Escape from the universe - [wild, but fun, speculations from physicist Michio Kaku]

I'm no physicist, but doesn't the term "universe" include everything? That being the case, where is there room for a parallel universe? Wouldn't it be included in the first? Just wondering....

Sorry for the tardy response.

You're right that the term 'universe' can be used to denote the sum total of all physical entities and processes, although it's not clear that the term when so-used is well-defined (it's not quite the same as 'the set of all sets', but still...).

But more often the term 'universe' is used to denote only our own expanding cosmic bubble, which includes all astronomically observable objects and processes as well as a much, much vaster region that inflated (and continues to inflate) just before the thermalization event we call the Big Bang (this has not been definitively established, of course). If the term 'universe' is used in this way, then other cosmic bubbles (should there be any) could reasonably be called 'parallel universes'.

As Kaku writes, the theory of inflation

postulates a turbo-charged expansion of the universe at the beginning of time. The inflationary universe idea neatly explains several stubborn cosmological mysteries, including the flatness and uniformity of the universe.
But since physicists still do not know what drove this rapid inflationary process, there remains the chance that it could happen again, in an endless cycle. This is the chaotic inflationary idea of Andrei Linde of Stanford University, in which "parent universes" bud "baby universes" in a continuous, neverending cycle. Like soap bubbles which split into two smaller bubbles, universes can constantly sprout from other universes.

Having recently re-read the article I linked to in post #89 on this thread, I can recommend it as a mind-stretching (if speculative) attempt to come to grips with some of the consequences of inflationary cosmology for our understanding of ourselves and our place in the 'multiverse'.

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