What happens if we treat the observer as a quantum object in an experimental set-up? I don't have a specific model of an 'observer' - all suggestions are welcome. I'm curious whether the consequences are compatible with the principle of relativity (that observers shouldn't be 'discriminated') or involve superluminous changes. Also, would it lead to an infinite regress ? What if the observer is 'biased' ? Consider the double slit experiment with photons ( for sake of simplicity). We could treat the screen , for instance, as the retina of an 'observer'.