Abner Shimony was born the same year as John Bell but outlived him by 25 years.

Shimony earned a Ph.D. in philosophy from Yale in 1953 supervised by Rudolf Carnap and nine years later a Ph.D. in physics from Princeton, studying under Eugene Wigner.

Shimony taught first at MIT, then at Boston University for many years with a dual appointment at Yale.

A major research interest was exploring the possible conflict between quantum physics and relativity, something that had worried Albert Einstein all his life.

In his lifetime, Shimony did more to promote John Bell's idea of an "inequality theorem," one that might disprove (or prove) quantum mechanics, than possibly any other person.

Just five years after Bell's work, Shimony in 1969 developed an empirically testable form of the Bell inequality, known as the CHSH inequality after the four contributors, John Clauser, Michael Horne, Shimony, and Richard Holt.

Clauser and colleague Richard Freedman did the first experimental test of Bell's inequality in 1971, with results that weakly validated standard quantum mechanics. This was followed by many hundreds of similar tests over the following decades, down to the present day.

Shimony authored the Stanford Encyclopedia of Philosophy article on Bell's Theorem. In an early version(2009), he argued that the perfect correlations of opposite spin states in the entangled pairs is a consequence of the conservation of angular momentum. This conservation principle is the common cause of the perfect correlations of entangled particles.

[By] conservation of angular momentum the photon pair emitted in the cascade has total angular momentum 0, and if the photons are collected in cones of small aperture along the z-direction the total orbital angular momentum is small, with the consequence that the total spin (or polarization) angular momentum is close to 0 and therefore the polarizations of the two photons are tightly correlated.

"Bell's Theorem," Stanford Encyclopedia of Philosophy, 2009 (retrieved January 23, 2022)

Shimony said that Bell likely assumed that quantum mechanics would violate his "ad hoc" inequality, because quantum mechanics had been so well established.

When Bell published his pioneering paper in 1964 he did not urge an experimental resolution of the conflict between Quantum Mechanics and Local Realistic Theories, probably because the former had been confirmed often and precisely in many branches of physics.

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Between 1973 and 1984, Shimony helped organize and contribute to thirty-six issues of a newsletter called Epistemological Letters: Hidden Variables and Quantum Uncertainty.

These privately published newsletters were circulated to about 180 of the most prominent physicists in the world. It contained contributions on the foundations of physics inspired by the work of John Bell, which in turn had been inspired by David Bohm's revival of Louis de Broglie's "pilot wave theory" and their idea of "hidden variables." Bell was a major contributor, often publishing a preprint on EL before publishing it in a physics journal.

In 1984, Jon Jarrett gave a talk at Harvard, and was a guest at the Boston University Center for Einstein Studies and the Center for the History and Philosophy of Science.

In meetings that included, among others, Shimony and Don Howard, Jarrett presented ideas from his 1983 thesis Bell's Theorem, Quantum Mechanics, and Local Realism and introduced a number of new technical terms that have become a major part of philosophical discussions of entanglement.

In his thesis, Jarrett claimed that Bell’s local causality condition (which Jarrett calls “strong locality”) is logically equivalent to the conjunction of two subsidiary conditions, which Jarrett describes respectively as “locality” and “completeness.” This is known as Jarrett's "Decomposition theorem."

These two conditions Abner Shimony made famous as "parameter independence" and "outcome independence."

Shimony also suggested the term "Passion-at-a-Distance" instead of Einstein's Spooky Action-at-a-Distance Although Shimony did not say what he meant by passion, we do acquire distant knowledge "passively," without actively doing anything to the distant particle.

In 2009, one of Shimony's students, Don Howard, elaborated on Shimony's thinking.

In 1984, Abner Shimony invented the expression, "passion at a distance," to characterize the distinctive relationship of two entangled quantum mechanical systems. It is neither the local causality of pushes, pulls, and central forces familiar from classical mechanics and electrodynamics, nor the non-local causality of instantaneous or just superluminal action at a distance that would spell trouble for relativity theory. This mode of connection of entangled systems has them feeling one another's presence and properties enough to ensure the strong correlations revealed in the Bell experiments, correlations that undergird everything from superfluidity and superconductivity to quantum computing and quantum teleportation, but not in a way that permits direct control of one by manipulation of the other. Intended to echo Aristotle's distinguishing of "potentiality" from "actuality" as different senses of "being," Shimony's "passion at a distance" is all about tendency and propensity, not the concreteness whose misplacement in realm of the physical was lamented by Alfred North Whitehead.

Quantum Reality, Relativistic Causality, and Closing the Epistemic Circle 2009, p. 3

But the particles do not (passionately?) "feel one another's presence and properties."
That would require instantaneous actions at a distance.

The "strong correlations revealed in the Bell experiments" are the consequence of a basic conservation principle underlying both classical and quantum mechanics. We describe it as a "common cause" in the shared past light cone of the two particles.

For many years, experimenters and theorists searched for "loopholes" in the experiments that might indicate something wrong with quantum mechanics. Bell had tantalized experimenters with the chance of a Nobel Prize if something was found to be wrong with quantum mechanics. Such a result would "shake the world," he told John Clauser. But every new test has only further confirmed the theory of quantum mechanics.

Shimony also defined two other "conditions," one he called the "factorization condition," the other "Bell's locality condition."

Wave function factorizability means a quantum state's multi-particle wave function can be written as a simple product of independent, single-particle functions. Erwin Schrödinger challenged Einstein's idea that two systems that had previously interacted can be treated as separated systems, and that a two-particle wave function ψ₁₂ can be factored into a product of separated wave functions for each system, e.g., ψ₁₂ → ψ₁ ψ₂.

Instead, the wave function for two entangled particles is a superposition of product states and will remain so until one particle is measured or the wave function is decohered by environmental interactions.

The probability of either the | ψ₁₊ ψ_2- > or | ψ_1- ψ₂₊ > state | ψ₁₂ >² is 1/2.

In either case the total spin is zero, conserving spin angular momentum. But the spin of each particle is completely random, up or down half the time, producing the perfectly correlated spins that are the basis for quantum key distribution (QKD), the most secure method for encrypting secret messages.

Notice the similarity with Schrödinger's famous superposition of live and dead cats.

which simply means there is a fifty percent chance of finding the cat dead or alive!

Just as there is never a cat both dead and alive, there is never a particle with spin up and down at the same time.