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Quantum Mechanics

Foundations Experiments and Quantum Reality

EPR asked whether the quantum state gives a complete description. Bell showed how specified local hidden-variable assumptions constrain correlations, turning part of that debate into an experimental question. Contextuality tests and interferometer experiments ask related but distinct questions.

Reading sequence

Section titled “Reading sequence”
  • EPR Argument explains the 1935 challenge to quantum-mechanical completeness through elements of reality, locality, and entangled position-momentum correlations.
  • Bohm’s Spin Version of EPR explains how the spin-singlet reformulation made EPR correlations finite-dimensional, normalizable, and ready for Bell-test reasoning.
  • Bell’s Theorem as Historical Turning Point explains how Bell transformed the EPR debate into quantitative inequalities that experiments could test.
  • Bell Inequality Experiments surveys how separated correlation measurements test Bell inequalities, control loopholes, and support careful interpretation.
  • Aspect Experiments explains the 1980s optical Bell tests, including two-channel analyzers, time-varying settings, historical impact, and remaining loopholes.
  • Loophole-Free Bell Tests explains modern Bell tests that close the major detection and locality loopholes under explicit assumptions.
  • Kochen–Specker Contextuality Experiments explains how experiments test noncontextual hidden-variable assumptions using compatible measurements and contextuality inequalities.
  • Delayed-Choice Experiments explains Wheeler-style late measurement choices in interferometers without retrocausal overstatement.
  • Quantum Eraser Experiments explains how which-path markers, erasure measurements, and coincidence sorting recover conditional interference without signaling.
  • What These Experiments Do and Do Not Prove synthesizes the experimental constraints while preventing overclaims about signaling, consciousness, and interpretation.

Put the ideas to work

Section titled “Put the ideas to work”

Read EPR → Bohm’s spin example → Bell’s theorem → experimental tests. Keep the CHSH assumptions beside the data analysis. Delayed-choice and quantum-eraser experiments can change which correlations are examined; they do not demonstrate a controllable message to the past. The final comparison explains the limits of each conclusion.

References

Section titled “References”
  • A. Aspect, J. Dalibard, and G. Roger, “Experimental Test of Bell’s Inequalities Using Time-Varying Analyzers,” Physical Review Letters 49, 1804-1807, 1982, DOI: 10.1103/PhysRevLett.49.1804.
  • J. S. Bell, “On the Einstein Podolsky Rosen Paradox,” Physics 1, 195-200, 1964, DOI: 10.1103/PhysicsPhysiqueFizika.1.195.
  • N. Bohr, “Can Quantum-Mechanical Description of Physical Reality be Considered Complete?,” Physical Review 48, 696-702, 1935, DOI: 10.1103/PhysRev.48.696.
  • A. Einstein, B. Podolsky, and N. Rosen, “Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?,” Physical Review 47, 777-780, 1935, DOI: 10.1103/PhysRev.47.777.
  • M. Jammer, The Philosophy of Quantum Mechanics, Wiley, 1974.