Fast dynamics and high effective dimensionality of liquid fluidity

Fluidity, the ability of liquids to flow, is the key property distinguishing liquids from solids. This fluidity is set by the mobile transit atoms moving from one quasi-equilibrium oscillatory point to the next. The nature of this transit motion is unknown. Here, we show that flow-enabling transits form a dynamically distinct sub-ensemble where atoms move on average faster than the overall system and which has a manifestly non-Maxwellian velocity distribution. This is in contrast to solids and gases where no such distinction of different ensembles can be made and where the velocity distribution is always Maxwellian. The non-Maxwellian distribution of transits can be described by an exponent {\alpha} corresponding to high effective dimensionality of space. This dimensionality is close to 4 at melting and exceeds 4 at high temperature. {\alpha} has a maximum as a function of temperature and pressure in liquid and supercritical states, returning to its Maxwell value in the solid and gas states