Doggedness has carried the best scientists through the mire of public mistrust... provided they're right, says Len Fisher.

Scientists have always had trouble overcoming public distrust of new ideas, especially when those ideas seem to contradict the "common sense" of the time. Galileo was imprisoned by the Pope, Darwin was vilified from the pulpit, and Einstein was subjected to abuse from a group of pro-Nazi academics in the book 100 Authors against Einstein . The response of all three was to demonstrate the courage of their convictions by persisting along their chosen paths. Galileo used his time in prison to write Dialogues Concerning Two New Sciences, which became a turning point for science in the Western world. Darwin continued to publish evidence in support of his theory of evolution, and Einstein when told that 100 academics had proven him wrong, commented mildly, "It would only have taken one", and went about his business unperturbed.

Persistence is an admirable quality in a scientist, especially when it comes to developing and promoting revolutionary ideas, but it also helps if those ideas are right. One of the main problems in overcoming public distrust of new ideas is that it can be so difficult to distinguish the brilliant from the bizarre.

Take, for example, Jacques Benveniste's well-publicised 1988 claim that pure water can carry a "memory" of homeopathic molecules that were previously dissolved in it but subsequently diluted out. Consider also American scientist Peter Fong, who tried adding Prozac to water in which clams were growing. In 1998, he earned an IgNobel prize for his contribution to the happiness of clams, but in fact his experiments were a perfectly serious (and successful) attempt to find a cheap replacement for the very expensive chemicals that were then used to induce synchronous spawning.

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Benveniste's experiment, on the other hand, was scientific nonsense, because other experiments have shown that water is unable to retain any permanency that would allow "memory" in a way that a computer has memory.

Without specialist knowledge, though, how could the public be expected to judge which of these two experiments was brilliant, and which bizarre? Benveniste has persisted with his claim, and has scored two IgNobel prizes in the process, not least for the claim that the "information" supposedly memorised by water can be transmitted over telephone lines and the internet.

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So, persistence is not (or ought not to be) enough to convince a sceptical public. It needs something more - for example, a demonstration that the claim works. When pilots in the Second World War were lost because of stalling and crashing airplanes, Frederick Lindemann (Baron Cherwell), the Government's chief scientific adviser, calculated the best way to bring an aircraft out of a stall. When his mathematics failed to convince pilots, he took an aircraft up himself and deliberately put it into a stall to show that his method worked. Fortunately, it did.

Sometimes fortune intervenes to save scientists the trouble of personally demonstrating that their ideas are right. British proponents of space travel in the 1950s suffered considerably at the hands of the Astronomer Royal, Sir Harold Spencer Jones, who declared in 1957 that "space travel is bunk". Two weeks later, Sputnik was launched.

But sometimes demonstrations are not enough. When Galileo offered to show the moons of Jupiter through his newly developed telescope to his long-time critic Gulio Libri, Libri refused to look, saying that he knew the truth already. When Libri died, Galileo commented tartly that he might at least now be able to view the moons while on his way to heaven.

And sometimes demonstrations can be deemed too risky. When Benjamin Wilson, an amateur electrical experimenter and court painter to King George III, became convinced that the sharply pointed lightning rods recommended by Benjamin Franklin were a dangerous American innovation, he failed to convince his fellow members of the Royal Society that blunt rods were better. So he turned to the King, whose love of things American had not been enhanced by the War of Independence. The King promptly ordered that all of the Franklin rods fitted to Royal Buildings should be removed or fitted with cannon balls.

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It helps to have royalty on your side, but these days public trust in royalty is on a par with public trust in scientists, and the arguments that scientists advance must be sufficiently persuasive in their own right. This is not always the case, and the ensuing debate tends to take the same form, no matter whether it concerns nuclear power, animal experimentation or genetically modified crops. A scientist will say that the benefits far outweigh the risks, or that the risks are negligible. An opponent (sometimes another scientist) will say that the risks are greater than have been admitted, and that the process should not be undertaken until there can be an assurance that no risk is involved.

Both sides are indulging in hubris. To say that the benefits will be far-reaching, or that the risks are "negligible", suggests the scientist can predict the future. But the opponents of new technologies need to show the same modesty. In demanding that no technology should be accepted if it carries an element of risk, they are exposing themselves to the same argument they apply to its proponents. What gives them the right to demand that we take the risk of not introducing the new technology, which may be every bit as great (and as difficult to quantify) as the risk of introducing it? Sometimes the decision is clear-cut, for example, when the risk of a new vaccination is tiny compared with the advantages. Not all decisions are straightforward, though. And communication between the proponents and opponents of a new technology becomes especially difficult when the media and the public demand black-and-white answers to questions for which there are no such responses.

Modern scientists have a harder row to hoe than earlier generations because the public is better informed and more likely to question the scientists' suggestions and decisions, especially with regard to technological change.

There is no simple solution, but scientists need to recognise that this assessment is not theirs alone to make. The size of a risk, or of a benefit, is a matter of community perception. Scientists can inform that perception by providing the public with facts and arguments on which to base it, but they cannot determine it. Their best chance to influence it beyond the point of providing information lies in sharing the process of science and in being open about the reasons behind the assessments that they make. Scientists can do no more, but they should do no less.

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Len Fisher is a visiting research fellow in the physics department at Bristol University. He won an IgNobel for calculating the optimal dunking time for a variety of biscuits. His book Weighing the Soul is published this week by Weidenfeld & Nicolson, ?12.99. Times Higher readers can get copies for a special price of ?10.99 by calling 01903 828503 and quoting JAWTS.