Measurement problem

In plain terms

Here is the problem -- arguably THE problem. Left alone, a quantum system evolves smoothly, reversibly, keeping every superposition intact. Measured, it delivers one definite outcome and the alternatives vanish. The theory contains both behaviours and refuses to say where one ends and the other begins. What counts as a measurement? A detector? An eyeball? A graduate student?

This is not a philosophical itch. The two rules are mathematically incompatible -- one linear and reversible, the other neither -- so a theory holding both without a boundary is not a closed description of anything.

Every serious interpretation is, at bottom, a proposal for which rule to sacrifice. Many-Worlds keeps the smooth evolution and drops definite outcomes. Collapse theories keep the outcomes and modify the evolution. The question is old, unresolved, and entirely legitimate.

In CSD

CSD's move: nothing abrupt ever happens on the substrate. The underlying motion is deterministic and volume-preserving throughout; what changes at a measurement is which region of the epistemic space the trajectory gets recorded against. Both textbook rules become views of one process.

What keeps this from being just another story is the trilemma -- three theorems that stake out what any account must give up. No volume-preserving map implements exact collapse. No continuous dynamics correlates a pointer perfectly everywhere on a connected arena. And approximate collapse has a stated price: accuracy costs ready- state improbability, quantitatively.

So the corpus does not dissolve the measurement problem by narrative. It proves which combination of desiderata is impossible, then says openly which one CSD abandons. That is what separates a result from an interpretation.

Mathematically

Three impossibility results on the pointer arena: no exact collapse by a measure- preserving map; no everywhere-correlating continuous propagator on a connected arena; a quantitative accuracy-versus-improbability bound.

All three are CSD-free in statement -- measure theory, topology, and an estimate respectively. Any rival account with the corresponding structure inherits them. They cannot be cited against this programme without being cited against the citer.