critical mass

critical mass (countable and uncountable, plural critical masses)

1. (nuclear physics) The minimum amount of fissile material needed to support a self-sustaining nuclear chain reaction.
   • 2016, Carter Hydrick, Critical Mass […] ‎, 3rd edition, TrineDay, →ISBN:

     […] 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.

2. (by extension, figurative) The minimum amount of something or the minimum number of people needed to trigger a phenomenon.
   • 1993, Gerald Marwell, Pamela Oliver, The Critical Mass in Collective Action, Cambridge University Press, →ISBN, page 87:

     […] 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.

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

     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).

   • 2023, Eleanor Catton, Birnam Wood, page 19:

     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.

• subcritical mass
• supercritical mass

• tipping point

• “critical mass”, in Merriam-Webster Online Dictionary, Springfield, Mass.: Merriam-Webster, 1996–present.
• “critical mass”, in Cambridge English Dictionary, Cambridge, Cambridgeshire: Cambridge University Press, 1999–present.
• “critical mass” in Longman Dictionary of Contemporary English, Longman.