ost people are familiar with the idea that the human brain is divided into two halves, a logical left and a creative right. Few people realize, though, that the left brain, far from being coldly Vulcan in its outlook, is in fact very eager and cheerful and accepting, while its artistic counterpart on the right is generally brooding and suspicious. Even the most logical people need both halves to function; in the meticulous "peer review" process of modern science, the left brain fits new details into existing theories, until the right brain smells a rat and refuses to believe. It then forces the left brain to either discard anomalous data, or to craft a new theory to replace the old. Either action will bring the two brain halves into harmony again.
Rarely has this principle been more evident than in Salt Lake City, Utah, on the 23rd of March, 1989, when Doctors Stanley Pons and Martin Fleischmann announced that a five-year research program had culminated in the discovery of cold fusion. Pons was chairman of the Chemistry Department at the University of Utah, while Fleischmann held a similar post in the electrochemistry department of England's University of Southampton, so while their claim was extraordinary, it was by no means incredible.
Overcoming repulsion
Fusion is, at its simplest, the squishing together of light atomic nuclei such as hydrogen into heavier ones like helium, a process which releases copious amounts of energy while producing very little waste--often just neutrons and gamma rays. But atomic nuclei are composed mainly of protons, which are electrically charged and repel each other strongly. Overcoming this repulsion normally requires an electron-proton gas (or "plasma") at temperatures of 10 million degrees Kelvin or more. This temperature can be compared with the speed limit in a large parking lot--fiery collisions between cars become likely only above some threshold speed.
In nature, this sort of fusion is thought to occur only in the very hottest places--the insides of stars. On Earth it first occurred in the briefly star-like brilliance of the world's first thermonuclear explosion, courtesy of Edward Teller's 1951 hydrogen bomb prototype, codenamed "Item." Since that time, fusion has occurred on a smaller scale in reactors of various designs, but the energies involved are enormous, and human ingenuity has yet to devise a controlled fusion power plant that produces more energy than it takes in. Today's estimates generally place that technology some 20-50 years in the future, which, ironically, is the same development time experts predicted back in 1951. Plasmas are tough to control, particularly at 10 million degrees Kelvin, so this "holy grail" of nuclear engineering may stay in the future for even longer than that--maybe forever.
Conversely, any scheme for fusing atoms at lower temperatures, perhaps in a gaseous or liquid or solid state, would rely either on quantum/statistical fluctuations in the speed and position of nuclei (freak accidents in our imaginary parking lot), or on a catalyst of some sort that increases the likelihood of catastrophic collision (say, a bunch of Ford Pintos rolling around backwards).
There is a cold fusion process called muon-catalyzed fusion, in which subatomic particles called muons are introduced into heavy water. This is ordinary water (H2O) whose hydrogen atoms have eaten either one neutron, roughly doubling their mass, or two neutrons, roughly tripling it. The double-mass hydrogen is called "deuterium," and is stable over long periods of time, while the triple-mass hydrogens are "tritium" and have a half-life of about 12.5 years (i.e., it's mildly radioactive).
Since muons have the same charge as electrons but are much heavier, they can occasionally displace electrons in deuterium and tritium atoms. This makes the atoms even heavier than before, and consequently less able to fend each other off in a low-speed collision. It turns out these mistreated atoms can be made to fuse not only at room temperature, but at cryogenic (very cold) temperatures as well. This process has been on sound theoretical and experimental footing since 1957, when L.W. Alvarez first demonstrated it in an experiment which would eventually win him the Nobel prize. Unfortunately, muon-catalyzed nuclear reactions are fairly tame, and return far less energy than is required to make the muons in the first place, at least with current technology. Don't expect a muon-powered water heater in your basement anytime soon.
Nuclear chemistry in a jar
Pons and Fleischmann's extraordinary claim was to have produced room-temperature fusion using nothing but a glass jar of heavy water, a voltage source, and two electrodes. This is the familiar "electrolysis" apparatus from Junior High chemistry: a means to separate water molecules into hydrogen and oxygen, which bubble out of the water as gasses. The only difference is that the Utah scientists used a coil of platinum wire and a palladium rod as their electrodes. The idea was for the palladium--a heavy, gold-like metal which readily absorbs hydrogen--to fill up with deuterium atoms over a period of weeks, their dense packing increasing the odds of spontaneous nuclear fusion, until finally the apparatus began producing measurable quantities of excess heat.
And indeed, Pons and Fleischmann reported a heat output tens to hundreds of times what any plausible chemistry in the jar would yield. Unusually, though, they announced their results in a press conference, rather than in peer-reviewed scientific journals. That's generally considered a no-no. Worse, the details of their experiment were not fully documented, owing to University of Utah patent concerns. This put the right brains of many scientists in a decidedly skeptical frame of mind, especially when major labs around the world were unable to reproduce the results or to explain them as being the product of any known nuclear or chemical reactions.
What followed is one of the ugliest chapters in 20th century science, with widespread accusations of incompetence and fraud, and numerous careers ruined. The U.S. patent office stopped accepting applications related to cold fusion, respectable journals stopped accepting articles. Hounded by bad press, Pons and Fleischmann retreated to virtual hiding in the south of France, and the words "cold fusion" joined "antigravity" and "perpetual motion" as the province of crackpots. Repelled by this taint of quackery, many researchers fled to new hotbeds of nuclear chemistry, including ball-lightning fusion, and sonoluminesence-induced fusion (which was featured semi-accurately in the 1996 action movie Chain Reaction). Most abandoned the field altogether.
What's often forgotten in all this is that dozens of quite respectable institutions, including NASA, Los Alamos National Laboratories and the French Atomic Energy Commission, did replicate the Pons-Fleischmann experiment successfully, and even reported finding trace fusion byproducts such as neutrons and tritium, and sometimes copper, silver, and other metals contaminating the palladium which were not present before the experiment began, and which could be the products of a nuclear process called transmutation. Research continues to this day in the U.S., Europe and Japan, and an annual Cold Fusion conference draws hundreds of physicists and chemists, many of them with impeccable credentials.
The mysterious process
Is there really an effect? Many researchers will tell you that impurities in the heavy water and/or palladium play a huge role in the experiment's outcome. Palladium is also prone to microcracks which interfere with the consistent absorption of deuterium, and there may be a minimum current density in the palladium cathode, below which strange effects are not observed. Those claiming occasional success today have often mixed and matched exhaustively--using the same materials-science methods that tamed high-temperature superconductors. One popular approach involves plastic or carbon beads coated with palladium or sometimes with other metals such as nickel and titanium.
Still, depending on who you talk to, progress has either been nonexistent, because the whole thing is nonsense, or painfully slow, because the underlying process remains mysterious. And research has certainly been hampered by limited funding, limited credibility, and limited supplies of palladium, which is a rare metal closely related to platinum. Also, even at top-flight nuclear laboratories such as Los Alamos, researchers complain of inconsistent performance with apparently identical materials and apparatus. This by itself is a rather extraordinary claim!
The early '90s were a time of deep frustration for even the most legitimate cold fusion proponents, for whom all mainstream channels for publication were closed, leaving their eager left brains unable to bounce theories and data off the right brains of their peers. But in recent years, everyone's favorite haven of free-speech, the Internet, has come to the rescue. Although keyword searches are hampered by the existence of a popular but sadly eponymous Web authoring tool, the World Wide Web offers several hundred pages on cold fusion. Moreover, Usenet's sci.physics.fusion newsgroup includes lively and, er, heated discussions on all manner of exotic fusion schemes. This may exasperate traditional plasma-fusion researchers, many of whom see the group as their domain, but their squabbling is peer review of the genuine scientific sort, involving the left and right brains of hundreds of credible scientists.
So whether the Pons-Fleischmann effect is real or not, these exchanges may eventually yield some brilliant new insights that will put a Mister Fusion on your flying car after all.
Wil McCarthy is a rocket guidance engineer, robot designer, science fiction
author and occasional aquanaut. He has contributed to three interplanetary
spacecraft, five communication and weather satellites, a line of
landmine-clearing robots, and some other "really cool stuff" he can't tell
us about. His short fiction has graced the pages of Analog,
Asimov's, SF Age and other major publications, and his
novel-length works include Aggressor Six, the New York Times Notable
Bloom, and upcoming The Collapsium.
