“Although absolute zero will for ever remain beyond our reach, we have achieved probably the next best thing.” These were the words of George Pickett, who has died aged 85, discussing his work on nuclear refrigeration at Lancaster University, the purpose of which was to produce the lowest possible laboratory temperatures, a necessity for numerous scientific studies.
At such low temperatures – close to -273.15C, or what is known as absolute zero, the point at which an object has no heat at all – the motion of atoms and subatomic particles ceases almost completely. The rules of classical physics break down, allowing scientists to study the enigmatic world of quantum mechanics, determining how elementary particles move and interact.
Understanding these concepts offers insight into materials such as superconductors, which allow electricity to flow without resistance or loss over great distances, or superfluids, which display very low viscosity as their atoms lose their usual random motion. Superfluids can be used for cooling magnets with strong magnetic fields and for helping detect exotic subatomic particles.
However, the most significant application of Pickett’s work lay in increasing our understanding of the big bang, the early origins of the universe and the creation of its structures, such as the chains of galaxies that now populate space. He and his team worked with helium-3, a stable isotope of the more common helium-4, which is used for party balloons. Formed in stars, helium-3 can be heated to very high temperatures, but also becomes a liquid superfluid if cooled close to absolute zero.
In its superfluid state, helium-3 provides a tool for studying the properties of the early universe. For instance, it can mimic cosmic phenomena such as the turbulent expansion of the universe following the big bang, and the subsequent formation of stable structures such as galaxies. Because it can exist at extremely high temperatures – such as those present at the formation of our universe 13.8bn years ago – and also very low temperatures, similar to that of the residual radiation left over from the big bang (-270.424C), it is practical for modelling how our universe evolved. Pickett noted these qualities and exploited them.
In the early 1990s, Pickett’s team conducted experiments, later dubbed “the big bang in a drop of helium”, which aimed to capture the first fraction of a second of our universe’s existence, before it began to cool rapidly. Because classical physics ceases at the low temperatures where helium-3 becomes a superfluid, it is possible, in a laboratory, to heat the liquid to the extremely high temperatures present in the big bang by passing neutrons through it and without it becoming a gas.
At first the heated liquid helium-3 was homogenous and uniform, exactly like the universe at the moment of its creation. But then the neutrons began to create bubbles and vortices, and, as it cooled, the helium began to display areas of greater and lesser density. The more dense areas were analogues of the over-dense regions in the real universe whose gravity would later drag in matter to form galaxies with space and vacuum between them. “We were hopeful we would see such an outcome,” Pickett later said. “But really we had no idea how successful the end result would be.”
Although Pickett did not become a Nobel laureate himself, when the American team of David Lee, Douglas Osheroff and Robert Richardson won the 1996 Nobel prize for physics for their discovery of superfluidity in helium-3, they cited this earlier work of Pickett and his team as being crucial to their success. Pickett’s team did, however, achieve and hold for many years the record for the lowest temperature ever attained when, in 1993, they cooled copper immersed in liquid helium-3 to 7 microkelvin, or seven millionths of a degree above absolute zero.
Pickett was born in Biddenham, Bedfordshire, to George, an engineer, and Lelia (nee Okell), and from Bedford modern school went to Magdalen College, Oxford, where he gained a DPhil in physics. After a post at Helsinki University, in 1970 he joined Lancaster University, where he would remain throughout the rest of his career. In 1988 he was awarded a chair in low-temperature physics and went on to develop the ultra-low temperature laboratory that would define his academic career.
Fluent in various Scandinavian and Slavic languages, he received honorary doctorates from universities across Europe, while in the UK he was elected a fellow of the Royal Society in 1997, and the following year, alongside a Lancaster University colleague, Tony Guénault, was jointly awarded the Simon Memorial prize, conferred every three years for distinguished work in experimental or theoretical low-temperature physics. In 2002 he helped create the European Microkelvin Platform – a consortium of ultra-low-temperature laboratories that trains young researchers in the discipline.
His wife, Deborah (nee Fonge), whom he met in Oxford while she was working for the university forestry department, predeceased him, as did his subsequent partner, Cora Martin. He is survived by his daughters, Elizabeth and Catherine.
• George Richard Pickett, physicist, born 10 April 1939; died 21 July 2024
