Simultaneity in Special Relativity...
The simultaneity paradoxes of special relativity can be demonstrated in a simple gedanken (thought experiment). Consider a train moving through a station, exactly its length, at nearly the speed of light. When the middle of the train is at the middle of the station, a flash bulb goes off in a camera, mounted in the center of the train, to commemorate the event.
Observers on the train and in the station observe the light moving outwards in a sphere. However, on the station, they say that the expanding shell reaches the ends of the station at the same time, while observers on the train say that the light reaches the front and back of the train at the same time. Since the train moves forward at nearly the speed of light, the back of the train will be one-fourth the way through the station when the light arrives there.
Obviously, what appears simultaneous to one observer is not simultaneous to another.
Now, let's to back to the Dirac equation and its interpretation. If past and future on the train become muddled with the present to the observer on the station, he or she can't determine exactly when the flash goes off. Simultaneity is not an issue, because the ordering of events becomes muddled.
What is the physical source of this effect? I remark that, in special relativity, the apparent mass of a rapidly moving object appears to increase indefinitely. At some point, the density of the object exceeds the Schwarzchild criteria, and it becomes a black hole. No information escapes the object, until it slows down once again.
If this last speculation holds true, it would appear that discarding uniticity and unidimensional time, with a prediction that an extended quantum charge field surrounds every macroscopic object, may have interesting dynamical consequences.