In general relativity, time (as a constituent of spacetime) can be thought of as part of the fabric of the universe, whereas in quantum mechanics time is a parameter that governs the evolution of a quantum system. Puzzlingly, however, some mathematical attempts to merge general relativity and quantum mechanics end up without any role for time whatsoever. The time parameter simply disappears from the equations,30 leaving one with the impression that we actually live in a block universe composed only of three spatial dimensions.
