Science Snippet #1

The solar neutrino problem was a long-standing mystery in physics.
When scientists first measured neutrinos coming from the Sun, they detected only about one-third of the number predicted by solar models. Initially, it wasn’t clear whether the experiments were flawed or the models of the Sun were incorrect.

It turns out that people were simply missing them! Early detectors could only detect electron neutrinos and it was later discovered that neutrinos can change “flavors”—from electron neutrinos into muon or tau neutrinos—while traveling to Earth. This was BIG NEWS in the science world because it meant that neutrinos do in fact have mass (there was even a Nobel Prize won for this). And in fact, they have three different possible mass states.

Getting complicated? Not to worry. Here’s a cool way to think of it:

Imagine you are running a coffee shop and want to create the perfect “flavour” of coffee. You do this by mixing together three different types of coffee beans from your grinder: Brazilian (mass state 1), Colombian (mass state 2), and Sumatran (mass state 3).

Here’s the menu of coffees you can make with these three mass states:

• Electrino (electron neutrino): 2 scoops Brazlian, 1 Colombian, a tiny pinch of Sumatran
• Muonccino (muon neutrino): 1 scoop Brazilian, 1 scoop Colombian, 1 scoop Sumatran
• Tau Latte (tau neutrino): A tiny pinch of Brazilian, 1 scoop Colombian, 2 scoops Sumatran

But for some reason, the barista you hired, Sunny, only knows how to make the Electrino, so that’s all she makes. Also she refuses to come to the coffee shop, so she brews it all at home and pours in in a large carafe, which gets brought to the shop by a courier. To make things worse, the carafe she picked has a bizarre property: instead of keeping the coffee blended, it keeps the three bean types separate as they travel, and each type sinks through the carafe at a slightly different speed.

• The light Brazilian grounds (mass state 1) sink the fastest.
• The medium Colombian grounds (mass state 2) sink at a medium speed.
• The dense Sumatran grounds (mass state 3) sink the slowest.

After its journey, you open the carafe and pour the whole thing into a new cup, mixing whatever arrived together.

• What she sent: The perfect “Electrino” mix.
• What arrived: Because the grounds sank at different speeds, the proportion that comes out is now different. The fast Brazilian grounds might have mostly settled, while the slow Sumatran grounds are still suspended.

Your customer takes a sip. Instead of the bright “Electrino” flavor, they taste something much darker and richer. Based on the taste, they declare: “This is a Tau Latte!”.

The flavor has oscillated from an Electrino to a Tau Latte during its journey.

Why this proves mass:

• If the beans were massless (or all had the same mass): All the coffee grounds would sink through the carafe at the exact same speed. The original perfect mixture would be perfectly preserved. Your customer would receive an “Electrino” and detect exactly what was sent. No oscillation would occur.
• The fact that the final flavor changed proves that the three components (the mass states) behaved differently during the journey because of their inherent properties. The only way for them to separate is if they have different “mass,” which causes them to sink at different rates.

The oscillation is the change in the detectable flavor mixture caused by the mass-dependent travel of the individual components. Now you know some neutrino physics! And now I’m craving coffee…