Record layer

In plain terms

Suppose outcome probabilities really are the volumes of regions in some space of states. You still owe an account of the outcome itself, as after the experiment something in the world, a pointer, a grain of silver, a memory, holds which result occurred, and a theory that prices outcomes but can't say where the outcome is written has stopped one step short.

The record layer is that last step, and it asks for two things. First, the outcome regions must be fixed by the apparatus alone, in the way that a referee's rulebook doesn't depend on which team is playing. Second, the record must be a physical configuration of the arena, the space of everything that exists in CSD, so it's an ontic fact, one that holds independently of anyone's knowledge, selected by the one real trajectory.

Nothing mystical is on offer. A record is structure the arena already has, singled out by where the trajectory went.

In CSD

This is the programme's near frontier, and it's partly built. The partition fixed by the context exists, as outcome regions, called basins, are defined from the apparatus's rate field, the outcome weights the apparatus assigns at each point of the state space, with no preparation anywhere in the definition, and their weights come out as the Born weights, the probabilities quantum mechanics assigns. For the qubit, the simplest quantum system, with two outcomes, the whole story is proved end to end. At higher dimension the analysis indicates that the contextual structure, the dependence of the outcome regions on the whole measurement context, doesn't sit on the base alone, the base being the projected state space, and the corpus places it in the fibre, the part of the arena lying above each state. That placement narrows where the mechanism can be, though it rests on refuting one natural class of base candidate rather than on a no-go.

What remains open, and is stated as open, is deriving the fibre mechanism from de- isolation dynamics, the physics of a system losing its isolation during measurement, rather than exhibiting it. The record layer is where the reconstruction is completed or not.

Mathematically

The proved tier is that a measurable simplex-valued rate field on the base defines pairwise-disjoint basins whose epistemic probability at preparation psi is the Born weight, from a partition that never mentions psi. Sequential and mixed-state versions run through the Luders tier.

The open tier is dynamical and not kinematic, as no interaction Hamiltonian generating the basins is constructed, and the corpus says so in the module that would need it.

Related entries

• De-isolationNothing collapses, as a measured system stops being isolated, and measurement is what de-isolation dynamics looks like from inside.
• Measurement flowA deterministic, volume-preserving flow carries out a measurement, and the volumes of its pointer blocks are the Born weights, for every preparation.
• Pointer basisA measuring apparatus doesn't record what you ask it to, as it records what it can keep, and what it can keep is decided by its interaction with the surroundings and not by the experimenter.
• CollapseIn CSD the quantum state never jumps, and that's a theorem about volume-preserving maps rather than a preference among interpretations.
• Record light coneRecords are safe from distant meddling by theorem, as anything that happens outside the light cone can shift the outcome written into the arena's fibre by no more than a bound that collapses factorially with distance.