Reposting from Less Wrong:
What started my deconversion from realism is watching smart people argue about interpretations of QM, Boltzmann brains and other untestable ontologies. After a while these debates started to seem silly to me, so I had to figure out why. Additionally, I wanted to distill the minimum ontology, something which needn’t be a subject of pointless argument, but only of experimental checking. Eventually I decided that external reality is just an assumption, like any other. This seems to work for me, and saves me a lot of worrying about untestables. Most physicists follow this pragmatic approach, except for a few tenured dudes who can afford to speculate on any topic they like. Max Tegmark and Don Page are more or less famous examples. But few physicists worry about formalizing their ontology of pragmatism. They follow the standard meaning of the terms exist, real, true, etc., and when these terms lead to untestable speculations, their pragmatism takes over and they lose interest, except maybe for some idle chat over a beer. A fine example of compartmentalization. I’ve been trying to decompartmentalize and see where the pragmatic approach leads, and my interpretation of the instrumentalism is the current outcome. It lets me to spot early many statements implications of which a pragmatist would eventually ignore, which is quite satisfying. I am not saying that I have finally worked out the One True Ontology, or that I have resolved every issue to my satisfaction, but it’s the best I’ve been able to cobble together. And I am not willing to trade it back for a highly compartmentalized version of realism.