One hundred years ago, Werner Heisenberg retreated to the island of Helgoland, where he built the foundations of the first full formulation of quantum mechanics. Finding its matrices repugnant, Erwin Schrödinger developed a mathematically equivalent formulation with a wavefunction and a wave equation. Either way, physics would never be the same again: in quantum mechanics, measurement affects what can be known, and predictions can only ever be probabilistic.

A century has not sufficed to fully understand or exploit the theory – and high-energy physicists today find themselves at an interesting juncture. Detector designs are beginning to push quantum limits. Quantum computing is in its “noisy intermediate-scale” era, poised to apply its remarkable parallelism to simulations beyond the reach of classical supercomputers. And with efforts to move beyond the Standard Model at least temporarily frustrated, increasing numbers of theorists are returning to grapple with the foundational assumptions of quantum mechanics. In this special edition, Carlo Rovelli and David Wallace explore a jungle of ideas to resolve questions that have defied consensus since the earliest days of the theory.

Elsewhere in these pages: Fermilab’s last word on muon g-2; DESY brings practical plasma-wakefield acceleration a step closer; ATLAS and ALICE make the first differential measurements of the radial flow of quark-gluon plasma; a farewell to Mary K. Gaillard; and much more.

Read the digital edition of this new issue on the CERN Courier website.

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