The philosopher William James once wrote, “Like the old woman who described the world as resting on a rock, and then explained that rock to be supported by another rock, and finally said it was ‘rocks all the way down,’ he who believes this to be a radically moral universe must hold the moral order to rest either on an absolute and ultimate should or on a series of shoulds ‘all the way down’.” QBism is an interpretation of quantum theory that stands in radical contrast to all other interpretations. This is because it views the quantum mechanical Born Rule not as a statement of an is, but as a statement of a should. In QBism, the Born Rule is a normative suggestion any sufficiently-schooled decision-making agent should strive to attain when considering various hypothetical actions she might take upon the world—it is a story not of one possible quantum measurement and the creative force it entails, but many. Yet the Born Rule, even in this normative role, is not purely logical; it is empirical. It is something we use in the light of a world whose character we have come to call “quantum’”—if the world were a different world, we would use a different calculus for making our best decisions.
But then, what does the Born Rule teach us about the actual stuff of the world? QBism finds a hint of an answer in its insistence that quantum theory be universal. On the one hand, I, a user of quantum theory, am an agent, but on the other, I am a plain old physical system to any other agent who might want to take an action upon me. Are we, the sufficiently-schooled users of quantum theory, the only lumps of matter that have the privilege to play such a dual role? QBism suspects not, but rather that the autonomy we have as agents goes all the way down—i.e., that it is the autonomy of its parts that is the basic stuff of our universe (or more properly our “pluriverse,” as James would call it).
For this project, we will gather a number of physicists, philosophers, and historians who are concerned with trying to get this question straight: What exactly is the metaphysic underlying QBism? Is there some crisp sense in which autonomy goes all the way down?