Planck, units, and modern metrology

Abstract

Every problem that Max Planck approached during his long and distinguished career turned out, one way or another, to be motivated by thermodynamics and considerations of entropy. This was so, in particular, when Planck formulated the correct formula for the spectrum of black-body radiation, whose interpretation made him the earliest pioneer of quantum mechanics. With his formulation of the third law of thermodynamics he gave the entropy a specific and definite value, which – to his own surprise – was closely related to the action quantum h, which we now call Planck's constant.