Quantum mechanics is weird^(*), therefore physicists have sought for years another possible explanation (theory) for empirical evidence compatible with the so-called Einstein’s principle of local realism.

The paradox of Einstein, Podolsky and Rosen⁽¹⁾ —a sleeping beauty in science— was advanced as an argument that quantum mechanics could not be a complete theory but should be supplemented by additional (hidden) variables to restore to the theory causality and locality.

In 1964 John Stewart Bell showed that no physical theory of hidden local variables can ever reproduce all the predictions of quantum mechanics⁽²⁾. Bell’s theorem has been used to put local realism to test.. And a number of increasingly sophisticated Bell test experiments since, has convinced the physics community —in general— that local realism is untenable, i.e. quantum mechanics is weird.

However, physicist are also worried that those experiments have a number of important loopholes⁽³⁾, problems of experimental design or set-up that affect the validity of the experimental findings. One important loophole is the so-called ‘freedom-of-choice loophole’. Bell’s test requires certain measurements to be performed with random settings⁽⁴⁾.

A Bell test, which challenges the philosophical worldview of local realism against experimental observations, is a randomized trial requiring spatially-distributed entanglement, fast and high-efficiency detection, and unpredictable measurement settings. While technology can perfect the first two of these, and while technological randomness sources enable device-independent protocols based on Bell inequality violation, challenging local realism using physical randomizers inevitably makes assumptions about the same physics one aims to test.

Bell himself noted this weakness of physical setting choices and argued that human free will could rigorously be used to assure unpredictability in Bell tests.

In 2016, the Big Bell Test⁽⁴⁾ intended to close the ‘freedom-of-choice loophole’ by collecting random decisions from humans instead of random number generators.

We recruited 100,000 human participants to play an online video game that incentivizes fast, sustained input of unpredictable bits while also illustrating Bell test methodology. The participants generated 97,347,490 binary choices,

To be sure, the Big Bell Test doesn’t close all the loopholes. Local realism can never be excluded entirely. We will never be able to rule out superdeterminism —the complete absence of free will— using scientific methods (And btw, the assumption that the world is not superdeterministic is needed to do science in the first place.)

But wait, by using humans to make the choices, we are only translating the problem of true randomness to the human realm, cause… Do we really have free will, or is it all an illusion? We don’t know but as John H. Conway and Simon B. Kochen stated in the Free Will Theorem⁽⁵⁾:

if indeed there exist any experimenters with a modicum of free will, then elementary particles must have their own share of this valuable commodity.

In other words, you can go ask the elementary particles!!

The Big Bell Test places us before a disquieting conclusion, one of those of a conditional variety that opens an interesting thought avenue.

if humans have free will, then some physical events have no cause.

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(*) I am sure you’ve found more than once the —widely attributed to Feynman and probably apocryphal— dictum “If you think you understand quantum mechanics, you don’t understand quantum mechanics.”

(1) Einstein, Albert, et al. ‘Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?’ Physical Review, vol. 47, no. 10, 1935, p. 777.

(2) Bell, John S. ‘On the Einstein Podolsky Rosen Paradox’. John S Bell On The Foundations Of Quantum Mechanics, World Scientific, 2001, pp. 7–12.

(3) Larsson, Jan-Ake. ‘Loopholes in Bell Inequality Tests of Local Realism’. Journal of Physics A: Mathematical and Theoretical, vol. 47, no. 42, 2014, p. 424003.

(4) The BIG Bell Test Collaboration, et al. ‘Challenging Local Realism with Human Choices’. Nature, vol. 557, no. 7704, May 2018, pp. 212–16. arXiv.org, doi:10.1038/s41586-018-0085-3.

(5) Conway, John, and Simon Kochen. ‘The Free Will Theorem’. Foundations of Physics, vol. 36, no. 10, 2006, pp. 1441–1473.

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