An argument for the block universe

2.) If two events are simultaneous, they are equally real. (So if, for example, we believe that whatever happens now is real, then two events happening now are both real; if we believe that future events are unreal, then simultaneous events in the future are both unreal.)

3.) For any two events X and Y related in time, there is one observer who sees T as simultaneous with X, and another observer who sees T as simultaneous with Y.

(To use the concrete example of the YouTube video I linked to, make T the lightning strike at the front of the train, X the lightning strike at the back, then imagine Y as a third lightning strike that the guy on the train sees as simultaneous with T.)

4.) Thus, X and Y are both simultaneous with T.

5.) Therefore if X is real, then Y is real.

6.) But X and Y are any two events related in time, whether the past and present, the present and future, the past and future, etc.

7.) Therefore, if any event in time is real, then all of them are real.