Gregory Benford's "Reason not to Publish" (flash fiction, science fiction): Who is God, & why did He create the universe?
This is not a story for sf novices. You must have already read a lot of genre fiction to not throw out this story as utter nonsense; I know I would have done it at that stage.
Story summary.It's about a "mathematical physicist" who has observed jitters during a leisure walk in the woods: "jitter was not a fluttering bird, but an entire tree jumping in and out of focus... whole tree and all around it flickered, went grainy and sometimes vanished."
He has seen this behavior before - in computer simulations when the machine resources are low. Lot of investigations & observations at different places, & he realizes he & the world around him are parts of a computer simulation - computer at the edge of its capacity.
There is an implicit assumption in the story that Programmer God cares more about humans, than about rest of the Creation! Now with the human world population increasing, & computer resources already running low, God must delete some details.
How to survive so you don't get deleted? Make yourself interesting to Programmer God! How?
Fact sheet.First published: Nature, December 2007.
Note: Download link no longer exist; see Ross' comment at bottom.