Abstract

There is a long tradition, very much alive in the present day, of irrealism about quantum states—that is, of denying that quantum states represent anything in physical reality. In this chapter, I will argue that the grounds we have for taking quantum states to represent physical properties of the systems to which they are ascribed are as strong as the grounds we have for taking atoms or electromagnetic waves to be real and to have something like the properties we ascribe to them. I will take it for granted that we do, indeed, have sufficient grounds for belief in the reality of atoms and electromagnetic waves. It is not my intention to try to convince a committed scientific anti-realist to make an exception for quantum states. The issue at hand is orthogonal to the age-old struggle between scientific realists and anti-realists. My targets here are those who deny that quantum states represent anything in physical reality from a standpoint that holds that one can, indeed, under certain circumstances ascribe reality to entities that are not directly observable, but take it that there are reasons specific to the quantum context for denying ontological import to quantum states.