A huge detector is necessary to record the sub-atomic particles

The scientists are said to be "shocked" at the size of the effect they have seen.

"It's a most astonishing result," said Professor Val Fitch of Princeton University. "It is quite unexpected and very, very interesting."

The new discovery made by scientists in the United States and Japan has given them a glimpse of the fundamental way in which the Universe is made.

It shows that the Universe is a very perplexing place when viewed at the sub-atomic scale. And it may explain why we are here at all.

Mirror image

Scientists believe that, in many ways, antimatter is the mirror image of ordinary matter only with opposite electrical charges. But the puzzle is that there is almost no antimatter in our Universe.

Across the length and breadth of the cosmos, antimatter only turns up in minute quantities in very special circumstances.

At the beginning of the Universe, the Big Bang, scientists believe that there were equal amounts of matter and antimatter. But in the Universe's earliest moments something happened to cause most of the antimatter to disappear.

Finding out if antimatter is slightly different to matter could explain why it disappeared. And that is what the recent experiments seem to have done.

Tantalising results

They were carried out at Fermilab, a sub-atomic particle accelerator facility near Chicago, US. The scientists looked at the behaviour of sub-atomic particles called B-mesons and have cautiously reported finding "tantalising" results that show that matter and anti-matter do not obey the same laws of physics.

The phenomenon they think they spotted is technically called direct Charge-Parity (CP) violation. It means that particles behave differently if you swap matter for anti-matter and also swap left and right.

Physicists say that this "asymmetry" would have been important during the first moments of the Big Bang and may have resulted in almost all anti-matter being destroyed.

The observation of direct CP violation is an exciting one for physicists as it disagrees with all the currently held theories about the nature of matter.

"It's just sensational," said Professor James Cronin who received a Nobel prize for a related discovery in 1964.

Complexity revealed

He showed that K-mesons made from ordinary matter did not behave exactly like those made of antimatter. But the latest experiments show a much stronger effect and more of the underlying complexity.

Earlier this century, scientists predicted and then made microscopic amounts of antimatter. They realised that matter and antimatter together results in annihilation in a flash of energy.

If antimatter had not vanished from our Universe, then it is possible that all the cosmos would now consist of nothing but radiation - with no matter at all.

More Fermilab experiments and calculations are planned to see if the new observations can be understood. In the meantime, if you want to know why we are here, it is all about the difference between left and right - just look in a mirror.