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.
Originally from http://i.imgur.com/ckxfccq.gif
, and found via +Jane Shevtsov
and +W Younes