Comments on A Neighborhood of Infinity: The Curious Rotational Memory of the Electron, Par...

Nice exposition!

Possibly worth pointing ou...

2007-04-02T12:00:00.000-07:00

Nice exposition!

Possibly worth pointing out that the universal cover is actually "universal" in the technical sense that it's initial in some appropriate category, here the category of covers of X and homotopy classes of (surjective?) maps.

My quantum mechanics prof demonstrated SU(2) using...

2007-04-02T10:22:00.000-07:00

My quantum mechanics prof demonstrated SU(2) using a belt as well. I thought he was just a little eccentric, I didn't realise it was a trick due to Dirac.

There was a talk at Perimeter Institute a while ago by Sundance Bilson-Thompson, who is trying to build a preon model out of braids and ribbons. If his model is true, the electron is described by SU(2) because it is really made of tiny belts!

How about, for an N-fold cover, take a belt that's...

2007-04-01T14:42:00.000-07:00

How about, for an N-fold cover, take a belt that's N times the circumference of a wheel, and span it out with another wheel, mounted just to help keeping things tight - resulting in something vaguely like a bicycle chain mechanism.

Now, for each revolution of the wheel, viz every 2π rotation, you end up at a different point along the belt, but after N of them, you get back to the point you started.

Would this capture the structure needed?

Derek,

That's the Feyman plate trick which ...

2007-03-31T19:43:00.000-07:00

Derek,

That's the Feyman plate trick which I was lucky enough to see Feynman perform many years ago.

Another way to demonstrate the double cover that y...

2007-03-31T19:39:00.000-07:00

Another way to demonstrate the double cover that you can do in the comfort of your own home is to rotate your hand at the wrist keeping your palm facing upward at all times through 360 and then 720 degree rotation. At 360 degrees your arm certainly will not be in it's original state, but it will at 720.