Index Key:  PHY054
Author:     lord corwin
Subject:    Relativity of spin
Text:       Is it not a basic assumption in relativity theory an object is 
motionless relative to itself?  If this is so, should this not also include 
spin?  It seems to me that with only itself as a reference, an object cannot 
be spinning, but if this were so, then I would not understand how central 
force could work, or even exist.

Response #:  1 of 1
Author:      Arthur Smith
Text:        Well, relativity and quantum mechanics have not been reconciled  
...yet... Actually, though, your statement is not really true.  A point object 
ought to be motionless with respect to itself, yes, but an extended object can 
be rotating, and there is a real meaning to rotation in our universe.  
Relativity eliminates the idea of a special frame of reference for 
translational motion, but there is still a special rotational frame of 
reference in our universe, and an object that is rotating relative to this 
frame really does experience the centripetal acceleration and corresponding 
apparent centrifugal force that tends to pull rotating objects apart.  And, I 
guess, an elementary particle with spin really has some angular momentum.