  Quantum decay of a relativistic scalar field from a false vacuum is a
fundamental idea in quantum field theory. It is relevant to models of the early
Universe, where the nucleation of bubbles gives rise to an inflationary
universe and the creation of matter. Here we propose a laboratory test using an
experimental model of an ultra-cold spinor Bose gas. A false vacuum for the
relative phase of two spin components, serving as the unstable scalar field, is
generated by means of a modulated radio-frequency coupling of the spin
components. Numerical simulations demonstrate the spontaneous formation of true
vacuum bubbles with realistic parameters and time-scales.
