Antimatter Pseudoscience
Few topics in science excite the popular imagination more than antimatter, perhaps because the idea sounds like science fiction that you can really believe in. For the same reason, it should not be surprising that when a story about antimatter surfaces in the news cycle—as regularly happens—the real science sometimes gets parked on the shelf and media-promoted pseudoscience takes over.
Matter
To put antimatter pseudoscience in perspective, we first need to recall a few things about the genuine article. Atoms of the chemical elements that form the matter of the world around us are themselves constructed from just three varieties of fundamental particle: protons, which carry a positive electric charge; electrons, which carry an equal amount of negative charge; and neutrons, which have no charge at all, although, like the other two, they have magnetic properties. The hydrogen atom is the simplest of all. It consists of a single electron bound by electrical attraction to a nucleus consisting of a single proton. It is therefore electrically neutral. Atoms of heavier elements just have more electrons bound to their nuclei consisting of an equal number of protons and a variable number of neutrons. They are, then, normally neutral.
Another Matter
Even before all this was established, the idea was entertained that a kind of mirror matter might exist made of particles with reverse “signed” attributes like charge and magnetism. Thus Arthur Schuster (Schuster 1898), observing that electric charge plays an important role in nature, asked the rhetorical question, “If there is negative electricity, why not negative gold?” Some thirty years later, English physicist Paul Dirac showed that if quantum mechanics and special relativity—the two cornerstones of modern physics—are to hold simultaneously, it must be possible for counterparts of the three fundamental particles to exist that have the same mass as, but opposite electric, magnetic, and other properties to, the originals. These he called “antiparticles.” We might then legitimately ask: If there are antiparticles, why not antimatter?1 Foreseeing this possibility, Dirac (Dirac 1933) intimated: “We must regard it as an accident that the earth (and presumably the whole solar system) contains a preponderance of negative electrons and positive protons. It is quite possible that for some of the stars it is the other way about… . There would be no way of distinguishing them by present astronomical methods.” Positively charged antielectrons, produced in the atmosphere by cosmic rays, were duly discovered (and soon afterwards found emerging from some radioactive substances). A few decades later negatively charged antiprotons were produced in the laboratory by directing fast-moving protons into metal targets. Antineutrons, displaying opposite magnetic properties to neutrons, were almost immediately added to the list, and nuclei of heavy antihydrogen (which consist of one antineutron and one antiproton) followed ten years or so later. Very recently, a few antihelium nuclei have been seen.