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NUCLEAR PHYSICS revives controversial cold-fusion experiments Researchers found no evidence for the phenomenon, first proposed 30 years ago.

BY ELIZABETH GIBNEY Some scientists welcomed the scrutiny to be vanishingly small. But, if it were possible, brought by the Google project. But Frank this phenomenon would bring enormous ince 2015, Google has been funding exper- Close, a theoretical physicist at the University energy benefits. iments into cold fusion — the theory that of Oxford, UK, says that the scientific main- Google’s team of 30 researchers pursued , the process that powers the stream has shunned the topic for good reason: three experimental strands linked to cold SSun, can produce energy in a table-top experi- no one has managed to independently repro- fusion. In one, they tried to load ment. Two scientists first made sensational duce the finding and more worthwhile topics with amounts of suggested to be claims about achieving the phenomenon — have emerged, he says. necessary to trigger fusion. But at high con- promising endless, cheap energy — 30 years centrations, the team was unable to create sta- ago, but their results were quickly debunked and NOTORIOUS CLAIMS ble samples. A second strand followed up on the topic is now considered a scientific taboo. In March 1989, two US-based chemists, Stanley 1990s work by US physicists who claimed to Google’s project — revealed this week in Pons and , announced have generated anomalous levels of — — found no evidence that cold fusion is that they had seen signs of nuclear fusion when another heavy isotope, created only possible, but made some advances in measure­ they ran a current across two palladium plates through nuclear reactions — by bombarding ment and materials- techniques that the in water laden with deuterium, a heavy iso- palladium with pulses of hot deuterium ions. researchers say could benefit energy research tope of hydrogen. Others quickly pointed out The Google team found no tritium production (C. P. Berliguette et al. Nature http://doi.org/ errors in their experimental procedure and no in this set-up. c6dh; 2019). The team also hopes that its work experiment has ever reproduced the result. But A final strand heated metallic powders in will inspire others to revisit cold-fusion experi- cold fusion — now commonly referred to as a hydrogen-rich environment. Some current ments, even if the phenomenon still fails to low-energy nuclear reactions — has retained proponents of cold fusion claim that the pro- materialize. a persistent following that continues to claim cess produces excess and unexplained heat, “This is not just a chase for cold fusion,” evidence of success. which they theorize is the result of fusing says Matthew Trevithick, a research pro- Google’s US$10-million project aimed elements. But across 420 tests, the team found gramme manager at Google in Mountain View, to test the cold-fusion claims rigorously, no such heat excess. California. “If it were, I don’t think we would says Trevithick. However, the researchers say that both palla- have maintained an interest of this calibre of Nuclear fusion is thought to happen only in dium experiments warrant further study. The team for so long.” extreme environments such as the Sun, where proposed effects in the tritium experiment The Google team explored three experimen- high temperatures and pressures cause hydro- could be too small to measure with current tal set-ups involving and hydrogen that gen atoms to overcome their mutual repulsion equipment, they say. The team also says that have been proposed to generate cold fusion. and fuse into helium, releasing enormous further work could produce stable samples at Their results have been published across amounts of energy. The probability of atoms extremely high deuterium concentrations. 12 papers over the past 2 years. fusing at much lower temperatures is thought All the projects pushed the frontier of experimental methods, says Trevithick, including developing “the best in the world” to detect even slight excesses of heat under extreme experimental conditions. These could potentially be used to test future claims. PUSHING THE ENVELOPE “I think that the authors have done a really good job,” says David Williams, an electro-

MARGOT INGOLDSBY/AP/SHUTTERSTOCK MARGOT chemist at the University of Auckland in New Zealand — especially in how they have navigated the controversial topic. Pushing the envelope of measurement science is also important, says Williams, whose team did some of the first failed replication studies of the original claim. But Close, who was involved in early repli- cation attempts, says that being unable to rule an idea out completely does not mean there is good reason to pursue it. “If somebody I was investing my money in started doing this, I Chemist Martin Fleischmann (left) was part of a team that claimed to have produced cold fusion in 1989. would withdraw my money,” says Close. ■

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