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charon writes:

There might be no getting around what Albert Einstein called "spooky action at a distance." With an experiment described [February 7th] in Physical Review Letters — a feat that involved harnessing starlight to control measurements of particles shot between buildings in Vienna — some of the world's leading cosmologists and quantum physicists are closing the door on an intriguing alternative to "quantum entanglement."

[...] In the first of a planned series of "cosmic Bell test" experiments, the team sent pairs of photons from the roof of [Anton] Zeilinger's lab in Vienna through the open windows of two other buildings and into optical modulators, tallying coincident detections as usual. But this time, they attempted to lower the chance that the modulator settings might somehow become correlated with the states of the photons in the moments before each measurement. They pointed a telescope out of each window, trained each telescope on a bright and conveniently located (but otherwise random) star, and, before each measurement, used the color of an incoming photon from each star to set the angle of the associated modulator. The colors of these photons were decided hundreds of years ago, when they left their stars, increasing the chance that they (and therefore the measurement settings) were independent of the states of the photons being measured.

And yet, the scientists found that the measurement outcomes still violated Bell's upper limit, boosting their confidence that the polarized photons in the experiment exhibit spooky action at a distance after all.

Source: https://www.quantamagazine.org/20170207-bell-test-quantum-loophole/

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