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  1. For the record

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    Our pick of the best recent quotes and comments

    It’s a very fragile thing…and you have gone to look at it from the eyes of God

    Pope Francis speaking to astronauts aboard the International Space Station

    Francis became the second pontiff – after Pope Benedict – to phone the ISS, in which he noted that the Earth is “too fragile and it passes in a moment”.

    The psychological effect [is] definitely a challenge

    Retired astronaut Scott Kelly quoted in the Guardian

    Kelly, who recently spent 11 months on the International Space Station, says it was hard to come back to Earth and lead a normal life having been in a controlled environment for a year and being told what to do on a daily basis.

    The supercollider will be a beacon of freedom

    CERN physicist Peter Jenni quoted in Foreign Policy

    China is planning a huge circular collider that would have a circumference of around 55 km, yet some have raised concerns about how international the project will be.

    Maybe we were extra anxious with the first child, as parents. But we relax a bit as more children come along

    Astrobiologist Charles Lineweaver from the Australian National University quoted in Nature

    India is building a successor to Chandrayaan-1 – the country’s first Moon mission that launched in 2008 – which will include a lunar lander.

    A lot of the science I put in the books is set-decoration rather than anything deeper

    English author Philip Pullman quoted in the Observer

    Pullman, the brains behind the His Dark Materials trilogy, says that his knowledge of science is “paper-thin” despite concepts such as dark matter and the multiverse appearing in the books.

    I’m still an experimental person – there’s physics and chemistry as well

    Vancouver-based physicist James Hoyland from Kwantlen Polytechnic University quoted in Metro

    Hoyland, who is competing on The Great Canadian Baking Show that premiered last month on CBC, notes that there is some truth to the saying that “cooking is art but baking is science”.

  2. Seen and heard

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    Weird and wonderful stories from the world of physics

    (Andrea Voß-Acker / ESA)

    Gravitational waves make their mark

    If you want to add a physics twist to your seasonal greetings cards, you now can thanks to Germany’s Federal Ministry of Finance. They have announced two new postage stamps that will go on sale in the country on 7 December. A 0.40 stamp will feature the European Space Agency’s Gaia satellite and will be the first German stamp to include a metallic coating. Gaia was launched in 2013 to measure the positions and distances of astronomical objects, including stars and planets as well as comets. A 0.70 stamp, meanwhile, depicts the gravitational waves that emerge from the collision of two black holes based on simulations carried out by researchers at the Albert Einstein Institute (AEI) in Potsdam, Germany. “The ministry did not announce whether letters equipped with the new gravitational-wave stamp will be transported at the speed of light,” quipped the AEI.

    Zeroing in on the answer

    How old is zero? That question has opened up a row between an international group of researchers and the University of Oxford after the Bodleian Library in Oxford noted that an ancient Indian text, known as the Bakhshali manuscript, had been dated to between 300 and 900 CE. The manuscript was discovered in 1881 in a field in Bakhshali, near Peshawar in present-day Pakistan, and was acquired by the library in 1902. The document includes arithmetic and was a manual for merchants trading across the Silk Road. The library noted that the text contained the oldest known written zero but it could not be classed as a “true” zero as it was only shown as a marker for an empty decimal place and not as a fully-fledged number. Now a group of historians from Canada, France, Japan, New Zealand and the US have voiced their disapproval over such a stance. They say that as the historical manuscript contains calculations such as long multiplication, it would have been necessary to use zero as a number. They also claim that the document includes statements such as “having added one to zero”. The debate is sure to continue before, er, zeroing in on a solution.

    Theory of happiness

    How much would you pay for a short letter written by Albert Einstein on the pursuit of happiness? Einstein wrote the letter during a lecture tour in Japan in 1922 after a bellboy at the hotel where he was staying – the Imperial Hotel in Tokyo – delivered a message to the physicist. When Einstein went to tip the boy, he realized he didn’t have any money so instead wrote a note to him on hotel letterhead that read (in German): “A calm and modest life brings more happiness than the pursuit of success combined with constant restlessness.” The letter, dubbed his “theory of happiness”, went on sale in October at the Winner’s Auctions and Exhibition in Jerusalem. While it was only estimated at $5000–8000, the price rocketed after intense bidding, eventually going for an eye-popping $1.56m. A second note that Einstein wrote at the time on a second sheet of paper with the words “Where there’s a will, there’s a way” sold at the same auction for only $250,000.


    (University of Cambridge)

    Free for all

    Still on famous physicists, the PhD thesis of the University of Cambridge physicist Stephen Hawking has been made freely available to read by the university library’s Office of Scholarly Communication. Hawking completed his PhD – entitled “Properties of expanding universes” – in 1966 when he was 24 years old. To mark Open Access Week 2017, in late October, the 117-page tome was posted on the university’s Apollo open-access repository, which is already home to some 15,000 research articles and 2400 theses. Within hours of Hawking’s opus being posted online, demand was so great that the site crashed. However, according to the university, it was still downloaded more than 60,000 times in the first 24 hours before access was restored. “By making my PhD thesis open access, I hope to inspire people around the world to look up at the stars and not down at their feet,” Hawking noted.

  3. Neutron-rich nickel-78 is doubly magic

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    Magic factory The Radioactive Ion Beam Facility at RIKEN in Japan. (RIKEN)

    Two independent experiments have verified that the radioactive nucleus nickel-78 is “doubly magic”, as predicted by the nuclear shell model. The nucleus contains 28 protons and 50 neutrons, which makes it an ideal candidate to test if the shell model applies to nuclei with relatively large numbers of neutrons.

    The idea that there are nuclei with “magic numbers” of protons or neutrons (2, 8, 20, 28, 50, 82 and 126) that are more stable than others was first pointed out by Maria Goeppert-Mayer in 1949. It led to the development of the nuclear shell model, for which she shared the 1963 Nobel Prize for Physics.

    The idea behind the model is that protons and neutrons fill nuclear orbitals just as electrons fill orbitals in atoms. When a nucleus has a magic number of neutrons, for example, its outer shell of orbitals is completely filled with neutrons. As the energy gaps between shells are relatively big, moving a neutron from a full shell into the next empty shell is difficult, which makes the nucleus relatively stable.

    Nickel-78 should be doubly magic because it has full proton and neutron outer shells. Being different particles, protons and neutrons occupy different orbitals. They can, however, feel each other’s presence via the strong force, which perturbs the orbitals so much that the shell model breaks down and new magic numbers emerge. This is known to occur in some nuclei that have high ratios of neutrons to protons.

    Now, international teams working independently at the ISOLDE facility at CERN in Switzerland and at the Radioactive Ion Beam Factory (RIBF) at the RIKEN lab in Tokyo have gained important insights into nickel-78 by studying the copper-79 nucleus, which has an extra proton. The RIKEN researchers carried out spectroscopic measurements of copper-79 nuclei in an excited energy state, which revealed that it is best described as having one proton in the next shell above the closed 28-proton shell – thus confirming the shell model. The ISOLDE team took a very different approach and instead made precise measurements of the masses of the copper isotopes copper-75 to copper-79. This allowed them to conclude that copper-79 is best described as a doubly-magic nickel-78 nucleus with one proton in the next shell (Phys. Rev. Lett. 119 192501 and 119 192502).

    Hamish Johnston

  4. Has liquid metallic hydrogen on Jupiter been recreated?

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    Under pressure Researchers used diamond-anvil cells to try to make liquid metallic hydrogen at conditions found on Jupiter (Mohamed Zaghoo / Harvard Seas)

    Two researchers at Harvard University in the US claim to have created liquid metallic hydrogen in the lab at conditions that exist inside gas-giant planets such as Jupiter and Saturn. Mohamed Zaghoo and Isaac Silvera came to this conclusion after squeezing liquid hydrogen to pressures of 140–170 gigapascals (1.4 million atmospheres) in a diamond-anvil cell and laser-heating it to 1800–2700 K (PNAS 114 11873).

    They noticed the reflectance of their sample increased until – at a certain transition temperature – it abruptly rose to 50–55%, which Zaghoo says are “values typical of metallic behaviour”. Assuming that their liquid hydrogen is a simple metal with free electrons, Zaghoo and Silvera calculated the conductivity from this reflectance, finding it to be six to eight times higher than a previous value measured by William Nellis, also at Harvard, for shock-compressed liquid hydrogen in 1996.

    The existence of such a metallic state inside Jupiter is the reason why the planet has a magnetic field. However, Zaghoo says his results imply that Jupiter’s field is stronger than previously thought and that it originates much nearer to the surface than assumed, given that his experiment took place at conditions found at just 84% of the planet’s total radius. In fact, he reckons Jupiter’s dynamo layer extends out to at least around 91% of the radius, claiming that new results from the Juno space mission support those conclusions.

    Not everyone is convinced. “Their experiments are not for the conditions of relevance to the outer region of Jupiter,” warns David Stevenson, a planetary scientist from the California Institute of Technology. “What they did is extrapolate outwards to lower pressure, and this is debatable.”

    Nellis, meanwhile, who works at Harvard independently from Silvera’s group, says his 1996 measurement is reliable because he measured the conductivity directly by electrical probing, whereas “to derive conductivity from a free-electron theory [as Zaghoo and Silvera have done] can introduce unknown systematic errors”. Moreover, Nellis measured a different phase of metallic hydrogen to those seen in the current experiment and it is unclear which might exist on Jupiter.

    Philip Ball

  5. Cryo-free maser runs continuously at room temperature

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    Candid camera Masers could someday be used in security scanners. (CC BY-SA 3.0 / Brijot)

    The first continuous-wave, solid-state maser to operate at room temperature has been created by researchers in the UK. The diamond-based device could lead to the development of ultra-sensitive microwave amplifiers that need no cryogenic cooling. Such devices could have a wide range of applications including security scanning and medical imaging.

    A maser is essentially a microwave version of a laser, in which coherent electromagnetic radiation is emitted when stimulated electrons relax to a lower energy level and a resonant cavity then amplifies the light. But while the laser has revolutionized the world, the demanding operating conditions of masers has limited their practical use.

    The original masers – invented in 1958 – were based on microwave transitions in atoms or molecules in a vacuum chamber. The vacuum requirement made these early devices bulky and low in power, but a big step forward occurred two years later with the development of the solid-state maser, which used a crystal of cryogenically cooled ruby as the cavity.

    Although masers have proved useful in radio telescopes and atomic clocks, they need to run at very low temperatures, which has made them impractical for everyday technology such as airport body scanners. In 2012, however, Mark Oxborrow of the UK’s National Physical Laboratory, along with Jonathan Breeze and Neil Alford of Imperial College London, devised a new maser scheme in which an optical laser “pumped” electrons from a lower energy level to a higher one in a soft polymer – p‑terphenyl – doped with pentacene.

    Their device could operate at room temperature, but worked only in the pulsed regime, whereas many maser applications, such as microwave detectors, require continuous-wave operation. Moreover, p‑terphenyl is a poor thermal conductor, limiting its ability to dissipate the heat generated by non-radiative decay processes. The material also melts at just 230 °C, meaning that even if an organic maser could operate continuously, it would be rapidly destroyed.

    Now, however, Breeze, Alford and colleagues have implemented a similar scheme in a maser cavity made from synthetic diamond impregnated with negatively charged nitrogen-vacancy (NV) centres. Diamond is an ideal medium because it has the highest recorded thermal conductivity of any material.

    Laser pumping drives electrons into an excited state that rapidly decays to one of three spin sub-levels of the ground state. By applying a moderate magnetic field to the NV centres, the researchers manipulated the sub-levels’ energies so that the electrons most commonly decayed into a state lying above another sub-level.

    The resulting population inversion between the bottom two sub-levels leads to maser emission, with the researchers able to tune the energy gap – and thus the maser frequency – by tweaking the magnetic field. Being so stable, the maser was operated continuously for up to 10 hours with no drop in output (arXiv:1710.07726).

    Tim Wogan

  6. Muons reveal large void in Great Pyramid

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    Inside job Members of the ScanPyramids collaboration at Khufu’s Pyramid. (ScanPyramids Mission)

    A large void hidden deep within Khufu’s Pyramid at Giza in Egypt has been discovered by detecting the muons that shower the Earth. The measurements were made by the ScanPyramids collaboration, which includes researchers from Egypt, Japan and France. They used three separate muon-imaging techniques to study the pyramid, which was built in about 2500 BC and is also known as the Great Pyramid and the Pyramid of Cheops.

    The idea of using muons for imaging was pioneered in the 1960s by the future Nobel-prize-winning physicist Luis Alvarez, who placed a muon detector in a chamber in the nearby Pyramid of Khafre. Known as muography, the technique relies on the fact that muons travel relatively unhindered through the air but get absorbed by stone. So if more muons than expected reach a detector in the pyramid, they must have passed through an air-filled void.

    In 2016 chemical-emulsion muon detectors developed at Nagoya University in Japan were deployed in the Queen’s Chamber – the lowest known chamber in the pyramid. Much like photographic film, the emulsion reacts chemically when exposed to muons, leaving 3D tracks that indicate the directions from which the particles came. As well as detecting known voids, these detectors provided the first evidence for a previously-unknown large void about 30 m long.

    To verify its existence, scientists from the KEK particle-physics lab in Japan installed instruments comprising layers of plastic scintillator, which measure muon trajectories, at a separate location within the Queen’s Chamber. Outside the pyramid, meanwhile, physicists from France’s nuclear-research agency CEA monitored the muon flux through the pyramid using gas-filled “micromegas” detectors.

    As a result of the three different 2D images taken from three different angles, the team could locate the void in 3D. A computer reconstruction based on the data suggests it is similar to the Grand Gallery of the pyramid – an inclined passage about 47 m long. The new void is, however, 50–70 m above ground level, putting it above the Grand Gallery. It is not clear, though, if the void is a single chamber or multiple chambers, or whether it is horizontal or inclined.

    Hamish Johnston

  7. Misconduct rocks ETH Zürich

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    Bullying allegations have resulted in the closure of the Institute for Astronomy at a top Swiss university, as Michael Banks reports

    The executive board of one of Switzerland’s leading universities – ETH Zürich – has launched an independent enquiry in response to allegations of misconduct at its former Institute for Astronomy (IfA). The IfA was closed in August after several students raised concerns about the management practices of senior staff at the institute. According to a statement from ETH Zürich, the investigation will now take “a more detailed look” at the situation and that it could lead to “additional measures” being taken.

    The problems at ETH Zürich came into the open in February when allegations were made by “several doctoral students” against a female professor who worked at the IfA. While the professor has not been identified by ETH Zürich, she has been named elsewhere as Marcella Carollo. According to the allegations, Carollo demonstrated “inept management conduct” towards her students.

    A month later – at their own request – the students, who have not been named, were reassigned to a different supervisor. After the university’s executive board discussed the issues – which have not been made public by ETH Zürich – an agreement was reached that Carollo would be given support if she wanted to supervise doctoral students in the future.

    According to its statement, ETH Zürich decided to close the IfA in August because Carollo was married to another professor in the IfA, Simon Lilly – a set-up that ETH Zürich says was “not ideal”. While the two researchers remain in the physics department at ETH Zürich, the rest of the IfA staff have been integrated into a newly created Institute for Particle Physics and Astrophysics.

    “Having identified the problematic circumstances, the priority was to reform the inappropriate personnel structure as quickly as possible so as to rectify the situation,” the statement says. “Nowadays such a [husband-and-wife] pairing within the same institute would no longer be possible.” While ETH Zürich’s board “commended the prompt and appropriate action” that was taken, its enquiry will focus on how “poor management” can be quickly escalated higher up within the organization. “The alleged conduct falls well short of the standards we expect of our professors, and so we took swift action,” says ETH Zürich president Lino Guzzella. “The official enquiry allows us to take an even closer look at the facts and decide whether further measures still need to be taken.”

    However, some astronomers have voiced concerns about how ETH Zürich has dealt with the situation and how the institution blamed it on the couple being married. Writing on Twitter, astronomer Jessie Christiansen from NASA’s Exoplanet Science Institute at the California Institute of Technology says that ETH Zürich needs to “try harder”.

    “As part of a married astronomer couple working at the same institute, I can assure you this [working alongside one’s spouse] is not the problem,” she wrote, adding that the issues rather emerge due to a “clear conflict of interest” such as a married couple supervising the same student or chairing the same committee. “I’d like to think we’re smart enough to put some protections in place that aren’t a blanket ban [on married couples],” she says.

    Yet within days of ETH Zürich’s decision to launch an enquiry, 24 researchers – some of whom had been supervised by Carollo – published a letter in support of Carollo, whom they mentioned by name, pointing out that she and her colleagues built a “world class astronomy institute in less than a decade”. The authors of the letter add that many of Carollo’s students have successfully gained tenure-track positions and that she has been a strong promotor of women in astronomy. “If at times she comes across as a relentless task master, this owes to her commitment to her students and desire to maximize their career chances,” they write.

    We urge all scientists to reflect on how they can be better supervisors

    A week later almost 700 researchers had signed a separate open letter in support of the ETH students. “We note the substantial career risk incurred on those who have come forward to report such incidents, and we express our support for students and early-career researchers at ETH and everywhere else who have been victims of bullying and who want to be able to focus on their research,” says the letter. “We urge all scientists to reflect on how they can be better supervisors, and to commit to ongoing training and self-improvement in this area.” The letter calls on ETH Zürich to make the recommendations from the independent review public, adding that “bullying has no place in astronomy”.