By the mid-20th century, particle physics had a beautiful set of equations — the Standard Model — describing the elementary particles and three of the four fundamental forces (electromagnetism, weak and strong) in a consistent way. But there was a puzzle: in its natural form the maths predicts all particles to be massless, while the electron clearly has mass, the W and Z bosons are very massive, and the photon is massless. In 1964 three independent groups — François Englert and Robert Brout in Belgium; Peter Higgs in Scotland; and Gerald Guralnik, Carl Hagen and Tom Kibble in London — proposed the same fix: a field (today the 'Higgs field') permeates every point of the universe; particles acquire inertia, i.e. mass, by interacting with it. Such a field should have a quantum, a particle that could in principle be detected. That particle was the one sought for half a century.

The theory was elegant; the experiment was brutal. Producing a Higgs by exciting the field briefly required collision energies far above 100 GeV — and even if produced, the particle lived only ~10⁻²² seconds and could not be seen directly, only inferred from the tracks of its decay products (two photons, four leptons, etc.). CERN's LEP collider in the 1990s and Fermilab's Tevatron in the early 2000s searched and fell short. Then near Geneva, 100 metres below the Franco-Swiss border, the 27-km Large Hadron Collider (LHC) was built — at €9 billion, with 40 countries collaborating, after 30 years of planning and construction. It opened in 2008, was shut down almost immediately by a catastrophic magnet failure, and started serious physics in 2010. At two separate points around its ring, cathedral-sized detectors called ATLAS and CMS chased the same question independently.

On the morning of 4 July 2012 in CERN's main auditorium, the two collaborations — which had deliberately kept their analyses blind to each other — showed the same number: a new boson at around 125 GeV/c², with ~5-sigma significance (a chance of about 1 in 3.5 million of being a fluke). Peter Higgs, 83, watched from the audience with tears in his eyes: "I never expected this to happen in my lifetime." Subsequent measurements of the particle's spin, parity and decay channels confirmed it really is the Higgs. The 2013 Nobel Prize in Physics went to Higgs and Englert; Brout had died in 2011, and the exclusion of Guralnik, Hagen and Kibble has been debated ever since.

The scientific meaning is clear: the Standard Model's last missing piece, sought for 50 years, was completed; the source of mass for elementary particles (not the mass of atoms — most of that comes from the strong force — but the mass of the electron, the quarks and so on) was demonstrated experimentally. The cultural meaning is broader: the LHC is the largest international science project built since the end of the Cold War, and most of the theorists who had postulated the 'God particle' lived to see it confirmed. The Higgs completed the Standard Model — but it did not answer dark matter, the mass hierarchy or quantum gravity; the LHC is still chasing those today.