Saturday, August 13, 2011

Bosons and Fermions

Want to know what bosons and fermions are in simple terms, without any misspellings? This article gives it to you in very "simple" terms.

The difference between them is just spin. But in this context, spin is a quantum number of angular momentum. It is a bit like the particle is spinning, but that is really just an analogy, since point-like fundamental particles could not spin, and anyway fermions have a spin such that in a classical analogy they would have to go round twice to get back where they started. Quantum mechanics is full of semi-misleading analogies like this.

Regardless, spin is important.

Bosons have, by definition, integer spin. The Higgs has zero, the gluon, photon, W and Z all have one, and the graviton is postulated to have two units of spin. Quarks, electrons and neutrinos are fermions, and all have a half unit of spin.

There! You are now ready to work on a QFT problem! :)

All kidding aside, sometime it is handy to have a simple, laymen-level explanation. One would hope that this will lead to more questions and more attempts at understanding.


1 comment:

Steve said...

I would actually claim that the above is wrong. When we use the words boson or fermion, we are referring to the statistics (how the wavefunction(al) behaves under interchange of identical particles). This is why they are called Bose-ons and Fermi-ons after Bose-Einstein statistics and Fermi-Dirac statistics, respectively. It is true that spin and statistics are coupled (in dimensions greater than two), but I would not say that this is the correct definition of the terms. At the very least, it leaves out perhaps the most important difference between the two.