Page 1113 – Physics World

Home » Page 1113

Physics World 2015 Focus on Astronomy and Space is out now

By Louise Mayor

Woolly hats are being donned and there’s a nip in the air as the longest night of the year in the Northern hemisphere approaches. All this darkness makes it the perfect season to gaze up at the stars, planets and puffy nebulae above. But binoculars and amateur telescopes can only enhance the view by so much. To really push the boundaries of how far and how fine we can see, we must turn to international telescope projects both on the ground and in space.

To update you on what we think are the most exciting current and future projects we bring you the Physics World Focus on Astronomy and Space, which you can read free of charge in its entirety.

One particularly ambitious imaging effort is described in the article “Portrait of a black hole“, in which Physics World reporter Tushna Commissariat reports on how a group of astronomers plans to take the first-ever image of a black hole. Despite their name, black holes are apparently not black and the Event Horizon Telescope collaboration has already begun pointing a network of ground-based telescopes at its target: Sagittarius A*, the supermassive black hole at the centre of our galaxy.

(more…)

Throwing the book at bad ideas

If you believe in scientific progress, you will agree that the fate of all theories is to be replaced with better ones. Newton’s theory of gravitation was good; Einstein’s was better; someday we will find one that is better still, and so on. But does this mean that better theories are actually held back by inferior ones? In other words, if “wrong” ideas had not been so widely accepted, might “right” (or less wrong) ideas have arrived sooner?

To judge from comments I’ve seen in (and about) several recent popular-science books, some eminent scientists seem to think so. Their arguments are rather like a scientific version of Gresham’s law: the economic principle that “bad money drives out good”. This law got its name in the 19th century, but it was remarked upon much earlier by (among others) Nicolaus Copernicus – the father of heliocentric theory. He observed that when pared-down gold and silver coinage circulated widely, people hung on to any unadulterated currency they could find. Eventually, only the bad currency changed hands.

Copernicus’s link with Gresham’s law adds irony to the views of cosmologist Joe Silk, who argued (in a Nature review of Frank Wilczek’s book A Beautiful Question, which I reviewed for Physics World in October) that Copernicus’s Sun-centred universe was “held back” by Ptolemy’s Earth-centric, epicycle-laden version. According to the physicist Steven Weinberg, meanwhile, Ptolemy himself suffered from similar problems: in his book To Explain the World (see “The cradle of modern science”), Weinberg sighs that the ancient astronomer allowed his scientific acuity to be clouded by the “bad theory” of astrology. Weinberg also argues that the 14th-century French polymath Nicole Oresme was on the threshold of discovering heliocentrism before he “finally surrendered” to the misconceived Ptolemaic orthodoxy – the good idea crowded out by a bad one. (In a nice twist, Oresme, too, is sometimes credited with Gresham’s law.)

Cosmology is not the only sphere in which this notion that “bad ideas drive out good” supposedly applies. In To Explain the World, Weinberg also argues that René Descartes’ muddled ideas in physics “delayed the reception of Newtonian physics in France”. Meanwhile, in chemistry, the putative element phlogiston is often portrayed as a bone-headed impediment to Antoine Lavoisier’s oxygen-based system. And in the closest thing I’ve seen to a suggestion that science would work a whole lot quicker if history didn’t get in the way, the evolutionary biologist Jerry Coyne has proposed that “if after the fall of Rome atheism [and not Christianity] had pervaded the Western world, science would have developed earlier and be far more advanced than it is now”. That’s just one of many reasons why Coyne has argued (most recently in his book Faith Versus Fact) that “science and religion are incompatible”.

Historians of science tend to be much more relaxed about “wrong” ideas. Their task, after all, is not to adjudicate on science but to explain how ideas evolved. This requires them to understand theories in the context of their times: to see why people thought as they did, not to hand out medals for getting things “right”. In other words, they do history. At its worst, however, this position has sometimes led to the suggestion that there is no right and wrong in the history of science. In this extreme “relativist” view, modern science is no more valid than medieval philosophies, and today’s theories have gained acceptance solely because of social and political factors, not because they are objectively any better.

Plenty of scientists and historians have exposed this view as an imposture; David Wootton’s recent book The Invention of Science is but one example. But even if we reject extreme relativism and accept that science develops ever-more-reliable theories about the world, must we also conclude that better theories are delayed by worse ones?

I believe this idea should be resisted, but not so much because it makes for bad history (although it does), or because it gives the likes of Weinberg licence to call Plato silly and Francis Bacon irrelevant (see what I mean?). Rather, I think the scientific version of Gresham’s law denies the realities of how science is done.

No-one sticks with a wrong theory, in the face of a better one, knowing that it is wrong. We do so because we are human and stubborn and attached to our own ideas, and also because we are terribly prone to confirmation bias, seeing only what suits our preconceptions. But whatever the reason, we also think the old theory is actually better – that it gives a better account of why things are the way they are. In other words, at least some of our reasons for sticking with old theories are the same as those that prompt us to come up with new (and occasionally better) theories.

What’s more, theories aren’t good solely (or even) because they are eventually proved “right”. They are good if (among other things) they offer an adequate account of why things are the way they are, without too many arbitrary assumptions. They should be both consistent with and motivated by observations, and ideally they should also have a degree of predictive power. Ptolemy’s cosmology met those conditions, more or less, for centuries. So did Newton’s theory of gravity. In contrast, Max Planck’s proposed quantum fell short, at least at first. Taken at face value, quanta undermined the Newtonian physics that was otherwise so successful, without (at that point) a compelling reason to do so. That’s why Planck initially regarded quanta as a mathematical convenience, rather than real physical entities. Just imagine if Newton himself, lacking even Planck’s motivation, had pulled quanta arbitrarily out of a hat – would that have been a “good” theory? I think not.

We love to deride people who dismissed an idea that proved to be right. But sometimes they had good grounds for doing so. There was no widely accepted empirical evidence for quantization as a fundamental property until Einstein’s work on the specific heat of solids in 1907; contrary to common belief, studies of the photoelectric effect didn’t offer compelling support until several years later. A similar defence can even be made for the cardinals who allegedly refused to look through Galileo’s telescope to confirm his claims with their own eyes. After all, the telescope was a new invention of unproven reliability (could one be sure it didn’t create illusions?), and without some practice it was far from easy to use or to interpret what one saw.

So how can we distinguish “good” theories from “bad” ones? When we are taught the scientific method at school, the answer is, usually, “Do an experiment!” Indeed, Richard Feynman (in one of his many quotable moments – see “Between the lines”) attested that “Nature cannot be fooled”. Unfortunately, the notion that experiments can be trusted to deliver a clear verdict on the rights and wrongs of theories is simplistic – just ask anyone who has had to defend their conclusions against rival interpretations. In peer review, your clean, decisive experimental result quickly becomes a battle against potential confounding factors and alternative explanations. If you’ve experienced that, you have encountered something called the Quine–Duhem thesis, which says, in essence, that there’s always more than one way to read the data. (More strictly, the thesis is that no scientific hypothesis can make predictions independently from other hypotheses.)

Of course, some experiments are decisive. In The Invention of Science, Wootton cites the early 16th-century voyages of Amerigo Vespucci, which showed that the New World was a separate continent, not the “back end” of Asia – thereby destroying the theory that the Earth was made of non-concentric spheres of earth and water, with the solid sphere breaking the surface of the liquid one at just one place. But even so, the Quine–Duhem thesis deserves to be much better known among working scientists. Add in the current talk of a “replication crisis” in the life and social sciences (Nature 526 163), and the fantasy that experiments resolve everything – so-called “experimental realism” – looks increasingly threadbare.

Some famous scientists have stated explicitly that they refuse to accept experiment as the ultimate authority anyway. If observations of the 1919 solar eclipse had failed to support general relativity, Einstein averred that “I would have been sorry for the dear Lord, for the theory is correct.” His Princeton colleague, the mathematician Herman Weyl, claimed that “My work always tries to unite the true with the beautiful; but when I had to choose one or the other, I usually chose the beautiful.” Not all theorists hold such strong views about beauty as a guide, but even so, if a theory were dropped the moment an experimental result seemed to contradict it, progress would be impossible.

Ultimately, science does seem able to find ever more dependable, more accurate, more predictive theories. It works. But this doesn’t mean we should imagine that bad theories or ideas hold back good ones. To do so is to put the cart before the horse, or to suppose that history has a goal (something that, of all people, an evolutionary biologist like Coyne ought to recognize as a mistake). Instead, we need to explore in detail how science evolves: as Wootton puts it, “to understand how reliable knowledge and scientific progress can and do result from a flawed, profoundly contingent, culturally relative and all-too-human process”. When we start wishing away history, we lose sight of that process.

Electron lifetime is at least 66,000 yottayears

The best measurement yet of the lifetime of the electron suggests that a particle present today will probably still be around in 66,000 yottayears (6.6 × 10²⁸ yr), which is about five-quintillion times the current age of the universe. That is the conclusion of physicists working on the Borexino experiment in Italy, who have been searching for evidence that the electron decays to a photon and a neutrino; a process that would violate the conservation of electrical charge and point towards undiscovered physics beyond the Standard Model.

The electron is the least-massive carrier of negative electrical charge known to physicists. If it were to decay, energy conservation means that the process would involve the production of lower-mass particles such as neutrinos. But all particles with masses lower than the electron have no electrical charge, and therefore the electron’s charge must “vanish” during any hypothetical decay process. This violates “charge conservation”, which is a principle that is part of the Standard Model of particle physics. As a result, the electron is considered a fundamental particle that will never decay. However, the Standard Model does not adequately explain all aspects of physics, and therefore the discovery of electron decay could help physicists to develop a new and improved model of nature.

This latest search for electron decay was made using the Borexino detector, which is designed primarily to study neutrinos. It is located deep under a mountain at the Gran Sasso National Laboratory to shield it from cosmic rays and comprises 300 tonnes of an organic liquid that is viewed by 2212 photomultipliers.

Photon hunting

The Borexino team focused on a specific hypothetical decay process in which an electron in the organic liquid decays to an electron neutrino and a photon with energy 256 keV. This photon then goes on to interact with electrons in the liquid to produce a distinct flash of light that is detected by the photomultipliers.

The physicists sifted through all of the photomultiplier signals recorded from January 2012 to May 2013, looking for signatures of a 256 keV photon. To do so, they first had to subtract the signals from a number of unrelated processes that occur in the detector and produce similar amounts of light as a 256 keV photon. These include the radioactive decays of several trace isotopes in the detector, as well as light from the neutrino collisions that Borexino is designed to detect. After taking these background signals into consideration, the team was able to say that no electron decays were observed during the 408-day run.

Borexino’s organic liquid contains a vast number of electrons (about 10³²), and the fact that no electron decays were seen during the search allowed the team to estimate a minimum value for the average lifetime of the electron. The researchers’ minimum lifetime of 6.6 × 10²⁸ yr is more than 100 times greater than the previous lower limit of 4.6 ×10²⁶ yr. This was measured back in 1998 by the Borexino Counting Test Facility, which was a precursor to the current experiment.

Invisible channels

Gianpaolo Bellini, who is spokesperson for Borexino, told physicsworld.com that if the detector could be further purified to virtually eliminate all background radiation, the minimum lifetime measurement could be boosted to greater than 10³¹ yr. He points out that Borexino could also be used to search for decays into the “invisible channel” whereby an electron is converted into three neutrinos, or could even look for the “disappearance” of an electron into extra dimensions.

Victor Flambaum of the University of New South Wales in Australia told physicsworld.com that searches for the violation of apparent symmetries are very important because even a small violation can have profound implications on our understanding of the universe. Flambaum, who is not a member of the Borexino team, points out that the experimental discovery that charge–parity (CP) symmetry is violated was made by observing the decays of kaons. CP violation plays an important role in our current understanding of why there is much more matter than antimatter in the universe.

The search is described in Physical Review Letters.

The life and times of Einstein – 'A vagabond and a wanderer'

Falling in: Sir Roger's sketch of a black hole collapse, at his talk (Courtesy: Tushna Commissariat) — Falling in: Sir Roger Penrose’s sketch of a black-hole collapse. (Courtesy: Tushna Commissariat)

By Tushna Commissariat

So much has been said about Einstein and his general theory of relativity (GR) that one would assume there isn’t two entire days worth of talks and lectures that could shed new light on both the man and his work. But that is precisely what happened last weekend at Queen Mary University London’s “Einstein’s Legacy: Celebrating 100 years of General Relativity” conference, where a mix of scientists, writers and journalists talked about everything from the “physiology of GR” to light cones and black holes, to M-theory and even GR’s “sociological spin-offs”.

The opening talk, “Not so sudden genius”, was given by journalist and author of “Einstein: A hundred years of relativity“, Andrew Robinson. The talk was very fascinating and early on Robinson outlined that Einstein stood on the shoulders of many scientists and not just “giants” such as Newton and Mach. But he also acknowledged that the scientist was always a bit of a loner and he preferred it this way. Robinson rightly pointed out that until 1907, Einstein was “working in brilliant obscurity” and later, even once fame found him, rootlessness really suited Einstein’s personality – he described himself as “a vagabond and a wanderer”.

(more…)

Pierre Auger cosmic-ray observatory set for expansion

The Pierre Auger Observatory – the world’s largest cosmic-ray observatory – is set for a $14m upgrade that will also see its operations extended until 2025. The AugerPrime upgrade will involve installing scintillation detectors alongside the 1660 existing water Cerenkov detectors. This will enable more precise measurements of the mass of particles that make up cosmic rays, as well as help to identify the origin and nature of such particles.

The facility, which covers an area of 3000 km² in Argentina, measures the cascade of secondary particles produced when a cosmic ray hits the Earth’s atmosphere. By observing these particles, astronomers can obtain information on the mass, direction and energy of the original cosmic ray.

Recent results have shown that at the highest energies – 10¹⁸–10²¹ eV – the number of cosmic-ray particles decreases much faster than at lower energies. A better understanding of the mechanisms responsible for this flux suppression should help infer the maximum energy of cosmic rays and identify what is responsible for accelerating cosmic rays to such high energies. However, this requires more detailed measurements of the highest energy rays.

Unique capabilities

The new 4 m² scintillators will complement the existing Cerenkov water detectors and enable electrons and muons to be separated in the secondary shower more efficiently. Researchers will also be aided by a 23 km² area of new buried muon detectors. “The ratio of electrons to muons turns out to be very sensitive to the mass of the primary particle,” says Pierre Auger Observatory spokesperson Karl-Heinz Kampert. “AugerPrime will address a number of fundamental scientific problems that cannot be addressed anywhere else within the next decade or more.”

Measuring the fluxes of both muons and electrons should make it easier to identify cosmic rays that are high-energy protons. This is important because they are deflected less by cosmic magnetic fields and do a better job of pointing back to their distant sources than cosmic rays that are heavy, highly charged, nuclei.

“It has been said that identifying the sources of cosmic rays is the ‘holy grail’ of our field,” says Gordon Thomson, co-principal investigator for the Telescope Array cosmic-ray observatory in Utah. “This is exactly the aim of the AugerPrime project. The technique of counting both muons and electrons in air showers has been used successfully in previous experiments, and I believe it will work very well for the Auger experiment also.”

Better electronics

Work will start on the upgrade next year, which will also include faster and more powerful electronics to facilitate the new detector components and enhance the overall performance of the observatory.

Nature’s ups and downs

When Norman Lockyer, an astronomer and science writer with a day job as a clerk at the War Office in London, approached the publishing house Macmillan and Company in 1869 with a proposal for a new weekly journal about science, few could have predicted the outcome. The journal in question was Nature, and given its influence over the past 146 years, it is hard to believe that Melinda Baldwin’s Making Nature is the first full-length book to be written about it.

As Baldwin explains, Lockyer had originally intended Nature to appeal to both scientists and the general public, but the former refused to write in a way that could be understood by the latter, and the journal soon focused on researchers. However, Lockyer’s double-stranded philosophy is still in evidence in the modern Nature, where the “front half” contains news, opinion articles, book reviews and other magazine-style content aimed at a wide readership, while the “back half” is home to research papers aimed at specialists. Lockyer also established the idea of the journal being a player in the game, rather than merely reporting what was happening.

In its early decades, Nature was not the place where scientists sent their best work, but by the 1890s it was fast becoming the place where they could find out about and discuss exciting results that had been published elsewhere. The avalanche of new physics kicked off by the discovery of X-rays in November 1895 is a good example. Wilhelm Röntgen submitted his paper (written in German) to the Physical Medical Society of Würzburg on 28 December 1895 and sent copies to other physicists around the world, including Lord Kelvin in Glasgow and Arthur Schuster in Manchester. The discovery was widely reported in British newspapers in early 1896, and there was a short report in the issue of Nature dated 16 January 1896. However, Nature quickly showed what it was capable of, with the next issue containing an English translation of Röntgen’s paper; a paper from the Scottish engineer Alan Archibald Campbell-Swinton reporting that he had successfully repeated Röntgen’s experiments; and letters from Schuster and James Thomas Bottomley, a physicist at the University of Glasgow.

Although the paper reporting the discovery of X-rays was published in a German journal, Nature’s speed and engagement with researchers in the UK at the time meant that it was at the heart of the action as modern physics took shape. Relatively little of the original work was published in Nature but, as with X-rays, the journal played an important role in spreading news of the latest developments. All this was to pay dividends in the form of original research papers in later years from James Chadwick, Niels Bohr and Enrico Fermi (although Nature did reject Fermi’s seminal paper on the theory of beta decay).

By the 1930s Nature editorials increasingly covered topics outside the UK, notably the suppression of scientists in the Soviet Union and the threats posed by the rise of the Nazi party in Germany. However, the Second World War restricted the number of pages the journal could print, and its front half entered a lull. There were some highlights in this period, such as the publication of the double-helix structure of DNA in 1953, but as one long-time contributor put it: “almost anything could get into it at the time, if it wasn’t actually wrong”.

The lull ended when John Maddox was appointed editor in the mid-1960s. A former physics lecturer turned science journalist, Maddox immediately set about shaking up Nature’s front half, dealing with a backlog of 2000 submissions awaiting a decision and overhauling the journal’s approach to peer review. In 1971, however, Maddox took the bold decision to split Nature into three: Nature Physical Sciences was published on Monday, Nature New Biology on Wednesday and Nature on Friday. While this move clearly prefigures the more recent explosion in Nature-branded titles, it was not a success financially (the cost of a subscription remained the same as printing and postage costs soared), or editorially (being published in one of the “offcuts” felt like a demotion to authors), and the new titles were folded back into Nature at the end of 1973.

By that time, Maddox had been replaced by the geophysicist David Davies, who began to place greater emphasis on the use of external referees for papers that had survived scrutiny by Nature’s own editors. But in 1980 Davies decided he was ready for a new challenge, and, to many people’s surprise, Maddox returned. Baldwin focuses on two notorious incidents during this second term: the Benveniste affair and cold fusion. In 1988, in one of the more bizarre episodes of modern science, Maddox decided – against the advice of referees and his own staff – to publish a paper on homeopathic dilution by Jacques Benveniste and co-workers. He then led a team of investigators to Benveniste’s lab to watch the experiments being repeated. The team was unimpressed, the results were discredited (but never retracted) and Maddox emerged with his reputation somewhat tarnished. Baldwin argues (convincingly in my view) that his unorthodox behaviour was driven by his belief that Nature should follow Lockyer’s lead and take an active part in science.

His fingers burned by the Benveniste affair, Maddox was more cautious when cold fusion arrived the following year. Briefly, Nature rejected a paper by Martin Fleischmann and Stanley Pons, accepted a paper on muon-catalysed cold fusion that made more modest claims, and then proceeded to publish a series of articles that poured cold water on both. Active, yes, but also more orthodox.

Maddox stepped down in 1995, and under his successor Philip Campbell (previously editor of Physics World), both Nature and its parent company have continued to grow and prosper. This poses a challenge to the historian: if you are writing a history of an institution that is still going strong, when should the book end? Baldwin concludes with a disappointing chapter about current trends in publishing: Nature is at the centre of several important debates about scientific publishing, but Making Nature covers them fleetingly, if at all. Open access and the growth of Nature-branded journals are both mentioned, but it is odd not to discuss the degree to which Nature Publishing Group is staking its future on two open-access publications – Scientific Reports and Nature Communications (which now employs more manuscript editors than Nature itself) – while continuing to launch new subscription journals at an ever-increasing rate.

However, the biggest omission, I feel, is a failure to analyse the remarkable influence that Nature and two other journals – Cell and Science – exert on researchers in the life sciences and biomedical research. Many early-career researchers in these fields believe that they need a paper in one of these journals to stand a chance of getting a permanent position. This state of affairs is generally attributed to the high “impact factors” (a measure of how often papers are cited) of these journals, but Baldwin is silent on how Nature went from being ranked 109th by impact factor in 1975 to being “unquestionably top of the journal hierarchy, rivalled only by Science and Cell”. Part of the reason is that it now publishes considerably fewer papers per week than it did in 1975.

Given the focus of earlier chapters on the Benveniste affair and cold fusion, it also seems odd not to mention some of the high-profile scandals that have rocked science since then, and to overlook the “reproducibility crisis” that Nature has covered at length in its front half. The Benveniste affair would have been an ideal starting point for such a debate. There is more to be written about the history of Nature.

2015 University of Chicago Press £31.50/$45.00 hb 328pp

Physics in the family

Black-and-white photo of Sir Lawrence Bragg and his wife Lady Alice Bragg — **Tellers of tales** Lady Alice and Sir Lawrence Bragg were keen observers of science and society in the 20th century. (Courtesy: AIP Emilio Segre Visual Archives)

Recent years have seen a surge of material released on the lives and works of William Henry Bragg and William Lawrence Bragg, the father-and-son team who shared the 1915 Nobel Prize for Physics. Their prize, awarded “for their services in the analysis of crystal structure by means of X-rays”, recognized research that fundamentally changed the way we think about molecules and crystals, and laid the foundations for modern crystallography. This wonderful book – published in the centenary year of the Braggs’ Nobel prize – adds to this trend by giving us, for the first time, the family stories of Sir Lawrence Bragg (WLB) and his wife, Lady Alice Bragg, in their own words.

But Crystal Clear is far more than the autobiographies of the two main players. Rather, it tells the story of their lives – scientific, political, social and personal – in four quite distinct voices. The first voice is that of Mike Glazer, an emeritus professor of physics at the University of Oxford, who gives a brief but essential history of the scientific events behind the Braggs’ Nobel prize and a summary of WLB’s career in the book’s foreword. Glazer also relates the events that led to the present volume (the original material for which he edited “with the lightest of touches”) and adds succinct footnotes throughout. This material is essential to fully appreciate the story being told.

The ensuing chapters are personal recollections from WLB, Lady Alice and their younger daughter Patience Thomson. There is of course plenty of science, but at heart this is a love story, of the kind that encompasses so much more than just romance: it is also about family, ancestry, children, gardening, sketching, painting, sailing, bird-watching and (especially) holidays. We see the enduring, loving relationship between WLB and Lady Alice, and we develop a picture of the family as a very normal one confronted by abnormal events. The Braggs experienced the very pinnacle of scientific achievement and mixed socially and professionally with other scientists at the very top (as well as leading politicians and royalty), but they also endured two world wars and the loss of close family members and friends. And they were not immune to the enormous changes in society in the 20th century, especially for women.

Patience Thomson’s portion of the book, entitled Meet My Mother and Father, provides a personal perspective on her parents and siblings, including her thoughts about some incidents that are also mentioned in the autobiographies of WLB and Lady Alice. In addition, her account features some wonderful material not found elsewhere. Many quite surprising images are evoked in these passages, among them that of WLB mowing the lawn of a friend, Lady Thomson (the widow of J J Thomson, discoverer of the electron), using a mower “pulled by a pony wearing leather booties, so as not to make holes in the lawn”.

William Lawrence Bragg (In His Own Words) is more formal, and commences with the author’s birth in 1890 in Adelaide, South Australia, where his father (WHB) was professor of mathematics and experimental physics. It describes his childhood growing up in Adelaide, followed by the family’s return to England with his father’s appointment at the University of Leeds in 1909. Unsurprisingly, WLB’s account covers in considerable detail the important scientific phases of his career: the appointment at Manchester, the National Physical Laboratory and the Cavendish Chair at Cambridge. We are given insight into physical science in the first half of the 20th century as experienced by one of its pre-eminent practitioners, and WLB’s account is peppered with the names of many other famous scientists from physics, chemistry and crystallography. His part of the family story ends quite abruptly, however, in 1951; the heavy demands that followed his move to the Royal Institution in 1954 apparently left little time for WLB to finish his account.

WLB mentions surprisingly little of his family background, but his wife takes a different tack. In Alice Grace Jenny Bragg: “The Half Was Not Told”, she relates many stories about her parent’s ancestors, the Hopkinsons and the Cunliffe-Owens. Her childhood and schooling are described in detail, including some fascinating extracts from her mother’s diary. According to her daughter Patience, Lady Alice was deeply religious, and the title of her account seems to come from a Biblical verse (1 Kings 10:7); it was perhaps intended to mean “half the story has never been told”. But while she was a devoted member of the Anglican High Church, her husband was “a blue sky worshipper”: he stayed at home and worked in the garden on Sundays.

Lady Alice’s account includes many anecdotes and observations on her family, close friends and scientific colleagues of WLB. Some of these are rather quaint and even somewhat surprising: on meeting her future father-in-law, for example, she writes that “Sir William Bragg was a large man, beaming genially but rather silent. He made pleasing noises, a way of communication common to scientists, I was to discover.”

Several events recounted in these autobiographies remind us that we are now a century past the tragic events of the First World War. This conflict greatly affected the family: Alice’s brother, Eric Hopkinson, was killed in Belgium in June 1915; Robert Bragg, WLB’s brother, died at Gallipoli in September 1915; and Cecil Hopkinson, Alice’s cousin, was wounded on the western front in 1915, dying in England in 1917. The family was also affected by, and sometimes intimately involved in, the social changes that occurred in the first half of the 20th century, many of which provide a background to specific events and recollections. Alice had numerous public roles, including Mayor of Cambridge (her official title was “His Worship Mr Mayor”), and she served on the Royal Commission for Marriage and Divorce for four years. The changing expectations of mothers are conveyed with humour in the delightful essay “Learning from daughters”, written by Lady Alice in 1966.

Lady Alice’s account finishes with WLB’s death in 1971, which was preceded by “five happy years of retirement living in Suffolk, where we could garden and WLB could paint”. Both WHB and WLB were talented artists, and the book includes numerous beautiful sketches by WLB as well as two by WHB (regrettably reproduced too small to fully appreciate his fine attention to detail). In his foreword, Glazer notes that “Crystallography is by its nature both a highly mathematical and a visual subject,” and many of its practitioners would certainly share this view.

Although Alice survived her husband by 18 years, the final words of her account appear to have been written soon after his death, and movingly sum up their journey together: “After that there is no more to be told. I have the joy of children, grandchildren and all our friends… I look back with gratitude, knowing that I have had the greatest of human experiences, that of loving and being loved.”

2015 Oxford University Press £35.00hb 448pp

Algae ‘breaststroke’ is synchronized from within

Biophysicists have long wondered how swimming micro-organisms co-ordinate the motions of their arms – or flagella – as they propel themselves through water. Now, researchers at the Delft University of Technology in the Netherlands have shown that the single-cell alga Chlamydomonas reinhardtii synchronizes its two flagella via internal fibres within the cell, rather than via interactions with the surrounding fluid – as had been previously thought.

Many bacteria and algae, and other tiny cells, possess whip-like appendages called flagella, which they use to propel themselves. Similar, shorter-moving filaments, known as cilia, are also found on the surface of many cells, which perform functions such as moving fluids and other particles over the cell. Flagella and cilia tend to synchronize their beating motions with one another. This co-ordinated beating is often vital to the role of these filaments, but the physical mechanism behind the synchronization in not well understood.

Synchronized breaststroke

Most research on synchronization has focused on Chlamydomonas reinhardtii, a single-cell green alga that swims with two flagella that beat in opposite directions and perform a breaststroke-like motion. Previous studies have suggested that the synchronization is driven by hydrodynamic coupling in the liquid surrounding the cell. The idea is that the flow generated by one flagellum acts on the other flagellum and vice versa, causing them to move in synchronicity. However, these studies are far from conclusive, and there is also some evidence that other mechanisms are involved.

To study the extent to which flagella respond to hydrodynamic forces, Daniel Tam and colleagues held individual C. reinhardtii at the tip of a pipette inside a flow chamber. The team then sloshed fluid back and forth across the alga and recorded the motion of the flagella.

The researchers found that while the breaststroke-like movement of the flagella can be controlled by external flow, the hydrodynamic forces needed for synchronization are greater than those produced by the beating flagella. The flagella did synchronize with the external flow, but only if the forcing frequency of the flow was very close to the natural beating frequency of the flagella. The intrinsic beating frequencies – the rates at which single flagellum beat in isolation – of the flagella of C. reinhardtii individuals, however, differ from each other by as much as 30%. The researchers calculate that to generate hydrodynamic forces large enough to drive one another at such frequency differences, the flagella would need to produce flows 30 times the natural swimming speed of the algae.

Internal connection

From these observations, the team was able to conclude that synchronization is caused by fibres within the cell. “Chlamydomonas doesn’t react as strongly to flows as we would have expected,” Tam explains, which means it is “very likely that hydrodynamic interaction does not play a role in the synchronization”. He cautions that this does not rule out the idea that hydrodynamic flows drive synchronization in other micro-organisms.

As for how C. reinhardtii is able to perform the breaststrokes, Tam and colleagues suspect that synchronization occurs via a contractile fibre – the distal striated fibre – that connects the two flagella. This had been suggested previously but never tested. Tam and his team investigated the significance of this intracellular coupling using a mutant strain of C. reinhardtii that has defects in the contractile fibre – the vfl3 mutant. They found that the two flagella in mutant algae always beat in an asynchronous fashion.

The study is described in Physical Review Letters. In a review that accompanies the letter, Marco Polin of the University of Warwick in the UK and Idan Tuval of the Mediterranean Institute for Advanced Studies in Spain write that “The results, which the authors unfortunately only describe qualitatively, are clear: without the fibres, the flagella fail to synchronize. These experiments are promising, and unequivocally point to the importance of intracellular mechanical coupling.”

Raymond Goldstein and colleagues at the University of Cambridge in the UK have completed a comprehensive study of the nature of synchrony and the significance of intracellular connections in C. reinhardtii and other related organisms, with a preprint available on the arXiv server. Goldstein told physicsworld.com that they found “the vfl mutants can display synchrony if the flagella are close enough together – it varies how close they are cell by cell – exactly as you would expect from hydrodynamic coupling”, but this involves a different front-crawl-like swimming motion. This, he explains, “is evidence that the two processes, hydrodynamics and internal coupling, compete” to determine the form of flagella synchronization that is observed.

Welcome to Lightfest

Birmingham’s new central library resembles a fancy wedding cake, and a recent light-themed festival at the building certainly brought plenty of cheer. Lightfest was a celebration of light in science, art, technology and culture – held in connection with the International Year of Light and Light-based Technology (IYL 2015). This video captures some of the highlights of the event as various students and researchers give light-themed demonstrations to the public.

Lightfest was organized by Aston University and the choice of a public venue in central Birmingham, UK, enabled the event to reach out beyond the scientific community. “The basic idea is that researchers meet the public – particularly young people – and inspire people to take up science as a career, or to engage more with science,” says Paul Harris of the European Commission, which provided funding for the event. Among the demos featuring in this video are a “laser harp”, an “LED cube” and an experiment to show how different coloured gummy bears filter light in different ways.

“One of the most inspiring things about this year has been the way it’s brought together a uniquely wide variety of communities,” says Beth Taylor, chair of the IYL 2015 UK national committee, one of the speakers to officially open the event. If you want to find out more about the themes and goals of IYL 2015, take a look at this film we produced at the opening ceremony held in Paris back in January.

As an official media partner of IYL 2015, we have also commissioned a series of films that explore the impact of light and light-based technologies on people’s lives. Each film reflects the culture and geography of the country in which it was produced, telling captivating personal stories. You can view all of these films, along with articles about light, in this free-to-access digital collection, which you can read via your desktop or on your smartphone or tablet using our digital-magazine app.

Twin alien civilizations, the ancient genetics of cancer, and marvellous Maxwell and his wonderful equations

It’s raining life: could two nearby planets exchange living organisms? An artist’s impression of one planet in the Kepler 36 system as seen by its neighbour.
(Courtesy: Harvard-Smithsonian Center for Astrophysics/David Aguilar)

By Hamish Johnston and James Dacey

There is an intriguing article about alien life this week in The Conversation. “Twin civilizations? How life on an exoplanet could spread to its neighbour” is by David Rothery of the Open University and is a popular account of a paper that will soon be published in the Astrophysical Journal. The paper is inspired by the star Kepler 36, which has two planets that are in very close proximity to each other. While the Kepler 36 worlds are not suitable for life, the paper’s authors – Jason Steffen and Gongjie Li – explore possible exchanges of life between two Earth-like planets in similarly close orbits. Rothery explains that debris flung off one of the planets would stand a good chance of finding its way to the surface of the other planet after a relatively brief journey through space.

(more…)

Browse articles by content type

Physics World 2015 Focus on Astronomy and Space is out now

Throwing the book at bad ideas