A life in spacetime
A worldline places events in a temporal geometry. It helps us think beyond an isolated present without supplying a theory of the observer.
A worldline is a path through spacetime representing the successive events associated with an idealised object. A person has spatial extent, so a worldtube is more precise for the whole body; a worldline can represent a chosen point or an approximation. In either case, the temporal description reaches beyond a single instantaneous condition.
Thinking this way changes the question of identity. A person’s childhood and adulthood can occupy different portions of one temporally extended history. The description accommodates substantial change without demanding that the person have the same properties at every event. Whether those portions constitute one enduring person remains a philosophical question, not something settled by drawing a line.
The connection to eternalism is suggestive. A temporal geometry represents earlier and later events within a common structure. Eternalism takes the further step of granting those events equal ontological standing. A model’s ability to represent a history and a claim that all represented events exist should remain distinguishable.
The distinction also corrects a tempting image of “everything happening simultaneously.” Equal existence is not simultaneity. Events can exist at different times. Einstein’s treatment of time coordinates concerns how temporal relationships are assigned; it does not compress every event into one enormous present.
Finally, the geometry does not require a consciousness travelling outside the physical description. It represents the organism’s successive conditions, including whatever physical processes accompany experience. A separate witness may be proposed, but it adds explanatory obligations. Its existence cannot be inferred just because the worldline is depicted all at once on a page.
The restrained implication is already powerful. A life can be considered through its temporal extent rather than identified exclusively with its latest condition. Eternalism makes that extent ontological. A theory of consciousness must then explain how experience belongs to such a life; a theory of personal identity must explain what unifies it.