A widely accepted belief or theory is an orthodoxy. You could call the scientific theory of gravity an orthodoxy, since it's generally considered to be an established fact.
The word orthodoxy comes from the Greek root words orthos, which means right, true or straight, and doxa, opinion. So orthodoxy describes the one true opinion. The noun orthodoxy, pronounced "OR-thuh-dock-see," is most commonly used to talk about religious beliefs. When you conform to the orthodoxy of a particular religion, you follow its accepted doctrines, like a Christian's belief in an all-powerful God.