Wait for it to render, then click some column to reveal the pattern. It is Ok if it is difficult to understand. It is still cool (my favorite elementary cellular automaton, too!) I will share a project that can do all 256 rules as soon as I make it a nice GUI. This one is kind of a case study of Rule 73, because it identifies oscellations.
MORE: http://scratch.mit.edu/projects/44786142/ SIMPLE EXPLANATION Rule 73 is a "cellular automaton", meaning it manipulates arrays of 1s and 0s to form output. The black pixels are 1s, and the white are 0s. Each line of pixels is used to create the next by applying some rule (in this case, Rule 73). In this way, extremely simple rules can create patterns with interesting mathematical properties. COMPLEX EXPLANATION The first line of pixels is randomly generated. The nth line is rule 73 applied to the (n - 1)th line. Separators are placed on either end of the screen to prevent unwanted behavior brought about by the edges having permanent 0 values. Rule 73 is applied for some pixel at position x in line n (written as the point (x, n)) by checking the pixels at (x - 1, n - 1), (x, n - 1), and (x + 1, n - 1). By looking at these three pixels, we get some binary number, as black pixels are treated as 1 and white are 0. If x is not on the screen, it is treated as 0. Depending on this number, we get the next generation. 000 -> 1 001 -> 0 010 -> 0 011 -> 1 100 -> 0 101 -> 0 110 -> 1 111 -> 0 It is called "rule 73" because if we look at this sequence and write it as "01001001", this is the binary form of the number 73. Rule 73 results in interesting patterns. The vertical separators (the pattern 0110) remain permanent after they first appear, meaning the array gets segmented into discrete, isolated "channels". Because these channels are self-contained, by the pigenhole principle, we can expect some form of oscellation. Any arbitrary line of pixels is bound to reappear within sufficient time (specifically, 2^(channel width) + 1). This is interesting to observe, as random pixels will eventually converge into these oscellating patterns. Once the array has been loaded, click on some channel to analyze the oscellation. It will color each period red or blue. More: http://en.wikipedia.org/wiki/Elementary_cellular_automaton
