Since childhood, I've obsessed about existence. What is existence? What's the extent of existence? What's the purpose of existence? Now, six decades on, having explored many things, I'm no surer (and feeling no smarter), but I continue my pursuit. 

What's the largest, surest fact about existence that I can know with confidence? For me, it's the vastness of the cosmos. The universe is huge, but it is only with recent discoveries that we can realize how inconceivably immense the universe, or multiple universes, may actually be.

It's now one of humanity's ultimate questions — and until relatively recently, we didn't know enough to even ask it. How many universes exist?

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