IT was in a flash of inspiration while walking in the Cairngorms that Professor Peter Higgs came up with the idea of a particle that gives matter mass and holds the fabric of the universe together.
Almost 50 years on from that moment, the 83-year-old, who is now retired from the University of Edinburgh, wiped a tear from his eye as scientists said they had found what appears to be the "God particle", named the Higgs boson after the quiet physicist.
Teams at the Large Hadron Collider (LHC), the £2.6 billion atom-smashing machine near Geneva, said the new sub-atomic particle they have discovered is "consistent" with the Higgs boson.
The results are preliminary and more work is needed before the scientists can be sure of what "species" of particle they have captured. Even then, no-one can say whether the discovery will ever have any direct practical application.
But yesterday, at a packed seminar at the Geneva headquarters of Cern, the European Organisation for Nuclear Research, the scientific world hailed the "momentous" discovery.
Mr Higgs wiped a tear from his eye as the findings were announced. He said: "I would like to add my congratulations to everyone involved in this achievement. It's really an incredible thing that it's happened in my lifetime."
Mr Higgs's groundbreaking proposal, conjured up in 1964, was that particles acquire mass by interacting with an all-pervading field spread throughout the universe. The more they interact, the more massive and heavy they become.
A boson particle was needed to carry and transmit the effect of the field – the Higgs boson.
Mr Higgs later said of the discovery: "I certainly had no idea it would happen in my lifetime at the beginning, more than 40 years ago, because people had no idea about where to look for it, so it's really amazing for me to find out that it's really enough ... for a discovery claim.
"I think it shows amazing dedication by the young people involved with these colossal collaborations to persist in this way, on what is a really a very difficult task. I congratulate them."
Finding the Higgs is vital to the Standard Model, the theory that describes the web of particles, forces and interactions that make up the universe.
Without the Higgs boson to give matter mass and weight, there could be no Standard Model universe. If it was proved not to exist, scientists would have to tear up the theory and go back to the drawing board.
In December last year, LHC scientists revealed they had caught the first tantalising glimpses of the particle.
Since the initial excitement the scientists have sifted through vast quantities of data from billions of high-energy collisions in an effort to reduce the chances of being wrong.
Yesterday they confirmed that two of the LHC's giant detectors, CMS and Atlas, had delivered results that reached the definitive "five sigma" level of proof.
A sigma is a measure of how likely it is that a finding is down to chance. At five sigma, the likelihood of a statistical fluke is one in a million.
Professor John Womersley, chief executive of the Science and Technology Research Council, said: "It's a momentous day for science."
Dr Phil Clark, of Edinburgh University, who is based at Cern, has been working on the Higgs boson since 2008.
The Edinburgh University graduate, who was taught by Mr Higgs, co-leads the Atlas Simulation project at Cern.
Speaking from Switzerland after the announcement yesterday, he told The Herald: "This feels surreal. We've known for a few weeks, but to see people's reaction was very moving."
Asked how the discovery might change people's lives, he responded: "We haven't found anything conclusive, so that's impossible to predict, though if other particles like this exist, it could help explain the expansion of the early universe.
"What it has done is make the future look much more exciting. We have a whole new area to zone into. We now have to prove the particle has zero spin."
Asked if the team were celebrating, Dr Clark said: "Mr Higgs is flying back to Edinburgh from Switzerland this afternoon on an EasyJet flight. We asked EasyJet if they have champagne on board, and discovered it is £16 for a tiny bottle."
The LHC, the largest scientific instrument ever built, lies in a tunnel with a circumference of 17 miles (27.4km) that straddles the French-Swiss border near Geneva.
Protons, the "hearts" of atoms, are fired around the ring in opposite directions at almost the speed of light. When they smash together, huge amounts of energy are converted into mass and new particles created which then decay into lighter particles.
Higgs bosons emerge from the maelstrom but only very fleetingly – for less than a trillionth of a second – before decaying. By tracing the decay patterns, the scientists were able to find the "fingerprint" of the Higgs.
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