Plate trick

In mathematics and physics, the plate trick is any of several particular physical demonstrations of the mathematical theorem that SU(2) double covers SO(3), or sometimes this fact itself. 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.

Sometimes this is called Feynman's plate trick or Dirac's belt trick. Topologists usually call this the belt trick, although some knot theorists, such as Louis Kauffman have dubbed it the quaternionic handshake. The reference to quaternions is because the action of SU(2) considered as the unit quaternions, on the 2-sphere, considered as pure unit quaternions, gives the double covering.

The plate trick is the mathematical physics reason why particles in a four-dimensional spacetime are either fermions or bosons.

ee also

*Orientation entanglement
*Tangloids

External links

* [http://www.evl.uic.edu/hypercomplex/html/dirac.html Air on the Dirac Strings]
* [http://gregegan.customer.netspace.net.au/APPLETS/21/21.html Animation of Dirac belt trick]
* [http://www.evl.uic.edu/hypercomplex/html/handshake.html Video of Kauffman's quaternionic handshake]