What exists resides in the now. What exists is temporal because it is dynamic and constantly changes and the change is tensed because cause and effect produces the change.
What exists in the now creates tensed facts that are unalterable.
The change is deterministic outside of the observer's ability to choose. The ability to choose comes from the capacity to remember what things were like and the ability to anticipate what things will be like. Memory and reason.
Choice creates the potential to break the bonds of determinism.
Once the choice is made it becomes unalterable.
The now is eternal. Divide infinity in half, what do you have? Calculate how many moments eternity holds?....
The truth is always simple.