[Vo]:Measuring Spin

[Nigel Dyer]

I have been musing about spin and Leonard Susskinds lectures and books 
have got me thinking in a slightly different way:  There is very much 
LENR related, but I will start with a 'simple' question
In the Stern Gerlach experiment the act of 'measuring' the spin of the 
particle has an effect on the spin, in that the information about the 
spin in the non-measured axis has been destroyed.  In what sense has the 
state of the particles spin been changed and what mediates the change. 
Can it be thought of as in terms of a virtual photon exchange?.  I 
assume that overall there must be conservation of spin, so in what sense 
has the spin state of the rest of the system been changed?
Nigel