Food for thought but not fuel for a starship

Physicists in Geneva have created the first 'antimatter' atoms, but it's far from being the stuff of science fiction novels and Star Trek episodes. Tom Wilkie reports
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Like Alice stepping through the looking glass, European physicists have started to explore the mirror image to our everyday world by creating the first atoms on earth composed entirely of "antimatter".

Professor Walter Oelert and his colleagues have made anti-hydrogen at the European Laboratory for Particle Physics, CERN, near Geneva. Like Tweedledum and Tweedledee, it appears identical in every respect to its twin, ordinary hydrogen - the simplest chemical element in the universe.

But the constituents of anti-hydrogen have physical properties that exactly cancel out those of the normal atom, so if one atom touches its antimatter counterpart they annihilate each other in a burst of energy.

Talk of "antimatter engines" and "positron drives" will be familiar even to a casual viewer of Star Trek, where the vast energy released when matter and antimatter collide is used to power the USS Enterprise. But the CERN physicists have not boldly gone and developed a new energy source.

Despite his team's achievement, Professor Oelert was "extremely pessimistic" that his discovery would ever lead to a new type of energy. "Even if it were possible to produce a lot of antimatter, the technological problems of keeping it are enormous," he said.

For a start, their harvest was meagre: just nine atoms of anti-hydrogen created over a period of three weeks, each one of them lasting only for about 40 billionths of a second, travelling at nearly the speed of light some 10 metres before their extinction on collision with an atom of ordinary matter. More energy was consumed by the particle accelerator at CERN, where they were created, than was liberated at their demise.

"This discovery opens the door into a completely new anti-world," said Dr Neil Calder, a CERN spokesman. "This may be a tiny Alice in Wonderland door ... through which we can get to a completely new understanding of the reality of the universe."

The British physicist Paul Dirac was the first to predict the existence of antimatter, in 1928, as a result of his theory marrying quantum mechanics with Einstein's theory of special relativity. But although the "Dirac equation", as it is now known, is today recognised as a creation of genius, it appeared at the time to be a complex piece of abstract mathematics.

Few people believed him, the concept seemed so outlandish. Dirac predicted that electrons - the ordinary particles that orbit the atomic nucleus, form chemical bonds between atoms and which carry electrical current along metal wires - should have a counterpart. Where the electron was negatively charged, the "positron" - anti-electron - should be positively charged and all the other quantum numbers denoting the nature of the particle should be reversed.

In 1932, Dirac's prediction was vindicated when a young American called Carl Anderson pictured the tracks left behind by positrons in a shower of cosmic rays. But the properties of antimatter took an even more bizarre twist in the late 1940s, when the American theorist Richard Feynman extended Dirac's theory and showed that antiparticles were really just ordinary particles but were travelling backwards in time.

With this sort of pedigree, antimatter has fascinated physicists ever since and the motivation behind the present experiments is to check that the theories hold good. Making anti-hydrogen is a crucial step because hydrogen is the most important material in the universe - it accounts for about three-quarters of all the matter there is.

Much of what physicists have learnt about the cosmos has come from a study of ordinary hydrogen. If its antimatter counterpart behaves differently, even in the tiniest detail, most of the established theories would have to be rethought.

Gerald Gabrielse, a professor of physics at Harvard, described the results from CERN as a "very interesting demonstration". But he stressed the need to compare antimatter atoms with ordinary atoms. "We will have to wait and see if we can compare the atoms with high accuracy to see if they are the same or not. That is where the real punch line is," Professor Gabrielse said.

To make the comparisons the researchers will have to slow down and then hold the antimatter atoms still for some time - possibly several weeks. But antimatter's tendency to annihilate everything it touches makes it rather like the universal solvent of schoolboy chemistry folklore - if you have a substance that dissolves everything, what can you keep it in?

CERN's researchers are now busily devising ways of "bottling" antimatter. They hope to build traps composed of electrical and magnetic fields to confine the antimatter atoms without touching them.