Science Forums 2

[CraigD]

Originally Posted by Pluto

… subatomic particles have a spin and you would expect the seed to form matter that has a spin. Maybe this can be explained by the wave theory and the wave centres of every so called particle.

To the best of my knowledge, there’s no connection between spin in quantum mechanics and spin in classical mechanics (ie: angular momentum) we’ve been discussing in this thread. Note that, per the first linked article above:

the spin of quantum mechanical systems ("particle spin") possess several non-classical features and for such systems spin angular momentum cannot be associated with rotation but instead refers only to the presence of an 'angular momentum-like' property.

In short, the use of the word “spin” in quantum mechanics appear to be one of may cases where it’s connection to classical mechanics is only an analogy intended to help make the often counterintuitive formalism of QM more comprehensible. I’ve long wondered if this nomenclatural approach is effective – that is, if, when considering all potential students, it enhances or retards comprehension.

It’s pretty easy to show that particle spin and angular momentum are unrelated, via thought experiment such as the following:

• You have 2 solid spheres made of the same material (eg: iron cannon balls), one massing 1 kg, the other 100, floating in vacuum (eg: in outer space).
• By applying force to either sphere, you can give either one an arbitrarily great or small angular momentum. The small sphere can be made to spin fast, or the large one made to have no detectable spin.
• However, the total quantum spin of the particles in the spheres does not change. The 100 kg sphere has 100 times the total quantum spin of the 1 kg sphere.
• Therefore, there is no connection between the angular momentum of a macroscopic body and the quantum spin of its constituent particles.