Experiment #6 · Scientific experiment

Bell Test Experiments

Locality, realism, and entanglement

John S. Bell (theorem); Alain Aspect et al. (canonical experiment) · 1964 / 1982 (loophole-free, 2015) · Quantum foundations

First published: J. S. Bell, "On the Einstein Podolsky Rosen Paradox", *Physics* 1 (1964): 195–200. Aspect, Dalibard, Roger, "Experimental test of Bell's inequalities using time-varying analyzers", *Phys. Rev. Lett.* 49 (1982).

No theory that is both local and admits definite pre-existing values can match the observed correlations.

Bell's theorem shows that any local hidden-variable theory must satisfy certain inequalities relating correlation statistics across pairs of entangled particles. Quantum mechanics predicts violations of those inequalities — and the experiments (Aspect 1982; loophole-free Hensen 2015, Giustina 2015, Shalm 2015) confirm violations to high statistical significance. The result is one of the most important metaphysical findings of twentieth-century physics: at least one of *locality* (no causal influence faster than light) and *realism* (measurement outcomes correspond to pre-existing properties) must be given up.

Formulation

Two entangled particles separated to space-like intervals are measured along independently-chosen axes. Local hidden-variable theories require correlation statistics |S| ≤ 2 (the CHSH inequality). Quantum mechanics predicts and experiments observe |S| ≈ 2√2 ≈ 2.83, with loophole-free experiments (2015) closing locality, detection, and freedom-of-choice loopholes simultaneously.

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Dimensions Engaged

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Space

Directly contradicts strict Space · Locality: either the correlations require non-local connections in some sense, or the spatial separation of "things" is itself less fundamental than the joint state.

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Time

Bears on Time · Direction and Freedom via the "superdeterminism" loophole: a sufficiently determined past could in principle correlate measurement-setting choices with hidden variables. Most physicists reject this; the price is high.

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Matter

Forces Matter · Ontological Status: standard "realism" — that properties have definite values prior to measurement — cannot be retained alongside locality. Entanglement is a relation that is not reducible to local intrinsic properties of the parts.

Responses — How Schools Engage

Affirms / takes the bait 3

Quantum Realism

The wave function is the real entity; entangled systems have no separate states. Locality, as classical physics framed it, simply fails — there is one joint state, not two correlated local ones.

Relationalism

Relational quantum mechanics (Rovelli): properties exist only relative to systems with which they are correlated. There is no "view from nowhere" from which to ask whether the spins are non-locally connected; the question reflects a residual absolutism.

Structuralism

Bell tests are the strongest single argument for ontic structural realism: the entangled pair has no factorisable inventory of intrinsic properties — only the relational structure is real.

Reframes the question 3

Multiverse Theory

Everettian: there is no faster-than-light influence because there is no single outcome to influence. Locality is preserved at the level of the branching wavefunction; "non-locality" is an artifact of demanding a single outcome.

Naturalism

Bohmian mechanics retains realism (particles have positions) but pays with explicit non-locality: the pilot wave acts instantaneously across space. The experiment is taken to favour pilot-wave over collapse readings, not to refute realism.

Determinism

A small minority defend superdeterminism (’t Hooft): the freedom-of-choice loophole was never closed in the metaphysically relevant sense, because no choice in a fully determined world is free. Locality and realism survive at the cost of treating the experimenters as cogs.