Cold fusion is a type of nuclear reaction that scientists believe might happen at or near room temperature. This would be very different from "hot" fusion, which occurs naturally in stars, is used in hydrogen bombs, and is tested in early fusion reactors. Hot fusion happens at temperatures in the millions of degrees. Cold fusion is also different from another type of fusion called muon-catalyzed fusion. Scientists have not yet developed a widely accepted theory that explains how cold fusion might work.
In 1989, two scientists at the University of Utah, Martin Fleischmann and Stanley Pons, claimed their experiment with heavy water produced unusual heat ("excess heat") that they said could only be explained by nuclear processes. They also reported finding small amounts of nuclear reaction byproducts, such as neutrons and tritium. These substances are created when deuterium, found in heavy water, fuses. Their experiment involved using electrolysis to break down heavy water on a palladium electrode. The results received widespread media attention and sparked hope for a new, inexpensive energy source. However, neutrons and tritium are also found in tiny amounts in nature, produced by interactions with cosmic rays and radioactive decay in the atmosphere and Earth.
Many scientists tried to repeat the experiment using the limited details provided. Confidence in the findings dropped after many failed attempts, retractions of earlier claims, and the discovery of errors in the original study. By late 1989, most scientists no longer believed cold fusion was valid, and it became known as "pathological science." In 1989, the U.S. Department of Energy (DOE) concluded there was not enough evidence to support cold fusion as a useful energy source and decided not to fund further research. A second DOE review in 2004 reached similar conclusions and also did not fund cold fusion research. Today, because few cold fusion studies are published in major scientific journals, they do not undergo the same level of scientific review as other research.
Some interest in cold fusion has continued over the years. For example, a 2019 study published in Nature described a failed attempt to replicate cold fusion using funding from Google. A small group of researchers still studies cold fusion, often referring to it as low-energy nuclear reactions (LENR) or condensed matter nuclear science (CMNS).
History
Nuclear fusion usually happens at temperatures in the tens of millions of degrees. This process is called "thermonuclear fusion." Since the 1920s, scientists have wondered if fusion could occur at much lower temperatures by using a metal to help hydrogen fuse. In 1989, Stanley Pons and Martin Fleischmann, a top electrochemist, claimed they had observed this "cold fusion" in an experiment. Their announcement caused excitement in the media, but most scientists later criticized their findings after others could not reproduce the results. Despite this, some researchers continue to study cold fusion, believing it could be real.
The ability of palladium to absorb hydrogen was known as early as the 19th century by Thomas Graham. In the late 1920s, scientists Friedrich Paneth and Kurt Peters reported that hydrogen absorbed by finely divided palladium at room temperature could transform into helium through nuclear catalysis. However, they later retracted their claim, stating the helium they measured came from air, not the experiment.
In 1927, Swedish scientist John Tandberg claimed he fused hydrogen into helium using an electrolytic cell with palladium electrodes. He applied for a patent to produce helium and energy but was denied after Paneth and Peters retracted their findings and Tandberg could not explain his process. After deuterium was discovered in 1932, Tandberg continued experiments with heavy water. His final experiments with heavy water were similar to those later conducted by Fleischmann and Pons, though they were unaware of Tandberg’s work.
The term "cold fusion" was first used in 1956 in a New York Times article about Luis Alvarez’s research on muon-catalyzed fusion. In 1986, Paul Palmer and Steven Jones of Brigham Young University used the term "cold fusion" to describe "geo-fusion," the possible fusion of hydrogen isotopes in planetary cores. Jones had previously coined the term "piezonuclear fusion" in a 1985 paper.
The most famous cold fusion claims came from Stanley Pons and Martin Fleischmann in 1989. Their work initially interested scientists, but nuclear physicists later questioned their findings. Pons and Fleischmann did not retract their claims but moved their research to France after the controversy.
Fleischmann, from the University of Southampton, and Pons, from the University of Utah, hypothesized that high compression and deuterium mobility within palladium, achieved through electrolysis, might cause fusion. They used a calorimeter—a heat-measuring container—to test their theory. They applied current to a palladium cathode and heavy water for weeks, renewing the water periodically. Most deuterium left the cell as gas, but some may have accumulated in the cathode. Most of the time, the heat produced matched the energy input, and the temperature stayed around 30°C. However, in some experiments, the temperature suddenly rose to 50°C without changes in input power. During these phases, the heat output exceeded the energy input. These high-temperature events repeated in some experiments but eventually stopped.
In 1988, Fleischmann and Pons sought funding from the U.S. Department of Energy. They had previously used $100,000 of their own money to fund experiments. Their proposal was reviewed by Steven Jones of Brigham Young University, who had studied muon-catalyzed fusion and written about "cold nuclear fusion" in Scientific American in 1987. Jones and Fleischmann’s teams met in Utah to share research. Fleischmann and Pons claimed their experiments produced "excess energy" not explained by chemistry alone, believing it could be patented. Jones, however, focused on neutron measurements, which were not commercially valuable. To avoid conflicts, the teams agreed to publish results together, though their accounts of a March 1989 meeting differed.
By mid-March 1989, both teams planned to publish their findings. Fleischmann and Jones agreed to send papers to Nature via FedEx on March 24. However, Pons and Fleischmann, pressured by the University of Utah, broke their agreement and announced their results at a press conference on March 23. They claimed the work would be published in Nature but instead submitted it to the Journal of Electroanalytical Chemistry. Jones, upset, faxed his paper to Nature after the press conference.
The announcement received widespread media and scientific attention. Scientists were more open to unexpected discoveries after the 1986 discovery of high-temperature superconductivity. Some were reminded of the Mössbauer effect, a nuclear process in solids that was once unexplained but later understood.
The claim of a clean energy source came at a time of global concern over oil dependence, environmental issues, and nuclear safety. At the press conference, Pons, Fleischmann, and Chase N. Peterson, backed by their scientific reputations, claimed cold fusion could solve environmental problems and provide limitless energy using seawater. They stated their results had been confirmed many times and were confident in their findings. In a press release, Fleischmann said, "What we have done is to open the door of a new research area… continued work is needed to understand the science and determine its value to energy economics."
Later research
In 1991, a scientist who supported cold fusion estimated that around 600 researchers were still studying it. After 1991, cold fusion research continued but received little public attention. Groups working on cold fusion faced challenges in securing funding and keeping their programs active. These small groups of researchers continued experiments using methods developed by Fleischmann and Pons, even though the scientific community largely rejected their work. In 2004, the Boston Globe estimated that only 100 to 200 researchers were still working in the field, many of whom faced harm to their reputations and careers. After the main controversy over Pons and Fleischmann ended, cold fusion research was supported by private and small government funds in the United States, Italy, Japan, and India. In 2019, a report in Nature stated that Google had spent about $10 million on cold fusion research. Scientists at well-known research labs, such as MIT and Lawrence Berkeley National Lab, worked to develop reliable methods to re-examine cold fusion. Their conclusion was that no evidence of cold fusion was found.
In 2021, after a 2019 report in Nature described unusual findings that might suggest some fusion activity, scientists at the Naval Surface Warfare Center, Indian Head Division, announced they would form a team from the Navy, Army, and National Institute of Standards and Technology to study the topic further. Most researchers have struggled to publish their work in major scientific journals. Many now refer to their field by names like Low Energy Nuclear Reactions (LENR), Chemically Assisted Nuclear Reactions (CANR), or Lattice Enabled Nuclear Reactions (LENR) to avoid the negative associations of "cold fusion." Researchers who continue their work say the original controversy caused the field to be ignored by the scientific community. They also note a lack of funding and difficulty publishing in top journals. University researchers often avoid studying cold fusion because it could harm their careers.
In 1994, David Goodstein, a physics professor at Caltech, described cold fusion as a field that had been excluded by the scientific community. He noted that cold fusion research rarely appears in scientific journals, preventing it from being properly reviewed. Cold fusion researchers often accept their findings without criticism, fearing it might give critics more reasons to dismiss their work.
Since 1989, U.S. Navy researchers at the Space and Naval Warfare Systems Center (SPAWAR) in San Diego have studied cold fusion. In 2002, they published a report titled "Thermal and nuclear aspects of the Pd/D2O system," asking for funding. This and other research led to a 2004 review by the U.S. Department of Energy (DOE). In 2003, the U.S. Secretary of Energy, Spencer Abraham, ordered the DOE to review the field again after new research was shared, including a 2002 report from SPAWAR and papers from Italian researchers. Cold fusion researchers were asked to submit a summary of all evidence since 1989. The 2004 review found that most reviewers were unsure if experiments produced heat energy. Most reviewers said the effects were not repeatable and that experiments were not well documented. They concluded that cold fusion evidence was still not convincing and did not recommend a federal research program. They suggested agencies might fund individual studies in specific areas, such as material science and particle analysis.
Cold fusion researchers said the 2004 report showed they were being treated like other scientists and increased interest in the field. However, in 2009, a BBC article noted that problems from the original cold fusion announcement, such as unverified results, still existed. In 2012, Sidney Kimmel, a wealthy investor, gave $5.5 million to the University of Missouri to create the Sidney Kimmel Institute for Nuclear Renaissance (SKINR), which studies hydrogen interactions with metals under extreme conditions. In 2013, Graham K. Hubler, a nuclear physicist, became the institute’s director. One SKINR project aims to repeat a 1991 experiment that recorded high neutron emissions, which were stopped due to funding issues. The new experiment has reportedly seen similar neutron emissions.
In 2016, the U.S. House Committee on Armed Services asked the Secretary of Defense to report on the military usefulness of recent LENR advancements.
Reported results
A cold fusion experiment usually includes:
Electrolysis cells can be open or closed. In open systems, gas produced during electrolysis is allowed to escape. In closed systems, the gas is collected, such as by recombining it in another part of the setup. These experiments aim to reach a steady state, where the solution is replaced regularly. Some experiments, called "heat-after-death" tests, measure heat after the electrical current is turned off.
The simplest cold fusion setup uses two electrodes placed in a solution with palladium and heavy water. The electrodes are connected to a power source, allowing electricity to flow through the solution. Even when unusual heat is reported, it may take weeks to appear—this time is called "loading time," the period needed to fill the palladium electrode with hydrogen.
Early experiments by Fleischmann and Pons found small amounts of helium, neutron radiation, and tritium, but these results could not be reliably repeated. Neutron radiation was sometimes detected, but at levels close to normal background levels, making it hard to study nuclear reactions.
Excess heat is measured by comparing energy input and output. Normally, these match within experimental limits. In Fleischmann and Pons' experiments, the cell sometimes heated up without more electricity being used. If this heat was real, it would mean unexplained energy. Their experiments suggested 10–20% more heat than expected, but others could not confirm this. Researcher Nathan Lewis found that the heat was estimated, not directly measured.
Because excess heat and neutrons could not be consistently produced, and experiments had errors, most scientists stopped studying cold fusion. In 1993, Fleischmann reported "heat-after-death" experiments, where heat was measured after stopping the current. This method has been used in later claims.
Nuclear reactions usually create particles that can be seen moving. Fleischmann and Pons claimed to detect neutrons and tritium, but the neutron levels they reported were much higher than expected from normal fusion reactions. In 2009, researchers claimed to find high-energy neutrons using special detectors, but their findings need more detailed analysis to confirm.
Some researchers have reported detecting elements like calcium, titanium, and others in cold fusion experiments. A 2004 report to the U.S. Department of Energy said deuterium-loaded materials could detect fusion products, but the evidence was not strong enough to prove fusion occurred.
A major criticism of cold fusion was that deuteron-deuteron fusion should produce gamma rays, which were not found. Later, researchers claimed to detect X-rays, helium, neutrons, and changes in elements. Some experiments used light water and nickel instead of heavy water. The 2004 DOE review noted that cold fusion supporters did not provide a clear explanation for the lack of gamma rays.
Proposed mechanisms
Scientists studying cold fusion have not reached a clear agreement on how it works. One idea suggests that hydrogen and its types, such as those found in a material called palladium hydride, can be taken in by certain solids at very high densities. This process increases pressure, which reduces the average distance between hydrogen types. However, this reduced distance is not enough to produce the high fusion rates reported in early experiments, as it is ten times lower than expected. Another idea proposes that higher hydrogen density inside palladium and a lower energy barrier could allow fusion to occur at lower temperatures than predicted by Coulomb's law. The concept of electrons in the palladium structure shielding hydrogen nuclei was presented to a 2004 government commission, but the group concluded that the explanations were not convincing and did not align with existing physics theories.
Criticism
Criticism of cold fusion claims usually focuses on two main points: either pointing out that fusion reactions are unlikely to occur in electrolysis setups, or questioning the accuracy of measurements showing excess heat. These measurements are often considered unreliable due to poor methods or controls. There are several reasons why known fusion reactions are not a likely explanation for the excess heat and cold fusion claims.
Nuclei are all positively charged, so they strongly repel each other. Without a catalyst like a muon, very high energy levels are needed to overcome this repulsion. Based on known fusion rates, the rate of uncatalyzed fusion at room temperature would be 50 billion trillion times too low to explain the reported excess heat. In muon-catalyzed fusion, muons help bring deuterium nuclei closer together, increasing fusion rates. However, deuterium inside a palladium lattice is farther apart than in gas, which should reduce, not increase, fusion reactions.
In the 1920s, scientists Paneth and Peters discovered that palladium can absorb up to 900 times its volume of hydrogen gas, storing it at thousands of times atmospheric pressure. They believed this could increase fusion rates by loading palladium with hydrogen. Later, Tandberg used electrolysis to force palladium to absorb more deuterium, anticipating experiments by Fleischmann and Pons. These scientists hoped hydrogen nuclei would fuse to form helium, which was needed for zeppelins in Germany, but no helium or increased fusion was ever found.
Geologist Palmer once suggested that helium-3 in Earth’s crust might come from fusion inside catalysts like nickel or palladium. This idea led Steven Jones and others to replicate Fleischmann and Pons’ experiment in 1986, using a palladium cathode in heavy water. Fleischmann and Pons believed pressure would be high enough to cause fusion, but cold fusion experiments only reach pressures about 10,000 to 20,000 times atmospheric. John R. Huizenga later said they misinterpreted a scientific equation, leading them to overestimate the pressure needed for fusion.
Conventional deuteron fusion involves two steps, creating an unstable intermediate nucleus. Experiments show three possible decay paths for this nucleus, with different probabilities. Only one in a million intermediates take the third path, making its products rare. If 1 watt of energy were produced from deuteron fusions, the resulting neutrons and tritium would be easily detected. Some researchers reported helium production without detecting neutrons or tritium, which would require the third path to be much more common than expected, contradicting known probabilities. These reports also failed to detect gamma rays, which the third path normally emits.
The known decay rate and spacing between atoms in metals make it hard to explain how excess energy from fusion could transfer into the metal lattice without measurable radiation. Experiments also show that fusion ratios remain constant at different energies, with pressure and chemical environment causing only small changes. Early theories suggested a process called the Oppenheimer–Phillips process, but it was too weak to explain observed changes.
Cold fusion experiments use an energy source, a platinum group electrode, deuterium or hydrogen, a calorimeter, and sometimes detectors for byproducts like helium or neutrons. Critics argue that results are not consistently reproducible, and some researchers claim poor quality control or inconsistent hydrogen loading might explain this. Others question errors in calorimetry measurements and energy calculations.
In 1989, after Fleischmann and Pons announced their results, many groups failed to reproduce their findings. However, a few groups, including one in India and another in Texas, reported creating tritium. In 1990, a researcher in Minnesota claimed excess heat. These groups found that only some of their cells produced results, while others did not. Over time, researchers claimed many successful replications, but reliable results remained difficult to achieve. Reproducibility is a key part of science, and its lack led most scientists to doubt cold fusion claims. A 2004 report by the U.S. Department of Energy concluded that cold fusion research should focus on confirming or disproving excess heat claims.
Some researchers, like McKubre and ENEA, suggest that cells with a deuterium-to-palladium ratio below 100% (or 1:1) may not produce excess heat. Many failed experiments from 1989 to 1990 did not report their ratios, which could explain inconsistent results. Achieving this ratio is difficult, and some palladium batches crack under pressure, preventing proper loading.
Publications
In 1989, the ISI listed cold fusion as the scientific topic with the most published papers among all fields. Julian Schwinger, a Nobel Prize winner, supported cold fusion in the fall of 1989 after many scientists had criticized early reports about it. He tried to publish his paper titled "Cold Fusion: A Hypothesis" in Physical Review Letters, but experts who reviewed it strongly rejected it. This rejection upset Schwinger, and he left the American Physical Society in protest.
After 1990, the number of papers about cold fusion dropped quickly because of two reasons: scientists stopped working in the field, and journal editors refused to review new papers. As a result, cold fusion no longer appeared on the ISI lists. Scientists who found negative results stopped studying it, while those who continued were often ignored. In 1993, Fleischmann published his final paper in Physics Letters A, which was one of the last papers he wrote to be challenged by a skeptic.
In 1990, the Journal of Fusion Technology created a regular section for cold fusion research, publishing more than a dozen papers each year. This gave researchers a mainstream place to share their work. However, when the journal’s editor-in-chief, George H. Miley, retired in 2001, the journal stopped accepting new cold fusion papers. This change showed how important supportive and influential people were to keeping cold fusion research visible in certain journals.
The decline in cold fusion research has been called a "failed information epidemic." At first, many scientists supported the theory, but later, interest dropped sharply, leaving only a small group of supporters. This pattern is similar to what happens in "pathological science," which lacks shared ideas and methods. Without common goals, researchers worked separately, making it harder to move toward accepted scientific practices.
Cold fusion research continued in some journals, such as Journal of Electroanalytical Chemistry and Il Nuovo Cimento. Other papers appeared in Journal of Physical Chemistry, Physics Letters A, International Journal of Hydrogen Energy, and several Japanese and Russian journals. Since 2005, Naturwissenschaften has published cold fusion papers, and in 2009, it added a cold fusion researcher to its editorial board. In 2015, Current Science, an Indian journal, published a special section focused on cold fusion.
In the 1990s, groups that studied cold fusion and their supporters created non-peer-reviewed publications like Fusion Facts, Cold Fusion Magazine, Infinite Energy Magazine, and New Energy Times. These magazines covered cold fusion and other energy topics that were not widely discussed in traditional scientific journals. The internet also became a major tool for cold fusion researchers to share their work and communicate with others.
Conferences
Cold fusion researchers faced challenges for many years in getting their work accepted at major scientific meetings. This led to the creation of their own conferences. The first International Conference on Cold Fusion (ICCF) took place in 1990 and has been held every 12 to 18 months since. At early conferences, some attendees avoided criticizing papers or presentations out of fear that doing so might help critics outside the field. This lack of criticism allowed unqualified individuals to spread ideas and made it harder for serious scientific research to progress. Many critics and skeptics stopped attending these conferences, except for Douglas Morrison, who passed away in 2001. In 2004, the International Society for Condensed Matter Nuclear Science (ISCMNS) was formed, and the conference was renamed the International Conference on Condensed Matter Nuclear Science. This change was explained in later research, but the name was changed back to the original in 2008. Cold fusion research is sometimes called "low-energy nuclear reactions" (LENR) by its supporters. However, sociologist Bart Simon noted that the term "cold fusion" still helps create a shared identity for the field.
Since 2006, the American Physical Society (APS) has included cold fusion discussions at its semiannual meetings. This inclusion does not mean the society has become less skeptical. Starting in 2007, the American Chemical Society (ACS) also added invited symposiums on cold fusion to its meetings. An ACS program chair, Gopal Coimbatore, stated that without a proper forum for discussion, the topic would not be addressed. He also said, "With the world facing an energy crisis, it is worth exploring all possibilities."
During the American Chemical Society meeting from March 22–25, 2009, a four-day symposium was held to mark the 20th anniversary of the cold fusion announcement. Researchers from the U.S. Navy's Space and Naval Warfare Systems Center (SPAWAR) reported detecting energetic neutrons using a heavy water electrolysis setup and a CR-39 detector. These findings were previously published in Naturwissenschaften. The researchers claim the neutrons suggest nuclear reactions occurred. However, without detailed analysis of the number, energy, and timing of the neutrons, and without ruling out other possible sources, the scientific community is unlikely to accept this interpretation.
Patents
In 1989, the University of Utah seemed to act to ensure it had priority over the discovery and patents related to cold fusion before a joint publication with Jones. On 12 April 1989, the Massachusetts Institute of Technology (MIT) announced it had applied for its own patents based on work by one of its researchers, Peter L. Hagelstein, who had sent papers to journals between 5 and 12 April. An MIT graduate student also applied for a patent, but it was reportedly rejected by the U.S. Patent and Trademark Office (USPTO) in part because of a 1989 experiment by MIT’s Plasma Fusion Center that showed negative results. On 2 December 1993, the University of Utah gave all its cold fusion patents to ENECO, a new company created to profit from cold fusion discoveries. In March 1998, the university stated it would no longer defend its patents.
The USPTO now refuses to grant patents for cold fusion. In 2004, Esther Kepplinger, a USPTO official, explained that this decision was based on the same reasoning used for perpetual motion machines: they do not work. Patents must prove an invention is "useful," which depends on the invention’s ability to function. USPTO rejections based solely on an invention being "inoperative" are rare, as they require proof that the invention cannot work at all. However, in 2000, a cold fusion patent rejection was upheld in a Federal Court because the inventor could not prove the invention’s usefulness.
A U.S. patent might still be granted if it is renamed to avoid direct ties to cold fusion, but this approach has not been successful in the United States. Many patents cannot avoid mentioning Fleischmann and Pons’ research due to legal rules, which alerts reviewers that the patent is related to cold fusion. In 1999, David Voss noted that some patents resembling cold fusion processes have been granted by the USPTO. One inventor had his applications initially rejected by nuclear science experts but later revised them to focus on electrochemical parts, which were reviewed by electrochemistry experts who approved them. The inventor claimed his work involved "new nuclear physics" unrelated to cold fusion. In 2004, Melvin Miles received a patent for a cold fusion device. In 2007, he tried to remove all references to "cold fusion" from his patent to avoid rejection.
At least one cold fusion-related patent has been granted by the European Patent Office.
A patent legally prevents others from using or benefiting from an invention. However, the public often sees a patent as a sign that an invention is valid. A person who held three cold fusion patents stated that these patents were valuable and helped attract investments.
Cultural references
A 1990 film titled Bullseye!, directed by Michael Winner and starring Michael Caine and Roger Moore, mentioned the Fleischmann and Pons experiment. The film is a comedy that follows conmen attempting to steal scientists' claimed discoveries. However, the film received negative reviews and was described as "not funny."
In Undead Science, sociologist Bart Simon provides examples of cold fusion in popular culture. He explains that some scientists use the term "cold fusion" to describe exaggerated claims with no evidence. Science ethics courses also use cold fusion as an example of "pathological science." Cold fusion has appeared as a joke in television shows such as Murphy Brown and The Simpsons. It was also used as the name for a software product, Adobe ColdFusion, and a brand of protein bars (Cold Fusion Foods). Additionally, it was used in advertising as a term for impossible science, such as in a 1995 Pepsi Max advertisement.
The 1996 action-adventure film Chain Reaction includes a plot based on a theoretical version of the cold fusion principle. The 1997 action-adventure film The Saint follows a story similar to the Fleischmann and Pons experiment, though with a different ending. In Undead Science, Simon suggests that the film may have influenced public opinions about cold fusion, making it seem more like science fiction.
An episode of the science fiction television series Outer Limits, which aired on June 26, 1998, features an ex-student who returns to his university with bombs he created using cold fusion technology. After being expelled from the physics program, he threatens to detonate a bomb unless authorities execute five people he dislikes. Most scientists believe cold fusion is impossible, so he proves his claim by detonating a smaller bomb on campus remotely.
In the tenth episode of the 2000 science fiction TV drama Life Force ("Paradise Island"), a character named Hepzibah McKinley (played by Amanda Walker) believes she has successfully developed cold fusion based on her father’s incomplete research. The episode explores the potential benefits and practicality of cold fusion in a post-apocalyptic world dealing with global warming.
In the 2023 video game Atomic Heart, cold fusion is the primary source of technological advancements. The video game Fallout and its television series also feature cold fusion as a major energy source.