NOVA: “Particles Unknown” (Sprockets Music, WGBH, PBS, 2021)

by Mark Gabrish Conlan • Copyright © 2021 by Mark Gabrish Conlan • All rights reserved

Last night I watched two interesting but somewhat frustrating documentaries on PBS’s science night, Wednesday: a NOVA segment called “Particles Unknown” dealing with the neutrino and an episode of an apparently short-lived show (imdb.com lists only four shows, all from 2018) called Impossible Builds about particularly weird and difficult construction projects. When I went to school we were still being taught in science classes that there were just three components of atoms – protons, neutrons and electrons – even though by the 1960’s others had already been documented and there was a whole new scientific discipline, particle physics, that researched them. I was still being taught the comfortable model of an atom as being like an infinitesimally smaller version of a solar system – a nucleus of protons and neutrons, with a bunch of electrons orbiting the nucleus like planets. It wasn’t until I got to high school that I was introduced to Heisenberg’s “uncertainty principle,” which among other things said that electrons don’t orbit their nuclei in neat little circular or oval paths, but they move in fields of probability and we need elaborate equations to determine the likely odds that an electron is in a particular part of space relative both to its nucleus and everything else. (I’m probably way underexplaining this and any real scientist who reads this will probably laugh his or her head off – and I say “his or her” because, despite the scientific world’s partially earned reputation for sexism, a lot of the talking heads interviewed for this show were women particle physicists.)

Like a lot of other subatomic particles beyond the basic three, the neutrino was first thought of as a hypothesis before there was any objective evidence for its existence; as it often has in its almost 100-year-old history as a discipline, particle physics had run into a problem where the experiments they could do were generating results that could only be explained if something they didn’t know existed was causing them. The problem was something called “beta decay,” in which atoms lose bits of negative charge and appear to lose energy in the process – violating the principle of so-called “conservation of energy,” which holds that energy can change forms but never be lost completely. If the principle of conservation of energy was correct, the only way to explain beta decay was if some other particle was emerging and carrying off that energy with it. A German physicist named Wolfgang Pauli published a paper in 1930 that first suggested the possibility of a neutrino (which he named for the Italian word neutra, meaning neutral – because his hypothesized that the neutrino had no electric charge: this was actually two years before British physicist James Chadwick announced his discovery of the neutron, a particle slightly larger than a proton with no charge that is included in almost all atomic nuclei). In 1934 Enrico Fermi, still heading a physics group at the University of Rome (five years before he fled fascism and ended up in the U.S., where in 1942 he built the first nuclear reactor and helped pave the way for nuclear weapons), published his own paper arguing for the existence of both neutrinos and positrons (particles the size of electrons but with a positive instead of a negative charge).

Having decided that neutrinos exist, the next step facing particle physicists was finding a way to detect them, which since they’re so very tiny and disappear almost immediately is not easy to do. In 1956, four American researchers – Clyde Cowan, Frederick Reines, Francis Harrison and Harold Knuse – published a paper in Science in which they claimed to have found neutrinos being produced by nuclear reactors, along with something called an “electron antineutrino,” which is an electron produced when a neutron splits and becomes a proton (apparently the neutron is simply a proton plus an electron, and when it breaks apart it becomes a big particle with a positive charge and a much smaller particle with a negative one, the same size and charge as an electron but carrying a lot more energy). The Wikipedia page describes their experiment as follows: “[A]ntineutrinos created in a nuclear reactor by beta decay reacted with protons to produce neutrons and positrons. The positron quickly finds an electron, and they annihilate each other. The two resulting gamma rays (γ) are detectable. The neutron can be detected by its capture on an appropriate nucleus, releasing a gamma ray. The coincidence of both events – positron annihilation and neutron capture – gives a unique signature of an antineutrino interaction.”

Unfortunately, this experiment only produced one-third the number of neutrinos the researchers were expecting, and after several failures physicists came to the conclusion that there were actually three kinds – called “flavors” – of neutrinos and that Cowan, Reines and their colleagues were only detecting one flavor. Later attempts to measure neutrinos from the world’s largest and most powerful nuclear reactor – the sun – also led to results that counted only one-half to one-third of the number they were expecting, which became known as the “solar neutrino problem.” The explanation physicists came up with was that not only are there at least three flavors of neutrinos, plus a fourth flavor they hadn’t known about before, but neutrinos are perpetually changing flavors. This in turn meant that, whereas physicists had previously assumed neutrinos have no mass, they must have mass because, according to Einstein’s theories, only something with mass can change shape. The show ends with the provocative notion that that mysterious fourth flavor of neutrino might be a bridge between the matter and energy we know about and the so-called “dark matter” and “dark energy” that they estimate makes up 95 percent of the stuff in the universe.

This NOVA episode was introduced, as usual, with a sponsor acknowledgment to the “David H. Koch Fund for Science” – which used to be called the “David H. Koch Fund for the Advancement of Science” and which always raises my hackles because David H. Koch and his brother Charles are also ultra-Right-wing political donors who, by denying human-caused climate change themselves (they’re part of an ultra-rich family that made their money in fossil fuels) and funding politicians who are against doing anything to stop it, they are retarding the advancement of science as well as threatening the human race’s very survival. It’s one of those fascinating programs that is told in the usual golly-gee-whillikers manner of most science programs on TV and proposes an intriguing scientific mystery that doesn’t seem to have any real-world utility. It’s hard for me to get excited about subatomic physics when the two biggest things that have happened as the result of it – nuclear weapons and nuclear power – are both disastrous for the potential future of the human race. Despite some so-called “environmentalists” who are insisting against all evidence to the contrary that nuclear power is a reasonable alternative to carbon fuels because it doesn’t involve combustion (forgetting not only the inherent danger all nuclear energy poses to human survival but the huge carbon footprint of the nuclear fuel cycle as a whole), I’ve long believed all uses of nuclear energy (with a few strictly limited exceptions, such as X-rays and radiation treatments for cancer) should be banned. I don’t mind giving scientists money to explore neutrinos, but I’m not going to expect their researchers to benefit ordinary people’s lives in any way.