  Metastable `false' vacuum states are an important feature of the Standard
Model of particle physics and many theories beyond it. Describing the dynamics
of a phase transition out of a false vacuum via the nucleation of bubbles is
essential for understanding the cosmology of vacuum decay and the full spectrum
of observables. In this paper, we study vacuum decay by numerically evolving
ensembles of field theories in 1+1 dimensions from a metastable state. We
demonstrate that for an initial Bose-Einstein distribution of fluctuations,
bubbles form with a Gaussian spread of center-of-mass velocities and that
bubble nucleation events are preceded by an oscillon - a long-lived,
time-dependent, pseudo-stable configuration of the field. Defining an effective
temperature from the long-wavelength amplitude of fluctuations in the ensemble
of simulations, we find good agreement between theoretical finite temperature
predictions and empirical measurements of the decay rate, velocity distribution
and critical bubble solution. We comment on the generalization of our results
and the implications for cosmological observables.
