by Jean Matricon and Georges Waysand, Rutgers University Press. Hardback ISBN 0813532949, $65; paperback ISBN 0813532957, $26.
After carefully investigating the behaviour of matter under new conditions, physicists then try to explain what they find. So it happened with cryogenics. It is much easier to light fires than to invent refrigerators, so the physics of high temperatures was initially much more familiar. However, the laws governing the behaviour of hot gases when extrapolated backwards suggested that something strange should happen if matter could be cooled to -273 °C, “absolute zero” on the new Kelvin temperature scale. Fourteen billion years after the Big Bang, the natural universe is screened from absolute zero by the all-permeating cosmic background radiation at 2.7 K, the faint echo of the Big Bang, and only recently have laboratory experiments descended the last few rungs of the temperature ladder. But such a natural barrier was long unsuspected, and in the second half of the 19th century one gas after another was liquefied triumphantly in the quest to approach absolute zero. However, helium remained stubbornly gaseous until Kamerlingh Onnes established a purpose-built laboratory in Leiden.
After setting this scene, The Cold Wars (what “wars”?) charts the progress of cryogenic physics after the liquefaction of helium at 4.2 K in 1908 opened up a new frontier. Painstakingly probing the behaviour of materials at these temperatures, Onnes discovered the phenomenon of superconductivity – the virtual disappearance of electrical resistance. The origins of this phenomenon, and its interplay with magnetic fields, long remained a mystery. Meanwhile, physicists noticed that liquid helium itself behaved bizarrely below about 2.2 K – becoming a superfluid with almost no viscosity. With the emergence of quantum ideas in the 1920s, attention focused on the possible link between superfluidity and Bose-Einstein condensation – when particles sink into the lowest possible quantum energy state, creating new types of matter. Thirty years later, John Bardeen, Leon Cooper and Robert Schrieffer suggested that pairs of electrons could account for the mystery of superconductivity.
The Cold Wars enthusiastically traces the history of cryogenic physics and superconductivity, with its triumphs and disappointments, and is a good introduction to an intriguing subject. However, it does not venture into the elegant modern quantum theory of phase transitions, which satisfyingly relates to a wider range of phenomena. Superfluid helium is still some way from absolute zero, and only in the past decade have physicists been able to achieve total Bose-Einstein condensation and demonstrate what happens when all particles accumulate into a single energy state, but this too is beyond a strictly superconducting horizon.
A major area for applications of superconductivity is in the powerful magnets that guide charged-particle beams in modern accelerators, but the book only covers this in passing and does not mention the world’s largest superconducting project – the 27 km LHC ring using superfluid helium that is now being constructed at CERN. (The only reference to particle-physics developments is an achievement of high magnetic fields at Fermilab “in 1963” – which was before plans for that US laboratory had even been drawn up.)
The Cold Wars is the English translation, with French government support, of La guerre du froid (Editions Seuil). The book concludes with the emergence of the new cuprate “high-temperature” superconductors. The search for superconductivity at still higher temperatures and the explanation of how this happens remains a glamorous research focus, and a final chapter updates these developments beyond what could have been described in the original 1994 edition.
