Here follows my translation into English of the very clear explanation of the physics behind the Fleischmann-Pons experiment, given in 2010 to a wide audience by the Italian theoretical physicist Emilio Del Giudice, in one of his popular conferences:
“The famous article by Fleischmann and Pons published in the ‘Journal of Electroanalytical Chemistry‘ was very well written, so Giuliano Preparata and I thought we had figured out what was the phenomenon, and we felt that such explanation fit very well with our ideas about ‘coherence‘, which at the time Giuliano was developing.
The original paper by Fleischmann and Pons published on the J. Electroanal. Chem.
So, within a month and a half, we wrote a paper in which we proposed a possible explanation of the phenomenon. It should be said that the deuterium nuclei are formed by a proton and a neutron, so two deuterium nuclei consists of two protons and two neutrons, which would correspond to a helium nucleus if they were held together.
Given that, because of the Einstein’s Theory of Relativity the energy of an helium nucleus is a bit lower than the sum of the energies of the two deuterium nuclei, the fusion process leads not to a stable helium nucleus, but to a helium nucleus that I would say ‘hot’, i.e. that must get rid of energy. How can it get rid of this excess energy?
One option is usually studied by nuclear physicists, namely that the two nuclei come together on their own, without connections with others, in the empty space. There are no third bodies to which immediately transfer the excess energy. Due to momentum conservation, the only way that the core has to dissipate this energy is to break.
In practice, from the core is ejected a proton or a neutron, or, with a probability of 1/1,000,000, a gamma photon, namely a ‘packet’ of electromagnetic energy. And this is the conventional nuclear fusion, or ‘hot fusion‘, so called because the nuclei are electrically charged, so they repel and a big effort is required to bring them closer to one another.
Simple calculations show that, to achieve the kinetic energies necessary to keep off nuclei enough to produce a nuclear fusion, it takes temperatures of millions of degrees, which we find only in the stars or in a nuclear bomb. For example, the hydrogen bomb, or H-bomb, is composed of a nuclear fission bomb which acts as a detonator, developing the temperatures required to ignite the nuclear fusion of deuterium.
To realize a hot fusion reactor, on the other hand, is a real challenge, because there are no materials that can withstand temperatures of millions of degrees, and to prevent the nuclei from touching the walls with the aid of powerful magnetic fields is an extremely difficult enterprise. Therefore, the hot fusion is certainly the energy of the future, in the sense that it will never have a present!
Using a metaphor, we can say that the problem of merging the two nuclei is in a way similar to the meeting of two candidate lovers that, if they can to overcome the hurdle of their bad character, would lead to an overwhelming passion. The just described road of the hot fusion, in this metaphor, corresponds to a ‘rape’.
There may be, however, another way to nuclear fusion, and it is the ‘cold fusion’, i.e. a fusion that does not require the high temperatures necessary for the hot fusion. In practice, instead of increasing the kinetic energy of the nuclei, we decrease the potential energy. In my metaphor, it is the path of ‘seduction’. But since the two nuclei repel, they cannot follow this route by themselves: a third body is required.
So if, instead of being in the empty space, we are in the matter – where there are not only positive charges but also negative charges, the electrons – there may find clouds of electrons that facilitate the fusion of two deuterium nuclei favoring their approach, a bit like the ‘old aunt’ who, once allowed two young people meet and fall in love, then disappear from the scene.
So, we could understand why, if the deuterium nuclei were placed not in the empty space but inside a metal – where there is an abundance of electrons that can perform the function of the old aunt – there is a density threshold such that when it is exceeded deuterium nuclei spontaneously begin to merger, as found by Fleischmann and Pons”.
EMILIO DEL GIUDICE (1940-2014) was an Italian physicist who has worked in the field of condensed matter. Theoretical physicist and professor at the University of Naples and pioneer of string theory in the early Seventies, later became known for his work with Giuliano Preparata at the Italian National Institute of Nuclear Physics (INFN). It is also known for its excellent qualities of popularizer, in particular on quantum mechanics.