Call it a fluke, a mystery, a miracle. Or call it the biggest
problem in physics. Short of invoking a benevolent creator, many
physicists see only one possible explanation: Our universe may be but
one of perhaps infinitely many universes in an inconceivably vast multiverse. Most of those universes are barren, but some, like ours, have conditions suitable for life.
The idea is controversial. Critics say it doesn’t even qualify as a
scientific theory because the existence of other universes cannot be
proved or disproved. Advocates argue that, like it or not, the
multiverse may well be the only viable nonreligious explanation for
what is often called the “fine-tuning problem”—the baffling observation
that the laws of the universe seem custom-tailored to favor the
emergence of life.