Quantum Theory Drawn from a QBist Perspective

Quantum theory is the foundation for nearly all modern physics.  Since its discovery, it has never failed, and without it our technological society would not exist.  Without the quantum, there would be no transistors, no lasers, no smart phones—we might as well be living in 1907.  But this foundation actually sits on shifty sands.  Some physicists look into quantum theory and see evidence that the universe is a vast web of instantaneous connections (Einstein called it “spooky action at a distance”); some look into it and see not one universe, but a continuum of parallel worlds (Marvel Comics calls it “the multiverse”).  Still others—a tiny minority—look into quantum theory and see an overpowering message that its terms have not so much to do with nature itself, but with our place in nature.  This is the stance of QBism.  In QBism, the role of quantum theory’s mathematical formalism is to make better decisions and better gambles as we confront nature.  Metaphorically, the physicist is like a tiny euglena caught up in nature’s stream, and quantum theory, like the euglena’s tail, is his best tool yet for navigating that course.  But this is not to say that we might not learn about nature itself by studying the tool’s composition, form, and function.  Not by accident, this takes us back to 1907, when the philosopher William James first espoused the philosophy of pragmatism.  Crucial to pragmatism is the idea that our world is always on the make; the big bang—the very creation of the universe—is not just something remote and at the beginning of time, but intimate and all around us.  As James put it, pragmatism gives a vision of the world where “new being comes in local spots and patches.”  So too does QBism, but now the thought is based on our best physical theory.  In this talk, I will aim to explain these ideas to a broad audience.