In search of the God particle

Science is all about big ideas. But few come bigger than the 'Higgs bosOn' – a theory that may unlock the universe's deepest secrets. Steve Connor reports on the experiment of the century

It is not everyday that someone's name becomes inextricably linked with God. But it is not everyday that someone comes up with a theory that could help to unify the many disparate forces of the universe. All the more strange, then, for the man behind the sub-atomic "God particle" to be an unassuming grandfather living in modest retirement in one of the more sedate districts of Edinburgh.

Indeed, Professor Peter Higgs, 78, is modesty personified. A theoretical particle physicist, it took him 20 years before he could even bring himself to call the God particle by its more scientific name – the Higgs bosOn. Up to that point, he preferred the more prosaic term, "scalar boson".

He still squirms when people refer to it by the deified moniker coined many years ago by a brasher colleague. "I find it embarrassing because, although I'm not a believer myself, it's the sort of misuse of terminology that might offend some people," he said. And if Peter Higgs is anything, he's not someone to go around offending people.

He first formulated the theory behind the sub-atomic particle named after him in the 1960s, and for almost half a century it has remained as elusive as stardust. That could all change later this year, however, when one of the world's biggest experiments is switched on deep beneath the Alpine meadows on the Franco-Swiss border, the home of the European Centre for Nuclear Research (Cern) near Geneva.

Within a 27km-long, circular tunnel – as big as the Circle line on the London Underground – atom will be smashed into atom at something approaching the speed of light. The machine, called the Large Hadron Collider (LHC), is built to produce energy levels expected to be powerful enough to shake out the elusive Higgs bosOn from its seemingly inescapable prison within the atomic nucleus.

The Higgs is just one of the discoveries that the LHC is expected to make. The international team of physicists behind the project believes that the LHC will almost certainly produce a jewel box of discoveries that will light up the infinitesimally small world of sub-atomic physics.

"The actual discovery of the Higgs bosOn, if it happens, is only one part of the programme. There is vastly more for the machine to do," Professor Higgs said. "I'm most excited for instance about the possible identification of super-symmetry particles – symmetrical particles of the particles we already know".

Supersymmetry refers to the "grand dance" of particles in the universe. We know of about a dozen sub-atomic particles, which have exotic names such as quark, lepton and neutrino. Yet for every kind of particle, there may a super-symmetrical partner.

The trouble is, we can only see one of the partners in each dancing couple, with the "significant others" remaining invisible. If supersymmetry is confirmed by the LHC it will help scientists towards the ultimate goal of a unified theory for the fundamental forces of nature – in particular the force of gravity which so far lies outside the realm of the forces known at the quantum level of the sub-atomic particle.

"The reason it's exciting is that I'm interested in a unified theory of forces, in particular quantum gravity," Professor Higgs said.

Although long retired from research, he still possesses a child-like wonder of the world which we cannot see but which is so critical to some of the most important questions at the centre of our understanding of creation, the universe and the end of time.

Professor Higgs was speaking to the press yesterday after spending much of the weekend seeing the LHC for the first time, before it is sealed in preparation for the switch-on in summer. It was the first time he had been to Cern since 1985, and the first time he had spent any appreciable time there since a short research project in 1976.

"The sheer scale of the detectors is overwhelming. It's far more impressive than anything you get out of photographs," he said. The detectors in question are four huge underground instruments, some as big as a gothic cathedral, which will act as microscopes to identify a Higgs particle in a fraction of the split second it takes to make an appearance before it disappears once more.

Professor Higgs said he is 90 per cent certain the LHC will find his particle when it reaches its full working potential, perhaps in a year's time. If the machine does find the Higgs, it will cap an extraordinary career for the Bristol-born mathematician, given that he first proposed the idea more than 40 years ago when he was a young theoretical physicist at the University of Edinburgh.

It will also solve one of the most pressing problems in science because the Higgs bosOn lies at the heart of matter itself. In particular it is supposed to explain why objects have mass and while some phenomena – such as light – do not.

Professor Higgs was the first to propose the theory that the reason why objects have mass is because they interact with an invisible field, now called the Higgs field. Heavier particles interact more strongly, whereas photons (light particles) do not interact at all. Without this Higgs field, everything – from proton to planet – would be as insubstantial as a light beam.

When Higgs first came up with the idea, few people took him seriously and even the then editor of a leading physics journal – who was based at Cern – thought it was too conjectural to be published. "At the time I started this work, it was rather an unfashionable thing to be interested in, certainly on this side of the Atlantic ... my colleagues thought I was a bit of an idiot," Professor Higgs recalled.

"A colleague told me that at Cern they didn't see what I was talking about had much to do with particle physics. So I added on a few extra paragraphs [to the original scientific paper] and sent it off across the Atlantic to [the journal] Physical Review Letters, which did accept it," he said.

Four decades later, Cern is in pole position in the race to be first to find the Higgs although its advantage has been eroded. The LHC should have opened three years ago but, as with all big engineering and construction projects, it was dogged by delays.

Meanwhile, another atom smasher at the Fermi Laboratory in the United States may have come close to solving the problem. Professor Higgs said the Fermi Lab scientists may have already done it, but may not yet be in a position to prove it because the critical evidence may still locked up in data obscured by background noise.

Professor Higgs said that it's not something he's going to mention to the people at Cern. "It's a possibility. I think the race is a very close thing. Fermi Lab are obviously trying very hard, they have a disadvantage compared to LHC when it starts, in terms of lack of luminosity, comparatively speaking – so it's for them to find it," he said. "But it could be there in their data, but not just found in the analysis, yet. They are certainly hoping that they'll get their first indication before the LHC gets going."

But time is running out for the Fermi Lab, as the giant, supercooled magnets at the LHC are being prepared for their task of keeping the particle beams swirling round the tunnel with pin-point accuracy at the rate of more than 22,000 times a second.

Just the amount of supercooling involved is stupendous – enough deep freeze to keep 140,000 kitchen fridges just above absolute zero, which is –273C. In fact, when it is fully operational, the LHC will be the coldest place in the known universe. There are enough supercooled cables in the LHC to go around the equator 6.8 times, and enough filaments in the cable strands to stretch to the sun and back five times – and enough left over for a few return trips to the moon.

The immense energies involved in making the atomic collisions happen have already generated unwelcome publicity for the LHC. Some scientists have suggested that they may generate mini black holes, which have led others to suggest that these black holes could somehow merge to form a larger, destructive entity that could swallow up the entire earth.

"The black hole business has become rather inflated," said Professor Higgs, irritated by the suggestion that the LHC could become an unwitting doomsday machine. "Even the theorists who are suggesting that mini-black holes are things that could be produced are not predicting black holes large enough to swallow up chunks of the universe. I think the publicity has rather got out of hand and some people have misunderstood it," he said.

Hysteria aside, Professor Higgs seemed pleased that so many people outside the rarefied world of particle physics and cosmology are taking an interest in what will happen at Cern in the coming few years. He for one is certain that something awesome is about to happen, even if his particle is not found – although he thinks that is unlikely.

"I'd be very puzzled if it wasn't discovered ... If you don't have something like a Higgs bosOn ... if it's not that, what the hell is it? If it's not found, I no longer understand what I think I understand," he said.

And if it is found? "I shall open a bottle of something."