Is Psi real?

Sabine Hossenfelder has a very interesting Youtube video (see this) telling about the article "Experimental demonstration of the PBR test on a superconducting processor" (see this). The experiments are argued to support the view that wavefunctions really exist and therefore the ontic view of quantum theory.

To my first understanding, the argument goes very roughly as follows.

1. By reading the original article one learns that there are 3 options: a) epistemic option (EO), b) hidden variable option, and c) ontic option. For a) given values of hidden variables can correspond to several quantum states and for b) only to a single one: in this case one can say that quantum state describes reality rather than our incomplete knowledge of it. For option c) hidden variables could mean finite measurement resolution so that the state in a given resolution can correspond to several states in an improved resolution.

   In EO there are hidden variables and Ψ gives a kind of average description. In state function reduction it is updated. Sabine however notes that Bohr proposed epistemic interpretation but did not accept hidden variables!

2. The PBR (Pussen, Barret, Rudolph) theorem is the second piece of argument. Suppose that one has two independently prepared states. The assumption, call it IP, is that in this case the distribution of hidden variables is a product of the distributions for the states. PBR theorem states that if IP holds true, standard quantum theory excludes EO. PBR is like Bell's theorem excluding local hidden variables.
3. One can empirically test the IP hypothesis. In the simplest situation, one can take two non-orthogonal states obtained as rotations of qubits. One can quantum entangle them and measure the value of either qubit. One can arrange so that for some outcomes the reduction probability vanishes. If this is not the case then IP fails and epistemic options could hold true. In this case it can happen that there is no definite outcome as in standard quantum measurement theory.

   Measurement errors are however present and the deviation from IP prediction allowed by the epistemic option could be interpreted as measurement error if one is not careful. One must construct a model for measurement errors and show that the measurement errors are below the bounds predicted by the EO.

   This is done and the conclusion is that the findings exclude the epistemic option.

How does this relate to TGD? Already in the relativistic wave mechanics Ψ is replaced with a spinor field and quantum states are constructed using fermionic oscillator operators so that the question is of whether the quantum states are real or only epistemic.

1. In the TGD framework, Ψ is replaced at the fundamental level by what I call spinor field in an infinite-D "world of classical worlds" (WCW). Its spinor structure can be seen as a "square root" of the metric structure and the Fock state basis provides a representation of Boolean algebra. Geometry and logic would be closely related.

   WCW spinor modes are Fock states for the second quantized spinor fields in H=M⁴×CP₂. If WCW metric is real then also the fermion fields are. Same applies to space-time surfaces X⁴ as 4-D Bohr orbits or particle-like 3-surfaces and H.

2. Why the interpretations, and the epistemic interpretation in particular, would be needed in the first place? The reason is that quantum measurement theory leads to a conflict between non-determinism quantum measurement and deterministic time evolution of Ψ and various classical fields.
3. In TGD, the basic problem of the quantum measurement theory finds a solution in terms of zero energy ontology (ZEO) forced by holography= holomorphy principle in turn forced by the conditions that general coordinate invariance can be realized without the path integral over space-time surfaces, which unavoidably would lead to non-renormalizable divergences. Therefore the interpretations are not needed and WCW spinor fields and also the geometrized classical fields can be real.

For a summary of earlier postings see Latest progress in TGD.

For the lists of articles (most of them published in journals founded by Huping Hu) and books about TGD see this.