The multiverse

If we define "universe" as "all there is" or "all that exists," then obviously, by definition, there can be only one universe.

But if we define "universe" as "all we can ever see" (no matter how large our telescopes) or "space-time regions that expand together," then many universes may indeed exist. There is nothing in science more awesome, more majestic. To discern the nature of ultimate reality, one must begin with the challenge of multiple universes.

So what is a "multiverse"?

As physicist and Nobel laureate Steven Weinberg told me on "Closer to Truth" (the source of all following interviews), "The word 'universe,' I suppose, should properly mean the whole thing - everything. But when we think of 'universe,' we sometimes use the word to mean just our Big Bang, the things we can see out to almost 14 billion light-years in all directions. And in this manner, it's reasonable to question: Is our universe unique? Are there multiple Big Bangs? Could there be multiple Big Bangs in different senses?"

"We started calling it a 'multiverse,'" meaning the entire ensemble of innumerable regions of disconnected space-time, said Andrei Linde, the Russian-American physicist now at Stanford. He developed the theory of "eternal chaotic inflation," which generates ever-increasing numbers of universes without end. Scientists created the neologism "multiverse," Linde continued, "because we found that what we had called 'the universe' can be divided into extremely large regions, which may have different laws of physics. And one part may be suitable for life, and other parts unsuitable."

Go to space.com article

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Video credits: science time and TED ED