> All observers will agree that Alice throws a ball which Bill later catches I think this needs qualification. If I am stood directly behind Alice or Bill the

> All observers will agree that Alice throws a ball which Bill later catches I think this needs qualification. If I am stood directly behind Alice or Bill then it is possible I never see the interaction at all even though I am an observer, just as if I hold a two identical pencils together and look at them from the correct angle I observe only a single pencil. The important thing is in all cases, observers "see" space-time interactions as the geodesic of the event projected on to their own observational frame. Through that projection it is possible to lose degrees of freedom which can be space-time etc. It's through this projection that HUP emerges since if in the observational frame the time dimension is limited, the projected time axis of the event tends toward zero.