Upstairs is a place from which it is possible to look down on cross-sections of world lines in the mortal realm. It follows from this that the world lines of bodies Upstairs are at right angles to the world lines of bodies in the mortal realm.
However, is Upstairs also a place that changes along the same temporal dimension as the mortal realm so that it, Upstairs, is in a different state in the early twenty first century than it was in the late twentieth century? This latter proposition would entail that world lines Upstairs are parallel to those in the mortal realm.
It is also possible that, since I am blogging while reading, I am getting it all wrong. However, in that case, my errors will be way stations along the road towards completer comprehension.