Galileo/Copernicus wrote about Catholicism? If a ranking system treats your expertise in one area as being relevant to another it's not doing its job. Accepted, religion is a bit of a special case given the way it tends to encourage views on subjects as broad as "how the universe came into being" or "how to be a good person" (and those views are almost never "religion isn't your best guide"), but a good page ranking algorithm should still be able to only apply "expertise" rating when it applies specifically to terms in the search phrase.