Scientists hope to discover secret world inside atoms


SCIENCE HAS struggled for centuries to explain the universe and its hidden structure. Despite this effort we can still only account for a paltry 5 per cent of its contents - the stars and planets we see through our telescopes.

Yet we stand on the threshold of a new understanding, not just of the universe but also the secret world deep inside atoms.

The source of this great potential was explained last night by Prof Rolf-Dieter Heuer, the incoming director general of Cern, Europe's nuclear research facility. Cern hosts the world's largest single scientific experiment, the Large Hadron Collider (LHC), a €4 billion particle accelerator. It will smash atoms together at near light speed to create energies not seen since the Big Bang that formed the universe 14 billion years ago.

Prof Heuer last night delivered the 2008 Annual Statutory Public Lecture of the School of Theoretical Physics in the Dublin Institute for Advanced Studies. TCD and UCD host it in alternate years, but this year's host UCD kindly agreed to transfer the lecture to the RDS, and to promote it in co-operation with the RDS and The Irish Times.

The LHC will allow particle physicists to carry out collisions that will reach energies much higher than ever before. The results of these experiments will inform us not only about the structure of atoms but also about the structure of the universe.

Accomplishing this requires exceptional energies and the LHC will provide these energies, Prof Heuer said before his lecture.

The LHC will send two hydrogen nuclei around its 27km long underground ring at close to the speed of light before smashing them together. This would release about the same energy released should a mosquito fly into your cheek, he said. But it will deliver this energy at a near infinitely small point many thousands of times smaller than the width of a human hair. This would create not just high energies but high-energy densities. "What matters is the energy density. We create energy densities close to the moments after the Big Bang," he said. These high-energy densities are required to "see" inside atoms to explain their structure. The higher the energy, the better able you are to see very small structures.

He used a simple idea to explain this, describing how while walking along on a very dark night you are stopped by a picket fence. You can't see it but know there is a barrier hindering you and you want to understand what it is.

You throw a basketball against it and it bounces back every time. You switch to a tennis ball and it bounces back some of the time. If you scale down to something the size of a pinhead you will be able to understand the shape of the fence and also manage to "see" the knot holes in the timber.

The LHC goes to higher and higher energies for this reason and this is why it can at once provide information about the micro world and the macro world.

Central to this understanding is a theoretical concept known as the Higgs particle, he said.

It is theoretical because it hasn't been seen yet, but the LHC will reach energies high enough to see it - provided it is there at all. "The Higgs is one of the only things that is missing in our understanding of the visible universe."

If found it will be detected emerging from a particle collision and will become the latest in a long line of subatomic particles first seen in this way. But proving its existence may immediately help in our understanding of the invisible universe, the so-called dark matter and dark energy that together make up 95 per cent of the complete universe, he said.

There are properties about the Higgs that are also theorised for dark matter.

Prof Heuer stressed that he was not making a direct connection between them, but understanding the Higgs could help in our efforts to explain dark matter.