The bubble universe model is a variant of the inflationary model of the big bang. This model, proposed by physicist Andrei Linde, postulates that our universe is one of many that grew from a multiverse consisting of vacuum that had not yet decayed to its ground state.

In standard inflation, inflationary expansion occurred while the universe was in a false vacuum state, halting when the universe decayed to a true vacuum state. The bubble universe model proposes that different parts of this inflationary universe (termed a multiverse) decayed at different times, with decaying regions corresponding to universes not in causal contact with each other.

Variants of the bubble universe model postulate multiple false vacuum states, which result in lower-energy false vacuum child universes spawned which in turn produce true vacuum state child universes within themselves. Alternatively, it is possible that our present universe is itself in a state of false vacuum, with dark energy representing the nonzero vacuum energy density. If this is correct, then parts of our universe might be expected to decay to a state of true vacuum at some point in the distant future.