Spin

One of the most important characteristics of quantum mechanics is the idea of spin of sub atomic particles.  Spin for a subatomic particle is a property that looks , when measured, a bit like spin or rotation of magnet. It is also known as intrinsic spin.  

The main difference in contrast to normal spin is  that quantum spin is quantised in one direction or another, in other words it is in discrete states.  Because it is quantised it means it doesn't actually spin. It is just a property like positive or negative charge. 

Spin takes on values that are either integer or non-integer. For example:

Non-integer spin


Integer spin:

  • 0 - spin particles ( these are scalar particles, like the Higgs Boson)
  • 1 - spin particles ( these are force carriers like photons, gluons)


Spin is a useful way to classify particles because of the way they end up behaving ( their behaviour is described using something called quantum statistics, which is just a way of calculating a probability of a particle being in a particular place)

Particles with non-integer spin are called fermions, particles with integer spin are called bosons. 



The stern gerlach experiment showed that silver atoms are deflected in a magnetic field. They are either effected one of two ways: up or down;  in contrast to just a smear as would be expected if it was a classical mini magnet. image: wikipedia

Spin of the electrons is what gives elements all their unique properties including how magnetic they are. It also leads to the the property of the Pauli’s Exclusion Principle of electron shells/levels in the elements.


Reference and further detailed reading


Commentary

Here is a really useful video describing the concept of quantum spin. It includes a really nice animation of the weirdness of spin.