Of Martians, aerodynamics, and fathering the bomb

TODAY, May 2UU7, page 63) of Tlie Martians of Science: Five Physicists Who Changed the Tiventieth Centiirif by Istvan Hargittai (Oxiord U. Press, 2006) pointedly evaluates Michael Gom's 1992 biography of aeronauticist Theodore von Karman as brief and uncritical. (And I would add, replete with names, many of which add little benefit.) But Gom, like others thus far, seems to have overlooked Jolin von Neumann's contribution to aerodynamics. Early attempts to deal numerically with aerodynamic flows that develop shocks ground to a halt in rezoning the shock too finely for computation to proceed. With Robert Richtmyer, von Neumann demonstrated an algorithm for introducing an "artificial viscosity" that sets a lower bound to shock thickness without violating any physics,' Computational physicists are indebted to these two scientists for much of present-day understanding of such diverse problems as supersonic aerodynamics and supernova explosions.