Consider the Higgs boson — the latest fundamental particle to be discovered, in 2012 — which lives for less than a billionth of a billionth of a second and can travel less than a millionth of a millionth of a meter. Compared to those tiny scales, the physicists operating the particle colliders that momentarily give rise to Higgs bosons exist for long, long times at distances far, far away. This far-off perspective is captured by the S-matrix. To see how the S-matrix works, imagine that, instead ...