# Can spin be modeled as a spinning vector until "measured" ?

#### Jilang

I was wondering it the projection of the measurement axes onto a spinning vector modelled by a plane would produce correlations of entangled particles in line with what is found by experiment. Does anyone know of any discussions on this subject? Would this lead to stronger correlations than spin modelled as a vector?

Related Quantum Physics News on Phys.org

#### HomogenousCow

Spin is sort of like a physical rotation but not in physical space, so no you can't model it as a physical rotation.

#### Jilang

Usually it's a vector right? I meant that the direction of the vector is rotating.

#### Mentz114

Gold Member
I was wondering it the projection of the measurement axes onto a spinning vector modelled by a plane would produce correlations of entangled particles in line with what is found by experiment. Does anyone know of any discussions on this subject? Would this lead to stronger correlations than spin modelled as a vector?
No. What you propose is local hidden-variable theory.

#### gre_abandon

You know for a spin 1/2 particle its state is represented by a vector in C^2 and measurement is modeled as a projection. I am not sure what you are really asking but I think reading a book on quantum computation will help clarify your question. Generally any book on quantum computation will talk about spin 1/2, measurement, entanglement etc.

#### Jilang

I am wondering if it could be modelled as a real vector in three dimensional space spinning very fast in a plane until a magnetic field is introduced, upon which it precesses around the field instead?

#### gre_abandon

I am wondering if it could be modelled as a real vector in three dimensional space spinning very fast in a plane until a magnetic field is introduced, upon which it precesses around the field instead?
No, the state of a spin 1/2 particle is a vector in 2d complex vector space rather than a vector in 3d real space.

#### Jilang

Isn't the state just a representation of what we might find on measurement? Isn't QM silent about what is going on until that point?

#### Hornbein

My favorite article on the interprettion of spin is:
http://people.westminstercollege.edu/faculty/ccline/courses/phys425/AJP_54(6)_p500.pdf
Ohanian clains that spin is actual angular momentum contained in the momentum density of the wave function, intgrated over space.
Thanks for this, I've been look for such a thing. This is pretty much what I thought, that it is essentially circular polarization, but I didn't have the math to back it up.

The ultrasimple version is derived from an earthy expression of James Carville. Why does the electron spin? Because it can. If a physical system has a degree of freedom, it will use it if it can.

#### Jilang

I have a problem with the Bloch sphere. The poles represent the z components of spin rather than the spin itself.....

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving