Agreement is not yet a Bell test
Two instruments can agree because their particles carried common instructions from a source. Entanglement evidence therefore needs more than a striking correlation at one pair of settings. A Bell test compares several setting-dependent statistics with a bound implied by a specified class of local models.
Clauser’s and Aspect’s experiments made that comparison concrete for photons. The 2022 prize also recognized Zeilinger’s work on entangled photons and quantum information. Award year, original experiment date and later improvements are separate entries in this history.
Read the evidence: Aspect (2022), Experimental tests of Bell’s inequalities: a first-hand accountNobel Prize in Physics 2022 — popular science background
State the bound and its assumptions
For binary outcomes labelled plus and minus one, the CHSH combination below uses the mean product at four setting pairs. Its local bound assumes local factorization and setting choices statistically independent of the hidden variables. Outcomes must be handled by a declared sampling rule.
The bound is not a fit parameter. A violation with defensible uncertainty constrains the models satisfying these assumptions. It does not demonstrate faster-than-light messaging, and it does not eliminate every logically imaginable hidden-variable theory.
Read the evidence: Larsson (2014), Loopholes in Bell inequality tests of local realism
What was not detected matters
If a calculation keeps only detected coincidences, detection can select an unrepresentative sample. A fair-sampling assumption cannot be silently treated as an experimental result. Random, rapid setting choices and suitable spacetime separation address a different concern: communication between the relevant measurement events.
Aspect’s changing-analyzer work was an important step, not a claim that every loophole was closed in one early experiment. Later teams combined stronger source, detector and timing designs. A 2015 photon experiment by Giustina and collaborators reports simultaneous closure of the most significant loopholes. Its precise inequality and analysis should be read on their own terms, not described as simply a raw coincidence CHSH calculation.
Read the evidence: Aspect (2022), Experimental tests of Bell’s inequalities: a first-hand accountGiustina et al. (2015), Significant-loophole-free test of Bell’s theorem with entangled photons
A p-value is not the probability that locality is true
A statistical test asks how surprising a record would be under a null model and its assumptions. It does not directly assign a posterior probability to a worldview. Choices about trial boundaries, losses, setting predictability and stopping rules belong in the analysis before interpreting significance.
The Bell Lab can expose how finite counts and detection efficiency affect a teaching sample. Its event generator is not an independent physical source closing real spacetime or detector loopholes. State tomography adds a different, calibrated reconstruction; error correction adds a recovery protocol. Neither should be counted as a replacement Bell experiment.
Read the evidence: Larsson (2014), Loopholes in Bell inequality tests of local realismGiustina et al. (2015), Significant-loophole-free test of Bell’s theorem with entangled photons