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Franken-physics

Image of a depiction of the monster made by Dr Frankenstein

“How,” Mary Godwin asked herself, did I come up with “so very hideous an idea?”

In the summer of 1816, Mary and her lover (soon to be husband) Percy Shelley met Lord Byron in Switzerland. It rained a lot, so rather than hiking as planned they spent time indoors reading ghost stories. At one point Byron suggested they each write their own. At first, Mary had writer’s block, but then recalled a conversation between Percy and Byron about scientific experiments in which researchers caused parts of animals to flinch by applying electricity, which then made them speculate about the principle of life. That night Mary had a dream in which a technician sent a spark into an assemblage of body parts. The thing began to move, and then opened its eyes.

The next day Mary told her companions she had an idea.

Out of control

That’s the story Mary Shelley told of the origin of Frankenstein in her introduction to its second edition (1831). Thanks to two centuries of theatre and film adaptations, most people know the basic plot, which centres on an out-of-control monster built by a well-meaning but careless scientist named Victor Frankenstein. The story is now embedded in our language. The prefix “Franken-”, as in “Frankenfoods” and “Frankenfish”, is often used to create a charged word referring to a terrible thing that should not have been created because it is an unnatural product of rampant consumerism. Frankenwords are catchy, wave a red flag, provoke fear, and seem to endow those who use them with unclouded moral judgement.

But the story that unfolds in Shelley’s novel is not so simple.

In 2014 two humanities scholars at the University of New Mexico published an article in Science and Engineering Ethics (21 1139) that envisioned Victor Frankenstein submitting his research to an institutional review board (IRB), or panel of the sort now mandatory in the US for research involving human or animal subjects. “Had Frankenstein had to submit an IRB proposal,” wrote the authors, “tragedy may have been averted, for he would have been compelled to consider the consequences of his experiment and acknowledge, if not fulfil, his concomitant responsibilities to the creature that he abandoned and left to fend for itself.”

The article cleverly exhibits Frankenstein’s potential for teaching contemporary research ethics. At the same time, though, the article exemplifies the familiar but erroneous way in which the story is understood: as a tale about the creator and the creation. To determine the ethics of the experiment, the authors looked into possible carelessness or ill intent on the part of Frankenstein, and the potential for the creature to do harm.

Numerous adaptations of the story reflect that version too. In the 1931 film Frankenstein, starring Boris Karloff, the creator unwittingly installs an abnormal brain in the creature. The creature, a property destroyer and serial killer, is evil from the start.

Other interpretations, though, blame Victor Frankenstein, the monster’s creator. At one point in Shelley’s story, he calls the monster “my own spirit let loose”. In these psychological interpretations, Victor’s act is motivated by his internal demons, such as the trauma of losing his mother before he leaves for university. “Knowledge is the awareness that Frankenstein is not the monster,” runs a joke. “Wisdom is the awareness that Frankenstein is the monster.”

Certain other interpretations blame Victor’s ambition: to create life in the lab without thinking of the rest of world. Such ecological interpretations, behind “Frankenfood” language, find the monster to symbolize the breakdown of responsible human stewardship of nature.

In a 2011 article in the Breakthrough Journal entitled “Love your monsters: why we must care for our technologies as we do our children”, the French philosopher Bruno Latour proposed that the moral of Frankenstein is that technologies should not be unleashed without human guidance. The scientists who discover things like nuclear fission, for instance, are responsible for its applications. This is a parental interpretation: constantly care for your creations or you’re a bad parent!

But Shelley’s story, read attentively, wrecks such interpretations. She leaves no indication the beast has anything but a normal brain. The creature himself gives a persuasive reason for his behaviour: “I was benevolent and good; misery [his rejection by humans] made me a fiend.” Shelley’s story indeed carries a shockingly contemporary message: the creature is the extreme refugee, unable to assimilate into the country where he’s thrown without his consent, whose inhabitants not only reject but vilify him.

In Shelley’s story, too, Victor’s ambitions are not outlandish but shared by the professors who taught him science in the first place, who seek to “penetrate into the recesses of nature, and show how she works in her hiding places”. Like them, he is thrilled, saying: “None but those who have experienced them can conceive of the enticements of science.”

Nor was the science implausible. “Mary Shelley based Victor Frankenstein’s attempt to create a new species from dead organic matter through the use of chemistry and electricity on the most advanced scientific research of the early 19th century,” writes Shelley’s biographer Anne K Mellor. “Her vision of the isolated scientist discovering the secret of life is no mere fantasy but a plausible prediction of what science might accomplish.”

The critical point

The evil that erupts in Shelley’s story therefore cannot be blamed entirely on electricity, careless scientists, or an out-of-control creation, but also on the climate in which Victor conducts his research. It therefore recalls another contemporary predicament: that of bank employees whose managers instruct them to handle their accounts ethically but who must work in a banking climate with overwhelming incentives not to do so. For physicists and other scientists, Shelley’s story rings an alarm bell, not because of some breakdown in the system – bad behaviour, brains, or breeding – but because nothing broke down.

Now that’s a hideous idea.

Antiatoms yield their first optical spectrum

The first measurement of an atomic transition in an antiatom has been made by researchers working in the ALPHA collaboration at CERN in Geneva. The team measured the frequency of a specific transition in antihydrogen, which consists of a positron (an antielectron) bound to an antiproton. Although the result is no different from that measured in normal hydrogen, the group says that more sensitive versions of its experiment might one day reveal a new matter–antimatter asymmetry in nature.

The transition in question is between the 1s (ground) and 2s (excited) states of antihydrogen. This process could be sensitive to a violation of what is known as charge, parity and time reversal (CPT) symmetry. This states that the behaviour of any physical system remains unaltered under the combined reversal of charge, spatial coordinates and time. Although CPT symmetry has solid theoretical support, experimentalists are nevertheless keen to put it to the test. Its violation, for example, might explain why the universe today appears to consist almost entirely of matter – even though equal amounts of matter and antimatter were thought to have been produced during the Big Bang. “Other symmetries that were thought to be inviolable have been broken before,” notes ALPHA spokesperson, Jeffrey Hangst of Aarhus University in Denmark.

ALPHA, like a number of other antimatter experiments at CERN, takes its antiprotons from the lab’s Antiproton Decelerator, and then slows down and cools the particles before combining them with chilled positrons from a sodium-22 source. The resulting sub-kelvin atoms of antihydrogen are then trapped – thanks to their tiny magnetic dipole moments – in a potential well created by the careful overlap of several magnetic fields.

Antiatoms drop out

To carry out their spectroscopic measurements, Hangst and colleagues fire a laser beam into the magnetic trap and let it bounce numerous times between two mirrors. The laser’s frequency is tuned to roughly half that of the 1s to 2s transition in normal hydrogen. This is because the transition involves the absorption of two photons, and its precise frequency is determined to some extent by the presence of the trapping magnetism. Some of the antiatoms should then be excited and drop out of the trap as a result of one of two mechanisms – either by absorption of a third photon to become ionized, or by having their spin flipped. The researchers then repeat the process with the laser tuned to different frequencies, as well as with no laser at all.

Carrying out the whole procedure 11 times, the group found that on average just under 60% of antiatoms left the trap with the laser tuned to the 1s-2s transition, while no antiatoms (within the bounds of statistical error) dropped out when the laser was tuned to a different frequency or when it was switched off. The researchers say that the antiatoms underwent the transition at the expected frequency and therefore behaved no differently from normal hydrogen.

Although the result does nothing to threaten CPT symmetry, Hangst argues that it testifies to the enormous technical progress that has been made in the field of antiatom research – first in producing atoms of antihydrogen, then in cooling them, and then in trapping them. In particular, his group has recently made progress in two areas. They have trapped significant numbers of antiatoms at the same time – up from about one to around 14 within the past year. They have also created a resonant cavity around the magnetic trap in order to boost the intensity of the laser light to the point where it could interact with the very few antiatoms present.

Opening salvo

ALPHA’s achievement has earned praise from other antimatter groups at CERN. Ryugo Hayano of the University of Tokyo and spokesperson of the ASACUSA experiment, describes the research as “a very important milestone”, while AEgIS spokesperson Michael Doser says it constitutes the “opening salvo in precision spectroscopic measurements of antihydrogen”.

All, however, agree that it will not be easy boosting the precision achieved in the latest work by the roughly five orders of magnitude needed to match the sensitivity already obtained in spectroscopic measurements of ordinary hydrogen. Doser says there will be “many challenges” in doing this, including how to prepare antiatoms at millikelvin temperatures, in order that more of them can be trapped magnetically, and how to better reduce or disentangle the effect of the magnetic fields on the energy levels of the antiatoms. But he adds that ALPHA has been “quite effective at coming up with solutions” to all of the technical problems they have encountered to date.

Hangst says that the collaboration’s next step will be to plot the shape of the 1s-2s resonance when the Antiproton Decelerator switches on again next spring. So far he and his colleagues have just made measurements on one side of it.

Pain and delight

Indeed, Gerald Gabrielse of Harvard University in the US, who is spokesperson of the ATRAP experiment, says: “I look forward to the day when either ALPHA or ATRAP eventually traces out a complete 1s-2s resonance lineshape at a significant precision”. He adds that his group actually started working towards antihydrogen spectroscopy ten years earlier than did ATHENA (the predecessor to ALPHA), saying that his “parental delight” at the latest work is “only tempered by the pain that I feel in ATRAP not getting the first suggestive result”.

However, according to Walter Oelert of Mainz University in Germany, who led the team that produced the first antiatoms, the contest for higher precision remains very much on. “It is by no means clear which collaboration will reach the 10-15 target first,” he says, “although ALPHA can celebrate the first step.”

The research is reported in Nature.

The Science of Heaven

 

By Richard de Grijs in Beijing

Good things come to those who wait. Indeed, it has been almost six years since we initially thought about making an astronomy documentary set in China – and we finally showed it in public last month. The Science of Heaven premiered on 30 November 2016 at my institution, the Kavli Institute for Astronomy and Astrophysics at Peking University. By all accounts, it was very well received. While we are ironing out some final issues before releasing it publicly in early 2017, you can watch the trailer (above).

(more…)

Images of 2016 in physics

As science journalists, we are fortunate at Physics World that the stories we cover are often highly visual. Physics and astronomy are full of eye-catching imagery – the scientific results, the technologies and the diverse range of people involved in the scientific endeavour. The images in this collection tell some of the key stories from the world of physics in 2016.

New boss at CERN

Photo of CERN DG Fabiola Gianotti

January began with a changing of the guard at the CERN particle-physics lab near Geneva. Italian physicist and former ATLAS spokesperson Fabiola Gianotti became the15th director-general of the lab since it was founded in 1953. On 1 January she succeeded Rolf-Dieter Heuer, who has stepped down after seven years in charge to take up a place on a new seven-member panel that will provide scientific advice to the European Commission. “My priority as CERN director-general will be to expand and maintain CERN’s excellence in four areas: science; technology and innovation; education; and peaceful collaboration,” Gianotti said. For CERN’s flagship experiment, the Large Hadron Collider (LHC) it has been a fairly quiet year in terms of breakthrough science, especially once the “bump” at 750 GeV in data collected by the ATLAS and CMS detectors was confirmed in August to be a mere statistical fluctuation. On the bright side, the LHC itself has performed very well, with the ATLAS and CMS detectors recording 60% more collisions than expected during its proton run from April to the end of October – more than a quadrillion (6.5 × 1015) collisions, at an energy of 13 TeV.

A historic ripple

Graphical representation of the waveform of event GW150914

The physics story of the year was the LIGO collaboration’s announcement on 11 February that it had made the first ever direct detection of gravitational waves. The waves were produced from the collision of two black holes of 36 and 29 solar masses, respectively, which merged to form a spinning, 62-solar-mass black hole, some 1.3 billion light-years away in an event dubbed GW150914. The signal or “chirp” as it became known was detected on 14 September 2015 and was measured by the newly upgraded aLIGO detectors – one in Hanford, Washington, and the other in Livingston, Louisiana. The discovery ends a decades-long hunt for these ripples in space–time, and marks the beginning of the era of gravitational-wave astronomy. It also provides evidence for one of the last unverified predictions of Einstein’s general theory of relativity. Not content with grabbing the headlines once, the LIGO collaboration announced in June that it had confirmed a second set of gravitational waves, which had passed through LIGO’s detectors on 26 December 2015. For all of these reasons and more, the LIGO collaboration was the clear winner of the 2016 Physics World breakthrough of the year.

Political earthquakes

Photo of Brexit protests

Out there in the world of politics, it is fair to say that developments in 2016 have divided opinion in highly divisive ways. The first political earthquake to strike the Western world occurred on 23 June when the British public voted narrowly in favour of leaving the European Union (EU) in a referendum. 51.89% of voters opted for leave, while 48.11% plumped for remain. The vote was preceded by vitriolic campaigns, with politicians on both sides of the debate being roundly criticized for scaremongering and providing misinformation in some cases. UK science has traditionally done well out of EU funding. The UK’s Office for National Statistics estimates that the UK contributed €5.4bn between 2007 and 2013 to research spending in the EU and received back €8.8bn.

The impending Brexit has also cast doubt over the futures of EU citizens working in physics departments across the UK, and over Britons working in Europe. Moreover, question marks remain over the role British scientists will play in European projects once the nation has left the EU. Scientists have been among those frustrated with the lack of information from the British government regarding its Brexit plans (assuming of course they have some plans).On 2 July scientists were among the thousands of people to join the “March for Europe” rally in London, which called for transparency among political leaders to outline their vision for the future of Britain in Europe.

Photo of Donald Trump

Of course, the second political earthquake to strike the West was the unexpected victory of Donald Trump in the US election. Trump’s inauguration is scheduled to take place on 20 January, but many scientists – particularly in the climate science community – are already fearful of what Trump’s presidency might bring. Trump of course previously described the concept of global warming as a hoax “created by and for the Chinese in order to make U.S. manufacturing non-competitive”. Before even taking office, Trump has selected Scott Pruitt – an outspoken sceptic of climate change – as the next administrator of the Environmental Protection Agency. Meanwhile, Rex Tillerson the chief executive of oil and gas giant ExxonMobil will be Trump’s secretary of state while oil drilling proponent Rick Perry will head the Department of Energy. A senior Trump campaign advisor has also indicated that NASA will no longer take on climate projects under a Trump administration.

As with the Brexit campaigns, migration issues played a key role during the US presidential campaign. Trump famously promised to build a wall along the Mexico–US border (to be paid for by Mexico) and to ban Muslims from entering the US. It is too early to say whether the historic outcomes of these two votes will lead to brain drains from the UK and US but that is the fear of some. As 2016 draws to a close, uncertainty is the name of the game.

FAST developments

Aerial photo of FAST telescope

Uncertainty is not a word in the official dictionary of the Chinese Communist Party especially when it comes to large-scale construction projects. One of the nation’s latest milestones is to boast the world’s biggest single-aperture radio telescope – the Five-hundred-meter Aperture Spherical Telescope or “FAST” as it is better known. FAST comprises 4450 reflecting panels, which provide it with a collecting area of 30 football pitches – more than twice as big as the 305 m diameter radio telescope at Arecibo Observatory in Puerto Rico. Located deep in the hills in the south-western province of Guizho, the ¥1.5bn ($180m) telescope saw its first light in September and will cover a frequency range of 70 MHz to 3 GHz. Dark matter investigation and the detection of distant astronomical objects are among the key research areas. In October it was also announced that FAST would be joining the Breakthrough Listen programme, founded by Russian physicist-turned-entrepreneur Yuri Milner. Launched in July 2015, the programme claims to be the most comprehensive, intensive and sensitive search ever undertaken for artificial radio and optical signals.

A rocky neighbour

Artist's impression of Proxima b

While Milner and company probe the far reaches of the universe for an alien broadcast, the presence of extra-terrestrial life may be closer to home than we could have imagined. In August the international Pale Red Dot collaboration announced that it had clear evidence of at least one planet orbiting Proxima Centauri, the closest star to the Sun. The exoplanet – dubbed Proxima b – has a minimum mass of about 1.3 times that of the Earth and is therefore most likely a terrestrial planet with a rocky surface, and has a short orbit of around 11.2 days. Our newly found neighbour also lies within its star’s habitable zone, meaning that it could, in theory, sustain liquid water on its surface, and may even have an atmosphere.

What will ultimately determine the habitability of the planet – including whether it currently has liquid water on its surface and an atmosphere – depends entirely upon its formation history. According to the researchers, an answer to this question could be sought using a 3.5 m telescope. “This is a planet in our neighbourhood and maybe we will finally send out a probe and take a picture from somewhere other than Earth,” said Pale Red Dot member Pedro Amado from the Instituto de Astrofísica de Andalucía in Granada, Spain.

Marooned on a comet

OSIRIS narrow-angle camera image of Philae

Elsewhere in the universe scientists working on the Rosetta space mission have managed to locate the final resting place of their Philae lander on the surface of comet 67P/Churyumov–Gerasimenko The discovery came nearly two years after the lander was lost as it bounced onto the comet’s surface. You have to look very carefully to see Philae in the above images taken by Rosetta’s high-resolution camera. The wayward lander is wedged into a dark crack on the comet and the instrument’s orientation clearly reveals why establishing communications was so difficult, following its landing on 12 November 2014. The images were taken on 2 September by the OSIRIS narrow-angle camera, as Rosetta came within 2.7 km of the surface.

Nobel for topological trio

Photos of David Thouless, Duncan Haldane and Michael Kosterlitz

2016 was a great year for David Thouless, Duncan Haldane and Michael Kosterlitz who shared the Nobel Prize for Physics “for theoretical discoveries of topological phase transitions and topological phases of matter”. All three winners hail from the UK but have spent much of their professional careers in the US. The science behind this year’s prize tied together three concepts in physics and mathematics, namely: topology; quantum phase transitions; and states of matter. The result is what the Nobel committee described as “beautiful mathematical and profound physical insights”. Indeed, the laureates’ research has laid the theoretical basis for a variety of condensed-matter staples including superconductors and thin magnetic films.

Physics of fullness

Microscope image of and emulsion

Imagine if you could make foods that make you feel full after eating a small portion, sating your hunger and preventing you from overeating. Such a technology could play an important role in the fight against growing rates of obesity and improve the health of millions worldwide. The above image is of an emulsion of oil droplets in water – something that is found in many foods. In “Hungry for solutions” Cait McPhee, who is a biophysicist at the University of Edinburgh, explains how “functional ingredients” could be added to emulsions such as salad dressings to deliver satiety. These ingredients could be developed using soft-matter physics and could be used to create foods that trigger biological processes that lead to sensations of satiety. This article appeared in the November issue of Physics World, which focused on the physics of food.

Shifting ground in Italy

Radar map of central Italy showing the effect of the October earthquake

On 30 October this year a 6.5-magnitude earthquake struck central Italy – the largest earthquake in the country for over three decades. This image has been made using radar data from the European Space Agency’s Copernicus Sentinel-1 satellites and shows the devastating effect of the earthquake. Significant east–west ground displacements are visible in the area hit by the earthquake with an eastwards shift of about 40 cm near Montegallo and a westwards shift of about 30 cm centred in the area of Norcia. As well as these shifts, the satellite detected a vertical displacement, with the ground sinking by 60 cm around Castelluccio but rising by about 12 cm around Norcia. The Italian peninsula is prone to earthquakes due to the continuing collision of the African and Eurasian tectonic plates and central Italy has been hit by smaller earthquakes this year.

Penguin physicist

Photograph of African penguins

What do penguins, polymer physics and pattern recognition all have in common? In this “Penguin physics” feature the polymer physicist Peter Barham explains how a casual conversation with a zookeeper in Australia led to his involvement in the development of new technologies for identifying individual African penguins in biological studies. His first attempt was a new type of plastic flipper identification band to replace metal bands – which appeared to have a negative impact on swimming. Later, he enrolled the help of computer scientists to see if pattern recognition systems could be used to identify birds without the need of any bands.

Barham’s is a wonderful tale of a physicist who quite by chance became a penguin biologist. Find about more about his penguin research in this short video:

Flash Physics: Helium half-quantum vortices, Tokamak Energy gets £10 million, magnetic switch controls heat

Half-quantum vortices spotted in superfluid helium-3 at long last

The first observation of half-quantum vortices (HQVs) in superfluid helium-3 has been made by physicists at Aalto University in Finland and the P L Kapitza Institute in Russia. A superfluid vortex is a point-like object around which superfluid flows. The flow is quantized in units of h/m, where h is Planck’s constant and m is the mass of the constituent particles of the superfluid. HQVs can occur when the constituent particles are bound pairs of more fundamental particles. This is the case for helium-3, which when cooled forms “Cooper pairs” of atoms which behave collectively as a superfluid that will keep flowing without dissipating energy. The Cooper pairs have both spin and orbital angular momentum and interactions between these two quantities can result in HQVs when the superfluid is in a confined environment. This was first predicted in superfluid helium-3 in 1976 and has been seen in several physical systems including high-temperature superconductors, where pairs of electrons form HQVs. Now, Aalto’s Samuli Autti and colleagues have confined superfluid helium-3 in a material called nafen, which contains a forest of aligned strands that are separated by about 35 nm. The helium fills the spaces between the strands and the team creates vortices by rotating the sample around the axis defined by the strands. While they could not see the HQVs directly, they used nuclear magnetic resonance to measure the rotation via a signal generated by the magnetic moments of the helium nuclei. “In the future, our discovery will provide access to the cores of half-quantum vortices, hosting isolated Majorana modes – exotic solitary particles,” says Autti. “Understanding these modes is essential for the progress of quantum information processing [and] building a quantum computer.” The work is described in Physical Review Letters.

Magnetic switch controls heat

A new magnetic switch that controls the flow of heat has been made by Joäo Ventura and colleagues at the University of Porto in Portugal. At its heart is a cylindrical container that is about three quarters full of a magnetic nanofluid – a substance that contains nanometre-sized magnetic particles and flows in the presence of an applied magnetic field. The side of the container is thermally insulated and the top and bottom are capped with material that is a good conductor of heat. In the off position, the nanofluid absorbs heat from the bottom of the cylinder but most of this heat is unable to pass through the gap at the top. To put the switch in the on position, a magnetic field is applied along the axis of the cylinder. This causes the nanofluid to jump up and come into contact with the top of the cylinder – allowing heat to transfer from the nanofluid to the top of the cylinder. The team made two prototype switches – one with a 1 cm-tall cylinder and the other 3 cm – that were tested with a temperature gradient of 35°C. They found that the smaller switch operated efficiently at switching frequencies of up to 30 Hz, while the larger device started to flag at about 10 Hz. The team was also able to control the temperature of an LED using one of their switches. The device is described in Nano Energy and could someday be used to ensure that fuel cells, solar cells and other devices operate at their optimal temperatures.

UK fusion-energy company gets £10m boost

Photograph of David Kingham

The UK-based company Tokamak Energy will receive £10m in additional investment from Legal & General Capital and the private investor David Harding. Based in Oxfordshire, the firm is building a compact tokamak fusion reactor with the aim of confining and heating a plasma so that nuclear fusion can occur. According to research published by the company, a facility based on their technology should be capable of delivering 100 MW of electricity, which is about one tenth of the output of a conventional fusion reactor. Tokamak says that its next prototype reactor should be built by March 2017 and that it expects to heat plasmas to 100 million degrees by the end of next year. “The world-class facilities in Oxfordshire and 50 years of solid scientific progress with tokamaks have laid the groundwork for a UK fusion industry, and our latest major investment from UK backers demonstrates further recognition of fusion as the most exciting opportunity available to investors anywhere,” said David Kingham, chief executive officer at Tokamak Energy.

 

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Dual optical clock races towards peak precision

A new optical clock that is insensitive to an important source of noise has been developed by physicists at the National Institute of Standards and Technology (NIST) in the US. The researchers believe the new design, which allows the clock to reach its peak precision much more quickly than before, could provide a step towards allowing optical clocks to be used in a wider range of applications than is possible today.

Optical lattice clocks trap atoms in a standing-wave potential created by two counter-propagating laser beams. A third laser is used to repeatedly excite and de-excite a specific atomic transition, which gives the “ticks” of the clock. Such a clock’s principal advantage over a similar timekeeper based on trapped ions is that technical difficulties currently prevent more than one ion being used at a time. This makes ion clocks prone to the inherent quantum randomness in the way the ion behaves when excited by the laser – called the quantum projection noise. In contrast, thousands of neutral atoms can be used in the same trap at once and this greatly reduces the quantum projection noise.

In 2013, Andrew Ludlow and colleagues at NIST in Boulder, Colorado, demonstrated two optical lattice clocks that are stable to within a record-breaking half a second in the age of the universe. Physicists have proposed that, if such clocks could be made robust enough to be taken out of the laboratory, the precise measurements of time dilation taken at various points on Earth could give important insights into the internal composition of our planet. Taking such clocks to space could allow physicists to look for deviations from Einstein’s general theory of relativity and quantum effects in gravity.

Billiard balls

“Dick noise” is an important effect in optical clocks and it arises because the atoms cannot be monitored continuously. “They’ll typically stay around [in the trap] for a few seconds before molecules of background gas bump into them and knock them out like billiard balls,” explains Ludlow, “and so we have to get some more.” During the “dead time” while they do this, the laser frequency can vary slightly. The effect of these random variations can be averaged down by measuring for many hours, but this is experimentally cumbersome.

Researchers have tried to minimize the problem using ultra-stable clock lasers. “The clock laser is becoming the most difficult part of the experiment,” explains team member Marco Schioppo, who is now at Heinrich Heine University of Düsseldorf in Germany. “The laser cavity must be as isolated as possible from the environment, both thermally and vibrationally. The clock laser is definitely the one piece of equipment it is extremely difficult to move anywhere.”

Schioppo, Ludlow and colleagues have now produced a clock containing two trapped atomic ensembles – essentially a timekeeper comprising two optical clocks. While one trap is being refilled and its atomic state prepared and measured, the laser is locked to the other trap. This has been proposed before, says Ludlow, but the researchers are the first to implement it successfully in an optical lattice clock: “To be able to do it with just two clocks, you need to make sure that the amount of time you can coherently interact with the atoms is at least the same as the amount of dead time,” he explains. “For a long time, the dead time would be much larger than the spectroscopy time.”

Simple, robust laser

The new clock reaches extreme stability 10 times faster than the team’s 2013 clock. “As soon as you improve the instability, you decrease the timescale for your measurement, and then you’re really able to pin down systematic effects more effectively,” explains Schioppo. The researchers suggest that, as the laser is permanently locked to one cavity or another, a simpler, more robust laser system could also be used.

“I think it’s a big step forward,” says optical-clock specialist Helen Margolis of the National Physical Laboratory in Teddington, UK. Quantum metrologist Piet Schmidt of Germany’s Leibniz University Hannover agrees, although he adds that the numerous difficulties the researchers had to overcome leave him wondering if the work provides a plausible route towards a simpler or more portable clock: “You need to have your two clocks synchronized extremely well to not lose a cycle of your clock laser. If you can come up with a way of producing a more stable laser source you could possibly have the same gain for less effort, but that remains to be seen.”

The research is described in Nature Photonics.

A lobster-eye view of the universe

When the BepiColombo spacecraft begins its journey to Mercury in 2018, it will carry a unique payload: the first X-ray telescope bound for orbit around another planet. In the past, such telescopes have been too unwieldy for interplanetary travel thanks to the massive nature of traditional X-ray reflecting optics. With BepiColombo, ­however, a revolutionary type of optic means that this joint European Space Agency (ESA) and Japan Aerospace Exploration Agency mission could usher in a fundamental change to the way we do X-ray astronomy.

The high energies of X-ray photons mean that they penetrate into and are absorbed by traditional telescope mirrors rather than reflecting off them. To avoid this problem, X-ray telescopes use mirrors aligned along the photons’ direction of travel, which corral these high-energy particles and deal them a glancing blow that sends them towards the telescope’s focus at a shallow angle. Traditionally, these mirrors have consisted of chunky rings of glass or metal shells, but they add substantially to a spacecraft’s mass. Since interplanetary missions have strict mass constraints, X-ray telescopes simply haven’t been able to fly on them.

The Mercury Imaging X-ray Spectrometer (MIXS) aboard BepiColombo gets around this problem with a new design featuring micro-pore optics. Instead of one large glass ring, optics of this type are composed of a series of micro-channel plates: thin glass wafers covered in myriad square holes, or pores, just a few dozen microns across, and coated in reflective iridium. These plates are so light that the entire MIXS instrument has a mass of less than 10 kg – a sharp contrast to the optical system aboard NASA’s Chandra X-ray Observatory, which comes in at a whopping 1000 kg.

Direct comparisons are perhaps a bit unfair, since the two instruments have very different scientific goals. Nevertheless, “The fact that the optics are so lightweight is the only way you can get this type of technology onto an interplanetary spacecraft,” says Adrian Martindale, instrument scientist for the MIXS and a researcher at the University of Leicester, UK. Although an X-ray collimator previously featured on NASA’s MESSENGER mission to
Mercury, Martindale explains that BepiColombo, which is due to enter Mercury’s orbit in 2024, will be the first to carry a bona fide X-ray telescope to another planet. Its job will be to map the composition and elemental abundances of the Mercurian surface, and measure the planet’s auroral zone, where cosmic rays excite elements in the surface to release X-rays.

Lobster eyes consist of many square-shaped cells that reflect light to a focus along shallow grazing angles

The idea for developing X-ray optics along these lines dates back to the 1970s, when Roger Angel, an astronomer at the University of Arizona, US, was inspired by the eyes of lobsters and other crustaceans. While their geometry is not exactly the same as the MIXS system, lobster eyes also consist of many square-shaped cells that reflect light to a focus along shallow grazing angles. However, the lobster-eye technology did not really come of age until the 21st century, when a University of Leicester team led by the late George Fraser began developing it for X-ray observations.

X-ray vision

“George was one of the most brilliant physicists I have ever known,” says Emilie Schyns, micro-channel plates product manager at PHOTONIS France SAS, which manufactures the plates used in the MIXS. Schyns explains that the company’s longstanding relationship with Leicester dates back to the 1990s, when Fraser, who died in 2014, was working in the ultraviolet domain using PHOTONIS’ custom-made micro-channel plates. The micro-pore optics technology on MIXS “evolved out of that working experience”, Schyns says.

The plates manufactured for X-ray astronomy differ from standard micro-channel plate technology in several ways. One is that standard plates are active charge amplifiers with 1000 V running through them, whereas micro-pore optics contain no electronics. Another key difference is the shape of the holes. These are normally round, but to ensure a point-like image at X-ray wavelengths, rather than a diffuse glow caused by photons reflecting in different directions off a curved edge, the holes in MIXS are square.

Currently, PHOTONIS is the world’s only manufacturer of square-pore micro-channel plates. Paul O’Brien, head of Leicester’s Department of Physics and Astronomy, describes the 40-step process of making the plates as “optical cookery”, noting that getting the right curvature for the required focal length involves a proprietary method of heating and moulding the specially chosen glass. The finished plates are then tested using Leicester’s X-ray beam line – the only facility of its kind in the UK, according to O’Brien.

Despite this challenging manufacturing and testing process, micro-pore optics are garnering a lot of attention. Already there are plans for them to appear in the X-ray telescope onboard the French-led Space Variable Objects Monitor (SVOM) mission, which will track down the sources of gamma-ray bursts (GRBs). Although the micro-channel plates don’t have the spatial resolution to pinpoint exactly where on the sky a GRB is, these stellar explosions will be the strongest X-ray emitting objects in that part of the sky, so such accuracy isn’t required.

Meanwhile, a team from NASA’s Goddard Space Flight Center hopes to use the micro-pore optics on a proposed mission that would fly to the International Space Station and hunt for the sources of gravitational waves from a perch on the station’s robotic arm. Similarly, a Chinese proposal called the Einstein Probe hopes to use the optics to find gravitational-wave sources and track down X-ray flares from black holes.

The hunt is on

All three of these missions take advantage of the fact that micro-pore optics can be optimized for wide-field as well as narrow-field observing. This is an important new development for X-ray astronomy, since instruments such as Chandra or ESA’s XMM-Newton satellite only have fields of view of half a degree (about the size of the full Moon in the night sky). The ability to search large swathes of the sky for the sources of gravitational-wave mergers or the afterglows of gamma-ray bursts is “the next big thing in astronomy”, O’Brien says, adding that it is “nice to see technology developed for a planetary mission being used in very different ways”.

The wide field-of-view and limited spatial resolution is not to the detriment of MIXS, since the resolution depends on the number of X-rays detected. However, a different type of optics is required in situations where good angular resolution is important. This is the case for ESA’s upcoming Athena (Advanced Telescope for High-Energy Astrophysics) mission, which is scheduled to launch in 2028 with a next-generation technology called silicon-pore optics on board.

Although the design of silicon-pore optics draws on the same mass-saving principles as the micro-pore optics aboard BepiColombo, O’Brien explains that in other respects, they are very different technologies. Instead of carefully prepared glass plates, the reflecting optics on Athena will be made from silicon wafers, the smoothness of which (down to a few Ångstroms) makes them perfect for reflecting X-rays. Using this existing technology means that “we can leverage the large investments that the silicon wafer industry has already made”, says Giuseppe Vacanti of Cosine Measurement Systems, a Netherlands-based company tasked with developing prototype optics and, potentially, putting them into full-scale production.

A metallic block

To make the silicon-pore optics, silicon wafers are cut into plates and a series of ribbed channels about 1 mm across are sawn into each one. The sides of the plates opposite the ribs are then coated in highly reflective layers of materials such as iridium and boron carbide, which improve reflective efficiency at higher energies. When these coated plates are stacked together, the ribs act like the holes in micro-channel plates. A silicon mandrel shapes the plates to the required curvature, after which they are stacked together, 35 plates per block, with each block combined with others to form mirror modules. “The difficulty comes in making sure that when you stack them up, you maintain the optical quality and don’t introduce any distortions,” says Vacanti. “It’s more a matter of being careful than the process being complex.”

The prototypes currently have angular resolutions of around eight arcseconds, but Cosine hopes that further refinements to the manufacturing process will reduce this to four or five arcseconds. This would be considerably short of Chandra’s 0.5 arcsecond resolution, but enough to resolve almost all of the X-ray sources that Athena can detect, and with a much larger collecting area. The company aims to demonstrate a finished prototype with four to five arcsecond resolution by 2019; move into mass production the following year; and complete all of the mirror modules by 2025, three years before launch, to allow time for assembly and testing. These are ambitious goals, however, and to meet the deadline Vacanti says that they will have to stack one plate every two minutes – a task that currently takes up to 20 minutes. “The challenge is to carefully place the plates in their stacks fast enough but to not lose any of the precision that we have achieved,” explains Vacanti.

Mission possible

Like the micro-pore optics, silicon-pore optics are receiving interest from elsewhere. NASA is considering a silicon-pore optics-based mission called Arcus, which would use X-rays to study everything from interstellar dust to black holes and galaxy formation. The team at Leicester is also working on proposals for additional missions featuring micro-pore optics. However, their future involvement on missions outside of Europe is currently uncertain. “The Chinese would like us to be involved with their missions, but that requires the UK Space Agency to fund the instrument that we would build,” says O’Brien. “But of course they’re focusing on European missions, so it’s hard to get money for that sort of thing.”

New applications for both types of optic will likely continue to be developed, opening up fresh possibilities for X-ray astronomy. For example, lightweight optics could be used for novel pulsar-based navigation systems. By detecting X-rays from these spinning neutron stars, spacecraft could become self-guiding, eliminating the need to triangulate with Earth-based listening stations. Scientists in other fields may also take advantage of the small, lightweight micro-channel plates to build portable, tabletop devices that were impossible or too expensive before. “Over the next ­decade or two there’s going to be a spate of instruments using these optics,” enthuses O’Brien. “All that hard work is now paying off for what is becoming a very successful story.”

Robust defence of string theory wins Physics World’s 2016 Book of the Year

Why String Theory? by Joseph Conlon

Abstract, mathematically complex and (so far) unsupported by direct experimental evidence, string theory attracts plenty of criticism. Yet it remains an incredibly active area of research, with thousands of physicists and mathematicians around the world working on strings and related ideas. The reasons for its continued popularity are eloquently presented in Joseph Conlon’s book Why String Theory?Physics World‘s Book of the Year for 2016.

“String theory is much more than just a candidate theory of quantum gravity – people can use it for all sorts of reasons,” Conlon says. “Whatever your interests in physics are, it gives you things to think about.” To explain why this is, Conlon – a string theorist at the University of Oxford – begins the book by describing the origins of string theory and showing how it has changed over the years. Later chapters address the chief reasons why string theory continues to be a popular research topic. These include the theory’s status as a candidate theory of quantum gravity and the interest it poses to mathematicians, but also its applications to quantum field theory, cosmology and particle physics.

Conlon’s emphasis on string theory as something that is useful, even if it is not the ultimate “theory of everything”, is unusual in popular writing about string theory – or indeed any physical theory. This clear-eyed and distinctive approach helped Why String Theory? stand out in a strong shortlist of books that are all novel, well-written and scientifically interesting to physicists – the criteria used to determine Physics World‘s Book of the Year.

Conlon told Physics World that he wrote the book in order to “let the other side of my brain loose” after time spent writing formal scientific papers, and his dry, often acerbic wit is sometimes aimed at string theory’s advocates as well as its detractors. At one point, he describes multiverse-based thinking as “incontinence of speculation joined to constipation of experiment,” while at another he advises those who seek “proof” of a certain string theory principle that “physics is not mathematics, and those with scruples on this matter can be well advised that the math department on campus is generally in the next building down the street”.

Why String Theory? had stiff competition from the other nine books on the 2016 shortlist. Unusually, we have singled out one of these books for special recognition. Cosmos: the Infographic Book of Space has a very different format from the other books on our list, conveying information about space exploration, planetary science, cosmology and more via a series of colourful and elegant infographics. Written by Stuart Lowe and Chris North, with input from designer Mark McCormick, the book is both visually stunning and packed with fascinating ideas, and its innovative and well-executed approach earned it Highly Commended status in our competition.

To hear more about these books, you can listen to the latest Physics World podcast, in which our book experts – reviews editor Tushna Commissariat and past reviews editor Margaret Harris – discuss the winner and three other books on the 2016 shortlist with science communicator Andrew Glester, creator of the Cosmic Shed podcast.

This is the eighth year the magazine has picked a Book of the Year. Previous winners include Trespassing on Einstein’s Lawn, Amanda Gefter’s personal quest to understand the meaning of “nothing” (2015); Stuff Matters, Mark Miodownik’s salute to everyday materials science (2014); and The Strangest Man, Graham Farmelo’s landmark biography of Paul Dirac (2009).

Book of the Year 2016

We love talking about great physics books. In fact, we could go on about them for hours. The sparkling writing and deft analogies. The precise explanations that draw out the essence of complex concepts. The humorous anecdotes that make the research process come alive. We love it all, and as usual at this time of year, we’re sharing our thoughts on a few of the year’s best popular-physics books in a special edition of the Physics World podcast.

As with last year’s Book of the Year announcement, we teamed up with local science communicator Andrew Glester to record the 2016 edition in his garden shed, where he can often be found musing about “science fiction, science fact and everything in-between” for his podcast the Cosmic Shed. It was a trifle chilly in the shed this year, but thanks to hot drinks and some lively conversation, the time flew by as Glester quizzed Physics World’s current reviews editor, Tushna Commissariat, and her predecessor Margaret Harris about their favourite books of the year.

The decision about which of these books should be Physics World’s 2016 Book of the Year was an unusually tough one, for reasons you’ll hear about in the podcast. We congratulate all of the shortlisted authors on their fantastic books, and we hope that everyone will find something to appreciate on this list.

Shortlist for Physics World Book of the Year 2016 (alphabetical by author)

The Jazz of Physics: the Secret Link Between Music and the Structure of the Universe by Stephon Alexander

Why String Theory? by Joseph Conlon

Storm in a Teacup: the Physics of Everyday Life by Helen Czerski

Big Science: Ernest Lawrence and the Invention that Launched the Military-Industrial Complex by Michael Hiltzik

Strange Glow: the Story of Radiation by Timothy Jorgensen

Cosmos: the Infographic Book of Space by Stuart Lowe and Chris North

Spooky Action at a Distance: the Phenomenon that Reimagines Space and Time by George Musser

Goldilocks and the Water Bears: the Search for Life in the Universe by Louisa Preston

Reality Is Not What It Seems: the Journey to Quantum Gravity by Carlo Rovelli

The Pope of Physics: Enrico Fermi and the Birth of the Atomic Age by Gino Segrè and Bettina Hoerlin

Flash Physics: Xavier Barcons to lead ESO, molecular fountain, X-ray phase-contrast imaging goes mainstream

Xavier Barcons will lead European Southern Observatory

The Spanish astronomer Xavier Barcons will take over as director general (DG) of the European Southern Observatory (ESO) in September 2017, replacing the current DG Tim de Zeeuw who completes his mandate. Barcons is a professor at the Spanish Council for Scientific Research in Madrid and is an expert in the field of X-ray astronomy. He served as ESO council president in 2012–2014 and is currently chair of the organization’s Observing Programmes Committee. Based in Garching, Germany, the ESO has three observing sites in Chile. “I look forward to seeing the European Extremely Large Telescope (E-ELT) come to fruition and overseeing the further development of the Very Large Telescope, Atacama Large Millimeter/submillimeter Array (ALMA) and many other projects at ESO,” said Barcons.

Fountain gives physicists time to study molecules

A molecular fountain has been created that allows molecules to be observed for very long times as they free fall. Created by Hendrick Bethlem and colleagues at Vrije University in the Netherlands, the technique involves cooling ammonia molecules to milliKelvin temperatures and then launching them upwards at about 1.6 m/s. The molecules can then be studied in free fall for as long as 266 ms. This set-up is similar to atomic fountains, which allow very precise measurements to be made of atomic energy levels and form the basis for atomic clocks. A molecular fountain has proven much more difficult to create because molecules can vibrate and rotate – and this makes it very difficult to cool and manipulate them using conventional laser techniques. Bethlem and colleagues overcame this problem by using electric field gradients to exert forces on ammonia, which is a polar molecule. The team says that its new molecular fountain could be used to look for tiny deviations from the Standard Model of particle physics – which could be revealed by tiny shifts in molecular energy levels. Tests of the equivalence principle of Einstein’s general theory of relativity could also be done by measuring the acceleration due to gravity experienced by different types of molecule. The fountain is described in Physical Review Letters.

X-ray imaging technique could improve cancer treatment

X-ray phase-contrast imaging

An X-ray imaging technique that could only be done at large synchrotron facilities has been adapted for widespread use by Sandro Olivo at University College London and colleagues. Called X-ray phase-contrast imaging (XPCI), the method involves measuring changes in the phase of an X-ray beam as it travels through a sample. This is unlike conventional X-ray imaging, which measures the attenuation of the X-ray beam. The technique is better able to distinguish structures in living tissue, making it ideal for medical imaging. XPCI is also better at finding tiny cracks and defects in materials and could also be used to detect the presence of weapons and explosives in baggage. However, XPCI could only be done using the laser-like X-ray beams produced by synchrotrons – which are huge electron accelerators. Now, Olivo and colleagues have developed a technique that allows XPCI to be performed using X-rays generated by conventional medical sources. It involves first passing the X-rays through a “mask” containing an array of apertures to create a number of beams. These then interact with the sample before passing through a second mask to a detector. This configuration converts differences in phase to differences in measured intensity. “We’ve now advanced this embryonic technology to make it viable for day-to-day use in medicine, security applications, industrial production lines, materials science, non-destructive testing, the archaeology and heritage sector, and a whole range of other fields,” says Olivo. The technology has already been licensed to Nikon Metrology UK for use in a security scanner and UCL and Nikon are currently developing a medical scanner.

 

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