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Letting the sunshine in

Photo of a burst of sunlight and a golden stalk of wheat

By 2050 the world’s population will have reached nine billion. How can the Earth provide the resources to sustain all these people? This topic is tackled in the book Project Sunshine, in which authors Tony Ryan and Steve McKevitt explain how world population growth has led to a “perfect storm” of intertwined water, food and energy shortages, with climate change as a backdrop.

The book’s preface and its first two chapters describe how the discovery of fossil fuels was followed by a population explosion, albeit one that is predicted to plateau at the afore-mentioned figure of nine billion. Here, the authors introduce their ideas (which are fleshed out later in the book) on how it is possible to provide sufficient food and energy for nine billion people in a “sustainable” way. The book then takes what appears at first to be a detour, as the authors go back to the Big Bang to explain the various sources of energy that exist. Subsequent chapters describe the evolution of humans and give a brief history of societal developments, showing how human activities before the discovery of fossil fuels were constrained by the time it took for the principal source of energy – wood – to replenish itself.

Descriptions of nuclear power, non-solar renewables, solar power and energy storage show how sufficient energy can be provided for the expanding world population. Food production is also examined, discussing contentious aspects such as genetically modified plants. The final chapter stresses the need to view solar power “as a must-have, not a nice-to-have”, reminding us that this means that the wheel has turned full circle: “Until 350 years ago, mankind was living like any other animal, beholden to the solar cycle.”

The authors – who are respectively a polymer chemist and pro-vice chancellor at the University of Sheffield, and an expert in communications and consumerism – could hardly have picked a more important or universally interesting topic. The latest report by the Intergovernmental Panel on Climate Change (released on 27 September this year) lends their book topicality, as global warming (although not their main focus) is mentioned in many places, while the gap between energy requirements and supply and how to address it are constant preoccupations for anyone who has the remotest interest in current affairs. Ryan and McKevitt address these questions, treading the fine line between being too technical or too woolly. While the authors do have a solar axe to grind, their book also complements Sustainable Energy – Without the Hot Air by the Cambridge physicist David MacKay (UIT, Cambridge 2009), in that both agree it is possible to act to solve energy problems – and, moreover, that it is imperative to do so.

I have quibbles. The authors state early on that “all of our energy comes from the Sun”, yet this is not quite true. Geothermal energy, which is mentioned in the book, results from the radioactive decay of elements inside the Earth; like nuclear power, it originates in elements that were created mainly in supernovae. And on the subject of nuclear power, it is also worth noting that the chapter devoted to it does not talk about waste disposal, even though difficulties with the permanent disposal of high-level waste argue against this form of electricity generation (see “Too hot to handle“). Another quibble is that while the book shares its name with a network of researchers at the University of Sheffield, and the two are related (the aim of the Sheffield “Project Sunshine” is to develop new ways to use the Sun’s energy more efficiently to increase food production and provide renewable energy), this link is not mentioned until page 197.

The authors of Project Sunshine also have little to say about sourcing materials for renewable-energy generation in a sustainable way. For example, a shortage of indium metal is currently forcing a rethink of how to make the transparent conducting films needed for electrodes in solar cells, as these films are currently made from indium tin oxide. And in the chapter on solar power, there is no discussion of thin-film solar cells made from inorganic semiconductors such as copper indium gallium selenide (CIGS) and their sustainable replacements, even though this type of cell offers many advantages. For example, they are typically 50 times thinner than cells made from multicrystalline silicon, and the efficiency of some CIGS cells made on flexible polymer substrates has reached 20% – not far off the 28% of single-crystalline silicon.

Finally, there is no mention of the crash in the price of solar photo-voltaic (PV) modules in the last few years. A consequence of excess production in China, the price crash has made solar cells much cheaper than could have been anticipated just a short while ago, but it has also led to the loss of 100 out of 350 companies that produce them and inhibited development of new PV technologies. As noted in Project Sunshine, the cheapness of the new technologies relative to crystalline silicon has been an important rationale driving their progress. In the light of the fast-changing nature of the field of energy supply, I suggest that the authors might wish to cover such topics in a blog, perhaps one linked to the Sheffield Project Sunshine.

No book can cover everything without sacrificing readability. Several books have been published recently that address the politics of energy, an example being The Energy of Nations by Jeremy Leggett (Routledge, London 2013). Project Sunshine complements these books by placing energy in the context of the history of the planet going back to the Big Bang, and as a result is an absorbing read with a clear story to tell.

  • 2013 Icon Books £16.99hb 320pp

Web life: Empirical Zeal

What is the site about and who’s behind it?

Empirical Zeal is a blog that covers mind-blowing science from a wide range of disciplines, but especially physics and evolutionary biology. Its zealously empirical author is Aatish Bhatia, a PhD student in the physics department of Rutgers University in New Jersey, US. For a year or so in the late 2000s Bhatia wrote a conventional physics blog called High Energy Mayhem in which he described typical PhD-student activities such as going to conferences, attending seminars and attempting to get to grips with various mathematical tools. Since then, however, both Bhatia’s scientific interests and his blog have evolved considerably. His current research focuses on developing and applying new computational tools for genome analysis, and his new, general-public-friendly blog is an irresistible mix of everyday and esoteric science, backed up with some serious but accessible quantitative analysis.

Can you give me some examples?

Bhatia often uses blog posts or videos created by others as jumping-off points for his own work. For example, one post from July features a video in which the British science presenter and comic Steve Mould makes a long chain of beads “levitate” as it is poured out of a jar. The video is jaw-dropping, and Mould offers a good description of the physics behind it. However, Bhatia takes things several steps further, creating a mathematical model of the falling chain and using motion-tracking software to compare the model’s prediction to a slowed-down version of Mould’s video. Another recent post begins with a video of a “rolling swarm” of caterpillars, and goes on to explain that these swarms are essentially a squishier version of the moving walkways in airports: caterpillars in the top few layers can travel at speeds several times faster than an individual bug can crawl, thanks to the motion of the bottom layers. Calculating the speed of the Nth layer of caterpillars is, however, left as an exercise for the reader.

Anything else I should know?

In addition to physics and evolution, Bhatia also has a strong interest in education. Earlier this year, he helped make a video for TED-Ed (the educational wing of the online science/culture/ideas juggernaut) about the physics of fluids and the ways in which large and small swimming creatures have adapted to move through them. The video carries the arresting title “The physics of sperm vs. the physics of sperm whales”, and is worth watching for the animations alone. Another post takes an in-depth look at the “monkey and the hunter” problem found in many undergraduate physics textbooks, analysing not only the problem itself but also how its presentation has changed over the years.

Can you give me a sample quote?

From a post in June: “I just read an interesting new physics paper. It’s called ‘Statistical mechanics of the US Supreme Court’, and it attempts to understand how Supreme Court judges influence each other when voting, using techniques from the physics of magnetism… Imagine you had a magnet. If you zoom in to this magnet with the right kind of microscope, you’d see tiny little microscopic magnets – each of which can either align with or against each other. These micro-magnets (or spins, which is what physicists call them) can flip their directions, and they can influence each other – every micro-magnet tries to get the other ones to align with itself. Some micro-magnets are more influential than others, and they can convince many others to flip in their direction. Turns out, this magnet model maps nicely to the Supreme Court problem. Just as the micro-magnets influence each other’s orientation, and arrive at an emergent magnetization, the Supreme Court judges can influence each other’s votes, and from their deliberations emerges a final vote.”

Chaos reigns in unexpected places

Chaotic behaviour could emerge within systems where all motion dies out due to the effects of dissipation, according to a new study carried out by researchers in Hungary and the US. The team makes the surprising claim that characteristic features reminiscent of chaos, such as the butterfly effect or fractals, would be seen in a system without any energy input. The new work suggests that a wider range of processes – such as chemical reactions evolving towards their equilibrium or coalescing binary stars that lose energy to gravitational waves – might be chaotic. This would make such processes much less predictable than previously thought.

Sensitive systems

A chaotic system is a dynamic system that is highly sensitive to its initial conditions. The smallest difference in these initial conditions could lead to widely diverging outcomes, making any long-term predictions of its outcome impossible to predict. Normally, such chaotic behaviour is seen in transient systems that are constantly evolving – the system’s dynamics are either non-dissipative or the system is constantly subject to some external force. Such systems undergo transient chaos – a phenomenon in which most trajectories are influenced by a small subset of trajectories that remain chaotic forever.

But what happens with systems in which motion eventually stops due to dissipation? Called “doubly transient”, these systems are the ordinary processes that we encounter in daily life – for example, a spinning coin that wobbles erratically but ultimately stops due to friction. New research led by Adilson Motter of Northwestern University in the US shows that even such systems can exhibit the hallmarks of chaos.

Doubly transient

Motter uses another example of such a system, describing a pendulum that is displaced sideways and then given additional pushes periodically. Thanks to the periodic pushes, the pendulum would never stop as a result of the energy input and this is the scenario of (ordinary) transient chaos. However, if you leave the pendulum alone it will stop thanks to the air friction, regardless of the initial condition. Such a system undergoes “doubly transient chaos” – a phenomenon in which trajectories behave erratically for a transient period of time but then they stop due to dissipation. Systems exhibiting doubly transient chaos do not have any trajectory that remains chaotic forever.

The research was based on both mathematical calculations and numerical experiments. In the experiment, the team’s model system comprised a magnetic pendulum made up of three identical magnets (i.e. three possible final stable states) placed at the corners of a triangle, with the pendulum suspended above the centre of the triangle. The pendulum is subjected to the effects of gravity, attractive magnetic forces, and drag due to air friction. The team found that its pendulum showed signatures of doubly transient chaos.

Surprisingly chaotic

“Perhaps the most surprising result is that, although it looks at first sight similar to the case of transient chaos, doubly transient chaos has fundamentally different dynamical and geometrical properties,” explains Motter. The team found that classical parameters, such as the rate at which the trajectories approach their final states (i.e. toward an attractor) “increases exponentially fast as a function of time, rather than being constant as is the case of transient chaos”, according to Motter. The researchers also found that the fractals separating different basins of attractions have integer dimensions, rather than fractional ones, meaning that their complexity reduces upon magnification.

According to the researchers, their significant and surprising results could have implications for varied and diverse processes from the evolution of chemical reactions towards equilibrium to merging vortices in dissipate flows, to games such as dice throwing, and to large-scale celestial events such as the coalescence of spinning binary-star sources of gravitational waves. “It follows from our study that in all such processes, the outcomes are all far less predictable than anticipated,” says Motter. Now, it is important to study doubly transient chaos in a variety of systems from different domains to identify the universal properties of this phenomenon as well as exploring its applications, according to Motter.

The research is published in Physical Review Letters.

How to build a "memcomputer"

Is this a nascent memcomputer? (Courtesy: Oak Ridge National Laboratory)

By Hamish Johnston

There is a fascinating paper this week in Nature Physics about chaotic behaviour that has been spotted in a ferroelectric material. It’s an unexpected discovery that the researchers claim could lead to the development of computers that resemble the human brain.

The story begins with Anton Ievlev and colleagues at Oak Ridge National Lab in the US using the tip of a scanning probe microscope (SPM) to draw patterns on the surface of a ferroelectric material. Ferroelectrics have a spontaneous electric polarization, the direction of which can be reversed by applying an electric field.

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NASA launches MAVEN probe to Mars

NASA has launched a mission to Mars that will investigate how the planet lost its liquid water and how solar radiation is slowly eroding its atmosphere. The mission – Mars Atmosphere and Volatile Evolution (MAVEN) – was launched from Cape Canaveral Air Force Station in Florida by an Atlas V Centaur rocket at 13:28 local time yesterday.

Costing $671m, MAVEN will spend the next 10 months travelling to Mars, arriving at the red planet in September 2014. When the probe gets there, it will then be put in a highly elliptical orbit in the Martian atmosphere, being 100 km from the planet’s surface at its closest approach and 80,000 km away at its most distant. MAVEN, which took 10 years to design and build, will carry eight instruments including a spectrometer, a magnetometer and a spectrograph.

Mars has an atmosphere that is composed mainly of carbon dioxide (95%) together with argon (2%), nitrogen (1.9%) and oxygen (0.14%). MAVEN will use its instruments to measure the current rate of atmospheric loss – a process that began about four billion years ago when Mars’s protective magnetic field mysteriously disappeared – to understand how the planet transitioned from a warm, wet planet to a dry desert. The information gathered by MAVEN is also expected to help scientists grasp when conditions on Mars might have been most suitable for life to evolve.

“MAVEN joins our orbiters and rovers already at Mars to explore yet another facet of the red planet and prepare for human missions there by the 2030s,” NASA Administrator Charles Bolden said after the launch. “This mission is part of an integrated and strategic exploration programme that is uncovering the mysteries of the solar system and enabling us to reach farther destinations.”

Working in tandem

MAVEN’s launch comes just 13 days after the Indian Space Research Organisation sent its country’s first craft to Mars; it will also study’s the red planet’s atmosphere. Dubbed Mangalyaan, the probe will arrive at the red planet in September 2014, just two days after MAVEN.

“Some of the measurements that [Mangalyaan will] make are similar to those that Maven will carry out and that’s not a bad thing,” Jeffrey Plescia, a Mars researcher at Johns Hopkins University in the US, told physicsworld.com. “The interaction between the solar wind and the Martian exosphere is a dynamic system that varies in both space and time. Having two spacecraft at different locations will provide a much better 3D perspective on the processes and rates.”

How do you make a pear-shaped nucleus?

In less than 100 seconds, Peter Butler explains that, contrary to popular belief, most nuclei are not spherical but instead take on deformed shapes. Usually these shapes are high symmetry, because of the quantum-mechanical interactions between protons and neutrons inside the nucleus, but in rare cases these interactions can lead to more asymmetric forms, as was demonstrated recently as the REX-ISOLDE facility at CERN, where researchers created pear-shaped nuclei.

Watch more from our 100 Second Science video series.

Physicists reveal a quantum Cheshire cat

“It’s the most curious thing I ever saw in my life!” Alice thought to herself when she saw a Cheshire cat disappear and leave only its grin behind. It is not only in Wonderland, however, that properties of objects can exist independently of the objects themselves. That is the conclusion of a group of physicists from Israel and the UK, which has shown how the strange laws of quantum mechanics permit a photon to be in one place and its circular polarization in another.

This counterintuitive result was achieved thanks to the quantum-mechanical concept of post-selection. In classical physics, the initial conditions of a set of particles and the rules governing the behaviour of those particles are in principle enough to determine the properties of the particles at any arbitrary point in the future. That is not the case in quantum mechanics, in which a particle’s evolution is inherently probabilistic. So while the results of a measurement carried out on a set of particles will have a known probability distribution, individual results cannot be predicted.

Post-selection, pioneered by Yakir Aharonov of Tel Aviv University, involves preparing a group of particles in some initial state, measuring each of the particles at a certain point in time, and then making a second set of measurements at a slightly later time. The results of the intermediate measurements will, on average, imply certain results for the later measurements but will not determine them. If the group is then split into sub-groups according to these later results, the identity of the members of those various sub-groups is information that can only be obtained after the final measurements, and not before.

Superposition of paths

In the latest work, Aharonov has teamed up with Sandu Popescu of the University of Bristol, Daniel Rohrlich of Ben Gurion University and Paul Skrzypczyk, then at Cambridge University. The group has devised an experiment, which it says can be implemented with current technology, in which individual horizontally polarized photons pass through a beamsplitter and then traverse a series of optical devices before being registered in one of three detectors. When leaving the beamsplitter, each photon is in some kind of superposition of two different paths that it can take to reach the other devices, the two paths representing the two arms of an interferometer (see figure “An optical Cheshire cat”).

Schematic of the proposed Cheshire-cat experiment

The devices are chosen and arranged so that the first of the detectors only clicks when the photon is in a specific superposition state, and it is this state that is post-selected. The researchers then consider what happens to the photon – the Cheshire cat – and its polarization – the grin – in that post-selected state. They find that while any photon detector would reveal the photon to always travel along the left-hand arm, a polarization detector would occasionally measure angular momentum in the right-hand one. “We seem to see what Alice saw,” the researchers write, “a grin without a cat!”

The researchers point out that this analysis falls down because it relies on the two kinds of detector being used at different times, and that if they were to be used simultaneously, the detectors would always show the photon and its polarization together in the same arm. But Aharonov and colleagues argue that they can “regain the paradox” by carrying out what are known as “weak measurements”, which do not provide definitive values of particle parameters but do have the virtue of not completely destroying a particle’s quantum state, as usually happens during the measurement process.

Making weak measurements

The researchers say that weak measurements can be made of the photons’ trajectory by replacing the first detector in their hypothetical experiment with a CCD camera and by placing a sheet of glass in one of the arms. Deflection by the glass – which reveals photons to have travelled down that arm and which would be registered by the camera – is made deliberately much smaller than the width of the photon beam, with the resulting uncertainty then reduced via multiple measurements. Analogously, polarization is measured by placing a suitable optical element in one of the arms and recording a deflection at right angles to that caused by the glass sheet.

The crucial point about this revised set-up, explains the Israeli–UK team, is that it can be used to measure different parameters at the same time. As such, the researchers claim, putting both the glass and the optical element in the right arm of the interferometer would prove that the polarization could exist independently of its photon. Which would mean, the researchers write, that they had “finally found [the] Cheshire cat”.

“Beyond the mainstream”

Having had to wait for a 21 months between posting its proposal on the arXiv preprint server and seeing it published in New Journal of Physics, Popescu acknowledges that his group’s scheme was not well received by all of the referees who reviewed it. “It is beyond the mainstream,” he says. “But quantum mechanics has been around for almost 100 years and people still don’t understand it profoundly. Discovering effects like this, which expose the weirdness of quantum mechanics, may help.”

Popescu says that the Cheshire-cat effect is quite general – that there is nothing in principle to prevent the separation of, say, an electron’s spin and charge, or an atom from its internal energy. Indeed, an alternative to the current experimental proposal would involve cutting off a group of electrons from its own magnetic field. Being a group phenomenon, he points out, this would have the advantage of revealing the Cheshire cat unambiguously at a single instant in time rather than as the average of a series of repeated measurements, but would, he says, require experimental techniques beyond the realm of current technology.

Antonio Di Lorenzo of the Federal University of Uberlandia in Brazil agrees that the experiment proposed by Aharonov and co-workers could be used to find quantum Cheshire cats. But he says they are mistaken in the criterion that they use to identify their quarry. Rather than consider the outputs of the “cat detector” and “smile detector” separately, he argues, they should instead establish the product of these two outputs. A non-zero answer, he says, would reveal the cat.

  • Find out much more about weak measurement in “In praise of weakness” by Aephraim Steinberg, Amir Feizpour, Lee Rozema, Dylan Mahler and Alex Hayat

Colliding exhibits, influential researchers, edible particle-detectors and more

Collider exhibition at London's Science Museum (Courtesy: Nick Rochowski for the Science Museum)

 

By Matin Durrani and Tushna Commissariat

If you’re in the tiny minority of people whose job title says “particle physicist”, chances are you’ll have been to CERN at least once in your career to help build a detector, analyse some collision data or muse in the cafeteria over supersymmetry (or the apparent lack of it so far). But for the rest of the world, going to the Geneva lab is simply not on the agenda, which is one reason why the Science Museum in London has this week unveiled a big new exhibition devoted to CERN’s Large Hadron Collider. Entitled simply Collider, the exhibition “blends theatre, video and sound art with real artefacts from CERN” that will, say organizers, “recreate a visit to the famous particle-physics laboratory”.

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Four quarks for Muster Mark?

Family of four? (Courtesy: Shutterstock/paul_june)

By Tushna Commissariat

In June we reported that physicists working on the BESIII experiment in Beijing and the Belle experiment in Tsukuba, Japan found evidence for a new “charged charmonium” called Zc(3900). A “charged charmonium” is a particle that is made of four quarks – something that had never been seen before. Since that discovery, the BESIII collaboration says it has made “a rapid string of related discoveries” of four-quark particles. “While quarks have long been known to bind together in groups of twos or threes, these new results seem to be quickly opening the door to a previously elusive type of four-quark matter,” says Frederick Harris, spokesman for the BESIII experiment. “The unique data sample collected by the BESIII collaboration has continued to yield a stream of clues about the nature of multi-quark objects.”

(more…)

Quantum state endures for 39 minutes at room temperature

Quantum states have been shown to endure in a room-temperature solid-state device for a whopping 39 minutes, shattering the previous record of 2 s. The feat was achieved by physicists in Canada, the UK and Germany, who used phosphorus atoms in silicon as their quantum bits – or qubits. The breakthrough offers hope that normally fragile quantum states could be made robust enough to be used in practical quantum computers or even in “quantum money”.

Quantum computers are designed to exploit the counterintuitive idea that tiny objects can exist in more than one state at the same time. Rather than processing bits – which are either 0 or 1 – such devices instead manipulate qubits, which can be 0 and 1 simultaneously. Vast numbers of operations could therefore, in principle, be carried out in parallel and rendering these devices far quicker than classical computers.

But anyone trying to build a working quantum computer has to deal with the fact that qubits tend to be incredibly fragile, which means the quantum information they hold is rapidly destroyed by external noise. One way of getting around this problem is to cool the qubit to near absolute zero to minimize its exposure to thermal noise. But working at such low temperatures is not particularly practical, which is why researchers are keen on find qubits that can operate at room temperature.

Record breakers

The new record-breaking system has been created by Mike Thewalt of Simon Fraser University and colleagues, by storing quantum information in the nuclear spins of phosphorous atoms in a silicon crystal. The idea of using these nuclear spins is not new and the system has already been shown to retain quantum information for long times at extremely low temperatures. But even at 10 K, this “coherence time” drops precipitously to just a few milliseconds.

To get around this problem, Thewalt and colleagues took advantage of the fact that phosphorous atoms in silicon at room temperature tend to give up their electrons and become positive ions. Removing the electrons eliminates an important link between the nuclear spins and surrounding electrical noise. Nuclear spins can therefore retain quantum information for much longer than those in neutral phosphorous.

The downside is that removing the electrons makes the nuclear spins so well isolated that they cannot be “read” or “written” to. So to get around this problem, the team first cooled its crystal to 4.2 K and used laser and radio frequency (RF) pulses to put neutral phosphorous atoms into specific quantum states. A laser pulse then ionized the atoms before the crystal was warmed up to room temperature (298 K).

Under these conditions, RF pulses were used to perform a “spin echo” measurement of the coherence time, which was found to be 39 minutes. The crystal was then cooled back down to 4.2 K and another laser pulse was used to neutralize the phosphorus ions before the quantum information was read out using a sequence of laser and RF pulses.

Walking round the lab

Although measurements reveal that the coherence time at room temperature is 39 minutes, team member John Morton from University College London says that under these conditions, it would be possible in principle to remove the crystal from the cryostat and carry it around the lab while the spins maintain their coherence. What’s more, repeating the experiment with the sample at 4.3 K revealed a coherence time of as long as three hours.

Stephanie Simmons from the University of Oxford, who is also part of the team, says that while 39 minutes “may not seem very long”, it takes just 10 microseconds to flip the nuclear spin of a phosphorus ion – the type of operation used to run quantum calculations. “In theory, over 20 million operations could be applied in the time it takes for the superposition to naturally decay by 1%,” she says.

On the money

Morton adds that it is unlikely that anyone would build a quantum computer that is cycled between 4.2 and 298 K and so qubits based on phosphorous ions would probably be operated at cold temperatures where their even longer coherence time would be an asset. However, he points out that such a system could be used to create “quantum money”, which in principle would be impossible to counterfeit.

The serial number of a “banknote” could, for example, be encoded into the nuclear spins at 4.2 K before the system is heated to room temperate and carried about until it is “spent” by cooling it down. The serial number could then be read out, but a counterfeiter trying to copy the quantum serial number would be thwarted by the “no-cloning” theorem of quantum mechanics, which prevents an unknown quantum state to be copied.

Although the team has shown that ionized phosphorous qubits can endure for very long times, there is more work to be done before the nuclear spins could be used in a quantum computer or quantum money. The measurements were made simultaneously on a collection of about 10 billion ions and physicists must now work out how to read and write information to an individual ion – and also how to get two or more ions to interact with each other to create quantum-logic devices.

Thewalt told physicsworld.com that physicists at the University of New South Wales in Australia have already worked out a way of reading and writing information to individual ions – albeit at low temperatures – and are now looking at how they could be entangled. Meanwhile, Thewalt’s team is now looking at other atoms in silicon, including arsenic, antimony and bismuth.

The research is described in Science.

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