Quantum Darwinism creates a precise framework for this seemingly (but not genuinely) obvious and mundane fact: it says that the states we can measure are ones that are able not just to imprint themselves in many replicas in the environment, but specifically to do so in many different parts of the environment – so that we can find them out without having to look everywhere. The states we can measure are the ones that are most easily found out. There’s a bizarre corollary to this picture. In general, when we measure a property of a quantum system by probing its ‘replica’ in the environment, we
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