The LHC is the largest and most powerful machine humanity has ever built — a 27-kilometre ring under the Franco-Swiss border that accelerates protons to 99.9999991% the speed of light and collides them to recreate conditions a fraction of a second after the Big Bang.
Operated by CERN near Geneva, the LHC accelerates two beams of protons in opposite directions and crosses them head-on inside four detectors.
The main tunnel is a 27-kilometre loop about 100 metres below the border of France and Switzerland. Two proton beams race around it in opposite directions inside ultra-high vacuum pipes, guided and focused by thousands of magnets, until they are steered to collide at four points.
Roughly 9,300 superconducting magnets bend and squeeze the beams, carrying enormous currents with zero resistance. To superconduct they are cooled with liquid helium to 1.9 kelvin (−271°C) — colder than the 2.7 K of outer space, making the LHC one of the coldest places in the universe.
Protons reach 99.9999991% of light speed and collide at a combined 13.6 tera-electronvolts, momentarily concentrating enough energy to conjure new, heavier particles out of pure energy — as E=mc² allows. Each detector sees up to 40 million collisions a second.
The largest detector ever built for a collider — 46 m long, 25 m tall. A general-purpose instrument that co-discovered the Higgs boson and hunts for dark matter, extra dimensions and anything beyond the Standard Model.
The Compact Muon Solenoid pursues the same physics as ATLAS with a completely different design, built around a colossal superconducting solenoid. Two independent detectors cross-checking each other is how the Higgs discovery was confirmed.
Studies collisions of heavy lead nuclei, which briefly melt protons and neutrons into a quark-gluon plasma — the state of matter that filled the universe microseconds after the Big Bang.
Focuses on the subtle differences between matter and antimatter by studying "beauty" quarks, probing why the universe is made of matter at all when the Big Bang should have made equal amounts of both.
The Higgs boson (2012). The LHC's crowning achievement was confirming the Higgs boson, the particle tied to the field that gives other particles their mass — the final missing piece of the Standard Model, predicted nearly 50 years earlier and worth the 2013 Nobel Prize in Physics.
The data problem. The detectors generate petabytes of raw data per second — far too much to store. Real-time "trigger" systems throw away 99.99%+ of collisions, keeping only the rare, interesting events, which are then crunched by CERN's Worldwide LHC Computing Grid across hundreds of data centres.
High-Luminosity LHC. A major upgrade now underway will pack far more collisions into each beam crossing from the late 2020s, sharpening measurements of the Higgs and improving the odds of spotting rare new physics.
The next machine. CERN is studying a Future Circular Collider — a ~91 km successor ring that would dwarf the LHC, aiming to reach energies where the deepest open questions in physics might finally break open.
> Sources: CERN · home.cern. Figures reflect the LHC's Run 3 configuration.