Re: [Phys-l] basic laws of motion +- vectors +- angular momentum

[John Denker <jsd@av8n.com>]

On 12/09/2008 12:32 PM, Steve Highland wrote:
> Thanks very much for bringing this up again.  It has bugged me for ages.

:-)

> Is there any way to "work backwards" from quantum mechanical angular
> momentum ideas to some sort of classical analog?

Sure.  Start from the Lagrangian.  The Lagrangian
knows all and tells all.  The QM phase is exp(i S)
where S is the action.  Now pass to the classical
limit (via the "stationary phase" approximation).
This leaves us with the principle of least action
(or rather extremal action).  This produces all
of classical mechanics.

This process of going from QM action to classical
action is profoundly analogous to going from
physical optics to geometric optics.

> And is rotation a relative or absolute concept? 

Rotation = angle is relative.
Rotation = /rate/ of rotation is absolute.

This is different from linear motion, where both
position and rate-of-change of position are relative.

> I really have a big problem with imagining the
> whole universe rotating around a particle instead of the particle spinning
> while the universe just sits there. 

Well, good, you /should/ have problem with that.
The spinning universe would have readily observable
centrifugal fields and Coriolis effects.