This is a way of plotting the behavior of many Jot programs at once. Each circle corresponds to one program, and the size and color of the circle is determined by how long the program takes to execute. If the program does not terminate in the allotted time, then we color the circle black.
Programs are generated as random bit strings, since any string of bits is a syntactically valid Jot program. We map these strings of bits into a 2D plane using the Hilbert Curve.
The maximum program length starts small but increases over time. Since longer programs tend to take longer to run, this is why the circles get larger over time.