Scientists say they have cracked a nearly eight-decade-old riddle involving the Moebius strip, a mathematical phenomenon that has also become an icon of art. Popularised by the Dutch artist MC Escher, a Moebius strip entails taking a strip of paper or some other flexible material. You take one end of the strip, twist it through 180 degrees, and then tape it to the other end. This creates a loop that has an intriguing quality, dazzlingly exploited by Escher, in that it only has one side. Since 1930, the Moebius strip has been a classic poser for experts in mechanics. The...