Published online by Cambridge University Press: 01 January 2022
In a series of recent papers, Simon Saunders, Fred Muller, and Michael Seevinck have collectively argued, against the folklore, that some nontrivial version of Leibniz’s principle of the identity of indiscernibles is upheld in quantum mechanics. They argue that all particles—fermions, paraparticles, anyons, even bosons—may be weakly discerned by some physical relation. Here I show that their arguments make illegitimate appeal to nonsymmetric, that is, permutation-noninvariant, quantities and that therefore their conclusions do not go through. However, I show that alternative, symmetric quantities may be found to do the required work. I conclude that the Saunders-Muller-Seevinck heterodoxy can be saved.
Many thanks to Simon Saunders, Fred Muller, and Michael Seevinck for several illuminating conversations on this topic. I am also grateful to Steven French, James Ladyman, and audiences in Paris, Bristol, and Cambridge. A large debt of gratitude is owed to Nick Huggett and Jeremy Butterfield for extensive comments, conversation, and encouragement. Finally, I am grateful to the Arts and Humanities Research Council and the Jacobsen Trust for their financial support during the writing of this article.