Google seems to have jumped the gun by a few minutes, but their title image tells me that today is M.C. Escher's birthday! Well, it would be if he hadn't been born 105 years ago. His art has lost some of its mind-bending power through overexposure, but the stairs from Labyrinth are a great example of his lasting influence.

Escher's art, while great fodder for college dorm room posters, is also a jumping point off for brilliant discussions on recursion and counterpoint in another favorite book of mine, Goedel, Escher, Bach: The Eternal Golden Braid. Zeno's paradoxes of motion, explaining why motion is impossible, Lewis Carroll's Tortoise and Achilles, Alan Turing, and an artificial intelligence named SHRDLU all make fascinating appearances. This book was formative in my intellectual growth as a youngster, but only after rereading it recently did I realize that I hadn't understood any of it. Douglas Hofstadter is clearly a mad genius. Check it out if you can - -it's HUGE, but you can read sections one by one.