Noncausal Page-Wootters circuits

Understand

One of the most fundamental open problems in physics is the unification of general relativity and quantum theory to a theory of quantum gravity.

• An aspect that might become relevant in such a theory is that the dynamical nature of causal structure present in general relativity displays quantum uncertainty.
• This may lead to a phenomenon known as indefinite or quantum causal structure, as captured by the process matrix formalism.
• Due to the generality of that framework, however, for many process matrices there is no clear physical interpretation.