Cold Fusion: What Do the Laws of Nature Allow and Forbid?

This talk will not be a summary of the theoretical contributions to this Conference: I think that the individual papers that this book collects can give a much better representation of the work that is now going on in the field than i can possibly attempt to give in a short talk. As a partial excuse I may quote a recent review article of mine^[1], where I try to discuss the most significant theories of cold fusion, and the fact that nothing much new has happened in the last few months. Nor will I discuss cold fusion in the non-equilibrium conditions prevailing in Titanium^[2], fracto-emission^[3] and 'lukewarm' fusion^[4]. I shall rather try to examine first the strange facts of hydrogen incorporation into Palladium, and then I shall discuss the phenomena of cold fusion in relation to those facts. In the light of the known experimental data I will then discuss the general features of what i might call 'possible' and 'impossible' theories of cold fusion, somehow drawing a demarcation line between which theoretical ideas can and cannot explain those observations, given the well estabilished and accepted general laws of condensed matter (Quantum Electro Dynamics, QED) and nuclear physics (Quantum Chromo Dynamics, QCD). My discussion will follow quite closely a paper recently completed in collaboration with M.Fleishmann and S.Pons[5].