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Web Extra: Another cosmic thought-experiment

Decades ago, another physicist thought of using the distant universe to test quantum theory.
RELATED TOPICS: QUASARS
An elliptical galaxy is warping the light from a background quasar, resulting in two images of the same body.
The October 2014 Astronomy article, “Can the cosmos test quantum entanglement?” introduced an experiment my colleagues and I have proposed: using distant active galaxies called quasars to choose detectors’ settings in a real-world test of the limits of Bell’s theorem, itself one of the most important quantum mechanical results of the past century. We need pairs of quasars on opposite sides of the sky that emitted their light at least 12.1 billion years ago to ensure that there would not have been enough time for either of them to be influenced by each other or anything else since the universe’s beginning.

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