The first of some 5,000 magnets that will bend particles at near light-speed around a huge tunnel under Switzerland and France has been lowered into place.
The first of many magnets is lowered beneath the Earth (Image: Maximilien Brice/Cern)
It is part of the Large Hadron Collider (LHC), a powerful machine being built in the 27km-long accelerator facility at the famous Cern lab, near Geneva.
The LHC is designed to probe beyond our current understanding of physics.
The giant superconducting dipole magnet was lowered 50m down a special shaft at 1300 GMT on Monday.
Delivery of the 15m-long, 35-tonne structure to its final location marks the beginning of LHC installation.
The LHC will recreate the searing-hot conditions that existed just fractions of a second after the Big Bang.
Scientists hope this will enable them to see new physics, and discover the sought-after Higgs boson, or "God particle", which explains why matter has mass.
Researchers may even find new dimensions and generate mini-black holes.
When completed, two parallel tubes will carry high-energy proton particles in opposite directions around the LHC tunnel at super-fast speeds.
The superconducting coils in the LHC's dipole magnets allow them to carry extremely high currents without any loss of energy.
It was lowered 50m through a special shaft (Image: Maximilien Brice/Cern)
This enables them to produce the powerful fields required to control the trajectory of the protons around the Cern tunnel.
To reach a superconducting state, the magnets have to be cooled to a temperature of -271C, close to absolute zero, the theoretical lowest temperature attainable.
In addition to big dipole magnets, the LHC will be equipped with hundreds of other, smaller magnets.
Once in position, all magnets will be connected to a cryogenic system using superfluid helium to maintain the accelerator at the required super-cold temperature.
After they are lowered underground, the magnets need to be conveyed through a transfer tunnel to the main LHC tunnel, which lies at a depth varying between 50m and 150m.
Vehicles have been specially designed to deliver the magnets to their final destinations.
The narrowness of the tunnel complicates these handling operations, making it impossible for two loads to pass each other.