Following the initial success of 1911, the Solvay Conferences (Conseils Solvay) have been devoted to outstanding preeminent open problems in both physics and chemistry. The usual schedule is every three years, but there have been larger gaps.
Perhaps the most famous conference was the October 1927 Fifth Solvay International Conference on Electrons and Photons, where the world's most notable physicists met to discuss the newly formulated quantum theory (1927 attendees shown below). The leading figures were Albert Einstein and Niels Bohr. Einstein, disenchanted with Heisenberg's "Uncertainty Principle," remarked "God does not play dice." Bohr replied, "Einstein, stop telling God what to do." (See Bohr-Einstein debates.) Seventeen of the twenty-nine attendees were or became Nobel Prize winners, including Marie Curie, who alone among them, had won Nobel Prizes in two separate scientific disciplines.