Generally Quantum mechanics divides a system what is to be observed and an observer. This is generally taken to be some human being. But why restrict it to such? Why not a particle?
Is there a good physical reason or philosophical reason for this to dismissed as not sustainable?
I'm thinking here specifically of the Copenhagen interpretation, or of its modern incarnation consistent histories. I understand that decoherence in consistent histories completely replaces the idea of the wave collapse in the Copenhagen Interpretation.
Essentially, the idea of observed system and an observer is supplemented with an environment, which on the face of it seems entirely natural. The idea of decoherence comes from statistical physics.
I'm suggesting that a particle that acts like an 'observer' needs to 'know' what state the observed system is in to 'know' how to react to it. Decoherence resolves the superposition of states in the observed system to a probability mixture.