Is the wavefunction real in CSD?

The short answer

"Is the wavefunction real?" runs two questions together, whether something in the world corresponds to it, and whether it's the complete story of what exists, and CSD's answers come apart cleanly as yes, and emphatically no.

Yes, because the quantum state isn't a fiction or a mere betting position. Every point of the arena, the underlying state space, projects to a definite quantum state, so the state tracks a genuine feature of the world, and if you had access to the world's actual configuration you could read the state off it.

No, because the state is radically incomplete. The projection that produces it is many-to-one, so many different underlying configurations give the same quantum state, and everything that decides measurement outcomes, the fibre coordinate that distinguishes those configurations and the outcome basin the trajectory occupies, lives in what the projection forgets. Treating the state as the whole world is exactly the move that generates the measurement problem, and treating it as a lossy coordinate dissolves the problem.

The longer answer

The state's dual character is structural rather than rhetorical. Functionally the state is epistemic, as it summarises what a preparation fixes, and its update on measurement is learning and not a physical jump. Ontologically its supports are disjoint, as distinct states describe disjoint sets of arena points, and that's why the reality theorems aimed at models with overlapping supports don't bite.

The programme's discipline is to refuse the shorter slogans in both directions. "The wavefunction is everything" overclaims what the quantum state carries, as the analysis of the fibre places record-forming content, the structure that decides outcomes, above the state at higher dimension, on a chain of constraints that stops short of proving the base can't carry it. "The wavefunction is nothing" ignores that the state is a faithful coordinate of the real arena.

What is actually proved

The formal content is the projection structure, a measurable many-to-one pi from the arena to the projective sector, the epistemic measure exact on the base and spread on the fibre, and the record layer's theorems placing outcome-deciding structure in the fibre at N >= 3.

The operational stratum's state notion, density operators and effects, is proved consistent with the volume stratum wherever both speak.

Related entries

• Ontic vs epistemicWhat exists is one question and what a measurement context lets you say is another, and most quantum paradoxes are category errors between the two.
• Psi-epistemicThe quantum state is what you know and not what exists, and the hard part was always saying what it's knowledge of, so CSD's whole architecture is an answer to that.
• Does the PBR theorem rule out CSD?No. For exactly prepared pure states, CSD satisfies the very conclusion the PBR theorem argues for, as two distinct states correspond to sets of underlying world- states that don't overlap at all, and that's a proved theorem rather than something arranged by hand.
• QBismQBism is epistemic all the way down, as the quantum state is one agent's betting book and there's nothing underneath, and CSD agrees about the state and insists on the underneath.
• Does the excess-baggage theorem count against CSD?No. The excess-baggage theorems say any model with real underlying states beneath quantum mechanics needs a continuum of them, and CSD's constraint surface is a continuum from the outset, so the requirement is met before it's raised.