Quantum mechanics exploded on to the intellectual scene in 1925. Within 18 months following the first paper by Werner Heisenberg, its radical ideas resonated in more than 200 publications across the world, most of them authored by “untenured” scientists under the age of 30. The resulting theory was a collective product that no single authority could claim, but it had a major geographical centre – the Copenhagen Institute of Theoretical Physics – where most of the informal, pre-published exchange of ideas occurred and where every participant of the new community aspired to visit. A rare combination of circumstances and resources – political, diplomatic, financial, and intellectual – allowed Niels Bohr to establish this “Mecca” of quantum theory outside of traditional and more powerful centres of science. Transitory international postdoctoral fellows, rather than established professors, developed a culture of research that became the source of major innovations in the field.