The Large Hadron Collider

CERN built a 27-kilometer ring under the Swiss-French border, accelerates protons to 99.9999991% the speed of light, and smashes them together to recreate conditions from a trillionth of a second after the Big Bang. The LHC confirmed the Higgs boson in 2012 — a particle theorized in 1964 that explains why anything has mass. It cost $13.25 billion and required 10,000 scientists from 100 countries. When it was turned on, some people genuinely feared it would create a black hole that would swallow Earth. It didn't.