![\"Researcher](\"\/\/media.nature.com\/w800\/magazine-assets\/d41586-019-01683-9\/d41586-019-01683-9_16747656.jpg\")
<\/div>\n<\/div>Chemist Martin Fleischmann (pictured with US politician Marilyn Lloyd) was part of a team that claimed to have produced cold fusion in 1989.<\/span>Credit: Margot Ingoldsby\/AP\/Shutterstock<\/p>\n<\/figcaption><\/figure>\n <\/p>\n <\/p>\n Since 2015, Google has been\u00a0funding experiments into the controversial science of cold fusion<\/a>\u00a0\u2014 the theory that nuclear fusion, the process that powers the Sun, can produce energy in a table-top experiment at room temperature. Two scientists first made sensational claims about achieving the phenomenon \u2014 promising endless, cheap energy \u2014 30 years ago, but their results were quickly debunked and the topic is now considered a scientific taboo.<\/p>\n Google\u2019s project \u2014 revealed in a peer-reviewed\u00a0Nature<\/i>\u00a0Perspective1<\/a><\/sup>\u00a0this week \u2014 found no evidence that cold fusion is possible, but made some advances in measurement and materials-science techniques that the researchers say could benefit energy research. The team also hopes that its work will inspire others to revisit cold-fusion experiments, even if the phenomenon still fails to materialize.<\/p>\n \u201cThis is not just a chase for cold fusion,\u201d says Matthew Trevithick, a research programme manager at Google in Mountain View, California. \u201cIf it were, I don\u2019t think we would have maintained an interest of this calibre of team for so long.\u201d<\/p>\n The Google team explored three experimental set-ups that have been proposed to generate cold fusion \u2014 two involving palladium and hydrogen, and one involving metallic powders and hydrogen. None found evidence of fusion. The results have been published across 12 papers over the past 2 years: 9 in peer-reviewed journals and 3 on the arXiv preprint server.<\/p>\n Some scientists welcomed the scrutiny brought by the Google project. But Frank Close, a theoretical physicist at the University of Oxford, UK, says that the scientific mainstream has shunned the topic for good reason: no one has managed to independently reproduce the finding and more worthwhile topics have emerged, he says. \u201cThere is no theoretical reason to expect cold fusion to be possible, and a vast amount of well-established science that says it should be impossible,\u201d says Close, who was involved in efforts to replicate the original 1989 experiment.<\/p>\n <\/p>\n Notorious claims<\/strong><\/p>\n In March 1989, two US-based chemists Stanley Pons and Martin Fleischmann\u00a0announced that they had seen excess heat and fusion-reaction products<\/a>\u00a0\u2014 signs of nuclear fusion \u2014 when they ran a current across two palladium plates in water laden with deuterium, a heavy isotope of hydrogen. Others quickly pointed out errors in their experimental procedure. Since then, two\u00a0US Department of Energy reviews<\/a>\u00a0have found no evidence of the phenomenon .<\/p>\n But cold fusion \u2014 now commonly referred to as low-energy nuclear reactions \u2014 has retained a persistent following that continues to claim evidence of success.<\/p>\n Google\u2019s US$10-million project aimed to test the cold-fusion claims rigorously in a field that lacked credible scientific data, says Trevithick. Another goal was also to push methods in challenging experimental conditions. But, he adds: \u201cThe fact that the pay-out could be huge is definitely a component of our interest.<\/p>\n <\/p>\n Energy sink<\/strong><\/p>\n Nuclear fusion is thought to happen only in extreme environments such as the Sun, where high temperatures and pressures can cause hydrogen atoms to overcome their mutual repulsion and fuse into helium, releasing enormous amounts of energy. Some\u00a0experiments on Earth<\/a>\u00a0are trying to replicate the phenomenon, but haven\u2019t yet proved that they can generate enough energy to make up for the vast amounts they need to run.<\/p>\n The probability of atoms fusing at much lower temperatures is thought to be vanishingly small. But, if possible, this phenomenon would bring enormous benefits by doing away with fusion\u2019s vast energy requirements.<\/p>\n Google\u2019s team was made up of 30 researchers who had no strong opinions on cold fusion. All had access to each other\u2019s data and apparatus, and could review each other\u2019s work.<\/p>\n The researchers pursued the three experimental strands that they deemed sufficiently credible. In one, they tried to load palladium with amounts of deuterium hypothesized to be necessary to trigger fusion. But at high concentrations the team was unable to create stable samples.<\/p>\n A second strand followed up on 1990s work by US physicists who claimed to have generated anomalous levels of tritium \u2014 another heavy hydrogen isotope, created only through nuclear reactions \u2014 by bombarding palladium with pulses of hot deuterium ions. Google\u2019s analysis of nuclear signatures showed no tritium production from this experiment.<\/p>\n A final strand involved heating up metallic powders in a hydrogen-rich environment. Some current proponents of cold fusion claim that the process produces excess and unexplained heat, which they theorize is the result of fusing elements. But across 420 tests, the Google-funded team found no such heat excess.<\/p>\n But the researchers say that both palladium experiments warrant further study. The hypothesized effects in the tritium experiment could be too small to measure with current equipment, they suggest. The team also says that further work could produce stable samples at extremely high deuterium concentrations, where interesting effects might occur.<\/p>\n All the projects pushed the frontier of experimental methods, says Trevithick, including developing \u201cthe best calorimeters in the world\u201d to detect even slight excesses of heat under extreme experimental conditions. These could potentially be used to test future claims.<\/p>\n<\/div>\n <\/p>\n <\/p>\n Pushing the envelope<\/strong><\/p>\n \u201cI think that the authors have done a really good job,\u201d says David Williams, an electrochemist at the University of Auckland in New Zealand \u2014 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.<\/p>\n The techniques the team developed to load palladium may also help researchers to boost the hydrogen storage capacity of materials being studied for use in batteries and fuel cells, says George Chen, an electrochemist at the University of Nottingham\u2019s China campus in Ningbo.<\/p>\n Trevithick notes that in one case his team has not been able to reach even the hypothesized starting conditions for fusion, so have not fully eliminated the possibility that it occurs.<\/p>\n But Close says that being unable to rule an idea out completely does not mean there is good reason to pursue it. \u201cYou cannot prove a negative in science,\u201d he says. If Google wants to invest in cold fusion \u2014 that\u2019s up to them, he says. But \u201cif somebody I was investing my money in started doing this, I would withdraw my money\u201d, says Close.<\/p>\n Curtis Berlinguette, a chemist at the University of British Columbia in Vancouver and one of the project\u2019s principal investigators, is sceptical of the \u201cclassic\u201d cold-fusion experiments. But he was excited to do the work and thinks that a new generation of creative scientists could develop methods that drive fusion reactions at low temperatures. Some might judge the team harshly but the project simply explored an underexplored space \u2014 which was off limits because of prejudice, he says. \u201cThis is what we are supposed to do as scientists.\u201d<\/p>\n <\/p>\n Nature<\/span>\u00a0569<\/strong>, 611 (2019)<\/p>\n <\/p>\n <\/p>\n <\/p>\n UPDATES & CORRECTIONS<\/strong><\/p>\n Clarification 28 May 2019<\/strong>: An earlier version of this story said that Google\u2019s Matthew Trevithick recruited 30 researchers for the cold-fusion project. In fact, Trevithick recruited four principle investigators, who put together their own teams.<\/p>\n<\/li>\n<\/ul>\n<\/div>\n <\/p>\n <\/p>\n (\uc6d0\ubb38: \uc5ec\uae30<\/a>\ub97c \ud074\ub9ad\ud558\uc138\uc694~)<\/p>\n <\/p>\n <\/p>\n <\/p>\n","protected":false},"excerpt":{"rendered":"\n