Cold fusion is being mentioned a lot lately because of some new setup that apparently works. This is an unverified claim.

See for example:


http://hardware.slashdot.org/story/11/01/24/1550205/Italian-Scientists-Demonstrate-Cold-Fusion
http://www.physorg.com/news/2011-01-italian-scientists-cold-fusion-video.html
http://www.wipo.int/pctdb/en/wo.jsp?WO=2009125444&IA=IT2008000532&DISPLAY=DOCS
http://www.journal-of-nuclear-physics.com/files/Rossi-Focardi_paper.pdf 

(Archived copy of that last link in the Wayback Machine, given frequent http 403 errors from that page.)


While we should give the scientific community time to evaluate the set up and eventually replicate the results, there is undoubtedly some skepticism that cold fusion would work at all, because the claim is quite extraordinary.

In the past, after Fleischmann and Pons announced their cold fusion results, in perfectly good faith, they were proven wrong by subsequent experiments.

What are the experimental realities that make Fleischmann and Pons style cold fusions experiments easy to get wrong?

Would the same risks apply to this new set up?

This was beautifully answered theoretically right away at the 1989 APS session in NY, I think by Koonin.    Theoretically, for any sort of fusion one needs to overcome the Coulomb repulsion of the relevant nuclei, on the order of MeV in order to allow the nuclei to get close enough for their wave functions to overlap and fuse.  Because of the phenomenom of quantum mechanical tunnelling, this can be reduced to tens to hundreds of kev.    So temperatures of >> 10^5 K, or cold muons (which outweigh electrons by 200x) are required to reduce the internuclear distance (as in muon catalyzed cold fusion, a real phenomenon), or some other special mechanism is required to allow this close approach. 

However, for any sort of chemically catalyzed fusion, i.e. via the valence electrons, to take place, the binding energy of the two H atoms to the catalyst would have to be so high, that the particular configuration of the low energy valence electrons, etc. would necessarily be entirely irrelevant to the problem, i.e. whatever their arrangement they could not possibly catalyze the fusionable nuclei to approach close enough to fuse.   So no clever packing arrangement, quasiparticles, special adsorbtion, special crystal lattice structures, etc. could ever alter this conclusion.   Whatever was happening at such low energy scales would appear as a kind of irrelevant fluff compared to the energy scale of the internuclear distance necessary for fusion.    

Therefore valence electron catalyzed cold fusion would violate the fundamental laws of quantum mechanics, nuclear physics, etc.   Leggett and Baym also published an argument like this around the same time (summarized for free here).  Koonin and Nauenberg published an accurate calculation here, showing that if the mass of the electron were 5-10 times larger than it really is, chemically calalyzed fusion could work.   Note however, that the reaction rate depends on the electron mass very, very strongly, so that this remains impossible in our universe. 
