Ed. note: This is a sequel to “Random Babblings from a Confused Physicist-in-Training,” which appears in issue #50.
Events on the quantum scale depend on probability a lot, more so than on the macroscopic scale. This particle may or may not interact with that one; this reaction may or may not take place; this electron may or may not be emitted from this beta-decaying neutron. But have no fear. Such happenings are commonplace. Probability is the backbone of quantum mechanics.
And so, on the macroscopic scale, with gazillions of particles and events and reactions taken into account, we see a sort of fuzzy probability of how often this happens and how often that happens.
Speaking of beta decay, which I mentioned above, I must remark on the existence of a most peculiar particle: the neutrino. Or rather, I’ll talk about its antimatter counterpart, the antineutrino. When a neutron decays, it breaks down into four components: a proton, an electron, an antineutrino, and light.
Why, you ask, must all four components be there? Why can’t a neutron just break down into a proton plus light? Or a proton plus an electron? Or lots of electrons? The answer is simple.
The total mass of the proton, the electron, and the antineutrino is equivalent to the mass of the neutron before it decays minus the energy of the light. Mass is equivalent to energy, after all: E=mc2. Since energy must be conserved and the total mass of the electron, the proton, and the antineutrino is less than the mass of the neutron, the reaction must produce extra energy to compensate for the remaining neutron mass. That energy is emitted in the form of electromagnetic radiation, or light (though not necessarily visible light).
The proton and the electron must each be there to compensate for the mass not converted into energy. They must also be there because each is a charged particle. The proton has a +1 charge, and the electron has a -1 charge. Add them together, and you get 0, the neutral charge of the neutron. Conservation of electrical charge must be observed.
Lastly, why must there be an antineutrino? The answer is simple. Lepton number must also be conserved. What is lepton number, you ask? The electron is a lepton. There are six types of leptons: the electron, the muon, the tau particle, the electron neutrino, the muon neutrino, and the tau neutrino. Each of these has an antimatter component. The antineutrino I am referring to is the electron antineutrino, or positron antineutrino (the positron is the antielectron). It has a lepton number of 1 (as all antimatter leptons do), while the electron has a lepton number of +1. Add them together, and you get 0, the lepton number of the neutron, because neutrons are not leptons (and neither are protons).
So. This is how beta decay works.
Now I will discuss the neutrino. It has very little mass, if any. Apparently, this is a matter (pun not intended) of some controversy. It has no charge. And it interacts hardly at all. I read in a book some time ago that the average neutrino can pass through 35 million light-years of solid lead without interacting with anything. Amazing indeed.
But ... here is where this relates to probability. For if you have a gazillion neutrinos, you are bound to detect some of them. I recall vaguely some experiments in which a few dozen neutrinos were detected out of ... a really large number of them.
And of course, this relates to Hogwarts. In J.K. Rowling’s Harry Potter and the Sorcerer’s Stone, Harry receives a letter from Hogwarts School of Witchcraft and Wizardry, inviting him to attend their academy. His uncle, having something of a distaste for such matters, refuses to let Harry read it. More and more letters arrive, until piles and piles of them rain down the chimney. And Harry’s uncle keeps them all from him. This indeed does remind me of those physicists in the lab, trying to detect a few reactions out of gazillions of neutrinos that hardly interact with anything. The resemblance is clear, I hope.
And this makes me wonder why I just wrote all this about probability, neutrinos, and Hogwarts. Perhaps you can enlighten me. Alas, I am bewildered. If you are reading this editorial before most of the other content in this issue, I wish you a safe trip through the Bewildering jungle. Enjoy.
Copyright © 2003 by The Invincible Spud
