The Ready gang have been doing more experiments lately, and I ought to summarise the recent discoveries in reaction-diffusion systems. You may remember Robert Munafo’s ‘U-skate’ configuration, which propagates through space even when bombarded with radiation:
[youtube=http://www.youtube.com/watch?v=_sir7yMLvIo]
Well, lately Tim Hutton and Robert Munafo have collaborated to extend this work into three dimensions. The Munafo glider doesn’t function properly, but Tim realised it can be stabilised by adding three nearby spheres. The entire complex moves along its axis of symmetry. (Warning: these videos are on a toroidal grid, so configurations can appear to exit one face of the box and re-emerge from the opposite face.)
[youtube=http://www.youtube.com/watch?v=WYZVffOaRgA]
It is very sensitive to initial conditions. Drawing it incorrectly can cause the front to detach from the stabilising balls and twist in a double-helix, as Robert did inadvertently:
[youtube=http://www.youtube.com/watch?v=0Fp6v0m801g]
The story doesn’t end here. Robert added a fourth sphere to it, which still results in a functional glider. However, it breaks the symmetry, causing it to exhibit a rotational bias. This propels the glider in a helical path. Helical paths are also followed by flying insects with damaged wings, or indeed electrons in a uniform magnetic field.
[youtube=http://www.youtube.com/watch?v=B03lcPEmSOQ]
If you watch the video, you’ll see the regular and helical gliders bounce off of each other a couple of times before coalescing and cohering. The result itself moves even more chaotically than before. To return to the entomological analogy, try gluing two fruit flies together and watch how the complex moves*. I can guarantee it will resemble this video.
*Actually, don’t do it. Drosophila melanogasters have rights!
Interesting things can happen in two dimensions as well. Check out Tim Hutton’s video of SmoothLife, a continuous cellular automaton by Stephen Rafler:
[youtube=http://www.youtube.com/watch?v=KJe9H6qS82I]
The original program uses the Fast Fourier Transform to accelerate computation. This is not the time to discuss Fourier transforms and their applications, but I won’t object to you tentatively supposing that there might be a small probability that such a topic may later be considered for possible inclusion on cp4space. Don’t quote me on that, though.