picturing spin

Jeff Lee · science forum beginner Joined: 18 May 2005 Posts: 3

I always hear how, under rotation, a spin 1/2 particle doesn't return to its
origin state until the rotation angle is 4\pi. Mathematically this is no
problem for me being just some facts stemming from the 2-forld cover of the
Lorentz group, but what does this rotation mean practically speaking in the
lab? Is this an active rotation? Is it passive? How do I picture this
operationally?

PD · science forum Guru Joined: 03 May 2005 Posts: 4363

Jeff Lee wrote:

Richard Schultz · science forum Guru Joined: 28 Apr 2005 Posts: 339

In article <1116430513.380163.31930@o13g2000cwo.googlegroups.com>, PD <pdraper@yahoo.com> wrote:

: This is known as the "Coffee Cup Proof of the Existence of Spinors".

I've seen a series of photographs of Richard Feynman making that demonstration
(was it in _The Feynman Lectures_?), although I believe that he either
called it or strongly implied that it should be called the "Dancing Girl
Proof of the Existence of Spinors."

-----
Richard Schultz schultr@mail.biu.ac.il
Department of Chemistry, Bar-Ilan University, Ramat-Gan, Israel
Opinions expressed are mine alone, and not those of Bar-Ilan University
-----
"Logic is a wreath of pretty flowers which smell bad."

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