This is pretty much the original interpretation of quantum mechanics, put together by the founders of the theory (see History of Quantum Mechanics). It was proposed, before all the principles given here were fully understood, so that one could have a working conceptual picture of the relation between theory and observation.

In the Copenhagen interpretation (which has several forms), the defining idea is that the physical world divides into an atomic-level world where wave function behavior dominates and a macroscopic, ‘classical,’ Newtonian world of detectors and observers. The macroscopic world was presumed to have only a single version.

There are four problems here. First, it is logically inconsistent to assume that large-scale objects, made up of ‘atoms,’ do not obey quantum mechanics. Second, it was not specified what the macroscopic world was made up of, but it presumably was objectively existing particles. However, we see from No Evidence for Particles that there is no evidence for anything being in physical existence besides the wave functions. Third, the interpretation seems to implicitly assume there is Collapse of the Wave Function. But again, there is no evidence for this. Finally, it is not explained in the interpretation why the properties of the large-scale world should agree so exactly with the quantum mechanical predictions (see the example below). Thus the Copenhagen interpretation, the oldest and probably most popular of the interpretations, cannot be logically defended. (See also Can Quantum Mechanics Show Us the Nature of Reality?)

Suppose we have a single hydrogen atom that is initially in its lowest energy state (see History of Quantum Mechanics). It collides with an ion or a fast-moving electron and gets boosted into a sum of higher energy states. Each of these states then decays over time into a lower energy state plus a single ‘photon’ (photon-like wave function). Each of these ‘potential’ photons goes through a prism and then hits a screen covered with film grains. We know each of the many photon-like wave functions will have one of the wavelengths predicted by the Schrödinger equation for the hydrogen atom and we know that one and only one of the film grains will be exposed. The question is: How does the set of ‘Copenhagen’ macroscopic systems (assuming each film grain is a macroscopic system), with no specified mathematical theory for its evolution, evolve in time so that just one grain, at one of the predicted wavelengths, becomes exposed?