# The End of a Classical Ontology for Quantum Mechanics?

## Abstract

**:**

## 1. Introduction

## 2. Causal Symmetry and Classical Ontology

#### 2.1. The No-Go Theorems

#### 2.2. Ontological Models

#### 2.3. Einstein–Bell Realism

- Quantum mechanical probabilities are epistemic;
- Quantum mechanics is local;
- Quantum mechanics is consistent with the no-go theorems.

## 3. The Shrapnel–Costa No-Go Theorem

#### 3.1. Process Matrix Formalism

#### 3.2. Causation Does Not Explain Contextuality

our ontic process captures the physical properties of the world that remain invariant under our local operations. That is, although we allow local properties to change under specific operations, we wish our ontic process to capture those aspects of reality that are independent of this probing.[4] (p. 8)

#### 3.3. Interpreting the Result

all aspects of a physical scenario other than the choices of settings and the observed outcomes…Such aspects include what kind of systems are involved, the laws describing such systems, boundary conditions, etc.[4] (p. 18)

## 4. The End of a Classical Ontology?

the tension that would need to be resolved is between: (i) the solution of a Cauchy problem from freely, arbitrarily and (ideally) completely specifiable initial data; and (ii) the symmetric expectation that the final boundary be equally freely, arbitrarily and completely specifiable. One way to escape this tension would be to remove the freedom to completely specify data on the final boundary: an agent controlling the final boundary would just happen to ‘choose’ a measurement that concords with the deterministic evolution of the ontic state. However, this would break the symmetry between the final and initial boundaries and would also remove the element of control that renders the Price–Wharton picture causally symmetric. To retain the symmetry would thus require some as-yet-unspecified principled constraint that limits an agent’s ability to freely, arbitrarily and completely specify both initial and final boundary data. This constraint must be such that the aspects of the ontic state on the initial Cauchy surface that are a consequence of the choices specified at the final boundary are not epistemically accessible before the final boundary is specified—and vice versa.[3] (p. 7)

## 5. Final Thoughts

## Funding

## Acknowledgments

## Conflicts of Interest

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Evans, P.W.
The End of a Classical Ontology for Quantum Mechanics? *Entropy* **2021**, *23*, 12.
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**AMA Style**

Evans PW.
The End of a Classical Ontology for Quantum Mechanics? *Entropy*. 2021; 23(1):12.
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**Chicago/Turabian Style**

Evans, Peter W.
2021. "The End of a Classical Ontology for Quantum Mechanics?" *Entropy* 23, no. 1: 12.
https://doi.org/10.3390/e23010012