by centuries of immersion in seawater and abrasion by sand, but it still has the familiar rhombohedral shape. Finally, tangible proof that sailors carried sunstones! Well, not quite. Not only is it totally unknown why the crystal was on board, but the ship is from Elizabethan England, not the Viking age.

The Alderney “sunstone”.

All the same, Ropars and colleagues claim that it supports their theory that these crystals were used for navigation. They point out, for example, that it was found close to a pair of navigational dividers. But, says Bruyns, “navigational instruments were kept in the captain’s and officers’ quarters, where their non-navigational valuables were also stored.” All the same Bruyns is sympathetic to the idea that, rather than being a primary navigational device, the crystal might have been used to correct for compass errors caused by local magnetic variations (such as proximity to iron cannons), which was done at that time by looking at the sun’s position on the horizon when it rose or set. Ropars points out that birds use the same recalibration of their magnetic sensors using polarization of sunlight at sunrise and sunset. “We’re now looking for possible mentions of sunstones in the historical Navy reports of the 15th and 16th centuries”, he says. But however intriguing that idea is, it has no bearing on a possible use of sunstones for navigation in the pre-compass era. “The Alderney finding is from a completely different period and culture to the Vikings”, Ropars acknowledges.

Finding the right questions

One way to view the latest work on sunstones is that it could at least have ruled out the hypothesis in principle. But don’t historians need a good reason to regard a hypothesis as plausible in the first place, before they get concerned about whether it is possible in practice? Otherwise there is surely no end to the options one would need to exclude. And there is the difficult issue of the documentary record. Lots of what went on a millennium and more ago was not written down, and much of what was is now lost. All the same, there is a rich literature, at least from the Middle Ages, of the techniques and skills of trades and professions, while early pioneers of optics like Roger Bacon and Robert Grosseteste in the thirteenth century offer a pretty extensive summary of what was then known on the subject. It’s not easy to see how they would have neglected sunstones, if these were widely used in navigation. Ropars says that the Icelandic sagas aren’t any longer the only textual source for sunstones, for the Icelandic medieval historian Arni Einarsson pointed out in 2010 that sunstones are also mentioned in the inventory lists of some Icelandic monasteries in the fourteenth and fifteenth centuries, where they were apparently used as time-keeping tools for prayer sessions. But monks weren’t sailors.

The basic problem, says Salt, is that scientists dabbling in archaeology often try to answer questions that, from the point of view of history and anthropology, no one is asking. This has been a bugbear of the discipline of archaeoastronomy, for example, in which astronomers and others attempt to provide astronomical explanations of historical records of celestial events, such as darkening of the skies or the appearance of new stars and other portents. Explanations for the Star of Bethelem have been particularly popular, but here too Salt thinks that it is hard to find any examples of a historically interesting question being given a compelling answer. [See, e.g. J. British Astron. Assoc. 114, 336; 2004]. One of the most celebrated examples, also revolving around optical physics, was the suggestion by artist David Hockney and physicist Charles Falco that painters in the Renaissance such as Jan van Eyck used a camera obscura to achieve their incredible realism. The theory is now generally discounted by art historians.

“‘Could the Vikings have used sunstones’ is a different question to ‘did the Vikings use sunstones”, which is what most historians are interested in,” says Salt. “A paper that tackles a historical problem by pretty much ignoring the historical period your artefact comes from seems to me to be eccentric.” Ropars agrees that “experimental science can exclude historical hypotheses, but isn’t sufficient to validate them.” But he is optimistic about the value of collaborations between scientists and historians or archaeologists, when the historical facts are sufficiently clear for the scientists to develop a plausible model of what might have occurred.

Could it be, though, that we’re looking at the sunstone research from the wrong direction? One of its most attractive outcomes is not an answer to a historical question, but a rich mix of mineralogy, optics and human vision that has inspired the invention of a charming device which, using only methods and materials accessible to the ancient world, enables navigation under adverse conditions. It would be rather lovely if the modern “Viking Sunstone Compass” were to be used to cross the Atlantic in a reconstructed Viking ship, as was first done in 1893. It would prove nothing historically, but it would show how speculations about what might have been can stimulate human ingenuity. And maybe that’s enough.

The reconstructed Viking ship the Sea Stallion sets sail.

Further reading
J. B. Friedman & K. M. Figg (eds), Trade, Travel and Exploration in the Middle Ages: An Encyclopedia, from p. 441. Routledge, London, 2000.

A. Englert & A. Trakadas (eds), Wulfstan’s Voyage, from p.206. Viking Ship Museum, Roskilde, 2009.

G. Horváth et al., Phil Trans. R. Soc. B 366, 772 (2011).

G. Ropars, G. Gorre, A. Le Floch, J. Enoch & V. Lakshminarayanan, Proc. R. Soc. A 468, 671 (2011).

A. Le Floch, G. Ropars, J. Lucas, S. Wright, T. Davenport, M. Corfield & M. Harrisson, Proc. R. Soc. A 469, 20120651 (2013).

G. Ropars, V. Lakshminarayanan & A. Le Floch, Contemp. Phys. 55, 302 (2014).


Note: A version of this article appears in New Scientist this week. A pdf of this article is available on my website here.

Wednesday, March 18, 2015

The graphene explosion

I haven’t found any reports of the opening of Cornelia Parker’s new solo show at the Whitworth in Manchester. Did the fireworks go off? Did the detonator work? Here, anyway, is what I wrote for Nature Materials before the event.


If all has gone according to the plan as this piece went to press, Manchester will have been showered with meteorites. An exhibition at the University of Manchester’s Whitworth art gallery by the artist Cornelia Parker is due to be opened on 13th February with a firework display in which pieces of meteoritic iron will be shot into the sky.

The pyrotechnics won’t be started simply by lighting the blue touchpaper. The conflagration will be triggered by a humidity sensor, switched by the breath of physicist Kostya Novoselov, whose work on graphene at Manchester University with Andre Geim won them both the 2010 physics Nobel prize. The sensor is itself made from graphene, obtained from flakes of graphite taken from drawings by William Blake, J. M. W. Turner, John Constable and Pablo Picasso as well as from a pencil-written letter by Ernest Rutherford, whose pioneering work on atomic structure was conducted at Manchester.

That graphene (oxide) can serve as an ultra-sensitive humidity sensor was reported by Bi et al. [1], and has since been refined to give a very rapid response [2]. Adsorption of water onto the graphene oxide film alters its capacitance, providing a sensing mechanism when the film acts as an insulating layer between two electrodes. These sensors are now being developed by Nokia. The devices used for Parker’s show were provided by Novoselov’s group after the two of them were introduced by the Whitworth’s director Maria Balshaw. Novoselov extracted the graphite samples from artworks owned by the galley, using tweezers under careful supervision.

“I love the idea of working on a nano level”, Parker has said. “The idea of graphene, something so small, being a catalyst.” She is not simply talking figuratively: doped graphene has indeed been explored as an electrocatalyst for fuel cells [3,4].

Parker has a strong interest in interacting with science and scientists. In 1997 she produced a series of works for Nature examining unexpected objects in a quasi-scientific context [5]. Much of her work focuses on connotations of materiality, associations arising from what things are made of and the incongruity of materials repurposed or set out of place. Her installation Thirty Pieces of Silver (1988-9) used an assortment of silver objects such as instruments and cutlery flattened by a steamroller. She has worked with the red crepe paper left over from the manufacture of Remembrance Day poppies, with lead bullets and gold teeth extruded into wire, and with her own blood. Perhaps even her most famous work, Cold Dark Matter: An Exploded View (1991) – the reconvened fragments of an exploded shed – was stimulated as much by the allure of the “matter” as by the cosmological allusion.

“I like the garden shed aspect of scientists”, she has said, “the way they like playing about with materials.” Unusually for an artist, she seems more excited by the messy, ad hoc aspects of practical science – the kind of experimentation for which Rutherford was so renowned – than by grand, abstract ideas. The fact that Novoselov and Geim made some of their graphene samples using Scotch tape to strip away layers from graphite no doubt added to its appeal. Parker also recognizes that materials tell stories. There’s a good chance that both Blake and Rutherford would have used graphite from the plumbago mines of Borrowdale in Cumbria, about 80 miles north of Manchester and the source of the Keswick pencil industry. So even Parker’s graphene might be locally sourced.

1. Bi, H. et al., Sci. Rep. 3, 2714 (2013).
2. Borini, S. et al., ACS Nano 7, 11166-11173 (2013).
3. Geng, D. et al., Energy Environ. Sci. 4, 760-764 (2011).
4. Fei, H. et al., ACS Nano 8, 10837-10843 (2014).
5. Anon., Nature 389, 335, 548, 668 (1997).