Scientists may have finally tracked down the elusive "God particle" that gives matter mass and holds the physical fabric of the universe together.
Teams at the Large Hadron Collider, the £2.6 billion "Big Bang" atom-smasher near Geneva, said they had found a new particle "consistent" with the Higgs boson.
The discovery was described as "momentous" and "a milestone". But the results are preliminary and more work is needed before the scientists can be sure about what they have captured.
Observations so far show it looks and acts like the long-sought particle that has eluded them for 50 years.
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 proven not to exist, scientists would have to rip up the theory and go back to the drawing board.
Professor Peter Higgs, the retired British physicist from Edinburgh University who lent his name to the particle, heard the announcement with other scientists at a packed seminar in Geneva.
The 83-year-old professor hit on the concept of the Higgs mechanism in 1964 while walking in the Cairngorms.
Known for his unassuming nature and shunning the limelight, he wiped away a tear as the historic significance of the findings became apparent.
"I am astounded at the amazing speed with which these results have emerged," he said. "I never expected this to happen in my lifetime and shall be asking my family to put some champagne in the fridge."