All eyes were on the election of Donald Trump as US president earlier this month, whose win overshadowed two big appointments in physics. First, the particle physicist Jun Cao took over as director of China’s Institute of High Energy Physics (IHEP) in October, succeeding Yifang Wang, who had held the job since 2011.

Over the last decade, IHEP has emerged as an important force in particle physics, with plans to build a huge 100 km-circumference machine called the Circular Electron Positron Collider (CEPC). Acting as a “Higgs factory”, such a machine would be hundreds of times bigger and pricier than any project IHEP has ever attempted.

But China is serious about its intentions, aiming to present a full CEPC proposal to the Chinese government next year, with construction staring two years later and the facility opening in 2035. If the CEPC opens as planned in 2035, China could leapfrog the rest of the particle-physics community.

China’s intentions will be one pressing issue facing the British particle physicist Mark Thomson, 58, who was named as the 17th director-general at CERN earlier this month. He will take over in January 2026 from current CERN boss Fabiola Gianotti, who will finish her second term next year. Thomson will have a decisive hand in the question of what – and where – the next particle-physics facility should be.

CERN is currently backing the 91 km-circumference Future Circular Collider (FCC), several times bigger than the Large Hadron Collider (LHC). An electron–positron collider designed to study the Higgs boson in unprecedented detail, it could later be upgraded to a hadron collider, dubbed FCC-hh. But with Germany already objecting to the FCC’s steep £12bn price tag, Thomson will have a tough job eking extra cash for it from CERN member states. He’ll also be busy ensuring the upgraded LHC, known as the High-Luminosity LHC, is ready as planned by 2030.

I wouldn’t dare tell Thomson how to do his job, but Physics World did once ask previous CERN directors-general what skills are needed as lab boss. Crucial, they said, were people management, delegation, communication and the ability to speak multiple languages. Physical stamina was deemed a vital attribute too, with extensive international travel and late-night working required.

One former CERN director-general even cited the need to “eat two lunches the same day to satisfy important visitors”. Squeezing double dinners in will probably be the least of Thomson’s worries.

Fortuantely, I bumped into Thomson at an Institute of Physics meeting in London earlier this week, where he agreed to do an interview with Physics World. So you can be sure we’ll get Thomson put his aims and priorities as next CERN boss on record. Stay tuned…

• For more about the future of particle colliders, check out our feature interview with Tulika Bose, Philip Burrows and Tara Shears.

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If you love science and are near London, the Royal Society runs a wonderful series of public events that are free of charge. This week, I had the pleasure of attending the Royal Society Milner Prize Lecture, which was given by the quantum cryptography pioneer Artur Ekert. The prize is described as “the premier European award for outstanding achievement in computer science” and his lecture was called “Privacy for the paranoid ones: the ultimate limits of secrecy“. I travelled up from Bristol to see the lecture and I enjoyed it very much.

Ekert has academic appointments at the University of Oxford, the National University of Singapore and the Okinawa Institute of Technology. He bagged this year’s prize, “For his pioneering contributions to quantum communication and computation, which transformed the field of quantum information science from a niche academic activity into a vibrant interdisciplinary field of industrial relevance”.

Ekert is perhaps most famous for his invention in 1991 of entanglement-based quantum cryptography. However, his lecture kicked-off several millennia earlier with an example of a permutation cypher called a scytale. Used by the ancient Greeks, the cypher conceals a message in a series of letters written on a strip of paper. When the paper is wound around a cylinder of the correct radius, the message appears – so not that difficult to decipher if you have a set of cylinders of different radii.

Several hundred years later things had improved somewhat, with the Romans using substitution cyphers whereby letters are substituted for each other according to a secret key that is shared by sender and receiver. The problem with this, explained Ekert, is that if the same key is used to encrypt multiple messages, patterns will emerge in the secret messages. For example, “e” is the most common letter in English, and if it is substituted by “p”, then that letter will be the most common letter in the encrypted messages.

Maths and codebreaking

Ekert said that this statistical codebreaking technique was developed in the 9th century by the Arab polymath Al-Kindi. This appears to be the start of the centuries-long relationship between mathematicians and code makers and breakers that thrives today at places like the UK’s Government Communications Headquarters (GCHQ).

Substitution cyphers can be improved by constantly changing the key, but then the problem becomes how to distribute keys in a secure way – and that’s where quantum physics comes in. While classical key distribution protocols like RSA are very difficult to crack, quantum protocols can be proven to be unbreakable – assuming that they are implemented properly.

Ekert’s entanglement-based protocol is called E91, and he explained how it has its roots in the Einstein–Podolsky–Rosen (EPR) paradox. This is a thought experiment that was devised in 1935 by Albert Einstein and colleagues to show that quantum mechanics was “incomplete” in how it described reality. They argued that classical physics with extra “hidden variables” could explain correlations that arise when measurements are made on two particles that are in what we now call a quantum-entangled state.

Ekert then fast-forwarded nearly three decades to 1964, when the Northern Irish physicist John Bell came up with a mathematical framework to test whether an entangled quantum state can indeed be described using classical physics and hidden variables. Starting in the 1970s, physicists did a series of experiments called Bell tests that have established that correlations observed in quantum systems cannot be explained by classical physics and hidden variables. This work led to John Clauser, Alain Aspect and Anton Zeilinger sharing the 2022 Nobel Prize for Physics.

Test for eavesdropping

In 1991, Ekert realised that a Bell test could be used to reveal whether a secret communication using entangled photons had been intercepted by an eavesdropper. The idea is that the eavesdropper’s act of measurement would destroy entanglement and leave the photon pairs with classical, rather than quantum, correlations.

That year, Ekert along with John Rarity and Paul Tapster demonstrated E91 at the UK’s Defence Research Agency in Malvern. In the intervening decades E91 and other quantum key distribution (QKD) protocols have been implemented in a number of different scenarios – including satellite communications – and some QKD protocols are commercially available.

However, Ekert points out that quantum solutions are not available for all cryptographic applications – they tend to work best for the exchange of messages, rather than the password protection of documents, for example. He also said that developers and users must ensure that QKD protocols are implemented properly using equipment that works as expected. Indeed, Ekert points out that the current interest in identifying and closing “Bell loopholes” is related to QKD. Loopholes are situations where classical phenomena could inadvertently affect a Bell test, making a classical system appear quantum.

So, there is much more work for Ekert and his colleagues to do in quantum cryptography. And if the enthusiasm of his talk is any indication, Ekert is up for the challenge.

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I’ll admit that this year’s Nobel Prize for Physics took us here at Physics World by surprise. Trying to guess who might win a Nobel is always a mug’s game but with condensed-matter physics having missed out since 2016, our money was on research into, say, metamaterials or twisted graphene winning. We certainly weren’t expecting machine learning and artificial intelligence (AI) to come up trumps.

Machine learning these days has a huge influence in physics, where it’s used in everything from the very practical (designing new circuits for quantum optics experiments) to the esoteric (finding new symmetries in data from the Large Hadron Collider). But it would be wrong to think that machine learning itself isn’t physics or that the Nobel committee – in honouring John Hopfield and Geoffrey Hinton – has been misguidedly seduced by some kind of “AI hype”.

Hopfield, 91, is a fully fledged condensed-matter physicist, who in the 1970s began to study the dynamics of biochemical reactions and its applications in neuroscience. In particular, he showed that the physics of spin glasses can be used to build networks of neurons to store and retrieve information. Hopfield applied his work to the problem of “associative memories” – how hearing a fragment of a song, say, can unlock a memory of the occasion we first heard it.

His work on the statistical physics and training of these “Hopfield networks” – and Hinton’s later on “Boltzmann machines” – paved the way for modern-day AI. Indeed, Hinton, a computer scientist, is often dubbed “the godfather of AI”. On the Physics World Weekly podcast, Anil Ananthaswamy – author of Why Machines Learn: the Elegant Maths Behind Modern AI – said Hinton’s contributions to AI were “immense”.

Of course, machine learning and AI are multidisciplinary endeavours, drawing on not just physics and mathematics, but neuroscience, computer science and cognitive science too. Imagine though, if Hinton and Hopfield had been given, say, a medicine Nobel prize. We’d have physicists moaning they’d been overlooked. Some might even say that this year’s Nobel Prize for Chemistry, which went to the application of AI to protein-folding, is really physics at heart.

We’re still in the early days for AI, which has its dangers. Indeed, Hinton quit Google last year so he could more freely express his concerns. But as this year’s Nobel prize makes clear, physics isn’t just drawing on machine learning and AI – it paved the way for these fields too.

• For more on the role of AI in scientific reserach, check out the dedicated Aritifical Intelligence page.

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Since 1988 Physics World has boasted among its authors some of the most eminent physicists of the 20th and 21st centuries, as well as some of the best popular-science authors. But while I am, in principle, aware of this, it can still be genuinely exciting to discover who wrote for Physics World before I joined the team in 2011. And for me – a self-avowed book nerd – the most exciting discovery was an article written by Isaac Asimov in 1990.

Asimov is best remembered for his hard science fiction. His Foundation trilogy (1951–1953) and decades of robot stories first collected in I, Robot (1950) are so seminal they have contributed words and concepts to the popular imagination, far beyond actual readers of his work. If you’ve ever heard of the Laws of Robotics (the first of which is that “a robot shall not harm a human, or by inaction allow a human to come to harm”), that was Asimov’s work.

I was introduced to Asimov through what remains the most “hard physics”-heavy sci-fi I have ever tackled: The Gods Themselves (1972). In this short novel, humans make contact with a parallel universe and manage to transfer energy from a parallel world to Earth. When a human linguist attempts to communicate with the “para-men”, he discovers this transfer may be dangerous. The narrative then switches to the parallel world, which is populated by the most “alien” aliens I can remember encountering in fiction.

Underlying this whole premise, though, is the fact that in the parallel world, the strong nuclear force, which binds protons and neutrons together, is even stronger than it is in our own. And Asimov was a good enough scientist that he worked into his novel everything that would be different – subtly or significantly – were this the case. It’s a physics thought experiment; a highly entertaining one that also encompasses ethics, astrobiology, cryptanalysis and engineering.

Of course, Asimov wrote non-fiction, too. His 500+ books include such titles as Understanding Physics (1966), Atom: Journey Across the Subatomic Cosmos (1991) and the extensive Library of the Universe series (1988–1990). The last two of these even came out while Physics World was being published.

So what did this giant of sci-fi and science communication write about for Physics World?

It was, of all things, a review of a book by someone else: specifically, Think of a Number by Malcolm E Lines, a British mathematician. Lines isn’t nearly so famous as his reviewer, but he was still writing popular-science books about mathematics as recently as 2020. Was Asimov impressed? You’ll have to read his review to find out.

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