As brilliant as it was, Everett’s thesis left one important question unanswered: if a large object can really be in two places at once, why don’t we ever observe that? Sure, if you measure its position, the two copies of you in the two resulting parallel universes will each find it in a definite place. But that answer turns out not to be good enough, because careful experiments show that large objects never act like they’re in two places at once, even if you don’t look at them. In particular, they never display wavelike properties that make so-called quantum interference patterns. It wasn’t
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