PFE016: Fermions (Halloween edition)

My Halloween costume this year focused more on execution than actual appearance. Jeff and I were identical fermions, specifically electrons.

This may be a little bit outside the scope of this blog, but is fun anyways and shows some of the truly bizarre properties of physics.

As you may or may not be aware, everything that you see around you is made up of particles. Teeny little things that each have different properties. Most of your regular everyday stuff is protons, neutrons, and electrons. Light is also a particle, (sort of). There are many more, enough that in the 60s the term "particle zoo" was coined to describe all of them.

All of these particles can be classified into either fermions or bosons based on their spin. Spin should not be thought of as anything like a baseball spinning, but rather as simply a property of the particle. For example, protons, neutrons, and electrons are all fermions while photons (light particles) are bosons.

One of the main properties of fermions is that two identical fermions cannot exist in the same state at the same time. So two electrons cannot be at the same energy and the same spin direction. Electrons can be spin up or spin down so, for Halloween, Jeff and I wore the same thing and were never in the same room unless one was standing and the other sitting (spin up vs. spin down).

$$|\downarrow\rangle_{PD}\otimes|\uparrow\rangle_{JM}\quad\quad\quad\quad=\quad\quad\quad\quad|\uparrow\rangle_{PD}\otimes|\downarrow\rangle_{JM}$$

I included the relevant braket notation for the physicists present. It is interesting to note that each state is identical. That is, in the eyes of physics, there is no way to differentiate between electrons. So one of them spin up and the other spin down is entirely indistinguishable from when the spins are flipped.

Those are some awfully scary fermions.