No physical mechanisms predefines future events (or is there one ?).
So, I could state that the future does not exist yet and the past as ceased to exist.
in that statement I have a problem with the definition of existence. Does the definition of existence exist itself ? This is (is it ?) more a problem of terminology than philosophy or physics.
Anthropologically speaking this is the best answer. Our brain needs a certain span of time to establish perceived reality.