The difference between an event being

If an event is

For example, imagine throwing a dart at a square, and imagine that this square is the only thing in the universe. There is physically nowhere else for the dart to land. Then, the event that "the dart hits the square" is a sure event. No other alternative is imaginable.

Next, consider the event that "the dart hits the diagonal of the square exactly". The probability that the dart lands on any subregion of the square is equal to the area of that subregion. But, since the area of the diagonal of the square is zero, the probability that the dart lands exactly on the diagonal is zero. So, the dart will

Source: Wikipedia

*almost sure*and*sure*is the same as the subtle difference between something happening*with probability 1*and happening*always*.If an event is

*sure*, then it will always happen. No other event (even events with probability 0) can possibly occur. If an event is*almost sure*, then there are other events that could happen, but they happen*almost never*, that is with probability 0.**Cool Example**: Throwing a dartFor example, imagine throwing a dart at a square, and imagine that this square is the only thing in the universe. There is physically nowhere else for the dart to land. Then, the event that "the dart hits the square" is a sure event. No other alternative is imaginable.

Next, consider the event that "the dart hits the diagonal of the square exactly". The probability that the dart lands on any subregion of the square is equal to the area of that subregion. But, since the area of the diagonal of the square is zero, the probability that the dart lands exactly on the diagonal is zero. So, the dart will

**almost surely**not land on the diagonal, or indeed any other given line or point. Notice that even though there is zero probability that it will happen, it is still possible.Source: Wikipedia

Mahalanobis - am 2007-04-02 22:37 - Rubrik: mathstat