No. Like Shaula, I wouldn't call that mainstream, even though a number of high profile physicists have toyed with the idea. It was Guth who came up with inflation, but I believe it was Vilenkin, with his "eternal inflation," who introduced the idea of pocket universes, which is a specific solution to the highly speculative, highly conjectural, and highly controversial idea of the multiverse.
Originally Posted by noncryptic
In that scenario, the boundary of any pocket universe is defined by the decay of the inflaton field, which is moving outward at the speed of light. Nobody needs to be concerned about encountering that boundary.
Everyone is entitled to his own opinion, but not his own facts.