  Electric fields can spontaneously decay via the Schwinger effect, the
nucleation of a charged particle-anti particle pair separated by a critical
distance $d$. What happens if the available distance is smaller than $d$?
Previous work on this question has produced contradictory results. Here, we
study the quantum evolution of electric fields when the field points in a
compact direction with circumference $L < d$ using the massive Schwinger model,
quantum electrodynamics in one space dimension with massive charged fermions.
We uncover a new and previously unknown set of instantons that result in novel
physics that disagrees with all previous estimates. In parameter regimes where
the field value can be well-defined in the quantum theory, generic initial
fields $E$ are in fact stable and do not decay, while initial values that are
quantized in half-integer units of the charge $E = (k/2) g$ with $k\in \mathbb
Z$ oscillate in time from $+(k/2) g$ to $-(k/2) g$, with exponentially small
probability of ever taking any other value. We verify our results with four
distinct techniques: numerically by measuring the decay directly in Lorentzian
time on the lattice, numerically using the spectrum of the Hamiltonian,
numerically and semi-analytically using the bosonized description of the
Schwinger model, and analytically via our instanton estimate.
