Rare Events In Phase Change Dynamics
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Boiling and cavitation are initiated by rare microscopic fluctuations. Even under strongly stretched or superheated conditions, liquids may remain metastable for long times, until an unlikely fluctuation produces a vapour nucleus large enough to trigger the phase transition. Nucleation is therefore an intrinsically stochastic process controlled by free-energy barriers. At the microscopic level, the new phase emerges through the probabilistic formation of transient clusters. Most of them rapidly dissolve, but with vanishing probability, a critical nucleus forms, allowing the system to escape the metastable basin. This statistical-mechanical nature of nucleation implies that phase-change inception cannot be understood without explicitly addressing rare-event dynamics. A major challenge stems from the enormous separation of time scales involved, since nucleation times scale exponentially with the barrier height. This work discusses how rare-event techniques grounded in Large Deviation Theory, combined with multiphase fluctuating hydrodynamics, provide access to the most likely nucleation pathways and their probabilities, enabling predictive estimates of phase change in agreement with experiments.
