A Neo-Copenhagen Quantum Mechanics

An analysis of the quantum measurement problem is presented which is a modest modification of the standard one often called the Copenhagen interpretation. The starting assumption is that QM is universal, and that all evolutions are unitary. We must also assume that the set of evolutions is restricted to allow the existence of stable structures for the equipment in our laboratory, including the measurement devices. The devices need some macroscopic properties to make the outcomes of the experiments stable data. There should not exist superdevices capable of retrieving the information needed to reverse these evolutions. As a result the quantum coherences complementary to the outcomes of experiments will typically be inaccessible and there is no need to remove them by decoherence. We need devices designed such that the outcome of an experiment is indicated by a pointer with the property that it has a definite but random final state. We then find that the outcomes of experiments can be considered factual data, and random in a classical sense. They can be considered to happen in a single world.