“Although absolute zero will forever remain beyond our reach, we have probably reached 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 aim of which was to produce the lowest possible laboratory temperatures, a necessity for many scientific studies.
At such low temperatures – close to -273.15C, or what is known as absolute zero, the point where an object has no heat at all – the movement of atoms and subatomic particles almost completely stops. The rules of classical physics are breaking down, allowing scientists to study the enigmatic world of quantum mechanics and determine how elementary particles move and interact.
Understanding these concepts provides insight into materials such as superconductors, which allow electricity to flow over great distances without resistance or loss, or superfluids, which exhibit very low viscosity as their atoms lose their usual random motion. Superfluids can be used to cool magnets with strong magnetic fields and to help detect exotic subatomic particles.
However, the most important application of Pickett’s work lies in our understanding of the big bangthe 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 gas used in party balloons, which can be heated to very high temperatures (it is formed in stars) but also becomes a liquid superfluid when near cooled to absolute zero.
In its superfluid state, helium-3 provides a tool for studying the properties of the early universe. For example, it can simulate cosmic phenomena such as the turbulent expansion of the universe after 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 13.8 billion years ago – and also very low temperatures, similar to those of the residual radiation left over from the Big Bang (- 270,424C), is practical for modeling how our universe evolved. Pickett noticed and exploited these qualities.
In the early 1990s, Pickett’s team conducted experiments, later dubbed “the big bang in a drop of helium,” that aimed to capture the first fraction of a second of our universe’s existence, before it started to cool down quickly. Because classical physics stops at the low temperatures where helium-3 becomes a superfluid, in a laboratory it is possible to heat the liquid to the extremely high temperatures present in the big bang by sending neutrons through it and without it ‘ become a guest.
Initially, the heated liquid helium-3 was homogeneous and uniform, exactly like the universe at the moment of its creation. But then the neutrinos began to create bubbles and vortices, and as it cooled, the helium began to show regions of greater and lesser density. The denser regions were analogs of the overdense regions in the real universe whose gravity would later drag matter in to form galaxies with space and vacuum between them. “We were hoping we would see an outcome like that,” Pickett said later. “But we really had no idea how successful the end result would be.”
Although Pickett did not become a Nobel laureate himself, they cited this earlier work of Pickett and his team when the American team of David Lee, Douglas Osheroff and Robert Richardson won the Nobel Prize in Physics in 1996 for their discovery of superfluidity in helium -3. as crucial to their success. However, Pickett’s team held the record for the lowest temperature ever reached for many years 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 (née Okell), and from Bedford modern school he went to Magdalen College, Oxford, where he gained a DPhil in physics. After a post at the University of Helsinki, he joined Lancaster University in 1970, where he would remain for 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 several Scandinavian and Slavic languages, he received honorary doctorates from universities across Europe, while in the United Kingdom he was elected a Fellow of the Royal Society in 1997, and the following year, with a colleague from the Lancaster university, Tony Guénault, was jointly awarded. the Simon Memorial Prize, awarded every three years for outstanding work in experimental or theoretical low-temperature physics. In 2002, he helped create the European Microkelvin Platform – a consortium of ultra-low-temperature laboratories training young researchers in the discipline.
His wife, Deborah (née Fonge), whom he met in Oxford while working for the university’s forestry department, predeceased him, as did his later partner, Cora Martin. He is survived by his daughters, Elizabeth and Catherine.
