How does eternal inflation produce many postinflationary regions?

In the context of cosmology, eternal inflation produces numerous postinflationary regions because the transition from an inflationary state to ordinary expansion does not occur simultaneously everywhere.1

In many inflationary models, the transition to noninflationary expansion happens at different times in different locations. This creates a scenario where regions always exist where the transition has not yet taken place and inflation continues indefinitely. Because this process of inflation is eternal, it constantly generates an arbitrarily large or infinite number of postinflationary regions—bubbles of ordinary space-time—within a common, expanding background.1

This model suggests that our own observable universe may be just one of these many postinflationary regions produced by the ongoing process of eternal inflation.1