On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) [(s+)_z 
> + (s-)_z] .
> If the x-component of spin is measured by passing the spin-1/2 particle 
> through a Stern-Gerlach with its field oriented along the x-axis, the 
> particle will ALWAYS emerge 'up'.

*Why?  Won't the measured value be along the x axis in both directions, in 
effect Up or Dn? AG*

In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]
> and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]
> (where _z, _x, are the z-component and the x-component of spin)
> so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = (s+)_x.   (pure state, not 
> mixture state)..
> AGrayson2000 asked "If a system is in a superposition of states, whatever 
> value measured, will be repeated if the same system is repeatedly 
> measured.  But what happens if the system is in a mixed state?"
> Does Everett's "relative state interpretation" show how to interpret a 
> real superposition (like the above, in which the particle will always 
> emerge 'up') and how to interpret a mixture (in which the particle will 
> emerge 50% 'up' or 50% 'down')?

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