00 1 Physics with exotic probability theory

Probability theory can be modified in essentially one way while maintaining consistency with the basic Bayesian framework. This modification results in copies of standard probability theory for real, complex or quaternion probabilities. These copies, in turn, allow one to derive quantum theory while restoring standard probability theory in the classical limit. The argument leading to these three copies constrain physical theories in the same sense that Cox’s original arguments constrain alternatives to standard probability theory. This sequence is presented in some detail with emphasis on questions beyond basic quantum theory where new insights are needed.