  Diffusivity, a measure for how rapidly a fluid self-mixes, shows an intimate,
but seemingly fragmented, connection to thermodynamics. On one hand, the
"configurational" contribution to entropy (related to the number of
mechanically-stable configurations that fluid molecules can adopt) has long
been considered key for predicting supercooled liquid dynamics near the glass
transition. On the other hand, the excess entropy (relative to ideal gas)
provides a robust scaling for the diffusivity of fluids above the freezing
point. Here we provide, to our knowledge, the first evidence that excess
entropy also captures how supercooling a fluid modifies its diffusivity,
suggesting that dynamics, from ideal gas to glass, is related to a single,
standard thermodynamic quantity.
