Barandes, Jacob A. (2026) The Trouble with Weak Values. [Preprint]

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Abstract

In quantum theory, a weak value is a complex number with a somewhat technical definition: it is a ratio whose numerator is the matrix element of a self-adjoint operator and whose denominator is the inner product of a corresponding pair of state vectors. Weak values first appeared in the research literature in a pair of papers in 1987 and 1988, and were originally defined as the results of a special kind of experimental protocol involving non-disturbing measurements combined with an explicit form of post-selection. In the years since, subsequent papers on weak values have produced a number of important practical spin-offs, including new methods for signal amplification and quantum-state tomography. The present work is not concerned with those practical spin-offs, but with historical and ongoing attempts to assign weak values a transparent, single-system interpretation, as well as efforts that invoke weak values to make a number of exotic claims about the properties and behavior of individual quantum systems. This paper challenges these interpretational claims by arguing that they involve several forms of fallacious reasoning.

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Item Type:	Preprint
Creators:	Creators Email ORCID Barandes, Jacob A. jacob_barandes@harvard.edu 0000-0002-3740-4418
Keywords:	philosophy of physics, quantum foundations, ABL rule, weak values, weak measurements, post-selection, statistics, selection bias, measurement, quantum mechanics, quantum theory, probability, philosophy of probability, uncertainty principle
Subjects:	General Issues > Scientific Metaphysics Specific Sciences > Physics Specific Sciences > Probability/Statistics Specific Sciences > Physics > Quantum Mechanics General Issues > Theory/Observation
Depositing User:	Dr. Jacob Barandes
Date Deposited:	10 Feb 2026 13:26
Last Modified:	10 Feb 2026 13:26
Item ID:	28148
Subjects:	General Issues > Scientific Metaphysics Specific Sciences > Physics Specific Sciences > Probability/Statistics Specific Sciences > Physics > Quantum Mechanics General Issues > Theory/Observation
Date:	9 February 2026
URI:	https://philsci-archive.pitt.edu/id/eprint/28148

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