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MIT wants quasars to help put free will to rest

Ringing the Bell on inequality

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The last of three loopholes held to remain in Bell's Theorem, “setting independence”, is under the spotlight with an MIT research group saying that quasars could be used as random number generators and help prove* the validity of quantum mechanics.

(*The Register is well aware that quantum mechanics has withstood the most rigorous tests science has been able to throw at it: there remains, however, a theoretical question that's been elusive.)

Bell's work presents one of the longest-standing tests for the validity of quantum mechanics. In a classical universe, he explained, there is a limit to the correlation between entangled particles; hence, if scientists can demonstrate non-locality, their experiments support quantum mechanics.

Enter “setting independence”, also given the shorthand “free will”: the idea that someone attempting an experiment testing quantum mechanics is unable to act completely independently of the system they're trying to measure.

To put this in the form of a question: in measuring polarisation as the basis for testing the entanglement of two photons, how can the researcher guarantee that the system they're trying to test isn't somehow influencing the instrument settings they're using for the test?

And as MIT explains here, that could create an experimental bias in favour of quantum physics.

MIT Department of Physics professor David Kaiser, postdoc Andrew Friedman, and Jason Gallicchio from the University of Chicago, believe they've come up with a scheme that would guarantee the independence of their settings: base the experiment on quasars that are so far apart, they cannot possibly have any “causal contact” in the last 14 billion years.

This means that a random characteristic of each quasar can be proven to be completely independent.

For example: having generated a pair of entangled particles, the researcher needs to work out what characteristic is to be tested for each of them. Instead of (say) tossing a coin to make the decision for each particle, a telescopic observation of a very distant quasar would be used instead.

“In other words, quasar A determines the settings to detect particle A, and quasar B sets the detector for particle B,” MIT states. “If, after multiple measurements with this experimental setup, scientists found that the measurements of the particles were correlated more than predicted by the laws of classical physics, Kaiser says, then the universe as we see it must be based instead on quantum mechanics.”

The researchers believe that experiments could be designed using today's technology – which means that the last “nonlocality” loophole may be on the way to getting a test. ®

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