Title: Problem of time - Wikipedia
Headings: Problem of time
Problem of time
Contents
Time in quantum mechanics
Overturning of absolute time in general relativity
Proposed solutions to the problem of time
Weyl time in scale-invariant quantum gravity
The thermal time hypothesis
References
Further reading

Content: It is regarded as part of an a priori given classical background with a well defined value. In fact, the classical treatment of time is deeply intertwined with the Copenhagen interpretation of quantum mechanics, and, thus, with the conceptual foundations of quantum theory: all measurements of observables are made at certain instants of time and probabilities are only assigned to such measurements. Special relativity has modified the notion of time. But from a fixed Lorentz observer's viewpoint time remains a distinguished, absolute, external, global parameter. The Newtonian notion of time essentially carries over to special relativistic systems, hidden in the spacetime structure. Overturning of absolute time in general relativity
Though classically spacetime appears to be an absolute background, general relativity reveals that spacetime is actually dynamical; gravity is a manifestation of spacetime geometry. Matter reacts with spacetime: Spacetime tells matter how to move;