  The Jarzynski equality (JE) is a remarkable statement relating transient
irreversible processes to infinite-time free energy differences. Although
twenty years old, the JE remains unfamiliar to many; nevertheless it is a
robust and powerful law. We examine two of Einstein's most simple and
well-known discoveries, one classical and one quantum, and show how each of
these follows from the JE. Our first example is Einstein's relation between the
drag and diffusion coefficients of a particle in Brownian motion. In this
context we encounter a paradox in the macroscopic limit of the JE which is
fascinating, but also warns us against using the JE too freely outside of the
microscopic domain. Our second example is the equality of Einstein's $B$
coefficients for absorption and stimulated emission of quanta. Here resonant
light does irreversible work on a sample, and the argument differs from
Einstein's equilibrium reasoning using the Planck black-body spectrum. We round
out our examples with a brief derivation and discussion of Jarzynski's
remarkable equality.
