We cannot see farther into the universe because the big bang happened only 14 billion years ago and light from distant regions has not had enough time to reach Earth. Yet subtle clues are beginning to reveal some of the properties of the regions of space hidden beyond our cosmic horizon. Our world appears to be only a small part of a “multiverse,” an expanse vastly larger than the visible universe, and for the most part completely different from it.

To account for what we do see, cosmologists invented a theory many years ago called “inflation,” in which a brief, ultra-accelerated expansion of the early universe stretched space to a size far greater than what we observe. Inflation explains why, despite the violence of the big bang, the universe appears to us uniform and smooth, and the theory has made predictions confirmed by measurements of subtle variations in the radiation left over from the big bang. But inflation does not really make the universe more uniform — just huge. If inflation is correct, then the billions of light-years that our telescopes probe are a mere dot on a far vaster canvas.

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