h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

It was off topic for the thread where you posed the question, so here's my poor answer:

Executive summary: spin is one of those quantum things that you just have to accept that have no analogue in the macroscopic world. It doesn't mean "spin" like you'd spin a ball on its axis. Similarly, there is a quantum property called "colour" which has nothing to do with reflecting certain frequencies of light and absorbing others.

OK, longer and more complicated answer: go here:

http://hyperphysics.phy-astr.gsu.edu/hbase/spin.html

Selected highlights from that are:

"Experimental evidence like the hydrogen fine structure and the Stern-Gerlach experiment suggest that an electron has an intrinsic angular momentum, independent of its orbital angular momentum..."

Translation: it APPEARS, if you measure certain of its properties in a certain way, to be a point charge spinning on its axis. But...

"An angular momentum ... could indeed arise from a spinning sphere of charge, but this classical picture cannot fit the size or quantized nature of the electron spin. The property called electron spin must be considered to be a quantum concept without detailed classical analogy."

Translation: it's weird, and you can't picture what it's really like because it isn't LIKE anything you have any experience of directly.

"The term "electron spin" is not to be taken literally in the classical sense ... electrons show no "size"... down to a resolution of about 10^-3 fermis, and at that size a preposterously high spin rate of some 10^32 radian/s would be required to match the observed angular momentum."

Translation: only SOME of the measurements you make on electrons make them appear to be spinning point charges. Some other measurements you can make show how that model is an inadequate description.

Hope this helps...

H.