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In social dynamics, critical mass is a sufficient number of adopters of a new idea, technology or innovation in a social system so that the rate of adoption becomes self-sustaining and creates further growth. The point at which critical mass is achieved is sometimes referred to as a threshold within the threshold model of statistical modeling.
The term "critical mass" is borrowed from nuclear physics, where it refers to the amount of a substance needed to sustain a chain reaction. Within social sciences, critical mass has its roots in sociology and is often used to explain the conditions under which reciprocal behavior is started within collective groups, and how reciprocal behavior becomes self-sustaining. Recent technology research in platform ecosystems shows that apart from the quantitative notion of a “sufficient number”, critical mass is also influenced by qualitative properties such as reputation, interests, commitments, capabilities, goals, consensuses, and decisions, all of which are crucial in determining whether reciprocal behavior can be started to achieve sustainability to a commitment such as an idea, new technology, or innovation.