Ernst Mach (1838–1916)

Today is the birthday of Ernst Mach who was born in Brno, Austrian Empire (now Brno, Czech Republic), in 1838. Mach is most well-known for his work studying shock waves. He used Schlieren photography to capture images of the shock waves created when a bullet moved faster than the speed of sound. It was for this work that the ratio of the speed of an object to the speed of sound in a medium was named the Mach number in his honor. He was also an active philosopher, though this often led him to take positions that were contrary to the evidence of the time, including the existence of atoms. Some of his criticisms of Newton’s understanding of space and time influenced Einstein’s work on relativity, but Einstein later rejected Mach’s criticism as physically unsound. Outside of physics, Mach also made contributions to physiology—connecting the sense of balance to fluid in the inner ear—and psychology—an optical illusion that bears his name.

Date in History: 18 February 1838