Laszlo Tisza, whose career spanned major developments in 20th-century physics, died on 15 April 2009 in Newton, Massachusetts, at the age of 101. He witnessed the birth of quantum mechanics at close hand, knew many of the leading figures, and made significant contributions of his own.
Laci, as he was known to his many friends, was born on 7 July 1907 in Budapest, Hungary. He wryly described his high school in Buda as challenging, but not as challenging as the schools across the river in Pest where Eugene Wigner, John von Neumann, and Edward Teller studied. In 1926 Laci enrolled in mathematics at the University of Budapest. Two years later his studies led him to physics at the University of Göttingen, where David Hilbert was reluctantly becoming engaged with quantum mechanics, Emmy Noether was at the center of modern algebra, and Richard Courant was teaching fluid dynamics.
Laci heard about quantum mechanics from a Danish friend and enrolled in the first-ever course on the subject, presented by Max Born. Laci then moved to Leipzig to work with Teller under Werner Heisenberg. He received his doctoral degree from the University of Budapest in 1932, but then his career was abruptly interrupted. Two months after Laci defended his thesis, the fascist Hungarian government arrested him on the basis of his friendship with communist students and imprisoned him for 14 months.
Upon Laci’s release, Teller recommended him to Lev Landau to work in his theoretical group at the Ukrainian Physical-Technical Institute in Kharkov; Laci joined the institute in January 1935. He passed Landau’s “theor-minimum” program, making him number 5 of the approximately 35 physicists who passed that legendary examination. In 1937 the political climate at Kharkov deteriorated abruptly. Landau fled to Moscow, where he was arrested the following year. Laci managed to return to Budapest. Once again Teller stepped in and recommended him to Fritz London in Paris. At the Institut Henri Poincaré, London was working on superconductivity and the properties of liquid helium. He arranged a research appointment for Laci in the group of Paul Langevin at the nearby Collège de France. It was there that Laci did his most important work.
In December 1937 superfluidity in liquid helium was discovered by Peter Kapitza in Moscow and John Allen and Don Misener in Cambridge, UK. In one of their long walks together, London described to Laci his idea that superfluidity was a manifestation of Bose–Einstein condensation (BEC). Laci realized that that should lead to two velocity fields in liquid helium. One field would be viscous and carry entropy, and the other would have zero viscosity and zero entropy. His proposal explained how liquid helium could flow through a slit without resistance while also causing damping in a torsional disk oscillator. In 1938 he published a short note in Nature establishing for the first time the two-fluid model. His note also pointed out how the model could explain the recently discovered fountain effect. Laci also predicted that in the superfluid phase of the liquid, heat should propagate as “temperature waves,” later called “second sound” by Landau. Temperature waves were observed experimentally in 1946.
Despite the successes that Laci’s two-fluid model has come to enjoy, London was initially negative about it. Landau rejected London’s BEC proposal and ignored Laci’s model. In 1939 Laci published a detailed paper on his theory in Comptes Rendus, but World War II intervened, and he did not get to see the published version until peace had returned. In June 1940 part of Langevin’s laboratory was evacuated to Toulouse, which was not yet occupied by the Nazis. Once again Laci managed to escape, leaving Marseille in early February 1941 for Madrid and Lisbon and then traveling by boat to New York to join relatives and friends in Cambridge, Massachusetts. A few months later, he obtained the position of instructor at MIT, where he eventually became a professor.
Laci had a warm and generous personality. Despite Landau’s indifference to his work, for instance, he always spoke of Landau with reverence and portrayed his time at Kharkov as a golden period in his life. Laci was an outstanding teacher with a broad and deep understanding of physics that reflected his studies with Born, Landau, Teller, and other luminaries. At MIT he was a friend and mentor to Jack Steinberger, and his graduate students included Herbert Callen, Martin Klein, and Quin Luttinger. Laci’s intellectual interests centered on the foundations of thermodynamics and quantum mechanics and on the philosophy of science. His major work was his theory of generalized thermodynamics. He liked best to discuss foundational questions, but he also had a great appreciation for hiking, good wine, and good food. Laci retained his zest for life and his passion for fundamental problems, and he continued to work on the foundations of quantum mechanics until shortly before his death.
With Laci’s passing, a link to a golden age of physics, but also to an age of unprecedented oppression, is broken. Laci was always cheerful. Perhaps his harrowing political escapes allowed him to appreciate more fully than most the joys of living and working in a free society.
