6. Interpreting the quantum

This chapter surveys various proposals to interpret—that is, make sense of—quantum mechanics. We could attempt to think of quantum mechanics in purely instrumentalist terms, as an algorithm to predict observed experimental results. But this fits badly with scientific practice and is probably not viable. We could attempt to modify quantum mechanics itself to resolve the paradoxes, and there are some simple models that attempt to do that: some are ‘hidden-variable’ theories that add extra properties to the theory, some are ‘dynamical-collapse’ theories that modify the theory’s equations. But none of these models succeed in reproducing quantum theory’s predictions outside a relatively narrow range of applications. Or we could try to take the apparent indefiniteness of quantum mechanics literally, and interpret it as a theory of many parallel worlds. The correct interpretation of quantum mechanics remains controversial, but the search for understanding and interpretation of the theory has led to very substantial scientific results and is likely to lead to more.