Collapse

In plain terms

Here is the problem. The textbook says that when a measurement happens, the state discontinuously jumps to match the outcome. Is that jump a physical event, or an update to a description? The dispute is as old as the theory, and the stakes are real: a physical jump would be abrupt, irreversible, unexplained by any equation in the theory, and apparently instantaneous across any distance.

An update, on the other hand, needs no physics at all -- when you learn which box the ball is in, your probabilities collapse and nobody is alarmed. The whole question is whether quantum collapse is more like the ball.

CSD's answer is the ball -- but with a twist that makes the answer checkable rather than rhetorical: on a volume-preserving substrate, a physical collapse is not merely unnecessary. It is impossible.

In CSD

The corpus proves that no measure-preserving map implements exact collapse. So a deterministic, volume-conserving substrate could not contain a collapse process even if its designer wanted one. The stance becomes a constraint -- and CSD is on the record as unable to cheat.

What replaces the jump is a record. System and apparatus evolve together under the one dynamics; the record fixes which epistemic region the trajectory realises; and the update rule the textbook postulates separately falls out of the record construction. The thing that changes discontinuously is the summary. The world underneath does what it was always doing.

Mathematically

No measure-preserving map on the arena implements exact collapse. Approximate collapse exists but is priced: accuracy is bounded against ready-state improbability, with the exchange rate explicit.

The post-measurement update is then derived rather than postulated -- it appears as the block projection realised on the pointer arena, an output of the record construction.