spin...spin....

[tomc]

Hello,

 

My name is Tom - I'm new to the Science Forums. I am not a scientist - just someone who has a general interest in physics. Not sure if this is the proper area in which to ask for HELP regarding the spin of a particle.

 

Up to now, my searches have lead me to believe that "spin" is a term that refers to a paticular "behavior" of a particle with fractional and whole number notation and does not imply actual rotation of a particle. This "behavior" could have been given any term.

 

However, I don't quite understand what this particle "behavior" is.

 

Any help would be appreciated.

 

Thanks,

 

Tom C

[AlphaNumeric]

Classically, like Newtonian dynamics, has angular momentum obeying the equation [math][L_{i},L_{j}] = \epsilon_{ijk}L_{k}[/math]. Quantum spin obeys the equation [math][s_{i},S_{j}] = \epsilon_{ijk}S_{k}[/math]. So they have the same mathematical form and so they are called 'spin' in both cases.

 

I doubt you recognise the equations I've just posted, but I don't have time to explain them.

[Klaynos]

Basically spin is a result that drops out of quantum mechanics, we call it spin and draw a comparison to classical angular momentum because it has the same mathematical form, and some very similar effects such as conservation of angular momentum.

[swansont]

As previous posters have stated, the behavior is angular momentum, but is not due to any physical motion such as rotation or revolution about some axis.

 

The fractional or whole number notation is the projection of the angular momentum vector along an axis. The notation AlphaNumeric mentioned means that the various components don't commute — you can't know them simultaneously. So we choose one axis to look at (usually labeled as the z axis) and measure the value of the projection of ther angular momentum onto that axis. Then, in units of [math]\hbar[/math], you can have half-integral or integral units of angular momentum, e.g. 1/2 or 1. This is quantized, so changes in the projection of the spin happen in whole units, so a spin 1/2 particle can be "spin up," with [math]\frac{1}{2}\hbar[/math] or "spin down, with [math]-\frac{1}{2}\hbar[/math], but no value in between. Similarly, a spin 1 particle will have a projection of 1, 0 or -1.

[Tom Vose]

Hello,

 

My name is Tom - I'm new to the Science Forums. I am not a scientist - just someone who has a general interest in physics. Not sure if this is the proper area in which to ask for HELP regarding the spin of a particle.

 

Up to now, my searches have lead me to believe that "spin" is a term that refers to a paticular "behavior" of a particle with fractional and whole number notation and does not imply actual rotation of a particle. This "behavior" could have been given any term.

 

However, I don't quite understand what this particle "behavior" is.

 

Any help would be appreciated.

 

Thanks,

 

Tom C

 

 

Hi, Tom... It's Tom...

 

The reason why it can't refer to an actual spin, as in a classical spin rotation as that of a planet, is that a pointlike particle cannot spin on an axis with a recognizable radius. So a pointlike particle can have a dipole moment and an angular frequency, but cannot have any three-dimensional qualities.

 

 

The angular momentum of particle is then said to have a similar math to that of the spin of a particle. [math]S_{ij}S_{j} = \epsilon_{ijk}L_{k}[/math] where [math]L[/math] is replaced by [math]S[/math].

 

If an electron had a classical spin, it would need to spin faster than light itself.