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The Massive Many

Week of June 8, 1998

I wonder sometimes if tackling such issues as the eventual fate of the Universe is something for the Bitesized Astronomer to try on these pages. However, there are times that the news is very big, but it just seems too weird for most people that aren't astronomers. When that happens, I feel like I have to butt in.

Neutrinos are odd little subatomic particles (like electrons and protons) that have never been directly seen. Their existence was first postulated to help balance out certain events that were observed by subatomic physicists (no, not little teensy scientists, but people that study very small things). Sine then, their existence has been proven and there have even been different types of these "little neutral ones" (which is what the name neutrino literally means). The Sun gives off neutrinos as part of the atomic fusion going on in the Sun's core. A team of physicists were out to study the Sun's neutrinos, but got a big surprise.

One of the biggest questions about neutrinos is whether they have mass or not. Lots of particles are massless; photons are a good example. One way to figure this out is has to do with the fact that anything without mass travels at the speed of light, and anything with mass must travel slower. If we could measure the speed of a neutrino, we could figure out the mass. The problem is, if they do travel slower than light, it's only a hair slower, and we cannot measure the difference.

A team of physicists recently set out to observe solar neutrinos, but got the surprise of their lives when they found (through a complicated and subtle chain of reasoning) that the tiny ethereal neutrino does indeed appear to have a very small, but definite mass. Why is this important? What's the big deal about such a small particle?

The answer this time is simple: sheer numbers. The neutrino is a common product of almost all nuclear reactions, so common, in fact that the Universe is almost literally filled with them. Billions pass through you every second! (Don't worry, they are so unreactive that you could live a lifetime without having even one getting absorbed by your body, and even then it would only affect one tiny atom out of countless ones inside of you). If these little guys have mass, then by the virtue of their numbers alone they may actually contribute significantly to the mass of the Universe, and that is a very big question indeed.

The conclusion that neutrinos have mass has not yet been confirmed, but if true it has profound effects on almost every aspect of cosmology and physics. I've said it before, and no doubt I'll say it again: it is an amazing thing that something like the entire Universe can be directly affected by something so small.

©2008 Phil Plait. All Rights Reserved.

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