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Fifteen years after the first controversial claims hit the headlines, cold fusion refuses to die. A small cadre of die-hard advocates argues that experiments now produce consistent results. The physics establishment continues to scoff, but some scientists who have been watching the field carefully are convinced something real is happening. And now the U.S. Department of Energy has decided that recent results justify a fresh look at cold fusion.

Fusion of the nuclei of hydrogen atoms powers the sun, and promises nearly limitless energy on Earth. But fusion is extraordinarily difficult to tame because nuclei strongly repel each other. The tremendous heat and pressure inside the sun can overwhelm this repulsion, and thermonuclear bombs can attain those conditions, fleetingly, on Earth. But building a fusion reactor that can convert that tremendous heat into useful energy has posed an immense challenge. After decades of research, the conditions needed for fusion still can be attained only briefly, and these experimental fusion reactions produce less energy than is needed to ignite them.

Physicists were stunned when two University of Utah electrochemists, Stanley Pons and Martin Fleischmann, claimed in 1989 that they had achieved nuclear fusion at room temperature. Their experiment packed deuterium-the stable heavy isotope of hydrogen-into palladium electrodes. After many hours of operation, they reported that more heat was generated than a purely chemical reaction could have produced. At first it looked like Pons and Fleischman might have come up with a revolutionarily easy way to tap fusion energy, and laboratories around the world rushed to try the experiment for themselves. The simple-looking experiment proved virtually impossible to reproduce, however, and within weeks, most physicists wrote off cold fusion as a mistake-an experimental result that contradicted the known laws of physics.

Yet the potential of limitless energy lured a band of would-be revolutionaries who kept on working the problem. Often they found nothing. Sometimes, however, their experiments appeared to produce more energy than they expected from chemical reactions; at other times they detected traces of potential fusion reaction products, suggesting that some previously unknown physical effects may be at work.

The evidence for “new physics” has been building for years, says Peter Hagelstein, associate professor of electrical engineering and computer science at MIT, who chaired the tenth International Conference on Cold Fusion in Cambridge last August. Experiments performed under properly controlled conditions reliably produce more heat than standard theory predicts. Nuclear products show up in about the right amounts to account for this excess heat. Patterns have emerged that explain previous anomalies. When Hagelstein saw how pieces of the puzzle were fitting together at the August meeting, he urged the Department of Energy to reconsider a field that had been cast out of orthodox science soon after its birth.

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