By James Dacey
On Saturday, there were almost 600 sister events across the globe in support of the March for Science gathering in Washington, DC. One such event occurred in Bristol, UK, where Physics World magazine is produced, which featured a march and speeches from science communicators. I popped along to the event with my camera and here are some of the most eye-catching signs from the day.
Thousands of people took to the streets of Washington, DC on Saturday 22 April to voice their support for science. Endorsed by more than 200 scientific organizations including the American Physical Society, the March for Science sought to promote the value of science – and scientists – to society. It was part of a co-ordinated series of similar protests at almost 600 other venues around the world.
The Washington march had been organized to coincide with Earth Day and many protestors held placards with environmentally-themed messages such as “We want solar! With science”, “There is no planet B” and “The tides are rising – and so are we”. Others, meanwhile, were concerned about science budgets. “We need to make a statement that basic research funding is important for this country,” said Shawn Westerdale, an experimental physicist.
Although the organizers intended the event in Washington not to be political, some protestors had a clear message for politicians in the Trump administration. “It’s an abomination what’s going on,” said Bob Bruninga, an engineer. “Science is not political, but if there are some people who don’t want to understand science and they want to make it a political game, then they can. Science is truth.”
Those views were echoed by theoretical biophysicist Lauren McGough – another protestor who joined those marching from the Washington Monument to Capitol Hill. “Science research funding and general truth are under threat in the current administration and I am really concerned about what that’s going to mean for basically the whole American public and, in the end, the Earth,” she told Physics World.
Kenan Diab – a physicist holding an umbrella and a placard stating “Theoretical physics uncovers beautiful new possibilities” – felt the march could have long-term benefits. “One should take a stand on the correct side, which is to believe in the existence of an objective reality,” he said. “If that’s a partisan issue that’s sad, but hopefully our actions will make it non-partisan again.”
Astronomers have observed a single supernova appearing at four different locations in the sky. The multiple images are caused by gravitational lensing – a phenomenon first predicted by Albert Einstein as part of his general theory of relativity. It occurs when the gravity of a huge cosmic object bends and magnifies the light of a more distant object. In this case, a galaxy in between the type Ia supernova (called iPTF16geu) and Earth is magnifying the star’s light more than 50 times over and splitting it to create the four separate images. As type Ia supernovae have a well-known intrinsic brightness, the increased signal drew the attention of astronomers when it was seen by the intermediate Palomar Transient Factory (iPTF) – a wide-field sky survey based at Palomar Observatory in the US. Ariel Goobar from Stockholm University in Sweden and colleagues were able to resolve iPTF16geu’s separated images using the Hubble Space Telescope, the W.M. Keck Observatory in Hawaii and the Very Large Telescope in Chile. “Normally, when we view a lensed object we don’t know the intrinsic brightness of that object, but with type Ia supernovae, we do,” says Goobar, “This will allow us to better quantify and understand the phenomenon of gravitational lensing.” Type Ia supernovae, often referred to as “standard candles”, are used to study the expansion rate of the universe. The astronomers hope that iPTF and the network of scientists and telescopes called the Global Relay of Observatories Watching Transients Happen (GROWTH), will help discover similarly lensed type Ia supernovae. The work is presented in Science.
Germanium is much better at producing electron spins than had been previously thought – according to Federico Bottegoni and colleagues at the Polytechnic University of Milan in Italy and the University of Grenoble-Alps in France. The discovery could be a boost to researchers trying to develop spintronic devices, which use the spin of the electron to store and process information in much more efficient ways than possible with conventional electronics. The spins are generated by the spin Hall effect (SHE), which involves an electrical current flowing through a material in which the electrons experience an interaction between their spin and orbital angular momentum. Under certain conditions, spin-up electrons will veer off in one direction and spin-down electrons in the opposite direction. The overall effect is a spin current that flows in a direction perpendicular to the electrical current. This leads to an accumulation of spin-up and spin-down electrons at opposite edges of the material. Previous studies of the SHE in germanium revealed very small spin currents, which is why the material had been overlooked for spintronics. Once a spin current is created in germanium, however, it is longer-lived than spin currents in other materials. Bottegoni and colleagues realized that large amounts of spins could accumulate in germanium, despite the relatively weak spin current. When they tested this in the lab, they found that the accumulated spin density in germanium is about 100 times greater than that seen in indium gallium arsenide and on a par with gallium arsenide. Unlike these two compound semiconductors, germanium is compatible with silicon – which makes it more attractive for practical spintronic applications. The research is described in Physical Review Letters.
China has successfully docked a cargo craft with its Tiangong-2 space lab, taking a major step towards establishing a permanent space station by 2022. On Thursday China launched the Tianzhou-1 cargo resupply spacecraft and two days later it successfully docked with Tiangong-2 in an automated manoeuvre. Tianzhou-1 can carry six tonnes of goods and two tonnes of fuel, although it did not have any actual supplies as there are no astronauts aboard Tiangong-2. The cargo vessel and Tiangong-2 will now have two further docks, including one that will be accelerated to take six hours rather than the usual two days. Tiangong-2 was launched in September 2016 and a month later two Chinese astronauts spent a month aboard the lab in what was the country’s longest-ever manned space mission. It is unlikely that Tiangong-2 will be occupied again and instead China will begin launching the Tiangong-3 station from 2018.
By Sarah Tesh
With the World Snooker Championship taking place at the moment, it’s that time of year when those of us who are usually snookered by the game are suddenly in its pockets. Right on cue, Phil Sutton from Loughborough University in the UK helps bridge the gap between science and snooker. In his video big break, he looks at why players use chalk on their cue tips. Interestingly, there is a right way to help you spin out a 147 and a wrong way that could leave you pocketing the white.
The influence of science and scientists on US government policy is being downgraded by the administration of US president Donald Trump – according to the physicist and former science adviser John Holdren. However, Holdren is hopeful that both the US Congress and private industry will reject some of Trump’s planned cuts to science funding.
Holdren served as presidential science adviser and head of the Office of Science and Technology Policy (OSTP) during Barack Obama’s presidency. He told Physics World that it was still unclear whether Trump will appoint a science adviser and senior OSTP staff, who must be approved by the Senate. “I think it would be a serious error if the president does not create a very serious science and technology capability in the White House.”
He believes that the Silicon Valley entrepreneur Peter Thiel is currently advising Trump on science and technology. “It’s pretty clear he knows a lot more about technology than about science. There’s a rumour that the OSTP may be more technology-heavy than science-heavy.”
While OSTP leadership appointments are on hold, Holdren says that “one member of the Trump ‘landing team’, Michael Kratsios, has been working very hard to understand the role of science adviser”. “I’m told that he has a good idea of the role. But will he have the ear of the Trump administration? He may be pretty lonely.”
Holdren says that one week before the presidential inauguration in January a member of Trump’s campaign team visited the OSTP. “We spent an hour talking about the functions of the OSTP and the science adviser. We had prepared a very detailed transition book with documentation of all the OSTP’s responsibilities, which we handed over. That was the last we heard.”
Holdren fears that the influence of scientists at the White House is waning. He says that Trump’s proposed budget in March “shows no sign of any significant input from anyone who understands science’s role in making recommendations on government policy for government agencies’ science and technology budgets”. Holdren hopes that the budget will be rejected by the US Congress, and calls the plan “a major setback for research, climate science, energy research – just devastating cuts for government support in domains where companies aren’t involved”.
Holdren points out that the proposed cuts will affect programmes that have direct benefits to American society – citing the $6bn drop in the budget of the National Institutes of Health and proposed cuts to NASA’s Earth-observation programmes.
However, Holdren believes that initiatives in science education and the Obama climate action plan both have strong industry support. Although under threat, he says these programmes are likely to survive. “The majority of technology companies accept that climate change is real and we need to do something about it,” he says, adding that the US must ensure that it remains competitive in the development of climate-friendly technologies.
An interview with Holdren will appear in the May issue of Physics World.
Three physicists have made TIME magazine’s 100 Most Influential People for 2017. In its 14th year, the list highlights those individuals that make the most impact worldwide rather than the most popular or famous. Listed together within the pioneers category (rather than individually like most others), the three physicists honoured by TIME are astronomers searching for exoplanets. Natalie Batalha is the lead scientist for NASA’s Kepler space telescope and is the first woman at NASA to make the list. Her work includes the mission’s first confirmation of a rocky planet outside the solar system and she has identified more than 5100 possible exoplanets over her career. Also honoured is Guillem Anglada-Escudé of the Queen Mary University of London in the UK who discovered the exoplanet orbiting our closest neighbouring star, Proxima Centauri, and Michaël Gillon of the University of Liège in Belgium who announced in February the discovery of Trappist-1. Other scientists on this year’s list include artificial intelligence researcher Demis Hassabis and Guus Velders, an atmospheric chemist.
A careful study of data from the LIGO gravitational wave detectors could reveal whether black holes have “hair” – physical properties other than mass, angular momentum and electrical charge. Einstein’s general theory of relativity says that black holes have no hair – they are “bald“– but making the observations needed to confirm this is extremely difficult. Now, physicists in the US and Canada have calculated that information about black-hole hair could be extracted from the gravitational waves that are created just after two black holes merge to form one larger black hole. The new black hole begins its life as a rotating distorted sphere that changes shape until it becomes a sphere in a process called ringdown. If black holes are bald, the gravitational waves emitted during ringdown should be as expected for a black hole with specific values of mass, angular momentum and electrical charge. Any deviation would point to the existence of hair. While a LIGO measurement of the ringdown of an individual black hole is too noisy to provide a definitive answer, Huan Yang of Princeton University and colleagues have worked out that ringdown data from a number of different black holes could be combined to reveal the presence of hair. Writing in Physical Review Letters, they say that the answer could come after one year of observation time once the LIGO detectors have been upgraded to their ultimate design sensitivities.
A year-long search for signals from alien civilizations has yet to find any evidence for the existence of intelligent life on other planets. Funded by the physicist and billionaire investor Yuri Milner, the Breakthrough Listen initiative has acquired several petabytes of data using the Green Bank Radio Telescope in West Virginia, Lick Observatory’s Automated Planet Finder in California and the Parkes Radio Telescope in Australia. These data are being analysed by researchers at the SETI Research Center at the University of California, Berkeley, who are scanning through billions of radio channels in a search for unique signals that might indicate the presence of technology developed by extra-terrestrial civilizations. The team has now released an analysis of data from the Green Bank telescope. This identifies 11 “events” in the 1.1–1.9 GHz band that have the highest likelihood of being associated with alien technologies. These are signals with features not expected from astronomical sources such as narrow bandwidth or certain patterns of pulsing or modulation. However, further detailed analysis of the 11 events suggests that it is unlikely that any of them were created by the technology of a distant civilization. “Although the search has not yet detected a convincing signal from extra-terrestrial intelligence, these are early days,” said Berkeley’s Andrew Siemion. “The work that has been completed so far provides a launch pad for deeper and more comprehensive analysis to come.”
Printed electronics are viewed as a cost-effective and scalable route to new technologies, although the performance of these devices tends to rely less on the printer and more on the ink. Researchers at Trinity College Dublin, in collaboration with scientists at Delft University of Technology and Toyota Motor Europe, have now fabricated vertically stacked thin-film transistors (TFTs) from dispersions of two-dimensional nanosheets. Combining high performance with ease of manufacture, these nanosheet-based TFTs have the potential to compete with organic and nanotube-based electronics.
The nanosheet inks are made using a process known as liquid-phase exfoliation, where layered materials in bulk form are broken down and dispersed in liquids. Over the last 10 years this has become an established method for efficiently producing a whole library of two-dimensional materials. Due to the widely varying properties of these nanosheets, every component in the TFT can be printed: conducting graphene nanosheets are used for the electrodes, semiconducting transition-metal dichalcogenides such as molydenum disulphide or tungsten diselenide form the channel, and a boron nitride (BN) dielectric layer acts as a separator.
When printed, the inks form porous nanosheet networks (PNNs) that can be printed layer-by-layer. Their high porosity allows for the use of electrolytic gating, where liquid electrolyte contained within the network is used as a gate dielectric. During operation, ions in the liquid accumulate at the boundary between the electrolyte and the active material due to the application of a gate voltage. Charged ions at the interface then separate, forming an electrostatic double layer and inducing current to flow through the external circuit.
The research team, led by Adam Kelly and Toby Hallam, measured the electrical transport characteristics of different PNNs using a simple set up involving gold electrodes and an ionic liquid electrolyte (Science 356 6333 69). They found that the transconductance, a measure related to the gain a transistor is capable of delivering, is directly proportional to the thickness of nanosheet network. This allows the electrical characteristics of the device to be tuned by their printing conditions, with transconductance values as high as 6 mS reported by the team.
Large capacitance values were also measured for thick PNNs, due to the large amount of free volume available for ion adsorption. This gives these devices transport properties similar to those of benchmark TFTs, though such high capacitances do hinder switching times. Fortunately, the researchers believe that further experimentation with the ionic liquid electrolyte will enhance switching speeds.
Building on these results, the team built a fully functional TFT using only porous nanosheet networks: graphene electrodes, a tungsten diselenide channel and a BN separator. These vertically stacked devices have on:off ratios of more than 25 and a transconductance of 22 μS. Such transfer characteristics are promising for devices that are still the early stages of development, and further improvements should be possible in the future.
Full details are reported in Science.
In February 2016 researchers at the Advanced Laser Interferometer Gravitational-wave Observatory (aLIGO) in the US announced a ground-breaking discovery – on 14 September 2015 they had made the first ever direct detection of gravitational waves. After decades of trying to observe these ripples in space–time, the scientists had at last addressed the final unverified prediction of Einstein’s general theory of relativity. Success was quickly followed by success and a few months later a second detection was reported.
In both cases (called GW150914 and GW151216 respectively), as well as a less statistically significant event (LVT151012), the gravitational waves were produced by two stellar-mass black holes in a binary orbit that merged to form one larger black hole. While the detection events are a significant breakthrough, they are still shrouded in mystery. “Previous to this, we never observed a black hole binary system, which leads to the natural question – how did these come to be?” says LIGO scientist Amber Stuver, who was not involved in this current work.
So far, several scenarios have been proposed but they struggle to explain all observed events under one framework. Now, however, scientists at the University of Birmingham in the UK and the University of Amsterdam in the Netherlands have developed a model that can describe all three events via one evolutionary path.
Before LIGO’s detections, it was thought that stellar-mass binary black-hole systems would either not form at all or, if they did, they would be too far apart to merge within the age of the universe. For two black holes to merge within the age of the universe, they have to begin very close together by astronomical standards – no more than a fifth of the distance between the Sun and Earth. But black holes are produced by massive stars that expand to be much larger than this distance during their stellar evolution.
To solve this problem Simon Stevenson from Birmingham’s Gravitational Wave Group and colleagues developed a simulation platform called Compact Object Mergers: Population Astrophysics and Statistics (COMPAS). “It is a tool for both predicting the evolution of massive stellar binaries and statistically comparing these predictions against observations,” explains team member Ilya Mandel.
Using COMPAS, the group propose an “isolated binary evolution via a common envelope phase”. This means that two massive stars begin with a quite wide separation. As these stars evolve and expand over time, they interact and undergo several episodes of mass transfer, the last of which is called a “common envelope”. This is a very rapid, unstable transfer that envelops both stellar cores in a dense cloud of hydrogen gas. The formation and subsequent ejection of this shared gas cloud is strong enough to take energy away from the orbit, bringing the stars close enough to merge. At this stage in their evolution, the stars are small enough in volume not to be in contact with each other despite their proximity, and they subsequently continue orbiting before merging as black holes billions of years later.
To reach this model, Stevenson, Mandel and colleagues had to make a series of assumptions about physical processes that govern stellar and binary evolution. For example, astronomers do not know the extent to which very massive stars expand and how much mass they lose through winds during evolution. With COMPAS, the researchers produced stellar binary models based on their assumptions and computed their statistical properties. They could then compare these predictions to the observational data and make adjustments accordingly.
“There are a lot of basic assumptions made to come to these results and many more to test,” comments Stuver, “but it is impressive that this one evolution scenario can explain all three of the gravitational wave events.”
“There are a lot of basic assumptions made to come to these results and many more to test,” comments Stuver, “but it is impressive that this one evolution scenario can explain all three of the gravitational wave events.”
As well as providing an explanation of the binary process, the simulation has also helped the team understand what type of stars can form such systems. They suggest that the massive stars have low metallicity, meaning they are almost entirely made up of hydrogen and helium. While 2% of the Sun is other elements, these massive counterparts would contain only 0.1%.
Writing about their proposed model, presented in Nature Communications, Mandel says that, “while [the work] doesn’t yet prove that this is indeed the dominant formation channel for forming merging binary black holes, and while this is almost certainly not the unique channel for doing so, it does allow us to build a robust framework for analysing future observations.”
The researchers hope to improve their model and figure out which assumptions are right by using data from other stellar systems, such as neutron-star binaries, supernovae and X-ray binaries. “The long-term goal is to combine all of these observations to understand how massive stars and binaries evolve,” says Mandel. “We very much look forward to further LIGO detections, and to incorporating other rich observational data sets, in order to gain a better understanding of the lives (and deaths) of massive stars.”
By Margaret Harris
If you’re finding the pace of geopolitical news a bit too rapid at the moment, spare a thought for physicists and engineers working in the nuclear energy sector.
Towards the end of last month, the venerable energy firm Westinghouse Electric issued a press release in which it proudly announced that its AP1000 reactor – a relatively new “passively safe” design in which the reactor core is kept cool without the need for powered pumps or other “active” equipment – had passed a major UK regulatory review. Ordinarily, this would be cause for celebration. The so-called “Generic Design Assessment” process takes years, and completing it helps pave the way for building AP1000s within the UK. An international partnership called NuGen has long hoped to do just that, on a site near Sellafield in north-west England, so in normal times, you might expect it to be celebrating, too.
Sensors made from carbon nanotubes could offer a superior alternative to current activity tracking technology. Devices developed at the University of California, San Diego, are flexible enough to bend within layers of fabric, and can track specific types of motion as well as recording vital signs such as temperature and heart rate. These developments are promising for real-time monitoring of patients living at home, through telemedicine and those working in extreme environments, like astronauts in space.
PhD student Long Wang and Professor Kenneth J Loh, researchers in the UCSD’s department of structural engineering, produced the flexible sensors using carbon nanotubes (CNTs) and fabric with an ingenious, cost-effective manufacturing process (Smart Mater. Struct. 26 055018). An ink consisting of CNTs and latex is mixed together and sprayed onto glass, where it is then annealed to produce a freestanding thin-film network of nanotubes. Once two electrodes have been attached, the film is then sandwiched between two layers of fabric and ironed together to produce a flexible fabric sensor.
These multipurpose sensors not only record heart rate, but they can also accurately track motion in a finger and even monitor respiration. When attached to a finger, the flexible nature of the thin film allows the sensor to bend and flex as the finger moves. This change in shape alters the electrical resistance across the film, which makes it possible to determine the bending angle.
Similarly, if strapped around the torso, the film changes in shape as the chest expands during inhalation, subsequently changing the resistance. When the person breathes out, the film returns to its original shape and the resistance drops again.
The sensor can also be used to monitor skin temperature. As the film is heated, there is again a change in the electrical resistance. These changes can be calibrated using measurements taken with a thermocouple, which allows the resistance change to be converted to the temperature of the skin.
Sensors like this are useful beyond the realms of logging the stats of your run or cycle ride. It’s still early days, but Wang and Loh have successfully combined an easy fabrication route with the versatility needed to take a number of important measurements. Their results show that the technology is on track to be used extensively for easy, non-invasive, real-time monitoring of individuals in a variety of environments.
