Hugo Martin Tetrode (7 March 1895, in Amsterdam – 18 January 1931, in Amstelveen) was a Dutch theoretical physicist who contributed to statistical physics, early quantum theory and quantum mechanics.
In 1912, Tetrode developed the Sackur–Tetrode equation, a quantum mechanical expression of the entropy of an ideal gas. Otto Sackur derived this equation independently around the same time.[1] The Sackur–Tetrode constant, S0/R, is a fundamental physical constant representing the translational contribution to the entropy of an ideal gas at a temperature of 1 K and pressure of 100 kPa, where R is the gas constant.
From Amsterdam, Tetrode corresponded with Albert Einstein, Hendrik Lorentz and Paul Ehrenfest on quantum mechanics and wrote several influential papers on quantum mechanics which were published in the German physics journal Zeitschrift für Physik. In particular, the Machian notion that elementary particles only act on other elementary particles and not themselves was a key idea in the formulation of the Wheeler–Feynman time-symmetric theory.