I read on the 'Ask A Mathematician/Ask A Physicist' blog that sound waves behave differently in an even-number of dimensions than they do in odd-number dimensions - that they 'double-back'. Why is this - and what does 'double-back' mean? http://www.askamathematician.com/2012/05/q-what-would-life-be-like-in-higher-dimensions/ "Sound waves too. In odd dimensions other than 1 (3, 5, 7, …) waves behave the way we normally see and hear things: a wave is formed, it moves out, and it keeps going. However, in even dimensions, and 1 as well, (1, 2, 4, 6, …) waves “double back” on themselves. You can see this in ripples on the surface of water (2-D waves)."