Of Martians, aerodynamics, and fathering the bomb

Barton Bernstein’s review ( Physics Today, May 2007, page 63 ) of The Martians of Science: Five Physicists Who Changed the Twentieth Century by István Hargittai (Oxford U. Press, 2006) pointedly evaluates Michael Gorn’s 1992 biography of aeronauticist Theodore von Kármán as brief and uncritical. (And I would add, replete with names, many of which add little benefit.) But Gorn, like others thus far, seems to have over-looked John 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. ¹ Computational physicists are indebted to these two scientists for much of present-day understanding of such diverse problems as supersonic aerodynamics and supernova explosions.