 There is thus an even wider problem, which we can call the problem of the classical regime of quantum mechanics, and quite analogous to the measurement problem. Can quantum mechanics be applied to the description of classical systems? We can deny it (as orthodox approaches do), but then what are classical systems in the first place? And if we apply quantum mechanics also to the systems that seem to populate our everyday world, can we derive from quantum mechanics the behaviour that is characteristic of such ‘classical’ systems? But such a derivation appears impossible. To put it crudely: if everything is in interaction with everything else, everything is generically entangled with everything else, and that is a worse problem than measuring apparatuses being entangled with measured systems.