Cold Fusion

Is cold fusion that is, the fusion of two deuterium nuclei at about room temperature a possibility, or can this process be eliminated by theoretical arguments alone?

Answer

Cold fusion at room temperature is a real but unlikely possibility. The key idea is the quantum mechanical overlap of the wave functions of two nearby H-2 nuclei, for example. Their wave functions always overlap, no matter how far apart they are. However, the bigger the value of the wave function overlap, the more probable will be the possibility of the fusion process to make a He-4 nucleus.

Of course, there is a Coulomb barrier to be overcome. In the 1940s came the proposal that muonic atoms a proton with a muon replacing the electron might allow fusion because the muonic atom ground state puts the muon so close to the nucleus on average that the muonic atom appears neutral to the approaching proton. However, calculations have shown that the produced He isotope decays too quickly for this scheme to succeed in fusion energy production.

In gaseous form at room temperature, two colliding H-2 nuclei do not get close enough for a large wave function overlap, being strongly repelled by electrical forces acting between two positive nuclei. In a solid, however, at room temperature, H nuclei in neighboring lattice sites experience enormous accelerations, as large as 10¹⁴ m/s² in random directions. Sometimes these accelerations are toward each other, so the two protons can approach very close and perhaps fuse into a He nucleus. However, the actual calculation reveals the rarity of this event.

Despite the extreme improbability of deuteron fusion at room temperatures, so-called cold fusion, research groups worldwide continue its pursuit, as revealed in the references below.