Information versus Physicality: On the Nature of the Wavefunctions of Quantum Mechanics

Abstract

The physical states of matter and fields are represented in the quantum theory with complex valued wavefunctions, or more generally by quantum states in an abstract linear vector space. Determining the physical nature of wavefunctions remains an open problem that is at the very core of quantum mechanics, About a decade ago, Pusey, Barrett and Rudolf (PBR) claimed to prove an ontologically real status of wavefunctions by ruling out $ψ$-epistemic models. The result was obtained by associating wavefunctions to hypothetical distributions of notional physical states, and by examining whether some physical states were associated with more than one wavefunction, a criterion they chose for defining a wavefunction as `epistemic'. I show that the starting assumption in the PBR argument, of associating a wavefunction with a distribution of physical states, is flawed and contradictory to the linear structure of quantum mechanics coupled with its quadratic Born's rule. Since none of the axioms or calculations of observable statistical results in the standard quantum theory depends on specifying the physical nature of a $ψ$-function, the considerations in the PBR paper, involving a standard process of the preparation and projective measurements of quantum states, cannot address the ontological status of the wavefunctions in space and time.