This proved to be one of our most popular polls yet, with 214 responses. Of these, a narrow majority (55%) said that yes, they considered themselves physicists, while 15% chose “no” and 30% agreed that for them, “it’s complicated”.
A number of people were kind enough to explain their responses in the poll’s comments section. We really appreciate this, because it tells us a lot more than the raw numbers can. For example, judging from the comments, there seems to be some difference of opinion over the question of what makes a physicist a physicist.
For some, it’s primarily down to training or education. “I feel that I really can’t call myself a physicist because I don’t have anything hanging on the wall saying ‘Tom Sullivan is hereby granted and honoured as a physicist’, “ wrote, er, Tom Sullivan, who answered “it’s complicated”. Another who mentioned training was Kate Oliver, a science writer who regularly contributes to Physics World’s “Lateral Thoughts” humour column. “I like to consider myself a physicist as I have the relevant training, read about it and think like it,” she wrote, explaining her “yes” vote. However, she added, “since I haven’t been in the lab for three years, my ‘physicistique’ may have expired”.
The idea that physicist-hood might carry an expiry date suggests an alternative definition – one that focuses not on who you are or what you know, but on what you do. (The philosopher Jean-Paul Sartre, who believed that “to do is to be”, would love this definition.) Like Oliver, Bruce Etherington is a science communicator with a physics degree, but he answered “it’s complicated” because “Most practising physicists would probably not consider me to be one.” Another in the “it’s complicated” camp, Steve Douglas, wrote “I think to be a physicist you’ve got to specialize in it, rather than just be pretty good at it.”
At physicsworld.com, we tend towards a pretty broad definition of physicist – one that encompasses, at minimum, those who have studied physics at degree level (or higher) and who remain interested in learning about it.
But since these Facebook polls are about your views, not ours, we’ll leave the last word to Michael Eliachevitch, a soon-to-be physics student who wrote that “being a physicist means [being] part of a large adventure to discover the world we are living in”. Good luck on your adventure, Michael!
Where does space begin? The answer to this question is a little arbitrary because the Earth’s atmosphere does not abruptly end. In practice, the recognized start of space lies at an altitude of 100 km, known as the Kármán line, which is where the atmosphere becomes too thin to obtain sufficient lift for aeronautical purposes. The atmosphere at this altitude is still enough to create a significant drag on a satellite, which is why satellites must usually fly at some 250–300 km above the Earth’s surface.
At this altitude, the level of vacuum – about 10–6 mbar – means that the thermal performance of a satellite is dominated by radiative transfer rather than convective transfer, as on the ground. This fact, combined with the complexity and cost of servicing an orbiting satellite, means that anything sent into space has to be rigorously tested in a simulated space atmosphere using a “thermal vacuum test chamber”.
Fixed ultrahigh-vacuum systems used in particle accelerators and other similar systems can be baked at high temperatures to drive off adsorbed water vapour and contaminants from chamber walls and test equipment. This is not possible with space-borne equipment because of the materials used and the highly sensitive nature of some of the components. A typical bake-out of a complete spacecraft is instead usually limited to temperatures of 50–60 °C, which results in the out-gassing load still being very high during testing.
What this means in practice is that high-capacity pumping systems have to be used to reach and maintain the required vacuum levels. Typically, a vacuum level of between 10–7 and 10–5 mbar is needed in a test chamber that may vary in size between that required for a relatively small “cubesat” (measuring 10 × 10 × 10 cm) and one needed to test a large satellite the size of a bus.
For smaller systems, a turbo pump is sufficient to overcome the outgassing load from the chamber and test item, with oil-free systems being used to minimize the contamination risk. For larger systems a combination of turbo pumps, 20 K cryo-pumps and 4 K helium cryo-panels are used to achieve the typical pumping requirement of 500,000 l s–1. Cryo-systems are preferred because they are relatively cheap and are good at pumping water and nitrogen (which are dominant in the chamber at that operating pressure) at high speeds.
Care has to be taken in preparing both the test item and the test chamber itself to ensure that both are clean from a molecular and particulate point of view. For optical instruments, molecular contaminants degrade the overall instrument sensitivity, which is exacerbated at individual wavelengths by specific absorption of particular materials, such as silicones. Particulate contamination contributes to a scattered background, which reduces image contrast and can reduce the life and stability of mechanisms in the optical chain.
Identifying the presence of particulate contamination is relatively easy as clean-rooms can be used to assemble the instruments, with regular inspections helping to maintain cleanliness to the required standard. Preventing and identifying molecular contamination, however, is not so simple. Using known low-outgassing materials as well as proven cleaning and assembly techniques provides a good starting point, but with most items, a bake-out at the maximum temperature of a subsystem is required – as is proof of the outgassing level obtained under common predefined conditions – before the subsystem can be integrated into the spacecraft. Invaluable tools for this work are a residual gas analyser to identify the nature of contaminants and a thermoelectric quartz crystal microbalance to measure the absolute rate of outgassing.
Another key part of the on-ground testing is to simulate the expected thermal conditions the satellite may encounter. This is usually done using a combination of local radiator panels, with a temperature-controlled shroud providing a representative global view. This allows the test item to be driven in a representative way between its expected operating temperatures. During this thermal cycling, functional and optical testing is performed to test and calibrate the onboard systems and ensure all the scientific requirements are met. For a small instrument, this may take just a few days, while a larger calibration campaign may take months of testing. The work may be painstaking, but it is essential to a mission’s success.
If you are having trouble with your heart or struggling to communicate because of a debilitating disease, a new hi-tech tattoo could soon offer help. That’s the claim of an international team of researchers that has created tattoo-like devices that can monitor heart beats, brain waves and muscle contractions.
The devices stick to skin without adhesives and move naturally with the body. The team has also integrated electrical and temperature sensors, transmitting antennas, receivers, power sources, lights and the gamut of basic circuit elements into the tattoos.
The conventional way of monitoring electrical signals given off by the heart and other organs involves electrodes smeared with conductive gel and held on with tape. However, such devices restrict the patient’s movement and normal readings are difficult to attain because the wearer is likely to be affected by presence of an electrode.
“If you want something that can be worn without irritation, with robust adhesion that doesn’t create any discomfort, you want it to match the mechanical properties and deformability of the skin,” explains John Rogers of the University of Illinois, Urbana-Champaign, who leads the research. With this goal in mind, the team came up with a circuit design that allows a semiconductor device to stretch and contract with human skin.
Semiconductor squiggles
While commercial semiconductors such as silicon and gallium arsenide make effective circuits, they are also are stiff and brittle. To make them flex and stretch, the team shaped them into extremely thin squiggles. “We take a silicon wafer that is half a millimetre thick and slice very, very thin membranes,” Rogers tells physicsworld.com. This reduces the silicon to a thickness of 50 or 100 nm, which is enough to allow it to flex. To allow the silicon to stretch, the researchers then etched the material into serpentine shapes.
“The metal interconnect wiring, the contact pads, the resistors – pretty much everything, I think, can be fashioned into these shapes,” says Rogers. The squiggly components are assembled onto a sheet of polyamide and then the circuit is transferred to a breathable elastic sheet of modified polyester that is just 30 µm thick. The completed device attaches to skin much like a temporary tattoo, clinging by Van der Waals interactions between the polyester sheet and skin, without the need for adhesive.
Karen Cheung, a specialist in bio-micro-electromechanical systems at the University of British Columbia who was not involved in the work, says the system “represents a huge improvement over current non-invasive electrodes”.
Controlling a computer game
University of Illinois researchers Dae-Hyeong Kim, Nanshu Lu and Rui Ma placed tattoos on their foreheads, chests, legs and throats to test the abilities of these sensors in reading brain waves, heart beats, muscle contractions from walking and activity in the throat when speaking. In the speech trial, the sensor could differentiate between the spoken words “up”, “down”, “left” and “right”, allowing Ma to control a strategy computer game called Sokoban.
“One can imagine using this technology to make huge improvements in assistive technology for patients of spinal-cord injury or neurodegenerative disease, such as amyotrophic lateral sclerosis,” says Cheung. She believes that these electronic tattoos could be worn comfortably for long periods of time, helping patients to “regain independence and quality of life”.
While wires were used to power and receive signals from the tattoos, the team also integrated power sources and transmitter antennas on other systems. However, what Rogers calls the “ultimate” device, combining sensors with a power source and a wireless data system, has yet to be made.
Tiny photovoltaic cells and induction coils, which convert an external alternating electric field into a current, were both tested as power sources. Rogers says that the induction coils are best for temporary uses, while photovoltaics need a storage device if they are to provide a reliable, long-term power supply. But batteries would increase the weight of the device, so the researchers have also suggested scavenging energy from the motion of the wearer.
We had so many responses to last week’s Facebook poll – which asked “Do you consider yourself a physicist?” – that we’re giving everyone a few more hours to respond before we blog about the results. So if you haven’t yet answered yes, no or it’s complicated, there’s still time to do so via our Facebook page.
In the meantime, I’d like to conclude this round of career-related polls with a somewhat less metaphysical question:
If you have a degree in physics, which option best describes what you do for a living?
We’re interested in sectors here, not specific job titles, so to get you started, we’ve listed five options – engineering, finance, IT, research and teaching – that more rigorous surveys suggest are popular among physics graduates. However, if you don’t fit in any of these boxes, you’re more than welcome to add your own category (legal? medicine/health? communications?).
Speaking of being rigorous, we at physicsworld.com are well aware that Facebook polls aren’t. However, that does not mean they’re useless, or even “just a bit of fun”. We’re interested in hearing from you and we take your opinions seriously – they help us keep in touch with what individual members of the physics community think and care about. So treat these polls like the office water cooler, departmental common room or anywhere else that people gather to share their views – and if you want proper statistics on physics education and research, try the Institute of Physics’ policy department instead.
The latest video report from our globe-trotting multimedia team offers an “up close and personal” take from the bleeding edge of the Earth sciences, as told to us by faculty and graduate students in the geosciences department at the University of Texas at Dallas (UT Dallas).
Filmed in the spring as an add-on to our coverage of the American Physical Society March Meeting in Dallas, the interviews cover a lot of ground – to be expected for a discipline that aims to unlock the secrets of the solar system’s most active planet.
Carlos Aiken and colleagues, for example, are using an approach called cybermapping (which integrates laser scanning, digital photography and satellite positioning, among other sensors) to build 3D photorealistic models of surface geology around the world. Their work is being applied in oil exploration and education (for virtual field trips).
Meanwhile, fellow researcher John Ferguson is applying a technique called 4D microgravity – essentially ultraprecise gravitational measurements, a few parts per billion of the Earth’s gravitational field – to monitor the success (or otherwise) of CO2 sequestration in underground reservoirs.
Another important strand of the UT Dallas geosciences programme is the use of remote sensing (specifically, space geodetic satellite observation) to understand changes in Earth systems over time. “There’s much more to it [remote sensing] than pretty pictures,” explains Alexander Braun.
“You can actually measure real physical parameters – such as the [Earth’s] gravity field or magnetic field – and, more importantly, you can detect surface deformation. The Earth is a very active planet and it is crucial for us to understand when and where it is moving.”
In the second video (below), senior scientists in the UT Dallas geosciences programme explain what attracted them to a career in the Earth sciences. It seems if you like to travel and have a hankering for the outdoors then Earth sciences could be just the ticket.
Or, as Bob Stern puts it, “It’s really a remarkable opportunity to get out and see things that no-one else gets to see – that you would never see as a tourist.”
John Ellis is a busy man. When he is not clocking up air miles almost every week travelling between London and the CERN particle-physics lab near Geneva, then a string of appointments and meetings leave him just as hard to get hold of. Indeed, after waiting 40 minutes at his office before finally getting the chance to start our interview (Ellis had just flown in from Switzerland and had immediately gone into another meeting), our time together abruptly ran out as yet a further appointment loomed. A follow-up phone call was arranged with the caveat that “if I do not reply the first time, please try again – I am a bit in-and-out”.
The meetings and travel reflect a hectic time for Ellis. After turning 65 last month, the UK-born theorist had to relinquish a full-time position at CERN (although he still keeps his office at the lab and has a “guest professor” position). But instead of putting his feet up and “watching Doctor Who all day”, Ellis accepted a post at King’s College London that allows him to carry on doing his own research, as well as building up a group and mentoring students.
Ellis’s self-proclaimed “period of transition” comes at a time of high excitement at CERN as it ramps up the Large Hadron Collider (LHC) in its search for physics beyond the Standard Model. Ellis has worked at CERN for nearly 38 years, and has been part of the LHC from its very first days in 1984, when he was involved with imagining what potential science the LHC could do. With the LHC now about to possibly show the first signs of those predictions, he is very much looking forward to the coming year. “At the moment, it’s going gangbusters,” says Ellis. “This year the LHC is going to explore virgin territory. Whether there are any virgins in the territory, however, is an altogether different question.”
Of course, it was not always going gangbusters at CERN. In September 2008, just nine days after protons were circulated in both directions at the LHC, an electrical connection between a dipole magnet and a neighbouring quadrupole magnet failed, causing two tonnes of helium to be released with such force that some magnets broke their anchors to the concrete floor.
After CERN spent more than a year fixing the damage, the LHC is finally back on track, although it will close by the end of 2012 for another 18 months of repairs and upgrades. Ellis is frank about the failings, however. “Clearly, the blowout was a failure at a technical and management level,” he says. “I do wonder if we could have avoided it if we had been slower and more systematic in commissioning and testing the LHC – maybe there was too much of a hurry to get it into operation.”
Ellis admits there was a particular pressure to get the LHC ready before the end of the five-year term of then CERN director-general Robert Aymar in 2008. “I am not suggesting he was responsible for cracking the whip, but everyone saw [the end of his tenure] as a natural milestone to get the LHC into operation,” he says. However, with the failure now behind them and the machine breaking records every day, Ellis heaps on praise for the way the CERN management, in particular former LHC project leader Lyn Evans and the current director of accelerators Steve Myers, got the machine back up and running. “It now looks like an excellent machine and has taken more data to date than had been promised for the whole of this year,” he says.
Needle in 100,000 haystacks
One of the most high-profile areas of research at the LHC is the search for the Higgs boson and in the 1970s Ellis was instrumental in putting it on the experimental agenda and proposing a way that it could be spotted by the LHC’s predecessor – the Large Electron–Positron Collider (LEP) – by the particle radiating a Z-boson. In the end, despite possible last-minute hints, LEP could only put a lower limit on the mass of the Standard Model Higgs boson at 114.4 GeV/c2 with a 95% confidence level.
Ellis dubs the Higgs boson a “known unknown” but nevertheless compares the difficulty experimentalists have in looking for the Higgs to searching for a needle in a “hundred thousand haystacks”, in which the needle is made not from metal but from hay itself. So how do you know if you have found significant pieces of hay? “The answer is that you spot a lot of pieces of hay with the same properties, say all with an energy of 117 GeV,” says Ellis. “Then you can say you have something meaningful.”
Ellis adds that when it comes to discovering the Higgs boson, it is not going to be a clear-cut event “jumping out of the screen at you” but rather that there will be many alternative explanations that need to be taken into account. Indeed, that was evident in early April when an internal note from members of the ATLAS collaboration claiming evidence of the Higgs boson was leaked to a popular physics blog, sparking media coverage around the world. The result was later quashed when follow-up studies by the ATLAS collaboration found no confirmation of such a signal. “The ATLAS internal document should not have got outside,” concedes Ellis. “But it’s impossible these days to suppress information, as Ryan Giggs knows all too well,” he says, referring to the Manchester United star’s failed attempt to stop revelations about his private life being made public. Ellis says that there will be many more such leaks about the Higgs in the future, and probably about other potential discoveries too, including supersymmetric particles, dark matter and even extra dimensions.
Currently, the Tevatron collider at Fermilab in the US is also closing in on the search for the Higgs boson, having released limits extending beyond what LEP was able to achieve. Yet Fermilab’s search is likely to be curtailed before it has really got going, with the imminent closure of the Tevatron in October to make way for experiments in neutrino and muon physics. Ellis admits that if a Fermilab hint of a Higgs were to be confirmed at CERN, then Fermilab researchers “would have every right to be pissed off”. However, Ellis admits that he would be “happy” even if the LHC failed to spot the Higgs at all. “If it was proved that there is no Higgs boson, that would be much more exciting,” he says. “It would mean that all the ideas we have been working with for 47 years are garbage and that gives the new generation of young at heart physicists the opportunity to come up with something better.”
Europe bound
Ellis was born in Hampstead, London, in 1946. After studying physics and mathematics at A-level, he went to the University of Cambridge in 1968 to take the mathematical tripos and stayed there to do a PhD in theoretical physics – on the applications of group theory. “I was interested in symmetry and group theory, and not so much interested in doing theory for theory’s sake,” he recalls. “I think it is key to be able to test things experimentally rather than just doing abstract stuff.”
Ellis first went to CERN in 1968 during his undergraduate degree to attend a summer school, but it was during his final year as a PhD student, in 1970, that he got a real taste of the environment at CERN. Ellis was only meant to work at CERN’s theory division for a few months but, with the support of his PhD supervisor Bruno Renner, he instead stayed for his whole final year. “I really enjoyed the international atmosphere at CERN, meeting people with different backgrounds, not to mention the Spanish girls,” he recalls.
After two one-year postdocs at the Stanford Linear Accelerator Center (as it was then known) and at the California Institute of Technology, Ellis returned to CERN in 1973 wanting “in some naive way, to help build up European and British physics”. It was during his early days at CERN that Ellis made perhaps his most important breakthrough, when he worked out a way to test for gluons – uncharged particles that carry the strong nuclear force through which quarks interact with each other.
In the early 1970s theorists were convinced that the gluon must exist, but there was only indirect evidence of it in proton-proton collisions. Together with Graham Ross and Mary Gaillard, Ellis proposed testing for the gluon via the collision of an electron and positron that would produce a quark and antiquark pair. In additional to producing normal two-jet events, one of those quarks could then radiate a gluon, which could be seen via a third jet of hadrons shooting out in another direction.
Two particle-collider projects were being constructed at that time – the Positron-Electron Tandem Ring Accelerator at the DESY lab in Hamburg and the Positron Electron Project at SLAC – that would have sufficient energy to observe clear-cut three-jet events. Ellis pestered experimentalists at DESY to begin searching for signs of the gluon, and when they did, in the middle of 1979, they discovered it.
Following Ellis’s breakthrough, the US tried to poach him again in 1978 when SLAC offered him a tenured position. The bait was tempting and Ellis went on a five-month sabbatical only to return to Europe and take up a tenured position at CERN instead. “I didn’t expect I would have a long career at CERN,” says Ellis. “I am not one of those guys who has a checklist of career objectives. I felt that CERN had great potential for the future and exciting projects, so I thought I would like to stay.”
Ellis went on to become leader of CERN’s famed theory division from 1988 to 1994. During his tenure the division grew significantly as a result of creating a formal programme for PhD students as well as providing opportunities for scientists from developing countries to get CERN fellowships. Ellis regrets that in 2003 the theory division lost some of its official status when it was absorbed within the “very large” physics division. “I think the status of the theory division has gone down over the years – back in the 1970s it had a higher profile than it does today,” says Ellis.
Planning the next big thing
Piled higher and deeper
As well as enjoying the hunt for new particles at CERN, Ellis is also looking to the future, much as he did when he took part in the 1984 design review of the LHC, when the collider was still a mere glint in a physicist’s eye. He is, for example, heavily involved in the design of the next-generation Compact Linear Collider (CLIC), most of the R&D design for which is being carried out at CERN, with the CLIC team expected to release a conceptual design study later this year. CLIC, which could measure precisely any of the new particles that the LHC might discover, is, however, up against a competing plan called the International Linear Collider (ILC). Both will collide electrons with positrons but, while the ILC will use superconducting technology to collide particles with energies of around 500 GeV, CLIC will collide particles at 1 TeV or more using a novel “two-beam acceleration technique”.
Ellis admits that, because of the likely shortage of future funding, only one of these competing designs will actually be built. “The driver is physics, when the known unknowns become known knowns, we will then know how much energy we need to explore what the LHC discovers,” says Ellis. “Eventually, a choice must be made between the different technologies, but until the LHC reveals new physics there is no rush to decide which one to choose.”
In person
Born: London, 1946 Education: BSc and PhD University of Cambridge (1964–1971) Career: SLAC (1971–1972), California Institute of Technology (1972–1973), CERN (1973–present), King’s College London (2010–present) Hobbies: visiting archaeological sites and reading about ancient history, listening to music from Purcell to the Prodigy Family: married, one daughter, one son
Readers who want an immediate explanation for the title of The Madame Curie Complex – perhaps while waiting for their own copy of this splendid book to arrive in the post – should visit the webcomic xkcd. A recent edition of the comic, entitled “Marie Curie”, features a zombie version of Curie (earlier comic strips have starred a zombie Richard Feynman) giving advice to a young woman who aspires to scientific greatness. After reminding the youngster that she was not the only great woman physicist, the zombie Curie explains that trying to emulate scientific idols is a bad idea. “You don’t become great by trying to be great,” she observes. “You become great by wanting to do something, and then doing it so hard that you become great in the process.”
In her introduction to The Madame Curie Complex, author Julie Des Jardins notes that the myth of Curie cuts both ways: in her words, women have been both “empowered and stigmatized” by her example. Certainly, Curie has been an inspiration around the world. One case that I refer to in my own teaching is the Egyptian physicist Karimat El-Sayed, a groundbreaking researcher and advocate for the education of women in the Arab world. When asked about Curie in a 2003 interview with the Cairo weekly newspaper Al-Ahram, El-Sayed observed that this foreign woman – who discovered radium and became the first scientist to win two Nobel prizes – had “changed [her] life.”
For others, however, Curie’s status as an outstanding example has a negative effect. In particular, Des Jardins highlights the work of science historian Margaret Rossiter, who observed that Curie’s successes were of such unattainable, mythical stature that they allowed “men to disqualify women – and women to disqualify themselves – from science”.
Much publicity attended Curie’s two American tours, which took place in the 1920s and were the brainchild of an American magazine editor. The tours succeeded both in raising money for research and spreading awareness of Curie’s stature. However, the overblown publicity machine surrounding the tours also spun her as a maternal saint and humanitarian martyr. This image is patently false – Curie was simply a brilliant, dedicated scientist, and the humanitarian results of her work were a welcome by-product rather than her main goal. The image is also insidious because it turned her into an icon that real scientists who wish to be productive should not try to emulate.
Des Jardins is a historian at Baruch College, New York, and like all good historians, she not only delivers solid facts, but also provides an analysis that weaves these facts into a coherent story. She chooses to examine three periods of US science: the birth of science as a profession in the late 19th century, the mid-20th century “heroic age” and the late 20th century, coinciding with the rise of second-wave feminism (the first wave having encompassed, among other things, the campaign for women’s right to vote). In each period, she examines in great depth the lives and careers of a number of women – beginning, of course, with Marie Curie and those American tours.
Des Jardins provides excellent introductions to each section, preparing readers for the historical insights that emerge from the ensuing biographical chapters. The first section, “Assistants, Housekeepers, …” gives us a snapshot of women’s scientific participation and education up through the late 19th century, showing how education led to narrow career paths that permitted women to engage in science only in highly selective ways – separate, yet unequal. Some women from this era, including Curie and the industrial engineer Lillian Gilbreth, would prove exceptions to this rule; intriguingly, both were widowed early in life from men who were their partners in science as well as marriage. Other women profiled in the chapter include Wilhelmina Fleming, Annie Jump Cannon and other women associated with Harvard’s observatory. Their life and work trajectories – though diverse – illustrate the limits placed on women during this period.
The book’s second section (“The Cult of Masculinity”) describes the mid-20th-century tendency to consider women who did “empirically objective work” as mere technicians, never fully fledged scientists in the heroic mould of an Einstein or a Fermi. This was possible in part because theory was considered more exalted than experiment. Des Jardins also fleshes out the prototypical scientist of the time by citing Anne Roe’s 1953 psychological study of 64 elite scientists: all male, they tended to be loners and oldest children, and, if married, they were often more excited by their work than by their wives.
The final section (“American Women and Science in Transition”) introduces us to a time when intellectuals like Rachel Carson, Thomas Kuhn and Evelyn Fox Keller were producing work that “question(ed) the very foundations upon which scientific progress had been measured”. Des Jardins traces relevant threads of social history from this era, including the publication of Betty Friedan’s The Feminine Mystique and the passage of the 1964 Civil Rights Act, followed by Title IX of the Educational Amendments of 1972, which prohibited sex-based exclusion or discrimination in educational programmes or activities funded by the Federal government.
This period also saw the founding of various societies to support women within established scientific organizations. The American Physical Society’s Committee on the Status of Women in Physics, for example, was founded in 1971. (The Institute of Physics, which publishes Physics World, set up its first Women in Physics committee in 1985.) Feminist philosophers of science such as Sandra Harding began to trace the problem of women in science to the androcentric, racist and classist underpinnings of science itself. At the same time, the nature/nurture debate re-emerged in full swing. It remains alive and well to this day, as does the Madame Curie Complex.
A question that frequently crops up in feminist science studies is whether there is even such a beast as “feminist science” – in other words, scientific work done in accord with the principles of feminism, regardless of whether feminist ideology consciously drives the practitioner. It is difficult to make the case that such a thing exists in physics, but Des Jardins offers a clear example from the field of primatology. In chapter 7 she lays out an astute study of the lives and work of Jane Goodall (who studied chimpanzees), Dian Fossey (gorillas) and Birute Galdikas (orangutans), whose revolutionary methods and findings bucked the prevailing wisdom of their previously male-dominated field.
All three women were recruited and nurtured by Louis Leakey, who was convinced that women were more patient and that they “read social cues and observed the nature around them differently from men”. Like Curie before them, Goodall, Fossey and Galdikas were represented in the popular media in ways that reinforced sexist stereotypes (for example, as a heroic madwoman or a mother to all living things). But again like Curie, the portrayal of their achievements also “inverted assumptions about women and western science”.
As a physicist, I found chapter 4, “Those science made invisible: finding the women in the Manhattan Project”, particularly fascinating. Many of the women at Los Alamos were non-scientist wives who were whisked away with their husbands to a bizarre enclave of babies and barbed wire, where secrecy and domesticity merged. But there were also women workers: roughly 10% of the workforce at the plutonium facility in Hanford, Washington, was female and the figure at Los Alamos was even higher.
These workers ranged from dining hall staff to technicians, chemists and physicists like Leona Libby – a scientific peer of the men who disguised her pregnancy under baggy overalls. Yet postwar essays and biographies by participants, including Laura Fermi, display what Des Jardins calls “cultural amnesia”, seeing only the men as true contributors. Scientists like Teller were “kings” and there were no corresponding “queens”. In the 1990s, when the physicists Ruth Howes and Caroline Herzenberg attempted to isolate and evaluate women’s contributions to the wartime project, they found it a difficult task. As they described in their book Their Day in the Sun: Women of the Manhattan Project (Temple University Press, 1999), information about what these women did was frequently absent from both oral memories and the written record.
This invisibility is a theme that pervades the book, and is encapsulated in its subtitle “The Hidden History of Women in Science”. Much of the invisibility of historical women lies in the narrow definition of what constitutes a “significant” contribution. If this definition is broadened such that it is sensitive to what women were encouraged or permitted to do by the culture in which they lived, scientific women emerge from historical shadows. One hopes that as women continue to enter science on an equal footing with men, we can look forward to a time when such culturally sensitive definitions become superfluous, and the queens take their deserved place with the kings of science.
Two independent groups of physicists have made important breakthroughs in the control of quantum computers based on trapped ions. Instead of controlling quantum bits (qubits) using multiple laser beams, the teams have used microwave sources, which are much easier to control and integrate within quantum circuits. The work could lead to practical quantum computers that incorporate large numbers of qubits on a single chip.
The most successful quantum-computing system so far has been the ion trap – in which information is encoded in the electron spin states of ions that are confined by electric fields. In such systems, the electron spins of multiple ions can be put into a single quantum state in which they are no longer independent of one another. In this “entangled” state, which has no analogue in classical physics, correlations between ions can be used to perform certain logical operations that would take an unfeasibly long time for a classical computer.
Entangling multiple spins
However, entangling two trapped ions had required a pair of carefully aligned ultraviolet laser beams – which cannot be produced easily on an integrated circuit. To entangle two pairs of ions, two pairs of laser beams were needed and so on. A practical quantum computer would need a processor containing thousands or even millions of qubits, so scientists have long sought a way to manipulate many trapped ions without large numbers of laser beams.
In 2001 Christof Wunderlich and a colleague of the University of Hamburg had the idea of replacing the lasers with microwave and radio sources, which can be produced and controlled much more easily. Such radiation had previously been used in other trapped-ion experiments, but using it to implement quantum logic operations was a highly revolutionary suggestion. This is because the type of interaction required for quantum logic is usually very weak for this radiation. However, the researchers suggested adding a magnetic field gradient to stimulate the interaction.
Magnetic muddle
Unfortunately, the need to use states that are sensitive to static magnetic fields makes the quantum states vulnerable to the magnetic noise found all around us, and the technique proved problematic. In 2008 physicists at the Ion Storage Group at the National Institute for Standards and Technology (NIST) in Boulder, Colorado, proposed eliminating the static magnetic-field gradient and using instead the oscillating field produced by the microwave source itself. The benefit being that the quantum states used in this scheme are less vulnerable to magnetic noise and more robust.
Both research groups now report significant advances in the journal Nature. Wunderlich’s group, now at the University of Siegen, together with colleagues from the Institute of Theoretical Physics in Ulm, have come up with a way to produce states that, while still sensitive to the applied magnetic-field gradient, are far less vulnerable to noise and thus can be preserved more than 100 times longer. In a commentary accompanying the papers, Winfried Hensinger of the University of Sussex compares the group’s scheme to a car’s suspension system, which decouples the body from the wheels so that bumps in the road do not disturb the driver.
The NIST group, meanwhile, goes further and performs all of the essential quantum logical operations (albeit on only two qubits) using microwave radiation delivered via a waveguide integrated into a chip. “We’ve integrated the mechanism that does the entanglement between the two ions into the trapping structure,” says Christian Ospelkaus, who built the experiment together with colleagues at NIST. “We no longer need to build a really complex and sophisticated laser system around the whole camp: we just send an electric current through the trap structure and that generates oscillating fields and it does all the other coherent quantum operations we need to do.”
‘Strong case’ for investment
Hensinger says that the two papers together constitute a significant advance for the field of ion-trap quantum computing. “The papers make a very strong case for a heavy investment in terms of time, people and money to push this technology forward. If you’re a bank asking yourself where you want to invest your money, these two papers are strong evidence that trapped ions have quite a significant capability.”
The work is described in Nature476 181 and Nature476 185.
Scientists have long wondered whether life originated on Earth or was seeded by biological-like molecules that arrived here from space. Meteorites could offer clues to this mystery because they are prime examples of extraterrestrial material that has made its way to our planet.
While such molecules have been discovered in meteorites since the 1960s, researchers could not be sure whether this is simply the result of contamination that occurred once the rocks reached Earth.
In this video, NASA scientist Michael Callahan explains why he and his colleagues are convinced that “DNA building blocks” discovered in 12 meteorites were formed in space – rather than being contamination picked up on the ground.
Researchers in the US say that they have discovered a new phenomenon in biology: metal-like conductivity along protein filaments. The result suggests that it could be possible to produce inexpensive conductive materials using micro-organisms – something that could “revolutionize” nanotechnology and bioelectronics, according to the team.
Derek Lovley and colleagues of the University of Massachusetts at Amherst made their discovery in networks of “bacterial filaments”. These are also known as “microbial nanowires” because they conduct electrons along their length. These are produced naturally by some bacteria and are about 3–5 nm wide and up to tens of micrometres long. The filaments bind bacteria together into clumps called microbial biofilms.
Lovley’s team looked at nanowires produced by the bacterium Geobacter sulfurreducens. The researchers measured electrical conductivities in the wires of around 5 mS cm–1, which is comparable to those of synthetic organic metallic nanostructures that are commonly used in the electronics industry. The wires were also seen to conduct over distances of centimetres, which is thousands of times the length of a bacterium itself.
Metallic first for biofilms
The researchers claim that this is the first time that metallic-like conductivity has been found in a biological material. Indeed, microbial biofilms are generally thought of as being electronic insulators.
Geobacter are anaerobic organisms that live in aquatic sediments and soils worldwide. They “breathe” by transferring electrons to iron oxides found in soil. This means that they could also be used to clean up groundwater contaminated with pollutants such as toxic and radioactive metals. “The bacteria use iron oxide in the same way that animals use oxygen,” explains team member Nikhil Malvankar. He says that what Geobacter does with its conducting nanowires is akin to a human breathing through a 10 km-long snorkel.
In the laboratory, Geobacter can grow on electrodes instead of on iron oxides and produce thick, electrically conductive biofilms. Lovely and colleagues took advantage of this fact for their experiments, in which they observed networks of nanowires spreading throughout the biofilm that was grown in a microbial fuel cell with acetate as the electron donor. This electron donor was modified so that the anode of the fuel cell – which acts as an electron acceptor to help the biofilm grow – was made up of two gold electrodes separated by a non-conducting gap of 50 µm.
Biological transistor
When a third electrode is then added to the system, the team discovered that the biofilm can act as a biological transistor that can be switched on and off by applying a voltage. “What is more, the conductivity of the biofilm can be tuned by simply changing the temperature – just like what happens in any metallic material,” says team member Mark Tuominen.
Using an atomic-force microscope with a conductive tip, the researchers observed that the current between the anode and the cathode increased as the biofilm grew on the electrodes. Confocal laser-scanning microscopy also showed that the cells formed a film that spread across the non-conducting gap. This bridge allowed the team to measure the conductivity of the biofilm.
“Long-range, metallic-like conductance along such protein filaments is a paradigm shift in biology that changes the way we think about how micro-organisms interact with their environment and each other,” says Lovley. “The structures can also interface with electronics, as we have shown.”
New energy-capture strategies
The findings could influence the design of energy-capture strategies, such as conversion of biomass and wastes to methane or electricity, Lovley claims. Looking further into the future, the discovery could lead to the development of new electronic materials – either produced by the micro-organisms themselves or engineered based on insights gleaned from the biological materials.
“I believe that research dedicated to improving our fundamental understanding of the components and mechanisms involved in charge transfer along bacterial nanowires is important and could have broad-reaching academic and practical implications,” comments Yuri Gorby of the University of Southern California, who was not involved in the work. “However, it is essential that those of us involved in this research maintain the highest standards for generating quality data that will withstand the test of time.”
The Massachusetts team is now looking into the mechanisms behind the metallic-like conductivity. “One of our future strategies is to genetically modify the amino-acid composition of the filaments and determine how this subsequently affects the conductivity of the bacterial nanowires,” reveals Lovley.
