> no known physical laws seem to require a single direction.
What would a physical law that required a single direction look like?
What would a physical law that required a single direction look like?
That physical limitation on how fast a mass can move is what keeps causality in check and things like the grandfather paradox from being possible.
Edit: now that I think more on it, this is probably a better law that ensures causality: https://en.wikipedia.org/wiki/Entropy#Second_law_of_thermody...