Who’s Afraid of the Measurement Problem? On the Incompatibility between Scientific Realism and Quantum Mechanics

Call ‘the realism problem’ the problem of providing realist understandings of quantum theory. Scientific realists usually claim that this problem is settled by solving the measurement problem. Nonetheless, people disagree about which is the best solution. In this paper I argue that the disagreement among certain views can be tracked down to the fact that there are different views about what the realism problem is supposed to be. I distinguish between an adequacy problem, a precision problem (which is the measurement problem), and a completeness problem. I argue that the reason why some people disagree is that they have different realist commitments: ‘relaxed’ realists like proponents of the information-theoretical interpretation of quantum theory, think it is enough to solve the adequacy problem, ‘modest’ realists like wavefunction realists instead believe that there is also a precision problem, while ‘robust’ realists like primitive ontologists insist that quantum theory, even if it solves the precision problem, still needs to be suitably completed. These attitudes are explained by the type of theories one finds satisfactory: while relaxed realists favor principle theories, robust realists prefer constructive theories, and modest realists provide non-constructive dynamical hybrids as long as they preserve locality and separability. This clarifies why the proponents of the information-theoretical approach endorse standard quantum mechanics with the collapse rule, wavefunction realists favor the many-worlds theory or GRW, and primitive ontologists support the pilot-wave theory.