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Flash Physics: Dark matter is smooth, UK boosts industrial physics, Pakistan honours Abdus Salam

Dark-matter distribution is smoother than previously thought

The distribution of dark matter in the universe appears to be smoother and more diffuse than previously thought – according to a study of wide-area images of the distant universe. Astronomers at the University of Edinburgh in the UK, Leiden University in the Netherlands, the Argelander Institute for Astronomy in Germany and the Swinburne University of Technology in Australia used the weak gravitational lensing of light from far-off galaxies to map the distribution of dark matter in intervening parts of the universe. The map is at odds with a prediction of dark-matter distribution that is based on the structure of the early universe based on measurements of the cosmic microwave background made by the Planck satellite. “Our findings will help to refine our theoretical model for how the universe has grown since its inception, improving our understanding of the modern-day universe,” says Hendrik Hildebrandt of the Argelander Institute. Edinburgh’s Catherine Heymans adds: “Unravelling what has happened since the Big Bang is a complex challenge, but by continuing to study the distant skies, we can build a picture of how our modern universe has evolved. The study is described in Monthly Notices of the Royal Astronomical Society.

UK provides £60m to boost industrial physics

The UK’s Engineering and Physical Sciences Research Council (EPSRC) has announced £60m for six new research hubs that aim to transform manufacturing in fields such as composite materials, 3D printing and medicine. The hubs, each receiving £10m, will draw together 17 universities and 200 industrial and academic partners to help turn research into products. The University of Huddersfield will lead a consortium to create a £30m Future Metrology Hub that will be based at the university’s Centre for Precision Technologies and will open next year. “Our vision is to develop new technologies and universal methods that will integrate measurement science with design and production processes to improve control, quality and productivity,” says physicist Jane Jiang, who will lead the Huddersfield hub. “These will become part of the critical infrastructure for a new generation of digital, high-value manufacturing, the so-called 4th industrial revolution, or Industry 4.0.” The other hubs are led by Cardiff University (semiconductors), the universities of Nottingham (composites), Sheffield (advanced powder processes), Strathclyde (advanced crystallisation) and University College London (targeted healthcare).

Pakistan renames physics centre after Abdus Salam

Photograph of Abdus Salam — Abdus Salam in 1987. (CC BY-SA 3.0/Bart Molendijk/Anefo)

Pakistan will rename a physics research centre in Islamabad after the Nobel laureate Abdus Salam, who died 20 years ago. Born in what is now Pakistan, Salam shared the 1979 Nobel Prize for Physics for his work on unifying the weak and electromagnetic interactions. However, he was never fully celebrated in his native country because he was a member of the Ahmadiyya community. Now, the prime minister Nawaz Sharif has announced that the National Centre for Physics at Quaid-i-Azam University in Islamabad will be called the Professor Abdus Salam Center fo Physics. There will also be five annual fellowships named after Salam, which will be awarded to Pakistani students pursuing PhDs in physics. In addition to his Nobel prize, Salam is remembered for founding the International Centre for Theoretical Physics in Trieste, Italy, in 1964. Now called the Abdus Salam International Centre for Theoretical Physics, the centre fosters the growth of mathematical physics in developing countries.

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Physics World’s shortlist for Book of the Year 2016

By Margaret Harris and Tushna Commissariat

The year 2016 has not covered itself in glory. Divisive elections, various natural and human-made disasters and a depressingly long obituary roll of well-loved celebrities mean that for many residents of planet Earth, this solar orbit has been one to forget.

But if, for a moment, we concentrate solely on the year in physics, the picture looks brighter. In particular, it’s been another strong year for popular-physics writing, and over the past few weeks, we have been determining which of the 57 books reviewed in Physics World in 2016 deserve to be on our list of the year’s best.

The books that appear on the shortlist below are all well written, novel and scientifically interesting to physicists – the criteria we’ve followed since 2009, when The Strangest Man, Graham Farmelo’s landmark biography of Paul Dirac, became our first “Book of the Year”. A couple of biographies appear on our 2016 shortlist, too, but they face stiff competition from books on big science, stringy science, loopy science, spooky science, jazzy science and more. There’s even a book of science infographics in the running – a first for a competition that is, naturally, dominated by words rather than images.

We’ll announce the winner of our “Book of the Year” award in the Physics World podcast in mid-December, but in the meantime, take a look at the shortlist. We think it’s proof, if you needed any, that the year 2016 had some redeeming features after all.

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Life as we do and don’t know it

Is there life beyond Earth? This fundamental and as yet unresolved question has long confronted humanity. With a limited understanding of the natural world around us for most of our history, this topic has been – and continues to be – a major theme in fiction. It is not only the likelihood of finding life beyond Earth, but also understanding the relationship between life and where it could emerge in the physical universe, that gave birth to the field of astrobiology. Thanks to huge advances in both technology and our understanding of the cosmos, the field of astrobiology has taken great strides in recent years. In Goldilocks and the Water Bears: the Search for Life in the Universe, author Louisa Preston traces the path of these developments in a beautiful narrative that is easy to comprehend while still being scientifically accurate.

The book opens with science fiction’s take on aliens, before going into the history of astronomy and the beginnings of astrobiology. From classic tales like HG Wells’ The War of the Worlds, to popular films that deal with everything from time travel to space invaders – such as Star Trek, Interstellar and E.T. the Extraterrestrial – Preston describes how extraterrestrial life is depicted in a range of English-language film, television and literature. The book then moves on to the basic science of what actually constitutes life, how one could define it and the fact that carbon is a basis for all Earth-based life forms.

In many ways, astrobiology transcends any single discipline – instead, it involves everything from cosmology to geobiology, making it a truly interdisciplinary endeavour. In order to understand the likelihood of life existing beyond Earth, we first need to understand the diversity of life on Earth, its evolution, and the physical conditions that allowed life to arise and thrive in the first place. The book talks about the importance of molecules such as DNA and RNA; the mechanisms and sources of energy that sustains life; the suitability of specific environments, and the importance of water including the liquid’s origins and even the possibility of life without water.

To truly fathom where life beyond Earth may exist, we also need to understand the prevalent planetary conditions within our solar system, as well as in an ever-increasing list of known exoplanets. The middle chapters of the book dig into the specific astronomical conditions that led to the development of terrestrial planets – such as heavy metallic elements – before focusing on planetary sciences. Preston – an astrobiologist and planetary geologist at the University of London – goes into the details of how exoplanets are detected using current techniques and looks towards the telescopes of the future. As the title of the book suggests, she also writes about habitable zones – from galaxy-wide Goldilocks “zones of metallicity” to smaller-scale habitable zones within a stellar system.

Star–planet interaction is one of the most researched subjects when it comes to habitability. Frequent news stories cite the discovery of new “habitable planets” and this popular topic of discussion has captured the attention of both the media and the public alike. However, most non-scientists do not know the criteria upon which habitability is determined. Although this topic is discussed at several places in the book, given the great amount of public interest, Preston could have gone into more detail on the topic. The book could have further educated the reader on how habitability is defined, explained how many factors such as the different types of stars, orbital radii and planetary atmospheres come into play and how a Goldilocks zone evolves with the evolution of the star itself.

Even though we have a fairly good understanding of how life evolved on our planet, our understanding of its origin is limited. Astrobiology has had much to gain from state-of-the-art telescopes and planetary probes, together with improvements in theoretical modelling. A growing area of research is to understand the physical underpinnings that drive life at the most fundamental level. A lot of work has been done on the link between life and the thermodynamic concept of entropy, and the computational “systems biology” approach to understanding life. These efforts are of tremendous interest in astrobiology, and as a physicist, I feel that these concepts should have been included too.

Preston does remind the reader that life can survive in surprisingly extreme conditions, before describing a variety of extremophiles, including the titular “water bears”, and discussing the known envelope of life. If I were to suggest reading just one chapter of the book, it would be chapter eight, titled “Extraterrestrial worlds: life not as we know it”. The section is thought-provoking and talks about possible life forms on other planets. The author describes how the physical, chemical and geological environment on our planet affected the evolution of life and relates it to other planetary conditions that we know of. She also talks about the production of possible biosignatures and how one could observe them with sophisticated telescopes as well as how to tell them apart from other non-biological mechanisms that could produce similar signatures or “false positives”. Preston also outlines how physiological characteristics such as bone density, skin tone and visual organs would vary wildly, even allowing for “sky whales” that could fly through alien clouds.

The breadth of expertise required to cover all aspects of astrobiology is very challenging and makes this a difficult book to write. Overall, despite some minor weaknesses, I enjoyed the book and would recommend it to high-schoolers and undergraduates as an introductory astrobiology book.

2016 Bloomsbury £16.99 288pp

Fermi: physicist with a capital F

Photo of the Via Panisperna boys: from left Oscar D’Agostino, Emilio Segre, Edoardo Amaldi, Franco Rasetti and Enrico Fermi — The Via Panisperna boys. From left: Oscar D’Agostino, Emilio Segrè, Edoardo Amaldi, Franco Rasetti and Enrico Fermi in 1934. (Courtesy: AIP Emilio Segrè Visual Archives, Segrè Collection)

Enrico Fermi – one of the great physicists of the 20th century – was a beacon for every Italian student of physics including myself. This sentiment is wonderfully captured in The Pope of Physics by Gino Segrè and Bettina Hoerlin, as they explain how Fermi’s colleagues bequeathed him with the title of “Pope”, thanks to his ability of using “the simplest of means [to] estimate the magnitude of any physical phenomena”. With their book, Segrè and Hoerlin present the first, long-awaited, English-language biography of one of the most creative and hard-working scientists of recent times.

Fermi is no stranger to both Segrè – a professor of physics and astronomy at the University of Pennsylvania, US – and his wife Hoerlin – teacher, health commissioner and author of Steps of Courage: My Parents’ Journey from Nazi Germany to America. That is because Segrè’s uncle was the Nobel-prize-winning physicist Emilio Segrè, who happened to be Fermi’s first student in Rome. The two families always maintained their friendship, even after they were forced to flee to the US in 1939 to escape Mussolini’s antisemitic regime – the Segrè family and Fermi’s wife, Laura, were Jewish. This long-standing relationship with relatives and close friends of the Fermi family helped Segrè and Hoerlin write about Fermi – who was once described by an Italian peer as a physicist with a capital F (the Italian for physicist being fisico).

The book opens with a depiction of Fermi’s early life, delving into his family roots and in particular, the deep bond he shared with his brother Giulio, who died prematurely. Written against the background of Italy in the early 1900s, these chapters leave the reader with a feeling of nostalgia for the “good old days”. The authors describe Fermi’s education and how his interest – or more aptly, his love – for physics blossomed, before going into Fermi’s time at the Sapienza University of Rome, where he spent his days nurturing his passion for hands-on work and his friendship with Franco Rasetti and Enrico Persico. This was the period during which Fermi began to immerse himself in the then new and revolutionary field of quantum physics.

The reader follows Fermi on his travels to Göttingen in Germany and Leiden in the Netherlands – where he spent a year interacting with some of the most famous scientists of the day, including Albert Einstein. The authors also talk about the exciting time during which Fermi worked with a group of talented young scientists – know colloquially as the Via Panisperna boys. Reading about these years, it becomes obvious that Fermi was a key driver in the advancement of quantum mechanics, from mathematical abstraction to experiment. His crucial contributions include helping build a clearer picture of the atom and explaining beta decay – the work that won him a Nobel prize in 1938 and provided the foundations for nuclear physics.

In parallel, the reader also learns about his personal story with his wife-to-be Laura, the not-so-warm relationship with his two children, along with the dangerous turn taken by politics in Italy. Fermi lived through a period of great changes due to the rise of Fascism, and the book reproduces the forboding atmosphere of the time quite remarkably. It describes how Fermi and his family did not return to Italy in 1938, after picking up the Nobel prize in Stockholm. The family’s story was similar to that of many other Jewish scientists at the time. Despite the fact that Fermi never took a public stand against Mussolini’s regime, he attempted to help his Jewish friends while preparing to leave for Columbia University in New York. The tension of those tumultuous times, which many of us have only heard of, is felt by the reader and it is a relief when the Fermis arrive safely in the US.

From here onwards, The Pope of Physics tells the story of the scientific discoveries leading up to the Manhattan Project. Although widely known, it is still surprising to read that the world’s first functioning nuclear pile was built under an abandoned football stadium. At the end of the war, the project was replaced by the Atomic Energy Commission and Fermi served on its influential general advisory committee – chaired by Robert Oppenheimer – while continuing his studies.

Although Fermi’s discoveries deeply advanced knowledge in many fields of physics – and made giant leaps for example in medical physics – his work formed the basis of one of the darkest creations of human knowledge: the atomic bomb. The book discusses this, and recounts how Fermi was among the first to warn military leaders about the potential negative impact of nuclear energy. Toward the end of his life, Fermi questioned his faith in society at large and its ability to make wise choices about nuclear technology.

The story ends with the last month of Fermi’s life – he died of stomach cancer at the age of 53. In the same rational way in which he looked at nature, he also looked at the end of his passage in this world. The final pages, describing his last conversations with friends and colleagues, are moving and show his great steadiness and dignity.

I thoroughly enjoyed this well-written book, which captures the lively life and times of Fermi. The book depicts what a truly a fascinating figure Fermi was, in an attention-grabbing manner. The reader enjoys a journey through the major physics discoveries of the time, which are placed in the proper historical context. Fermi’s achievements are covered in a way that is certainly satisfactory for a more scientifically inclined reader, but still comprehensible for a casual reader. If you’re interested in the history of science, and the story of someone who could be thought of as the most famous Italian scientist since Galileo Galilei, The Pope of Physics is the book for you.

2016 Henry Holt and Co $30.00hb 304pp

Robust structural colour is inspired by a tropical bird

A new way of producing structural colours – inspired by the nanoporous feathers of a brightly coloured South American bird – has been developed by researchers in the US, Switzerland and Saudi Arabia. The technique relies on a self-assembling, random network of sub-wavelength pores in a metallic alloy to produce a wide-range of colours. According to the researchers, their technique is more robust and easier to scale up for commercial fabrication, and could be used in a range of applications including lightweight coatings for cars and aircraft.

Animals use colours for a range of functions, from courtship displays to camouflage. While many of these colours are produced by pigments, others are produced by surface structures that interact with light and reflect specific wavelengths. Researchers have long been interested in such structural colouration because of its durability and many potential applications.

“Pigments fade away over relatively short times, while structural colouration can persist over time, as it is based on a structure,” explains Andrea Fratalocchi, an engineer at the King Abdullah University of Science and Technology in Saudi Arabia. “Beetle fossils from millions of years ago still preserve the colours.” He adds that as structural colours can be dynamically changed via structural alterations, they could be used for novel smart materials with adaptive camouflage properties. So far, the real-world applicability of surfaces engineered with photonic crystals or metamaterials to produce structural colours has been limited, however, due to issues with robustness, cost and scalability.

Vibrant feathers

Much of the structural colour in nature is also produced by photonic crystals or highly ordered arrays of nanofibres, but the plum-throated cotinga (Cotinga maynana), is different. The tropical bird’s vibrant blue feathers are produced by a disordered nanoporous network of keratin. The network of pores, which are typical smaller than 200 nm, interacts with light in such a way that only certain wavelengths of blue light are reflected.

To create a similar nanoporous network in a platinum–aluminium-based alloy, Fratalocchi and colleagues at ETH Zürich and Harvard University used a de-alloying process. They placed the alloy on a suitable substrate and then immersed it in a sodium-hydroxide solution. This removed most of the aluminium, leaving the platinum to form a porous network.

Lead researcher Henning Galinski, a physicist at ETH Zürich and Harvard University, told Physics World that the feathers and the porous metallic alloy share “the same design idea”, featuring sub-wavelength structures and being “achieved by self-assembly”. He adds, “The main difference is that the continga feather barbs are made of keratin.”

Yellow to blue

To control the colour produced, the porous alloy was coated with an ultra-thin, transparent layer of aluminium oxide. Without this covering, the material appears dark. But when the coating was added and increased in thickness, the colour changed, transitioning from yellow to orange, red and, finally, blue.

“Our networks seem disordered and random, but from a network perspective, they are pretty regular, meaning that each nanowire or strut in the network is, on average, connected to the same number of nanowires,” explains Galinski. “The connectivity can be controlled by changing the fabrication process. In this work, we decided to keep the connectivity constant and alter the interaction of light with the material by adding an ultra-thin ceramic layer.” He adds: “Increasing this layer step-wise from 7 nm to 53 nm, allowed us to enhance the coupling for a specific wavelength of light, resulting in the formation of vibrant structural colour.”

The researchers found that when light hits the surface of their material, it couples with surface plasmons – collective excitations of electrons – that then become trapped in the disordered surface. This creates regions where the electrical permittivity is near zero, separated by areas of high refractive index. The aluminium-oxide film changes these dynamics and increases the reflection of different wavelengths of light, depending on its thickness.

Simple chemistry

Galinski explains that because the technique is “based on simple wet-chemistry and coating technologies”, it can “produce robust colours on large spatial scales”. Fratalocchi adds: “Previous approaches focus on creating structural colours by assembling arrays of identical building blocks, or unit cells. This approach works only on very small scales, and is totally unsuitable for industrial and large-scale applications. Our material, conversely, is based on disorder, and at is totally scalable, opening this technology to real-world, commercial applications.”

Galinski says that structural colours have “wide potential as a future printing technology for various applications, ranging from bio-mimetic tissues to adaptive camouflage materials”. He adds that as the described technique is mechanically robust and extremely lightweight, it is “suitable for real-world industrial applications, such as automotive vehicles or airplanes, for which the weight is directly related to the fuel economy”.

The new material is described in Light: Science & Applications.

Flash Physics: Vibrots tumble and turn, string theorists bag Breakthrough Prize, microwave chip is a first

Vibrots tumble and turn

Vibrots are tiny devices that convert linear vibrations into rotational motion and are of great interest to scientists studying the collective motions of particles in physics, biology and chemistry. In this latest study, Christian Scholz, Sean D’Silva and Thorsten Pöschel of Friedrich-Alexander-Universität Erlangen-Nürnberg in Germany have created a vibrot that is powered by a vibrating floor – something that is common in the processing of granular materials, where collective motion can emerge. The cylindrical device is about 1 cm in diameter and is supported by seven legs, which are all bent at the same angle (see figure). The legs are springy and this causes the vibrot to rotate when subjected to vertical vibrations. In this latest work, Scholz and colleagues identified two distinct ways in which this motion occurs: “ratcheting” and “tumbling”. The ratcheting mode occurs at relatively low amplitudes of vibration. The legs of the vibrot move in synchrony as the floor vibrates up and down, with the device getting a rotational kick once every vibrational cycle – much like a ratchet. The tumbling mode occurs at higher vibrational amplitudes and does not involve the synchronous motion of the legs. In this mode, the legs tend to remain in the air for longer than one cycle of the vibration. Although the vibrot does rotate in tumbling mode, it does so in a very irregular manner with chaotic fluctuations. The research is described in New Journal of Physics.

String theorists bag 2017 Breakthrough Prize

The 2017 Breakthrough Prize in Fundamental Physics has been awarded to Joseph Polchinski of the University of California, Santa Barbara and Harvard University’s Andrew Strominger and Cumrun Vafa. The trio won for making “transformative advances in quantum field theory, string theory, and quantum gravity”. The three physicists share £3m in prize money. The Breakthrough Prize was inaugurated in 2012 by the Russian venture-capitalist Yuri Milner, who had studied theoretical physics. This is the third year that the prize has been awarded to string theorists. The award was presented yesterday at a gala ceremony at the NASA Ames Research Center in California, where celebrities such as actor Morgan Freeman rubbed shoulders with Breakthrough Prize funders including Facebook founder Mark Zuckerberg. A special prize was also given to LIGO founders Ronald Drever and Kip Thorne of Caltech and Rainer Weiss of the Massachusetts Institute of Technology. This prize was shared with more than 1000 physicists who worked on LIGO when it made the first-ever detection of a gravitational wave in 2015. Also awarded was the 2017 New Horizons in Physics Prize, which was given to five early career physicists.

Fully integrated microwave communications device is a first

Photograph of the integrated microwave chip — The integrated microwave chip, which measures 6 mm across. (Courtesy: Javier Fandiño *et al./Nature Photonics*)

The first photonic device for microwave signals with all of the necessary components fully integrated on a single chip has been produced by researchers in Spain. The design could have important implications for the next generation of wireless communication technology, where the increased requirements for data capacity will require the use of higher-frequency, multiplexed signals that traditional electronics cannot process effectively at the speeds required. Optical signal processing provides an obvious solution, but the cost of the components required has so far proved prohibitive to telecommunications applications. Researchers have attempted to bring down the costs, as well as the physical size and power requirements, by integrating more and more components onto single chips, although this has proved challenging. Now, José Capmany Francoy and colleagues at the Polytechnic University of Valencia have squeezed all of the components necessary for a microwave filter onto a single piece of indium phosphide – including a laser, a tunable optical filter and photodetectors. The optical filter is tuned by changing its temperature – which can be achieved by applying voltages to specific pins of the chip to power an internal heater. The device suffered severe problems: for example, the researchers had to measure the output optically because of interference when measuring the output as an electrical signal. Nevertheless, they believe technical design improvements and elimination of manufacturing imperfections should correct these problems, allowing the researchers to push on towards their goal of a fully integrated, programmable photonic microwave signal processor. The chip is described in Nature Photonics.

Zombie girls: a history

Radium-dial painters, mostly young working-class women, haunt the history of health physics. These young women with untreatable symptoms – whom the contemporary press and they themselves described as “the walking dead” – walk or more often hobble through Kate Moore’s book The Radium Girls. Their cases inspired the development of the field of radiation safety. The infamous photos of gross tumours overtaking the faces of pretty young women triggered a serious re-examination of the dangers of man-made radioactive isotopes in the 1920s, a time when merchants promoted radium as a miracle cure for whatever ails you. The case also led to the development of the first methods to detect radioactivity in living bodies. Indeed, the radium dial workers’ bodies became the raw material around which early health physicists created the notion of “permissible dose”.

Moore – a Sunday Times bestselling author – seeks to retrieve the life stories of the radium-dial painters in portraits of several dozen radium-dial workers who pursued lawsuits against watch companies in New Jersey and Illinois. In the 1910s and 1920s, the demand for glowing radium watch-faces grew yearly. Company managers advised their young female employees, paid by the piece, to work with paintbrushes, dipping the points in their mouth to sharpen them. Their counterpart painters in Germany used glass-pointed brushes that held their shape because scientists knew that radium was harmful. Moore shows that the US companies were aware that dipping brushes into one’s mouth was risky, but it was also the cheapest and fastest way to paint watch dials. As the desire for glow in the dark watches was insatiable during and after the First World War, the women painted and dipped all day long, rushing to keep up with the work.

The book makes for uncomfortable reading. Moore seeks to draw out the full effect of young lives painfully cut down in their prime. She swings between passages describing happy, pretty, dancing workers delighted to have cash in their pockets; to graphic details of the assault of radium accumulated in their bodies. The “girls” first started feeling aches and pains in their hips, knees and their jaws – their teeth wobbled painfully and when removed by dentists, the lesions did not heal. The young women developed anaemia, lost weight and felt chronically fatigued. As the ingested radium decayed, it broke down their bones into “honeycomb” configurations and ate into joints. Whole sections of the young women’s jaw bones gave way. Femurs snapped. Hip joints froze in place. Confused doctors treated the women, usually with casts and metal braces, measures that only increased their pain.

In the second half of The Radium Girls, Moore carefully replays the law suits against the Radium Dial Company in Ottawa, Illinois, and the US Radium Corporation in Orange, New Jersey. She shows the managers’ attempts to evade responsibility for damage, as they drew on a playbook of strategies deployed subsequently in the field of industrial hygiene. The radium-dial companies initially ignored their employees’ complaints of painful symptoms and the first early deaths. They claimed the women’s doses of radium were too low to cause problems, though male workers in labs and loading docks were provided leather aprons, gloves and a set of safety restrictions.

Glossing over the radium epidemic was easy. Until 1922 the industrial hygiene department at Harvard University was entirely funded by business, while regional public health offices bowed before the power of local industry. After several more young women died and many others became invalids, the rumours of the dangerous radium factories became a public-relations problem. When medical experts, hired by the companies themselves, ruled unexpectedly that radium poisoning could well be a factor, the reports were manipulated and hidden, and other more malleable specialists were found to vouch for radium’s supposed safety. As the lawsuits got under way, the companies courted public-health officials, lobbied for restricted workmen’s compensation laws, produced their own misleading public-health statements and did their best to sow confusion and stall legal rulings. As the years of court battles wore on, the plaintiffs increasingly had to turn over their bodies to use as evidence.

Moore spotlights Harrison Martland, the young and brash new chief medical examiner for Orange, New Jersey, who took the workers’ health complaints seriously. He collaborated to devise a way to ash the bones of a recently deceased radium worker and test the ash with an electrometer. These were the first measurements of radioactivity in the human body. Later, Martland came up with ways to count gamma rays coming from live patients and from radon in expired air from their lungs. Martland surmised that radium settling inside painters’ mouths produced bacteria that led to chronic infections and loss of teeth. He guessed that radium damaged blood-forming cells in bone marrow, leading to deadly anaemias. Radium, he reasoned, also settled in bones, made them brittle and produced sarcomas. He exhumed the body of a painter to make his point. The bone fragments, buried six years earlier, glowed in the dark grave.

At the time, toxicology demanded not just that statisticians show a significant increase in disease among radium-dial employees, but that the offending toxin be found in the bodies of the patients themselves. Martland’s measurements made a rare, lucid case in the history of what came to be known as “health physics”; radium known to be in the paint was also found in the workers’ bodies. Even with this clear-cut evidence, it took 14 years for the women to win their case in court.

Moore provides a happy ending for this story as she concludes that the “radium girls” drew attention to the dangers of the material, which spawned safe practices in the burgeoning Manhattan Project. She points to the Argonne Center for Human Radiobiology as a laboratory that promoted progress in radiation safety, with a “moral obligation to future generations”.

Unfortunately, I feel these are somewhat dubious claims. As the media attention about the dial-painters’ pain and death grew, scientists began to purposefully expose human subjects to man-made radioactive isotopes. Between 1931 and 1933, scientists at the Elgin State Hospital in Illinois injected half a dozen patients with 70 to 450 mg of radium-226. Later the Argonne lab located those patients, not to treat them, but to continue the experiment and measure retention of radium in their bodies. Scientists in the Manhattan Project began in 1943 to inject patients with the first micrograms of plutonium that they produced. In subsequent decades, the US Atomic Energy Commission funded hundreds of studies using human subjects exposed to internal and external radiation. Happy endings are nice, but I am not sure this sad tale deserves one.

2016 Simon and Schuster £16.99hb 320pp

Schrödinger’s Brexit, 'The Elements' remix, physics referees and American football

By Hamish Johnston

On Tuesday I was rushing to finish writing a news story about quantum superposition and got a phone call out of the blue from Roger Sawyer, who is deputy editor on BBC Radio 4’s afternoon news and current affairs programme PM. He had the brilliant idea that the meme of “having your Brexit cake and eating it too” had some sort of connection to quantum superposition – and wanted some advice from Physics World.

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Tiny device pumps out one electron at a time

Physicists should finally be able to rid themselves of the cumbersome and inaccurate definition of the ampere. That is the claim of metrologists in Germany, who have measured electrical current by counting single electrons travelling along a microscopic wire. The researchers say that their technique will allow scientists in a number of different disciplines to make better measurements of tiny currents.

The move to revamp the ampere is part of a more general overhaul of the SI system of units. It is envisaged that all seven base units – the ampere, second, metre, kilogram, kelvin, mole and candela – will be anchored to unvarying constants of nature. In particular, scientists are eager to redefine the kilogram, which is currently based on the mass of a specific lump of platinum-iridium sitting in a Paris safe and slowly shedding atoms.

It is partly to sever its link with the kilogram that metrologists are keen to redefine the unit of electrical current. At the moment, one ampere is defined as the current flowing in two narrow, infinitely long parallel conductors placed one metre apart in a vacuum that generate between them a force of 2 ×10^–7 N for every metre of length. This formulation is a problem because it means that the ampere is defined in terms of the kilogram (as well as the metre and the second) because force is equal to mass times acceleration. Also, nothing can be infinitely long, so this requirement must be approximated somehow.

Transistor-like device

This latest work was carried out by Frank Hohls and colleagues at the German National Metrology Institute (PTB) in Braunschweig and aims to define the ampere in terms of a certain (large) number of single electrons passing through a conducting channel in unit time. Central to the proposal is the construction of a “single-electron pump”, a transistor-like device that transmits just one electron when activated by a gate voltage. With the voltage oscillating perhaps several billion times a second, the device would generate a current that is large enough to calibrate an ammeter – thus revealing how accurate the instrument is.

The team made single-electron pumps from quantum dots – sub-micron sized conducting areas etched on to semiconductor substrates. Operating the pumps at millikelvin temperatures, they apply a roughly 0.5 GHz gate voltage and a second, fixed voltage across each dot to set up a time-varying potential well that briefly captures and then ejects single electrons. To establish the accuracy of their devices, the researchers use a specially developed amplifier that converts the current flowing through it into a voltage, which is measured by a voltmeter calibrated using two other quantum phenomena – the quantum Hall effect and the Josephson effect.

The researchers were able to measure the current transmitted by the pumps with an accuracy of 0.16 parts per million. This is fractionally better than they achieved with an earlier version of their device last year, which matched the accuracy of measurements that can be carried out using the existing force-based definition of the ampere – 0.2 parts per million. The new measurements were also done more quickly – requiring just 21 hours, rather than the several days employed a year ago. “The measurement set-up used in this experiment represents the state-of-the-art in small-current metrology,” says group member Hansjörg Scherer.

Aerosol counting

According to Scherer, who led the PTB effort to design the new amplifier, more accurate measurements made possible by the pumps could prove useful in a number of areas. Among them, he says, are the determination of radioactivity levels in ionization chambers and counting aerosol particles in the air.

Ian Mills, a metrology expert at the University of Reading in the UK, praises the “valuable and excellent work” being done on electron counting at the PTB. But he believes that a better definition of the ampere can be obtained simply by using the most accurate value for the electron charge available today – which is based on other measurements including that of the fine structure constant. That value of the ampere has an accuracy of about 20 parts in a billion and is, he says, most likely to be used in the new definition of the ampere that should be approved by the General Conference on Weights and Measures – the body that will authorize changes to the SI system. “I think the electron-counting experiments are fascinating,” he says, “but they are not yet sufficiently precise to compete.”

François Piquemal of the National Metrology and Testing Laboratory (LNE) in Paris, takes a slightly different view, arguing that electron counting offers a way of realizing the ampere in practice, rather than defining it. He maintains that single-electron pumps are best suited to measuring currents up to about a nanoamp, while an alternative approach – involving the combination of quantum Hall and Josephson standards through Ohm’s law – is best for larger currents. “In my opinion, these two methods are complementary for the future mise en pratique of the ampere,” he says.

The research is described in a paper that will be published in Metrologia.

Flash Physics: Earthquake puzzle solved, scientists write to Trump, nuclear pasta delays neutrinos

Earthquake-aftershock puzzle solved, say physicists

The idea that smaller earthquakes (aftershocks) follow major earthquakes is a well-established concept in geophysics. However, aftershocks are not explained by the avalanche model that is used to describe earthquakes and similar phenomena such as the cracking of solid materials. The model dictates that events such as earthquakes are random and therefore there should be no correlation between successive earthquakes. Now, Sanja Janićević, Lasse Laurson and colleagues at Aalto University in Finland have shown that this discrepancy could simply be a result of how aftershocks are measured. Writing in Physical Review Letters, the physicists describe experiments in which they monitored the cracking of a solid material. They found that when they set the detection threshold of their apparatus at high values – to avoid measuring noise – an individual avalanche event appeared as a sequence of seemingly unrelated events. However, when they reduced the detection threshold, what had previously appeared to be aftershocks were actually part of the main avalanche event.

Scientists post open letter to incoming Trump administration

More than 2300 scientists, including 22 Nobel laureates, have published an open letter calling on president-elect Donald Trump, his administration and Congress to “support and rely on science as a key input for crafting public policy”. The signatories, including the physics laureates Wolfgang Ketterle and Daniel Kleppner, say that federal agencies need to be led by officials with “demonstrated track records of respecting science as a critical component of decision making” and that the country’s public health and environmental laws must retain “a strong scientific foundation”. The letter also calls for the administration to “adhere to high standards of scientific integrity and independence in responding to current and emerging public-health and environmental threats”, as well as provide “adequate resources” to let scientists conduct their research. The letter remains open for signatures.

Nuclear pasta boosts supernova neutrino emission

Photograph of the SuperKamiokande detector — The SuperKamiokande detector could detect late-time neutrinos from galactic supernovae. (Courtesy: Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo)

The nuclear pasta that forms in supernovae should boost the numbers of late-time neutrinos emitted by the exploding stars – making it more likely that such events could be seen by neutrino detectors on Earth. Forming just before the core of a collapsing star reaches nuclear density, nuclear pasta comprises tubes, sheets and other pasta-like structures made from neutrons and protons. Charles Horowitz of Indiana University and colleagues used molecular-dynamics simulations to calculate how neutrinos produced in a supernovae scatter from nuclear pasta, and found that the pasta greatly increases the number of neutrinos emitted 10 or more seconds after core collapse occurs. Writing in an arXiv preprint, the team says that late-time neutrinos from a supernova in the Milky Way should be clearly visible to neutrino detectors such as SuperKamiokande in Japan. Detecting these neutrinos could provide important information about how stars collapse to form supernovae.

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