The cover story in the October 2016 issue of Physics World magazine – now live in the Physics World app for mobile and desktop – reveals the inside story of how military labs are opening up their research facilities to the world. You can read the article here too.
The October issue also looks at how breakthroughs in physics really occur – is it flashes of insight or just long, hard graft? – and examines why we could finally find discrepancies in the “equivalence principle” that inertial and gravitational mass are the same.
Don’t miss either the ding-dong over China’s plans to build a new collider, our interview with Nithaya Chetty on transforming South African astronomy, or Robert P Crease’s Critical Point column on the danger of “unknown unknowns”.
The negative refraction of electrons in graphene has been seen for the first time in experiments done by physicists in the US. The work represents an important advance in the fabrication of graphene electronic devices, and could lead to new applications of graphene such as low-power transistors.
Negative refraction can occur when light or other waves cross an interface between two different materials. The term “negative” is used when the direction of the light is bent in the opposite direction to that which occurs for conventional materials such as glass and water. Negative refraction is a property of some artificial metamaterials and can be used to bring diverging rays back to a focus – allowing for the creation of a perfect lens. First proposed by the Russian physicist Victor Veselago in 1968, various types of negative refraction materials have subsequently been produced and the concept has been applied to the design of invisibility cloaks. However, actually making practical metamaterials has proven to be very difficult.
In principle, it should be much easier to achieve negative refraction with electron waves in a semiconductor. For electrons in a solid, the equivalent quantity to the optical index of refraction is the Fermi wave vector. This intrinsic property points in the same direction as the electron flow in an n-type semiconductor – in which charge is carried by electron flow. In a p-type semiconductor, however, charge is carried by positive “holes” and the wave vector points in the opposite direction. At the interface between an n-type and a p-type semiconductor (a “p–n junction”), the Fermi wave vector therefore changes sign and negative refraction should result.
Too much reflection
In practice, however, no one has been able observe negative refraction at a p–n junction. The main reason is that in conventional semiconductors with an energy gap between the valence and conduction bands, an electron has to gain or lose energy to traverse a p–n junction. The result is that the vast majority of electrons are reflected at the junction rather than being transmitted across and therefore refracted.
Graphene is a sheet of carbon just one-atom thick and it has no band gap. Therefore p–n junctions made from graphene should be much more transparent to electrons than those made from other semiconductors. Nevertheless, previous attempts to see negative refraction in graphene have failed. In search of an explanation for this failure, Cory Dean of Columbia University and colleagues modelled electron transmission across the p–n boundary in graphene. They concluded the likely culprit was the atomic-scale roughness at the interface that is the result of conventional lithographic processes used to make the junctions.
“Say you shine a focused laser beam onto a piece of glass, you can see that it refracts and measure the change of direction quite easily,” explains Dean. “Now imagine that you take a piece of sandpaper and scuff the surface of the glass, the beam will get dispersed.”
Flaky solution
To get around this problem, the team fashioned a junction using the natural edge of a graphene flake. They attached multiple electrodes to both sides of the junction. By injecting the electrons on one side and placing the junction in a variable transverse magnetic field, they controlled the angle at which electrons approached the boundary. They then used the voltage on the electrodes on the other side to work out where the electrons had ended up after crossing the junction. By comparing their measurements with computer models, they obtained clear evidence of negative refraction.
The team believes that its findings could lead to several practical applications. Dean says that, in principle, the ability to bring a diverging electron beam back to a focus at one of two points could form the basis of an electronic switch. Such a switch could be operated using very small amounts of energy, and this could be used to boost the efficiency of electronic devices. Dean also suggests that some of the parallels with optical applications of negative-refraction materials – such as cloaking – could be exploited in practical devices: “I don’t think it’s too crazy to think that we could apply some of those same concepts to electrical devices in ways that just haven’t been thought about because the technology just hasn’t been there,” he says.
Theoretical Physicist Carlo Beenakker of Leiden University in the Netherlands is impressed by the work: “The big technical advance is that they’ve been able to make very thin, very abrupt p–n junctions,” he says. “That, by itself, could have very far reaching implications because we know p–n junctions have all kinds of electronics applications.” He is more sceptical about the usefulness of perfect lensing with electrons: “If you have an electronic device, you have a big ohmic contact and shoot in electrons from all directions, and they come out with all directions at the other side,” he says. “We don’t use angular resolution in semiconductor devices, probably because it’s not a robust way to operate a device.”
Weather nanoparticle-infused coatings to study ecological impact
In an attempt to study the ecological and health-related consequences of nanoparticles released into the environment, researchers at the National Institute of Standards and Technology (NIST) have subjected a commercial nanoparticle-infused coating to a weathering process. The technique offers an accelerated way to study the effects of weathering from ultraviolet radiation as well as simulated rainwater. To study the effects of weathering, the team exposed multiple samples of a commercially available polyurethane coating containing silicon-dioxide nanoparticles to intense UV radiation for 100 days inside the NIST SPHERE (Simulated Photodegradation via High-Energy Radiant Exposure) – one day inside the SPHERE was equivalent to 10 to 15 days outdoors. For the “NIST simulated rain,” the researchers used filtered water that was converted into tiny droplets, sprayed under pressure onto the individual samples, and then the run-off – with any loose nanoparticles – was collected in a bottle. The team found that humidity and exposure time are contributing factors for nanoparticle release, which may be useful in designing future studies to determine potential biological impacts. The research is published in the Journal of Coatings Technology and Research.
Alice keeps a secret for 24 hours
Information encoded into an optical signal has been kept secret for 24 hours by a team of physicists at the University of Geneva in Switzerland. The work is a demonstration of the “bit-commitment” protocol whereby one party (Alice) creates a binary number and keeps it secret from the world until an agreed time when it is revealed to another party (Bob). An important feature of the protocol is that Bob can verify that the value of the number has not been tampered with while it was being kept secret. The process involves Alice and Bob each having two agents that they alone control. Alice’s secret number is mixed with a series of random numbers, with the results exchanged back and forth between the agents. The encryption algorithm is such that Bob can only determine the value of Alice’s secret after the final round of exchanges is complete – and he can also work out if anyone has clandestinely changed its value. Last year, several members of the Geneva team managed to keep Alice’s secret for 2 ms by performing six information exchanges over 131 km of fibre. Now, Anthony Martin and colleagues have boosted that time to 24 h. While the separation between parties was shorter in this latest work (7 km), they achieved five billion exchanges of information over the 24 hour period. The team points out that it could extend this time to a year using a 10,000 km separation. The research is described in Physical Review Letters, and one possible application is tamper-proof voting, whereby a ballot could be kept secret until it was time to count
European XFEL appoints new chairperson
Looking ahead: Robert K Feidenhans’l was appointed the new chairman of the management board of European XFEL GmbH. He has served as a Danish delegate to the European XFEL Council and was chairman of the Council from 2010 to 2014. Currently, he is director of the Niels Bohr Institute at the University of Copenhagen. (Courtesy: European XFEL)
Physicist Robert Feidenhans’l has been appointed chairperson of the management board of the European X-ray Free Electron Laser (XFEL). The research facility is currently being built in Hamburg, Germany, and when complete next year it will generate X-ray beams 30,000 times per second, with each pulse lasting less than 100 fs (10–13 s) that will allow researchers to create “movies” of processes such as chemical bonding and vibrational energy flow across materials. The facility’s management board has five members including the chairperson, an administrative director, as well as three scientific directors. Feidenhans’l, 58, is currently head of the Niels Bohr Institute at the University of Copenhagen, Denmark, and will join the European XFEL on 1 January 2017. He will succeed Massimo Altarelli, who has been at the head of the board since it was founded in 2009, and will now retire. “I am delighted to see the European XFEL, to which I devoted all my efforts over many years, in excellent hands,” says Altarelli, adding that Feidenhans’l is “an eminent X-ray scientist, with huge prestige in the scientific community and with vast experience in the management of large research organizations, including international ones. I am sure he will lead the facility to outstanding success in its operation phase”.
You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on the optical behaviour of electrons in graphene.
On a dreary, nondescript September morning in 1933, the Hungarian physicist Léo Szilárd stood by the roadside in central London waiting for traffic lights to change so that he could cross. As he stepped off the kerb, “time cracked open before him and he saw a way to the future, death into the world and all our woe, the shape of things to come”.
That’s how Richard Rhodes describes Szilárd’s epiphany, in the opening of his magisterial history The Making of the Atomic Bomb (1986), of how nuclear fission might be unleashed in the world. Szilárd saw that a chain reaction involving the emission of neutrons, discovered only a year earlier by James Chadwick, might sustain the fission process of atomic nuclei and enable the liberation of atomic energy. HG Wells had already imagined this scenario in his prescient novel The World Set Free (1914), in which he coined the term “atomic bomb”.
Szilárd was in England as a Jewish refugee from Nazi Germany. His vision of a nuclear chain reaction became an experimental possibility when, five years later, scientists in Germany discovered spontaneous fission in uranium. That prompted Szilárd and Albert Einstein to write to US president Franklin D Roosevelt warning of the danger of a German atomic bomb and urging an American effort to develop one.
All the elements needed for a theory of sustained nuclear fission were in place by 1933, but it took a flash of insight to unify them in Szilárd’s mind. That happened not as he sat thinking in a laboratory office, but during the most mundane and innocuous circumstance.
It seems this is commonly the case for “breakthrough” moments, when scientists suddenly see how to solve a problem or to weave ideas productively together. You can’t arrange for these insights; there’s no magic formula. But given that scientific progress often depends on them, it’s odd that they are so rarely discussed. It’s as if a determination to present science as an objective enterprise driven by some systematic method creates a nervousness about admitting to the uncontrollable, almost numinous manner in which insight often arrives.
That’s why a workshop called the Physics Imagination Retreat, held at the University of Cambridge, UK, in late June, convened by the Imagination Institute and led by University of Pennsylvania psychologists Martin Seligman and Scott Barry Kaufman, was so unusual – and so revealing. Here a handful of leading physicists discussed how they conceptualize their research and how they find answers to problems. To judge from their testimony and that of others, these answers sometimes really do arrive in eureka moments.
It seems likely that at least some famous “eurekas” are the retrospective inventions of scientists or their biographers
That notion of sudden, complete resolution of a scientific problem has been challenged as a model of how science really works. Sure, eureka moments make for a catchy narrative in popular-science histories, but doesn’t science more often advance through hard graft rather than flashes of inspiration?
It seems likely that at least some famous “eurekas” are the retrospective inventions of scientists or their biographers. Close inspection of the notebooks of Louis Pasteur led historian of science Gerald Geison to question the story reported by the French physician’s son-in-law of how Pasteur discovered molecular chirality (handedness). The son-in-law’s story goes that, having separated by hand crystals of opposite chirality and found that they rotate polarized light in opposite directions, Pasteur rushed into the corridor shouting “Tout est trouvé!” – all is found. But he probably didn’t; the realization came to him more gradually. And while we’ll probably never know the whole truth about Newton’s falling apple, it’s very likely that the story was embellished, if not entirely fabricated, by the great man himself.
However, perhaps the pendulum has swung too far the other way. It seems clear that many scientists do, like Szilárd, have these abrupt insights. And possibly they are especially prevalent in theoretical physics, where problems and their solutions are often rather abstract and mathematized, and much of the work goes on inside the researcher’s head rather than relying on some decisive experimental result.
Can we hope to understand how such eureka moments come about? There’s unlikely to be any recipe for producing them, or even any unifying way of comprehending them. But to judge from the evidence of the Cambridge gathering, there do seem to be similarities and resonances: clues to how imagination does its work in physics. Here are some of them.
The moment of clarity
Michael Berry, a theoretical physicist at the University of Bristol, UK, who has made important discoveries in fields ranging from quantum chaos to classical optics, describes moments of insight as “claritons”, the “elementary particle of sudden understanding” – which he jokingly refers to as his sole contribution to particle physics. He warns of the corollary: that anticlaritons also exist, “a too-frequent unwanted arrival that annihilates yesterday’s clariton”.
Berry was struck by a clariton in 1985 “during a long journey in January, when it was so cold that ice formed on the inside of the windows of the usually overheated German train”. The clariton, he says, was suddenly seeing that there must be a connection between quantum mechanics, chaos and prime numbers.
“This was very soon after I had started to understand the already-conjectured connection between the arrangement of quantum energy levels in systems that are classically chaotic and the universal statistics of numbers called eigenvalues generated by random matrices,” he says. “The understanding was why the universality occurs, and where and how it breaks down.” His clariton was that the Riemann zeta function, a mathematical function related to the disposition of prime numbers, fits precisely into this mathematical framework. “Why suddenly then?” Berry wonders. “I don’t know.” What process generates a clariton?
Collaboration
Berry feels that most claritons involve an apprehension of connections between ideas or problems. And those in turn often arrive through talking. “My claritons often came during or very shortly after conversations with colleagues,” he says, “triggered by an off-hand remark that suddenly revealed connections between two or more of my scientific preoccupations that had previously existed separately in my mind.”
This stimulation from colleagues seems central to several such experiences. Polymer scientist Tom McLeish of Durham University, UK, described one at the Cambridge gathering. He and his collaborators had been working for many years with an experimental group in Germany that had obtained some odd-shaped neutron-scattering plots from polymer liquids. McLeish had been discussing their interpretation with a colleague, but was getting nowhere.
“So we’d just given up,” he says. “My colleague said goodbye to my secretary as he stood at the door. Then he turned round and looked at me – and we both said: ‘Free ends!’ When you make a polymer network you cross-link chains at random points, and there are always some dangling chain ends left over. We both realized in the same instant that these samples must have a significant concentration of these ‘semi-free’ segments, able to adopt any orientational configuration just like totally free chains. We somehow saw into the structure of the material immediately and deeply.”
“Sometimes something in the unconscious is actually doing better than our conscious thinking, and at some later point that gets kicked upstairs,” McLeish suggests. “That can be triggered internally when ready, or externally by some unconnected event.”
This meeting of minds isn’t always quite so magical. Sometimes it simply entails one researcher hearing something useful from someone who didn’t even know it was valuable. Michael Cates, a theoretical condensed-matter physicist at Cambridge (and the current occupant of Newton’s old chair of Lucasian Professor of Mathematics), describes the kind of conversation he has sometimes been involved in: “A says to B: ‘Do you think you could solve problem X with the method I’ve just come up with?’ B responds: ‘Hmm, yes. That should be possible. And if so I can also solve problem Y with it.’ Then A says: ‘What?! You mean my method solves problem Y? That’s unbelievable, I’ve been thinking about Y for three years and never got anywhere with it. It’s a really important problem,’ and B never had any inkling of that.”
Intuition
Several moments of realization attested by physicists invoke a conviction about the truth of a solution even before the technical proofs are worked through. The researchers sense that, having arrived at the “right” answer, they can fill in the details at their leisure. “I share the experience reported by several people, that the clariton is often the beginning of the solution of a problem rather than the fully formed solution,” says Berry. “Nevertheless, it is usually accompanied by the powerful conviction that analysis will demonstrate that it is right (anticlaritons notwithstanding).”
This was the case for mathematical physicist Andrew Parry of Imperial College London when he was working on a thorny problem in condensed matter: the theory of critical wetting, or how the shapes of fluid films that wet a solid surface change with temperature. For years this field had been plagued by a discrepancy between what seemed like the best available theory and the results of computer simulations.
Am I dreaming? Mathematical physicist Andrew Parry of Imperial College London was on holiday in Mallorca when a visual language – with which he could finally solve a years-long discrepancy in the field of critical wetting – came to him in dreams. (Courtesy: Carlos Rascon)
“The solution came to me partly as a guess, then a few weeks later fully in a dream,” says Parry. “While on holiday with my collaborator in Mallorca, I woke up and knew the answer. I knew where to start, where to rest in the middle and where to end in my proof – even though it didn’t yet exist.” He found the solution unfolding almost outside his volition, even though it involved many hours and pages of calculation.
“The three papers we wrote are about 300 equations long, yet almost all of them I knew beforehand as soon as I woke from my sleep that day in the Spanish sun,” he says. Not without some trepidation for fear of ridicule, he describes the experience as the closest he can imagine to a spiritual revelation, in which he became a mere vehicle for the emergence of a deep and beautiful truth. “I felt I’d come across something much bigger and more important than me,” he says. “I was in awe of it.”
It is a bit like pattern recognition: I develop a feeling I need to find a certain pattern, a certain structure, and then the pieces fall into place
Jon Keating
Mathematical physicist Jon Keating of Bristol has had the same experience of sensing an answer before actually proving it. “Sometimes I have an idea, or hear something new, and I have a strong sense that this will solve my problem, long before I go through the details. I’m not always right of course! But I have been right, and that does feel magical. It is a bit like pattern recognition: I develop a feeling I need to find a certain pattern, a certain structure, and then the pieces fall into place.”
“It is quite common that one recognizes the whole pattern as the right one without having to check the details,” he says. “Jigsaw puzzlers will know this feeling.”
Preparation
This role of intuition in science needn’t be seen as something entirely mysterious. Pasteur famously extolled the way that “fortune favours the prepared mind”. He was thinking of how happy experimental accidents may lead to new understanding, but purely theoretical breakthroughs too depend on having penetrated a problem deeply enough to spot the answer when it arrives.
Keating says that this preparation may involve an almost obsessive dwelling on a particular issue or set of questions. “I tend to have a number of pet problems that I keep in my head for a long time,” he says. “Every time I hear something new, I try it out on my problems. I know these problems so well that I tend to have a feeling as to what is needed to solve them, or rather why previous lines of attack have failed.”
Visual language Andrew Parry’s diagrams allowed him to express his problem in a new way. (Courtesy: Andrew Parry)
This isn’t just a question of thinking hard and long about a problem, but also of finding the right way to express it – a way that enables connections to become apparent. “It is frequently about finding the right formulation or realizing what pattern to look for, and also frequently about asking the question in the right way,” says Keating.
That was the key to Parry’s breakthrough on critical wetting. Rather than the pages of clunky maths he’d been wrestling with, he suddenly saw how to express the interactions between the liquid–vapour and liquid–solid interfaces in terms of pictures akin to Feynman’s celebrated diagrams for dealing with forces between fundamental particles. “It was the invention of this new [visual] language, which I just woke up with one day and could speak, that was so powerful,” he says. “Each time I got stuck, a new part of the language would just pop into my head and allow me to convert it into a new expression and to carry on with the manipulation. I felt I’d had a glimpse of the book of nature.”
In dreams
I used to be rather sceptical about the idea that scientists find answers in dreams. These occurred too often in 19th-century accounts to seem plausible: August Kekulé drowsing in front of a fire and seeing the ring structure of benzene as a snake swallowing its tail, or Dmitri Mendeleev dreaming of the correct arrangement of playing cards annotated with elemental symbols to construct his periodic table.
But as Parry attests, it seems that these things really do happen. At the Cambridge meeting, John Pendry of Imperial described such an experience from his early days as a scientist. “I had a very tricky problem in my PhD thesis: there were some trajectories in the complex plane that someone else had postulated. The sign of some derivative changed and this trajectory was normally a loop, and everybody drew a loop.” But this didn’t solve the problem. Then – “Suddenly it came to me in a dream: what happened was the loop twisted and it was two loops. The twisting meant that the change of sign was explained. It was just there in the morning.” Shades of Kekulé, to be sure.
Bedtime brainwaves John Pendry of Imperial College London reasons that dreaming of a solution to a problem makes sense, as your brain continues working on the same thing you’ve been thinking about during the day. (CC BY Per Henning/NTNU)
That sort of thing is not unusual, Pendry says. “A lot of people keep a notebook by the bed, for when they wake up and something is in their head. You go to bed, you’ve worked on the problem all day, you’re tired but the data is up there, and somehow your brain sorts it out.”
Sometimes these dream-stories can be uncanny. McLeish says that he was once trying to figure out, with the same colleague involved in his “corridor” insight, some of the complex morphologies that can arise in the de-mixing of binary fluid mixtures. “We could compute the patterns by simulation, but needed ways of quantifying them through relevant figures of merit,” he says. “In particular the topological quantity escaped us – think of it as the ‘density of holes’. We got nowhere.”
“Then one night I had a dream in which the space was partitioned into small cubes and all possible topological states of each cube enumerated, depending on how dividing surfaces crossed the sides and edges. It turned out that one could then endow this set of primitive cubes with a numbering system that would be additive in calculating the topological invariant of the whole structure.”
Excited by this realization, McLeish rushed in to see his colleague the next morning. “He greeted me by saying ‘Oh, I was just on my way to see you – I had this weird dream last night that if we divided the structure into little cubes…’.”
If you read that in history books, would you believe it?
Searching for answers
What might you learn from all this, the next time you’re stuck on a problem and desperately seeking inspiration? In the end, the advice is probably not very surprising or spectacular. Talk to a friend or colleague. Take a walk. Have a sleep. Anything, it seems, but simply trying to think harder. Stop telling yourself that you should be smarter, and give your unconscious a chance (it’s pretty smart too).
Chinese Taoists have a term for it: wu wei, “not acting”. If there really is a Tao of Physics, perhaps that’s where to find it.
Back in 2014 the physicist Stephen Hawking hit the headlines by warning that artificial intelligence (AI) “could spell the end of the human race”. Like many of Hawking’s policy pronouncements, this one had a mixed reception. But is artificial intelligence actually something to be afraid of? In her short but information-dense book AI: Its Nature and Future, Margaret Boden, a cognitive scientist at the University of Sussex, UK, attempts to give readers the information they need to form their own opinions.
At the outset, she introduces the five major “types” of AI and explains how these different branches have interacted (and sometimes clashed) with each other over the discipline’s relatively short history. Broadly speaking, Boden explains, AI researchers are either interested in life, or they are interested in mind. Those in the former group tend to work on the cellular automata, dynamical systems or evolutionary programming strains of AI, while those in the latter group are drawn to studies of artificial neural networks or the logic-based “classical AI” championed by Alan Turing and his later disciples.
Developing any kind of general AI system (that is, one that can react in a human-like way to a wide variety of situations and problems, and not just be really good at, say, playing chess) will, Boden argues, almost certainly require a combination of these approaches, and probably additional ones as well. As for the chances of super-human AI emerging, Boden places herself on the sceptical end of the spectrum. In an insightful final chapter that also touches on the emerging field of AI ethics, she argues that while the so-called “singularity” (the point at which machines become more intelligent – whatever that means – than humans) may be possible in theory, it is effectively never going to happen in practice.
2016 Oxford University Press £12.99/$18.95hb 156pp
Shrouded by forest in the southern Ural mountains, the Russian city of Ozersk offers its residents a peculiar mix of nuclear dystopia and domestic bliss. The birthplace of the Soviet nuclear-weapons programme remains a closed city, but in City 40, the Iranian-born US filmmaker Samira Goetschel and her film crew take you behind the barbed-wire fences for an unauthorized glimpse of what it was – and still is – like to live there.
Using archive footage, the 73-minute documentary (now available on Netflix in many countries) first shows how the city was created in 1945 around the Mayak nuclear plant. Then codenamed “City 40”, Ozersk was patterned on the US city of Richland, Washington, which housed the workers who produced plutonium for the “Fat Man” bomb detonated over Nagasaki, Japan. In both cities, citizens were lavished with higher-than-average salaries, along with good-quality housing, healthcare and education systems. Indeed, the most remarkable aspect of City 40 is the window it offers on the everyday lives of Ozersk residents, who were known to outsiders as the “chocolate people” during the Soviet era on account of the abundance of luxury foods available there. In one scene we see agile youths back-flipping in a park; in another we see citizens attending a theatre performance.
Meanwhile, we learn from local journalists and nuclear scientists that residents of the city suffer from high rates of cancer, with many lives cut short or damaged due to radiation-related health issues. The contrast is both uneasy and surreal. The film’s central character is a local human rights lawyer, Nadezhda Kutepova, who has long campaigned to open up the city to the outside world. At the documentary’s conclusion, we learn that since her final interview, Kutepova was accused of industrial espionage and plotting against the Russian nuclear industry, and that she and her four children have been granted political asylum in France. This, of course, raises some troubling questions about the ethics of documentary film-making, but as viewers it is hard to second-guess the relationship that developed between the film-maker and her contributors. We are, however, left with one glaring reality: City 40 may no longer be a state secret, but Russia will not be inviting the outside world for an authorized tour any time soon.
Like most people, we at Physics World seldom give much thought to what lies beneath city streets. For the past few months, however, the view from our office has been dominated by road works, and observing the fluorescent-jacketed contractors as they rip up existing pipes and cables and install new ones has given us a fresh appreciation for the city’s hidden infrastructure. Readers in search of similar insights (but without the constant rumble of heavy machinery outside their workplace) would do well to pick up a copy of Laurie Winkless’s book Science and the City: the Mechanics Behind the Metropolis. In it, Winkless, a physicist and writer based in London, UK, delves into the structures that define modern cities and the services that make them tick, from soaring skyscrapers to subterranean sewers.
Written in a chatty, informal style (at one point, Winkless refers to herself as “your friendly science guide”), the book is divided into chapters that focus on different components of city life, including electricity, water, roads and communication. Winkless is not, however, solely interested in explaining cities as they are now. She is also keenly attuned to the ways they may change in the future, and for physicists, this is likely to be the most appealing aspect of the book. Winkless’s scientific background is in thermoelectric devices that harvest waste heat and transform it into electricity, but thanks to conversations with experts in other fields, her book is dotted with numerous short, snappy accounts of the latest developments in a wide variety of “green” technologies.
Some of these technologies may never make it out of the lab, while others will, in Winkless’s judgment, “remain a toy for environmentally friendly millionaires”. A few, though, may already be on their way to a city near you. Both Dubai and the Chinese city of Qingdao launched pilot projects for hydrogen-powered trains in 2015. And those noisy construction workers outside Physics World’s office? They’re installing charging plates for a new hybrid-electric bus service.
The European Space Agency’s (ESA’s) seminal, 12-year-long Rosetta mission has concluded, as the probe made a controlled crash into the Ma’at region of comet 67P/Churyumov–Gerasimenko today. The agency confirmed the conclusion of the mission as the signal from Rosetta was lost upon impact at 11:19 GMT. Rosetta continued to take data and make measurements during its final descent, focusing on several “active pits” from which a number of the comet’s dust jets originate. During its drop, the orbiter studied the comet’s gas, dust and plasma environment very close to its surface, and took high-resolution images. All of the information has been relayed to Earth, and Rosetta researchers will now begin to dig through the last of the mission data.
“Rosetta has entered the history books once again,” says Johann-Dietrich Wörner, director general of ESA. “Today we celebrate the success of a game-changing mission, one that has surpassed all our dreams and expectations, and one that continues ESA’s legacy of ‘firsts’ at comets.”
Bumpy start
Rosetta’s mission first began more than a decade ago, when the spacecraft was launched in 2004. Its target was comet 67P/Churyumov–Gerasimenko, whose 6.5-year elliptical orbit around the Sun takes it from beyond Jupiter to between the orbits of Mars and Earth. Rosetta’s voyage included three gravity-assisted flybys of Earth and one of Mars. While en route to 67P, the spacecraft made detailed observations of two other asteroids – Šteins and Lutetia – revealing previously unknown information such as their core structures. Rosetta then spent nearly 31 months in hibernation before the researchers sent a signal waking it up in early 2014 – the year of its “rendezvous” with the comet, which was achieved that August.
In November 2014, the Rosetta team made history as they were the first not only to have a spacecraft orbit a comet, but also to land on one after their Philae probe touched down successfully on the surface. But this landing did not come without its problems. One of the probe’s thrusters malfunctioned and a harpoon that should have locked it to the surface could not lock on. As a result, the lander bounced and its final landing place was less than ideal. Philae found itself in the shadow of a crater, with not enough light hitting its solar panels. Despite this, the lander used all of its on-board devices and instruments for about 60 hours and managed to complete all of the planned observations before it entered hibernation mode on 15 November. It was then “woken up” nearly a year later as the comet approached the sun and recorded more data.
Collision course
The team only spotted Philae from Rosetta earlier this month, and the “final resting place” of the lander can be seen in images taken by Rosetta’s high-resolution camera. The images showed the tiny lander wedged into a dark crack on the comet and its orientation clearly reveals why establishing communications was so difficult, following the 2014 landing. The images were taken on 2 September by the OSIRIS narrow-angle camera, as Rosetta came within 2.7 km of the surface. Communications with Philae were officially turned off at the end of July this year, to save energy for the orbiter to run until today.
As Rosetta descended today, ESA scientists were busy monitoring the comet during the drop and retrieving data. For example, the orbiter’s Comet Pressure Sensor (COPS), found that the gas pressure around the comet’s nucleus was increasing as it descended. Also, some of the active pits in the target region had previously been spotted having intriguing, lumpy, metre-sized structures. The Rosetta team believe these could be the signatures of early cometesimals that agglomerated to create the comet in the early phases of solar system formation. “With the decision to take Rosetta down to the comet’s surface, we boosted the scientific return of the mission through this last, once-in-a-lifetime operation,” says current mission-manager Patrick Martin.
Rubber-duck
Data from the Rosetta mission have already provided a host of new insights into comets and their make-up. “One of the big surprises was the shape of our duck,” says project manager Matt Taylor, referring to the fact that the comet’s nucleus is made up of two distinct segments joined by a “neck”, giving it a “rubber-duck”-like appearance. The team now believe that the two lobes formed independently and later joined in a low-speed collision in the early days of the solar system.
Some of the earliest measurements of the levels of hydrogen isotopes on the comet have showed that much of the water it holds is heavy water. That is, the ratio of deuterium to hydrogen in the comet is much greater than the ratio found on Earth. This was a crucial finding, as it disproved the suggestion that comets supplied Earth with majority of its water.
Other measurements focussed on 67P’s coma, shape, composition, temperature, nucleus and surface features. These revealed a textured, dynamic comet that was covered in sand-dunes and ripples, spewing out jets of material. The team also discovered that the small rock has no global magnetic field. Another major discovery, only revealed earlier this year, is that the comet contained the amino acid glycine – a key building block of life. Numerous organic compounds were also detected, both by Rosetta from orbit and by Philae on the surface. These finding suggested that critical ingredients for life may indeed have been delivered to Earth by comets, rather than being created on our planet. It also suggests similar comets could also have delivered life elsewhere in the universe.
“Just as the Rosetta Stone, after which this mission was named, was pivotal in understanding ancient language and history, the vast treasure trove of Rosetta spacecraft data is changing our view on how comets and the solar system formed,” says Taylor. “Inevitably, we now have new mysteries to solve. The comet hasn’t given up all of its secrets yet, and there are sure to be many surprises hidden in this incredible archive. So don’t go anywhere yet – we’re only just beginning.”
The Rosetta comet landing was named the Physics World 2014 Breakthrough of the Year. Watch the video below to hear from Rosetta Mission manager Fred Jansen.
The first week of October is nearly upon us and the question on almost every physicist’s lips is “who will win this year’s Nobel Prize for Physics?”. The people’s favourite for 2016 seems to be the physicists who pioneered the LIGO gravitational-wave detectors. In February 2016 LIGO researchers announced that they had made the first ever detection of a gravitational wave – from two merging black holes. A few months later, a second detection was announced.
Normally, Nobel nominations are closed in January so it’s possible that LIGO missed the boat. However, both the first and second detections were actually made in 2015 – with the results subsequently published in 2016. So the LIGO pioneers could have been nominated before the deadline as the collaboration already knew it had detected gravitational waves. It’s all pure speculation, of course, as each year’s deliberations are kept top secret for 50 years.
So who could be claiming the prize for LIGO? Three people favoured by pundits are Rainer Weiss, Kip Thorne, and Ronald Drever. Drever and Weiss played crucial roles in designing and building LIGO, whereas Thorne calculated what gravitational waves would look like to the detector.
While few doubt that the trio is deserving of the prize, some commentators are calling for a collective prize given to the thousands of physicists working on LIGO. This could be a better reflection of how big physics is done, but there is no precedent for such a group prize.
Lagging behind: it can take a long time to win a Nobel prize. (IOP Publishing/Hamish Johnston)
The popularity of a LIGO prize got me wondering how common it was for a Nobel to be awarded just one year after a discovery. I delved into the vast archive of material on the Nobel Foundation website and produced the above histogram. It shows the frequency of time gaps between when a discovery was made and when the physics prize was awarded. I’d like to add a disclaimer that deciding exactly when the work was done is subjective, and often near impossible if the award is given for a body of work. So my data might not agree exactly with those of others, but I think it shows the general trend that most awards are given within 20 years of the work being done.
As far as I can tell, there are three instances when a physics Nobel was awarded a year after the work was done. The first was the 1957 award, which was given to Chen Ning Yang and Tsung Dao Lee for formulating a theory of parity violation for the weak interaction. The theory was proposed and verified experimentally in 1956.
The second is the 1984 prize, which went to Carlo Rubbia and Simon van der Meer for the 1983 discovery of the W and Z bosons at CERN. The final one-year gap involves the discovery in 1986 of the first high-temperature superconductor which won Georg Bednorz and Alexander Müller the 1987 Nobel.
So it is certainly possible that LIGO could feature in this year’s prize, if the nomination was made early enough.
At the other end of the scale, I reckon that there are three physics prizes that were awarded more than 50 years after the research was done. The first is the 1986 prize, which was shared by Ernst Ruska who was then 79 years old. Ruska won for his work on electron optics done in 1933. The other two were shared in 2003 by Alexei Abrikosov and Vitaly Ginzburg for independent work done in the early 1950s on superconductors and superfluids.
Personally, I think this year the award will go to Weiss, Thorne, and Drever – but I have never actually got a prediction right. If not them, I think we could see a prize for Michael Berry and Yakir Aharonov for their work on quantum topological and geometrical phases. If you’d like to get a good idea of who else could be in the running, check out this tournament-style chart that pits various superstar physicists against each other.
Please let us know who you think will win by leaving a comment below.
The Energy Technologies Institute (ETI) has called on the UK government to develop a policy framework to support the construction of small modular nuclear reactors. In its report, the ETI – a public-private partnership between companies and the UK Government that was founded in 2007 – says that the UK government has a “crucial” role to play in fostering investor confidence. If that is successful, the report notes that the first small modular reactor could be in operation by 2030. Small modular reactors are a type of nuclear fission reactor that have an output of less than 500 MW and could be used in remote locations.
Surface dewetting observed at long last
Lip service: the time sequence on the left runs from top to bottom and shows the wetting process. The time sequence on the right runs from bottom to top and shows the formation of a lip during the dewetting process. (Courtesy: Northumbria University)
The process of dewetting – whereby a thin film of liquid on a surface spontaneously forms bead-shaped droplets – has been observed directly for the first time by researchers at Northumbria University and Nottingham Trent University in the UK. The team used a technique called “dielectrowetting” to force a liquid to coat (or wet) a hydrophobic surface that is initially covered by a droplet. This involves applying an electric potential to a circular pattern of electrodes below the surface, which pulls the liquid downwards until it spreads over the surface to create a flat disc. The team then switched off the electric potential to observe dewetting, which they found is not simply wetting in reverse. While wetting involved a droplet flattening like a pancake (see image), dewetting began with a raised lip forming at the outer edge of the disc. This lip then moved inward at a constant speed until the disc has transformed into a droplet. According to Carl Brown of Nottingham Trent, theory and computer simulations both suggest that “the liquid tends to adopt the closest local equilibrium shape it can during dewetting”. He adds, “This explains the smooth rim shape which survives for most of the process”. Northumbria’s Glen McHale says the research could “spark a new line of research and lead to breakthroughs involving the use of liquids, such as better coatings and more effective self-cleaning surfaces”. The research is described in Science Advances.
D-Wave previews 2000-qubit processor
Black box: D-Wave’s superconductor-based qubits are isolated from the environment inside a large black box. (Courtesy: D-Wave Systems)
A computer comprising 2000 superconducting quantum bits (qubits) has been previewed by Canada-based D-Wave Systems. The new system has twice as many qubits as the firm’s previous model – the D-Wave 2X. The company claims that improvements to the new device’s control systems will allow it to run 1000 times faster than the D-Wave 2X and solve a broader range of problems. D-Wave has already sold previous versions of its systems to Lockheed Martin and to Google. However, the D-Wave devices are controversial: some physicists report that they outperform conventional computers on certain specialized calculations, while others say that they do not actually perform quantum calculations at all.
You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on the Rosetta comet mission.
By Matin Durrani
