Physicists attacking many-worlds (or inflation, or string theory) usually have a more serious objection to the idea of a multiverse: they denounce it as a prime example of “unfalsifiability.” This unwieldy word, a ghost of philosophy past, comes from the work of Karl Popper. Popper was a celebrated mid-twentieth-century philosopher of science who spent most of his career at the London School of Economics. Popper had once held truck with the logical positivism of his native Vienna but ultimately took an iconoclastic stance of his own. Rather than championing a verification theory of meaning, as
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