"Mass-energy is neither created nor destroyed..." It is then an effect of that rule, combined with our previous observation of the ship itself, which tells us that there's a ship that went over the cosmological horizon and now we can't see it any more.

It seems to me that this might be a point where logical reasoning takes it over from causal/graphical models, which in turn suggests why there are some problems with thinking about the laws of physics as nodes in a graph or even arrows as opposed to... well, I'm not really sure what specifically - or perhaps I'm just overapplying a lesson from the nature of logic where AI researchers tried to squeeze all the variety of cognitive processes into a logical reasoner and spectacularly failed at it.

Causal models, being as powerfull as they are, represent a similar temptation as logic did, and we should be wary not to make the same old (essentialy "hammer & nail") mistake, I think.

(Just thought I'd mention this so I don't forget this strange sense of something left not-quite-completely explained.)