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Reçu aujourd’hui — 29 mai 20256.5 📰 Sciences English

Teaching quantum physics to everyone: pictures offer a new way of understanding

29 mai 2025 Ă  16:49

Quantum science is enjoying a renaissance as nascent quantum computers emerge from the lab and quantum sensors are being used for practical applications.

As the technologies we use become more quantum in nature, it follows that everyone should have a basic understanding of quantum physics. To explore how quantum physics can be taught to the masses, I am joined by Arjan Dhawan, Aleks Kissinger and Bob Coecke – who are all based in the UK.

Coecke is chief scientist at Quantinuum – which develops quantum computing hardware and software. Kissinger is associate professor of quantum computing at the University of Oxford; and Dhawan is studying mathematics at the University of Durham.

Kissinger and Coecke have developed a way of teaching quantum physics using diagrams. In 2023, Oxford and Quantinuum joined forces to use the method in a pilot summer programme for 15 to 17 year-olds. Dhawan was one of their students.

Physics World is brought to you by IOP Publishing, which also publishes scholarly journals, conference proceedings and ebooks.

You can download the book The Ringed Planet: Second Edition free of charge for a limited time only. By Joshua Colwell, the book is a must read on Saturn and the Cassini mission. An updated and expanded third edition is also hot off the press.

Browse all ebooks here and remember that you can always read the first chapters of all IOPP ebooks for free.

This article forms part of Physics World‘s contribution to the 2025 International Year of Quantum Science and Technology (IYQ), which aims to raise global awareness of quantum physics and its applications.

Stayed tuned to Physics World and our international partners throughout the next 12 months for more coverage of the IYQ.

Find out more on our quantum channel.

 

The post Teaching quantum physics to everyone: pictures offer a new way of understanding appeared first on Physics World.

Secondary dose checks ensure safe and accurate delivery of adaptive radiotherapy

29 mai 2025 Ă  13:00

Adaptive radiotherapy, an advanced cancer treatment in which each fraction is tailored to the patient’s daily anatomy, offers the potential to maximize target conformality and minimize dose to surrounding healthy tissue. Based on daily scans – such as MR images recorded by an MR-Linac, for example – treatment plans are adjusted each day to account for anatomical changes in the tumour and surrounding healthy tissue.

Creating a new plan for every treatment fraction, however, increase the potential for errors, making fast and effective quality assurance (QA) procedures more important than ever. To meet this need, the physics team at Hospital Almater in Mexicali, Mexico, is using Elekta ONE | QA, powered by ThinkQA Secondary Dose Check* (ThinkQA SDC) software to ensure that each adaptive plan is safe and accurate before it is delivered to the patient.

Radiotherapy requires a series of QA checks prior to treatment delivery, starting with patient-specific QA, where the dose calculated by the treatment planning system is delivered to a phantom. This procedure ensures that the delivered dose distribution matches the prescribed plan. Alongside, secondary dose checks can be performed, in which an independent algorithm verifies that the calculated dose distribution corresponds with that delivered to the actual patient anatomy.

“The secondary dose check is an independent dose calculation that uses a different algorithm to the one in the treatment planning system,” explains Alexis Cabrera Santiago, a medical physicist at Hospital Almater. “ThinkQA SDC software calculates the dose based on the patient anatomy, which is actually more realistic than using a rigid phantom, so we can compare both results and catch any differences before treatment.”

ThinkQA SDC
Pre-treatment verification ThinkQA SDC’s unique dose calculation method has been specifically designed for Elekta Unity. (Courtesy: Elekta)

For adaptive radiotherapy in particular, this second check is invaluable. Performing phantom-based QA following each daily imaging session is often impractical. Instead, in many cases, it’s possible to use ThinkQA SDC instead.

“Secondary dose calculation is necessary in adaptive treatments, for example using the MR-Linac, because you are changing the treatment plan for each session,” says José Alejandro Rojas‑López, who commissioned and validated ThinkQA SDC at Hospital Almater. “You are not able to shift the patient to realise patient-specific QA, so this secondary dose check is needed to analyse each treatment session.”

ThinkQA SDC’s ability to achieve patient-specific QA without shifting the patient is extremely valuable, allowing time savings while upholding the highest level of QA safety. “The AAPM TG 219 report recognises secondary dose verification as a validated alternative to patient-specific QA, especially when there is no time for traditional phantom checks in adaptive fractions,” adds Cabrera Santiago.

The optimal choice

At Hospital Almater, all external-beam radiation treatments are performed using an Elekta Unity MR-Linac (with brachytherapy employed for gynaecological cancers). This enables the hospital to offer adaptive radiotherapy for all cases, including head-and-neck, breast, prostate, rectal and lung cancers.

To ensure efficient workflow and high-quality treatments, the team turned to the ThinkQA SDC software. ThinkQA SDC received FDA 510(k) clearance in early 2024 for use with both the Unity MR-Linac and conventional Elekta linacs.

Rojas‑López (who now works at Hospital Angeles Puebla) says that the team chose ThinkQA SDC because of its user-friendly interface, ease of integration into the clinical workflow and common integrated QA platform for both CT and MR-Linac systems. The software also offers the ability to perform 3D evaluation of the entire planning treatment volume (PTV) and the organs-at-risk, making the gamma evaluation more robust.

Alexis Cabrera Santiago and José Alejandro Rojas‑López
Physics team Alexis Cabrera Santiago and José Alejandro Rojas‑López. (Courtesy: José Alejandro Rojas‑López/Hospital Almater)

Commissioning of ThinkQA SDC was fast and straightforward, Rojas‑López notes, requiring minimal data input into the software. For absolute dose calibration, the only data needed are the cryostat dose attenuation response, the output dose geometry and the CT calibration.

“This makes a difference compared with other commercial solutions where you have to introduce more information, such as MLC [multileaf collimator] leakage and MLC dosimetric leaf gap, for example,” he explains. “If you have to introduce more data for commissioning, this delays the clinical introduction of the software.”

Cabrera Santiago is now using ThinkQA SDC to provide secondary dose calculations for all radiotherapy treatments at Hospital Almater. The team has established a protocol with a 3%/2 mm gamma criterion, a tolerance limit of 95% and an action limit of 90%. He emphasizes that the software has proved robust and flexible, and provides confidence in the delivered treatment.

“ThinkQA SDC lets us work with more confidence, reduces risk and saves time without losing control over the patient’s safety,” he says. “It checks that the plan is correct, catches issues before treatment and helps us find any problems like set-up errors, contouring mistakes and planning issues.”

The software integrates smoothly into the Elekta ONE adaptive workflow, providing reliable results without slowing down the clinical workflow. “In our institution, we set up ThinkQA SDC so that it automatically receives the new plan, runs the check, compares it with the original plan and creates a report – all in around two minutes,” says Cabrera Santiago. “This saves us a lot of time and removes the need to do everything manually.”

A case in point

As an example of ThinkQA SDC’s power to ease the treatment workflow, Rojas‑López describes a paediatric brain tumour case at Hospital Almater. The young patient needed sedation during their treatment, requiring the physics team to optimize the treatment time for the entire adaptive radiotherapy workflow. “ThinkQA SDC served to analyse, in a fast mode, the treatment plan QA for each session. The measurements were reliable, enabling us to deliver all of the treatment sessions without any delay,” he explains.

Indeed, the ability to use secondary dose checks for each treatment fraction provides time advantages for the entire clinical workflow over phantom-based pre-treatment QA. “Time in the bunker is very expensive,” Rojas‑López points out. “If you reduce the time required for QA, you can use the bunker for patient treatments instead and treat more patients during the clinical time. Secondary dose check can optimize the workflow in the entire department.”

Importantly, in a recent study comparing patient-specific QA measurements using Sun Nuclear’s ArcCheck with ThinkQA SDC calculations, Rojas‑López and colleagues confirmed that the two techniques provided comparable results, with very similar gamma passing rates. As such, they are working to reduce phantom measurements and, in most cases, replace them with a secondary dose check using ThinkQA SDC.

The team at Hospital Almater concur that ThinkQA SDC provides a reliable tool to evaluate radiation treatments, including the first fraction and all of the adaptive sessions, says Rojas‑López. “You can use it for all anatomical sites, with reliable and confident results,” he notes. “And you can reduce the need for measurements using another patient-specific QA tool.”

“I think that any centre doing adaptive radiotherapy should seriously consider using a tool like ThinkQA SDC,” adds Cabrera Santiago.

*ThinkQA is manufactured by DOSIsoft S.A. and distributed by Elekta.

The post Secondary dose checks ensure safe and accurate delivery of adaptive radiotherapy appeared first on Physics World.

“Zombie” volcano reveals its secrets

29 mai 2025 Ă  10:30

The first high-resolution images of Bolivia’s Uturuncu volcano have yielded unprecedented insights into whether this volcanic “zombie” is likely to erupt in the near future. The images were taken using a technique that combines seismology, rock physics and petrological analyses, and the scientists who developed it say it could apply to other volcanoes, too.

Volcanic eruptions occur when bubbles of gases such as SO2 and CO2 rise to the Earth’s surface through dikes and sills in the planet’s crust, bringing hot, molten rock known as magma with them. To evaluate the chances of this happening, researchers need to understand how much gas and melted rock have accumulated in the volcano’s shallow upper crust, or crater. This is not easy, however, as the structures that convey gas and magma to the surface are complex and mapping them is challenging with current technologies.

A zombie volcano

In the new work, a team led by Mike Kendall of the University of Oxford, UK and Haijiang Zhang from the University of Science and Technology of China (USTC) employed a combination of seismological and petrophysical analyses to create such a map for Uturuncu. Located in the Central Andes, this volcano formed in the Pleistocene era (around 2.58 million to 11,700 years ago) as the oceanic Nazca plate was forced beneath the South American continental plate. It is made up of around 50 km3 of homogeneous, porphyritic dacite lava flows that are between 62% and 67% silicon dioxide (SiO2) by weight, and it sits atop the Altiplano–Puna magma body, which is the world’s largest body of partially-melted silicic rock.

Although Uturuncu has not erupted for nearly 250,000 years, it is not extinct. It regularly emits plumes of gas, and earthquakes are a frequent occurrence in the shallow crust beneath and around it. Previous geodetic studies also detected a 150-km-wide deformed region of rock centred around 3 km southwest of its summit. These signs of activity, coupled with Uturuncu’s lack of a geologically recent eruption, have led some scientists to describe it as a “zombie”.

Movement of liquid and gas explains Uturuncu’s unrest

To tease out the reasons for Uturuncu’s semi-alive behaviour, the team turned to seismic tomography – a technique Kendall compares to medical imaging of a human body. The idea is to detect the seismic waves produced by earthquakes travelling through the Earth’s crust, analyse their arrival times, and use this information to create three-dimensional images of what lies beneath the surface of the structure being studied.

Writing in PNAS, Kendall and colleagues explain that they used seismic tomography to analyse signals from more than 1700 earthquakes in the region around Uturuncu. They performed this analysis in two ways. First, they assumed that seismic waves travel through the crust at the same speed regardless of their direction of propagation. This isotropic form of tomography gave them a first image of the region’s structure. In their second analysis, they took the directional dependence of the seismic waves’ speed into account. This anisotropic tomography gave them complementary information about the structure.

The researchers then combined their tomographic measurements with previous geophysical imaging results to construct rock physics models. These models contain information about the paths that hot migrating fluids and gases take as they migrate to the surface. In Uturuncu’s case, the models showed fluids and gases accumulating in shallow magma reservoirs directly below the volcano’s crater and down to a depth of around 5 km. This movement of liquid and gas explains Uturuncu’s unrest, the team say, but the good news is that it has a low probability of producing eruptions any time soon.

According to Kendall, the team’s methods should be applicable to more than 1400 other potentially active volcanoes around the world. “It could also be applied to identifying potential geothermal energy sites and for critical metal recovery in volcanic fluids,” he tells Physics World.

The post “Zombie” volcano reveals its secrets appeared first on Physics World.

Reçu hier — 28 mai 20256.5 📰 Sciences English

Shengxi Huang: how defects can boost 2D materials as single-photon emitters

28 mai 2025 Ă  17:01
Photo of researchers in a lab at Rice University.
Hidden depths Shengxi Huang (left) with members of her lab at Rice University in the US, where she studies 2D materials as single-photon sources. (Courtesy: Jeff Fitlow)

Everyday life is three dimensional, with even a sheet of paper having a finite thickness. Shengxi Huang from Rice University in the US, however, is attracted by 2D materials, which are usually just one atomic layer thick. Graphene is perhaps the most famous example — a single layer of carbon atoms arranged in a hexagonal lattice. But since it was first created in 2004, all sorts of other 2D materials, notably boron nitride, have been created.

An electrical engineer by training, Huang did a PhD at the Massachusetts Institute of Technology and postdoctoral research at Stanford University before spending five years as an assistant professor at the Pennsylvania State University. Huang has been at Rice since 2022, where she is now an associate professor in the Department of Electrical and Computer Engineering, the Department of Material Science and NanoEngineering, and the Department of Bioengineering.

Her group at Rice currently has 12 people, including eight graduate students and four postdocs. Some are physicists, some are engineers, while others have backgrounds in material science or chemistry. But they all share an interest in understanding the optical and electronic properties of quantum materials and seeing how they can be used, for example, as biochemical sensors. Lab equipment from Picoquant is vital in helping in that quest, as Huang explains in an interview with Physics World.

Why are you fascinated by 2D materials?

I’m an electrical engineer by training, which is a very broad field. Some electrical engineers focus on things like communication and computing, but others, like myself, are more interested in how we can use fundamental physics to build useful devices, such as semiconductor chips. I’m particularly interested in using 2D materials for optoelectronic devices and as single-photon emitters.

What kinds of 2D materials do you study?

The materials I am particularly interested in are transition metal dichalcogenides, which consist of a layer of transition-metal atoms sandwiched between two layers of chalcogen atoms – sulphur, selenium or tellurium. One of the most common examples is molybdenum disulphide, which in its monolayer form has a layer of sulphur on either side of a layer of molybdenum. In multi-layer molybdenum disulphide, the van der Waals forces between the tri-layers are relatively weak, meaning that the material is widely used as a lubricant – just like graphite, which is a many-layer version of graphene.

Why do you find transition metal dichalcogenides interesting?

Transition metal dichalcogenides have some very useful optoelectronic properties. In particular, they emit light whenever the electron and hole that make up an “exciton” recombine. Now because these dichalcogenides are so thin, most of the light they emit can be used. In a 3D material, in contrast, most light is generated deep in the bulk of the material and doesn’t penetrate beyond the surface. Such 2D materials are therefore very efficient and, what’s more, can be easily integrated onto chip-based devices such as waveguides and cavities.

Transition metal dichalcogenide materials also have promising electronic applications, particularly as the active material in transistors. Over the years, we’ve seen silicon-based transistors get smaller and smaller as we’ve followed Moore’s law, but we’re rapidly reaching a limit where we can’t shrink them any further, partly because the electrons in very thin layers of silicon move so slowly. In 2D transition metal dichalcogenides, in contrast, the electron mobility can actually be higher than in silicon of the same thickness, making them a promising material for future transistor applications.

What can such sources of single photons be used for?

Single photons are useful for quantum communication and quantum cryptography. Carrying information as zero and one, they basically function as a qubit, providing a very secure communication channel. Single photons are also interesting for quantum sensing and even quantum computing. But it’s vital that you have a highly pure source of photons. You don’t want them mixed up with “classical photons”, which — like those from the Sun — are emitted in bunches as otherwise the tasks you’re trying to perform cannot be completed.

What approaches are you taking to improve 2D materials as single-photon emitters?

What we do is introduce atomic defects into a 2D material to give it optical properties that are different to what you’d get in the bulk. There are several ways of doing this. One is to irradiate a sample with ions or electrons, which can bombard individual atoms out to generate “vacancy defects”. Another option is to use plasmas, whereby atoms in the sample get replaced by atoms from the plasma.

So how do you study the samples?

We can probe defect emission using a technique called photoluminescence, which basically involves shining a laser beam onto the material. The laser excites electrons from the ground state to an excited state, prompting them to emit light. As the laser beam is about 500-1000 nm in diameter, we can see single photon emission from an individual defect if the defect density is suitable.

Photo of researchers in a lab at Rice University
Beyond the surface Shengxi Huang (second right) uses equipment from PicoQuant to probe 2D materials. (Courtesy: Jeff Fitlow)

What sort of experiments do you do in your lab?

We start by engineering our materials at the atomic level to introduce the correct type of defect. We also try to strain the material, which can increase how many single photons are emitted at a time. Once we’ve confirmed we’ve got the correct defects in the correct location, we check the material is emitting single photons by carrying out optical measurements, such as photoluminescence. Finally, we characterize the purity of our single photons – ideally, they shouldn’t be mixed up with classical photons but in reality, you never have a 100% pure source. As single photons are emitted one at a time, they have different statistical characteristics to classical light. We also check the brightness and lifetime of the source, the efficiency, how stable it is, and if the photons are polarized. In fact, we have a feedback loop: what improvements can we do at the atomic level to get the properties we’re after?

Is it difficult adding defects to a sample?

It’s pretty challenging. You want to add just one defect to an area that might be just one micron square so you have to control the atomic structure very finely. It’s made harder because 2D materials are atomically thin and very fragile. So if you don’t do the engineering correctly, you may accidentally introduce other types of defects that you don’t want, which will alter the defects’ emission.

What techniques do you use to confirm the defects are in the right place?

Because the defect concentration is so low, we cannot use methods that are typically used to characterise materials, such as X-ray photo-emission spectroscopy or scanning electron microscopy. Instead, the best and most practical way is to see if the defects generate the correct type of optical emission predicted by theory. But even that is challenging because our calculations, which we work on with computational groups, might not be completely accurate.

How do your PicoQuant instruments help in that regard?

We have two main pieces of equipment – a MicroTime 100 photoluminescence microscope and a FluoTime 300 spectrometer. These have been customized to form a Hanbury Brown Twiss interferometer, which measures the purity of a single photon source. We also use the microscope and spectrometer to characterise photoluminescence spectrum and lifetime. Essentially, if the material emits light, we can then work out how long it takes before the emission dies down.

Did you buy the equipment off-the-shelf?

It’s more of a customised instrument with different components – lasers, microscopes, detectors and so on — connected together so we can do multiple types of measurement. I put in a request to Picoquant, who discussed my requirements with me to work out how to meet my needs. The equipment has been very important for our studies as we can carry out high-throughput measurements over and over again. We’ve tailored it for our own research purposes basically.

So how good are your samples?

The best single-photon source that we currently work with is boron nitride, which has a single-photon purity of 98.5% at room temperature. In other words, for every 200 photons only three are classical. With transition-metal dichalcogenides, we get a purity of 98.3% at cryogenic temperatures.

What are your next steps?

There’s still lots to explore in terms of making better single-photon emitters and learning how to control them at different wavelengths. We also want to see if these materials can be used as high-quality quantum sensors. In some cases, if we have the right types of atomic defects, we get a high-quality source of single photons, which we can then entangle with their spin. The emitters can therefore monitor the local magnetic environment with better performance than is possible with classical sensing methods.

The post Shengxi Huang: how defects can boost 2D materials as single-photon emitters appeared first on Physics World.

Air Force Research Laboratory Awards Moog Contract to Develop New Multimode Propulsion System to Enhance Dynamic Space Operations

28 mai 2025 Ă  14:30
Moog logo

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The post Air Force Research Laboratory Awards Moog Contract to Develop New Multimode Propulsion System to Enhance Dynamic Space Operations appeared first on SpaceNews.

Richard Bond and George Efstathiou share the 2025 Shaw Prize in Astronomy

28 mai 2025 Ă  14:00

The 2025 Shaw Prize in Astronomy has been awarded to Richard Bond and George Efstathiou “for their pioneering research in cosmology, in particular for their studies of fluctuations in the cosmic microwave background”. The prize citation continues, “Their predictions have been verified by an armada of ground-, balloon- and space-based instruments, leading to precise determinations of the age, geometry, and mass–energy content of the universe”.

Efstathiou is professor of astrophysics at the University of Cambridge in the UK. Bond is a professor at the Canadian Institute for Theoretical Astrophysics (CITA) and university professor at the University of Toronto in Canada. They share the $1.2m prize money equally.

The annual award is given by the Shaw Prize Foundation, which was founded in 2002 by the Hong Kong-based filmmaker, television executive and philanthropist Run Run Shaw (1907–2014). It will be presented at a ceremony in Hong Kong on 21 October. There are also Shaw Prizes for life sciences and medicine; and mathematical sciences.

Bond studied mathematics and physics at Toronto. In 1979 he completed a PhD in theoretical physics at the California Institute of Technology (Caltech). He directed CITA in 1996-2006.

Efstathiou studied physics at Oxford before completing a PhD in astronomy at the UK’s Durham University in 1979. He is currently director of the Institute of Astronomy in Cambridge.

The post Richard Bond and George Efstathiou share the 2025 Shaw Prize in Astronomy appeared first on Physics World.

No laughing matter: a comic book about the climate crisis

28 mai 2025 Ă  12:00
Comic depicting a parachutist whose chute is on fire and their thought process about not using their backup chute
Blunt message Anti-nuclear thinking is mocked in World Without End by Jean-Marc Jancovici and Christophe Blain. (Published by Particular Books. Illustration © DARGAUD — Blancovici & Blain)

Comics are regarded as an artform in France, where they account for a quarter of all book sales. Nevertheless, the graphic novel World Without End: an Illustrated Guide to the Climate Crisis was a surprise French bestseller when it first came out in 2022. Taking the form of a Socratic dialogue between French climate expert Jean-Marc Jancovici and acclaimed comic artist Christophe Blain, it’s serious, scientific stuff.

Now translated into English by Edward Gauvin, the book follows the conventions of French-language comic strips or bandes dessinées. Jancovici is drawn with a small nose – denoting seriousness – while Blain’s larger nose signals humour. The first half explores energy and consumption, with the rest addressing the climate crisis and possible solutions.

Overall, this is a Trojan horse of a book: what appears to be a playful comic is packed with dense, academic content. Though marketed as a graphic novel, it reads more like illustrated notes from a series of sharp, provocative university lectures. It presents a frightening vision of the future and the humour doesn’t always land.

The book spans a vast array of disciplines – not just science and economics but geography and psychology too. In fact, there’s so much to unpack that, had I Blain’s skills, I might have reviewed it in the form of a comic strip myself. The old adage that “a picture is worth a thousand words” has never rung more true.

Absurd yet powerful visual metaphors feature throughout. We see a parachutist with a flaming main chute that represents our dependence on fossil fuels. The falling man jettisons his reserve chute – nuclear power – and tries to knit an alternative using clean energy, mid-fall. The message is blunt: nuclear may not be ideal, but it works.

World Without End is bold, arresting, provocative and at times polemical.

The book is bold, arresting, provocative and at times polemical. Charts and infographics are presented to simplify complex issues, even if the details invite scrutiny. Explanations are generally clear and concise, though the author’s claim that accidents like Chernobyl and Fukushima couldn’t happen in France smacks of hubris.

Jancovici makes plenty of attention-grabbing statements. Some are sound, such as the notion that fossil fuels spared whales from extinction as we didn’t need this animal’s oil any more. Others are dubious – would a 4 °C temperature rise really leave a third of humanity unable to survive outdoors?

But Jancovici is right to say that the use of fossil fuels makes logical sense. Oil can be easily transported and one barrel delivers the equivalent of five years of human labour. A character called Armor Man (a parody of Iron Man) reminds us that fossil fuels are like having 200 mechanical slaves per person, equivalent to an additional 1.5 trillion people on the planet.

Fossil fuels brought prosperity – but now threaten our survival. For Jancovici, the answer is nuclear power, which is perhaps not surprising as it produces 72% of electricity in the author’s homeland. But he cherry picks data, accepting – for example – the United Nations figure that only about 50 people died from the Chernobyl nuclear accident.

While acknowledging that many people had to move following the disaster, the author downplays the fate of those responsible for “cleaning up” the site, the long-term health effects on the wider population and the staggering economic impact – estimated at €200–500bn. He also sidesteps nuclear-waste disposal and the cost and complexity of building new plants.

While conceding that nuclear is “not the whole answer”, Jancovici dismisses hydrogen and views renewables like wind and solar as too intermittent – they require batteries to ensure electricity is supplied on demand – and diffuse. Imagine blanketing the Earth in wind turbines.

Cartoon of a doctor and patient. The patient has increased their alcohol intake but also added in some healthy orange juice
Humorous point A joke from World Without End by Jean-Marc Jancovici and Christophe Blain. (Published by Particular Books. Illustration © DARGAUD — Blancovici & Blain)

Still, his views on renewables seem increasingly out of step. They now supply nearly 30% of global electricity – 13% from wind and solar, ahead of nuclear at 9%. Renewables also attract 70% of all new investment in electricity generation and (unlike nuclear) continue to fall in price. It’s therefore disingenuous of the author to say that relying on renewables would be like returning to pre-industrial life; today’s wind turbines are far more efficient than anything back then.

Beyond his case for nuclear, Jancovici offers few firm solutions. Weirdly, he suggests “educating women” and providing pensions in developing nations – to reduce reliance on large families – to stabilize population growth. He also cites French journalist Sébastien Bohler, who thinks our brains are poorly equipped to deal with long-term threats.

But he says nothing about the need for more investment in nuclear fusion or for “clean” nuclear fission via, say, liquid fluoride thorium reactors (LFTRs), which generate minimal waste, won’t melt down and cannot be weaponized.

Perhaps our survival depends on delaying gratification, resisting the lure of immediate comfort, and adopting a less extravagant but sustainable world. We know what changes are needed – yet we do nothing. The climate crisis is unfolding before our eyes, but we’re paralysed by a global-scale bystander effect, each of us hoping someone else will act first. Jancovici’s call for “energy sobriety” (consuming less) seems idealistic and futile.

Still, World Without End is a remarkable and deeply thought-provoking book that deserves to be widely read. I fear that it will struggle to replicate its success beyond France, though Raymond Briggs’ When the Wind Blows – a Cold War graphic novel about nuclear annihilation – was once a British bestseller. If enough people engaged with the book, it would surely spark discussion and, one day, even lead to meaningful action.

  • 2024 Particular Books ÂŁ25.00hb 196pp

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The evolution of the metre: How a product of the French Revolution became a mainstay of worldwide scientific collaboration

28 mai 2025 Ă  10:00

The 20th of May is World Metrology Day, and this year it was extra special because it was also the 150th anniversary of the treaty that established the metric system as the preferred international measurement standard. Known as the Metre Convention, the treaty was signed in 1875 in Paris, France by representatives of all 17 nations that belonged to the Bureau International des Poids et Mesures (BIPM) at the time, making it one of the first truly international agreements. Though nations might come and go, the hope was that this treaty would endure “for all times and all peoples”.

To celebrate the treaty’s first century and a half, the BIPM and the United Nations Educational, Scientific and Cultural Organisation (UNESCO) held a joint symposium at the UNESCO headquarters in Paris. The event focused on the achievements of BIPM as well as the international scientific collaborations the Metre Convention enabled. It included talks from the Nobel prize-winning physicist William Phillips of the US National Institute of Standards and Technology (NIST) and the BIPM director Martin Milton, as well as panel discussions on the future of metrology featuring representatives of other national metrology institutes (NMIs) and metrology professionals from around the globe.

A long and revolutionary tradition

The history of metrology dates back to ancient times. As UNESCO’s Hu Shaofeng noted in his opening remarks, the Egyptians recognized the importance of precision measurements as long ago as the 21st century BCE.  Like other early schemes, the Egyptians’ system of measurement used parts of the human body as references, with units such as the fathom (the length of a pair of outstretched arms) and the foot. This was far from ideal since, as Phillips pointed out in his keynote address, people come in various shapes and sizes. These variations led to a profusion of units. By some estimates, pre-revolutionary France had a whopping 250,000 different measures, with differences arising not only between towns but also between professions.

The French Revolutionaries were determined to put an end to this mess. In 1795, just six years after the Revolution, the law of 18 Geminal An III (according to the new calendar of the French Republic) created a preliminary version of the world’s first metric system. The new system tied length and mass to natural standards (the metre was originally one-forty-millionth of the Paris meridian, while the kilogram is the mass of a cubic decimetre of water), and it became the standard for all of France in 1799. That same year, the system also became more practical, with units becoming linked, for the first time, to physical artefacts: a platinum metre and kilogram deposited in the French National Archives.

When the Metre Convention adopted this standard internationally 80 years later, it kick-started the construction of new length and mass standards. The new International Prototype of the Metre and International Prototype of the Kilogram were manufactured in 1879 and officially adopted as replacements for the Revolutionaries’ metre and kilogram in 1889, though they continued to be calibrated against the old prototypes held in the National Archives.

A short history of the BIPM

The BIPM itself was originally conceived as a means of reconciling France and Germany after the 1870–1871 Franco–Prussian War. At first, its primary roles were to care for the kilogram and metre prototypes and to calibrate the standards of its member states. In the opening decades of the 20th century, however, it extended its activities to cover other kinds of measurements, including those related to electricity, light and radiation. Then, from the 1960s onwards, it became increasingly interested in improving the definition of length, thanks to new interferometer technology that made it possible to measure distance at a precision rivalling that of the physical metre prototype.

Photo of William Phillips on stage at the Metre Convention symposium, backed by a large slide that reads "The Revolutionary Dream: A tous les temps, a tous les peuples, For all times, for all peoples". The slide also contains two large symbolic medallions, one showing a female figure dressed in Classical garments holding out a metre ruler under the logo "A tous les temps, a tous les peuples" and another showing a winged figure measuring the Earth with an instrument.
Metre man: William Phillips giving the keynote address at the Metre Convention’s 150th anniversary symposium. (Courtesy: Isabelle Dumé)

It was around this time that the BIPM decided to replace its expanded metric system with a framework encompassing the entire field of metrology. This new framework consisted of six basic units – the metre, kilogram, second, ampere, degree Kelvin (later simply the kelvin), candela and mole – plus a set of “derived” units (the Newton, Hertz, Joule and Watt) built from the six basic ones. Thus was born the International System of Units, or SI after the French initials for Système International d’unités.

The next major step – a “brilliant choice”, in Phillips’ words – came in 1983, when the BIPM decided to redefine the metre in terms of the speed of light. In the future, the Bureau decreed that the metre would officially be the length travelled by light in vacuum during a time interval of 1/299,792,458 seconds.

This decision set the stage for defining the rest of the seven base units in terms of natural fundamental constants. The most recent unit to join the club was the kilogram, which was defined in terms of the Planck constant, h, in 2019. In fact, the only base unit currently not defined in terms of a fundamental constant is the second, which is instead determined by the transition between the two hyperfine levels of the ground state of caesium-133. The international metrology community is, however, working to remedy this, with meetings being held on the subject in Versailles this month.

Measurement affects every aspect of our daily lives, and as the speakers at last week’s celebrations repeatedly reminded the audience, a unified system of measurement has long acted as a means of building trust across international and disciplinary borders. The Metre Convention’s survival for 150 years is proof that peaceful collaboration can triumph, and it has allowed humankind to advance in ways that would not have been possible without such unity. A lesson indeed for today’s troubled world.

The post The evolution of the metre: How a product of the French Revolution became a mainstay of worldwide scientific collaboration appeared first on Physics World.

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