[orbifold]

The collapse just stands for the unknowable details of the interaction with the environment during measurement, a good quantum physics course will explain that and include experiments that make that clear. For instance the Stern-Gerlach experiment illustrates this well.

[GoblinSlayer]

Decoherence is a consequence of interaction between particles in the coherent state, environment plays no role there, you can do all experiments in the vacuum and they will still work the same way, obviously.