Cold fusion is a type of nuclear reaction that scientists think might happen at or near room temperature. It is very different from "hot" fusion, which happens naturally in stars, is used in hydrogen bombs, and is tested in experimental fusion reactors. Hot fusion requires temperatures of millions of degrees. Cold fusion is also different from muon-catalyzed fusion. Scientists have not yet developed a widely accepted theory to explain how cold fusion could work.

In 1989, two scientists at the University of Utah, Martin Fleischmann and Stanley Pons, reported that their experiment using heavy water produced unusual heat that they said could only be explained by nuclear reactions. They also found small amounts of nuclear reaction byproducts, such as neutrons and tritium, which are created when deuterium (found in heavy water) fuses. Their experiment used electrolysis of heavy water on a palladium electrode. The results received much media attention and raised hopes for a new, inexpensive energy source. However, neutrons and tritium are also found in very small amounts in nature, produced by cosmic rays and natural radioactive processes.

Many scientists tried to repeat the experiment, but most failed. Some earlier claims of success were later retracted, and problems with the original study were discovered. By late 1989, most scientists no longer believed cold fusion was real, and it became known as "pathological science." In 1989, the United States Department of Energy (DOE) said the results did not prove a practical energy source and decided not to fund cold fusion research. A second DOE review in 2004 also found no strong evidence for cold fusion and did not provide funding. Today, research on cold fusion is rarely published in scientific journals that experts review, so it does not receive the same level of scientific evaluation as other studies.

Some scientists continue to study cold fusion, though interest has been limited. For example, a 2019 study in Nature described a failed attempt to replicate cold fusion using Google funding. A small group of researchers still explores the topic, often using terms like "low-energy nuclear reactions" (LENR) or "condensed matter nuclear science" (CMNS) to describe their work.

History

Nuclear fusion usually happens at very high temperatures, in the tens of millions of degrees. This is called "thermonuclear fusion." Since the 1920s, scientists have wondered if fusion could also happen at much lower temperatures by using a metal to help hydrogen atoms combine. In 1989, Stanley Pons and Martin Fleischmann (a top electrochemist at the time) claimed they had observed this process, called "cold fusion." Their announcement caused excitement in the media, but most scientists later questioned their results because others could not reproduce the extra heat they reported. Despite this, some researchers continue to study cold fusion, believing their experiments show it is possible.

Palladium's ability to absorb hydrogen was known as early as the 1800s by Thomas Graham. In the late 1920s, scientists Friedrich Paneth and Kurt Peters reported that hydrogen could turn into helium at room temperature when absorbed by finely divided palladium. However, they later retracted their findings, saying the helium they measured came from the 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 his application was denied after Paneth and Peters retracted their work and because Tandberg could not explain the process. After deuterium was discovered in 1932, Tandberg continued experiments with heavy water. His final experiments with heavy water were similar to those of Pons and Fleischmann, though the latter were unaware of Tandberg's work.

The term "cold fusion" was first used in 1956 in an article about Luis Alvarez's research on muon-catalyzed fusion. In 1986, scientists Paul Palmer and Steven Jones of Brigham Young University used the term "cold fusion" to describe the possible existence of fusion involving hydrogen isotopes in a planetary core. Earlier, in 1985, Jones had coined the term "piezonuclear fusion" in a paper with Clinton Van Siclen.

The most famous cold fusion claims came from Pons and Fleischmann in 1989. At first, scientists were interested in their work, but nuclear physicists later questioned their results. Pons and Fleischmann did not retract their claims but moved their research to France after the controversy. They believed that using electrolysis to compress deuterium within palladium metal might cause fusion. They tested this by running electrolysis experiments with a palladium cathode and heavy water in a calorimeter, a container used to measure heat. For 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 about 50°C without changes in energy input. These high-temperature phases lasted for days and repeated in some experiments. During these times, the heat output was much higher than the energy input. Eventually, the high-temperature phases stopped in each cell.

In 1988, Pons and Fleischmann asked the U.S. Department of Energy for funding to expand their experiments. Before this, they had used $100,000 of their own money. Their proposal was reviewed by scientists, including Steven Jones of Brigham Young University, who had studied muon-catalyzed fusion and written about "cold nuclear fusion" in Scientific American in 1987. Pons, Fleischmann, and Jones met to share research. Fleischmann and Pons claimed their experiments produced "excess energy" not explainable by chemical reactions alone, which they thought could be patented. Jones, however, focused on measuring neutron flux, which had no commercial value. To avoid conflicts, the teams agreed to publish their results at the same time, though their accounts of a meeting in March 1989 differ.

In mid-March 1989, both teams planned to publish their findings. Fleischmann and Jones had agreed to send their papers to Nature via FedEx on 24 March. However, Pons and Fleischmann, pressured by the University of Utah, broke their agreement and announced their results at a press conference on 23 March. They claimed their work would be published in Nature but instead submitted their paper to Journal of Electroanalytical Chemistry. Jones, upset, sent his paper to Nature after the press conference.

Pons and Fleischmann's announcement received wide media and scientific attention. At the time, scientists were more open to unexpected discoveries, like the 1986 discovery of high-temperature superconductivity, which was quickly explained. The public was also interested in new energy sources due to past issues like the 1973 oil crisis, environmental concerns, and the dangers of nuclear power. In the press conference, Pons and Fleischmann claimed cold fusion could solve environmental problems and provide limitless clean energy using seawater. They said their results had been confirmed many times and had no doubts about them. Fleischmann was quoted as saying, "What we have done is to open the door of a new research area… our indications are that the discovery will be relatively easy to make into a usable technology…"

Later research

In 1991, a scientist who supported cold fusion research estimated that about 600 scientists were still studying the topic. After 1991, cold fusion research continued but received little public attention. Groups working on cold fusion faced challenges in securing funding and maintaining their programs. Despite being rejected by the mainstream scientific community, small groups of researchers continued experiments using methods developed by Fleischmann and Pons. By 2004, the Boston Globe estimated that only 100 to 200 scientists were still working in the field, many of whom faced harm to their reputations and careers. After the controversy surrounding 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, Nature reported that Google had invested about $10 million in cold fusion research. Scientists at well-known labs, such as MIT and Lawrence Berkeley National Lab, worked for years to develop strict scientific methods to re-evaluate cold fusion. Their conclusion was that no evidence of cold fusion was found.

In 2021, after Nature published findings in 2019 that suggested possible fusion reactions, scientists at the Naval Surface Warfare Center, Indian Head Division, formed a team with experts from the Navy, Army, and National Institute of Standards and Technology to study the topic further. Most researchers in the field have struggled to publish their work in major scientific journals. Many now refer to their field using names like Low Energy Nuclear Reactions (LENR) or Lattice Assisted Nuclear Reactions (LANR) to avoid the negative associations of "cold fusion." Researchers believe the original controversy caused the field to be ignored, and they face ongoing challenges in securing funding and publishing in top journals. University researchers often avoid studying cold fusion due to fear of ridicule and harm to 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 proper evaluation. Researchers in the field often accept experiments and theories without criticism, fearing that outside critics might dismiss their work. This lack of scrutiny has allowed unverified claims to spread, making it harder for serious research to gain recognition.

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 studies led the U.S. Department of Energy (DOE) to review cold fusion research in 2004. In 2003, the U.S. Secretary of Energy, Spencer Abraham, ordered the DOE to conduct another review after receiving a letter from MIT’s Peter L. Hagelstein and new research from Italian and other scientists. Researchers were asked to submit evidence from 1989 onward. The 2004 review found that most scientists were unsure if cold fusion produced energy, and even those who believed it did noted that results were not consistent or well-documented. The report concluded that cold fusion evidence was still not convincing and did not recommend a federal research program. Instead, it suggested that agencies consider funding individual studies in specific areas, such as material science and particle emissions.

Cold fusion researchers viewed the 2004 report positively, believing it showed they were being treated like other scientists and increased interest in the field. However, in 2009, physicist Frank Close noted that problems from the original cold fusion announcement, such as unverified results, still existed. In 2012, Sidney Kimmel, a wealthy businessman, donated $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 became the institute’s director. One project aims to repeat a 1991 experiment that recorded high neutron emissions, which were previously stopped due to funding issues. In 2016, the U.S. House Committee on Armed Services directed the Department 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 cell systems, gases produced during electrolysis are allowed to escape. In closed cell systems, these gases are collected, such as by combining them in another part of the system. These experiments aim to reach a steady state, where the solution is replaced regularly. Some experiments, called "heat-after-death" experiments, measure heat after the electrical current is stopped.

The simplest setup for a cold fusion cell uses two electrodes placed in a solution containing 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 the "loading time," which is how long it takes for the palladium electrode to absorb hydrogen.

Early experiments by Fleischmann and Pons found helium, neutron radiation, and tritium, but these results were not successfully repeated. The levels of these findings were too low to explain the heat they claimed and were inconsistent with each other. Some experiments have detected very small amounts of neutron radiation, but these levels were close to normal background levels and not useful for studying nuclear processes.

Excess heat is measured by comparing energy input and output. Normally, energy going in matches energy going out within the limits of the experiment. In Fleischmann and Pons' experiments, the cell's temperature increased without more electricity being applied. If this temperature increase was real, it would mean unexplained energy was present. Their experiments suggested about 10–20% more heat than expected, but most researchers could not reproduce this result. Nathan Lewis found that the excess heat in their original report was not measured directly but estimated from other data.

Because researchers could not consistently produce excess heat or neutrons, and because experiments had errors and gave conflicting results, most scientists concluded that heat production was not real and stopped studying cold fusion. In 1993, Fleischmann reported "heat-after-death" experiments, where heat was measured after the electricity was turned off. This method has been used in later cold fusion claims.

Nuclear reactions typically produce particles that move in visible paths. Fleischmann and Pons claimed to detect neutrons and tritium in their experiments. However, the expected number of neutrons from known fusion reactions would be much higher than what they reported. In 2009, Mosier-Boss and others claimed to find highly energetic neutrons using special detectors, but their findings require further analysis to confirm.

Some scientists have reported detecting elements like calcium, titanium, chromium, manganese, iron, cobalt, copper, and zinc in cold fusion experiments. Researchers such as Tadahiko Mizuno and George Miley have made these claims. A 2004 report to the U.S. Department of Energy (DOE) suggested that deuterium-loaded foils could detect fusion products, but the evidence was not strong enough to confirm the findings.

A major criticism of cold fusion was that deuteron-deuteron fusion into helium should produce gamma rays, which were not observed in experiments. Cold fusion researchers later claimed to find X-rays, helium, neutrons, and nuclear changes. Some experiments used light water and nickel cathodes instead of heavy water. The 2004 DOE panel noted that the theories explaining the lack of gamma rays were not well developed.

Proposed mechanisms

Scientists do not have a single agreed-upon explanation for cold fusion. One idea suggests that hydrogen and its isotopes can be absorbed into certain solids, such as palladium hydride, at very high densities. This process increases pressure, which decreases the average distance between hydrogen isotopes. However, this reduced distance is not sufficient to produce the fusion rates reported in early experiments, which are ten times higher. Another idea proposes that a higher concentration of hydrogen inside palladium and a lower energy barrier might allow fusion to occur at lower temperatures than predicted by Coulomb's law. The concept of electrons in the palladium lattice shielding hydrogen nuclei from each other was presented to the 2004 DOE commission, but the panel concluded that the explanations provided were not convincing and did not align with current physics theories.

Criticism

Criticism of cold fusion claims often focuses on two main issues: either arguing that fusion reactions cannot happen in electrolysis setups due to scientific principles, or questioning the accuracy of measurements showing extra heat. Scientists believe known fusion reactions are unlikely to explain the reported excess heat and cold fusion results.

Nuclei are positively charged and naturally push each other away. Without a catalyst like a muon, very high energy is needed to overcome this repulsion. At room temperature, fusion rates would be far too low to explain the heat reported in cold fusion experiments. In muon-catalyzed fusion, muons help deuterium nuclei get closer, increasing fusion. However, deuterium inside a palladium lattice is farther apart than in gas, which should reduce, not increase, fusion.

In the 1920s, scientists Paneth and Peters discovered that palladium can absorb large amounts of hydrogen gas. They thought this might help increase fusion rates. Later, Tandberg used electrolysis to load palladium with deuterium, a method similar to the later experiments by Fleischmann and Pons. These scientists hoped hydrogen nuclei would fuse to form helium, which was needed for zeppelins at the time, but no helium or increased fusion was found.

Geologist Palmer suggested that helium-3 in Earth might come from fusion inside catalysts like nickel or palladium. This led to experiments in 1986 using setups similar to Fleischmann and Pons, but no consistent results were found. Fleischmann and Pons believed high pressure would bring deuterium nuclei close enough to fuse, but their calculations were incorrect, as noted by John R. Huizenga.

Conventional fusion involves two steps, creating an unstable intermediate nucleus. Experiments show three possible decay pathways for this nucleus, with one pathway being extremely rare. If 1 watt of energy were produced from deuteron fusions, measurable neutrons and tritium should appear. However, some studies reported helium without these byproducts, which would require unusual branching ratios not supported by other experiments.

The energy from fusion should be detectable as radiation, but experiments show no such signs. Fusion rates remain constant at different energies, and pressure or chemical changes only slightly affect them. Early theories about the Oppenheimer–Phillips process were too weak to explain observed changes.

Cold fusion experiments use power sources, platinum electrodes, deuterium or hydrogen, calorimeters, and detectors for byproducts like helium or neutrons. Critics argue that results are not consistently reproducible. Some researchers claim inconsistent electrode quality or hydrogen loading might explain this. Others question errors in calorimetry methods.

After Fleischmann and Pons' 1989 claims, many groups failed to reproduce their results. A few, like a team in India and John Bockris’ group, reported success, but not all cells worked. Later, Richard Oriani reported excess heat in 1990. However, inconsistent results led most scientists to doubt cold fusion. The DOE 2004 report noted that reproducibility is a key part of science, and cold fusion’s lack of it raised concerns.

Researchers like McKubre and ENEA suggested that cells with lower deuterium-to-palladium ratios may not produce excess heat. Many early experiments did not report these ratios, which might explain failed reproductions. Achieving the needed ratio is difficult, as some palladium batches crack under pressure.

Publications

In 1989, the ISI found that cold fusion had the most published papers of any scientific topic. Nobel Laureate Julian Schwinger supported cold fusion after many scientists criticized early reports. He tried to publish his paper "Cold Fusion: A Hypothesis" in Physical Review Letters, but reviewers rejected it strongly. Schwinger was insulted and left the American Physical Society in protest.

After 1990, the number of cold fusion papers dropped sharply because scientists stopped working in the field, and journal editors refused to review new research. Cold fusion no longer appeared on ISI charts. Researchers who found negative results left the field, and those who continued publishing were ignored. A 1993 paper in Physics Letters A was the last published by Fleischmann and was one of the last to be challenged by a cold fusion skeptic.

In 1990, the Journal of Fusion Technology created a section for cold fusion papers, publishing over a dozen each year. This gave researchers a mainstream outlet. However, when editor-in-chief George H. Miley retired in 2001, the journal stopped accepting cold fusion papers. This shows how important supportive and influential people are for publishing cold fusion research in certain journals.

The decline in cold fusion publications is described as a "failed information epidemic." Support for the theory rose quickly, reaching about 50% of scientists, but then fell sharply, leaving only a small number of supporters. This pattern is called "pathological science." A lack of shared ideas and methods made collaboration difficult, slowing progress toward "normal" science.

Cold fusion papers continued to appear in journals like Journal of Electroanalytical Chemistry, Il Nuovo Cimento, Journal of Physical Chemistry, Physics Letters A, International Journal of Hydrogen Energy, and some Japanese and Russian journals. Since 2005, Naturwissenschaften has published cold fusion papers. In 2009, the journal added a cold fusion researcher to its editorial board. In 2015, the Indian journal Current Science published a special section on cold fusion.

In the 1990s, groups that continued researching cold fusion and their supporters created non-peer-reviewed publications like Fusion Facts, Cold Fusion Magazine, Infinite Energy Magazine, and New Energy Times. These covered cold fusion and other energy topics ignored by mainstream journals. The internet also became a major way for cold fusion researchers to share their work.

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) was held in 1990 and has occurred every 12 to 18 months since. At early conferences, some attendees avoided criticizing papers or presentations because they feared giving critics more arguments. This lack of criticism allowed unqualified individuals to participate and made it harder for serious scientific work 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 name change is explained in detail in the research section above. However, the conference returned to its original name in 2008. Cold fusion research is sometimes called "low-energy nuclear reactions" (LENR) by supporters. 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 topics in its meetings every six months. The APS clarified that this does not mean it has become less skeptical about the research. Starting in 2007, the American Chemical Society (ACS) also included special sessions on cold fusion at its meetings. An ACS program chair, Gopal Coimbatore, stated that without a proper forum, the topic would not be discussed. He added, "With the world facing an energy crisis, it is worth exploring all possibilities."

From March 22–25, 2009, the ACS meeting featured a four-day symposium 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. This result was previously published in Naturwissenschaften. The researchers claim the neutrons suggest nuclear reactions occurred. However, without detailed data on the number, energy, and timing of the neutrons, and without ruling out other possible sources, this conclusion is unlikely to be accepted by the broader scientific community.

Patents

Although details are not known, it seems that the University of Utah acted to ensure that the 23 March 1989 announcement by Fleischmann and Pons was published first, before sharing the discovery and its patents with Jones. The Massachusetts Institute of Technology (MIT) announced on 12 April 1989 that it had applied for patents based on the work of 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 denied 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 allowed ENECO, a new company formed to profit from cold fusion discoveries, to use its cold fusion patents. In March 1998, the University of Utah stated it would no longer protect its patents.

The U.S. Patent and Trademark Office (USPTO) currently refuses to grant patents for cold fusion. Esther Kepplinger, who was deputy commissioner of patents in 2004, explained that this decision uses the same reasoning as for perpetual motion machines: they do not work. Patent applications must prove that an invention is "useful," which depends on whether the invention can function. Usually, USPTO rejections based only 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, partly because the inventor could not prove the invention’s usefulness.

A U.S. patent might still be granted if it is given a new name to avoid direct ties to cold fusion, but this method 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 similar to cold fusion processes, using materials found in cold fusion, were approved by the USPTO. One inventor had his applications initially rejected by nuclear science experts but later revised the patents to focus on electrochemical details, which were reviewed by electrochemistry experts who approved them. The inventor claimed the process involved "new nuclear physics" unrelated to cold fusion. In 2004, Melvin Miles received a patent for a cold fusion device and later removed all references to "cold fusion" from the patent description to avoid rejection.

At least one patent related to cold fusion 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 holds three cold fusion patents stated that the patents were valuable and helped secure investments.

Cultural references

In 1990, a film called Bullseye! was made by Michael Winner. It starred Michael Caine and Roger Moore. The movie mentioned the Fleischmann and Pons experiment. The film was a comedy about conmen trying to steal scientists' findings. However, the film was poorly received and described as "not funny" by critics.

In Undead Science, sociologist Bart Simon discusses how cold fusion appears in popular culture. He explains that some scientists use the term "cold fusion" to describe claims with no proof. Science ethics courses also use cold fusion as an example of questionable scientific practices. Cold fusion has appeared in jokes on 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). It was used in advertising as a term for impossible science, such as in a 1995 Pepsi Max advertisement.

In the 1996 action-adventure film Chain Reaction, the story involves a theoretical variation of the cold fusion principle.

In the 1997 action-adventure film The Saint, the plot follows a story similar to Fleischmann and Pons, but with a different ending. In Undead Science, Simon suggests that the film may have influenced how the public views cold fusion, making it seem more like science fiction.

An episode of the science fiction TV series Outer Limits, which aired on June 26, 1998, features an ex-student who returns to his university with bombs made using cold fusion technology. He claims he will not detonate them unless authorities execute five people he dislikes. Most physicists believe cold fusion is impossible, so he proves his point by detonating a smaller bomb on campus remotely.

In the tenth episode of the 2000 science fiction TV drama Life Force ("Paradise Island"), the story focuses on cold fusion. It follows an eccentric scientist, Hepzibah McKinley, who believes she has perfected cold fusion based on her father's research. The episode examines the potential benefits and practicality of cold fusion in the series' post-apocalyptic global warming scenario.

In the 2023 video game Atomic Heart, cold fusion is the main reason for most technological advances. The video game Fallout and the TV series Fallout also feature cold fusion as a major energy source.