Great illustration of collective phenomena

 This is a great illustration of collective phenomena.  If you look closely, each dot is just moving around in a regular circle; but because the different circles are out of phase with each other, when you back away you see waves steadily moving across the screen.  It's a simple demonstration of how large-scale, collective phenomena can emerge from very simple small-scale behavior.  Things like this happen all over the place: water waves and sound waves, for example, work in basically the same way, with the small back-and-forth motions of individual molecules leading to compression patterns moving through the air. 

(Courtesy of forwarded mail from David Chen)