Ever since cold fusion's first proponents were laughed out of town in 1989, the alternative nuclear energy method has been, in the words of one physicist, "a pariah field, cast out by the scientific establishment." Indeed, the underlying premise of cold fusion — the idea that room-temperature atoms can fuse together, giving off massive amounts of heat that can be used to generate electricity — seems to violate central tenets of physics.
And yet, around 100 true believers worldwide have kept at it for 20 years, furtively working behind closed doors, desperate to prove that cold fusion — which promises a safe, clean and endlessly renewable form of energy production — really works.
Earlier this year, Andrea Rossi and Sergio Focardi, researchers at the University of Bologna in Italy, claimed to have built a new, commercially viable cold fusion machine called the Energy Catalyzer, or E-Cat. They say their reactor fuses atomic nuclei of nickel and hydrogen, turning 292 grams of 68 degree-Fahrenheit (20 degrees C) water into hot steam, and in the process generating 12,400 watts of energy using just 400 watts of input energy. The potential energy gain of the E-Cat is thus extreme.
On the surface, the whole thing sounds fishy, and it is fishy: Rossi and Focardi do not claim to know how the fusion reaction they are harnessing actually works, and they even shy away from giving details about their machine's design, explaining that it isn't patent-protected. Furthermore, experts at the U.S. Department of Energy (DOE) have conducted two thorough reviews of cold fusion research in the past — one in 1989 and the other in 2004 — and in both instances, they were not convinced by either the theory or the experimental results.
On the other hand, inexplicable as it may be, the E-Cat does seem to work. Just last week, Rossi and Focardi demonstrated its operation for two credible individuals: Hanno Essen, a theoretical physicist at the Swedish Royal Institute of Technology and chairman of the Swedish Skeptics Society, and Sven Kullander of Uppsala University, chairman of the Royal Swedish Academy of Sciences Energy Committee.
Essen and Kullander gave the E-Cat a solid thumbs-up. It produced too much excess heat to have been originating from a chemical process, they wrote in their report, adding that, "The only alternative explanation is that there is some kind of a nuclear process that gives rise to the measured energy production."
The Italian inventors plan to commercialize their machine, and the Greek government is even considering giving them the funds to do so. Could the DOE, the vast majority of physicists and engineers, and even physics itself, be wrong about cold fusion? If they are, then all of our energy problems might be solved.
A new physical effect
"Basically, there's a new physical effect that I think was found in the lab more than 20 years ago by Fleischmann and Pons [University of Utah electrochemists who were later derided for their work on cold fusion]," said Peter Hagelstein, an MIT professor of electrical engineering and computer science and one of the most mainstream proponents of cold fusion research. "It was not accepted by the scientific community. It's been laughed at and criticized. However, over the years the effect has continued to be seen."
"In a nutshell, it seems that [in cold fusion] there's a new kind of process involved in nuclei reactions," Hagelstein told Life's Little Mysteries, a sister site of LiveScience. "The essential difference is that in conventional nuclear physics, when nuclear energy is released, it comes out as nuclear radiation. In this process, when you make energy you don't get radiation at all, implying there's a new physical mechanism at work."
The other difference is that current nuclear reactors generate electricity by encouraging fission reactions — atoms breaking apart — whereas cold fusion is a process in which atoms somehow spontaneously fuse together.
Atoms don't just fuse, mainstream physicists argue. "Between two atoms there's a very great electric repulsion, called a Coulomb barrier," said Kent Hansen, an MIT professor emeritus of nuclear engineering. "Overcoming that barrier requires a huge amount of energy, so in order for it to happen, you need temperatures like those in the sun, where particles are moving very fast and can overcome the Coulomb barrier to fuse."
Quantum mechanics, the probability laws of the universe, allow for the miniscule yet real possibility that two particles could hop over the Coulomb barrier and fuse even at room temperature, but according to Hansen, that’s inconceivably unlikely.
"It is a scientific fact that you can throw a newspaper at the door, and it may go through. But the likelihood of that happening is so low that you can do it every second since the beginning of time and it won't actually happen," Hansen told Life's Little Mysteries.
The same goes for cold fusion. Some theoretical physicists have estimated that the chance of it happening is 1 in 1-with-40-zeros-after-it. That's small, but not zero. "Physics admits that there is a very low possibility of two particles at room temperature fusing together," Hansen said. "And that's what makes it difficult to say cold fusion can't happen."
Possible but implausible
Despite the infinitesimally small possibility, most scientists say cold fusion is implausible, and thus the research community gets little or no funding. Papers are categorically rejected by most peer-reviewed journals, and, similarly, the U.S. Patent Office rejects all patents having to do with it, equating the concept with that of perpetual motion.
That lack of patent protection stifles progress in the field, as researchers do not fully disclose their experimental designs to one another, Hagelstein said. Without seeing the guts of Rossi's and Focardi's machine, he has no idea if it actually works. "They've been keeping the technical details under wraps because they aren't patent protected, so it's hard to tell what they're doing from the photos and written descriptions. There is essentially no information that's useful to ascertain whether they've done it."
But he's optimistic that they might have. "There are a lot of other researchers who've been exploring technologies that are related and they've reported similar results," Hagelstein said. "[Rossi and Focardi] reported an immediate power gain of a factor of 10 and a long-term one of 20. There are other researchers who have reported the same power gain, so it's not out of line with the cutting-edge state of the art in the field."
In most cases, the alleged fusion reaction with its outburst of heat seems to occur when hydrogen, or its isotopes deuterium and tritium, are injected into a metal such as palladium. Proponents postulate that the presence of the metal somehow raises the likelihood that fusion will occur by 40 orders of magnitude, though no one knows why this should be the case.
David Goodstein, a Caltech physicist who is himself skeptical about cold fusion but doesn't categorically dismiss it, says the main problem is that experimental results in the field are rarely repeatable. No one has been able to demonstrate that cold fusion works consistently. In some cases, an energized injection of hydrogen, deuterium or tritium into a metal leads to an outpouring of heat, but in other cases it doesn't.
Cold fusion proponents, however, say they do consistently observe the fusion reaction when the ratio of hydrogen to metal atoms is greater than or equal to one. In other words, when the hydrogen atoms are really dense, and there's more than one of them for every palladium atom (or nickel or some other metal, as the case may be), cold fusion always sets in. Or so the cold fusion researchers say; since there's no peer-review process in the field, no one is sure what to believe.
The book on cold fusion might not close until it is allowed to fully open. "What you need is either total reproducibility or total irreproducibility," Goodstein said. Maybe Rossi's and Focardi's E-Cat machine works consistently. Maybe not. "If some arrangement could be made we would love to do a test of the E-Cat at MIT to verify that it works," Hagelstein said.
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Natalie Wolchover was a staff writer for Live Science from 2010 to 2012 and is currently a senior physics writer and editor for Quanta Magazine. She holds a bachelor's degree in physics from Tufts University and has studied physics at the University of California, Berkeley. Along with the staff of Quanta, Wolchover won the 2022 Pulitzer Prize for explanatory writing for her work on the building of the James Webb Space Telescope. Her work has also appeared in the The Best American Science and Nature Writing and The Best Writing on Mathematics, Nature, The New Yorker and Popular Science. She was the 2016 winner of the Evert Clark/Seth Payne Award, an annual prize for young science journalists, as well as the winner of the 2017 Science Communication Award for the American Institute of Physics.