attraction between the muon-shell of the invading atom and the nucleus of the invaded atom. The muon actually both helps the nuclei of the two atoms to approach each other and electrically shields them from mutual electrostatic repulsion.
It happens that the muonic atom can approach the other atomic nucleus closely enough for the strong force to come into play, especially if the two hydrogens are both of the deuterium variety. Fusion occurs, even in liquid hydrogen, and the muon shoots out and becomes able to "catalyze" some more fusions in the same manner, before its short lifespan finally ends.
When muon catalysis was first discovered, it was quickly analyzed to find out if the reaction could form the basis of a power plant. Unfortunately, its lifespan is too short, by a factor of five or six. (Perhaps if the atoms of deuterium, which we want to catalyze to fusion, were squeezed closer together, by a factor of more-than-that? Might "inertial-confinement fusion" efforts benefit if a few muons were injected into the implosion? It is the author's understanding that inertial-confinement fusion experiments involve a much higher squeeze than a mere factor of five or six.)
A not-formally-published analysis that the author once did, regarding muon catalysis, involved a fairly standard equation in particle physics that relates the energy and velocity of the reaction products to the probability that a particular reaction could occur (the higher the energy, the higher the velocities and the more closely the speed of light was approached, the less likely is the reaction). A speculation was formed that if the muon could somehow carry away some of the energy of the reaction of two fusing deuterons, then the reaction itself might take the form of D+D->He4, generally considered to be the "best" possible type of fusion reaction (and extremely rare in Nature). The analysis concluded that this might actually occur about 25% of the time—the muon leaves the scene of the fusion carrying quite a lot of energy and moves at a quite-high velocity—but the author knows of no tests that were conducted to measure the products of muon-catalyzed fusions in deuterium. It is still only a speculation that that possibility might ever occur.
The hypothesis described in Part Eight includes a mechanism by which a muon could be involved enough in a fusion reaction, despite not being able to "feel" the strong force, to carry away some of the energy of the reaction. This increases the author's hope that the analysis just mentioned might have some validity, even if the percentage turns out to be erroneous, and a variation of that analysis has therefore become part of the hypothesis in Part Eight.
One other thing about muons needs to be mentioned here. If a muon replaces an electron in a heavy atom like gold or mercury or lead, it will tend eventually to replace one of the innermost electrons of that atom, and, because it will orbit the nucleus 206 times closer than that electron, it will actually be orbiting the nucleus within the periphery of the nucleus. It does so without "significantly interacting" with any of the nucleons. It simply orbits due to the electromagnetic force, and doesn't normally do anything else. This means that under circumstances in which an electron (identical in most ways to a muon) might pass equally near a nucleus, we can expect that again no "significant interaction" will occur between the electron and any of the nucleons. The electromagnetic force might cause the electron to follow a hyperbolic path as it passes through the periphery of the nucleus, but nothing else need be expected.
5. Background: Metals, the Conduction Band, Alloys, and Hydrogen
In chemistry most of the chemical elements are described as having either "metallic" or "nonmetallic" properties. Some elements sometimes have properties of one and sometimes have properties of the other (tin becomes nonmetallic when the temperature drops low enough), and while these are called "transitional elements," the key observation at a given moment for any of them involves whether or not its properties are metallic.
Metals have a set of properties which are generally widely known and mostly need not be discussed here. The particular property which concerns us is the ability of a metal to conduct an electric current. This property exists because most of the atoms in the metal contribute an electron into a shared pool which is known as "the conduction band." Those electrons are able to freely move throughout the body of the metal, in-between its constituent atoms.
When different metals are mixed together (usually in the molten state), a thing known as an "alloy" is created and it generally remains true that most of the atoms in that alloy, regardless of type, have contributed an electron into the conduction band of the overall metal. (Alloys tend to be poorer conductors than pure metals, so it could well be true that many atoms fail to contribute.)
The chemical element hydrogen is normally a non-metal, but various theorists have reached the conclusion that it should be possible for hydrogen to exist in a metallic state. Special conditions such as extremely high pressures are expected to be required for metallic hydrogen to exist. Nevertheless, the idea that metallic hydrogen can exist at all automatically means two things which are very relevant to the hypothesis presented in Part Eight. First, for it to be metallic, it must have a conduction band. Second, for a conduction band to exist, each one of many individual atoms of hydrogen must have given away its sole electron into the shared pool! This means that metallic hydrogen is a place where loose nuclei can exist, "voluntarily" stripped of the electrons that normally prevent nuclei from getting anywhere near each other!
Another fact is that hydrogen is able to permeate certain metals, such as the element palladium, to a large extent. The extent can be truly remarkable. If you take an empty container and an equal container that surrounds a solid mass of pure palladium, and then apply pressure to feed hydrogen into the containers, you can actually pack more hydrogen into the solid palladium than you can pack into the empty container, at the same pressure! We might conclude from that observation the idea that the hydrogen is "alloying" with the palladium. It is quite logical that if hydrogen can exist in a metallic state, then it should also be able to exist as an alloying substance. So, isn't it obvious that if a hydrogen can add its sole electron into the conduction band of the palladium, no different from some other atom in an alloy donating an electron, then the extraordinarily tiny bare hydrogen nucleus will be floating in the crystal lattice of the metal—and that greater numbers of tiny nuclei can fit in a given volume of space than can fit whole hydrogen molecules there?
One problem with the preceding is that the chemical bond between two hydrogen atoms is a fairly strong bond, and that if the molecule breaks in order for the atoms to form an alloy, then where did the energy come from to break
