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Quiz of the year 2012 goes interactive

By Margaret Harris

A quiz of the year’s events has been a regular feature of Physics World‘s print edition since 2004, and in some years we’ve posted it on physicsworld.com as well. This year, however, we’re doing something different. For the first time, we’ve created a fully interactive version of the quiz, dragging it kicking and screaming into the Web 2.0 era.

The 2012 quiz can be found here and you’ll be able to check your score once you’ve gone through all of the 24 questions. Each question is based on an event or story that Physics World magazine has reported on this year, although it’s fair to say that some stories (such as the probable discovery of the Higgs boson) got more publicity than others (such as the version of Monopoly based on the life of a certain UK scientist).

Sadly, there is no prize except the “bragging rights” of getting a higher score than your friends and colleagues, but we hope you enjoy taking part.

The December 2012 issue of Physics World is out now

By Matin Durrani

If you’re a member of the Institute of Physics, it’s time to tuck into the December 2012 issue of Physics World, which contains a bumper reviews section with our pick of the best books for Christmas, including an extended Between the Lines.

We also take stock of the recent six-year jail sentences given to the seven Italian scientists and engineers who were members of the risk committee that gave advice to the public before the devastating 2009 L’Aquila earthquake.

If you’re a member of the Institute of Physics (IOP) you can access the entire new issue online through the digital version of the magazine by following this link or by downloading the Physics World app onto your iPhone or iPad or Android device, available from the App Store and Google Play, respectively.

For the record, here’s a rundown of highlights of the issue:

• Jail terms rock seismology – Jon Cartwright examines the fallout from the case of the seven earthquake experts who were recently jailed for making apparently misleading statements before a devastating earthquake hit the Italian city of L’Aquila in 2009

• Putting science on trial – Warner Marzocchi warns that the decision to sentence seven earthquake experts to six years in prison during the recent trial in L’Aquila could set a dangerous precedent for science

• Physics and painting – Robert P Crease looks at several books that examine how physics influenced artistic movements

• Unknown genius – A visionary who saw far ahead of his contemporaries, Edward Hutchinson Synge has been largely overlooked by the academic world, from which he worked in isolation before he was confined to a mental hospital at the age of 46. Denis Weaire, John F Donegan and Petros S Florides uncover his remarkable story

• Voyager – a mission for life – There may be no such thing as a “job for life” these days, but NASA’s Voyager mission to Jupiter, Saturn and beyond has kept hundreds of scientists busy for as much as 35 years. Mark Williamson reveals how researchers stay motivated and scientifically productive during such a long-term project

• Vital forces – Richard Jones reviews Life’s Ratchet: How Molecular Machines Extract Order from Chaos by Peter M Hoffmann

• What made Bell Labs special – Andrew Gelman reviews The Idea Factory: Bell Labs and the Great Age of American Innovation by Jon Gertner

• The why and how of it all – Tim Maudlin reviews Why Does the World Exist: an Existential Detective Story by Jim Holt and A Universe from Nothing: Why There is Something Rather than Nothing by Lawrence Krauss

• Forming a critical mass of experts – Geoff Vaughan reviews The Neutron’s Children: Nuclear Engineers and the Shaping of Identity by Sean F Johnston

• Von Neumann’s computer – Martin Campbell-Kelly reviews Turing’s Cathedral: the Origins of the Digital Universe by George Dyson

• New beginnings for nuclear – Jeroen Veenstra describes how his enthusiasm for nuclear energy led him to a new country, a new language and a role in developing the energy future

• Once a physicist – Meet Nick Dunbar – a financial journalist and editor of the Bloomberg Risk newsletter

If you’re not yet a member, you can join the IOP as an imember for just £15, €20 or $25 a year via this link. Being an imember gives you a full year’s access to Physics World both online and through the apps.

Table-top test targets quantum foam

One of the biggest challenges in physics – finding evidence for quantum gravity – could be tackled using a simple table-top experiment, according to Jacob Bekenstein from the Hebrew University of Jerusalem. Bekenstein, who is best known for studying the thermal properties of black holes, has come up with an interesting new proposal for using single photons to probe what is known as “quantum foam”. The foam, which was introduced in 1955 by the US physicist John Wheeler, is believed to exist on length scales so small that quantum fluctuations affect space–time.

Bekenstein’s proposal is the latest effort in the quest to understand how quantum mechanics can be unified with Einstein’s general theory of relativity – a problem that has eluded physicists since they first began to understand the quantum and relativistic worlds in the early 20th century. One of the main reasons why physicists have struggled with developing a theory of quantum gravity is a complete lack of experimental evidence. The problem is that the effects of quantum gravity are only expected to be measurable over extremely small distances.

Some theories of quantum gravity suggest that experiments must probe distances smaller than the Planck length, which is 1.61 × 10^–35 m. Probing this scale using an accelerator would involve colliding particles at enormous energies of more than 10¹⁶ TeV. This would be well beyond the capabilities of the Large Hadron Collider, which has a maximum collision energy of 14 TeV, or indeed of any conceivable future collider. Bekenstein’s proposal, in contrast, is much more modest; he says it could be done in a small physics lab mostly using existing equipment.

Photons at the ready

The experiment would involve firing single photons at a piece of glass or crystal, suspended by a tiny thread. When the photon moves from the vacuum into the material, it loses speed because the material has a higher refractive index than that of the vacuum. The result is that a tiny amount of momentum is transferred to the material, causing it to move an extremely small distance. In the case of a blue photon with a wavelength of 445 nm, Bekenstein says it would cause a 150 mg piece of high-lead glass to deflect by about 2 × 10^–35 m, which is on a par with the Planck length.

The bottom line is that if a photon is detected on the other side of the material, it means the mass was deflected by a distance greater than the Planck length. But if the energy of the photon is reduced (or alternatively the mass of the glass increased) until the deflection becomes equal to or smaller than the Planck length, then quantum gravity will affect how the glass responds to each photon.

In particular, Bekenstein believes that the presence of the foam would prevent the glass from recoiling in exactly the same way when struck by a succession of identical photons. Just as electromagnetic fluctuations can have measurable effects on much larger objects – an example being the Casimir force – space–time fluctuations should also affect how an object moves extremely small distances. In the case of Bekeinstein’s proposed experiment, photons would not be able to travel through the glass, which would be observed as a drop in the number of photons detected on the other side.

The experiment is challenging but not beyond what experimental physicists can do today
Jacob Bekenstein, Hebrew University of Jerusalem

Bekenstein admits that the experiment is “challenging”, but claims it “is not beyond what experimental physicists can do today”. Indeed, creating and detecting single photons is a routine part of quantum-optics experiments that are done in many labs around the world. Minimizing the effects of thermal noise will also be a challenge, with Bekenstein calculating that the apparatus must be cooled to about 1 K and operated in an ultrahigh vacuum of about 10^–10 Pa – both of which are achievable using existing technology.

Other table-top schemes

Bekenstein is not the only physicist to have proposed a table-top probe of quantum gravity. Earlier this year, for example, Igor Pikovski and colleagues at the University of Vienna and Imperial College London described a way of making optical measurements on a mechanical oscillator with a mass close to the Planck mass (about 22 μm). Indeed, Pikovski told physicsworld.com that Bekenstein’s plan seems feasible. “A big advantage is that physicists can control single photons very well and detect them extremely efficiently,” he says.

Pikovski also points out that the technique could prove very useful even if experimental issues prevent it from probing distances down to 10^–35 m. This is because some theories of quantum gravity predict that quantum foam or some other effect of quantum gravity could emerge at length scales as great as 10^–25 m.

While it is still not clear whether the table-top experiments proposed by Bekenstein, Pikovski or others will succeed, Pikovski believes that laboratory measurements will provide important information about quantum gravity within a decade or so.

The research is described in a preprint on arXiv and Pikovski’s proposal was published earlier this year in Nature Physics.

Prize-worthy books, part 2

By Margaret Harris

Well-written. Scientifically interesting. Novel.

These are the criteria we established in 2009 when Physics World started picking the year’s best physics books; and thanks to the current renaissance in science writing, we’ve never had trouble finding books that qualify.

In fact, the magazine reviewed so many good books in 2012 that we’ve decided not to rank them in a rigid top 10 list this year. Instead, we’ve drawn up a 10-strong shortlist (see below). Over the next few weeks, my colleagues and I will be trying to decide which of these outstanding books should be Physics World‘s Book of the Year for 2012.

We’ll announce the winner on 18 December during our regular books podcast, in which the genially impartial James Dacey will moderate while Physics World editor Matin Durrani and I champion a few of the books we like best.

In the meantime, though, we would love to hear your views on the shortlist. Is there a book that stands head-and-shoulders above the rest? Did we leave out your favourite among the books that Physics World reviewed this year? If so, let us know by e-mail at pwld@iop.org or vote for your favourite book from the shortlist below via our latest Facebook poll.

The shortlist for Physics World‘s Book of the Year 2012 (including brief descriptions and links to reviews).

A Hole at the Bottom of the Sea: The Race to Kill the BP Oil Gusher
After BP’s Macondo well blew out on 20 April 2010, company experts, government scientists and a “brain trust” of physicists assembled by US Energy Secretary Steve Chu spent months desperately trying to stem the flow of oil into the Gulf of Mexico. Joel Achenbach’s book about the disaster is a fast-paced and even-handed account of how things went wrong and who did what to fix them.

The Science Magpie: A Hoard of Fascinating Facts
Books of science trivia are a dime a dozen here at Physics World‘s reviews desk. Really good books of science trivia aren’t nearly as common. Simon Flynn’s grab-bag of stories from all branches of science exudes enthusiasm, breathing fresh life into a venerable format.

The Idea Factory: Bell Labs and the Great Age of American Innovation
In its heyday Bell Labs produced some of the most important and ubiquitous inventions of the modern era, from transistors and gas lasers to CCDs and wireless networks. Jon Gertner’s history of this “idea factory” describes what made Bell Labs special, and why none of today’s technological giants has replicated its success.

Erwin Schrödinger and the Quantum Revolution
Acclaimed science writer John Gribbin has written about Schrödinger’s physics several times before, beginning in 1984 with In Search of Schrödinger’s Cat. Now Gribbin is back with a biography of the man himself, skilfully combining Schrödinger’s scientific contributions with the quantum pioneer’s often complicated personal life and his legacy for both physicists and biologists.

The Geek Manifesto: Why Science Matters
In this polemical book, science journalist Mark Henderson argues passionately that science and critical thinking should be at the heart of public life, and he urges readers not to wait for someone else to make it happen. His book offers plenty of concrete suggestions on ways that so-called geeks can make their views count.

Life’s Ratchet: How Molecular Machines Extract Order from Chaos
Biophysics has mostly been left out of the boom in popular-physics writing, so we’re pleased to have Peter Hoffmann’s clearly written book about molecular motors and other nanoscale structures on our shortlist this year. Though not an easy read (particularly for physicists who haven’t studied biology since their schooldays), it does a very good job of capturing the excitement driving current research on this increasingly important topic.

How the Hippies Saved Physics: Science, Counterculture and the Quantum Revival
Quantum physics has always included some pretty trippy ideas, but its mind-blowing tendencies really came to the fore in the 1970s, thanks to a loose-knit group of physicists with a passion for Bell’s inequality and (in some cases) a penchant for psychedelic drugs. David Kaiser’s fascinating history of this unlikely bunch of insider-outsiders explains how they helped revive interest in the foundations of quantum mechanics.

How to Teach Relativity to Your Dog
Chad Orzel’s first book, How to Teach Quantum Physics to Your Dog, made it to No 2 on our list of 2010’s best physics books, thanks to its mixture of solid physics and gentle doggy humour. So it’s no surprise that its sequel has bounded into this year’s shortlist, ears cocked and positively slobbering with excitement at the prospect of a walk through Einstein’s special and general theories of relativity.

Pricing the Future: Finance, Physics and the 300-Year Journey to the Black–Scholes Equation
In the wake of the financial crisis, physicists on Wall Street have been harshly criticized, with no less an authority than Warren Buffet inveighing against “geeks bearing gifts” and the “financial weapons of mass destruction” they created. But how did physicists get into the financial industry in the first place? George Szpiro’s book brings the colourful history of econophysics to life.

Physics on the Fringe: Smoke Rings, Circlons, and Alternative Theories of Everything
Margaret Wertheim’s sociological study of physics crackpots is one of the year’s most thought-provoking books. Well argued and suffused with dry wit, this book asks important questions about what constitutes science and who gets to participate in it.

Vital forces

In many people’s minds, the primary focus of physics is on the very large (black holes, the distant universe and the problems of cosmology) or the very small (the Higgs boson and the other subatomic particles of high-energy physics). But there are some deep, unsolved mysteries of science that appear at scales much closer to our everyday experience. Of these, surely the most profound question is this: what distinguishes living from non-living matter? Ultimately, a naturalistic explanation of life must start with the blind forces of physics, but from these blind forces emerges the apparently purposeful action of living organisms, including ourselves. So what can physics contribute to the solution of this conundrum?

It is this question that physicist Peter Hoffmann attempts to answer in his book Life’s Ratchet: How Molecular Machines Extract Order from Chaos. Earlier generations thought that a so-called “vital force” had a literal and distinct existence, and by the early 19th century this force was beginning to be identified with the newly discovered and still mysterious phenomenon of electricity. But for Hoffmann, the road to understanding the vital force leads through statistical mechanics and his own experimental field: single-molecule biophysics.

Hoffmann covers this ground with an engaging mixture of historical sketches, homely analogies and personal anecdotes from his own experience as someone who trained as a condensed-matter physicist before striking out into new territory at the frontier between physics and molecular biology. The early part of the book contains some reiteration of familiar but important material on the subtleties of entropy. Thought experiments such as Maxwell’s demon get careful discussion, and Hoffmann gives due emphasis to the crucial point that requiring a global increase in entropy does not preclude local ordering, as demonstrated by the many self-assembly processes that occur at equilibrium.

The central image we are left with in this discussion is the “molecular storm” – the maelstrom of Brownian motion in which any biological nanoscale structure or mechanism has to exist, buffeted by the random thermal activity of the molecules around it. This is an unpromising environment, but such are the conditions under which the sophisticated nanoscale machines of cell biology must work. And as Hoffmann’s descriptions of various experiments demonstrate, these marvellously intricate molecular motors do not just work, they work astonishingly effectively and efficiently, and their collective action performs the familiar contraction of our muscles. This discussion brings us right up to date with current experiments and controversies in single-molecule biophysics.

The conceptual breakthrough that allows us to understand how a molecular machine can not only function in a Brownian environment, but even exploit its random motion, takes us back to an image familiar to many physicists from Richard Feynman’s famous lectures. Feynman’s “ratchet and pawl” argument illustrates that one cannot, without further input of energy, extract useful work from Brownian motion – as per the second law of thermodynamics. However, with an input of energy, you can rectify Brownian motion, using the forces generated by the random collisions of solvent molecules to generate directed motion. And it is this directed motion at the molecular level that, integrated to a large scale, leads to the purposeful motion of organisms. This idea is captured in a simple model by the French physicists Armand Ajdari and Jacques Prost: the Brownian ratchet. It is this concept that provides the “life’s ratchet” of the title.

Hoffman explains action but only begins to question purpose

As soon as one gets into the details of how any individual biological motor works, controversy starts, with the key question being “How applicable is this toy model to the particularity of that biological system?” Hoffmann’s coverage of the debate between proponents of “tightly coupled” motors and their opponents who favour “loosely coupled” models gives a flavour of the excitement associated with a field that is very much still developing. But ultimately, as Hoffmann correctly argues, these debates are about the details – fundamentally, all molecular motors are driven by the molecular storm of Brownian motion, whether or not the mapping to simple models is straightforward and easy to see.

In biology, details are important, and Hoffman does give us some of these by describing a variety of biological motors and what organisms use them for. The biology here is very rich, and as they skim past ATP synthase, helicases and RNA polymerase, some physicist readers may get the sense of rather too much biology being packed into too small a space. But we also learn about the physics details, such as what forces these molecules exert, and how these forces are measured through beautiful techniques such as force spectroscopy and optical tweezers.

Many things remain to be worked out, but Hoffmann makes clear that we are getting close to understanding part of what characterizes living matter. Such matter is capable of autonomous motion driven by molecular motors, which use an input of chemical energy to rectify the Brownian motion of the nanoscale environment. Hoffmann summarizes this view with the statement that “the force that drives life is chaos”. But there is still something missing here if we are trying to understand the purposeful action of living things: while Hoffmann explains the action, he only begins to address the question of purpose.

When we talk about the purpose of an organism, we can mean more than one thing. It is tempting to think that there is a purpose to an organism, one that is signalled by its design – but we know from Darwin’s arguments against the argument from design that this is treacherous ground. But organisms themselves have their own purposes. A bacterium swims away from a toxin or towards food because these actions might fulfil its purpose of maximizing its well-being. And Peter Hoffmann writes a book because this might fulfil his purpose of convincing other people that physics might be able explain some fundamental problems in biology. To provide a naturalistic explanation of how purpose, in this sense, arises remains a challenge that Hoffmann’s book only skirts around. Organisms process and integrate information about their environment, and depending on the outcome of that information processing, they act in one way rather than another. Underlying that act of “choice” must surely be the apparatus of signalling networks and gene regulation, and of the coupling of molecular shape change with the catalytic activity of enzymes that leads to chemical computing. And these most profound of scientific problems, too, must surely be susceptible to the insights and experimental techniques of physicists like Hoffmann.

What made Bell Labs special?

Bell Labs was a legendary place, an industrial lab in the outer suburbs of New York where thousands of scientists, working nine to five, changed the world’s technological history. Their inventions included the transistor, cellular communication networks and the theory of information, but amazingly, these were only a few of the major contributions to applied science and engineering that occurred in this set of famously close-packed labs. Year after year, Bell Labs scientists refined existing products and developed entirely new technologies. Those of us who spend time programming are familiar with Bell Labs as the home of C, Unix and the statistical package S (forerunner of the current open-source standard, R). And perhaps the most celebrated Bell Labs achievement in pure science was the 1963 discovery of cosmic microwave background radiation by Arno Penzias and Robert Wilson.

Coming up with the occasional breakthrough is one thing, but reliably producing innovation – that’s something special. It gets even cooler when you realize that so much was done at Bell Labs, and for so long, that the aforementioned discovery of Big Bang radiation – along with C, Unix, S and various fundamental, Nobel-prize-winning contributions to physics – go unmentioned in a new history of the labs called The Idea Factory. I say this not at all as a criticism of its author, the journalist Jon Gertner; rather, there was just so much going on at Bell that it cannot all fit in one volume.

Perhaps the most impressive part of the Bell Labs story is the workaday nature of its successes. Apart from Claude Shannon, inventor of information theory, the labs had no transcendent geniuses. True, William Shockley was a notable figure and, sure, John Bardeen is the only person to have received two Nobel prizes in physics. But they were not legendary minds on the scale of Fermi, Feynman or Von Neumann. Hence the fascination of Bell Labs as an idea factory where the institution gets as much credit as the scientists for the discoveries they made.

So what made Bell Labs special? To start with, it was well run, with managers who typically had strong technical track records of their own, appreciated scientific work and paid their staff enough to live comfortably – but not so much that they could just take their millions and quit. And as Gertner shows, Bell did benefit from some special circumstances. Monopoly profits meant the company could afford to hire top scientists and engineers, and with university jobs not paying very well and few get-rich-quick opportunities such as we have seen in Silicon Valley in recent years, the high pay and excellent working conditions at Bell Labs attracted many who might look elsewhere today.

Second, there was nothing to do at the labs all day but work. I have known lots of middle-aged professors who don’t spend much time teaching but don’t do any research either. At Bell Labs it was harder to be deadwood. Located as it was in the middle of nowhere, the Murray Hill campus was not a place to relax, and if you were going into the lab every weekday anyhow, you might as well work – there was nothing better to do. Several researchers, including Shannon and Shockley, had sharp mid-career productivity declines – but after they left Murray Hill.

In my own experience working at Bell Labs for three summers during the 1980s, I vividly recall a general feeling of comfort and well-being, along with the low-level intensity that comes from working eight-hour days, week after week after week. I did the research underlying my most-cited paper while working in complete freedom for six weeks at Bell Labs during the summer after completing my PhD. So maybe being stuck in the lab until 5 p.m. every day isn’t such a bad thing – though it might be impossible to replicate this sort of distraction-free workplace in the Internet era.

In its heyday from the 1940s to the 1970s, a Bell Labs job was said to be just like working at a research university, except the pay was better, the equipment was more up-to-date, the machine shop was available for all your needs and you didn’t have to spend time teaching or applying for research grants. At a university, research grants can be distorting – and mediocre researchers who happen to be good at getting them can stay on and on and on. At Bell, the financial motive was not grants but contributing to the company’s product lines. This seems reasonable to me, both because telephone service is a public good and because, as Gertner notes, the challenges of improving phone service motivated technical advances that benefited other areas as well. Although not mentioned in the book, Penzias and Wilson’s discovery is a good example, since it came as part of an effort to get cleaner telephone signals. There is, however, an irony here: as Gertner points out, Bell Labs scientists spent decades scrubbing the noise out of local and long-distance telephone calls, but the modern era of cell phones reveals that most customers prize convenience and connectivity ahead of sound quality.

In his concluding chapter, Gertner gives what I see as his book’s overriding message. “It is now received wisdom that innovation and competitiveness are closely linked,” he writes. “But Bell Labs’ history demonstrates that the truth is actually far more complicated…creative environments that foster a rich exchange of ideas are far more important in eliciting new insights than are the forces of competition.” Although competition has been “superb” at bringing “incremental and appealing improvements”, Gertner argues, “that does not mean it has been good at prompting huge advances (such as those at Bell Labs, as well as those that allowed for the creation of the Internet, for instance, or even earlier, antibiotics)”. This all sounds reasonable.

Gertner concludes that modern corporate labs do not allow the same combination of freedom and long-term thinking associated with Bell’s glory days. But perhaps, rather than asking where the next Bell Labs will come from, we as a society should be looking to create and support the next Massachusetts Institute of Technology. Gertner includes a tantalizing story of a proposal in the 1960s to create “Summit University,” a research institute in New Jersey that would have been closely connected to Bell and several other nearby industrial labs. The project was not carried out because the estimated $16m cost was deemed too high. In retrospect that decision seems unfortunate.

Italy cancels €1bn SuperB collider

Physics World can confirm rumours that the Italian government is to withdraw €250m from the €1bn SuperB particle accelerator, which was set to be built at the University of Tor Vergata on the outskirts of Rome. The decision, which effectively cancels the project, was made yesterday when Fernando Ferroni, president of the National Institute for Nuclear Physics (INFN), met Italian science minister Francesco Profumo to discuss funding for the project. “Given the difficult economic conditions of the country, the government is willing to confirm the contribution of €250m but not [for] the project,” says a government statement, which was released today and seen by Physics World.

As outlined in the statement, the INFN, which was set to build SuperB, will keep the €250m but will now spend the money on other projects. The INFN has already appointed two committees to look at what options it has, which includes converting SuperB into a scaled down “tau-charm factory” (called SuperC) or using the money elsewhere. The committees will report by 20 December, with a decision set for early January. Rumours of the funding cancellation first emerged on the blog A Quantum Diaries Survivor, which is written by the CERN-based researcher Tommaso Dorigo.

Mystery of antimatter

SuperB was designed to produce beams of electrons and positrons inside a linear accelerator to an energy of 6.7 GeV before injecting them into two rings each more than 1 km in circumference, where they would have then been collided to allow the decay of particles such as B mesons. The accelerator was expected to study the subtle differences in how particles and their antiparticles decay and could help shed light on the mystery of why there is so much more matter than antimatter in the universe.

One of the first things physicists were planning to look for is “charged lepton flavour violation” such as a tau lepton decaying into three muons without producing any neutrinos. The observation of such decays would point to new physics beyond the Standard Model. Indeed, earlier this year, physicists announced plans to add a free-electron laser to the facility, which would allow a range of research in materials science, biology and medicine, at a cost of around €75m.

Thumbs up?

Adrian Bevan from Queen Mary University of London – who is part of the UK’s SuperB contingent – told Physics World that the funding and construction plans for the project had only just undergone an independent review, which seemed to have given the project the thumbs up. Theoretical physicist Giorgio Parisi from the Laboratori Nazionali di Frascati, Rome, who has been a supporter of the project, told Physics World that he was “very disappointed” by the news.

SuperB was set to be built at a new site at the University of Tor Vergata called the Cabibbo Laboratory in honour of Italian particle physicist Nicola Cabibbo, who died in August 2010. The project would have been a competitor to Japan’s SuperKEKB – an upgrade to the existing KEKB collider – that is expected to come online by 2014 and will be able to produce more than 50 billion pairs of B mesons.

Physicists claim microwave-imaging ‘breakthrough’

Physicists in China say they have made a breakthrough in thermoacoustic imaging that could enable it to be used in hospitals within five years. The technique, which involves firing microwaves at tissue, had previously been considered too dangerous to use on humans, but the researchers have now employed what they say is a safer, nanosecond microwave source.

Thermoacoustic imaging was invented in the early 1980s. The idea is to expose tissue to a microwave pulse, which travels into the tissue until it is absorbed. Exactly how the pulse is absorbed depends on the type of tissue present. When the pulse is absorbed, it does not heat the tissue significantly because it is very short. The energy instead generates a moving deformation, which is an acoustic wave. The profile of this acoustic wave is detected using an array of transducers, and these data are used to create an image of the tissue through which the microwave pulse has passed.

The technique is considered attractive for certain patients, such as those at risk of breast cancer, because it has a higher contrast and is more penetrative than, for example, photoacoustic imaging. However, it has suffered from comparatively poor resolution, and the microwave doses employed hitherto have been considered unsafe for humans. For these reasons the technique has not yet been taken up by medicine.

Shorter, safer pulses boost resolution

Da Xing and colleagues at the South China Normal University in Guangzhou believe that thermoacoustic imaging could be a safe, high-resolution technique with the use of nanosecond microwave pulses. Theory suggests that the shorter the microwave pulse, the shorter the wavelength of the generated acoustic wave, and the higher the resolution. In addition, a shorter pulse reduces the exposure of tissue to harmful microwaves. The researchers’ breakthrough is to have developed such a nanosecond microwave source and apply it to thermoacoustics.

It’s great to see new applications of microwave technology finding their way to the biomedical-research community
Russell Witte, University of Arizona

“One obstacle in this area has been the difficulty getting access to cutting-edge pulsed-microwave technology, which has either been very expensive or highly classified in the US for many years,” says biomedical engineer Russell Witte at the University of Arizona at Tucson, US, who was not involved with the work. “So, it’s great to see new applications of microwave technology finding their way to the biomedical-research community.”

Xing and colleagues’ microwave source is based around a Tesla coil – a type of electrical transformer that can generate a high-voltage discharge. The researchers collect this discharge at a coiled antenna, which generates a microwave pulse of just a few nanoseconds’ duration. The subsequent microwave dosage, the researchers claim, is some 100 times lower than the safety standards set by the American National Standards Institute.

Tested on gelatin

The Chinese group tested the microwave source on samples consisting of copper wires, and rings made of gelatin. They found that they could image the samples at a resolution of 100 μm, which is five times better than previous thermoacoustic imaging devices. “Our device opens up exciting opportunities for non-invasive, high-resolution clinical thermoacoustic imaging,” says Xing.

Group member Cunguang Lou adds that, with suitable transducers for detection, the source could allow thermoacoustic imaging to be performed in real time, which has not been done before. “We can predict that thermoacoustic imaging will be used to image actual patients within five years,” he says.

“The scarcity of short-pulsed microwave sources has been a major bottleneck in the development of microwave-induced thermoacoustic tomography, which has the potential to image human bodies without using harmful X-rays or other ionizing radiation,” says biomedical engineer Lihong Wang at Washington University in St Louis, Missouri. He adds: “The development of this new microwave source will propel the growth of microwave-induced thermoacoustic tomography, especially toward microscopic imaging.”

The research is published in Physical Review Letters.

Cosmology, particle physics – and love

Still from the upcoming short film The Theory of Everything. (Courtesy: Catsnake)

By Matin Durrani

The e-mail arrived out of the blue last week. Did I want to attend a “private screening” in Covent Garden, London, of a new short film about cosmology, particle physics and love?

It sounded interesting, particularly when writer/producer Stephen Follows from Catsnake said that he had made the film with “some of the world’s leading dark-matter physicists, both at Imperial College and at CERN”.

I was even more intrigued when Follows added that the film had been funded by the Lovestruck dating agency as a promotional tool – apparently, the company was happy for him to make any film he liked, so long as it featured love somewhere along the line.

Follows took for inspiration the book The 4% Universe by the US science writer Richard Panek, which he had just been reading and which incidentally was second in Physics World‘s top 10 books of 2011. The title refers to the fact that “normal” matter makes up only 4% of the universe – the rest being dark matter (23%) and dark energy (73%).

What intrigued me was how exactly love could be brought into a story about cosmology.

Entitled The Theory of Everything, the film will be released online in early December so I won’t spoil the plot, such as it is. But suffice to say, the five-minute professionally produced film draws a parallel between the search for love and the search for dark matter. You know both are there even if you can’t see either for real. Love affects everyone just as dark matter and dark energy affect the universe.

If you think that sounds cheesy, well it could have been – in the wrong hands – but I was impressed with the film. It packs in a surprising amount of “real” science, which was accurate too, thanks to Imperial cosmologist Roberto Trotta, who acted as informal script adviser.

Visually, I liked the way the film tried to explain the expanding universe through the main character – an astronomer – dropping a jar of chocolate Smarties onto a table and showing them scatter in all directions. There’s also a nice touch where he uses the stem of a bunch of flowers as a measuring stick, snipping off the final 4% of the tip to illustrate just how small a fraction of the universe we really understand.

Both Follows and Trotta hope the film, which was made at an observatory in Mill Hill, London, reveals the human side of science. As Trotta told the audience before the screening, “There’s so much more to science and to creativity in science than meets the eye.”

Follows envisages the film being just the first in a series of projects carried out in partnership with Imperial. It will be released on YouTube and promoted on the London Underground and Facebook.

If you want some cosmic action before then, do check out our own film about a group of students trying to detect cosmic rays on a hot-air balloon.

Ultralight fractal structures could bear heavy loads

A team of researchers in Europe has shown that the density of large structures can be dramatically reduced, if they are designed using a fractal pattern. The researchers have worked out a way to calculate an optimal “hierarchal structure” built from a certain material so that it can withstand a given load. They claim that using such techniques could help in building highly efficient load-bearing structures that could be used in solar sails, cranes or other lightweight-yet-strong constructs.

A fractal is an object or a structure that is self-similar on all length scales. Fractal patterns are seen in nature at all scales – everything from a single fern leaf that resembles the entire plant, to clouds, snowflakes, blood vessels and cauliflowers shows a fractal pattern. A particular example that inspired this latest work is trabecular bone – the “spongy” bone that is found near joints in the human body. This bone has a sponge-like network of fibres that have a pseudo-fractal pattern, whereby the pattern is almost self-similar across a few scales. This makes the bone strong but light and capable of providing the necessary strength and stiffness.

Build and repeat

A hierarchical pattern – where the same base structure is repeatedly used at different length scales – is already used in architecture to build many large-scale structures. The Eiffel tower or large cranes are good examples of such structures, but such fractal patterns are used in architecture in a rather ad hoc manner, according to the researchers. Now, Yong Mao of the University of Nottingham, UK and colleagues have developed a theoretical framework for building structures where the optimal hierarchical order of the structure depends on the load it needs to withstand. Using this technique, the team constructed such a structure – a simple frame – from a polymeric resin, using a “rapid prototyping technique” – which is an advanced form of 3D printing.

For the first element in their structure, Mao and colleagues simply construct a hollow beam, which they refer to as the “generation-0” element. Different values of thickness and radii of the beam are considered, so that the strongest beam can be built, with the least amount of material. The robustness of this beam is then tested by applying a load along its length and along its axis, to see if it fails across either. “We do this to analyse the failure modes at each local level, so that the structure is not unnecessarily strong at each level…we optimize for what properties are necessary,” says Mao. He explains this further by saying that if a 50 kg table balanced on hollow steel legs it would be about 10 times lighter than one with solid steel legs and just as robust.

Generation-1 (left) and generation-2 (right) structures.

Generational changes

The next step, or “generation-1” structure, is a similar beam on a larger length scale. It is made up of the individual generation-0 beams in a triangular framework (see figure above, left). The generation-2 structure is then made by replacing each beam in the generation-1 structure with a full-scale version of itself, all assembled into a larger triangular frame. This can be repeated for one more level – a generation-3 element – and calculations show that the more hierarchical levels used, the less material that is needed to support a given load.

Strong structures

The team designed a number of different structures. It found, for example, that a crane boom made from generation-1 structures would be 100 times lighter than one made from solid steel. Another more fanciful application would be to use the technique to build the boom of a solar sail. These are large-scale structures in space that, in the future, could harvest solar radiation. The theoretical design for such sails involves booms that would be almost 100 m in length, but only need to be strong enough to withstand solar-radiation pressure. In this case, a steel generation-3 structure would be 10,000 times lighter than a solid beam.

3D printing

A drawback of this kind of fabrication is that imperfections could cause serious problems. “Even a small imperfection at a local scale could have a large impact as there is no extra material that could take the added stress and maybe that is why this kind of fabrication has not been practical to date,” explains Mao, who says that the team is also studying its models to better allow for such errors. But he is convinced that commercial techniques will improve over the coming year, providing the necessary precision tools. Mao also feels that the recently commercialized technique of 3D printing could really benefit the fabrication of these structures. “We could just upload our deferent designs to a program and people could download and print off the structures at home,” he says.

“In theory, a fractal would involve infinite number of generations…but that said, the same kind of complexity could be achieved in the future by assembling more and more generations,” says Mario Castro from Comillas Pontifical University in Spain, who was not involved with the work. “It would have been very intriguing if they had found a way in which these multiple-scale structures would have assembled by self-organization, as it happens in nature, but I think the work is really interesting.”

The work is published in Physical Review Letters.

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