  In the context of false vacuum decay at zero temperature, it is well known
that bubbles expand with uniform proper acceleration. We show that this
uniformly accelerating expansion suffers from an instability related to the
bubble size. This can be observed in Minkowski spacetime as a tachyonic mode in
the spectrum of fluctuations for the energy functional in the reference frame
in which the uniformly accelerating bubble wall appears static. In such a
frame, arbitrary small perturbations cause an amplifying departure from the
static wall solution. This implies that the nucleated bubble is not a critical
point of the energy functional in the rest frame of nucleation but becomes one
in the accelerating frame. The aforementioned instability for vacuum bubbles
can be related to the well-known instability for the nucleated critical static
bubbles during finite-temperature phase transitions in the rest frame of the
plasma. It is therefore proposed that zero-temperature vacuum decays as seen
from accelerating frames have a dual description in terms of finite-temperature
phase transitions.
