Caption: A cartoon of the multiverse with pocket universes---called universe domains in the figure.

The boundaries between the pocket universes are probably NOT sharp.

Cosmologists generally do a poor job of describing the multiverse with pocket universes.

Muffing or bluffing?

One view is that that the pocket universes are geometrically connected but we can't reach them since our and the space between them is expanding too quickly (Alexander Vilenkin & Max Tegmark, 2011, Scientific American, The Case for Parallel Universes).

On the other hand, it may be that some pocket universes are hyperspherical: curved 3-dimensional spaces that are finite, but have no boundaries (see below section Einstein, General Relativity, and the Einstein Universe. They may be black holes from the outside.???? Credit/Permission: © David Jeffery, 2004 / Own work.
Image link: Itself.
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