Cosmic Bell Test: Measurement Settings from Milky Way Stars

Understand

Bell's theorem states that some predictions of quantum mechanics cannot be reproduced by a local-realist theory.

• That conflict is expressed by Bell's inequality, which is usually derived under the assumption that there are no statistical correlations between the choices of measurement settings and anything else that can causally affect the measurement outcomes.
• In previous experiments, this "freedom of choice" was addressed by ensuring that selection of measurement settings via conventional "quantum random number generators" was space-like separated from the entangled particle creation.
• This, however, left open the possibility that an unknown cause affected both the setting choices and measurement outcomes as recently as mere microseconds before each experimental trial.