For Bell, the basics are locality (the belief that things can’t influence each other instantaneously across space) and realism (that there’s some way things simply are, independent of their being measured). His theorem, published in 1964, proved what’s known as Bell’s inequality.
As written, Bell’s theorem wasn’t testable, but in 1969 the physicist and philosopher Abner Shimony saw that it could be rewritten in a form suitable for the lab. Along with John Clauser, Michael Horne and Richard Holt, Shimony transformed Bell’s inequality into the CHSH inequality (named for its authors’ initials), and in 1972, in a basement in Berkeley, California, Clauser and his collaborator Stuart Freedman put it to the test by measuring correlations between pairs of photons.
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As written, Bell’s theorem wasn’t testable, but in 1969 the physicist and philosopher Abner Shimony saw that it could be rewritten in a form suitable for the lab. Along with John Clauser, Michael Horne and Richard Holt, Shimony transformed Bell’s inequality into the CHSH inequality (named for its authors’ initials), and in 1972, in a basement in Berkeley, California, Clauser and his collaborator Stuart Freedman put it to the test by measuring correlations between pairs of photons.

‘Metaphysical Experiments’ Test Hidden Assumptions About Reality | Quanta Magazine
Experiments that test physics and philosophy “as a single whole” may be our only route to surefire knowledge about the universe.
