  Despite its relevance in biology and engineering, the molecular mechanism
driving cavitation in water remains unknown. Using computer simulations, we
investigate the structure and dynamics of vapor bubbles emerging from
metastable water at negative pressures. We find that in the early stages of
cavitation, bubbles are irregularly shaped and become more spherical as they
grow. Nevertheless, the free energy of bubble formation can be perfectly
reproduced in the framework of classical nucleation theory (CNT) if the
curvature dependence of the surface tension is taken into account. Comparison
of the observed bubble dynamics to the predictions of the macroscopic
Rayleigh--Plesset (RP) equation, augmented with thermal fluctuations,
demonstrates that the growth of nanoscale bubbles is governed by viscous
forces. Combining the dynamical prefactor determined from the RP equation with
the free energy of CNT yields an analytical expression for the cavitation rate
that reproduces the simulation results very well over a wide range of
pressures. Furthermore, our theoretical predictions are in excellent agreement
with cavitation rates obtained from inclusion experiments. This suggests that
homogeneous nucleation is observed in inclusions, whereas only heterogeneous
nucleation on impurities or defects occurs in other experiments.
