'We only understand 4 per cent of the universe'

Ninety-six per cent of the cosmos is made of dark matter and energy whose composition we simply do not fathom, says James Watson Cronin, who won the 1980 Nobel for physics.

Most of the universe -- 96 per cent, to be exact -- is made of dark matter and energy whose composition we simply do not fathom, a Nobel laureate told physicists gathered this week to explore the intersection of the infinitely small and the infinitely large.

'We think we understand the universe, but we only understand four per cent of everything,' said James Watson Cronin, who won the 1980 Nobel for physics by proving that certain subatomic reactions escape the laws of fundamental symmetry.

According the most recent models, he said, 73 per cent of cosmic energy seems to consist of 'dark energy' and 23 per cent of dark matter, the pervasive but unidentified stuff that holds the universe together and accelerates its expansion.

The remaining four per cent consists of so-called 'normal matter' such as atoms and molecules.

Dark matter cannot be detected directly, because it does not emit or reflect light or radiation -- or not enough to be picked up by available tools.

But its presence can be inferred because its gravitational force deflects light from distant galaxies.

'We have an idea as to its parameters, but we still don't know what dark matter is made of,' said Stavros Katsanevas, head of France's national institute for nuclear and particle physics.

Most physicists attending the conference here on astroparticle physics think the basic ingredient is probably some as-yet undiscovered elementary particle, a relic of the 'Big Bang' that created the Universe around 13 billion years ago.