Is cold fusion truly impossible, or is it just that no respectable scientist can risk their reputation working on it? ... cold fusion (or LENR, for ‘low-energy nuclear reaction’) is the controversial idea that nuclear reactions similar to those in the Sun could, under certain conditions, also occur close to room temperature. ... was popularised in 1989 by Martin Fleischmann and Stanley Pons, who claimed to have found evidence that such processes could take place in palladium loaded with deuterium (an isotope of hydrogen). A few other physicists, including the late Sergio Focardi at Bologna, claimed similar effects with nickel and ordinary hydrogen. But most were highly skeptical, and the field subsequently gained, as Wikipedia puts it, ‘a reputation as pathological science’. ... We know that huge amounts of energy are locked up in metastable nuclear configurations, trapped like water behind a dam. There’s no known way to get useful access to it at low temperatures. ... There are credible reports that a 1MW version of his device, producing many times the energy that it consumes, has been on trial in an industrial plant in North Carolina for months, with good results so far. And Rossi’s US backer and licensee, Tom Darden – who has a long track record of investment in pollution-reducing industries – has been increasingly willing to speak out in support of the LENR technology field. ... We should certainly be very cautious about such surprising claims, unless and until we amass a great deal of evidence. But this is not a good reason for ignoring such evidence in the first place, or refusing to contemplate the possibility that it might exist.