Why do Planes Board from the Front?

One thing I noticed while traveling recently is that my planes appeared to board starting with the front, and ending with the back.  This inevitably creates a long line as people in the front stow their baggage in the overhead compartments and take their seats.  Meanwhile, everyone else has to wait to even get to their section of the plane.

Why not board starting with the people in the back?  That way you could have a lot more people stowing luggage and taking their seats at the same time.  The whole process would take less time this way.

One might argue that people in the front should board first because of special status, including flying first class.  But that assumes that this is a benefit.  You have more room to stretch in the airport waiting area than on the plane (even first class) and if you are sitting on the aisle, many people who have to pass you will bump you with their luggage.

Here's an analysis of the problem by a physicist: http://phys.org/news122215582.html.