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Home » Page 1329

Forming a critical mass of experts

A few years ago, some colleagues and I decided to set up a specialist group within the Institute of Physics (IOP) for physicists working in the nuclear industry. This task proved unexpectedly complex because questions were asked about the new group’s relationship to the IOP’s existing Nuclear Physics Group, its distinction from the Institute of Nuclear Engineers and – importantly – what it would be called. Eventually, we were able to set out an acceptable remit for the Nuclear Industry Group of the IOP, and all parties seemed satisfied with the result.

We did not realize it at the time, but I now suspect that our skirmish was only the latest in a long-running battle to determine an identity for nuclear professionals. In The Neutron’s Children: Nuclear Engineers and the Shaping of Identity, science historian Sean Johnston describes the opening salvoes in this battle, beginning with the nuclear-power programmes that sprang up in the US, UK and Canada in the aftermath of the Second World War. He follows them until the late 1960s, focusing firmly on the development of skills and expertise among the “nuclear engineers” who were needed to see these programmes to fruition.

The UK, US and Canada worked together on the Manhattan Project, but their nuclear interests diverged after the war’s end. This was partly down to the US’s McMahon Act of 1946, which excluded its wartime partners from information about nuclear systems, and forced the UK and Canada to develop their own. Initially, only the UK had a programme for power reactors, albeit one that was secondary to its programme for producing weapons-grade plutonium. However, it was not long before the US also began to think of nuclear power as a future source of electricity, and of reactors as a source for isotopes used in medicine and agriculture. Canada, for its part, had no interest in weapons, and put all its efforts into nuclear power.

Despite these different emphases, Johnston argues that all three countries faced the same questions. Who were the workers who would develop nuclear power systems? What knowledge did they need? What should be the roles of scientists (not just physicists, but chemists and biologists) and engineers? And which disciplines of engineering were required?

As Johnston shows, the difficulties of combining knowledge and approaches from science and engineering were not easily overcome. One of the barriers was geographic. In the US, scientific research was concentrated at the University of Chicago, while the Oak Ridge facility in Tennessee carried out engineering development and the remote Hanford site in Washington state hosted the plutonium production reactors. The UK also had clear distinctions between the different roles and sites. Harwell (Oxfordshire) carried out research, Risley (Lancashire) served as the engineering development centre and the reactors were built at relatively remote sites such as Windscale (Cumbria) and Dounreay (Caithness). One effect of this was that the sites had a tendency to work autonomously and not communicate well with each other, which led to poor overall control, as described by Harold Bolter in his book, Inside Sellafield. Efforts to mitigate this problem included, at one time, a regular private air service between north-west England and Dounreay in Scotland, where the landing was on the site runway from the days when the latter was a Fleet Air Arm base.

Even within a single site, the marriage between engineering and science was not always smooth. For example, the US plutonium production project was run by DuPont, a major industrial chemical firm. DuPont needed the scientists to determine the basic reactor physics data, and the scientists needed DuPont’s expertise in chemical engineering to produce a practical system. Eventually an uneasy collaboration led to more co-operation, and Johnston explains that this was thanks in part to the sterling efforts of scientists such as John Wheeler, who acted as an intermediary between DuPont and some of the more “recalcitrant” physicists, such as Eugene Wigner.

In the mid-1950s responsibility for training nuclear personnel (whether with scientific or engineering backgrounds) was largely in the hands of government-run facilities at Oak Ridge in the US, Chalk River in Canada and Harwell in the UK. All three operated reactor training schools, and it is worth emphasizing that they were entirely reactor-focused – the issue of waste was not high up on the agenda in those days, leading to many of our current clean-up and disposal problems. Gradually, though, university courses appeared to supplement site-based training. In the US, these included undergraduate courses, and this burgeoning university training – together with employment in both government-financed organizations and private companies – helped to clarify the identity of nuclear engineering as a profession. The UK, however, concentrated on postgraduate education, believing that while specific knowledge and expertise were necessary, these should be additional to basic training.

The UK’s engineering approach was also rooted more in practical expertise than formal qualifications, and site-based training for both scientists and engineers continued well into the 1980s. Partly as a result of this approach, the profession was slow to develop a separate status, and is arguably still not established. Canada, meanwhile, developed undergraduate courses in “nuclear engineering”, but their content was not easily defined and uptake was patchy, with many courses becoming unviable by the end of the 1960s. However, the relative absence of military influence on Canada’s nuclear specialists meant professionals there were less inhibited and their public visibility was high.

I joined the nuclear industry in the 1970s, which I suppose makes me one of the neutron’s grandchildren. However, many of the situations Johnston describes were still present. These included an uneasy alliance between scientists and engineers, who had different perks and conditions of employment; a lack of openness and a high degree of secrecy due to the industry’s military origins; and the relative geographical isolation of sites as a precaution against accidents. Johnston’s thesis is that these three characteristics, coupled with the industry’s origins in governmental programmes, were defining factors in the development of professional attitudes and approaches among nuclear practitioners. And all of them, Johnston argues, meant that members of the nuclear profession “might be perceived as suffering from arrested development, peculiar idiosyncrasies and worldview, insecure self-image, weak communication skills and poor socialization with their peers”.

I can recognize much of this generalization, as there were certainly a lot of oddballs around (and some today as well), although it does not seem to acknowledge the robust group lunchtime drinking culture that once prevailed. But nuclear power and its practitioners have other, more serious, crosses to bear. The industry, even when privatized, has never escaped the dead hand of government direction and manipulation. Nor has it really shaken off its military origins. Nuclear professionals have always had to fight battles for public acceptance, and today’s politicians seem to have no greater knowledge or willingness to face the real issues.

On the face of it, The Neutron’s Children might seem like a book of limited interest to the general reader, and the author’s punning use of terms from the nuclear field grates a bit (I say this even though – as the headline of this review shows – I do not mind a pun or two). Nonetheless, it is a fascinating account of how an entire industry developed from very sparse beginnings and, like all good histories, it offers lessons to be learned. The nuclear profession was created in a relatively short period after the Second World War, but its members were never given the security of future employment that would ensure a continuing cadre. Instead, there has been a waxing and waning of interest in nuclear power and, as a result, we are losing the continuity of our nuclear knowledge and expertise. If we are to fulfil the “nuclear renaissance” goal of developing and providing carbon-free electricity, we need to focus on creating the neutron’s great-grandchildren, and several generations beyond that – whatever we decide to call them.

Physics and painting

Discoveries in science do not just revolutionize science, but can also exert a deep and lasting impact on the visual arts and on literature. One famous example is the effect that Galileo’s telescopic discoveries had on Milton’s poetry, such as in his depiction of the cosmos in Paradise Lost. Writing about connections between physics and art, however, is difficult to do well. It is easy to draw superficial connections, but hard to establish genuine artistic motivation. Fortunately, several original and substantive books have recently appeared or been reissued that shed new light on how physics influenced art, and illustrate – quite literally – their points well.

Consider the groundbreaking book The Fourth Dimension and Non-Euclidean Geometry in Modern Art by the University of Texas art historian Linda Dalrymple Henderson, which was first published in 1983 and has just been reissued with a revised introduction. The book reviews late 19th-century developments in non-Euclidean geometry and the rise of popular interest in these geometries, and then examines this impact on painting in the first half of the 20th century.

Among topics of popular fascination was the ether – the invisible medium that supposedly filled space – which prominent scientists of the day linked with the fourth dimension as containing “the invisible order of things”. Other widely publicized physics discoveries involving invisible structures of reality included the electron, radioactive elements and X-rays. As the science historian Iwan Rhys Morus is quoted in the book as saying, at the start of the 20th century, “the boundaries of the real were so weak”.

Henderson insightfully describes how and why artists listened and responded creatively to these developments. Cubists connected their work most explicitly with the fourth dimension, but they were not alone. Henderson argues that, during the first three decades of the 20th century, the fourth dimension was a “concern common to artists in nearly every major modern movement [in painting]”. The idea of the fourth dimension encouraged artists to dispense with traditional perspective and to experiment with abstraction. It also re-energized their picture of themselves as visionaries able to communicate structures of reality that others could not detect.

For the first two decades of the 20th century, the fourth dimension was popularly associated with space. But after the 1919 confirmation of Einstein’s theory of general relativity, and Minkowski’s introduction of the notion of space–time, the fourth dimension began increasingly to be associated with time. This was still true when Henderson’s book first came out in 1983. Since then, the rise of string theory, brane theory and computer graphics have rehabilitated the artistic influence of the spatial interpretation, which Henderson covers in a new, 96-page “reintroduction” in the updated edition of her book.

Surrealist thinking

Modern physics also had a huge impact on the artistic movement known as Surrealism – a topic covered in Gavin Parkinson’s 2008 book Surrealism, Art and Modern Science: Relativity, Quantum Mechanics, Epistemology. Parkinson, who is an art historian at the Courtauld Institute of Art in London, shows that Surrealist artists responded in a culturally sophisticated manner to the complex political, philosophical, psychological and scientific climate of the time. Claiming to offer “the first comprehensive history, analysis and interpretation” of Surrealism’s enthusiasm for modern physics, Parkinson begins with a sketch of the early history of relativity and quantum theory – a section of the book that, he says, was a “nightmare” to write. However, physicists will find his account, which draws on authoritative histories, both accurate and engaging.

Parkinson then traces how (mainly French) Surrealist artists and authors appropriated the language, concepts and imagery of modern physics in defining and creating their work. One of the first was André Breton, Surrealism’s “chief theorist”, who was soon followed by Marcel Duchamp, Max Ernst, Salvador Dalí and others. Relativity and quantum mechanics inspired them, Parkinson writes, by showing the utter conventionality of 3D space and ordinary sense perception, and by revealing new aspects of the real.

Breton’s collaborator, Pierre Mabille, wrote in 1940 that physicists are “the legitimate heirs to the tradition of the marvellous”. Indeed, Parkinson argues convincingly that the main currents of modern art cannot be fully understood without knowing the impact of modern physics on the artists involved. Parkinson is not afraid to point out, however, where the artists were “facile”, “engagingly frivolous”, or simply out of their depth in appealing to physics concepts and imagery.

“Like a damp stained wall,” Parkinson writes, “quantum theory can conjure up just about any view of the world if stared at long enough.” But he shows brilliantly why these artists saw what they did, and how they incorporated it into their work. His story ends when Hiroshima began to end the love affair with modern physics, with the break-up culminating in 1958 with a Surrealist manifesto called Expose the Physicists, Empty the Laboratories.

The critical point

Henderson’s and Parkinson’s books document the impact of specific scientific discoveries on particular art movements in a thorough and careful way. Other books that discuss intersections between physics and science in an engaging, though less scholarly, way include Lynn Gamwell’s Exploring the Invisible: Art, Science, and the Spiritual (2002) and Leonard Shlain’s Art and Physics: Parallel Visions in Space, Time, and Light (1991, reprinted 2007). Gamwell is a curator and art historian, and her book is lavishly and cleverly illustrated; Shlain, who died in 2009, was a surgeon by training and wrote as an enthusiast rather than as an artist or scientist.

To me what is fascinating is just how physics exerts an influence on art in so many different ways. It has also influenced sculpture, music and literature – topics that I’ll have to leave to future columns. In the meantime, I welcome your thoughts on the matter.

Magnetic metamaterials could boost wireless energy transmission

Physicists in Spain have calculated that substantial amounts of energy could be transmitted through air by using special materials to shape the magnetic fields around conductors. Although the concept has yet to be verified in the lab, the researchers say that it could lead to a viable method of transmitting electrical power, as well as applications in magnetic sensors and studies of the brain.

The idea of transmitting significant quantities of electrical energy without using wires has a long history. In 1891 Nikola Tesla showed that electricity could be sent through the air using induction coils. He continued to work on the idea alongside his work on wired transmission, but energy losses prevented its large-scale implementation.

Now Alvar Sanchez and colleagues from the Autonomous University of Barcelona have used the theory of transformation optics to propose a new way of concentrating and transmitting electrical energy. Transformation optics is usually associated with creation of invisibility cloaks, superlenses and other devices that guide and focus electromagnetic waves in ways not possible with conventional materials. This is done using metamaterials with special optical properties that transform space in much the same way as the presence of mass deforms space – as described in Einstein’s general theory of relativity. In the case of an invisibility cloak, electromagnetic waves can be made to move smoothly around an object, joining up on the other side as if the object wasn’t there.

Magnetic cloaking

The Barcelona-based team has already published a series of papers that apply transformation optics to magnetic fields. In 2011 the researchers collaborated with electrical engineers at the Slovak Academy of Sciences to build a cloak that shields a region of space from static magnetic fields. Now in this latest research, they have focused on how transformation optics could be used to cause a magnetic field in one place to induce a field somewhere else.

The team created a computer model of a transmitter-receiver system with a magnetic field source at the centre of a shell. The shell is made from a metamaterial with a magnetic energy density that would always be zero. In the case of power transmission, the magnetic field source would be a current-carrying coil.

The presence of the shell causes all the energy contained in the inner field to be delivered to the outer edge of the shell. Therefore the magnetic field radiated around the magnet into space is much stronger than if the shell had been a normal magnet or free space. If a second metamaterial shell were placed close by, the magnetic field of the first shell would then induce a magnetic response on the surface of the second shell. In this case, the effect of the shell is to transfer magnetic energy from outside of the shell to the centre of the shell without any loss.

Low frequency fields

So far, so good – however there is one important caveat. Strictly speaking, the analysis only applies to static magnetic fields. To transfer the energy of an electric current by creating a magnetic field – and then extract the energy as an electric current at the other end – would involve a magnetic field that changes with time. Nevertheless, Sanchez explains that the researchers have preliminary data suggesting that the analysis holds for very low frequency fields. “If we want to extract useful energy from our ideas, it is true that we should work on low-frequency AC fields,” he says.

Beyond energy transmission, the researchers suggest the ability of the shell to concentrate magnetic fields into a small space could enhance the accuracy of magnetic sensors. This could extend the reach of a medical research technique called transcranial magnetic stimulation, in which parts of the brain can be temporarily activated or deactivated by magnetic fields.

Transformation optics pioneer John Pendry of Imperial College London is intrigued by this latest proposal and by the researchers’ previous work using transformation optics to manipulate magnetic fields. He finds the work with static magnetic fields to be “even more exciting than optical cloaking, because it demonstrates the unique power of transformation optics to operate not just on rays of light, but to get inside the wavelength (infinitely long for static fields) and control the electric and magnetic field components of electromagnetism.”

The research will be described in a forthcoming issue of Physical Review Letters.

Higgs hunters and Stephen Hawking bag new $3m prizes

A massive $3m in prize money is to be shared by seven physicists who headed CERN’s Large Hadron Collider (LHC) and its two main experiments – ATLAS and CMS – since 1994. The award – given for the discovery of a Higgs-like particle at the LHC – is one of two “special fundamental physics prizes” from the Fundamental Physics Prize Foundation, which was set up earlier this year by the Russian physicist-turned-entrepreneur Yuri Milner. Another prize of $3m has gone to the British cosmologist Stephen Hawking for his work on black holes, quantum gravity and the early universe.

One of the winners at CERN – CMS spokesperson Joseph Incandela – told physicsworld.com that he was “very happy” to win the prize. “It recognizes the huge effort of so many great people who provided so much creativity and brilliance to the experiments and the LHC accelerator complex that made this all possible,” he says. “I am honoured to be the leader of the experiment now, but I am like many others in the experiment who have spent 15 or 20 years of their career on this project.”

The six other CERN physicists to share in the prize are Lyn Evans, who masterminded the construction of the LHC, current ATLAS spokesperson Fabiola Gianotti and her predecessor in the job Peter Jenni, as well as Michel Della Negra, Guido Tonelli and Tejinder Singh Verdee, who are all from the CMS collaboration.

In an e-mail to the Guardian newspaper, Hawking said that “prizes like these play an important role in giving public recognition for achievement in physics” but added that “no-one undertakes research in physics with the intention of winning a prize”.

Fundamental matters

The Fundamental Physics Prize Foundation has also announced the winners of its three 2013 Physics Frontiers prizes. One Frontiers prize has gone jointly to Charles Kane of the University of Pennsylvania, Laurens Molenkamp of the University of Würzburg and Shoucheng Zhang of Stanford University for their prediction and discovery of topological insulators. The second award goes to Alexander Polyakov of Princeton University for his work on field theory and string theory, while the final prize is given to Joseph Polchinski of the University of California, Santa Barbara.

These winners of the Frontiers prizes all go on the shortlist for the 2013 Fundamental Physics Prize, which is worth $3m and will be awarded in March. Any Frontiers winner who does not scoop the main prize will still receive $300,000 each.

The foundation has also revealed the three winners of its 2013 New Horizons in Physics prizes. These are Niklas Beisert of ETH Zürich for his work on quantum gauge theory and string theory, Davide Gaiotto of the Institute for Advanced Study in Princeton for “far-reaching insights” into duality, gauge theory and geometry, and Zohar Komargodski of the Weizmann Institute of Science for his work on 4D field theories. Each theorist will receive $100,000.

Yuri Milner, 51, originally studied theoretical physics at Moscow State University but dropped out of a PhD in theoretical physics at the Lebedev Physical Institute. After a stint working at the World Bank in Washington, DC, he turned to investing in start-up companies, apparently making his millions by investing in Internet firms such as Facebook, Twitter and Zynga. The October 2012 issue of Bloomberg Markets magazine named him as one of the 50 most influential people who “move markets or shape ideas or policies”.

Flexible graphene transistor sets new records

Researchers at the University of Texas at Austin in the US say that they have made state-of-the-art flexible graphene field-effect transistors with record current densities and the highest power and conversion gain ever. The transistors also show near-symmetric electron and hole transport, are the most mechanically robust flexible graphene devices fabricated to date, and can be immersed in a liquid without any ill effects.

Graphene is a single, flat sheet of carbon arranged in a honeycombed lattice. It has many unique electronic and mechanical properties, such as extremely high carrier mobility – which means that it is an ideal material for use in ultrafast transistors. The material can also absorb light over a range of wavelengths in the electromagnetic spectrum from the visible to mid-infrared and is highly transparent to light. The fact that it is mechanically flexible while being incredibly strong is good news too.

The researchers, led by Deji Akinwande and Rodney Ruoff, made their graphene field-effect transistors (GFETs) directly atop patterned dielectrics on plastic sheets using conventional microelectronic lithography. The devices have a unique structure, explains Akinwande, in which multi-finger metal gate electrodes are embedded in the plastic sheet. They are also made using graphene that has been grown by chemical vapour deposition (CVD), which can now produce as good graphene flakes as can be obtained by exfoliation (the famous “sticky-tape” method).

Record properties

The innovative production technique means that graphene can easily be integrated and fabricated on plastic sheets that have been pre-patterned with metal gates. This produces transistors in which charge carriers can move extremely fast and in which electrons and holes move in the same way. The devices are also extremely compliant and can accommodate mechanical strains of up to 9% and can be bent and unbent over for more 20 continuous cycles – a record number for flexible GFETs.

“Overall, our transistors feature record circuit performance, the largest mechanical bending and the highest extrinsic cut-off frequencies (of about 2.23 GHz) to date for any graphene flexible nanoelectronic device,” says Akinwande. “What is more, the devices are liquid-resistant thanks to the fact that the surface of the graphene is passivated with silicon nitride and the plastic substrate is self-passivated. In short, we found that they could be accidentally dropped into everyday liquids, such as milk, tea or coffee, and can even survive being run over by a moving vehicle – all without suffering damage to their outstanding properties.”

Smart applications

The extremely flexible, high-performance devices could be ideal for smart, conformal, advanced electronics that could offer performance capabilities beyond today’s silicon-based technology while also being cheaper, lighter, more environmentally friendly and with arbitrary form factors, claims Akiwande. “Potential applications include flexible smartphones, displays, fabric and even smart walls,” he adds.

The team, which is presenting its work this week at the International Electron Devices Meeting in San Francisco, is now busy trying to make flexible wireless radios and mobile systems using the new GFETs at gigahertz frequencies. “From a basic research point of view, we are also looking into heat management in these devices on flexible plastic substrates, which is a major issue for transistors operating at high speeds and current densities,” adds Akinwande.

Laser pulse makes insulator conduct like a metal

An international team of physicists has shown that an extremely short pulse of light can be used to convert an insulator into a metal, allowing an electrical current to be switched on and off for intervals as short as a few femtoseconds. The technology could be used to create transistors that are 10,000 times faster than those available today. The effect could also form the basis of a cheap and easy way of characterizing ultrafast laser pulses – something that is currently very expensive to do.

The work is reported in two papers by the team that appear in the journal Nature. In the first paper, Agustin Schiffrin and Ferenc Krausz of the Max Planck Institute for Quantum Optics in Germany, Mark Stockman of Georgia State University in the US and colleagues describe what happens when you fire short yet intense laser pulses at a sample of silicon dioxide.

Silicon dioxide is an insulator with an energy bad gap of about 9 eV separating its valence and conduction bands. In contrast, the band gap in silicon is about 1.1 eV; this means that, in principle, a switch made from silicon dioxide could operate much faster than a conventional silicon switch. The problem, however, is that a silicon-dioxide switch would have to operate at very high electric fields, resulting in a destructive electrical breakdown.

Closing the gap

One way round this problem is to apply a strong electric field for an extremely short time, so that breakdown does not occur. When the field is applied, some of the electron states in the valence band increase in energy while some states in the conduction band decrease. The upshot of this is a significant reduction in the amount of energy required to create a conduction electron and the material becomes an electrical conductor.

The team created this brief electric field using laser pulses that are only 4 fs long – so short that they only contain about 1.5 cycles of an electromagnetic wave. The pulses are fired at a piece of silicon dioxide that has two gold electrodes on its surface. They are aimed at the 50 nm gap between the electrodes and the light is polarized so that its electric field is parallel to the silicon-dioxide surface and oscillating back and forth between the two electrodes (see figure).

Sweeping back and forth

The pulse creates conduction electrons, which feel the force of the pulse’s electric field. These are first swept towards one gold electrode and then towards the other as the direction of the field switches. This effect is measured by connecting the two electrodes by an ammeter and measuring the current.

To show that the band-gap modification and current generation were independent processes, the team did a second experiment involving two pulses. One pulse had its electric field running along the gap so it cannot sweep electrons towards the electrodes but can still modify the band structure. The second pulse had its electric field running between the electrodes. The second pulse was set at a much lower intensity, so it was able to sweep conduction electrons but not modify the band structure. As expected, a current was still seen.

While the experiment shows that a semiconductor can be switched to a conductor on a timescale of about 1 fs, it does not give direct evidence that the system reverts back to a semiconductor on a timescale of about 1 fs – something that would be crucial for building circuits that operate on femtosecond timescales.

Confirming femtosecond shutdown

To do this, the team did a second, more complicated experiment that is described in the second paper. This involved measuring the absorption and reflectance of light from a silicon-dioxide sample – which confirmed that the effect is indeed shut down in about 1 fs.

Schiffrin describes the work presented in Nature as a proof of principle that an intense, ultrafast laser pulse can be used to switch a solid-state device. “Now we can fundamentally have a device that works 10,000 times faster than a transistor that can run at 100 GHz,” Stockman adds. In order to explore this possibility, the team is now looking at how it could hook up two switches to make a logic gate. Coupling between devices could be achieved using plasmonics – which involves quantized oscillations of conduction electrons in a material.

While it may be straightforward to create such logic devices in the lab, anyone wanting to make practical commercial devices would first have to create low-cost lasers that can deliver the appropriate pulses. While this would be a significant technological challenge, Schiffrin believes that it should be possible.

In the shorter term, Schiffrin says that the silicon-dioxide and gold structures could prove very useful for characterizing the output of ultrafast lasers – something that currently involves measurements done in an ultrahigh vacuum and using expensive electron spectrometers. Indeed, the team already has a patent on that particularly application, says Schiffrin.

Which physics setting would be the best for a Hollywood movie about love?

By James Dacey

Facebook poll

Dark matter, dark energy and telescopes are not necessarily themes that you would expect to feature heavily in a short film about love. But they do in a new short film called The Theory of Everything that captures a romantic episode between two researchers working at a fictional observatory in Chile.

The film is described in this blog entry by my colleague Matin Durrani, who attended the film’s première in London. Matin quite enjoyed the film. I’ve got to say that I found the result slightly too far towards gorgonzola on the cheese scale – right from the opening scene where you see the observatory is called “Querido”, which roughly translates as “darling”. But I do really love the concept of the film and it got me thinking about different locations Hollywood filmmakers might consider when shooting their next feature-length movie. Can you imagine a rom-com set at CERN, for instance? Or a long, tension-filled love affair filmed at a big physics conference like the MRS March meeting?

What do you think? Let us know by taking part in this week’s Facebook poll.

Which physics setting would be the best for a Hollywood movie about love?

A particle-accelerator facility
A physics conference
An observatory atop a remote mountain
The International Space Station
A university research laboratory
Another location (please suggest by posting a comment)

To place your vote, visit our Facebook page.

In last week’s poll we asked you to pick which book you think should be Physics World‘s Book of the Year for 2012, presenting you with our shortlist of 10. The book that came out on top with 50% of votes was How the Hippies Saved Physics by David Kaiser. We’ll announce Physics World‘s choice of Book of the Year on 18 December, when our regular books podcast is released on physicsworld.com.

GRAIL mission peers beneath the Moon’s fractured surface

The first results from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission have been released. The new high-resolution gravity data reveal surface structures that were not previously seen. The data have also shown that the lunar crust is less dense and more fractured by massive impacts than had previously been thought. The mission has also spotted subsurface dykes buried deep within the lunar surface – these suggest that the Moon experienced a period of expansion while it was still forming. Furthermore, the GRAIL data have been used to create the highest resolution gravity map of a celestial body other than Earth.

Launched in September 2011 from Cape Canaveral in the US, the main aim of the $495m mission is to accurately map the gravity of the Moon using twin spacecraft named Ebb and Flow. GRAIL entered lunar orbit in December 2011 and its prime-mission science phase stretched from 1 March to 29 May this year, during which its twin spacecraft were in tandem orbits around the Moon at an average altitude of 55 km.

Far side of the Moon

The Moon is an ancient, airless, waterless body that is untouched by erosion – this means that its surface and interior preserve a record of what was going on in the young solar system. However, it has been difficult to study the Moon’s gravity and interior in its entirety because only one hemisphere ever faces the Earth. To overcome this, the GRAIL mission involves the continuous monitoring of tiny changes in the distance between two spacecraft as they orbit the Moon. These changes are caused by perturbations in the Moon’s gravitational field, which are related to topographic features and changes in density below the lunar surface. From these measurements, the researchers stitched together a high-resolution gravity map that shows that the Moon’s internal gravitational field is consistent with an extremely fractured crust.

Three papers based on the new data have been published in the journal Science by the international team of GRAIL researchers. In the first paper, head of the GRAIL mission Maria Zuber, of the Massachusetts Institute of Technology, and colleagues focus on the overall gravity map of the Moon and point out previously unseen tectonic structures. These include volcanic landforms, basin rings and crater peaks. Surprisingly, the team also found evidence that beneath the surface the lunar crust is almost completely pulverized. This suggests that during the first billion years of its life, the Moon may have endured much more fracturing from massive impacts than previously thought. This would also apply to the Earth and other terrestrial planets, and could have an important effect on planetary evolution.

GRAIL and LRO data graphic
GRAIL and LRO graphic

Tantalizing topography

To find the gravitational field for the Moon’s interior alone, Zuber’s team used topographic measurements from a laser altimeter aboard the Lunar Reconnaissance Orbiter (LRO), a separate spacecraft in orbit around the Moon. The scientists calculated the gravitational field that they expected the Moon’s topography to produce and then subtracted that field from the field measured by GRAIL. The team found that most of the local variations in the Moon’s gravity are caused by surface features, such as crater rims and mountains.

In the second paper, Mark Wieczorek, of the Institut de Physique du Globe de Paris, and colleagues show that the density of the Moon’s upper crust is less than previously thought and probably more porous. In most places on the Moon, they researchers found that the crust ranges in thickness from 34–43 km. However, the team also found that the crust beneath some major basins is now almost non-existent, indicating that early impacts may have excavated the lunar mantle.

Expanding theories

In the third paper, Jeffrey Andrews-Hanna, of the Colorado School of Mines, and colleagues report that the lunar crust appears to be riddled by igneous dykes. These are large sheets of cooled magma – hundreds of kilometres across – that seeped into the crustal fractures. The team believes that the dykes may have formed during a period of expansion early in the Moon’s history. According to Zuber, such fractures could affect the way a planetary body loses heat, while providing a pathway for the transport of fluids in its interior.

The researchers also point out that both GRAIL spacecraft have performed better than expected – the spacecraft are 200 km apart and they need to accurately measure the changes in the distance between them to within a few tenths of a micron per second. Instead, the spacecraft have outperformed and can resolve changes in distance to several hundredths of a micron per second.

Currently, GRAIL is on its extended mission for another three months, for which the team has a new set of objectives. The spacecraft have been lowered to half their original altitude; being closer to the Moon’s surface will greatly increase the resolution of collected data. The researchers are keen to see what new results the data will reveal.

The why and how of it all

“Nothing” is a tricky concept. Consider Descartes’ peculiar argument against the possibility of a vacuum: “If someone asks what would happen if God were to take away every single body contained in a vessel, without allowing any other body to take the place of what had been removed, the answer must be that the sides of the vessel would, in that case, have to be in contact. For when there is nothing between two bodies, they must necessarily touch each other.” Descartes, like many others, has confused the concept of a vacuum with that of nothing: a vacuum is empty space, but the empty space in the bell jar is still something. It has properties such as size and shape even if it fails to contain matter.

The distinction between a vacuum and nothing plays a central role in both Jim Holt’s Why Does the World Exist? An Existential Detective Story and Lawrence Krauss’s A Universe From Nothing: Why There is Something Rather than Nothing. By their titles, one might expect Krauss’s book to answer Holt’s question. But both authors tend to run together two distinct questions. One – Holt’s main quarry – is “Why is there something rather than nothing?” In Krauss’s book, the question that predominates is “How can something come from nothing?”

The predilection to regard these two questions as equivalent is puzzling, for no-one would confuse the question “Why is the universe matter rather than antimatter?” with the question “How can matter come from antimatter?”. The fact that “nothing” means different things in the two questions makes the muddle more severe. The nothing in Holt’s question is a state of universal and total absence: no matter, no fields, no laws, no space, no time, ever. The nothing in Krauss’s question is a different beast: for most of his book, “nothing” means a vacuum state in some physical theory.

Holt is a journalist with a background in philosophy, and his question is philosophical, so he consults philosophers. Adolf Grünbaum argues that there is no problem: the felt need for an explanation arises from an unjustifiable conviction that nothingness is somehow more probable or expectable than the existence of something. Absent any principle for preferring nothing over something, no explanation is required. Holt finds no flaw in Grünbaum’s argument, but it still does not feel right to him, so he presses on with other philosophers, physicists, theologians and even the novelist John Updike. It makes for an amusing and stimulating, if somewhat picaresque, tale; one recurring motif is that Holt imbibes significant quantities of alcohol while his interlocutors prefer caffeinated beverages.

Holt’s other interviewees include the theologian Richard Swinburne, who opines that the physical world exists because God made it and punts on the question of why God exists. Philosopher Derek Parfit focuses on the form that an explanation might take, considering how some property of the universe might account for its existence. Parfit calls such a property a “selector”. For the speculative cosmologist John Leslie, the selector is goodness: Leslie suggests that the universe exists because it is good, and hence ought to exist. One might also imagine other properties playing the explanatory role, such as simplicity or variety, but Parfit’s idea is that if there is a selector, we can get evidence for what it is by seeing which property (if any) the universe maximally exemplifies. This idea leads Holt, by a somewhat convoluted argument, to suggest that the relevant property might be mediocrity.

The physicists that Holt consults tend to be more on Grünbaum’s side. Steven Weinberg and David Deutsch both recognize the hopelessness of the explanatory regress: anything one invokes to explain the totality of existence must itself be something that exists. One can react to this by saying that we are always stuck with a mystery – or, as Grünbaum would prefer, by saying that there is nothing mysterious since no answerable question is left unanswered.

In his book, Krauss approaches the subject of nothingness as a cosmologist, and his question offers rather more for physicists to investigate. Suppose there is a certain physical state, not of the whole of existence but rather of just a part, that deserves the name “vacuum state”. The current universe, filled with stars and dark matter and radiation, is certainly not in that state. But the laws of physics might allow the current universe to evolve from the vacuum state. If that happened, and if we call the vacuum state “nothing”, then one can say that physics explains how something came from nothing.

If we call a vacuum state “nothing”, one can say physics explains how something came from nothing

Despite its title, however, the majority of Krauss’s book does not discuss this possibility. Rather, it summarizes our current cosmological picture of the history and fate of the observable part of the universe. We have strong evidence, for example, that the visible part of the universe currently consists of about 70% dark energy, 25% unknown dark matter, 4% invisible known matter and only 1% visible known matter. Observations indicate that the dark energy is causing the universe to expand at a quickening pace, and we can speculate where that will lead.

Krauss explains the evidence clearly and accessibly, and offers an important story about the triumphs of modern cosmology. But by itself, it does nothing to address either of our two questions, and Krauss does not really confront Holt’s question at all. He does devote some effort to arguing that the vacuum state can properly be called “nothing”, so that the current universe arising from a vacuum would be an instance of “something from nothing”. But that is not the same thing.

Let’s break down the issue into three parts. First, what can we reasonably surmise about the state from which the current universe arose? Second, by what right (if any) should such a state be called a vacuum state? Third, even if the current state arose from a vacuum state, why should we think that that would end our explanatory regress?

Unlike the detailed claims of modern cosmology mentioned above, the nature of the pre-inflationary state of the universe is a matter of conjecture. Was there any state that preceded our Big Bang, and if so was there anything before that? Does the very temporal notion of “before” break down, and if so, why say that the current state came from some other one? Does the regress in time go on forever or come to an end with an initial state? We have no clear answers to any of these questions, although various inflationary scenarios and hints from string theory provide fodder for speculation.

Krauss’s main argument for calling the initial state “nothing” arises from considerations of energy. He argues that according to a certain way of quantifying the total energy content of the universe, including the gravitational energy, the entire current universe might have zero energy. Wouldn’t that mean that we could get the universe “free”: something from nothing?

Well, no. As Krauss acknowledges, the calculation of total energy in Newtonian gravitational theory uses an arbitrary choice of gauge for the gravitational potential energy. The amount of potential energy can be changed at will without affecting the physics, and can in particular take negative values by choosing one particular state as the “zero potential energy” state. Given this freedom, one can make a choice that sets the total energy to zero, but one can also just as legitimately set it to any value one wishes.

Shouldn’t we be using the general theory of relativity rather than Newtonian gravity in any case? Perhaps, but as Krauss also admits, there is no accepted method for ascribing a gravitational potential energy in the general theory, much less a precise value of negative energy. Krauss does argue that we have good reason to think that the current universe is (nearly) flat, but this is not the same as “zero energy”.

Suppose all this could work out, and we came to see our universe as arising from some sort of quantum vacuum. We would still have the same question: why did things start out that way? Physicists invoke their own selector here, and it is neither goodness nor zero energy: it is symmetry. The “false vacuum” of inflationary theory (which Krauss mentions but does not explain) is not special because of its moral or its energetic properties: it is special because of its symmetries. Physicists apparently regard these symmetries as making the state “to be expected” or “not in need of further explanation”. Why this should be so is a question that neither of our authors manages to confront.

Von Neumann’s computer

George Dyson has written a fascinating but flawed history of the computer. The son of the distinguished physicist Freeman Dyson, he was born in 1953 and as a child was witness to the world of computing unfolding at the Institute for Advanced Study (IAS) in Princeton, New Jersey, where his father was a professor. In Turing’s Cathedral: the Origins of the Digital Universe, he revisits the scene of his childhood in order to set local events in the context of global computer development. The impression is of a child not quite making sense of the grown-up world (rather like the children in To Kill a Mockingbird).

The most glaring flaw in the book is that Dyson claims that the IAS computer was the first practical computer that ushered in the dawn of the computer age. Fact: the first practical computer was the EDSAC, completed at the University of Cambridge in May 1949; the IAS computer first worked some 18 months later, and several other computers came on stream between these dates. This error is a great shame because there is in this book an important story that deserves to be told – and Dyson has told it well – but the book’s credibility is undermined by this petty claim about the priority of the IAS computer over other machines, and a sprinkling of other historical infelicities. Otherwise, the book is meticulously researched: Dyson has made extensive use of the Princeton University archives, visited numerous other archives, and interviewed several of the participants – now mostly in their 80s. He has also raided the Princeton archives for a superb set of photographs.

The central figure in the book is John von Neumann. During the Second World War, Von Neumann was a consultant to the Manhattan Project at Los Alamos, and was heavily involved in the intensive mathematical calculations needed to design the atomic bomb. In 1944 this need for calculating power led him to the ENIAC, a clumsy electronic behemoth built by the University of Pennsylvania for the US Army’s Ballistics Research Laboratory. Von Neumann collaborated with the designers of the ENIAC to produce a more effective design, which we now know as the stored-program computer – the blueprint for the post-war computer revolution.

Prior to his involvement with the ENIAC team, Von Neumann had become aware of Alan Turing’s theoretical work on computing, which Turing had carried out in 1936 at Cambridge before becoming a research student at Princeton University. Von Neumann was the only member of the ENIAC group who was aware of Turing’s work and the degree to which it influenced the stored-program computer is uncertain. Dyson has no such uncertainties, hence the title of the book.

After the war Von Neumann established a project to build a computer at the IAS. The IAS, the epicentre of theoretical science, was decidedly sniffy about hosting a bunch of engineers and their machinery. But the development was allowed to go ahead, tucked out of sight in the basement of the mathematics department, next to the men’s toilets. Dyson gives an excellent account of the academic politics and the engineering heroics that brought the computer into existence.

Although the IAS computer was not the first, it was probably the most influential computer design of its era. Moreover, at least as important as the computer itself were the seminal reports produced by Von Neumann and his colleague Herman Goldstine between 1946 and 1948 that were eagerly devoured around the world. The IAS computer (which Dyson incorrectly calls the MANIAC; in fact it was never named) had numerous clones, including the (real) MANIAC at Los Alamos, the JOHNNIAC at the RAND Corporation, ORACLE at Oak Ridge, SILLIAC at the University of Sydney, the WEIZAC in Israel and a dozen more. Further, Von Neumann was a consultant to IBM, which based its first mainframe computers on the IAS design. But this was a time of simultaneous invention, and had the IAS computer not been built we would be in much the same place today.

In the post-war period, Von Neumann earned a reputation as one of the most hawkish of scientists, becoming a member of the Atomic Energy Commission and an advocate for the H-bomb. The MANIAC computer was built primarily for nuclear-weapons calculations, and it was at Los Alamos that Von Neumann and Stanislaw Ulam invented the famed Monte Carlo method. When conventional computer methods were too slow or intractable, the Monte Carlo method could be used to evaluate a system at random points. The result was a kind of scatter diagram that approximated the result – the more points evaluated, the greater the precision. The Monte Carlo method was soon applied across the sciences. Von Neumann went on to apply similar techniques to numerical weather prediction, presaging today’s massive use of high-performance computers for meteorological forecasting.

Dyson’s odyssey into the origins of computing takes in Von Neumann’s last brilliant foray into the theory of self-reproducing automata. Like Turing, Von Neumann was fascinated by the computer’s potential for autonomous behaviour. Whereas Turing speculated on the ability of a computer to think, Von Neumann pondered on the power of machines to reproduce themselves. He devised minimal (and entirely theoretical) cellular automata that could asexually reproduce themselves. As it happened, neither of them outlived the 1950s. Turing, as is well known, committed suicide in 1954. Von Neumann died of cancer in 1956; he was a witness to the 1946 Bikini nuclear tests, and the cancer may not have been unconnected. Both Turing’s and Von Neumann’s speculations of the 1950s remain distant but not-forgotten prospects.

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