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Quantum histories get all tangled up

Tracing a particle’s past requires multiple chronologies, physicists say

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1:00pm, January 25, 2016
forking road graphic

TEMPORAL FORK  When there’s a fork in the road, nature may take Yogi Berra’s advice and take it. A new experiment suggests that reality can split into multiple intertwined timelines, a phenomenon termed “entangled histories.”

Choose Your Own Adventure books are fun, but they let readers choose only one version of events at a time. Quantum mechanics, a new experiment suggests, requires that multiple adventures occur simultaneously to create a consistent account of history.

Nobel laureate Frank Wilczek at MIT and colleague Jordan Cotler, now at Stanford University, provide evidence for what they call entangled histories in a paper posted online January 12 at arXiv.org. The researchers proposed and collaborated on an experiment that started and ended by measuring a particular property of a photon; in between, the experimenters subtly probed the photon without disturbing its delicate quantum state. The head-scratching result was that there was no way to create a single chronology that could describe how the photon changed. Instead, there must be multiple chronologies that are entangled, sharing a quantum connection usually reserved for groups of

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