Twenty-three-year-old conjecture set to guide future quantum field theories. When John Cardy proposed a far-reaching principle to constrain all possible theories of quantum particles and fields1, he expected it to be quickly rebutted. But for almost 25 years that hasn’t happened — and it now seems that his theorem may have been quietly proved earlier this year. If the solution holds, it is likely to guide future attempts to explain physics beyond the current standard model. It will certainly have implications for any previously unknown particles that may be discovered at the Large Hadron Collider (LHC) at CERN, Europe’s particle...
