A causal domain is just a collection of things linked by mutual cause-and-effect relationships." "But isn't everything in the universe so linked?" "Depends on how their light cones are arranged. We can't affect things in our past. Some things are too far away to affect us in any way that matters." "But still, you can't really draw hard and fast boundaries between causal domains." "In general, no. But you are much more strongly webbed together with me by cause and effect than you are with an alien in a faraway galaxy. So, depending on what level of approximation you're willing to put up with, you could say that you and I belong together in one causal domain, and the alien belongs in another.
( Neal Stephenson )
[ Anathem ]
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