The concept of time travel and its effects on causality can be quite complex and speculative since time travel is purely hypothetical at this point. When discussing the scenario of someone traveling through time and witnessing their own future, it raises questions about the nature of causality and free will.
In a deterministic view of time, where events are predetermined and every action has a predetermined consequence, it could be argued that the person's observation of their own future was always part of the timeline. In this case, their actions in the past were already influenced by their knowledge of the future they witnessed.
However, if we consider a view of time where events are not predetermined and free will exists, the situation becomes more complicated. If someone travels to the future and witnesses events, their knowledge of the future could potentially influence their actions when they return to their own time. By changing their behavior based on what they saw, they could inadvertently alter the course of events, leading to a different future from what they initially witnessed.
This concept aligns with the idea of the Novikov self-consistency principle, which suggests that any actions taken by a time traveler in the past were always part of the timeline and do not create new causal loops or paradoxes. Essentially, any actions they take in the past were already part of history and cannot change it.
Ultimately, the effects of observing one's own future while time traveling would depend on the rules and mechanics of time travel in that hypothetical scenario. Different theories and fictional depictions of time travel propose varying possibilities and outcomes.