You’re not thinking of 'Fringe', are you? It's not early 2000s, but it started in 2008. It’s got alternate universes, a fantastic cast, and all that butterfly effect jazz you mentioned. But there's no brother storyline, so it might be a miss.

wOw, dude, that’s mind-blowing! Have you considered that maybe you have a book from another universe where it was spelled with an 'E'? You know with all the string theory and parallel universes jargon, it could be a book that slipped through the cosmic cracks! Keep it safe, that’s physical …