Greg Egan explores the concept of Wang tiles as a naturally occurring computer in his excellent novel "Diaspora": http://www.gregegan.net/DIASPORA/DIASPORA.htm

Greg Egan explores the concept of Wang tiles as a naturally occurring computer in his excellent novel "Diaspora": http://www.gregegan.net/DIASPORA/DIASPORA.html http://www.gregegan.net/DIASPORA/DIASPORA.html It gets a bit dense at times, but I would highly recommend it, especially if you are interested in turing complete systems.