03 January 2018

Massachusetts Institute of Technology researchers have proposed an experiment using distant quasars that may close the last major loophole of Bell’s inequality, namely, what physicists refer to as as “setting independence” or “free will”.

This loophole proposes that a particle detector’s settings may interact with events in the shared causal past of the detectors themselves to determine which properties of the particle to measure. This would imply that a person running the experiment does not have complete free will in choosing each detector’s setting. As a result, the experiment produces biased measurements which in turn suggests a correlation between particles that is greater than the real correlation.

David Kaiser, the Germeshausen Professor of the History of Science and senior lecturer in the Department of Physics, along with MIT postdoc Andrew Friedman and Jason Gallicchio of the University of Chicago, have proposed an experiment to close this loophole by determining a particle detector’s settings using distant quasars.

A laboratory setup would consist of a particle generator that produces pairs of entangled particles. One detector measures a property of particle A, while another detector does the same for particle B. A split second after the particles are generated, but just before the detectors are set, scientists would use telescopic observations of distant quasars to determine which properties each detector will measure of a respective particle.

The researchers reason that since each detector’s setting is determined by sources that have had no communication or shared history since the beginning of the universe, it would be impossible for these detectors to interact with anything in their shared past to give a biased measurement.

This experiment is feasible with present technology.