Everything we know suggests that the universe is unusual. It is flatter, smoother, larger and emptier than a “typical” universe predicted by the known laws of physics. If we reached into a hat filled with pieces of paper, each with the specifications of a possible universe written on it, it is exceedingly unlikely that we would get a universe anything like ours in one pick – or even a billion.

The challenge that cosmologists face is to make sense of this specialness. One approach to this question is inflation – the hypothesis that the early universe went through a phase of exponentially fast expansion. At first, inflation ..

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