critical mass

plural critical masses

1. countableuncountablenuclear physicsThe minimum amount of fissile material needed to support a self-sustaining nuclear chain reaction.

   […] Rhodes calculated the uranium bomb would eventually need “about 42 kilograms – 92.6 pounds,” which Rhodes then stated was approximately 2.8 critical masses. In other words, critical mass can be calculated to be about 15 kilograms.

   2016, Carter Hydrick, Critical Mass […] , 3rd edition, TrineDay, →ISBN

2. broadlycountablefigurativelyuncountableThe minimum amount of something or the minimum number of people needed to trigger a phenomenon.

   […] depending on the rare circumstance of there being a critical mass of persons whose combination of interests and resources is high enough to overcome the feasibility problem.

   1993, Gerald Marwell, Pamela Oliver, The Critical Mass in Collective Action, Cambridge University Press, →ISBN, page 87

   2 more examples

   The critical mass comprises the pioneers of an SNS who pay the start-up costs and set up a circle of acquaintances for newcomers; thereafter new subscribers to a mature SNS can join one after another rather than as a group (Heijden, 2004).

   2015, Giuseppe Riva, Brenda K. Wiederhold, Pietro Cipresso, editors, The Psychology of Social Networking, volume 1, Walter de Gruyter, →ISBN, page 204

   The problem was not just that they had never quite reached that point of critical mass where their income would finally exceed their many costs and liabilities, it was that breaking good, for Mira at least, had always meant more than simply breaking even.

   2023, Eleanor Catton, Birnam Wood, page 19

1. A direct action event in which bicycle riders travel through city streets as a group.