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Did space weather delay a train in 1841?

Back when I used to commute to Physics World’s Bristol, UK offices every day, I heard a lot of excuses explanations for why my train was delayed. Missing crew members. Road vehicles colliding with bridges. Even, on one memorable occasion, a herd of cows blocking the tracks.

One explanation I never heard, though, was the one proposed for a train that supposedly left the south-west English city of Exeter at 10.05 p.m. on 18 October 1841. According to an anonymous correspondent in Nature some 30 years later, this 10.05 train was delayed by 16 minutes because of “a very intense magnetic disturbance” that made it “impossible to ascertain if the line was clear”. This disturbance, the correspondent argued, was due to “the magnetic and auroral storms that have of late excited some attention and discussion in these pages”.

Such storms are now known as space weather, and in 2013 Trey Cade, a physicist who leads the Space Weather Research Lab at Baylor University in the US, made an intriguing suggestion: was this supposed 1841 delay the first recorded example of space weather affecting human technology?

An auroral detective story

According to the latest research, the answer is firmly in line with Betteridge’s law, which states that any headline that ends in a question mark can be answered by the word “no”. Although space weather was (and is) capable of delaying trains, it couldn’t have delayed the 10.05 from Exeter in 1841 for a very simple reason: the railway line in that part of England didn’t open until 1846.

That, however, raises a further question. Assuming Nature’s correspondent wasn’t making up the story of the aurora-delayed train, was he perhaps misremembering the date of a different, later storm?

To find out, a broad group of experts led by Lancaster University’s Jim Wild, and including personnel from the British Geological Survey, Natural Resources Canada, Nature, RMIT University in Australia and STFC RAL Space in the UK as well as Cade himself – dug into the data. By combining evidence from railway timetables, historical newspapers, records of solar observations, reports of aurorae and digitized geomagnetic records, they concluded that Nature’s correspondent – whom they tentatively identified as an electrical engineer called Nathaniel John Holmes – was probably thinking of a storm that took place on 18 October 1848, not 1841.

Photo of Brett Carter standing in front of the escalator at Melbourne Central Station. Two departure boards are visible in the background
Historical insights: Brett Carter of RMIT University (pictured at Melbourne Central Station in Australia) was part of the international team of experts who collaborated on the mystery of the delayed 10.05 from Exeter. (Courtesy: Michael Quin, RMIT University)

Having debunked the 1841 hypothesis, the authors of the new research, which is published in Space Weather, say that the earliest known example of space weather impacting human technology is now an incident involving telegraph systems on England’s Midland Railway in March 1847. If that still sounds rather early, Wild says that’s the point. “Society has been experiencing the effects of space weather on technology for almost as long as electrical technologies have existed,” he says. “The technologies affected have evolved from railway telegraphs to satellites…but the challenge remains the same: understanding the risk and ensuring society is resilient to its impacts.”

Raising awareness

According to Lasse Clausen, who studies space weather at the University of Oslo, Norway, but was not involved in the 10.05 from Exeter study, the biggest barrier to this understanding is a shortage of data about what’s going on in the Earth’s ionosphere, where space weather occurs. Although our ability to detect space weather has improved since the 1840s, he says that when it comes to predicting it, we’re roughly where conventional weather forecasting was in the 1920s. “Essentially, we can look out the window and say whether it’s raining or not,” he says.

Changing that will require additional funding, and for that, Clausen thinks raising awareness is essential. “The ionosphere is useful, but it’s not very sexy,” he tells me. The new study, he adds, is “a nice piece of detective work” that “firmly belongs in the ‘awareness raising’ category”.

The secret world of tribology

I have been involved in tribology for most of my working life, but even today it can feel like a well-kept secret. A highly interdisciplinary field with close ties to materials science, tribology is essentially the science and technology of friction, lubrication and wear between any moving surfaces. But tribology encompasses in part one age-old challenge.

I’m talking about the use of bearings, which dates back to at least 4600 BCE, when ancient Egyptians used wood log rollers to move large stone blocks during the construction of their pyramids. In 1500 Leonardo da Vinci used ball bearings in his conceptual helicopter design, while in 1740 the clock maker John Harrison invented caged roller bearings for his marine chronometer.

It was not until the mid-1960s that the word tribology was coined by the British engineer and entrepreneur Peter Jost after discussions with the then editor of the Oxford English Dictionary

The first patent on a ball bearing was granted to Philip Vaughan, an ironmaker from Carmarthen, Wales, bringing tribology firmly into the industrial world. But despite all the history, it was not until the mid-1960s that the word was coined by the British engineer and entrepreneur Peter Jost. After discussions with the then editor of the Oxford English Dictionary, the Greek word “tribos” – meaning rubbing – was suggested as a basis for describing the discipline.

This resonated with Jost, because the terms “tribo-chemistry” and “tribo-physics” were already in use. In an interview with the magazine Machinery Lubrication in 2005, Jost explained how “tribo science and tribo technology” then simply became shortened to tribology. “I felt that because it had a Greek basis, it could easily be adopted into a number of languages by most Western countries,” Jost recalled.

Wear’s the rub?

For the most part, the aim of tribology is to minimize friction and wear between components, which involves a knowledge of both materials and lubrication. Initially, the focus of the field was on moving parts in industrial or mechanical machines, such as bearings, gears, brakes and clutches. Indeed, one reason that the term came about was a conference in Cardiff in 1964 organized by the Iron and Steel Institute and the Institution of Mechanical Engineers (IMechE).

At the conference it became apparent that significant failures in plant machinery, which were being attributed to poor lubrication, were in fact due to a lack of fundamental design knowledge. These findings led to Jost chairing a UK government committee into lubrication education and research and the needs of industry. The resulting study – generally known as the “Jost report” – came out in 1964.

Now all this may seem like ancient history, which I suppose it is, but I was intrigued to discover that delegates to that 1964 conference visited the Llanwern steelworks at nearby Newport. As some of you may recall me describing, I also visited this site during my own student days, where I saw the steel rolling line in action. It was a truly impressive sight.

The total failure was remarkable, underlining just what can happen when moving parts fail without warning

From the viewing platform, I could see a massive volume of red-hot steel thunder along the rollers when, suddenly, there was a bang. Something failed and the steel landed in a crumpled mess all over the plant floor. We were safe but the total failure was remarkable to witness, underlining just what can happen when moving parts fail without warning.

The knock-on effect of this failure would have been costly and sustained. As well as a steel rolling line being out of action, new parts would have had to be sourced and old ones repaired. There’d have been quality concerns to address, safety reviews to be undertaken and the root cause of the problems to be worked out. Quite possibly all those jobs would have needed to be completed before production could restart.

What’s more, the failure of the machine’s moving parts, which depends on tribology, would have damaged the company’s reputation and led to customers annoyed with delays and late deliveries. It is this kind of event that those involved in tribology are trying to prevent, or at least minimize. By understanding tribology, in other words, engineers can design better machines and components.

What it says on the tin

This was made clear in the 1964 Jost report, which said that adopting good tribological practices could save the UK between 1% and 1.4% of its gross domestic product (GDP). In today’s money, that would amount to some £30bn, given that country’s GDP is a shade over £3 trillion. Put simply, designing and maintaining industrial equipment, based on a solid understanding of tribology, yields significant economic benefit.

More recently, a 2017 study by Kenneth Holmberg from the VTT Technical Research Centre of Finland and Ali Erdemir of the Argonne National Laboratory in the US (Friction (5 263) suggests that 20% of the world’s energy consumption originates in tribological contacts. And by the application of best practice, as much as 40% of this could be saved.

Rubbing along nicely

It’s generally accepted that there are three key ingredients for tribology:

  • Friction: the resistance encountered when one surface moves over another.
  • Wear: the loss or material from or damage to the surface due to continuous movement or contact.
  • Lubrication: the use of fluids or other substances to reduce friction and wear.

As a truly cross-functional discipline, tribology has strong overlaps with several fields, including:

  • Materials science: developing wear-resistant and self-lubricating materials.
  • Lubrication: design, additives, management.
  • Surface engineering: contact mechanics, adhesion, coatings, treatments.
  • Wear mechanisms: erosion, corrosion, tribo-corrosion.
  • Physics, chemistry and biosciences: medical, food and cosmetics applications.

More than 60 years after the publication of the Jost report, the influence of tribology continues to grow. Alongside its impact on transportation and manufacturing, tribology is also relevant to extreme environments from aerospace, nuclear power, marine and subsea to space technology, high-voltage electrical systems and even the human body. There are also applications in nano-tribology, cosmetics, food, computational, digital, tribotronics, geotribology, hydrogen and green tribology.

Tribology will help to reduce our carbon footprint and counter climate change

As chair of the IMechE’s tribology group committee and a member of the tribology group committee of the Institute of Physics, naturally I am biased. Still, I feel privileged to be part of the tribology community and the amazing things it achieves. Whether it’s making products more energy efficient, creating green lubricants, or making plant-based protein more palatable to meat eaters, tribology will help to reduce our carbon footprint and counter climate change.

So next time you brush your teeth, comb your hair, switch on a light or ride on a bus, spare a thought for tribologists and their dedication to making the world run smoothly. It’s hard to think of anything that doesn’t involve tribology at all.

  • The Institute of Physics is hosting the 5th Tribology and Net Zero seminar on 6 November in London co-organized with the Institution of Mechanical Engineers, the Royal Society of Chemistry, and the UK student chapter of the Society of Tribologists and Lubrication Engineers.

Heavy water isotopes make weather predictions more accurate

Weather forecasting relies on many different types of data to make accurate predictions: temperature, humidity and wind data are all used to build an accurate forecast. Researchers have now found a new way to improve weather forecasts, by adding data on water isotopes in the atmosphere.

For predicting weather, water vapour isotopes integrate key information on the history of their evaporation, condensation, mixing and transport. Heavy water (containing either deuterium or oxygen-18) exists in the atmosphere and the way that these water isotopes condense and evaporate is different to that of normal water molecules.

The release and absorption of latent heat when water condenses and evaporates is the primary energy source for atmospheric circulation. The vertical heating profile plays a major role in large-scale circulation, wave propagation, storm track positioning, cloud development and precipitation patterns. However, vertical heating structures and convective activity cannot be measured directly by satellite networks and have to be inferred instead, leading to biases and inconsistencies that degrade the accuracy of weather models.

Stable heavy water isotopes can provide a direct physical link between the latent heating processes in weather patterns through isotopic fractionation. Heavier water isotopes preferentially condense into the liquid phase because they have a greater binding energy and lower diffusive velocity. Additionally, heavy water doesn’t evaporate as easily as normal water.

Even though these water isotopes exist in small quantities, their relative abundance alters during evaporation and condensation. Observing this change in abundance of the isotopes allowed the researchers to understand where the water came from and what happened to it along the way – providing insights into the atmospheric conditions.

The research team – led by Kinya Toride from University of Colorado Boulder, NOAA and the University of Tokyo – examined data from the Infrared Atmospheric Sounding Interferometer (IASI), which provides large amounts of accurate long-term data on water vapour isotope ratios in the mid-troposphere. The researchers fed the data collected from satellite observations into a weather model using a technique called data assimilation. This approach takes the different isotope signals and translates them into the atmospheric variables that are used in weather forecasting – as the vapour behaviour alone was not sufficient to reveal atmospheric variables such as temperature, wind and humidity.

They found that inclusion of these data improved the estimation of wind, temperature and water vapour in the atmosphere, leading to more accurate weather forecasts. This included improving forecasts for up to five days ahead and providing more accurate predictions on heavy rainfall across many regions.

While it has long been theorized that water vapour isotopes could improve weather forecasting, this is the first study that has been able to show it using real-world data, rather than inside a controlled lab environment. But while the study was performed in conditions close to real operational forecasting, the researchers emphasize that it’s not something that can be implemented straightaway.

This is because there are limited real-time isotope data available and the operational forecasting models employed today by meteorologists are not designed to use such data. For isotope observations to be used in our everyday weather forecasts, a lot more real-time data will need to be collected and processed. Then either new models that incorporate these data will have to be developed or the current models will need to be adapted to include the water isotope data.

However, with more and more satellites being launched into our atmosphere, and the costs of them continuing to come down, it’s likely that more weather satellites will be available to provide these data in the coming years – and both meteorologists and weather presenters should be able to make good use of them.

The study, published in Nature Communications Earth & Environment, demonstrates the benefits of using water isotope data, particularly for predicting heavy rainfall. “Our long-term goal is to develop more accurate satellite observations of water vapour isotopes and integrate them into operational weather forecasting systems,” says co-author Kei Yoshimura from University of Tokyo in a press statement. “This additional layer of information can help make everyday forecasts more reliable.”

Cyril Hilsum, former GEC research boss and Institute of Physics president, dies aged 101

Cyril Hilsum, a former president of the Institute of Physics (IOP), which publishes Physics World, died on 23 September at the age of 101. In the 1970s Hilsum made pioneering contributions to liquid crystals paving the way for TV and computer liquid-crystal displays that are still widely used today.

Hilsum was born on 17 May 1925 and completed a degree in physics at University College London in 1945. He then joined the Admiralty Research Laboratory in Teddington before working at the Services Electronics Research Laboratory in Baldock.

Throughout his career, Hilsum focused on developing commercial applications for many areas of his research including creating the UK’s first semiconductor laser.

Cyril Hilsum at his house
Hilsum built a lab in his house in Pinner where he made his final invention – an ink with sensors to conduct electricity. At the age of 97, this earned him the last of more than 70 patents. (courtesy: Lindsey Hilsum)

In 1964 he moved to the Royal Radar Research Establishment in Malvern, Worcestershire, developing the first microwave oscillator based on the negative resistance effect in the semiconductor gallium arsenide.

His work on miniature radar systems led to Claribel, a device that detected the trajectory of a bullet and could be used to locate snipers.

He also led a team that developed the first stable liquid crystals that could be used in flat panel displays, an invention that garnered £100m in royalties for the British government.

In 1983 Hilsum was appointed chief scientist of GEC Hirst Research Centre, where he later became research director two years later.

Hilsum officially retired in 1995 aged 70, but worked part-time as chief science officer for Infi-tex Ltd, which produces force sensors for use in textiles.

A life in science

Hilsum served as president of the IOP between 1988 and 1990, in which year he was also appointed a Commander of the Order of the British Empire (CBE) for his “services to the electrical and electronics industry”.

Over his career, Hilsum was honoured with many prizes including three awards from the IOP: the Max Born Prize in 1987, the Faraday Medal (1988) as well as the Richard Glazebrook Medal and Prize (1998).

In 2007 he was awarded the Royal Society’s Royal Medal “for his many outstanding contributions and for continuing to use his prodigious talents on behalf of industry, government and academe to this day”.

Hilsum also encouraged more women to have careers in physics and engineering. He sponsored the Karen Burt Award at the Women’s Engineering Society, which was named after his daughter, an engineer, who died in 1997 aged 42.

Hilsum celebrated his 100th birthday last year at a special event held at the Royal Society of Chemistry.

Former IOP president Frances Saunders, who worked in liquid-crystal displays, told Physics World that Hilsum was a “true pioneer in applied physics”, adding that as well as finding applications for such emerging technologies he always wanted to ensure that the underlying physics or material science was properly understood.

“What also made him stand out was his vision for where a technology might go – in the early developments of LCDs his vision was that the display would become the computer with the computer chips attached to the back of the display and interacted with via touch screens,” adds Saunders. “He was right, of course, as we now have tablets and smart phones that do just that.”

Quiz of the week: which site has been rejected for the Thirty Meter Telescope?

Fancy some more? Check out our puzzles page.

Single-photon measurements confirm Richard Feynman’s vision of quantum mechanics

Physicists have confirmed the two foundational postulates of Richard Feynman’s path-integral approach to quantum mechanics in a real-world experiment for the first time. This comes nearly 80 years after Feynman first published his path-integral formulation, which describes the time evolution of quantum systems.

Fundamental thought experiments, such as Schrödinger’s cat, the Einstein–Podolsky–Rosen paradox and the quantum double-slit experiment have always been important for developing the theories of quantum mechanics. As technology improves, some thought experiments have been realized in the lab, confirming many aspects of quantum theory. However, thought and real experiments thus far have not addressed the fundamental question: how do quantum systems evolve between initial and final states? This question, explains Shi-Liang Zhu of South China Normal University in Guangzhou, lies at the heart of Feynman’s path integral postulates for his famous propagator equation.

The postulates, first proposed in 1948, have never been directly tested – despite their foundational role in modern physics. Indeed, the path-integral formulation has been critical for the development of fields ranging from quantum field theory to cosmology and has provided a unified framework that connects quantum mechanics with classical physics through the principle of least action. The path integral’s predictions also underpin modern quantum science, from condensed matter physics to quantum statistical physics.

As quantum theory was developed, several “pictures” emerged of how a quantum system evolves with time – including the Schrödinger and Heisenberg pictures. The Schrödinger equation, the Heisenberg equation and the Feynman propagator equation are formally equivalent formulations of quantum mechanics, explains Zhu. “However, while the first two are typically treated as fundamental postulates, the Feynman propagator equation is derived from two underlying postulates. This derivational asymmetry makes experimental tests of Feynman’s postulates particularly compelling.”

Not a simple sum

The first postulate is that a quantum particle does not travel along a single trajectory when moving from point A to point B; and instead every probable path contributes to its trajectory. The second postulate is that all possible paths have the same probability (or equal-magnitude amplitudes) and differ only by a path-dependent phase factor. This is very different from simply summing all the probabilities as in classical physics.

At time ti, explains Zhu, a particle is localized at xi with its wave function denoted as ψ(xi, ti). The probability of the particle reaching xf at time tf is therefore determined through all possible paths connecting points A at (xi, ti) and B at (xf,tf). The j-th path contributes a probability amplitude ϕj.

Feynman postulated that the probability P of the particle reaching xf at time tf equals the absolute square of the sum of probability amplitudes ϕj for all paths. As mentioned, all these contribute equally in magnitude, with each contribution’s phase being given by the classical action (in units of the Planck constant, ħ).

“We have now directly measured the probability amplitudes ϕj of more than 1.4 million possible paths taken by single photons in an optical system,” says Zhu. “We did this by dividing the region between the starting point A and the end point B into a  grid of points. We connected adjacent points by line segments and then measured the propagator for each segment. In total, there are 175 possible paths.”

The results from this experiment, which is detailed in Science Advances, validate the first postulate  with a mean absolute percentage error of 4.45% and a fidelity of 94.9%. They also confirm the second postulate with 94.7% fidelity.

Reconstructing millions of path amplitudes

The paper’s first author Yong-Li Wen notes: “because there were so many possible paths that the photons could take, the primary challenge in our experiments was to achieve sufficient accuracy to reconstruct millions of path amplitudes, since even marginal errors in individual propagator measurements accumulate multiplicatively, destroying phase coherence and rendering the reconstructed path distribution nearly random.

“We overcame this problem through four key technical advancements: amplifying the signals; designing a customized high-precision imaging system; implementing real-time normalization via a reference beam to correct for photon fluctuation errors; and making sure the set-up was mechanically stable on the nanoscale.”

These innovations improved single-photon propagator fidelity from 87.6% to 98.5%, something that allowed the team to resolve the global structure of path amplitudes with unprecedented precision.

The work establishes a powerful experimental framework for investigating path integrals in quantum systems, Zhu tells Physics World. “By confirming that quantum probabilities arise from path interference and that phases are governed by classical action, we provide experimental evidence supporting the view that quantum paths reflect physical reality rather than being mere mathematical artefacts.”

The high-precision propagator methodology could also be used to study quantum-to-classical transitions and decoherence mechanisms, where understanding the role of interfering paths is essential, he adds. And it could be extended to probe fundamental phenomena such, as entangled histories and indefinite causal order across multiple space–time points.

Beyond fundamental physics, the technique may make quantum simulations of complex condensed matter and quantum field theory phenomena, including instantons and magnetic monopoles, easier. “Perhaps most excitingly, by enabling precise propagator measurements in diverse environments, this framework could eventually be extended to interacting systems and curved space–times, allowing for valuable experiments with artificial quantum systems,” says Zhu.

Pathways to commercial and academic success in medical physics

This episode of the Physics World Weekly podcast features the medical physicist Nick Zacharopoulos, who is CEO of US-based Aktina Medical.

In conversation with Physics World’s Tami Freeman, Zacharopoulos reflects on the twists and turns in his career developing new technologies for radiation oncology. His journey began when he was a child helping his father build radiotherapy components in the family’s garage and led to academic and commercial success.

Zacharopoulos talks about his role in the development of a pivotable product for Aktina and how his persistence – and a chance lunch with a colleague – led to his enrolment in a PhD programme at McGill University.

Faster cryogenics speeds up quantum testing

Cool stuff The new RapidCycle 100 EC cryostat from Montana Instruments, which can cool down from room temperature to 4 K within an hour and warm back up again just as fast. (Courtesy: Montana Instruments)
Cool stuff The new RapidCycle 100 EC cryostat from Montana Instruments, which can cool down from room temperature to 4 K within an hour and warm back up again just as fast. (Courtesy: Montana Instruments)

As quantum computing enters its commercial phase, demand is growing for electronic components that can operate reliably at ultralow temperatures. But suppliers that routinely test the performance of their devices under a wide range of conditions rarely extend their characterization efforts to the cryogenic regime. Quantum developers must either test the components themselves, or run the risk that a faulty device ruins the performance of increasingly complex quantum machines.

“Quantum computers are often operated within a dilution refrigerator, which takes days or weeks to cool down,” says Ben Wilbur, a senior design engineer at cryogenics specialist Montana Instruments. “A single faulty component requires the whole system to be warmed up again, which can waste the best part of a month and slow down progress.”

To avoid that scenario Montana Instruments has designed and built a cryostat, called the RapidCycle 100  EC, that can cool down from room temperature to 4 K within an hour and warm back up again just as quickly. The overall cycle time is around three times faster than for similar systems, and a fraction of the time needed to cool down and warm up a large-scale dilution fridge.

Such a rapid cycle time offers an efficient solution for quantum engineers to validate electronic components before integration and for suppliers to measure the low-temperature response of their devices before shipping them out to customers. “From talking to different companies we know there is a market desire to test more components, but there is also a commercial impetus to streamline the testing process,” says product manager Patrick Gale.

Gale points out that many of the electronic components that are being used to build quantum computers have not been designed to operate at ultralow temperatures. As an example, radio-frequency devices play a critical role in many qubit architectures for controlling and reading out the quantum states, but manufacturers of these components are unlikely to have the expertise or equipment to know whether their components function effectively in this regime.

“This system is designed for companies that want to understand how their devices perform at ultralow temperatures, but without needing to hire a cryogenics engineer,” says Gale. “Having the capability to characterize their own components could offer suppliers a competitive advantage, allowing them to pre-qualify their devices and even to improve their low-temperature performance for quantum applications.”

Commercial drivers

The idea for the RapidCycle cryostat first emerged in 2023. Initial development results were promising, but more immediate priorities delayed efforts to engineer a commercially viable product. Around a year ago, as the need for faster cycle times became more urgent within the rapidly expanding quantum industry, the company restarted its design work. “We felt we were in a unique position to tackle this problem,” says Gale.

REQUIRED (courtesy: )
Speedy response Montana Instruments’ fast-acting cryostat lets quantum engineers validate electronic components and measure the low-temperature response of devices before being shipped to customers. (Courtesy: Montana Instruments)

But cutting the cycle time by a third was not an easy task. “Most of the thermal energy is from room temperature down to around 50–70 K, so that is where we needed to focus our development efforts,” says Wilbur. “Beyond that the temperature starts to drop much more rapidly, since the heat capacity of the materials become much lower close to absolute zero.”

While the original work had shown that rapid cool downs were feasible, further iterations were needed to achieve the target temperature of 4 K and to generate enough cooling power to maintain the device at that temperature during the test. “To optimize the performance we needed to think carefully about the materials we used, and about the amount of thermal mass that really needed to be in the system,” says Wilbur. “The more you have in there, the longer it will take to cool down.”

While there was a clear design focus to minimize the thermal mass, the system has been engineered to provide plenty of space and flexibility for testing electrical components. Samples can be mounted on a 100 mm platform, large enough to accommodate a diverse range of electronic components, while the configuration can easily be adapted to different testing protocols. Extra space has also been created around the sample to provide an easy-access wiring system that supports a flexible combination of RF and DC feedthroughs into the cryogenic environment.

“As these tests get more complicated, all the inputs and outputs to the sample can make the cryostat really messy,” says Wilbur. He explains that the unit has a tiered structure, with the sample space at the top and a lower housing that provides extra room for connecting and disconnecting the cables. “It really cleans up the wire management but also reduces the volume within the sample space to achieve a fast cycle time.”

Targeted design

Other design features have focused on the usability of the system, particularly for electronic engineers and technicians with limited knowledge of cryogenics. In keeping with the company ethos of making cold science simple, the complexities of the cool-down process – such as reaching the right vacuum level before engaging the cryocooler – are hidden from view. “The user just needs to set a target temperature and press the cool-down button,” says Gale. “The same for warm-up, all the temperature monitoring is done automatically so the user can just walk away.”

A touchscreen interface provides real-time readouts of the internal temperature, vacuum pressure and temperature stability, while the system can also be connected to a computer network to allow for remote control and monitoring. All the measurements taken with the system can easily be exported over the network connection, enabling them to be combined with other performance data that have been collected for device characterization.

Such automated processes are nothing new for Montana Instruments, which has built a reputation for building systems that allow users to focus on their own experiments and assemblies rather than the intricacies of the cryogenics. In this case, however, special attention was also paid to creating an integrated system that can operate within the constraints of a manufacturing environment. “We focused on consolidating the form factor to ensure that the unit doesn’t take up too much space on the production floor,” says Wilbur. “The cryostation and all the controls fit into a cart that can easily be wheeled around.”

Following the official launch of the RapidCycle earlier this year, Montana Instruments is expecting to ship the first commercial units in the next month or two. But Gale points out that some beta customers in the manufacturing sector have already been trialling the system. “The feedback has been positive,” he says. “With some simple training we have had them up and running in a day or two, and they really appreciate the fast cooldown.”

What can cutting a photon in half tell us about causality and local equivalence?

Illustration of a truncated photon
Chop and change The top panel shows a photon (represented as a wave) being reflected from a mirror. The wave is incident from left to right with the solid blue line showing the portion of the wave travelling left to right and the dashed line showing the portion of the wave that has been reflected back to the left. The lower panel shows the situation shortly after the mirror has been removed. The narrow central portion is the complicated transition region containing multiple photons. The region to the left shows a truncated photon state that is locally equivalent to a single photon. To the right is the truncated photon shown as locally equivalent to the vacuum state. (Courtesy: Isak Cecil Onsager Rukan, Jan Gulla, Johannes Skaar/Phys. Rev. Lett.)

Physicists in Norway have combined quantum mechanics with relativity to show that the act of “cutting a photon in half” has no immediate effect on how that photon appears to an observer outside of a small transition region where the truncation took place. Within that region, however, their calculations suggest that large numbers of photons are required to describe the truncated photon.

Light is complex. For some phenomenon, it exhibits particle-like behaviour, and for others, it exhibits wave-like behaviour. This duality is reconciled by quantum field theory, which describes light as both a particle and a wave at the same time. More precisely, in this framework, light can be considered as consisting of particles called photons, and these photons are defined as excitations in quantum electromagnetic fields.

A common technique in optical experiments is to chop a beam of light into divisions called pulses, and an interesting – and until recently, unexplored – question is what happens to a single photon when it is chopped? The physicists Isak Cecil Onsager Rukan, Jan Gulla and Johannes Skaar at Norway’s University of Oslo set out to answer exactly this question.

Can one cut a photon in half?

What do the researchers mean by cutting a photon in half? In the wave picture of light one can imagine an electromagnetic wave that is separated in two parts by an ideal shutter. Writing in Physical Review Letters, the trio considers that thought experiment with a set-up displayed in the upper portion of the figure.

Here, a photon is represented by an electromagnetic wave that is moving from left to right towards a mirror. If the mirror is ideal, then the photon is reflected completely.

A photon can be truncated by removing (either gradually or abruptly) the mirror while the wave is being reflected. Because some of the wave has already been reflected when the mirror is removed, the result is forward-moving and backward-moving modes – the solid and dashed lines respectively.

In this way, the action of removing the mirror has effectively “cut” the photon in half if we ignore the backward-moving modes.  The outcome is surprising. In the particle picture of light, one would expect to find or not find a forward propagating photon. However, calculations done by the trio show that the outcome is a complicated state consisting of a classical mix and a quantum superposition of multiple photons.

Shifting perspectives

Returning to our earlier definition of a photon, the absence of excitations of the quantum electromagnetic field corresponds to the absence of photons. This is called a vacuum (or empty) state. However, this notion of photons (and particles in general), is not always fixed, and can be observer or scenario dependent. For instance, what looks like a vacuum to a stationary observer, might look like radiation (a bunch of photons) to an accelerating observer. This is known as the Unruh effect.

In a similar manner, what is considered a vacuum state and a photon is different before and after the mirror is removed. This is because the presence of the mirror divides the physical space in half. The nature of excitations before and after the reflector is removed is different, thereby changing the notion of what is considered as a particle. The definition of vacuum in different frames (observers) is related mathematically by the Bogoliubov transformation. It is the same mathematics that also describes why black holes must eventually decay by emitting radiation. In this case the incoming vacuum state is related to outgoing thermal radiation via these transformations.

Using these mathematical tools, the researchers were able to calculate the complicated final state. First, they assumed that the reflector was removed instantaneously. In such a scenario, they had the unphysical result that the expected number of photons in the final state is infinity. If they assume that the mirror is slowly removed, they get a finite number of expected photons in the final state. However, you can still observe any number of photons. “There is a non-zero probability of observing any number of photons,” explains Skaar.

Nothing is faster than the speed of light

Understanding what happens when the mirror is removed requires the invocation of both classical and quantum physics. On one hand, the quantum state of the electromagnetic field changes on removal of the mirror, with the very definition of a particle or a vacuum state being a very non-local concept. This is because quantum mechanics requires that the excitation must be defined over the entire physical space. On the other hand, the classical principle of causality dictates that information cannot travel faster than the speed of light. As a result, the change in the physical state of the electromagnetic fields caused by the removal of the reflector cannot propagate faster than the speed of light. This means that, for an observer at a location far enough from the mirror such that light has not had enough time to travel there yet, should experience no change in physical state.

So, quantum mechanics requires the instantaneous change of the entire global physical state on removing the mirror, whereas causality requires a finite speed limit on the propagation of any change. The challenge for the Oslo trio was how to reconcile these two requirements.

They do this by considering what an observer can actually measure about the electromagnetic field at any point.  By considering only such localized measurements, the researchers ascertain that beyond a certain region around the mirror (which they call the transition region), the final state looks exactly like the initial state. This is illustrated in the lower portion of the figure.

On the right of the reflector, far enough such that light has not had enough time to travel there (right of the transition region), the region is indistinguishable from the vacuum state if one were to only rely on these localized measurements. Similarly, on the left side of the transition region, the state cannot be differentiated from a single photon state. This is known as “local equivalence” whereby a quantum state in a finite region is locally equivalent to another, if they cannot be distinguished by local measurements in that region.

Skaar comments, “We find it interesting that in quantum field theory, a complicated state can look very simple locally, in this case everywhere except in a narrow transition region.”

Thirty Meter Telescope rejects La Palma as alternative host site

Members of the Thirty Meter Telescope (TMT) International Organization have turned down Spain’s €1bn offer to build the instrument at the Roque de los Muchachos Observatory in La Palma. The package was put forward in July with funding also provided from the European Investment Bank and Spain’s Official Credit Institute. The decision makes Hawaii’s Mauna Kea as the only possible option for the telescope.

The TMT, if built, would use a segmented primary mirror consisting of 492 elements of zero-expansion glass for a 30 m-diameter primary mirror that will allow astronomers to resolve the faintest and oldest galaxies.

The TMT’s members include the University of California, the California Institute of Technology, Canada, India, and Japan.

Officials at the TMT have not released a final construction cost for the telescope, but it is expected to be at least $3bn, of which $2bn has been committed.

In 2009, the TMT organization choose Hawaii’s Mauna Kea peak as its location. However, in 2015 protests by indigenous Hawaiians, who regard the site as sacred, delayed the start of construction.

The issue forced officials to consider a change of location with the island of La Palma, belonging to Spain’s Canary Islands, proposed as its preferred alternative site in 2016.

Some astronomers, however, were concerned by the potential move given that La Palma’s environmental conditions may limit the telescope’s scientific potential. In particular, the warmer climate and lower elevation of La Palma compared to Mauna Kea could affect mid-infrared observations, which require dry, cool conditions.

Rival designs

Further woes hit the TMT project beginning in 2024 when the US National Science Foundation (NSF) announced it would only support the construction of the Giant Magellan Telescope (GMT) or the TMT – but not both facilities.

A year later, the NSF decided to pursue the GMT, which uses seven primary and seven secondary mirrors to give it an optical surface of 25.4 m. Building of the GMT is already under way at Chile’s Las Campanas peak with officials working toward a final design review.

In 2025, Spain then offered €400m to join the project if the TMT was built in La Palma. In July, the European Investment Bank and Spain’s Official Credit Institute said it would provide an additional €600m in loans towards construction.

Yet according to a statement from the Astrophysics Institute of the Canaries (IAC), which operates the Roque de los Muchachos Observatory, TMT officials have now rejected that offer.

The IAC say that TMT members were “unable to reach the consensus required to accept the financial offer”.

The IAC adds that despite the decision, the institute “remains fully committed to the scientific and technological development of the [Roque de los Muchachos Observatory]” and will continue to promote the installation of new infrastructure including the Cherenkov Telescope Array Observatory and the European Solar Telescope.

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