Even neutrinos have weight problems: 2015 Nobel Prize for Physics

Remember how in elementary school they taught you everything is made of atoms? And then remember how in middle school they said, no wait, atoms are actually made of electrons and protons and neutrons? Well, hold your breath because today, you’re going to learn about the most fundamental of all particles.

(In light of the recent Nobel Physics Prize, I’ll be focusing on the enigma that are neutrinos; more on that later.)

All of our scientific achievements and discoveries since the 30s have led to this conclusion: If you were to take Thor’s hammer and break any piece of matter- from a brick to a person as thick as a brick (you know who I’m talking about) – and continue to break it into smaller and smaller things, you’ll end up with the same set of particles. These particles are called fundamental particles and all matter in the universe in its entirety stems from these fundamental particles. Let that sink in for a moment. Everything that you have ever touched or seen or eaten is just a different arrangement of a handful of particles. From spiders to clowns. Everything. I’ll wait while you gather the blown-away pieces of your mind (which, by the way, is also made of these same particles.)

So yes. Fundamental particles. They can be categorized into two types: Quarks and Leptons. Each of these types has six corresponding particles. Here’s a neat little infographic, showing the classification:

Yes. Quarks have names such as “charm” and “strange.”

Since I’d be focusing on neutrinos, here’s a short introduction: They were considered to be massless particles (keep reading), are extremely small and electrically neutral.

Apart from these elementary particles there are also four fundamental forces. These comprise of the familiar electromagnetic force and gravitational force, and the not-so-familiar strong force and weak force. All of this, the particles and the forces are bundled neatly in a model called the Standard Model. Overall, the Standard Model gives a pretty good approximation of the world around us. Of course, it does leave some unanswered questions about things like dark matter and dark energy but we’ll leave that for another blog post.

What’s so special about neutrinos?

The 2015 Nobel Prize for Physics was awarded to Takaaki Kajita and Arthur B. McDonald, for their work on neutrinos. And this hasn’t been the first time work on neutrinos has resulted in a Nobel either. So what is so special about neutrinos?

The prediction of neutrinos was actually a desperate attempt at solving a conservation of energy problem. Wolfgang Pauli, the person who predicted the particle, didn’t believe in the existence of the particle himself! But predict he did, and the particle was found. In fact, the world is swarming with neutrinos. We’re being bombarded with these frisky particles every day. But because of the fact that they are electrically neutral and interact only by the weak force*, they are pretty hard to detect. To actually detect them, we need to get rid of interference from all the other sources. Basically, build your laboratories underground. (Now I know what else to do in my secret underground lair.)

Once the neutrinos were detected, however, scientists were faced with another problem. And it went something like this: The scientists knew that the sun produces one kind of neutrinos (the electron neutrinos) by Beta decay. (The original conservation of energy problem to solve which the neutrinos were predicted.) By doing some math (taking into account the energy produced by the sun etc) they calculated the number of electron neutrinos that should reach Earth. A whole lot of number crunching later, the scientists reached a theoretical number of these neutrinos that should be detected in their observatories. But because we live in a universe which is huge and complicated and which never ceases to surprise us, the scientists detected a far lesser number. A lot of head scratching followed and the question remained: What happened to the rest of these neutrinos? Did they disintegrate into nothingness? Did they fly straight to platform 9 ¾. Maybe the folks at Hogwarts are detecting an unexpected numbers of neutrinos too. If they do science that is. But I digress.

The answer to this question was partly obtained when other kinds or flavors of neutrinos were discovered. The observatories were then re-calibrated to detect these other kinds of neutrinos as well. And lo and behold, the number of theoretical solar (or electron) neutrinos matched with the total number of neutrinos detected. But then, this posed another problem. Somehow the neutrinos were changing form/flavor as they traversed the distance to the observatory. This was problematic because according to the standard model, the neutrinos didn’t have mass and this change in flavor of the neutrino could only be theoretically explained by giving certain mass to the neutrinos! (I won’t go deeper into this, at the moment.)

The Nobel Laureates, Takaaki Kajita and Arthur B. McDonald, proved that neutrinos do in fact change flavors and so must have some mass. This means that the Standard Model is incomplete. It further goes on to prove that even the most widely accepted theories can be fallible or incomplete. In Science, there is always room for discovery.

Until next time.

*Weak force is appreciable only at very small distance. So in effect, for a neutrino-particle interaction to occur, they would have to be virtually touching each other.


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