Up and running

THE restart on April 5th of the Large Hadron Collider (LHC), the world’s most powerful particle accelerator, marks the start of another journey by physicists into the unknown. After some teething problems at the end of a two-year shutdown, a beam of protons was sent whizzing around the LHC’s 27km-circumference ring, which straddles the Franco-Swiss border near Geneva. If subsequent tests are successful, the collider should be fully open for business again in June.

Before its shutdown for an upgrade in February 2013 the LHC found the Higgs boson, a particle required by theory to give mass to some other particles. This time it will hunt for signs of supersymmetry—a piece of theory which, if true, will make the universe a more comprehensible place. Supersymmetry predicts that known fundamental particles have heavier partners. The complementary properties of the light and heavy partners in these couples greatly simplifies the maths needed to describe what is going on in the underlying structure of reality. Moreover, one particular particle predicted by supersymmetry may be the constituent of “dark matter”, a mysterious substance detectable by its gravity that is five times as abundant in the universe as familiar atomic matter, and which thus shapes the pattern of galaxies seen in space. Thus does the largest scale of things depend directly on the smallest.