Cold fusion is making a scientific comeback

Earlier this year, ARPA-E, a US government agency dedicated to funding advanced energy research, announced a handful of grants for a field it calls “low-energy nuclear reactions,” or LENR. Most scientists likely didn’t take notice of the news. But, for a small group of them, the announcement marked vindication for their specialty: cold fusion.

Cold fusion, better known by its practitioners as LENR, is the science—or, perhaps, the art—of making atomic nuclei merge and, ideally, harnessing the resultant energy. All of this happens without the incredible temperatures, on the scale of millions of degrees, that you need for “traditional” fusion. In a dream world, successful cold fusion could provide us with a boundless supply of clean, easily attainable energy.

Tantalizing as it sounds, for the past 30 years, cold fusion has largely been a forgotten specter of one of science’s most notorious controversies, when a pair of chemists in 1989 claimed to achieve the feat—which no one else could replicate. There is still no generally accepted theory that supports cold fusion; many still doubt that it’s possible at all. But those physicists and engineers who work on LENR believe the new grants are a sign that their field is being taken seriously after decades in the wilderness.

“It got a bad start and a bad reputation,” believes David Nagel, an engineer at George Washington University, “and then, over the intervening years, the evidence has piled up.”

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Igniting fusion involves pressing the hearts of atoms together, creating larger nuclei and a fountain of energy. This isn’t easy. The protons inside a nucleus give it a positive charge, and like-charged nuclei electrically repel each other. Physicists must force the atoms to crash together anyway. 

Normally, breaking this limit needs an immense amount of energy, which is why stars, where fusion happens naturally, and Earthbound experiments reach extreme heat. But what if there were another, lower-temperature way?

Scientists had been theorizing such methods since the early 20th century, and they’d found a few tedious, extremely inefficient ways. But in the 1980s, two chemists thought they’d made one method work to great success. 

The duo, Martin Fleischmann and Stanley Pons, had placed the precious metal palladium in a bath of heavy water: a form of H₂O whose hydrogen atoms have an extra neutron, a form known as deuterium, commonly used in nuclear science. When Fleischmann and Pons switched on an electrical current through their apparatus and left it running, they began to see abrupt heat spikes, or so they claimed, and particles like neutrons.

Those heat spikes and particles, according to them, could not be explained by any chemical process. What could explain them were the heavy water’s deuterium nuclei fusing, just as they would in a star.

If Fleischmann and Pons were right, fusion could be achievable at room temperature in a relatively basic chemistry lab. If you think that sounds too good to be true, you’re far from alone. When the pair announced their results in 1989, what followed was one of the most spectacular firestorms in the history of modern science. Scientist after scientist tried to recreate their experiment, and no one could reliably replicate their results.

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Pons and Fleischmann are remembered as fraudsters. It likely didn’t help that they were chemists trying to make a mark on a field dominated by physicists. Whatever they had seen, “cold fusion” found itself at respectable science’s margins. 

Still, in the shadows, LENR experiments continued. (Some researchers tried variations on Fleischmann and Pons’ themes. Others, especially in Japan, sought LENR as a means of cleaning up nuclear waste by transforming radioactive isotopes into less dangerous ones.) A few experiments showed oddities such as excess heat or alpha particles—anomalies that might best be explained if atomic nuclei were reacting behind the scenes.

“The LENR field has somehow, miraculously, due to the convictions of all these people involved, has stayed alive and has been chugging along for 30 years,” says Jonah Messinger, an analyst at the Breakthrough Institute think tank and a graduate student at MIT.

Fleischmann and Pons’ fatal flaw—that their results could not be replicated—continues to cast a pall over the field. Even some later experiments that seemed to show success could not be replicated. But this does not deter LENR’s current proponents. “Science has a reproducibility problem all the time,” says Florian Metzler, a nuclear scientist at MIT.

In the absence of a large official push, the private sector had provided much of LENR’s backing. In the late 2010s, for instance, Google poured several million dollars into cold fusion research to limited success. But government funding agencies are now starting to pay attention. The ARPA-E program joins European Union projects, HERMES and CleanHME, which both kicked off in 2020. (Messinger and Metzler are members of an MIT team that will receive ARPA-E grant funds.)

By the standards of other energy research funding, none of the grants are particularly eye-watering. The European Union programs and ARPA-E total up to around $10 million each: a pittance compared to the more than $1 billion the US government plans to spend in 2023 on mainstream fusion.

But that money will be used in important ways, its proponents say. The field has two pressing priorities. One is to attract attention with a high-quality research paper that clearly demonstrates an anomaly, ideally published in a reputable journal like Nature or Science. “Then, I think, there will be a big influx of resources and people,” says Metzler.

A second, longer-term goal is to explain how cold fusion might work. The laws of physics, as scientists understand them today, do not have a consensus answer for why cold fusion could happen at all.

Metzler doesn’t see that open question as a problem. “Sometimes people have made these arguments: ‘Oh, cold fusion contradicts established physics,’ or something like that,” he says. But he believes there are many unanswered questions in nuclear physics, especially with larger atoms. “We have an enormous amount of ignorance when it comes to nuclear systems,” he says.

Yet answers would have major benefits, other experts argue. “As long as it’s not understood, a lot of people in the scientific community are put off,” says Nagel. “They’re not willing to pay any attention to it.”

It is, of course, entirely possible that cold fusion is an illusion. If that’s the case, then ARPA-E’s grants may give researchers more proof that nothing is there. But it’s also possible that something is at work behind the scenes.

And, LENR proponents say, the Fleischmann and Pons saga is now fading as younger researchers enter the field with no memory of 1989. Perhaps that will finally be what lets LENR emerge from the pair’s shadow.“If there is a nuclear anomaly that occurs,” says Messinger, “my hope is that the wider physics community is ready to listen.”