Usual spacetimes have no representation of the present time, or the difference between past, present,and future; thus they do not represent the flow of time as experienced in macrophysics, chemistry, biology, and the mind. I propose here a more realistic spacetime model: an evolving block universe, where the future boundary of spacetime represents the present time,and changes as time evolves along timelike worldlines. This necessarily involves existence of preferred surfaces of change that form the future boundary of spacetime; I argue these do indeed exist in any realistic spacetime model (the symmetry of the theory is broken by the geometry of the solution). I show how the evolution of these models may be expressed in usual ADM terms as long as the surfaces remain spacelike, and argue that this viewpoint automatically provides chronology protection. Issues remain as to what happens if these surfaces become timelike: I argue that this can only happen in extreme circumstances associated with back hole formation.
Reference: arXiv:1208.2611