Causality, Symmetries, and Quantum Mechanics

It is argued that there is no evidence for causality as a metaphysical relation in quantum phenomena. The assumption that there are no causal laws, but only probabilities for physical processes constrained by symmetries, leads naturally to quantum mechanics. In particular, an argument is made for why there are probability amplitudes that are complex numbers, which obey the Born rule for quantum probabilities. This argument generalizes the Feynman path integral formulation of quantum mechanics to include all possible actions that are allowed by symmetries, but only the lowest order terms are observable at the presently accessible energy scales. The notion of relational reality is introduced in order to give physical meaning to probabilities. This appears to give rise to a new interpretation of quantum mechanics.