An introduction to lockless algorithms

I don't think it's really about relativity; anything that you can model as a directed graph function just as well as a representation of a partial ordering.

For example think of two cars going from A to B along two different roads. Any time a junction joins the two roads you *might* be able to say who is ahead at that moment. However while the roads are running parallel it's possible (but not certain) that you cannot say that. That is because the points along the two routes form a partial ordering.