Are ‘identical quantum particles’ weakly discernible objects?

Abstract

According to classical physics the world consists of individuals, i.e., distinct objects that can bear their own characteristic names. In physics this individuality is standardly seen not as something primitive, but as based on qualitative physical differences – in accordance with Leibniz’s principle of the identity of indiscernibles (PII). In quantum theory the status of individual objects is notoriously more controversial than in classical physics. The symmetrization postulates that apply to the states of so-called identical particles appear to show that these “particles” do not obey Leibniz’s principle; and this in turn raises doubts about whether they are objects at all. Conventional wisdom among physicists is that a field-theoretical picture is actually more appropriate than a particle one (according to this point of view there are no particles, but only field quanta); by contrast, philosophers of physics seem to tend more to the view that quantum mechanics is about particles but that their individuality defies PII (see Muller and Saunders 2008, for relevant quotations).