What the heck is a boson?

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

The attractive physics of voting

Elections are complicated stuff: a bunch of people decide on what to do, a number of factors playing in. It looks pretty much impossible to understand physically.

Sure, nobody knows what goes through everyone else’s mind, but it’s possible to figure out some society-scale stuff. The principle is similar to teasing out values like air temperature and pressure in a room, without the need to track each air molecule as it goes about its business.

Indeed, physicists used an enormous playbook of models to tease out a bunch of details about society-scale stuff, from voter turnout to candidate performance. It all starts from how we make decisions, and the simplest way to look at it is magnets. Yup, magnets.

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Spins arranged on a grid, opposing ones (red links) are unstable and tend to flip to align to their neighbors (green links)

How magnets pick their poles is a staple of statistical physics. We model them a number of spins, tiny magnetic compass needles, that point up or down—vote democrat or republican, if you will. They each have a small magnetic field, and they all influence each other, trying to align to their neighbors or getting their neighbors to align with them. Likewise, our friends, relatives, and acquaintances occasionally convince us of their arguments, just as we convince them.

Of course, decision-making is immensely more complicated than that—magnetism is more involved too, by the way. Nevertheless, we can single out the effect of different factors, like the impact of social media.

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Credit: Gerd Altmann/pixabay

Facebook (far from being the only one) selectively presents us with voices we agree with, tuning out the rest. In magnetism terms, it’s as if spins could sever ties with neighbors pointing the opposite way. The effect? It’s easier to form bunches of aligned spins, in which no-one knows anyone that votes Trump. Society becomes polarized. Sounds familiar?

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Selective connections polarize the spin society, creating isolated clusters of spins that all stubbornly agree with each other.

This is a very simplified example (of a simple effect, for that matter). However, it shows that models can single out different effects. Therefore, they also show what knobs to turn to shift the election climate and the tone of the discourse one way or the other.

Obviously, we haven’t solved human behavior: it is very important to keep in mind that these are super-simplified models, and that a number of things factor into real-life elections. But if social and physical sciences talk, they will get better and better insights.

Meanwhile, go vote.

If you want more

Cover photo: CC0 Andreas Breitling, via pixabay.com

What the eff is an fMRI?

Some parts of the brain “light up” when we feel certain feelings, or listen to music, or tackle math problems. Certainly you’ve stumbled upon such news, given how frequently they end up in mainstream media. The technique used for these studies (and many others in neurosciences) is called functional Magnetic Resonance Imaging (or fMRI), which is an amazing thing, but also seems to have a few issues. I think we’ll be hearing about it in the near future, so it’s worth knowing what it’s all about.

An MRI machine. CC-BY-NC Penn State, via Flickr.

Let’s start from the beginning. The magnetic resonance imaging—MRI, the stuff sportspeople get done to assess injuries—uses magnetism and resonance (you don’t say!), or the unusual reaction of an object or material to stimuli of a specific frequency.

If, for example, we push someone on a swing every time they arrive all the way back, we’ll make them go higher than if we just pushed at random times. Simplifying (a lot), the MRI uses radio waves to push hydrogen atoms, of which there’s plenty in tissues rich in fat and water, like the brain.

Their nuclei have spin, a property that makes them react to magnetic fields somewhat like a compass would. The MRI machine applies a strong magnetic field, which aligns all the spins, then it hits them hits the atoms with a pulse of radio waves. If its frequency is just right (called resonance frequency), the wave will flip a few spins (not their atoms!) opposite to the magnetic field.

As soon as the pulse stops, it’s all back to normal, and atoms that flipped release a little energy. Recording these emissions with an antenna it is possible to distinguish tissues with different water contents, for example, different parts and layers of the brain, and build an image.

Simplified sketch of an MRI. The atoms (red balls) align along the green magnetic field until the magenta wave flips some of them. As soon as they can, atoms fall back to their original state, emitting energy recorded by the blue antenna. Credit: howequipmentworks.com

fMRI works by rapidly taking a lot of MRI pictures. Analyzing them we can understand what parts of the brain were more active at various time, because oxygenated blood rushes to these areas, producin a slightly different signal from that of “used” blood being flushed out.

The idea is simply genius. However, some recent studies urge caution and intense scrutiny on the statistical analysis used to process the images. In one of these studies, for example, a dead salmon seemed to react to pictures of humans.

That does not mean that the technique is rubbish, it just means we need to be careful. These studies are fundamental for research, because they let us identify issues. Only this way can we know what we’re doing and that we’re making the fullest and rightest use of the amazing results of spectacular techniques like fMRI.