The first report of ‘test-tube fusion’ came on the morning news. We debated the plausibilities energetically over the breakfast table. Relative roles were quickly established. Professorial habits die hard. I found myself conducting a tutorial explaining why it sounded about as probable as a flying pig. Naturally, dogmatism was contested. Science must always allow a vast benefit of doubt for anything striking at established doctrine. I must not dismiss the work of Professors Fleischmann and Pons out of hand. We agreed that we must wait for more evidence.
What I am going to say here is bound to sound slightly sceptical. I cannot give a clear (and greatly simplified) idea of how astonishing these reports are without silhouetting them against the conventional wisdom. True, they are not as far beyond the bounds of reason as Fred Hoyle’s notion that flu epidemics are due to germs coming in from Outer Space. They do not contravene a grand Law of Nature, like a perpetual motion machine. They are just not consistent with the theoretical picture one would build out of the various pieces of physics that must surely be involved.
This picture is remarkably coherent and complete. First, there is the physics of fusion. The essence of this is that when two deuterons get very close together they attract one another very strongly, and fuse together to make a nucleus of helium. In the process, a vast amount of radiation is given off, and can be absorbed in the surroundings, making them very hot. Put all this inside a star, and sunlight flows out for billions of years. Put it into a thermonuclear warhead, and you can set off a big bang. Put it under a steam boiler, and you have the makings of a nuclear power station.
Where do you get the deuterons from? The prescription is quite straightforward. Take about ten tons of ordinary tap water and pass an electric current through it, splitting it into oxygen and hydrogen gases. Go on electrolysing it like this, until there is only about a kilogram of the original water left. Most of this will be ‘heavy’ water, in which the place of hydrogen is taken by deuterium. Atom for atom, deuterium is chemically identical with hydrogen, except that it has twice the weight. Electrolyse the ‘heavy’ water, and collect this ‘heavy hydrogen’ as a gas. Pass a hefty electric discharge through the gas, to break up all the deuterium into the negatively-charged electrons and the positively-charged atomic nuclei. The latter are your deuterons.
Deuterium is abundant and easy to collect. You can buy it on the market at less than a million dollars a ton. Since a kilogram of deuterium has the potential fusion energy of tens of thousands of tons of coal – or TNT – it sounds like a bargain. The difficulty has always been to get the energy out in a controlled way.
Now you might think at first that all you had to do was to compress or freeze the deuterium gas until the deuterons are near enough together to fuse with each other. Fortunately that does not happen: if it did, heavy water would be highly explosive, and the oceans would boil away, just from the traces of it they contain. The reason is that deuterons are electrically charged, and repel each other when they are not already very close together. This repulsion is quite strong. It takes about ten thousand volts to bring two deuterons near enough to fuse. Think of two Victorian ladies in enormously wide crinolines, trying to embrace. The hoops of their dresses would keep them well beyond arm’s length. In scale, each hoop would be about a mile across. Deuterons cannot even come within shouting distance of each other without immense effort.
All this was clearly understood and tested, years ago, by hurling deuterons at one another in a high-energy particle accelerator. Of course, fusion by that means would be totally uneconomical as an everyday source of energy. The only way that could be imagined for getting out more energy than was put in was to induce a self-sustaining reaction in a mass of deuterium gas. This would happen if the gas could be raised to a very high temperature, where all the deuterons would be moving so fast that they would occasionally bang together with enough energy to fuse. Crowd the ladies together, play a furious waltz, and watch for warm encounters as the tempo increases.
The temperature in the core of the Sun, and in a thermonuclear warhead, is about a hundred million degrees. Hot fusion works splendidly, but blows everything apart. For the past forty years, scientists and engineers have been trying to hold some of this hot gas together with loops of magnetic field. Every now and then, they come back and say that they have pushed the temperature up a bit, and held it for a longer fraction of a second. The next step, they say, will need a larger, more elaborate device – and please could they have another million dollars, or ten million roubles or hundred million ecus to build it. Each time, they intimate that fusion power will be a commercial proposition in due course – in forty years, perhaps. JET is already as big as a concert hall, and still the horizon of exploitation is about forty years ahead.
Another type of hot fusion device would focus laser pulses from all directions on a tiny pellet of the nuclear fuel, compressing, heating, and ‘igniting’ it before it has time to fly apart. This seems to me more fun than magnetic confinement, but it is just as elaborate and even further from likely use.
Back now to Fleischmann and Pons. All they did was to pass a current through heavy water in such a way that heavy hydrogen was produced on the surface of a chunk of palladium. This is a metal chemically similar to platinum, with the well-known property of absorbing hydrogen (light or heavy) into itself in large quantities. In this situation, it mops up the deuterons drawn to it by the electric current until it is loaded with them.
What F & P claimed was that some of the deuterons inside the palladium are fusing together at an appreciable rate. Their evidence for this was indirect: they found that the apparatus was getting much hotter than they expected. Being experts in electrochemistry, they knew how to calculate the total amount of heat that should have been produced by all the different chemical reactions and physical currents in the system.Why was this much less than they measured?
Perhaps the possibility of ‘cold fusion’ had been so discounted that nobody had previously thought of looking for it. Perhaps, so they suggested, the deuterons are so crowded together in the interstices of the metal that some of them get within fusing range of one another. That is where I jibbed. Martin Fleischmann (who is Professor at Southampton University, a Fellow of the Royal Society and all that) would surely know that the electrical forces acting between the atoms of a solid are measured, at most, in tens of volts. The crystal lattice of the palladium is just not robust enough to withstand the thousands of volts needed to push two deuterons into fusion. Are the deuterons in the metal much more densely packed than they would be in solid, frozen deuterium, say? No, I don’t see a way out there.
This is the point we reached between us in our off-the-cuff breakfast-table analysis. Since then, the situation does not seem to have got any clearer. More questions have been raised than have been answered. There is still a complete stand-off between the experimental claim and the theoretical picture, with very few wild cards or jokers to reconcile them. Either F & P will eventually be sent off with very red faces, or one of the bulwarks of physics will have to be replaced.
Meanwhile, the scientific world has been heating itself up with reports of various other experiments designed to replicate or test or refute or explain F & P’s claims. People are looking for the neutrons and other distinctive radiation that ought to be produced by the fusion reaction. Some say the effect has been confirmed, others say not. Fancy theoretical schemes are being hastily put together to explain it, and fancy devices being hastily patented to exploit it commerically.
The most cheerful prospect has cold fusion completely displacing hot fusion for future energy supply. Never mind the billions that have already been spent on magnetic confinement: just imagine every city with an environmentally friendly neighbourhood powerstation, tanked up occasionally with heavy water concentrated in endless supply from the oceans. This prospect is not utterly absurd, but it is extravagantly rosy. Even if the F & P effect were confirmed, it might be much too feeble to be at all useful in that way.
This is the scientific backdrop against which the drama is being played. Events – some of them very unseemly – are happening much too fast to be followed closely by outsiders. I do not know myself exactly where they have got to today, and am not well enough informed to have strong views on where they are likely to get to tomorrow. At times like these, the most comfortable seat is on the fence, enjoying science-watching as a spectator sport, where the main thrill is seeing some of the professional performers coming a cropper, or behaving badly. These demigods are human, after all.
This is not dodging the issue. If I were inside this particular game – if I were planning to do research on it, or had to advise, say, the Central Electricity Generating Board on its capabilities – I would have to study all the evidence in detail, and try to make up my mind on its credibility. My decisions or advice would then speak for what I found that I believed. As it is, I decline to arrive at an opinion: that would be a full-time job, crowding out other non-trivial pursuits.
When scientific controversies erupt like this, one must obviously try to grasp the essential points at issue. The mere fact that these points are seriously disputed affects one’s world picture. But if one is not then prepared to participate fully in the dispute, the proper scientific attitude is temporary suspension of belief-forming activity. Most of the philosophies of science are weak in treating ‘belief’ as something one ‘has’, instead of seeing it as a relationship between thought and action. Even the sociological norm of ‘organised scepticism’ suggests a more decisive role for active thought than a situation might demand.
The controversy over ‘cold fusion’ is just a particularly striking example of a normal meta-scientific phenomenon. Every day, working scientists become aware of conflicts of evidence and/or opinion on research questions, and have to decide whether or not to get involved. Mostly these questions are highly specialised, and do not hit the headlines. How are you on William Little’s theory of organic superconductors, or the mystery of the missing solar neutrinos? For the few questions that go public, there are a hundred that only the experts know or care about.
All that such disputes have in common is that their outcomes are diverse. Sometimes they turn out to be rubbish – literally, in the case of ‘Polywater’. Occasionally they are fraudulent, as with ‘Piltdown Man’. Sometimes they seem to outsiders to be basically semantic, as with ‘Punctuated Evolution’. Sometimes they go on accumulating pros and cons for years, as with the ‘Dinosaur Catastrophe’. And just now and then, as with ‘Continental Drift’, they change the whole face of our scientific globe. I wonder how ‘cold fusion’ will look in the history books. Let’s wait and see. And watch for reports about neutrons, which ought soon to clinch the matter for us all.