You'll find this in the collection, Zima Blue and Other Stories.

It's one of those sci-fi stories that goes on about quantum babble and how there's a universe for every possible outcome of every possible situation.   To be honest, i think this theory is no different than the theory of god, both total nonsense made up by people who really don't understand Nature and how it works.

Then Alastair has our protagonists in this book starting a war over whether god is right or quantum babble is right -- which is just silly when all intelligent people already know that they're both utter nonsense, which i hope is the point that Alastair is making in this story?   Although, thinking about it, he has wrote some other really bizarre stuff that makes no sense in other books, like the sheep in Inhibitor Phase; so maybe Alastair really is a die-hard quantum babble-ist and thinks that quantum babble-ists everywhere should rise up and start a war against the god grovellers?   Who knows the true thoughts of fiction writers?

But, whatever, have a read, it's a fairly good story.

Coming next in the Alastair Reynolds reading list, from the year 2000, will be Merlin's Gun. ( )

The Kiwidinok are aliens who arrived on Earth bearing the gift of a new religion, based around quantum physics, as they can perceive realities branching. On Mars, a disciple of this religion has a fateful meeting with its human founder, who has a lot to reveal about the real truth of the religion. ( )