Quantum physics is strange, Nobel laureate Prof Alain Aspect readily conceded at the start of his lecture. Yet, as he reminded an audience at Stellenbosch University’s (SU) Endler Hall on Tuesday evening (27 October), strange does not mean irrational.
What followed was an intellectual expedition into one of science’s most bewildering frontiers, delivered with the confidence of a physicist who helped rewrite our understanding of reality.
Armed with intricate mathematical equations, experimental diagrams and a disarming sense of humour, the celebrated French physicist took his audience through more than a century of discoveries that have transformed the modern world and could do so again.
Aspect, who shared the 2022 Nobel Prize in Physics with John Clauser and Anton Zeilinger, delivered SU’s prestigious Chancellor’s Public Lecture on “The two quantum revolutions: From concepts to applications”. Aspect is celebrated for his foundational, pioneering experiments in quantum mechanics – most notably his closing of loopholes in tests of Bell’s inequalities, which definitively proved the reality of quantum entanglement.
The event formed part of the Nobel in Africa Symposium on Quantum Computing, hosted by the Stellenbosch Institute for Advanced Study (STIAS) in partnership with SU.
Welcoming the Nobel laureate, SU Rector and Vice-Chancellor Prof Deresh Ramjugernath reflected on the significance of bringing leading international scientists to African institutions. “Africa should not simply observe the next scientific and technological revolution from a distance. Our researchers and our students must be part of shaping it,” he said.
When strange science transformed society
Aspect’s central message was deceptively straightforward: Some of humanity’s most consequential technological advances emerged from scientific discoveries that initially seemed almost impossible to comprehend. “Quantum physics is strange, but it is not irrational,” he explained, describing a mathematical framework that accounts for phenomena classical physics cannot explain.
The first quantum revolution emerged from the discovery that light and matter can behave both as particles and waves. This apparent contradiction challenged conventional physics but ultimately helped scientists understand the structure and stability of matter.
Its practical consequences were enormous. Quantum mechanics provided the foundations for transistors, lasers and integrated circuits, making modern computers and fibre-optic communication possible. “The society of information and communication would not exist if this discovery had not been done,” Aspect noted.
His presentation, dominated by equations and complex experimental illustrations, made few concessions to the scientifically uninitiated. Yet his animated explanations and flashes of humour helped sustain engagement with ideas that undoubtedly stretched the understanding of many in the audience.
Einstein, entanglement and a Nobel Prize
The second quantum revolution, Aspect explained, rests on an even more extraordinary phenomenon: quantum entanglement. When two particles become entangled, their measurement results can display correlations that defy conventional expectations, even when the particles are separated by considerable distances.
To illustrate this, Aspect described two people tossing coins. Each person’s results appear entirely random, yet whenever one gets heads, the other also gets heads. Such correlations, under carefully chosen experimental conditions, reveal something fundamentally different from ordinary shared properties. The phenomenon fuelled a famous disagreement between Albert Einstein and Niels Bohr about the nature of physical reality.
In 1964, physicist John Bell developed a mathematical test that transformed their philosophical dispute into a question science could investigate experimentally. Aspect’s pioneering experiments in the early 1980s provided compelling evidence supporting quantum mechanics and challenging Einstein’s concept of local realism. The implications were profound. Entangled particles must be understood as parts of a quantum system whose properties cannot always be reduced to those of its individual components.
Aspect recalled the relief he experienced when Zeilinger independently confirmed his findings years later. For more than a decade, he had occasionally wondered whether his experiments contained an undetected mistake. When Zeilinger telephoned to confirm the results, Aspect joked, “I slept better.”
From scientific curiosity to technological possibility
Today, entanglement is helping scientists develop technologies ranging from secure quantum communication to extraordinarily sensitive measuring instruments. Quantum computers could eventually solve certain problems beyond the practical reach of conventional computers, while potentially using less energy for particular calculations.
Aspect nevertheless cautioned against premature expectations. Quantum simulators already work, while powerful digital quantum computers still face considerable theoretical and engineering challenges. “Nobody can answer with certainty, but many believe in it,” he said of the prospects for another technological revolution.
In a conversation following the lecture, Prof Francesco Petruccione, SU’s Pro Vice-Chancellor: Quantum Technology and Artificial Intelligence, asked what advice Aspect would offer South Africa. His recommendation was to concentrate investment on quantum technologies in which the country already possesses expertise, rather than attempting to pursue every competing approach.
For aspiring scientists, his message was equally practical: Pursue worthwhile questions, even when others are sceptical, while learning to explain convincingly why those questions matter.
The evening concluded on a lighter note when Prof Resia Pretorius, Vice-Dean (Research) in SU’s Faculty of Science, reflected on the man behind the scientific achievements. She recalled Aspect’s years teaching in Cameroon, his interest in card magic, which he playfully associates with quantum tunnelling, and even his experiments with cooking the perfect egg at precisely 63°C!
More poignantly, she recalled how John Bell had questioned Aspect about his job security when the young researcher proposed his ambitious experiments in 1975. Seven years of perseverance eventually produced the work that would earn him a Nobel Prize four decades later.
Pretorius reminded the audience that universities have a responsibility to create environments where young researchers can pursue difficult, unconventional questions. “We cannot promise our students a Nobel Prize, but we can give them the security to take bold risks, the time to wrestle with something difficult, and most of all, the respect of taking their curiosity seriously.”
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