A few weeks after the invasion of Ukraine by the Russian army, many scientific institutions felt the need to issue public statements against that war. At the time, I was president of the Commission for the History of Physics within the International Union of Pure and Applied Physics (IUPAP) and, as such, I took part in the discussions leading to the final declaration. The timing could not be better for historians of science to make a significant, albeit small, contribution: my commission was working on a project to seriously study the origins and development of IUPAP, which was about to celebrate its centenary. Paying attention to history was important so as to articulate a statement that would avoid past mistakes and incorporate positive experiences of the Union in its one-hundred-year history. Because, like other scientific international unions, IUPAP was born with an idea of peace in mind, yet it had to maneuver through times of war, both hot and cold.

It was after the tragedy of the Great War (1914-1918) that a new wave of internationalism in science took shape. If excessive nationalism had drawn Europe to its worse carnage in history, so the argument went, it was time for international institutions to collaborate in the construction of peace. And scientific research, understood as a cultural enterprise, was one such area in which collaboration rather than competition was to play a key role. In hindsight, one of the ironies of this search for peace was that the losers (Germany, Austria, Hungary, Bulgaria, and what remained of a now highly unstable Ottoman Empire) both collectively and individually, were banned from taking part in the new international order. That meant not only that their national academies could not join the new international unions, but also that individual scientists from those countries were excluded from meetings and collaborations sponsored by the unions. This was particularly poignant in the case of physics.

Indeed, international collaboration had a somewhat long tradition in fields like astronomy or geodesy due to the global scale of some of their research projects. But physics, while the “king of the sciences” in the nineteenth century, had not seen the international cooperation of national academies in the same way. That partly explains why, with the creation of the International Research Council (IRC) by delegates of twelve nations in July 1919, the International Unions of Astronomy (IAU), Geodesy and Geophysics (IUGG) and Pure and Applied Chemistry (IUPAC) immediately approved their initial statutes, soon to be followed by the Mathematical Union (IMU) and the Union for Scientific Radio Telegraphy (URSI); yet, a union of physics would have to wait, both in form and, especially, in practice.

In 1922, a number of physicists from France, Belgium, Britain, the USA and a few other countries met in Paris and came up with a first draft of statutes for an International Union of Physics. It was the young American experimentalist, Robert A. Millikan, who pushed for a name that included both pure and applied physics. The main goals of the Union were the promotion of up-to-date scientific bibliographies, the coordination of fundamental units, and the organization or sponsorship of international conferences. Those present at the meeting to celebrate the fiftieth anniversary of the Société française de physique (SFP) in Paris in December 1923 finally approved the statutes of IUPAP nominating the British and Nobel prize winner William H. Bragg as president, and Henri Abraham, professor of physics at the École Normale Supérieure, as secretary general. But it was informally agreed that the Union would remain basically dormant until it could be fully international; i.e., include German physicists.

By 1924, the vindictive philosophy of the IRC against the Central Powers was being challenged. The Council had grown and now included national academies from up to twenty countries, mostly neutral during the war and who did not see the need for such exclusionary policy. Also, an increasing number of individual scientists were pushing towards a more reconciliatory and inclusive internationalism. French and Belgian representatives were the most reticent to amend the statutes of the IRC and lift the foundational ban. So much so that real changes only came in 1931 when the IRC dissolved and the new International Council of Scientific Unions (ICSU) took its place. From then on, not only was internationalism a real possibility but also each individual scientific union was freer to organize itself as they saw fit.

In the 1920s, however, internationalism in physics materialized in other forms. Two are the best-known and most influential institutions on this aspect: the Solvay Conferences and Niels Bohr’s Institute for theoretical physics in Copenhagen. The former were the initiative of the Belgian industrialist Ernest Solvay to promote relatively small, truly international, by-invitation-only conferences to address pressing issues in both physics and chemistry. After the success of the first two meetings in physics in 1911 and 1913, the third and fourth Solvay meetings in 1921 and 1924 took part in the boycott against the Germans. But, by 1927, the mood had changed and the fifth Solvay conference in Brussels, which eventually became one of the most influential events in shaping the transformation of the early quantum physics into the new quantum mechanics, saw the presence of five German physicists: Max Planck, Albert Einstein, Wolfgang Pauli, Werner Heisenberg and Max Born. In a way, that success was partly due to the tradition that Bohr had managed to create in his institute in Copenhagen. Indeed, Denmark had been a neutral country during the war and the Carlsberg Foundation had generously funded a research center for theoretical physics to keep Bohr in the country. Thanks to both elements, Copenhagen became the central point for physicists and mathematicians to meet and freely exchange ideas on the new quantum physics.

But let us go back to the early history of IUPAP because, while Bohr had played a significant role in bringing together physicists from both sides of the war, he was also partly responsible for the failure of IUPAP to take off. In 1931, Bragg resigned and Millikan was appointed president. His plan was to use his tenure as a springboard for American physicists to become more and more internationally relevant, as well as to materialize the inclusion of the German physical society into IUPAP. He expected to achieve both goals with the organization of a major international physics conference in Chicago in 1933, year in which the wind city was celebrating its centenary. With the presence of a large number of invited physicists IUPAP might finally formalize the German membership.

Millikan’s grand plan did not succeed. First, the recession after the crash of 1929 affected the organization of events during the “Century of Progress” celebrations and money to invite scientists from abroad was short. Second, IUPAP and all other unions had one national scientific institution representing the country. But Germany had two such societies, the Deutsche Physikalischer Gesellschaft (DPG) and Gesellschaft für Technische Physik (GTP), and the attempts by Millikan and, especially Abraham, who was still serving as secretary, in correspondence with Planck and other German representatives could not settle the question as to which German society was to represent the country in the Union. And, third, the political climate in Germany was changing and the nazi ideology taking hold of the country was certainly not keen on internationalism.

Chicago did finally organize a minor scientific meeting, but it was far from being the major event Millikan had envisaged to expand and consolidate IUPAP. Promoters of the Union did not, however, give up and decided to use a major physics conference organized by the British Institute of Physics and the Royal Society in both London and Cambridge in October 1934 as the place to formalize German membership. And as a sign to underline the true international character of the Union, they offered the presidency to Bohr as icon of internationalism. The correspondence between Millikan, Abraham, Bohr, Schrödinger and a few other physicists show an amusing yet sad chain of misunderstandings: Abraham and Bohr thought Millikan had accepted the presidency by misreading a telegram of the latter; but Bohr did not want to get involved unless the German membership was fully signed, not simply promised. And that never happened.

So, Millikan having resigned and Bohr having rejected the presidency, the soul of the dormant union was its long-serving secretary, Abraham, who worked hard to find a candidate to act as president while things were clarified. In 1937, the Swedish physicist and Nobel Prize winner Manne Siegbahn agreed to be the president of IUPAP, but the Union was still short of activities, cohesion and a clear goal. It was also the indefatigable Abraham who continued his search for ways to keep the Union alive. He proposed a conference in Copenhagen in 1938, with the support of Bohr, or in Stockholm, organized by Siegbahn or, even as late as late as May 1939 he was thinking of a conference in Paris for 1940. None of them ever materialized and World War II not only destroyed the hopes and dreams of having a fully functional and international Union of Pure and Applied Physics, but even more poignantly, ended with the life of its most ardent defendant: Abraham was murdered in Auschwitz in 1943. As we shall see in the next installment, the Union reinvented itself after the war and had to learn how to navigate the new peace of the Cold War.

Further reading:

Lalli, R. and Navarro, J. (2024). Globalizing Physics: One Hundred Years of the International Union of Pure and Applied Physics. Oxford University Press. [Available in open access: https://academic.oup.com/book/58182]

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Chasing a decay that may never happen

The process, if it happens, must be extraordinarily rare. Current experiments are already sensitive to decays with half-lives greater than 10²⁶ years, far longer than the age of the Universe, and future detectors aim to probe even rarer events still.

One of the most promising technologies for this search uses xenon gas compressed to high pressure. When a charged particle moves through the gas, it ionizes xenon atoms and creates flashes of ultraviolet light. Electric fields then guide the liberated electrons toward sensors, allowing the event to be reconstructed in three dimensions. Xenon gas also allows exceptionally precise measurements of the energy deposited by the decay.

A neutrinoless double beta decay would release two electrons from a common point. As they travel through the gas, they follow winding paths and lose most of their energy at the ends of their trajectories, producing two small regions of concentrated energy deposition. This double-ended structure gives a characteristic signature that distinguishes the sought-after events from most background processes, which typically produce only a single electron track.

The main obstacle is that the drifting electrons spread out as they move through the gas. This diffusion blurs the image of the tracks, especially for events that occur far from the sensors. The amplification process used to make the faint electron signal detectable introduces further smearing. As a result, the distinctive two-electron pattern can become difficult to recognize, particularly deep inside large detectors.

ITACA (Ion Tracking with Ammonium Cations Apparatus)

An alternative approach ¹ is to image not only the electrons but also the positive ions left behind by the ionization process. Tiny amounts of ammonia (NH₃), around one hundred parts per billion, can be added to the xenon gas. Rapid chemical reactions convert the positive xenon ions into ammonium ions (NH₄⁺)almost as soon as they form, without significantly affecting the light signals or the transport of the electrons.

These ammonium ions move far more slowly than electrons and diffuse much less along the way. Electrons cross the detector in a few milliseconds, whereas the ions can take anywhere from a fraction of a second to several seconds to reach their own collection point. Because the ion cloud stays comparatively compact, it can preserve fine details of the original interaction that may already be lost in the blurred electron image.

The two effects turn out to work against each other in a useful way. Wherever an electron happens to be born close to its collecting sensors, its own image stays sharp, while the corresponding ions still have most of their long journey ahead of them and their image comes out blurred. Deep in the gas, far from the electron sensors, the opposite happens: the electron image becomes badly smeared over its long drift, but the ions in that region have only a short remaining distance to travel and arrive with their picture largely intact. Because the two blurring effects are anti-correlated in this way, at least one of the two pictures, electron or ion, stays sharp no matter where in the detector a decay occurs, keeping the overall reconstruction quality close to uniform throughout the full detector volume.

The ion image itself is recorded by letting the ions land on specially prepared molecular surfaces coated with fluorescent sensors that respond specifically to ammonium ions. When illuminated by a laser, only the molecules that have actually captured an ion light up. A microscope and camera system can then scan this surface and reconstruct the ion track with very high spatial resolution.

The researchers call this system ITACA, after Ion Tracking with Ammonium Cations Apparatus. The researchers themselves would be Penelope, waiting for a husband and king who may, or may not, appear.

Would ITACA be the final destination?

Simulations indicate that these ion images preserve the characteristic two-endpoint structure expected from neutrinoless double beta decay, even in the presence of background noise from unbound sensor molecules that occasionally glow on their own. The sharper topology this provides should make it substantially easier to reject events produced by natural radioactivity and other processes that can otherwise mimic the sought-after signal.

Taken together, the additional information carried by the ion tracks could reduce troublesome background events by roughly an order of magnitude beyond what current xenon-gas detectors achieve, and by close to a factor of twenty for some of the most problematic radioactive backgrounds, those whose energy lies dangerously close to the signal itself. Improvements of this size would substantially increase the chances of finally catching neutrinoless double beta decay in the act, and with it, the chance to learn whether the neutrino holds one of the most unusual properties in all of particle physics.

Author: César Tomé López is a science writer and the editor of Mapping Ignorance

Disclaimer: Parts of this article may have been copied verbatim or almost verbatim from the referenced research paper/s.

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The fall of the Roman Empire and major plague outbreaks: These events not only affected people but also reduced plant diversity on the Swiss Plateau, as human land use temporarily declined. Researchers led by Dr. Fabian Rey and Professor Oliver Heiri at the University of Basel report ¹.

Their analyses are based on sediment deposits in three Swiss lakes: Moossee near Bern, Burgäschisee near Herzogenbuchsee, and Hüttwilersee in Thurgau. The researchers extracted sediment cores from these lakes and then analyzed the material deposited in the sediments over the course of millennia. This allowed them to infer and date variations in both plant diversity and agricultural land use in the areas surrounding the lakes.

“This is an exceptionally comprehensive and precisely dated dataset,” says Oliver Heiri. “It allows us to reconstruct changes in plant diversity around the lakes over the past 7000 years at a time resolution comparable to long-term ecosystem studies in modern ecology – and for a period long before modern ecology existed.”

Agriculture made the landscape more diverse

Since the Neolithic period, plant diversity increased with increasing agricultural activity. “You might think that human impact must be bad for plant diversity, because that’s what we see today,” says Fabian Rey. “But agriculture back then made the landscape more diverse.” Before early agricultural activities, the Swiss Plateau was largely covered by forest and was therefore a relatively uniform ecosystem.

“As agriculture expanded, a mosaic of habitats emerged over time,” says Rey. Fields, pastures, hedgerows, and later orchards of tall fruit trees alternated across relatively small areas. This provided varied conditions for plants adapted to those specific environments.

However, there were also recurring periods when plant diversity declined sharply: For example, during the Migration Period following the fall of the Roman Empire, or when plague outbreaks claimed many lives in the Middle Ages. “In times when people were less able to continue farming, the forest grew back and plant diversity declined at the landscape level,” explains Heiri.

Times of crisis caused diversity to decline

More agriculture, more biodiversity: However, this parallel trend lasted only until around World War II. Over the past 80 years, plant diversity has declined sharply. The research team attributes this to the intensification of agriculture since then.

Instead of a fragmented mosaic of habitats, large, uniform areas have emerged that are easier to farm using heavy machinery. The increasing use of fertilizers and pesticides also caused many specialized plant species to retreat.

“However, our data also show that plant diversity has recovered from earlier declines when people returned to farming practices that included varied landscapes,” says Rey. This suggests that the trend of the past 80 years could also be reversed if farming practices change again.

Pollen from seven millennia

The data for the study are based on more than a decade of analyses of sediment cores, conducted in close collaboration with researchers from the University of Bern and the Department of Archaeology of Canton Thurgau. To collect the data, Fabian Rey extracted pollen samples from every centimeter of the cores, which he chemically processed, prepared, and analyzed under a microscope. For each sample, he identified 500 pollen grains, enabling him to determine the diversity of plants around the lake.

The intensity of agricultural use during each period was determined based on the presence of specific pollen in the samples – including both cultivated plants and species that thrive on farmland – as well as a comparison with archaeological and historical data.

The scientists dated the layers using the 14C method, a technique for determining the age of organic material. The sediment cores date back approximately 7000 years, to the Neolithic period.

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2026 marks 100 years since the death of Antoni Gaudí, the architect of the Basilica of the Sagrada Familia in Barcelona. While the temple’s beauty is extraordinary in its own right, it becomes even more profound when we explore the numerical patterns that lie behind its striking forms.

By contemplating the mathematical principles that underpin its structure, the visual harmony of the whole takes on a new dimension, endowing it with a renewed functionality, balance and coherence.

Mathematician Claudi Alsina i Català deeply studied the mathematics of the Sagrada Família. He undertook his initial studies in this field at the University of Barcelona, and supervised the doctoral thesis of Jordi Faulí, the architect currently in charge of the temple’s ongoing construction.

In his memoirs, Alsina stated:

Many had wondered whether the design of the Sagrada Família contained some module or system of proportions that guided the building’s metric relationships. (…) One Saturday afternoon, sitting at my desk at home, with all the data and documents on this mysterious proportional system – if indeed it existed – I discovered it. The 7.5-metre module and the ratios between the divisors of 12 (1:4, 1:3, 1:2, 3:4, 2:3, 1) seemed to explain a great deal.

12: the magic number

It is no surprise that the number 12 plays a prominent role in the structure of the church. Gaudí conceived the Sagrada Família as a synthesis of architecture and religious symbolism, and the number 12 features heavily in the Bible: Jacob’s 12 sons, the 12 tribes of Israel, the 12 apostles and the crown of 12 stars in the Book of Revelation are just a few examples.

But its significance is not merely symbolic. From a mathematical point of view, 12 is a number particularly well-suited to establishing proportions, as it has many divisors. According to Alsina, the relationships between these divisors account for much of the basilica’s proportional system.

The 7.5-metre module

Drawing on Alsina’s work, we invite you to take a brief mathematical tour of the Sagrada Família.

The temple’s dimensions are based on the number 12 and a module of 7.5m. It is 90m long (7.5 × 12) and 60m wide (7.5 × 8). The width of the main nave is 45m (7.5 × 6).

In terms of height, the highest vault is that of the apse, at 75m (7.5 × 10), followed by the vault of the transept at 60 metres (7.5 × 8). The nave vault is 45m high (7.5 × 6), the side aisle 30m (7.5 × 4), and the choir 15m (7.5 × 2).

The Tower of Jesus Christ is the central and tallest of the cathedral. It stands at 172.5 metres (7.5 x 23), close to the height of the landmark hill of Montjuïc. It is crowned by a four-armed cross, 17m high and 13.5m wide. Surrounding this are the four Evangelist Spires, which reach a height of 135m (7.5 x 18).

The 138-metre high Tower of the Virgin Mary is the second tallest in the basilica. It is crowned by a 12-pointed star, which rests on three supporting arms. This star has a diameter of 7.5m, and is made up of a regular dodecahedron, with pyramid-shaped pentagonal points rising from each face. Its reflections of daylight and night-time illumination lend this star a unique beauty.

Polyhedral towers

Polyhedrons also feature prominently in the towers of the Sagrada Família. The four towers of the Glory façade are topped by dodecahedrons, the four towers of the Nativity façade by truncated irregular octahedrons, and the four towers of the Passion façade by truncated cubes.

On each of the 12 towers, a spire rises above these polyhedrons. Those dedicated to the evangelists are crowned with regular icosahedrons containing spotlights that illuminate the large cross that sits atop the Tower of Jesus Christ. Just above each icosahedron is a sculpture that symbolically depicts each evangelist. There are numerous star-shaped polyhedrons throughout the church, particularly on the Nativity façade.

A forest of towers

Catenary arches feature prominently as key structural elements of the church, as they are a highly effective way to transfer loads to the ground without the need for additional support. They can be seen in the system of sloping columns that support the vaults of the interior naves, the vaults and ceilings themselves, and the Nativity façade.

Inside the Sagrada Família, there are four different types of column. All are double-helix torsion columns – each has a rounded, star-shaped polygonal base, and is formed by the intersection of two opposing Solomonic columns. Above each one is a knot from which different branches emerge, similar to those of a tree, which very efficiently support the towers and the roof of the church.

The skylights in the roof are also one-sheet hyperboloids. Made up of straight lines, they are easy to construct, and optimise the capture and projection of light.

The symbolism of 7 and 33

The church has other deeply symbolic hidden features. Take, for instance, the canopy above the high altar, which forms a regular heptagon 5 metres in diameter, whose seven sides symbolise the seven gifts of the Holy Spirit.

On the Passion façade there is a magic square in which the sum of all rows, columns and diagonals is 33. It appears to be inspired by the magic square featured in the engraving Melancholia I by Albrecht Dürer.

The mathematics that underpins the Sagrada Família makes it all the more beautiful. While the building itself is a sight to behold, a deeper understanding of the principles behind it inspires even greater admiration for the enduring genius of Antoni Gaudí.

 

This article is republished from The Conversation under a Creative Commons license. Original article.

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When energy storage is discussed in the context of the energy transition, the conversation almost invariably turns to electricity. Solar and wind power have made the temporal mismatch between energy production and energy demand one of the defining challenges of low-carbon energy systems, and technologies capable of storing electrical energy have consequently become central to discussions about decarbonization.

Yet this emphasis on electricity raises an interesting question. If a substantial fraction of the energy ultimately consumed by modern societies is required not as electricity but as thermal energy, should future energy systems necessarily store energy in electrical form?

The question may appear deceptively simple. Electricity plays a visible role in modern economies, powering everything from communications and transportation to industrial equipment and domestic appliances. Thermal energy, by contrast, often remains hidden within industrial processes, heating systems and manufacturing operations. Nevertheless, many of the activities that sustain modern societies depend primarily on heat rather than electricity.

Steelmaking, cement production, chemical manufacturing, food processing, paper production and numerous other industrial activities require thermal energy delivered under specific conditions of temperature, power and duration. In many cases, fossil fuels have historically fulfilled this role not because alternative energy sources were unavailable, but because combustion offers a relatively direct means of producing high-temperature thermal energy where and when it is required.

As renewable electricity becomes increasingly available, this situation may encourage a different way of thinking about energy storage. Rather than focusing exclusively on how electricity can be stored and later returned to the grid, it may also be worth considering whether part of that energy could instead be stored in forms intended for later thermal use.

Such an approach would not eliminate the need for batteries, nor would it necessarily be appropriate for every application. It does, however, suggest that thermal energy storage may represent a distinct scientific and engineering problem whose requirements differ from those associated with conventional electrical storage technologies.

Storing energy for later thermal use

At the heart of the discussion lies a relatively straightforward physical observation. Electrical energy can be converted into thermal energy with high efficiency through a variety of heating technologies. Once this conversion has taken place, the resulting energy may be stored within a material or chemical system and later recovered when thermal energy is required.

Importantly, what is stored is not temperature itself. Temperature is an intensive thermodynamic property and therefore cannot be accumulated in the same way as energy. Instead, thermal energy storage systems retain energy through changes in the state of a material, whether by increasing its temperature, inducing a phase transition or driving a reversible chemical reaction.

The simplest of these approaches is generally known as sensible heat storage. In such systems, energy is stored through an increase in the temperature of a material. Water provides the most familiar example, although industrial applications may employ molten salts, rocks, ceramics, graphite or other materials capable of operating under more demanding thermal conditions. The amount of energy stored depends on the mass of the storage medium, its heat capacity and the temperature interval over which it operates.

A second possibility involves latent heat storage, where energy is absorbed or released during a phase transition. Because phase transitions may involve substantial enthalpy changes while temperature remains relatively constant, these systems can store significant amounts of energy within comparatively narrow temperature ranges. This characteristic has made phase change materials attractive for applications in which thermal energy must be supplied near a particular operating temperature.

Even more ambitious concepts involve thermochemical storage. In these systems, thermal energy drives reversible chemical reactions, allowing energy to be stored in chemical form and later recovered when the reverse reaction occurs. Under certain conditions, such approaches could potentially enable storage over much longer timescales than conventional thermal systems, although their practical implementation remains associated with significant scientific and engineering challenges.

At first sight, these approaches may appear to offer relatively straightforward solutions. However, as is often the case in energy research, the situation becomes considerably more complicated once practical constraints are taken into account.

Materials operating at elevated temperatures may experience degradation through corrosion, thermal fatigue, creep, phase instability or other mechanisms whose importance depends on the operating conditions and storage medium. Repeated thermal cycling can gradually alter material properties, while large-scale systems introduce additional challenges related to heat transfer, containment and long-term reliability. In thermochemical systems, reaction kinetics, cycling stability and reactor design may become equally important considerations.

As a result, the central question is not whether thermal energy can be stored. It clearly can. The more difficult question is whether such storage can remain technically reliable, economically viable and operationally robust under the conditions required by industrial applications.

A maturity paradox

Interestingly, many of the technologies that could contribute to this objective are no longer at an early stage of development. Electric heat pumps, electric boilers, electric resistance heaters and several forms of sensible and latent thermal energy storage have reached relatively high levels of technological maturity. From a purely technological perspective, the challenge is therefore not always one of invention. In many cases, the relevant technologies already exist.

Yet this observation introduces a different question. If a number of these technologies are already mature, why does their future role remain difficult to assess?

Part of the answer may lie in the complexity of modern energy systems themselves. The behaviour of a heat pump, an electric boiler or a thermal storage unit can often be described in considerable detail. However, energy systems contain thousands of interacting components operating across multiple spatial and temporal scales. Incorporating detailed representations of thermal technologies into large-scale energy models may therefore become computationally challenging, particularly when such models are intended to optimize entire electricity, heating and industrial sectors simultaneously.

This creates an interesting tension. The physical behaviour of thermal technologies is often governed by complex thermodynamic processes, yet large-scale energy planning frequently requires simplified mathematical representations that remain computationally tractable. Determining how much detail can be removed without losing essential information remains an active area of research and may influence how the future role of thermal energy storage is assessed.

This distinction may help explain why thermal energy storage has attracted increasing scientific interest in recent years. A significant fraction of industrial energy demand is thermal rather than electrical, and many industrial processes require heat directly. Under such circumstances, converting electrical energy into thermal energy, storing it, and subsequently using it as heat may sometimes prove more practical than repeatedly converting energy between different forms.

Beyond storage

The implications extend beyond individual storage technologies. Some researchers have suggested that thermal energy storage could also contribute to system flexibility by partially decoupling heat demand from the instantaneous availability of renewable electricity. During periods of abundant renewable generation, electrical energy could be converted into thermal energy and stored for later use. If such approaches prove technically and economically viable at scale, they could potentially help reduce some of the temporal mismatches that arise in renewable-dominated energy systems.

Whether this possibility ultimately becomes significant remains uncertain. Industrial sectors differ substantially in their temperature requirements, operating schedules and process constraints. Storage technologies that appear promising in one context may prove less suitable in another. Likewise, systems that perform well under laboratory conditions may encounter unexpected limitations when deployed at industrial scales.

For this reason, thermal energy storage may be best understood not as a single technology but as a broad collection of approaches aimed at addressing a common problem. The details differ from one system to another, but the underlying question remains remarkably simple: if much of the energy consumed by modern societies is ultimately required in thermal form, what is the most effective way of ensuring that such energy remains available when it is needed?

Viewed from this perspective, the challenge is not simply one of storage. The objective of an energy system is not merely to retain energy for later use, but to ensure that energy remains available in a form compatible with the process that ultimately consumes it. In some cases that form may be electrical. In others, it may be thermal. Determining when each option is preferable remains an active area of research.

Whether any particular thermal energy storage technology ultimately becomes a major component of future energy systems remains unclear. What already appears increasingly difficult to ignore, however, is the observation from which the entire discussion emerges. A substantial fraction of the energy consumed by modern societies is required in thermal form. This fact alone may justify a closer examination of how such energy can be stored, transported and recovered efficiently. As researchers continue to investigate the materials, mechanisms and constraints involved, thermal energy storage may offer a useful reminder that decarbonization involves more than replacing one source of electricity with another. It may also require a deeper understanding of how energy itself is used.

The BRTA is a consortium that remains a step ahead of future socio-economic challenges worldwide and in the Basque Autonomous Community; it addresses them through research and technological development, thus projecting itself internationally. The BRTA centres collaborate to generate knowledge and transfer it to Basque society and industry so as to make them more innovative and competitive. The BRTA is an alliance of 17 R&D centres and cooperative research centres with the support of the Basque Government, the SPRI and the Chartered Provincial Councils of Araba, Bizkaia and Gipuzkoa.

References

1. Maruf, M. N. I., Morales-Espana, G., Sijm, J., Helistö, N., and Kiviluoma, J. (2021) Classification, potential role, and modeling of power-to-heat and thermal energy storage in energy systems: A review. arXiv. Available at: https://arxiv.org/abs/2107.03960
2. CIC energiGUNE (2022) Thermal energy storage: a key factor in energy transition. Available at: https://cicenergigune.com/en/blog/thermal-energy-storage-key-energy-transition
3. International Energy Agency (2024) Energy Efficiency 2024. International Energy Agency. Available at: https://www.iea.org/reports/energy-efficiency-2024

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Stars are rarely born alone

In the densest, coldest pockets of gas inside galaxies, gravity can trigger a burst of star formation in which thousands or even millions of stars emerge almost simultaneously from the same cloud. When enough stars form close together, their mutual gravity can hold them in a bound group for billions of years, producing a massive star cluster. Whether a newborn cluster survives its earliest years depends on how efficiently stars form locally and how strongly the surrounding galactic environment (rotating gas, gravitational tides, giant molecular clouds) pulls it apart. Regions deep inside a galaxy, where gas is dense and rotation is fast, are particularly fertile nurseries for long-lived clusters. The sparse, tranquil outskirts of a galaxy, by contrast, rarely produce clusters that survive.

L-Galaxies 2020, extended

To understand the full population of star clusters across billions of years of cosmic history, simulation is essential, because observations can only detect the brightest and nearest clusters. Tracking every cluster in a fully realistic simulation of an entire galaxy is, however, prohibitively expensive in computing time. A practical alternative is a semi-analytical model: a framework that combines large dark-matter-only simulations, which are relatively cheap to run, with a set of physical equations that describe how gas cools, stars form, galaxies merge, and heavy elements accumulate over time. A recent study ¹ has extended one such framework, called L-Galaxies 2020, to include the formation and long-term evolution of individual massive star clusters for the first time.

In the model, each galaxy is divided into twelve concentric rings. The gas density, star-formation rate, and gravitational stability of each ring are computed separately, allowing the simulation to identify which parts of a galaxy are likely to produce bound clusters and which are not. Cluster masses are drawn statistically from a mass function — a mathematical description of how common clusters of different sizes are — in which small clusters are far more numerous than massive ones, consistent with observations of nearby galaxies. Every newly formed cluster is also assigned an initial size, a chemical composition equal to that of the gas it formed from, and a position within its ring. The simulation then follows up to 2,000 individual clusters per galaxy across cosmic time.

Star clusters do not remain unchanged

As the most massive stars within a cluster age and explode as supernovae, the cluster steadily loses mass. Repeated close encounters between stars inside the cluster (a process called two-body relaxation) gradually eject stars from the system. Clusters orbiting through the disk of their host galaxy are further eroded by collisions with giant molecular clouds, which inject energy and cause stars to escape. When two galaxies merge, the violent redistribution of stars can fling disk clusters into the galaxy’s halo, where the tidal environment is calmer and clusters are more likely to survive intact. The simulation models all of these processes together.

The sheer complexity of the cluster population

The simulations reproduce several well-established observational benchmarks. Young, massive clusters are preferentially found in galaxies with high rates of star formation, matching data from hundreds of nearby galaxies. More massive galaxies contain more clusters overall and tend to host the most massive individual ones. The model also successfully reproduces the relationship between a galaxy’s mass and the average chemical richness (metallicity) of its cluster population: larger galaxies, which have had more time and more material for chemical enrichment through successive generations of stars, host clusters that contain more heavy elements such as iron.

One of the most striking findings is the sheer complexity of the present-day cluster population. The clusters visible around a galaxy today are not a single, uniform family. Some formed within the galaxy itself and remained in its disk. Others were dragged into the halo during major mergers that destroyed the disk structure of both colliding galaxies. Still others were imported wholesale from smaller satellite galaxies that were gradually torn apart and absorbed. This mixture of origins means that the cluster population encodes a detailed, if difficult to decode, record of every significant merger and episode of star formation a galaxy has undergone across its entire history.

Rich cluster, poor cluster

The chemical compositions of clusters offer another layer of information. Many galaxies appear to host two distinct populations of clusters: one relatively metal-poor group, thought to have been accreted from smaller, chemically primitive satellite galaxies, and one more metal-rich group, formed in situ from already-enriched gas. The simulations predict that this bimodality is present in roughly 20 to 50 percent of galaxies, and that it becomes less pronounced in the most massive systems, where extensive merger histories blend together populations from many different sources and smooth out any clear separation.

Size misfits

Not everything falls neatly into place. The physical sizes of star clusters — how large they are in space — remain difficult to reproduce across all galaxy types and masses simultaneously. Different assumptions about the initial sizes of newly formed clusters improve agreement with observations in some galaxies while worsening it in others. This persistent discrepancy points to gaps in the understanding of the earliest evolutionary phase of star clusters, when they are still embedded in their natal gas clouds and the surrounding environment shapes them most strongly.

Taken together, this work shows that it is now possible to follow individual star clusters through billions of years of galaxy formation within a computationally practical framework. The approach opens new avenues for using clusters as probes of galaxy assembly — not just by studying what they look like today, but by tracing their origins back to the specific mergers, gas inflows, and star-formation episodes that gave rise to them. What eighteenth-century astronomers admired as decorative curiosities in the sky turn out to be among the most informative archives of cosmic history that exist.

Author: César Tomé López is a science writer and the editor of Mapping Ignorance

Disclaimer: Parts of this article may have been copied verbatim or almost verbatim from the referenced research paper/s.

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In the Pilbara of Western Australia, some of Earth’s oldest rocks lie beneath the sky, as they have for billions of years. They are dark, weathered volcanic rocks, close to 3.5 billion years old, cut by veins and stewed by deep time.

Their survival is remarkable. Most rocks this old have moved back into Earth’s interior. These ones, still on the surface, have changed, but not enough to erase their first story.

In places, they still preserve the rounded forms of pillow basalts – lava that erupted underwater and cooled on an ancient sea floor.

The same rock record also holds some of the earliest widely accepted evidence for life on Earth. But looking closely on some surfaces you find fine lines that fan through the rock.

These are shatter cones – the frozen signature of a meteorite shock wave, and the clearest sign that something from space once struck Earth.

When our team first reported these rocks in 2025, we suggested they were part of an ancient impact crater at the ironically named North Pole Dome. But one question remained difficult: exactly how old was the impact?

In our new study, published in Geology, we used tiny mineral clocks inside the damaged rocks to show the impact most likely happened 3.024 billion years ago.

That makes North Pole Dome the oldest known impact structure on Earth, and the only recognised impact crater from the Archean, the period between 4 and 2.5 billion years ago.

The gift of deep time

This is a story about a scar on the early Earth. It is also about one of geology’s greatest gifts to society: the concept of deep time.

Humans have been around for some 300,000 years. But Earth is about 4.5 billion years old. Most of our planet’s story happened on timescales so vast, they’re difficult to imagine.

Rocks are the pages of that story. Some begin as lava flows, others as mud on a sea floor. Over time, Earth’s movements bury, harden, fold, heat and sometimes lift the rocks back to the surface. A geologist’s job is to work out the order of these pages and, where possible, put dates on them.

One way to do this is stratigraphy, the study of rock layers. If two lava flows lie on top of one another, the lower one is usually older. If a vein cuts through a rock, the vein must be younger than the rock.

But ancient rocks are rarely tidy. Over billions of years, layers can tilt, fold and erode. Geologists therefore use correlation. We match rocks from one place to another using their position, appearance, chemistry, magnetic signals or nearby layers with a precise date.

Correlation is powerful, but it’s a bit like working out where a loose page belongs in a damaged book. You may know whether it comes near the start, middle or end, but the page number itself is missing. That was the challenge at North Pole Dome; the signs of a meteorite impact were clear. But when did it happen?

Piecing the story together

Early estimates suggested an extremely ancient impact, based on where the shocked rocks sat in the local rock layers. A later Harvard-led study challenged this, arguing that the impact could have happened much later, anywhere between 2.7 and 0.4 billion years ago, a span equal to roughly half of Earth’s history.

Both interpretations depended on matching ancient rocks across a complicated landscape. In the Pilbara, that is difficult work. Linking one fine-grained black rock to another across the outback can be surprisingly hard.

So instead, we looked inside the rocks. Tiny crystals inside shocked rocks can act as clocks, recording when they formed or changed. In other words, mineral dating can sometimes recover the missing page number.

Tiny crystal clocks

The key mineral was zircon. Zircon is tiny, tough and unusually good at keeping time. It contains uranium, which slowly decays into lead. By measuring uranium and lead in a zircon crystal, we can estimate when that crystal formed, or when something strongly altered it.

In one shatter cone, we found several types of zircon. Some preserved ages older than 3.4 billion years. These likely reflect the ancient rocks that were hit.

But another group looked very different. These zircons had skeletal shapes, like tiny frozen lightning bolts. These can form when crystals grow or recrystallise very quickly under unusual conditions. Similar zircon textures have been found in impact rocks from the Moon. The best-preserved of these skeletal zircons gave an age of 3 billion years.

On its own, that still wasn’t enough. Skeletal zircon can form in more than one way, so we needed another clock. We found it in apatite, a phosphate mineral that also contains tiny amounts of uranium.

Apatite can grow when hot fluids move through broken rock – exactly the kind of system an impact creates, as heat and fractures drive water through a crater. The apatite gave the same age as the modified zircons.

Two clocks, in different minerals and different rocks, pointed to the same event about 3.02 billion years ago.

A rare moment from Earth’s violent youth

Other minerals told us what happened later. Muscovite, a shiny silver mineral in a vein that cut across the shatter cone, gave an age of about 1.66 billion years. The vein’s shape told us it must have formed long after the impact, when the rocks were disturbed again by some natural process.

But those events don’t date the impact – they are later chapters in the same damaged book.

The story of dating this crater shows Earth’s oldest history is not gone. It’s just hard to read. Unlike the Moon, Earth constantly destroys its ancient surface through erosion, burial, heating and plate tectonics.

Most craters from the early Earth have vanished. At North Pole Dome, one survived. Its rocks preserve the trace of a space impact from 3.024 billion years ago – a rare page from the violent youth of our planet, with the date still written in the stone.

 

This article is republished from The Conversation under a Creative Commons license. Original article.

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A thermometer seems to do something very simple: it turns heat and cold into a number. But that apparent simplicity hides a more awkward question: what had to be stabilised before “how hot” could be given a number?

Hasok Chang’s Inventing Temperature: Measurement and Scientific Progress is a history of that hidden work. Temperature is now among the most ordinary quantities in science. We read it from kitchen thermometers, weather apps, ovens, engines and laboratory instruments. Yet Chang shows that this simplicity had to be earned. Before temperature could become a measurable quantity, scientists had to decide what could count as a fixed point, how different instruments could be compared, and how a scale could be extended into regions where familiar thermometers no longer worked. Chang’s point is not simply that early thermometers were inaccurate. It is that measurement itself can be an achievement before it becomes a routine.

There was no obvious procedure waiting to be cleaned up; measuring temperature required scientists to make phenomena stable enough to be used as standards.

The trouble with fixed points

Take the boiling point of water. Today we learn that pure water boils at 100°C under standard atmospheric pressure. It sounds like the sort of fact that nature simply offers to anyone with a thermometer. In the eighteenth century, that simplicity was precisely what had to be secured.

In 1776, the Royal Society appointed a committee to bring some order to thermometry. Even the best thermometers of the period disagreed by several degrees Fahrenheit about where water boiled. Part of the problem was already understood: the boiling point varied with atmospheric pressure. But there were other complications. The manner of boiling itself seemed to matter. Water could bubble gently, boil irregularly or boil violently, and these different states did not always appear to give the same reading.

The fixed point did not disappear, but it became less innocent. If boiling water was to serve as a standard, scientists had to specify the circumstances under which it would do so.

Jean-André De Luc, a Genevan natural philosopher and one of the major eighteenth-century authorities on thermometry, pushed the difficulty further. He showed that water could be heated beyond its ordinary boiling point once dissolved air had been removed. In early trials, the water appeared to begin boiling continuously only when the surrounding oil bath reached temperatures as high as 140°C, though De Luc could not be sure that the water itself had reached that temperature. In a more controlled experiment, after weeks of patiently shaking water to expel the air, the airless water reached 112.2°C under normal atmospheric pressure before boiling explosively.

Chang quotes De Luc’s recollection that the operation lasted four weeks, during which he hardly ever put down the flask. The anecdote makes the labour of stabilising a fixed point tangible: a scientist eating, reading, writing, walking and receiving visitors while continually shaking a vessel of water. The point was serious. De Luc was not using our modern theory of nucleation. He was trying to distinguish what he called “true ebullition” from vapour formed around escaping air bubbles.

The boiling point remained useful, but only once its conditions of use had been specified. As Chang puts it, “if defensible fixed points do not occur naturally, they must be manufactured.”

That word, manufactured, can easily mislead. The point is not that scientists invented the boiling point by convention. They learned how to arrange vessels, fluids, pressures and instruments so that boiling could serve as a stable reference. Strictly speaking, the more reliable standard was not simply the temperature of boiling water but the steam point: the temperature of saturated steam at standard atmospheric pressure. This meant attending to pressure, using suitable vessels, exposing the thermometer to steam rather than plunging it into liquid water, and learning from the very impurities that purification had tried to eliminate. De Luc focused on dissolved air. Later work complicated the picture by showing that dust and other impurities also helped ordinary water avoid the strange behaviour seen in carefully purified vessels.

Fixity, then, did not emerge from nature in a pure state. It emerged from disciplined handling of a materially messy world.

When thermometers disagree

Even after fixed points had been established, another problem remained. Suppose we build two thermometers, one filled with mercury and the other with alcohol, and calibrate both at the freezing and boiling points of water. Between those points, the two instruments need not agree. A point marked as 50°C by one may not coincide with 50°C on the other.

Which one, if either, should define the scale?

The modern answer eventually appeals to theory. In ideal-gas theory, gas behaviour is tied in a simple linear way to absolute temperature, so gas thermometers can be treated as better approximations to thermodynamic temperature. But Chang’s historical question is sharper: how could such a conclusion be justified before the relevant theory and measurements had already been secured? The problem was not merely that different substances expanded differently. It was that choosing the right substance seemed to require the very temperature scale that the substance was supposed to provide. To know that a gas behaves ideally, we seem to need a trustworthy thermometer. To know which thermometer to trust, we seem to need to know which substance expands in the right way.

This is not a small technical inconvenience. The circularity lies close to the heart of measurement.

Henri Victor Regnault, one of the leading French experimentalists of the nineteenth century, did not solve the foundational problem by finding an unquestionable starting point. He made the demand more modest, but also more testable. Instead of trying to prove that one thermometer defined the true scale, he asked whether instruments of the same kind remained comparable with one another under controlled variations —for instance, different kinds of glass in mercury thermometers, or different densities of air in air thermometers.

This criterion proved powerful. Mercury thermometers made with different kinds of glass diverged by more than 5°C at elevated temperatures. Air thermometers filled with air at different densities stayed within about 0.3°C of each other. Regnault had not proved that the air thermometer was ultimately correct. He had shown that it behaved more consistently than its rivals.

The reason was not merely practical. If temperature is to be treated as a measurable physical magnitude, the same situation cannot be allowed to have several incompatible values merely because the instruments differ. Comparability was therefore not a trivial preference for neatness. It was a minimal condition for treating something as a measurable quantity at all.

Even so, Chang is careful not to turn Regnault into a hero who escapes circularity once and for all. There was no final proof. One could always imagine further parameters to vary. At some point, judgement was unavoidable: not arbitrary judgement, but trained judgement about when the convergence was good enough to support further work.

Progress without foundations

Chang calls this kind of process epistemic iteration. Scientific inquiry often begins by accepting an existing body of knowledge, not because it is certain, but because inquiry has to begin from inherited practices. Scientists then use that provisional starting point to refine, extend or correct the very system they first relied on.

The process is conservative and revisionary at the same time. It respects inherited standards, but it does not treat them as sacred.

The freezing point of mercury provides one of Chang’s clearest examples. When Henry Cavendish designed an experiment to determine it, he had to assume that mercury continued to expand regularly down to the point where it froze. That assumption had not been proved. Still, it was not a wild guess. It extended what was already known about mercury at ordinary temperatures.

Later, Claude Pouillet used Thilorier’s paste —a cooling mixture of solid carbon dioxide and ether— to connect several imperfect instruments: an air thermometer, a bismuth–copper thermocouple and alcohol thermometers. The different methods converged around −40°C for the freezing point of mercury. No single instrument provided an absolute foundation. The justification came from the way several fallible standards supported one another.

A similar pattern appears in the history of absolute temperature. William Thomson, later Lord Kelvin, first proposed an absolute scale using Carnot’s theory of heat engines. He later revised the scale in the light of Joule’s work on energy conversion. But an abstract thermodynamic definition still had to be connected with actual procedures. The Joule–Thomson work helped connect the abstract thermodynamic scale with actual gas thermometry, not by removing all assumptions, but by making them explicit enough to be corrected.

This is the form of progress Chang wants us to notice: not a march from darkness into light, and not the discovery of an indubitable foundation, but a self-correcting process in which inherited standards are used without being treated as sacred. Justification, in such cases, comes retrospectively, through the success of the corrections that those standards make possible.

Science by other means

One of the most provocative claims of Inventing Temperature is that history and philosophy of science can sometimes contribute to our knowledge of nature, rather than merely commenting on it. Chang calls this mode of inquiry complementary science.

The idea is not that historians and philosophers should replace laboratory scientists. It is that specialist science, precisely because it is so effective, leaves certain questions behind. Modern research moves forward by taking many things for granted. That is often necessary. But it also means that basic questions can become invisible. Complementary science begins where specialist science has, for practical reasons, stopped asking, not because the question is meaningless, but because it no longer belongs to the current research frontier.

Why do we trust the boiling point of water? How do we know that a thermometer remains meaningful outside the range in which it was calibrated? What happens when a phenomenon once known to experimenters disappears from textbooks and from ordinary scientific memory?

For Chang, these are not merely questions about science. At their best, they are questions about nature pursued through historical and philosophical means.

Superheating is a good example. The possibility that water can remain liquid above its normal boiling point was well understood by some eighteenth- and nineteenth-century investigators. De Luc explored it with extraordinary patience. Yet Chang argues that this knowledge later became marginal, simplified in textbooks, or forgotten. Recovering it is not antiquarianism. It changes what we take ourselves to know about water, boiling and the conditions under which familiar facts remain true.

That is why Inventing Temperature is not just a history of thermometers. It is also a challenge to a familiar picture of scientific knowledge. The facts we teach as elementary often look elementary only because the labour that made them possible has disappeared from view.

Why this matters

The next time a thermometer gives a number, the interesting question is not simply whether the instrument is accurate. It is what had to happen before such a number could mean anything at all.

Chang’s answer is that measurement is not the passive reading of nature’s own scale. It is the art of making the world answer a question reproducibly. To measure temperature, scientists had to make phenomena stable, instruments comparable and concepts robust enough to travel beyond the circumstances in which they first made sense.

It is quieter than the usual tale of discovery, but perhaps more revealing: before science can discover with instruments, it has to learn how those instruments can be made to speak.

References

Chang, H. (2004). Inventing Temperature: Measurement and Scientific Progress. Oxford University Press.

Chang, H. (1999). “History and Philosophy of Science as a Continuation of Science by Other Means”. Science & Education, 8, 413–425.

Kuhn, T. S. (1962). The Structure of Scientific Revolutions. University of Chicago Press.

Neurath, O. (1932/33). “Protocol Statements”. In Philosophical Papers 1913–194, 91–99.

Acknowledgements: This article was written with the support of the Basque Government Postdoctoral Programme for Doctoral Research Staff, 2023–2028.

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Androgenetic alopecia is characterized by a progressive hair loss. This represents a cosmetic issue, treated with a limited set of pharmacological tools such as minoxidil or finasteride. While these therapies can be effective in some patients, their results are often inconsistent and frequently accompanied by unwanted side effects. This has driven researchers to search for alternative approaches that do not simply mask the problem, but instead target the biological processes underlying hair follicle degeneration. A recent study by Luo and colleagues ¹ explores a particularly intriguing possibility: the use of tiny biological particles, known as exosomal extracelular vesicles, a tiny cargos that cells secrete to communicate and instric other cells. These are extremely small vesicles, essentially microscopic “packages” released by cells that contain proteins, signaling molecules, and genetic material. Their function is to communicate with other cells and influence their behavior. They plan to use this secretion to use its messages to stimulate hair regeneration through vascular and cellular repair mechanisms.

At the heart of this work lies a concept that may sound surprising at first. The researchers focused on dental pulp stem cells, a stem cell source obtained from the dental pulp of the third molars. These cells are known for their strong regenerative potential ²³⁴. Rather than grafting these cells directly, however, the study uses the exosomes that they naturally produce. Because exosomes can exert powerful effects without requiring direct cell transplantation, they are increasingly seen as promising tools for regenerative medicine. To understand how these exosomes might help with hair loss, the researchers designed a combination of laboratory and animal experiments. They first isolated dental pulp stem cells from human donors and confirmed that these cells retained their typical properties, including the ability to differentiate into multiple tissue types. From these cells, they extracted exosomes using a series of centrifugation steps designed to separate them from other cellular debris. The resulting particles were then carefully characterized using electron microscopy, which allowed the researchers to visualize their structure, and nanoparticle tracking analysis, which provided information about their size. These analyses confirmed that the isolated vesicles had the expected morphology and molecular markers of exosomes.

The next step was to determine whether these exosomes could influence the behavior of dermal papilla cells, a specialized cell population located at the base of hair follicles. These cells play a central role in regulating hair growth by producing signals that activate hair follicle stem cells. When dermal papilla cells lose functionality (as happens in androgenetic alopecia) hair follicles shrink and eventually stop producing visible hair. In cell culture experiments, the researchers exposed dermal papilla cells to the exosomes and observed their effects over time. Importantly, they used a well-established model of hair loss by treating the cells with dihydrotestosterone (DHT), a hormone known to impair hair growth and mimic the conditions of androgenetic alopecia. Under these conditions, dermal papilla cells typically show reduced proliferation and weakened regenerative capacity. However, when exosomes were added to the system, this negative effect was largely reversed. The treated cells proliferated more actively and showed improved migration, suggesting that they were regaining functionality. These functional improvements were accompanied by molecular changes. The researchers measured the expression of key genes associated with hair induction, such as alkaline phosphatase (ALP) and (alpha–Smooth Muscle Actin) α-SMA. They found that their levels increased significantly after exosome treatment. This indicates that the cells were not only surviving better, but were also recovering their ability to promote hair growth.

One of the most interesting aspects of the study lies in its attempt to uncover the biological mechanism behind these effects. To do this, the team used transcriptomic analysis (a method that allows scientists to examine changes in the activity of thousands of genes simultaneously). This approach revealed that exosome treatment activated a signaling pathway known as PI3K/Akt, which is widely involved in cell survival, proliferation, and tissue regeneration. At the same time, the treated cells showed increased expression of VEGFA (vascular endotelial growth factor A), a key molecule that promotes the formation of new blood vessels. This connection between cellular signaling and vascularization is crucial. Hair follicles are highly dynamic structures that require a constant supply of oxygen and nutrients to sustain growth. When blood flow around the follicle is compromised, the growth phase of the hair cycle is shortened, leading to progressive miniaturization of the follicle. By enhancing angiogenesis (the formation of new blood vessels) the exosomes appear to restore the microenvironment necessary for healthy hair growth. To confirm that this pathway was indeed responsible for the observed effects, the researchers performed inhibition experiments using LY-294002 a molecule that blocks PI3K/Akt activity. When this pathway was inhibited, the beneficial effects of the exosomes were almost completely abolished. The dermal papilla cells lost their ability to proliferate and to express hair-inductive markers, demonstrating that activation of PI3K/Akt signaling is not just associated with the process, but is required for it to occur. While these in vitro experiments provide valuable insights, the true test of any therapeutic approach lies in its performance in living organisms. To address this, the autors employed a mouse model of androgenetic alopecia. They induced hair loss in mice by administering dihydrotestosterone and then treated them either with exosomes, with minoxidil (as a positive control), or with no treatment. Over the course of two weeks, they monitored hair regrowth through direct observation and histological analysis. The results were striking. Mice treated with exosomes showed significantly faster and more robust hair regrowth compared to untreated animals. Their skin transitioned from the resting phase to the active growth phase earlier, and by the end of the experiment, they displayed visible hair comparable to that seen in the minoxidil-treated group (Figure 1). Furthermore, the microscopic examination of skin samples revealed further details, the exosome-treated mice had a higher number of hair follicles and increased dermal thickness, both indicators of improved hair regeneration. In addition, markers of cell proliferation were elevated, while the expression of the androgen receptor linked to the negative effects of DHT was reduced. Importantly, the molecular analyses performed on these tissue samples mirrored the findings observed in cell culture. The PI3K/Akt pathway was activated, and levels of VEGFA were increased, confirming that the same mechanism operates in vivo. These results suggest that exosomes not only improve the intrinsic functionality of dermal papilla cells, but also reshape the surrounding tissue environment in a way that supports sustained hair growth.

Taken together, this study offers a compelling example of how regenerative medicine is moving toward more refined and targeted approaches. Instead of transplanting cells, which can carry risks such as immune rejection or uncontrolled growth, it leverages the signaling capacity of exosomes to stimulate repair processes in a controlled manner. This cell-free strategy is particularly appealing because it combines biological complexity with practical advantages in terms of safety and scalability. At the same time, it is important to interpret these findings with caution. As with most preclinical studies, the results obtained in mice do not automatically translate to humans. Hair growth is regulated by a complex interplay of genetic, hormonal, and environmental factors, and what works in an experimental model may require significant adaptation before becoming clinically viable. Moreover, the long-term effects of exosome-based therapies remain to be fully understood. Nevertheless, the work by Luo and colleagues represents a significant step forward. By demonstrating that exosomes derived from dental pulp stem cells can restore hair growth through well-defined molecular pathways, the study not only identifies a promising therapeutic candidate but also provides a deeper understanding of the biological processes underlying hair regeneration. It highlights the importance of the vascular microenvironment and reinforces the idea that effective therapies must address not just the symptoms, but the underlying cellular dysfunction.

In a field where innovation has been relatively slow, this approach opens new avenues for research and clinical development. Whether exosome-based therapies will eventually become a standard treatment for hair loss remains to be seen, but the evidence presented here suggests that the future of regenerative dermatology may lie in harnessing the body’s own communication systems to repair and rebuild damaged tissues.

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This loss of clarity is particularly problematic when studying molecules with unpaired electrons. Known as radicals, diradicals, or molecular magnets, these systems possess unique magnetic, optical, and reactive properties that depend entirely on how their unpaired electron spins communicate with one another. When multiple unpaired electrons inhabit a single molecule or a cluster of molecules, their spins can align in the same direction (ferromagnetic coupling) or in opposite directions (antiferromagnetic coupling). To calculate these interactions, scientists rely on simplified historical models, such as the Heisenberg spin model, which treats molecules like networks of localized bar magnets. However, bridging the gap between a giant, complex quantum wave function and this simple bar-magnet picture has traditionally required complex mathematical projections or artificial modifications to molecular orbitals.

Spin-permutation diabatization

A elegant solution proposed by Alicia Omist and David Casanova ¹ to this long-standing dilemma comes in the form of a framework known as spin-permutation diabatization. Instead of altering the molecular orbitals themselves, this new strategy operates directly on the spin degrees of freedom within the quantum wave function. The method utilizes a fundamental quantum mechanical tool: the spin-permutation operator, a mathematical function that interchanges the spin coordinates of two electrons.

By repeatedly applying mathematical rotations that minimize what is called self-spin exchange, the Omist-Casanova algorithm acts like an automated dealer shuffling a deck of cards. It systematically rearranges the collective, delocalized adiabatic states until they transform into “diabatic” states. In this new diabatic representation, the mathematical haze clears, revealing a vivid, real-space map of precisely where the spin-up and spin-down electron densities are localized. Because this transformation is purely unitary, it preserves the exact quantum mechanics of the system while translating it into a language that aligns perfectly with classical chemical intuition.

The power of this approach becomes obvious when observing how electron spins behave during chemical reactions or inside advanced materials. Consider the simple molecule ethylene, which consists of two carbon atoms joined by a double bond. Under normal conditions, the electrons are locked tightly in a shared bond. However, as the molecule twists around its central carbon-carbon axis, this bond progressively weakens. By tracking the molecule through this twist, the spin-permutation framework shows exactly how the collective electron cloud breaks down, revealing two distinct, localized unpaired electrons settled on opposite carbon atoms.

Solar cells and organic electronics

The Omist-Casanova strategy is also shedding light on cutting-edge materials used in solar cells and organic electronics. In organic chromophores (molecules that absorb and emit light) the energy difference between a singlet state (where electron spins are paired) and a triplet state (where spins are unpaired) dictates how efficiently a material can perform. For example, in technologies like thermally activated delayed fluorescence, which powers vivid digital displays, a tiny energy gap between these states is required. By applying spin diabatization, it becomes clear that this energy gap is dictated by spatial separation. When the calculated spin-up and spin-down densities overlap heavily in the same region of a molecule, their mutual interactions are strong, resulting in a wide energy gap. Conversely, when the spins are coaxed onto entirely different atomic sites or separate fragments of a molecular pair, the interaction weakens, and the energy gap narrows dramatically.

A translator

Ultimately, this computational breakthrough provides an elegant translator for modern chemistry. By transforming complex, collective wave functions into an intuitive landscape of localized spins, it bridges the gap between abstract quantum mathematics and practical molecular design. It offers scientists a clearer lens through which to view molecular magnets, light-harvesting systems, and strongly correlated electrons, proving that we do not have to sacrifice physical intuition to achieve quantum accuracy.

Author: César Tomé López is a science writer and the editor of Mapping Ignorance

Disclaimer: Parts of this article may have been copied verbatim or almost verbatim from the referenced research paper/s.

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The world’s population is growing, people are living longer, and industry continues to expand. These changes bring many benefits, but they can also increase risks to human health. Over time, people are exposed to many substances in the environment, some of which may be harmful. At the same time, greater industrial activity means more chemicals are produced, used, and released, which can lead to higher levels of environmental contamination and greater human exposure.

It was during the 1980s that the field of neurotoxicology began to emerge, with early studies focusing on understanding how environmental contaminants and toxic substances affect the nervous system. At that time, researchers relied mainly on animal models such as frogs and mice, as well as embryonic tissues and neuronal cultures derived from these species.

Today, however, the limitations of these models are well recognized. They often fail to accurately reproduce the complex biological processes that occur in the human body. In addition, they can require significant time and resources, raise ethical concerns related to animal use, and present challenges when trying to translate results to humans due to fundamental physiological differences between species.

There is therefore a clear need to develop more realistic experimental models that better represent the human body and help us understand more accurately how toxic substances can affect the nervous system. Some of these contaminants are especially concerning because they are extremely small. Their tiny size means they can enter the body through the air we breathe, travel to the central nervous system, and in some cases even cross the blood–brain barrier to reach the brain directly. When this happens, brain tissue may be exposed to potentially harmful effects.

Researchers at GAIKER Technology Centre have focused their efforts on studying the neurotoxic effects of these contaminants on the central nervous system (CNS) ¹. To achieve this, they have developed an in vitro model of the human blood–brain barrier, as well as a model that mimics brain tissue using cell lines of human origin. Thanks to these advances, it is possible to significantly reduce the gap between experimental models and human physiology, providing a more accurate representation of human anatomy without the need to use animals in research, thereby avoiding ethical concerns.

Human cell lines are very useful in toxicology because they help researchers create models that are closer to real human tissues. By combining different types of cells, it is possible to build more advanced systems that better represent organs such as the brain. For example, neurons can be studied together with microglial cells, which are involved in the brain’s defense system. This allows researchers to better understand how contaminants may affect brain tissue.

In addition, researchers can recreate the human blood–brain barrier in the laboratory by combining endothelial cells and astrocytes. This barrier is one of the body’s most important defense systems, as it helps protect the brain by controlling which substances can pass from the bloodstream into nervous tissue. Reproducing it in the lab gives scientists a valuable tool to study what happens when contaminants encounter this protective layer. It allows them to explore whether harmful substances can alter the barrier, weaken its protective function, or even cross it and reach the brain. This kind of model is especially useful for understanding potential risks to human health and for identifying which contaminants may pose a greater threat to the nervous system.

To explore how useful these models are, the researchers tested them with different contaminants that people may come into contact within everyday life or through industrial activity. They then observed how the cells responded, paying special attention to signs of damage and inflammation. This approach helps provide a clearer picture of how harmful substances may affect the brain and supports the development of better tools to study potential risks to human health.

Overall, this work shows the value of developing human-based experimental models to better understand how environmental contaminants may affect the brain. These tools not only provide more realistic information about potential risks to human health, but also open the door to safer, more effective and more ethical ways of studying neurotoxicity in the future.

The BRTA is a consortium that remains a step ahead of future socio-economic challenges worldwide and in the Basque Autonomous Community; it addresses them through research and technological development, thus projecting itself internationally. The BRTA centres collaborate to generate knowledge and transfer it to Basque society and industry so as to make them more innovative and competitive. The BRTA is an alliance of 17 R&D centres and cooperative research centres with the support of the Basque Government, the SPRI and the Chartered Provincial Councils of Araba, Bizkaia and Gipuzkoa.

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