>>9249300No, the outcome can't be known. But, if an observer a half billion light years away is heading towards you, even at a brisk walking speed, their extended light cone is overlapping with your future of about 200 years. Now, from that distance, they obviously can't see that future, nor ever hope to interact with it, hence the 'extended' qualifier, but that isn't without consequences, and at smaller distances, and much higher speeds, this becomes a problem.
It's also possible to imagine spacetime geometries where it's an immediate problem and observations can be made. There probably isn't any combination of physical events that can cause such arrangements (certainly we've yet to observe any), but there's nothing otherwise preventing spacetime from taking such configurations. Just because all your tools are wood, and the wall is iron, does not mean there's nothing on the other side of the wall.
Similarly, one does not, for instance, assume all possibilities are taking place on the other side of an event horizon, only that you can't mathematically predict them or ever interact with them, but at the same time, naked singularities are theoretically possible, which would give you a view into a zone where space and time have swapped.
And of course, as a result of relativity and the fact that spacetime intervals can be negative, were FTL travel a thing, time travel in either direction would be a consequence. The causal violations this would cause is among the reasons we scoff when anyone suggests FTL is possible. In an undetermined universe, they would non-issue.
The future maybe undeterminable, but it is not undetermined.
