CERN is building a supercollider 100 km around.

Nature looks into a new push to build a really big (and really expensive) machine to work with really small particles:

CERN has taken a major step towards building a 100-kilometre circular supercollider to push the frontier of high-energy physics.

The decision was unanimously endorsed by the CERN Council, the organization’s governing body, on 19 June, following the plan’s approval by an independent panel in March. Europe’s pre-eminent particle-physics organization will need global help to fund the project, which is expected to cost at least €21 billion (US$24 billion) and would be a follow-up to the lab’s famed Large Hadron Collider (LHC). The new machine would be colliding electrons with their antimatter partners, positrons, by the middle of the century. The design — to be built in an underground tunnel near CERN’s location near Geneva, Switzerland — will enable physicists to study the properties of the Higgs boson and, later, to host an even more-powerful machine that will collide protons and will last well into the second half of the century.

This is “clearly a branching point” for the lab, says former CERN director-general Chris Llewellyn Smith. Until today, several other options were on the table for a next-generation collider, but the CERN Council has now made an unambiguous, unanimous statement. “This is a major step, to get the countries of Europe to say ‘Yes, this is what we would like to happen’,” says Llewellyn Smith, who is a physicist at the University of Oxford, UK.