After 15 years, cold fusion got a second chance at legitimacy from the U.S. Department of Energy, often seen by cold fusion advocates as their greatest enemy. This rematch, many hoped, would vindicate the field or kill it once and for all. Instead history repeated itself, with a verdict that evidence remained inconclusive.

Conventional physics holds that nuclear fusion ignites at multimillion-degree temperatures. In March 1989 controversy erupted when electrochemists Martin Fleischmann and Stanley Pons, then at the University of Utah, claimed room-temperature experiments with palladium electrodes in heavy water generated heat far in excess of any chemical reaction. The suggestion was that the deuterons--hydrogen nuclei bearing an extra neutron each--making up the heavy water were fusing.

Repeated experiments led to unpredictable results, and in November 1989 a special DOE panel found no convincing evidence for cold fusion. The panel remained open to further investigations through regular channels, but it recommended against research centers or special funding. In the aftermath, the scientific community for the most part decided cold fusion "was basically dead," says physicist Peter Hagelstein of the Massachusetts Institute of Technology.

Cold fusion investigations continued sporadically around the world in industry, university and government labs, including those at the Naval Research Laboratory in Washington, D.C., and, most recently, the Space and Naval Warfare Systems Command in San Diego. After the 10th International Conference on Cold Fusion, Hagelstein and fellow cold fusion proponents thought research had progressed far enough to request an update on the first review. "Recognizing a lot of work had been done in the last 15 years, I agreed," says James Decker, principal deputy director of science at the DOE.

Eighteen nuclear physicists, electrochemists and materials scientists reviewed research submitted by Hagelstein and his colleagues. In its December 2004 report, the DOE stated that when it came to whether the evidence for excess power was compelling or not, the panel split about evenly. When it came to whether nuclear reactions took place in the experiments, the report noted that two thirds of reviewers found the evidence unconvincing, one person found it compelling, and the remainder were somewhat convinced.

Experts cited many deficiencies in the interpretation of the data and the research methods, which used equipment far less than state of the art. But even some skeptical reviewers thought that experiments to look for the products of standard fusion reactions could be pursued to a clear conclusion. In the end, most reviewers suggested that funding agencies should entertain proposals of cold fusion studies via the conventional route of peer review. They concluded future research could investigate the properties of deuterium-loaded metals and look for fusion products with better tools and techniques.

Hagelstein thinks that the report downplays optimism among reviewers, and he contests the accuracy of its poll numbers. Still, he now feels that cold fusion proposals can gain positive recommendations. Of the DOE Decker says, "we've always been open to good proposals. We never said we would not fund proposals in cold fusion." But without dedicated programs, Hagelstein remarks, any cold fusion proposals will have to fight for money from programs that can disregard them as outside their area. When asked if this meant that nothing had changed since the last DOE review, Decker replies, "I think that may be a fair comment."