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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.

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Quite possibly related: 1, 2 ("An important aspect of the concept of measurement has been clarified in some QM experiments where a single electron proved sufficient as an "observer" — there is no need for a conscious "observer""), 3, 4, 5 –  Glen The Udderboat Jul 28 '13 at 15:17
    
Only one question. Isn't an electron in its own rest frame a potential observer? –  71GA Jul 28 '13 at 21:52
    
@Gugg that Wikipedia quote seems awfully exaggerated. The research it references proves weak measurements and can be interpreted as disproving the need for a conscious observer, but it doesn't go anywhere near saying that a single electron can act as an observer. –  Bruce Connor Jul 28 '13 at 22:21
    
(To the original question ) The formal answer is no, because observers are defined as conscious. The practical answer is no, because decoherence of the wave function requires interaction with a very large system (and evidence has been showing that collapse just might arise as an approximate consequence of that interaction). –  Bruce Connor Jul 28 '13 at 22:30
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How about this as an alternative to the question: What is the simplest system that can be an observer? Can such system be "unconscious": for example, has anyone thought up a quantum observer automaton, analogously with the finite state machine Maxwell Daemons considered by Bennett and others. Or is anyone doing research into such constructions? This would seem to be a wonderful research topic, if in the unlikelihood that someone isn't doing it already. –  WetSavannaAnimal aka Rod Vance Jul 29 '13 at 0:19
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