Activities in 1995-1996

From the Report for Academic Year 1995-1996
of the Institute for Advanced Study

PIET HUT has focused his research on various aspects of the dynamics of dense stellar systems. In an ongoing study of the `microphysics' of star clusters, he has determined cross sections for encounters between single stars and double stars, together with Douglas Heggie from Edinburgh and Steve McMillan from Drexel. This collaboration produced the first general expression for exchange cross sections for arbitrary mass ratios, a useful ingredient in reconstructions of the formation histories of X-ray binaries, millisecond pulsars and other dynamically formed stellar objects.

A detailed study of the `macrophysics' of star clusters has recently become possible, through realistic simulations of these clusters on a star-by-star basis, using the GRAPE-4, a special-purpose computer developed at Tokyo University. When it became operational, in the Fall of 1995, it was at a speed of 1 Teraflops the fastest computer in the world. Together with Jun Makino, from Tokyo University, and Steve McMillan, Hut has continued to develop new algorithms on the GRAPE-4, in order to treat arbitrarily complex simultaneous encounters between multiple star systems in the core of a dense star cluster. Some of the first results, obtained this way, are reported in the proceedings of IAU Symposium 174, edited by Hut and Makino.

Professor Hut organized a workshop at the National Center for Supercomputing Applications in Champaign/Urbana, in Dec. 1995, to discuss the scientific applications for the next-generation special-purpose computer, the GRAPE-6, planned to operate at a speed of 1 Petaflops, a thousand-fold increase over the current GRAPE-4. At the Petaflops Architecture Workshop, at Caltech in April 1996, the GRAPE team, including Hut, received a Petaflops Point Design Studies award, as one of the eight teams that had been chosen to receive funding from a combined initiative involving four government agencies (NSF, NASA, DARPA, and NSA), to stimulate advanced computing research.

At the Santa Fe Institute, Hut organized a workshop on Fundamental Sources of Unpredictability, together with James Hartle from UCSB, and Joseph Traub, from Columbia. This workshop formed one aspect of an ongoing program, sponsored by the Alfred P. Sloan Foundation, to explore the notion of `limits to scientific knowledge'. As part of this program, Professor Hut continued his collaboration with cognitive psychologist Roger Shepard from Stanford. Together, they organized several workshops at Stanford, bringing together researchers from such diverse areas as computer science, cognitive science, and European and Japanese philosophy.

In the area of philosophy of science, Hut has started several collaborative projects, with Bas van Fraassen, from Princeton University, Ronald Bruzina, from the University of Kentucky at Lexolve collaborations with the International Institute forrian Smith from the University of Indiana at Bloomington, Yoko Arisaka, from the University of San Francisco, as well as several philosophers in Tokyo, Kyoto, Sendai, and Fukuoka. Some of these activities involve collaborations with the International Institute for Advanced Study in Kyoto, through Takeyuki Hida and Ryosuke Ohashi. These various projects all center around the role that science plays in shaping our world views.

Last year, Professor Hut was elected as Corresponding Member of the Royal Netherlands Academy of Arts and Sciences.