The scientific method

'It's hard to imagine how thoughts could be transferred from one person to another. That doesn't mean that it cannot occur'

Many people have coincidences that they interpret as telepathy, such as knowing which friend is on the phone. Belief in such paranormal phenomena is very widely held. At a recent debate I had with the biologist Rupert Sheldrake, he presented many studies which claimed to support telepathy.

Some of these were based on subjects choosing the colour of a card held up by someone in another room, or knowing which of four friends were telephoning them. I know virtually nothing about telepathy, so what was my opposition based upon?

Foremost is the absence of reliable evidence on telepathy published in any of the conventional scientific journals. This, is of course, blamed on the supposed hostility of the scientific community to telepathy. But quite to the contrary, scientists would be wildly excited to investigate such a fascinating and surprising phenomenon if it existed. The real problem is that it fits all too well with what is known as pathological science.

It was a distinguished chemist, Irving Langmuir, who some 50 years ago coined the term. He was focusing on a number of phenomena, such as telepathy, which had startled the world of science during his career, but which had subsequently faded from view. Pathological science is characterised by having very small effects near the limits of detectability; the magnitude of the effect seems independent of the cause; there is usually a fantastic theory; and criticisms are met with ad hoc excuses. Telepathy fits some of these criteria. For example, attempts to reproduce the card-reading test failed. In addition it is hard to imagine how thoughts could be transferred from one person to another, for no known mechanism can at present be imagined. But that does not mean it cannot occur, as the history of science shows.

Consider Alfred Wegener in the Twenties, who put forward the idea that the continents of Africa and South America had once been joined together, but over millions of years had drifted apart. There was tremendous hostility to these ideas and it was only in the Sixties that new evidence, based on measurements on the earth's magnetic field, gave his ideas strong support.

Rather different is the case of the great physicist Lord Kelvin at the end of the 19th century. He would not accept the suggestion that the age of the earth could be of the order of millions of years. His opposition was based on the data relating to the cooling of the earth, but it was only later that it became clear that radioactivity heated the earth, and so made his calculations wrong.

Isaac Newton was also faced with criticism similar to that currently made about the paranormal. When he put forward his theory of gravity, that all bodies attracted each other with a force proportional to their mass and inversely proportional to the distance between them, it was, according to the great Leibniz, a return to occult qualities. Others said it was inexplicable by the current knowledge of mechanics.

To this Newton replied that, yes, it seemed to him a great absurdity that one body could act on another at a distance through a vacuum without the mediation of something else. But, and this is crucial, the evidence was overwhelming and he admitted that he had been unable to deduce the reason for these properties and said, "I do not feign hypotheses." Evidence is all.

One of the problems with telepathy is that it is hard to see what there is to investigate. The phenomena are so trivial. Is it really surprising that one sometimes knows who is on the phone? What would be impressive is the transfer of a telephone number by telepathy. If telepathy existed, the effects could be dramatic; just consider the benefits to bridge partners or friends in an exam. At present there is nothing for scientists to investigate other than why people have such beliefs.

Lewis Wolpert is Professor of Biology as Applied to Medicine at University College, London