The truth is relative

Einstein's theory may have to be turned on its head, but that's nothing new for science

It was a striking claim. If the group of scientists who asserted that light has slowed down were right, it would have been a blow to one of the cornerstones of modern science. Ever since Einstein devised his special theory of relativity, scientists have held that the speed of light in a vacuum is an absolute constant. Now it seems his most famous equation, E=mc2, may no longer hold true.

However, far from being shocked by last week's news, the scientific community is taking it in its stride. If Einstein did blunder, then in one respect it's nothing new. Scientists have been getting it wrong ever since Aristotle proposed that the sun revolves around the Earth. It's what scientists do. Getting it wrong is practically part of the job description.

The history of science is littered with distinguished names who made mistakes. The study of light, alone, reveals a rich catalogue of misconception. Kepler thought that light travelled with infinite velocity - not true. Galileo believed it would be possible to measure its speed by quickly covering and uncovering lanterns - not a chance. Newton claimed that light speeded up when it passed through a denser medium - quite the opposite.

But there is a huge difference between these almost commonplace errors and this latest news. The belief that the speed of light is constant has been accepted as an intrinsic truth for nearly a century. It is part of the modern paradigm. Even the first hint of its downfall is big news.

But we should be clear about what we are seeing here. Even if the speed of light has changed, we are not about to see the downfall of an absolute truth. Despite the assertions of some teachers, scientific theories are not absolute truths; they are just descriptions of the world, some of which fit better than others. Einstein's theories fitted the evidence available at the time. If new evidence arrives which proves him wrong, then scientists just get on with the job of devising a new theory.

Nor is this process anything new. Cherished beliefs about how the world works, often held by large numbers of people, have crumbled before. Scholars in 17th-century France clung to a world-view based on the philosophy of Descartes. In their universe the stars lay at the centre of swirling vortices and the planets moved through an ether. When Newtonian mechanics arrived, with its assertion that space was a vacuum and its description of gravity, it blew their ideas away.

In Victorian times, an erroneous consensus emerged about the age of the earth. The influential physicist Lord Kelvin asserted that it was 100 million years old. Such was Kelvin's reputation that other scientists fell over themselves to agree. Almost all geologists concurred, and even the naturalist Alfred Russel Wallace - who would have preferred a much older planet to support his theory of evolution - fell into line. However, within 30 years the consensus was shattered. Rutherford discovered that the age of rocks could be found by measuring their radioactivity. Today geophysicists put our planet's age at 4.5 billion years.

In comparison, Newton's physics had a good run for its money. It held sway for 200 years - about as long as the gold standard, which he also set. It was finally superseded when Einstein produced his new description of the universe: the theory that may now be under threat.

The possibility of tearing up one of science's holy texts is something that makes working in science an exciting and vibrant activity. It distinguishes it from the arts. Once a painting is hung in a gallery it is revered for perpetuity; once an equation is proved wrong, then, however much it was once regarded, it is discarded and forgotten. The possibility that someone can overturn an icon as famous as E=mc2 is startling to the outside world. It's as if Damien Hirst was let loose in the National Gallery to paint over an old master. Yet in science, such change is natural and applauded. In his middle age, Darwin expressed the hope that when he was older he wouldn't stick too rigidly to his views should they be challenged by a younger generation.

But in the distant past, natural philosophers were far too often unwilling to look for new evidence which might prove an old theory wrong. For 2,000 years doctors practised a medicine based on the ancient Greek idea of the four humours. They trusted their text books, rather than their own eyes. Even when the anatomy diagrams disagreed with what they saw in their patients, they were unwilling to accept that they were wrong. Today's scientists have no such respect for tradition. They are looking to challenge old theories, and actively seek out the evidence they need to do it.

The fact that the constancy of the speed of light is now being challenged, and by astronomy, should come as no surprise. As ever, astronomy is at the frontier of science. Like the wild west, this frontier is a lawless place; it's inhabitants hold no respect for rules - even ones laid down by Einstein. Armed with improved telescopes, they are now able to see further into the cosmos, and with greater detail, than ever before. It has given them a new confidence. In the past, when their observations didn't fit the theory, they were inclined to disbelieve their results. Now they are more likely to accept what they see, and challenge the theory. As early as 1999 some physicists realised that they could solve several of the outstanding problems in cosmology if they accepted that the speed of light has changed. If the new evidence proves correct, and light really has slowed down, it won't be a disaster; it may actually solve more problems than it raises.

On the other hand, if the varying speed of light remains unexplained, it will be in good company. There is much about the world that we still don't understand. Despite centuries of endeavour, science is still a long way from finding all the answers. Newton's laws describe how gravity behaves, but how it works is still a mystery. Darwin's theory of natural selection tells us how species evolved, but we have no idea how life itself started. When Crick and Watson unravelled DNA they revealed the genetic building-blocks of our brain, but the source of our free will is still an enigma. And, although physicists have traced back the history of the universe to a millisecond after the big bang, that is not the question on everyone's lips. "Who cares about the half second after the big bang?" asked Fay Weldon. "What about the half a second before?"

Where we came from, who we are and where we are going are the fundamental questions that people want answered. They have been around for thousands of years. Science may eventually find the answers, but expect a lot more mistakes along the way.

Martin Gorst is the author of Aeons: The Search for the Beginning of Time (Fourth Estate, £7.99).