Am. J. Phys. 86, 31–35 (2018).

There is something irresistible about Albert Einstein — no matter how often his results are confirmed or revisited in fresh contexts, having a theoretical or experimental finding anchored to Einstein's works lets us rest, it seems, a tad easier. But such connections can be rather inspiring, too, as Fred Gittes has proven.

Gittes derived two distinctly different results from Einstein's opus using the Jarzynski equality, a general relation between the change in free energy of a system and the amount of irreversible work performed on it. That equality, introduced in 1997, has become central in several branches of non-equilibrium thermodynamics, but has not found its way into general physics curricula and textbooks quite yet.

Gittes's contribution might help to change that. It shows that the Jarzynski equality implies both Einstein's classical relation between diffusion and drag coefficients in Brownian motion and his results on absorption and emission in quantum two-state systems. Adding to the scope, the latter connection is obtained without explicit reference to the bosonic nature of photons, whereas the former leads to apparently paradoxical, but explained, behaviour in the macroscopic limit.