When you connect an odd number of digital logic inverters in a
ring, you’ll get a Ring Oscillator – one of the simplest types.
This configuration has no stable state, so the 1s and 0s chase
each other around the ring, creating oscillations. Normally this
isn’t easy to visualize, but Make Flickr Pool contributor
ellindsey000 made a pendant that illustrates the principle
beautifully: This actually looks much better in person — I’m at
the 26C3 conference, where someone (sorry, I’ll try to get your
name!) built a replica based on ellindsey000′s photos. The LEDs
are ultraviolet, causing different spots in the center marble
(which contains uranium) to glow. What the video above doesn’t
show is that the UV LEDs are barely visible and the glow inside
the marble seems to move almost as if it was a liquid. The
schematic matches the construction in circular symmetry – both
are beautiful: More pictures: complete gallery, including how it
looks in daylight.