During the 1990s, the Large Electron Positron collider (LEP) and its four experiments – ALEPH, DELPHI, L3 and OPAL – turned high-energy particle physics into a precision science, constraining key Standard Model parameters. One of LEP’s most important legacies, however, is the 26.7 km-circumference tunnel that it bequeathed to the LHC. Today at CERN, 30 years after LEP’s first results, heavy machinery is once again carving out rock in the name of fundamental research. This month’s cover image shows civil-engineering works that have been taking place near ATLAS and CMS to make way for the high-luminosity LHC. Proposals for a much larger collider to follow the LHC have triggered significant geological, environmental and civil-engineering studies during the past five years, demonstrating the state of the art in tunnel design and construction methods. Also in this issue: a record field for an advanced accelerator dipole magnet; tensions in the Hubble constant; the ProtonMail success story; strengthening theoretical physics in southeastern Europe; and much more.
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