Two independent teams in the US have demonstrated the potential of using the optical properties of nanocrystals to create remote sensors that measure tiny forces on tiny length scales. One team is based at Stanford University and used nanocrystals to measure the micronewton-scale forces exerted by a worm as it chewed bacteria. The other team is based at several institutes and used the photon avalanche effect in nanocrystals to measure sub-nanonewton to micronewton forces. The latter technique could potentially be used to study forces involved in processes such as stem cell differentiation.
Remote sensing of forces at small scales is challenging, especially inside living organisms. Optical tweezers cannot make remote measurements inside the body, while fluorophores – molecules that absorb and re-emit light – can measure forces in organisms, but have limited range, problematic stability or, in the case of quantum dots, toxicity. Nanocrystals with optical properties that change when subjected to external forces offer a way forward.
At Stanford, materials scientist Jennifer Dionne led a team that used nanocrystals doped with ytterbium and erbium. When two ytterbium atoms absorb near-infrared photons, they can then transfer energy to a nearby erbium atom. In this excited state, the erbium can either decay directly to its lowest energy state by emitting red light, or become excited to an even higher-energy state that decays by emitting green light. These processes are called upconversion.
The ratio of green to red emission depends on the separation between the ytterbium and erbium atoms, and the separation between the erbium atoms – explains Dionne’s PhD student Jason Casar, who is lead author of a paper describing the Stanford research. Forces on the nanocrystal can change these separations and therefore affect that ratio.
The researchers encased their nanocrystals in polystyrene vessels approximately the size of a E coli bacterium. They then mixed the encased nanoparticles with E coli bacteria that were then fed to tiny nematode worms. To extract the nutrients, the worm’s pharynx needs to break open the bacterial cell wall. “The biological question we set out to answer is how much force is the bacterium generating to achieve that breakage?” explains Stanford’s Miriam Goodman.
The researchers shone near-infrared light on the worms, allowing them to monitor the flow of the nanocrystals. By measuring the colour of the emitted light when the particles reached the pharynx, they determined the force it exerted with micronewton-scale precision.
Meanwhile, a collaboration of scientists at Columbia University, Lawrence Berkeley National Laboratory and elsewhere has shown that a process called photon avalanche can be used to measure even smaller forces on nanocrystals. The team’s avalanching nanoparticles (ANPs) are sodium yttrium fluoride nanocrystals doped with thulium – and were discovered by the team in 2021.
The sensing process uses a laser tuned off-resonance from any transition from the ground state of the ANP. “We’re bathing our particles in 1064 nm light,” explains James Schuck of Columbia University, whose group led the research. “If the intensity is low, that all just blows by. But if, for some reason, you do eventually get some absorption – maybe a non-resonant absorption in which you give up a few phonons…then the fun starts. Our laser is resonant with an excited state transition, so you can absorb another photon.”
This creates a doubly excited state that can decay radiatively directly to the ground state, producing an upconverted photon. Or, it energy can be transferred to a nearby thulium atom, which becomes resonant with the excited state transition and can excite more thulium atoms into resonance with the laser. “That’s the avalanche,” says Schuck; “We find on average you get 30 or 40 of these events – it’s analogous to a chain reaction in nuclear fission.”
Now, Schuck and colleagues have shown that the exact number of photons produced in each avalanche decreases when the nanoparticle experiences compressive force. One reason is that the phonon frequencies are raised as the lattice is compressed, making non-radiatively decay energetically more favourable.
The thulium-doped nanoparticles decay by emitting either red or near infrared photons. As the force increases, the red dims more quickly, causing a change in the colour of the emitted light. These effects allowed the researchers to measure forces from the sub-nanonewton to the micronewton range – at which point the light output from the nanoparticles became too low to detect.
Schuck and colleagues are now seeking practical applications of their discovery, and not just for measuring forces.
“We’re discovering that this avalanching process is sensitive to a lot of things,” says Schuck. “If we put these particles in a cell and we’re trying to measure a cellular force gradient, but the cell also happened to change its temperature, that would also affect the brightness of our particles, and we would like to be able to differentiate between those things. We think we know how to do that.”
If the technique could be made to work in a living cell, it could be used to measure tiny forces such as those involved in the extra-cellular matrix that dictate stem cell differentiation.
Andries Meijerink of Utrecht University in the Netherlands believes both teams have done important work that is impressive in different ways. Schuck and colleagues for unveiling a fundamentally new force sensing technique and Dionne’s team for demonstrating a remarkable practical application.
However, Meijerink is sceptical that photon avalanching will be useful for sensing in the short term. “It’s a very intricate process,” he says, adding, “There’s a really tricky balance between this first absorption step, which has to be slow and weak, and this resonant absorption”. Nevertheless, he says that researchers are discovering other systems that can avalanche. “I’m convinced that many more systems will be found,” he says.
Both studies are described in Nature. Dionne and colleagues report their results here, and Schuck and colleagues here.
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Last year was the year of elections and 2025 is going to be the year of decisions.
After many countries, including the UK, Ireland and the US, went to the polls in 2024, the start of 2025 will see governments at the beginning of new terms, forced to respond swiftly to mounting economic, social, security, environmental and technological challenges.
These issues would be difficult to address at any given time, but today they come amid a turbulent geopolitical context. Governments are often judged against short milestones – the first 100 days or a first budget – but urgency should not come at the cost of thinking long-term, because the decisions over the next few months will shape outcomes for years, perhaps decades, to come. This is no less true for science than it is for health and social care, education or international relations.
In the UK, the first half of the year will be dominated by the government’s spending review. Due in late spring, it could be one of the toughest political tests for UK science, as the implications of the tight spending plans announced in the October budget become clear. Decisions about departmental spending will have important implications for physics funding, from research to infrastructure, facilities and teaching.
One of the UK government’s commitments is to establish 10-year funding cycles for key R&D activities – a policy that could be a positive improvement. Physics discoveries often take time to realise in full, but their transformational nature is indisputable. From fibre-optic communications to magnetic resonance imaging, physics has been indispensable to many of the world’s most impactful and successful innovations.
Emerging technologies, enabled by physicists’ breakthroughs in fields such as materials science and quantum physics, promise to transform the way we live and work, and create new business opportunities and open up new markets. A clear, comprehensive and long-term vision for R&D would instil confidence among researchers and innovators, and long-term and sustainable R&D funding would enable people and disruptive ideas to flourish and drive tomorrow’s breakthroughs.
Alongside the spending review, we are also expecting the publication of the government’s industrial strategy. The focus of the green paper published last year was an indication of how the strategy will place significance on science and technology in positioning the UK for economic growth.
If we don’t recognise the need to fund more physicists, we will miss so many of the opportunities that lie ahead
Physics-based industries are a foundation stone for the UK economy and are highly productive, as highlighted by research commissioned by the Institute of Physics, which publishes Physics World. Across the UK, the physics sector generates £229bn gross value added, or 11% of total UK gross domestic product. It creates a collective turnover of £643bn, or £1380bn when indirect and induced turnover is included.
Labour productivity in physics-based businesses is also strong at £84 300 per worker, per year. So, if physics is not at the heart of this effort, then the government’s mission of economic revival is in danger of failing to get off the launch pad.
Another of the new government’s policy priorities is the strategic defence review, which is expected to be published later this year. It could have huge implications for physics given its core role in many of the technologies that contribute to the UK’s defence capabilities. The changing geopolitical landscape, and potential for strained relations between global powers, may well bring research security to the front of the national mind.
Intellectual property, and scientific innovation, are some of the UK’s greatest strengths and it is right to secure them. But physics discoveries in particular can be hampered by overzealous security measures. So much of the important work in our discipline comes from years of collaboration between researchers across the globe. Decisions about research security need to protect, not hamper, the future of UK physics research.
This year could also be pivotal for UK universities, as securing their financial stability and future will be one of the major challenges. Last year, the pressures faced by higher education institutions became apparent, with announcements of course closures, redundancies and restructures as a way of saving money. The rise in tuition fees has far from solved the problem, so we need to be prepared for more turbulence coming for the higher education sector.
These things matter enormously. We have heard that universities are facing a tough situation, and it’s getting harder for physics departments to exist. But if we don’t recognise the need to fund more physicists, we will miss so many of the opportunities that lie ahead.
As we celebrate the International Year of Quantum Science and Technology that marks the centenary of the initial development of quantum mechanics by Werner Heisenberg, 2025 is a reminder of how the benefits of physics span over decades.
We need to enhance all the vital and exciting developments that are happening in physics departments. The country wants and needs a stronger scientific workforce – just think about all those individuals who studied physics and now work in industries that are defending the country – and that workforce will be strongly dependent on physics skills. So our priority is to make sure that physics departments keep doing world-leading research and preparing the next generation of physicists that they do so well.
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If aliens came to Earth and tried to work out how we earthlings make sense of our world, they’d surely conclude that we take information and slot it into pre-existing stories – some true, some false, some bizarre. Ominously, these aliens would be correct. You don’t need to ask earthling philosophers, just look around.
Many politicians and influencers, for instance, are convinced that scientific evidence does not tell the reality about, for instance, autism or AIDS, the state of the atmosphere or the legitimacy of elections, or even about aliens. Truth comes to light only when you “know the full story”, which will eventually reveal the scientific data to be deceptive or irrelevant.
To see how this works in practice, suppose you hear someone say that a nearby lab is leaking x picocuries of a radioactive substance, potentially exposing you to y millirems of dose. How do you know if you’re in danger? Well, you’ll instinctively start going through a mental checklist of questions.
Who’s speaking – scientist, politician, reporter or activist? If it’s a scientist, are they from the government, a university, or an environmental or anti-nuclear group? You might then wonder: how trustworthy are the agencies that regulate the substance? Is the lab a good neighbour, or did it cover up past incidents? How much of the substance is truly harmful?
Your answers to all these questions will shape the story you tell yourself. You might conclude: “The lab is a responsible organization and will protect me”. Or perhaps you’ll think: “The lab is a thorn in the side of the community and is probably doing weapons-related work. The leak’s a sign of something far worse.”
Perhaps your story will be: “Those environmentalists are just trying to scare us and the data indicate the leak is harmless”. Or maybe it’ll be: “I knew it! The lab’s sold out, the data are terrifying, and the activists are revealing the real truth”. Such stories determine the meaning of the picocuries and millirems for humans, not the other way around.
Humans gain a sense of what’s happening in several ways. Three of them, to use philosophical language, are deferential, civic and melodramatic epistemology.
In “deferential epistemology”, citizens habitually take the word of experts and institutions about things like the dangers of x picocuries and exposures of y millirems. In his 1624 book New Atlantis, the philosopher Francis Bacon famously crafted a fictional portrait of an island society where deferential epistemology rules and people instinctively trust the scientific infrastructure.
Earthlings haven’t seen deferential epistemology in a while.
We may think this is how people ought to behave. But Bacon, who was also a politician, understood that deference to experts is not automatic and requires constantly curating the public face of the scientific infrastructure. Earthlings haven’t seen deferential epistemology in a while.
“Civic epistemology”, meanwhile, is how people acquire knowledge in the absence of that curation. Such people don’t necessarily reject experts but hear their voices alongside many others claiming to know best how to pursue our interests and values. Civic epistemology is when we negotiate daily life not by first consulting scientists but by pursuing our concerns with a mix of habit, trust, experience and friendly advice.
We sometimes don’t, in fact, take scientific advice when it collides with how we already behave; we may smoke or drink, for instance, despite warnings not to. Or we might seek guidance from non-scientists about things like the harms of radiation.
Finally, what I call “melodramatic epistemology” draws on the word “melodrama”, a genre of theatre involving extreme plots, obvious villains, emotional appeal, sensational language, and moral outrage (the 1939 film Gone with the Wind comes to mind).
A melodramatic lens can be a powerful and irresistible way for humans to digest difficult and emotionally charged events.
Melodramas were once considered culturally insignificant, but scholars such as Peter Brooks from Yale University have shown that a melodramatic lens can be a powerful and irresistible way for humans to digest difficult and emotionally charged events. The clarity, certainty and passion provided by a melodramatic read on a situation tends to displace the complexities, uncertainties and dispassion of scientific evaluation and evidence.
One example from physics occurred at the Lawrence Berkeley Laboratory in the late 1990s when activists fought, successfully, for the closing of its National Tritium Labeling Facility (NTLF). As I have written before, the NTLF had successfully developed techniques for medical studies while releasing tritium emissions well below federal and state environmental standards.
Activists, however, used melodramatic epistemology to paint the NTLF’s scientists as villains spreading breast cancer throughout the area, and denounced them as making “a terrorist attack on the citizens of Berkeley”. One activist called the scientists “piano players in a nuclear whorehouse.”
The aliens studying us would worry most about melodramatic epistemology. Melodramatic epistemology, though dangerous, is nearly impervious to being altered, for any contrary data, studies and expert judgment are considered to spring from the villain’s allies and therefore to incite rather than allay fear.
Two US psychologists – William Brady from Northwestern University and Molly Crockett from Princeton University – recently published a study of how and why misinformation spreads (Science 386 991). By analyzing data from Facebook and Twitter and by conducting real experiments with participants, they found that sources of misinformation evoke more outrage than trustworthy sources. Worse still, the outrage encourages us to share the misinformation even if we haven’t fully read the original source.
This makes it hard to counter misinformation. As the authors tactfully conclude: “Outrage-evoking misinformation may be difficult to mitigate with interventions that assume users want to share accurate information”.
The best, and perhaps only, way to challenge melodramatic stories is to write bigger, more encompassing stories that reveal that a different plot is unfolding.
In my view, the best, and perhaps only, way to challenge melodramatic stories is to write bigger, more encompassing stories that reveal that a different plot is unfolding. Such a story about the NTLF, for instance, would comprise story lines about the benefits of medical techniques, the testing of byproducts, the origin of regulations of toxins, the perils of our natural environment, the nature of fear and its manipulation, and so forth. In such a big story, those who promote melodramatic epistemology show up as an obvious, and dangerous, subplot.
If the aliens see us telling such bigger stories, they might not give up earthlings for lost.
The post Why telling bigger stories is the only way to counter misinformation appeared first on Physics World.
A novel fusion device based at the University of Seville in Spain has achieved its first plasma. The SMall Aspect Ratio Tokamak (SMART) is a spherical tokamak that can operate with a “negative triangularity” – the first compact spherical tokamak to do so. Work performed on the machine could be useful when designing compact fusion power plants based on spherical tokamak technology.
SMART has been constructed by the University of Seville’s Plasma Science and Fusion Technology Laboratory. With a vessel dimension of 1.6 × 1.6 m, SMART has a 30 cm diameter solenoid wrapped around 12 toroidal field coils while eight poloidal field coils are used to shape the plasma.
Triangularity refers to the shape of the plasma relative to the tokamak. The cross section of the plasma in a tokamak is typically shaped like a “D”. When the straight part of the D faces the centre of the tokamak, it is said to have positive triangularity. When the curved part of the plasma faces the centre, however, the plasma has negative triangularity.
It is thought that negative triangularity configurations can better suppress plasma instabilities that expel particles and energy from the plasma, helping to prevent damage to the tokamak wall.
Last year, researchers at the University of Seville began to prepare the tokamak’s inner walls for a high pressure plasma by heating argon gas with microwaves. When those tests were successful, engineers then worked toward producing the first plasma.
“This is an important achievement for the entire team as we are now entering the operational phase,” notes SMART principal investigator Manuel García Muñoz. “The SMART approach is a potential game changer with attractive fusion performance and power handling for future compact fusion reactors. We have exciting times ahead.”
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