Competing to produce strings of random numbers, gamers across the globe helped test whether - as predicted by quantum mechanics - it is possible to violate local realism. The findings are reported in this week’s Nature.
There has been much discussion as to whether quantum theory provides a complete description of physical reality. Key here are locality and realism, the ideas that actions in one location cannot have immediate effects in other locations, and that physical systems have properties with given values even if we do not measure them. To investigate, researchers conduct so-called ‘Bell tests’. These measure quantum correlations between particles, to see whether they violate local realism in a manner that cannot be explained away by invoking hidden variables - factors unaccounted for in the current theory of quantum mechanics that would render the theory incomplete.
A common weakness in Bell tests, however, is the “freedom-of-choice” loophole; although researchers appear free in choosing the measurement settings of their experiments, there could be hidden factors influencing their choices. Consequently, random number generators are often used to select detector measurement settings - although as these are not truly random, measurement settings could still be affected by hidden variables.
Morgan Mitchell and colleagues from the BIG Bell Test Collaboration recruited around 100,000 participants from across the globe to produce a large enough supply of sufficiently random number sequences through a browser-based game - the “BIG Bell Quest”. Players were challenged to create unpredictable strings of zeros and ones to level up to higher difficulties. On 30th November 2016, gamers sustained a twelve-hour flow of over 1,000 bits per second to research teams who performed 13varied Bell tests and other tests of local realism using entangled photons, atomic ensembles and superconducting devices. Most tests found statistically strong violations of local realism, as expected from quantum theory.