QBism — Putting Quantum Mechanics into the Right Shape

In a 1951 paper, Richard Feynman wrote “The new theory asserts that there are experiments for which the exact outcome is fundamentally unpredictable, and one has to be satisfied with computing probabilities.  But far more fundamental was the discovery that in nature the laws of combining probabilities were not those of the classical probability theory.”  QBism is an interpretation of quantum mechanics which takes this as the very essence of the theory—it’s not parallel worlds, spooky action at a distance, or alive-dead cats.  But this now defines a research program:  How best to rewrite the quantum formalism to make the point overwhelmingly obvious?  When it is done, one is left with only one remaining mystery, expressible in terms of a fantastical geometric shape.  Why this shape?  How this shape?  Come find out.