Do We Need to Work 40 Hours a Week?

There are a lot of things that we take for granted in our day to day lives, and one of the big ones is how we spend a good portion of our waking hours.  Based on sophisticated youtube analytics we can determine that a majority of people watching this video are full-time employees working 40 hour weeks at their jobs  So is 40 hours really the optimal work week, and are their alternatives that are based more on economics rather than tradition?