Just to be clear: the laws of physics aren't a barrier -- given a conventional reference frame, even in relativity, everyone will agree on a total order of events (e.g. when using GPS receivers, atomic clocks and doing the math correctly). The problem is reliability of components.
Ordered Sequence of Events as seen by each collaborator. That's all that matters!
Past post with discussion:
https://news.ycombinator.com/item?id=9184779
(Other posts, but no other discussion)