Impossible Event
In probability theory, one says that an event happens almost surely (sometimes abbreviated as a.s.) if it happens with probability one. The concept is analogous to the concept of "almost everywhere" in measure theory. While there is no difference between almost surely and surely (that is, entirely certain to happen) in many basic probability experiments, the distinction is important in more complex cases relating to some sort of infinity. For instance, the term is often encountered in questions that involve infinite time, regularity properties or infinite-dimensional spaces such as function spaces. Basic examples of use include the law of large numbers (strong form) or continuity of Brownian paths.
Almost never describes the opposite of almost surely; an event which happens with probability zero happens almost never.
Read more about Impossible Event: Formal Definition, "Almost Sure" Versus "sure", Asymptotically Almost Surely
Famous quotes containing the words impossible and/or event:
“There are very few things impossible in themselves; and we do not want means to conquer difficulties so much as application and resolution in the use of means.”
—François, Duc De La Rochefoucauld (1613–1680)
“A society which allows an abominable event to burgeon from its dungheap and grow on its surface is like a man who lets a fly crawl unheeded across his face or saliva dribble unstemmed from his mouth—either epileptic or dead.”
—Jean Baudrillard (b. 1929)