Particles are strange. In more than one way: for example they behave as if they were spinning, like a top. But they aren’t moving at all. Even if they were, trying to imagine how some of them “spin” would probably melt your brain. The property that measures this “spinning” (though nothing is moving at all here!) is, creatively, called spin.

Some particles behave the same way no matter how you rotate them, they have spin 0. Some others look different if you rotate them, but will come back full circle after… well… a full circle turn: they have spin 1, like a spinning top. Some others come back the same after just half a turn (so not at all like a spin): they have spin 2. And so on.

The sphere on the left doesn’t change, no matter how much you turn it, like a spin 0 particle. The middle one is the same if you give it a full turn, like spin 1. The one on the right comes back after just half a turn, like it had spin2

Some particles have an additional coat of weird: they come back only after two full turns, they have spin 1/2. All the electrons, all protons and neutrons in all the atoms, indeed indeed all the quarks anywhere in the universe have spin 1/2.

These particles are called fermions, because Enrico Fermi was one of the people who described how they behave. Quantum mechanics dictates that no two fermions can be in the same exact same quantum state. This rule is called the exclusion principle, it’s what keeps atoms from melting into chaos. Ultimately, the exclusion principle is the thread suspending our universe’s order over an abyss of indistinguishable particles.

You could call this a fermion-based source of boson radiation. Credit: pexels/pixabay

Particles of integer spin (0, 1, …) don’t have to deal with this nuisance. They can traverse the quantum world oblivious of what their siblings do. All photons (spin 1) coming out of an ideal laser at the same time would be in the exact same quantum state.

Photons don’t usually come out of a laser exactly at the same time, and they are not exactly at the same place. But in principle they could be in the exact same place. Electrons couldn’t CC-BY-SA Andrea Pacelli/flickr

They are called bosons in honor of the work of Satyendra Nath Bose, who worked on describing them. Their job is hitting particles, to make them “feel” some fundamental interaction. Photons carry electromagnetic interactions, the Higgs boson carries the Higgs mechanism, which gives particles their mass, as Dr. Don Lincoln from Fermilab explains more in detail (though the video is a little dated).

If, instead of interacting with one of these so-called “fields”, particles interact with each other, they exchange short-lived “virtual” bosons, but that’s another story. So, if you’re wondering, you are 0% bosons.

If you want more
  • The great Veritasium made a nice video with an explanation of how spin actually works

Cover photo: CC0 Pexels/Pixabay


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