Entangled Hawking radiation emitted by an analogue black hole has been observed by a physicist in Israel. The experiment simulates the event horizon of a black hole using sound propagation in a Bose–Einstein condensate (BEC). The measurement shows that, if Einstein’s general theory of relativity holds at the boundary of a black hole, then black holes must emit radiation. Some physicists disagree, however, about whether the experiment fully validates the assumptions used to predict Hawking radiation.
In 1974 Stephen Hawking showed that general relativity and quantum field theory together suggested that photon pairs should be created at the event horizon of a black hole. One photon, carrying “negative energy”, would fall into the black hole; the other, carrying positive energy, would be emitted as radiation, giving the black hole a well-defined temperature. The theoretical implications of this are revolutionary, as it is unclear how the statistical thermodynamic definitions of temperature and entropy could apply to a black hole.
Physicists have not been able to study Hawking radiation because the temperatures of all known black holes are lower than that of the cosmic microwave background radiation. This makes their Hawking radiation effectively undetectable. However, in 1981 William Unruh of the University of British Columbia pointed out that the production of quantized sound waves – or phonons – in a BEC could be made mathematically equivalent to the predicted photon production at the event horizon of a black hole. Since then, various researchers have used this to build analogue black holes in the laboratory.
Bouncing light
In 2014 atomic physicist Jeff Steinhauer of the Israel Institute of Technology (Technion) in Haifa replicated a particular type of hypothetical black hole with two horizons in a BEC. He showed that, if radiation was excited, it would bounce between the two horizons, amplifying itself continuously to produce a type of laser. It was by no means certain that such a phenomenon could occur in a real black hole, however, as this would require radiation to travel faster than the speed of light between the horizons.
In the new research, Steinhauer has extended his model to cover the general case of a black hole. He swept a potential-energy step along a flowing BEC of rubidium-87 atoms. On one side, the flow was slower than the speed of sound in the condensate – allowing phonons to flow against the condensate. As the condensate travelled over the potential step, however, its speed became supersonic thus preventing phonons from travelling against the flow.
Steinhauer measured the spectrum of phonons in the condensate that are created by quantum density fluctuations at near-zero temperature. These are analogous to the photons created by fluctuations in the quantum vacuum (i.e. Hawking radiation) in a real black hole. The spectrum matched Hawking’s prediction. “The measurement reported here verifies Hawking’s calculation, which is viewed as a milestone in the quest for quantum gravity,” explains Steinhauer.
Fragile entanglement
Steinhauer also looked at the correlation between phonons on either side of the potential step. He found that, for all but the lowest frequencies, the correlation was too large to be due to chance. Therefore, he concluded, the phonons on either side of the step were entangled quantum mechanically. However, the degree of entanglement was less than predicted by quantum theory for most frequencies: “Entanglement is a fragile thing,” says Steinhauer, “There are several possibilities about what could destroy entanglement.” The fact that particles falling into black holes are apparently entangled with particles emitted from the surface is crucial to black hole thermodynamics, says Steinhauer, as it suggests they cannot then be entangled with each other. This rules out one possible way information could escape a black hole.
Renaud Parentani of Paris-Sud University is an expert on black hole analogues and is impressed with Steinhauer’s work: “The microscopic, detailed properties of the Hawking prediction of 1974 have now been observed in an analogue experiment,” he says. However, he is more sceptical than Steinhauer about the applicability to quantum gravity. “Sound waves in the condensate obey the same equations that Hawking used, having assumed that gravity could be treated as a passive arena,” he explains. “Therefore, by observing the phonons one indeed confirms the predictions made by Hawking, but one does not validate the assumptions used by Hawking. In fact, many physicists, in particular those working in string theory, consider that these assumptions are illegitimate because they apparently lead to the loss of information [in black holes],” he says.
The European Space Agency’s (ESA) Rosetta spacecraft has, as of this week, spent two full years in orbit around comet 67P/Churyumov–Gerasimenko, since it reached its destination in August 2014. While Rosetta was the mothership, it also deposited its “baby” lander called Philae onto the comet’s surface in November that year. Sadly Philae was switched off in July this year. If you feel like you want to relive the excitement of the initial launch, take a look at the video above. The folks over at Design and Data, who created Rosetta’s iconic cartoons and memorabilia for ESA, launched a plush-toy version of the spacecraft into space, to see how it would fare. Watch the video to see how their “mission” played out.
Healthy glow Low-pressure plasma processing of polymeric medical meshes by oxygen-discharge treatment (left) and plasma polymerization of bioceramics to enhance bone regeneration (right). (Courtesy: Cristina Canal, Technical University of Catalonia, Barcelona)
Plasmas – ionized gases – generated in vacuum have long played an important role in the surface processing of wafers in the electronics industry. Device makers rely on plasma methods to clean, etch and coat the various layers of a material that will form the computer chips driving our smartphones, laptops and other electronic goods. The popularity of plasma processing in the semiconductor industry has led to a boom in tools and equipment, but it is not just the electronics industry that benefits.
“Over the past 20 years, the success of plasma techniques in the semiconductor sector has given a tremendous boost to other fields, especially in the area of low-pressure systems,” says Uroš Cvelbar of the surface-engineering team at the Jožef Stefan Institute in Ljubljana, Slovenia. Researchers are now applying these methods across a wide range of emerging applications, with one of the fastest growing areas being the use of plasma processing in medical applications and in the development of biomaterials.
Versatile technology
“It has become a very broad field as there are just so many things that you can do with plasma and biomaterials,” says Cvelbar. “Here at the institute, we can deposit films, we can modify existing surfaces and add functionality – it’s a versatile technology.”
Cvelbar first became interested in the area through his background in plasma physics and materials science, and enjoys the interdisciplinary environment needed to take ideas forward. “Today, my group includes chemists, microbiologists, biotechnologists, as well as physicists,” he explains. “The team also collaborates with medical researchers and doctors through different institutes and clinical centres, as they are the end-users of the materials we’re developing.”
One of the most popular methods for processing biomaterials and polymer surfaces is to use low-temperature plasmas generated either by a radio frequency, microwave or DC source or by applying very fast pulses of electricity. “High voltages are normally used to create the cold plasma in the presence of a carrier gas at atmospheric pressures, whereas a vacuum has been applied mostly to clean and deposit materials,” says Cvelbar. “For cold plasma processing in a vacuum environment, the use of sources operated at microwave or radio frequencies is typical.”
Plasma processing offers a very clean environment and even the means for sterile processing, which makes it well suited to many medical uses. Another benefit is that the feedstock is typically made up of only a few substances, which helps to minimize – and even avoid altogether – residues that could otherwise cause problems later on in the application. What is more, ionized gas and plasma radicals – loose ions, neutral atoms and excited atoms or molecules – can kill, inactivate or completely destroy microbiological organisms, such as bacteria, viruses and fungi, after prolonged exposures.
You can perform in vivo treatment of wounds with plasmas generated at atmospheric pressure
For Cvelbar and other researchers, plasma-processing technology gives them lots of different avenues to explore. “With plasma, you are working with ions or other reactive species that modify or functionalize a surface in such a way to obtain better attachment of molecules for cell growth, or to enable biosensing of different chemical species,” he says. “You can also perform in vivo treatment of wounds with plasmas generated at atmospheric pressure.”
Medical efforts
Two strategies are currently being pursued. “One approach is to use the plasma to decontaminate the wound and kill unwanted bacteria on the surface [but] at the same time adding radicals that boost cell growth to accelerate the healing process,” Cvelbar explains. “The second strategy involves depositing activated collagen to coat the wound, which again could speed up the patient’s recovery compared with simply exposing the wound to the open air.”
In both cases, treating a wound would require a device that can be placed over the patient, which means that smaller, more portable atmospheric systems are set to play an increasingly important role as the technology matures.
So where are the sweet spots for vacuum? “Low-pressure systems are used mostly to treat and prepare materials that can be processed away from the body, such as artificial hips,” Cvelbar says. “Examples include coating implants with a bio-compatible material to encourage cells to grow around them by providing a scaffold, which helps to keep the devices in place once inside the body.”
Being bigger in size, low-pressure processing set-ups can be well suited for larger operations but there is a downside too: the construction of bigger chambers, the requirement for vacuum pumps, and the need for a range of measurement systems make such schemes more expensive. “Price is a factor, but if you want to do atom-by-atom manipulation where you need extremely high levels of process control, then low-pressure systems offer considerable value,” says Cvelbar.
There are other issues to think about too before deciding on which system is needed for a particular application. “If you are working on tissues or soft biological matter subject to potential evaporation, these cannot subsist in a low-pressure environment, and this needs to be managed,” Cvelbar adds.
Atmospheric challenges
Atmospheric systems present challenges as well – humidity, for example, can influence the treatment and add to the number of parameters that need to be controlled. Under ambient conditions, plasma species react with the surrounding air as well as with the target sample, which can make the desired outcome more complicated to achieve. “The advantage of a vacuum system is that it provides a very clean and well-known environment, which helps in controlling your process and delivering consistent results,” says Cvelbar. “With atmospheric systems you can have more unknowns and may have to rely more on post-processing analysis.”
As for Cvelbar’s own work, his team’s projects fall into several different categories. One is the plasma deposition of antibacterial coatings where the group – together with Anton Nikiforov and Christophe Leys at Gent University in Belgium – is using the technique to add polymers to the surface of target materials. The researchers then go down two routes. One is to apply classical wet-chemical processing to add nanomaterial, followed by a further coating to sandwich the tiny structures between the substrate and this top layer. The other is to dope the plasma with nanoparticles so that the additives become secured within the matrix upon impact with the substrate.
The team is also carrying out plasma processing of surfaces for improved drug loading, which allows more of the active substance to be adsorbed onto the sample – in this case, a textile material. “We are using this method to develop medical dressings and patches with more controlled and longer lasting drug-release characteristics,” says Cvelbar. “The drug is much more tightly bonded to the surface in the case of plasma-processed material.”
Device development A knitted polyethylene terephthalate (PET) vascular graft – an artificial implant that can replace veins that have been ripped in an accident or, say, a cancer operation (left). An untreated PET surface covered with cells from the inner side of veins (centre) and the same surface with improved adhesion/proliferation after being treated with low-pressure radio-frequency oxygen plasma treatment (right), making the implant more compatible with the body. (Courtesy: Martin Kolar)
The effect can be dramatic. As Cvelbar explains, when you take conventional oral antibiotics, the drug reaches peak concentration in the body relatively quickly, so that after barely eight hours you often need to take a new dose. A plasma-engineered patch or bone implant, however, not only requires patients to take fewer drugs orally, which can otherwise overload the body, but also releases the drugs much more slowly and directly at an infected area, thereby reducing the burden for the patient.
Other projects include the use of plasma-grown nanomaterials as a building block for sensors, which warn against the presence of carcinogenic or toxic molecules in the surrounding environment. Thanks to the plasma treatment, the researchers can engineer nanostructures that enable sensing devices with much faster response rates than existing solutions. Typically, the sensor consists of an array of active sites, each of which may be tailored to respond to a different molecular species. Comparing the signal response of these structures against a reference provides the team with the inner workings of a device.
“Medicine is major driver for the application of biomaterials and for research into this scientific field,” says Cvelbar, who advises anyone thinking of moving into this field to attend relevant meetings, which this year include the International Conference on Plasma Medicine (ICPM) being held in Bratislava, Slovakia, in September. Another relevant conference this year is the American Vacuum Society meeting in Tennesse, US, in November, while further ahead is the World Biomaterials Congress scheduled to take place in Glasgow, UK, in 2020.
From bench to bedside
For researchers targeting medical applications, one advantage of working with biomaterials is that this can often be the most straightforward way of introducing plasma medicine into clinical practice. Examples include modified materials that are implanted within the body or are used as surface patches. Gaining approval for the plasma processing of wounds and related treatments or applying plasma methods to kill cancer is – in contrast – typically a much longer journey.
“When you are dealing with living bodies, approval of a new therapy needs time to be evaluated,” Cvelbar warns. “However, for biomaterials, you will often have some standard cases and references that can be included to help with the evaluation process.”
Special issue
To highlight the latest developments in plasma-inspired biomaterials, Uroš Cvelbar has teamed up with Cristina Canal from the Technical University of Catalonia, Barcelona, Spain, and Masaru Hori of the University of Nagoya, Japan, to guest-edit a special issue of Journal of Physics D: Applied Physics from IOP Publishing, which also publishes Physics World. The article collection, which is now open for submission, covers all aspects of research connecting plasma and biomaterials – ranging from plasma preparation of biomaterials for different applications (including both soft and hard tissue, such as teeth and bone), as well as drug-delivery applications and antibacterial coatings. The special issue also focuses on biological interactions of the novel plasma-prepared surfaces with bacteria, cells and tissues. Novel developments for diagnostics and sensing will be showcased too.
More information on the special issue of Journal of Physics D on plasma-inspired biomaterials is available at this link, guest-edited by Uroš Cvelbar (e-mail uros.cvelbar@ijs.si)
When shrunk to the nanoscale, quasicrystals become plastic. That is the finding of an international team of researchers, which says that its results could potentially widen the material’s applications. Quasicrystals – materials in which the atoms show long-range order but have no finite, periodically repeated unit cell – have fascinated materials scientists ever since their Nobel-prize-winning discovery in 1984. Their practical use, however, has been limited by their brittleness.
Conventional crystals plastically deform through dislocations in their lattice that can allow individual unit cells to swap places relatively easily. This makes some crystals, such as pure metals like copper and gold, highly ductile. In quasicrystals, however, there are no unit cells, so it takes more energy to move dislocations. “Normally, the dislocations in quasicrystals are quite mobile at high temperatures,” says materials-scientist Yu Zou of Massachusetts Institute of Technology in the US. “However, below 500 °C, the dislocations are not that mobile, so this can make the quasicrystal very brittle.”
Doing the “dislocation climb”
The materials often break before they deform, making them hard to form into specific shapes and severely limiting their usefulness. At high temperatures, quasicrystals deform by a process called dislocation climb, in which dislocations move perpendicularly to the actual atomic movement or slip; it remained uncertain, however, whether plastic deformation of quasicrystals was even possible at room temperature without destroying the crystal lattice, and if so what the dislocation mechanism would be.
In 1921 Alan Griffith showed that the fracture strength of materials should increase as samples become smaller, as they can more effectively dissipate strain energy. This phenomenon has since been observed in other materials like ceramics that are brittle at macroscopic scales. Zou, previously at ETH Zurich in Switzerland, and colleagues used this property to increase the stress on a common quasicrystal called i-Al–Pd–Mn until it plastically deformed. A computer simulation suggested that, above sizes of around 500 nm, plastic deformation would preferentially occur by cracking, and the material would therefore quickly fail. At smaller sizes, however, dislocations in the lattice would be able to move without the material cracking.
Catastrophic failure
To test this, the researchers performed two experiments. First, they compressed single-crystalline pillars of i-Al–Pd–Mn ranging from 1.8 μm to 140 nm in diameter until they failed, and observed them using an electron microscope. As predicted, the larger pillars were brittle, with the 1.8 μm pillar failing catastrophically after being compressed by just 3% of its height. However, below 500 nm, the pillars became much more ductile, being compressible by more than 50% without any cracking.
They then tried bending the pillars – the results were qualitatively similar, although the pillars had to be even smaller before they became bendable – a 300 nm pillar snapped rather than bending, for example. This is not surprising, Zou explains, because bending a material stretches one side, and materials are often more brittle in tension than in compression. “If there’s a crack in a sample, compressive stress can make it very difficult for this crack to open and propagate,” he says, “However, if you have a tensile stress, it’s very easy.” Intriguingly, when the researchers examined the micropillars, they appeared to have deformed not by deformation climb but by deformation glide, in which the dislocations move in the same plane as the atomic slip.
“Real breakthrough”
The researchers have subsequently repeated the experiment with another quasicrystal with a different structure and found similar results, so they are confident the results apply to all quasicrystals. Zou suggests the results should lead to studies of quasicrystals at different temperatures. The data also suggest tiny quasicrystals could be useful: they deform elastically at lower stress levels than required to cause plastic deformation, and their high elastic modulus could make them useful for energy storage. In addition, quasicrystals have interesting photonic and electronic properties, so the small-scale plasticity could help engineers to exploit these.
“I think it’s a real breakthrough” says materials-scientist Jean-Marie Dubois of the University of Lorraine in France, who was not involved in the research. “There’s beautiful images of nanorods being deformed by increasing the load – to me, this is the most important part. They also prove that the material remains quasicrystalline during the deformation. The detail of the deformation mechanism is not entirely established, as this requires in situ diffraction studies and things like that rather than post mortem analysis, but at this stage I think it’s quite good.”
An interstellar navigation technique that taps into the highly periodic signals from X-ray pulsars is being developed by a team of scientists from the National Physical Laboratory (NPL) and the University of Leicester. Using a small X-ray telescope on board a craft, it should be possible to determine its position in deep space to an accuracy of 2 km, according to the researchers.
Referred to as XNAV, the system would use careful timing of pulsars – which are highly magnetized spinning neutron stars – to triangulate a spacecraft’s position relative to a standardized location, such as the centre-of-mass in the solar system, which lies within the Sun’s corona. As pulsars spin, they emit beams of electromagnetic radiation, including strong radio emission, from their magnetic poles. If these beams point towards Earth, they appear to “pulse” with each rapid rotation.
Some pulsars in binary systems also accrete gas from their companion star, which can gather over the pulsar’s poles and grow hot enough to emit X-rays. It is these X-ray pulsars that can be used for stellar navigation – radio antennas are big and bulky, whereas X-ray detectors are smaller, often armed with just a single-pixel sensor, and are easier to include within a spacecraft’s payload.
X-ray payload
By 2013, theoretical work describing XNAV techniques had developed to the point where the European Space Agency commissioned a team, led by Setnam Shemar at NPL, to conduct a feasibility study, with an eye to one day using it on their spacecraft.
Shemar’s team analysed two techniques. The simplest is called “delta correction”, and works by timing incoming X-ray pulses – from a single pulsar – using an on-board atomic clock and comparing them to their expected time-of-arrival at the standardized location. The offset between these two timings, taken together with an initial estimated spacecraft position from ground tracking, can be used to obtain a more precise spacecraft position. This method is designed to be used in conjunction with ground-based tracking by NASA’s Deep Space Network or the European Space Tracking Network to provide more positional accuracy. Simulations indicated an accuracy of 2 km when locked onto a pulsar for 10 hours, or 5 km with just one hour of observation.
The benefits of this method would be most apparent in missions to the outer solar system, says Shemar, where the distance means that ground tracking is less accurate than within the inner solar system, where the XNAV system could be calibrated. However, Werner Becker of the Max Planck Institute for Extraterrestrial Physics, who was not involved in the current work, points out that such a system would not be automated and would still rely on communication with Earth.
Shemar agrees, which is why his team also considered a second technique, known as “absolute navigation”. To determine a location in 3D space, one must have the x, y and z co-ordinates, plus a time co-ordinate. If a spacecraft has an atomic clock on board, then this could be achieved by monitoring a minimum of three pulsars – if there is no atomic clock, a fourth pulsar would be required. The team’s simulations indicate that at the distance of Neptune, a spacecraft could autonomously measure its position to within 30 km in 3D space using the four-pulsar system.
Limits to technology
The downside to absolute navigation is that either more X-ray detectors are required – one for each pulsar – or a mechanism to allow the X-ray detector to slew to each pulsar in turn would need to be implemented. It’s a trade-off, points out Shemar, between accuracy and the practical limits of technology and cost. Becker, for instance, advocates using up to 10 pulsars to provide the highest accuracy, but implementing this on a spacecraft may be more difficult.
While the engineering behind such a steering mechanism is complex, “it’s not miles out of the scope of existing technology,” says Adrian Martindale of the University of Leicester, who participated in the feasibility study. In terms of the cost, complexity and size of X-ray detector required for XNAV, the team cites the example of the Mercury Imaging and X-ray Spectrometer (MIXS) instrument that will launch to the innermost planet on the upcoming Bepi-Colombo mission in 2018.
“We’ve shown that we think it is feasible to achieve,” Shemar told physicsworld.com, adding the caveat that some of the technology needs to catch up with the theoretical work. “Reducing the mass of the detector as far as possible, reducing the observation time for each pulsar and having a suitable steering mechanism are all significant challenges to be overcome.”
In February 2017, NASA plans to launch the Neutron star Interior Composition Explorer (NICER), to the International Space Station. Although primarily for X-ray astronomy, NICER will also perform a demonstration of XNAV. As this idea of pulsar-based navigation continues to grow, “space agencies may begin to take a more proactive role and start developing strategies for how an XNAV system could be implemented on a space mission,” says Shemar.
Becker is a little more sceptical about how soon XNAV will be ushered in for use on spacecraft. “The technology will become available when there is a need for it,” he says. “Autonomous pulsar navigation becomes attractive for deep-space missions but there are none planned for many years.”
Thinking man: Rene Descartes may have got some scientific details wrong, but he revolutionized the approach to thinking scientifically. (Courtesy: Science Photo Library)
In the Wallace Collection in London is a sculpture entitled “Descartes Piercing the Darkness of Ignorance”. Completed by Robert Guillaume Dardel in 1782, the sculpture shows the French philosopher, mathematician and scientist struggling to free himself from thick, enveloping clouds, inspired by rays of the Sun emerging from a hole in their midst. It casts René Descartes (1596–1650), who played a foundational role in both describing and using the scientific method, as a triumphant liberator. “No other great philosopher,” observes the venerable Dictionary of Scientific Biography, “except perhaps Aristotle, can have spent so much time in experimental observation.”
Recently, however, Descartes’ image has come under attack. Despite being a pop-culture celebrity for his philosophical remark “I think, therefore I am,” Descartes is routinely scorned for scientific and philosophical missteps. In his 2015 book To Explain the World, for instance, the Nobel-prize-winning physicist Steven Weinberg writes: “For someone who claimed to have found the true method for seeking reliable knowledge, it is remarkable how wrong Descartes was about so many aspects of nature…his repeated failure to get things right must cast a shadow on his philosophical judgement.”
Weinberg elaborates in crisp, no-nonsense prose: “[Descartes] was wrong in saying that the Earth is prolate (that is, that the distance through the Earth is greater from pole to pole than through the equatorial plane). He, like Aristotle, was wrong in saying that a vacuum is impossible. He was wrong in saying that space is filled with material vortices that carry the planets around in their paths. He was wrong in saying that the pineal gland is the seat of a soul responsible for human consciousness. He was wrong about what quantity is conserved in collisions. He was wrong in saying that the speed of a freely falling body is proportional to the distance fallen. Finally, on the basis of observation of several lovable pet cats, I am convinced that Descartes was also wrong in saying that animals are machines without true consciousness.”
How, then, can Descartes deserve to be portrayed as a herald of enlightenment?
The answer lies literally in the clouds – those from which Descartes is emerging in Dardel’s sculpture. These symbolize the lingering influence both of Aristotle and of the Church.
Sequestration
Aristotle’s world was composed of different places (Earth and heavens) populated by different substances (on Earth, natural things and human creations) that obeyed different laws. In his work, The World, which Descartes planned to publish in 1633, he pictured a single universe full of mechanisms that obeyed the same laws. Plants, animals and human bodies were mechanisms (though the latter were connected to souls). The rest of the natural world, too, behaved mechanistically, from sticks and stones to the Sun, Moon and planets. “I have described…the whole visible world as if it were only a machine in which there was nothing to consider but the shapes and movements [of its parts],” Descartes wrote. The scientists’ job was to figure out the mechanisms.
Then Descartes learned of Galileo’s condemnation. Although he was living at the time in the Netherlands, where he was beyond the reach of the Roman Church, Descartes was a believing Catholic and refused to publish anything heretical. But a heliocentric universe, the reason for which the Church had condemned Galileo’s work, was central to Descartes’ mechanistic picture. He therefore withdrew The World and wrote an essay describing his personal path to the new science as the preface to three non-controversial scientific articles he published in book form.
Now known as the Discourse on Method, this essay is one of the finest pieces of philosophical writing. He wrote it in French rather than Latin, so “even those who have not been to school can understand it”. In it, Descartes describes how one day – after long frustrations not knowing which of his beliefs were true, false or ungrounded – he sequestered himself and tried to set aside all received opinions to see if, among all his ideas and opinions, he could hit bedrock.
He could. Try saying to yourself – and meaning it – “I am not now thinking.” You can’t. No politician, theologian or even a God can convince you otherwise. That was only the first of an entire realm of truths that Descartes found he could know and reason about without theology and authority being at all relevant. If you do science this way, starting from clear and distinct ideas and making sure the results hang together like mathematics, he argued, you can’t be heretical. Doing science is like sequestering yourself from the world and theological issues, and those who do it no more reject that world than sequestered members of a jury question the authority of the legal system that set them up.
The critical point
In the end, Descartes got many of the world’s mechanisms wrong. But this should not obscure Descartes’ foundational role in modern science. His far-reaching contribution was to demonstrate how much you can understand of the world when you compose and test mechanisms and models. In his widely read and influential Discourse, Descartes modelled for followers what it is to act like a scientist.
Imagine belittling Adam Smith’s credentials as an economist just because his “pin factory” – the famous thought experiment that he deployed to show the benefits of the division of labour and capitalism – couldn’t cut it in the modern marketplace. Or imagine disparaging Copernicus’s astronomical credentials because he pictured the planets as moving in circles rather than ellipses. While Weinberg is right that Descartes got many of the world’s mechanisms wrong, this does not affect Descartes’ foundational role in establishing the scientific method. For, ironically, Weinberg’s criticism is based on a mechanistic way of thinking that it was Descartes’ extraordinary contribution to help legitimate.
The American Physical Society (APS) has relocated the 2018 annual meeting of the Division of Atomic, Molecular and Optical Physics (DAMOP) over concerns about a new state law that discriminates against members of the lesbian, gay, bisexual and transgender (LGBT) community. The conference, which was due to take place in Charlotte, North Carolina, will now take place in Fort Lauderdale, Florida, in late May or early June of that year.
The relocation is due to the introduction of the Public Facilities Privacy & Security Act – also known as House Bill 2 (HB2) – in North Carolina. An aspect of that bill, which was passed in March, requires people to use public bathrooms that correspond to the gender on their birth certificate. The requirement puts transgender and non-conforming gendered people at risk of arrest if they enter a public bathroom of their gender identity. The law prevents any city in the state from differing from HB2 regarding bathroom rights.
Following the introduction of the law, DAMOP’s 12-member executive committee voted to move the meeting. As the division typically books its meeting three years in advance, it will incur a cancellation fee for withdrawing from the venue. However, that is likely to be small compared with the meeting’s overall total cost.
Member support
DAMOP members overwhelmingly agreed with the decision. “I’m very proud of the APS for making this move and taking a very clear action that shows that the APS values trans physicists,” says Elena Long, a postdoctoral researcher at the University of New Hampshire, who is a member of the APS Committee on LGBT Issues. DAMOP chair Steven Rolston, a quantum physicist at the University of Maryland, says that members are 10:1 in favour of the move, based on feedback he has received.
The APS has recently been working to improve the environment for LGBT+ physicists. In March, the APS committee on LGBT Issues published its LGBT Climate in Physics report – the culmination of two years spent outlining the status of the LGBT community within physics and the barriers its members encounter. It outlined six recommendations to increase inclusion and address the current discriminatory environment, which the APS council has now endorsed. “Physicists should be able to focus on their work, free from having to deal with all forms of harassment and discrimination,” says Long, who is the founder of LGBT+physicists – an online resource for physicists of gender and sexual minorities.
In the increasingly connected world we live in, outbreaks of viruses such as Ebola and Zika pose serious threats to populations and place serious strains on healthcare systems. Quarantines – states of enforced isolation – are a common measure taken to hinder the spread of disease. In this video, Alexandra Fogg of the University of Leicester, UK, introduces an approach to quarantines known as the SIR model, adopted by health officers to predict the spread of epidemics.
This is one of a collection of videos based on student projects from the University of Leicester’s “Physics Special Topics” course, in which students use their physics knowledge to define and answer a quirky or unusual research question. The videos are part of our 100 Second Science series.
Construction has begun on one of the world’s largest and most sensitive cosmic-ray facilities. Located about 4410 m above sea level in the Haizi Mountain in Sichuan Province in southwest China, the 1.2 billion yuan ($180m) Large High Altitude Air Shower Observatory (LHAASO) will attempt to understand the origins of high-energy cosmic rays. LHAASO is set to open in 2020.
Cosmic rays are particles that originate in outer space and are accelerated to energies higher than those that can be achieved in even the largest man-made particle accelerators. Composed mainly of high-energy protons and atomic nuclei, cosmic rays create an air shower of particles such as photons and muons when they hit the atmosphere. Where cosmic rays come from, however, has remained a mystery since they were first spotted some 100 years ago.
Cosmic showers
LHAASO aims to detect cosmic rays over a wide range of energies from 1011–1018 eV using a Cherenkov water detector, covering a total area of 80 000 m2, together with 12 wide-field Cherenkov telescopes. These two types of instrument, which are above ground, will spot the Cherenkov radiation emitted when a charged particle travels through a medium faster than light can travel through that medium. LHAASO will also consist of a 1.3 km2 array of 6000 scintillation detectors that will study electrons and photons in the air showers, while an overlapping 1.3 km2 underground array of 1200 underground Cherenkov water tanks will detect muons.
LHAASO is not the only facility in the world trying to study the origin of cosmic rays. The IceCube facility at the South Pole observes high-energy neutrinos, while the Pierre Auger Observatory in Argentina explores cosmic rays with energies above 1018 eV. “LHAASO will play a complementary role with existing detectors to offer a more comprehensive picture of the cosmic-ray sky,” says Yifang Wang, head of the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences.
Challenges ahead
According to IHEP researcher Zhen Cao, who is LHAASO’s chief scientist, the construction of LHAASO will not be easy, with the Cherenkov water detectors being particularly tricky. Benedetto D’Ettorre Piazzoli, a former vice president of the National Institute of Nuclear Physics (INFN) in Italy, who has been involved in Sino-Italian collaborations in cosmic-ray research, agrees, adding that combining all of these detector types will be difficult. “The deployment, debugging, and operations management of many thousands of detectors of different types is very challenging at a level never faced before,” he says.
D’Ettorre Piazzoli is, however, confident that the facility will play an important role in cosmic-ray research. “As LHAASO is a very large installation, with a large amount of many types of detectors allowing the observation of cosmic rays and photons over a wide range of energies, it is expected to provide detailed and statistically relevant information on the transition from the galactic to the extra-galactic contribution,” he adds.
LHAASO is an international collaboration that includes scientists from China, France, Italy, Russia, Switzerland and Thailand. First mooted in 2008, the facility won approval from the National Development and Reform Commission of China in December 2015. Haizi Mountain was selected as the site due to its high elevation and good accessibility – being only 10 km away from Yading Airport – the world’s highest – and about 50 km from Daocheng County, which will be the base for the LHAASO team.
Concerns have been raised by US watchdogs over NASA‘s ambitious plans to send astronauts to Mars in the 2030s. In two reports (see related links) published last week, the US Government Accountability Office (GAO) – which audits government agencies on behalf of the US Congress – warns that tackling “several technical challenges” with the Orion capsule for transporting astronauts to Mars would push costs above the current estimated price tag of $11.3bn.
NASA’s schedule to Mars involves a series of tests of the Orion crew capsule and the Space Launch System (SLS), which is designed to launch Orion towards the red planet. The agency plans its first launch of the SLS late next year – preferably in September and no later than November. Called Exploration Mission 1 (EM-1), the test flight will carry a crewless Orion capsule around the Moon.
The second flight, dubbed EM-2, meanwhile, will carry a four-person crew in the Orion capsule by April 2023. But NASA wants to fast track the launch for August 2021, in what it calls an “aggressive” push. The mission will lift astronauts beyond low-Earth orbit for the first time since the Apollo 17 Moon landing in 1972, where they will practise manoeuvres with the craft.
Later in the decade, NASA then plans to use a robotic mission to capture an asteroid and redirect it into lunar orbit. Astronauts on a fresh Orion mission will explore the asteroid and return to Earth with samples from it. That flight will serve to test new systems – such as solar electric propulsion – for the eventual Mars mission.
Risk and reward
The two GAO reports cast doubt on NASA’s schedule, adding that the cost estimate “lacked support”. They assert that NASA has to tackle a number of issues with the launch site at the Kennedy Space Center in Florida to accommodate the SLS, which could delay the launch beyond 2018. “All the programmes are working with very low management reserves in terms of dollars and time,” says Cristina Chaplain, GAO’s director of acquisition and sourcing management, who led the studies. “It makes it very difficult to manage a programme under those circumstances. It puts them in a position of deferring work to later stages, where it could be more costly and time-consuming to address.”
The GAO adds that NASA only has a 40% chance of meeting the August 2021 date for EM-2, and that by setting such a goal the agency is accepting higher risk. In a response included in the report, Bill Gerstenmaier, NASA associate administrator for human exploration and operations, concedes some of the criticisms, but regards others as unnecessary. “To date, as the GAO correctly noted, Orion continues to perform within the boundaries of the programme cost and schedule commitment,” he writes.
While the situation may seem serious, some regard it as not unusual, given the nature of crewed space missions. “I would have some concerns, but I’m not terribly worried,” says Scott Pace, director of George Washington University’s Space Policy Institute. “For Orion, cost and risk are being traded in a responsible manner.” Yet he questions the early target date for EM-1. “The political support for pulling the schedule in closer is not there now,” he says.
Meanwhile, the US government has approved the first commercial mission to the Moon. The Federal Aviation Administration’s Office of Commercial Space Transportation gave the go-ahead for the Moon Express company to send a robotic lander to the lunar surface next year. Based in Cape Canaveral, Florida, Moon Express plans to equip its small table-sized lander with experiments and commercial cargo, including some cremated human remains.
