the plate trick, also known as Feynman’s plate trick, Dirac’s belt trick, Dirac’s string trick, Balinese cup trick, spinor spanner, Bredon high-five, or quaternionic handshake, is any of several particular physical demonstrations of the mathematical theorem that SU(2) double-covers SO(3). The usual demonstration, as indicated by the name, is to hold a plate on one’s flat palm, then perform two subsequent rotations of the arm holding the plate, which results in the original position. In the cup variant, supposedly inspired by a Balinese candle dance, an open cup of water or wine is held in ones hand and rotated 720 degrees, or any multiple thereof, without spilling the liquid or loosening ones grip on the cup.
added 2013-08-06T14:01:03Z by anders