Critical mass is a term that became popularized during the development of atomic energy. Before an event could occur( energy release for reactors ), a minimal amount of atomic fission reactions would have to initiate simultaneously. Using this analogy, many people have adapted the analogy to fit spiritual development. James Redfield started the book, The Celestine Prophecy, with this title. In it, he explains that a cultural transformation is "occurring now because of the number of individuals having this awareness all at the same time." 

Several weeks ago, I was discussing some personal views I have of the future with one of the other participants at a Kunlun session. I went on to tell him I thought there would be a coming cosmic utopia in the universe, somewhat related to views found in other traditions. In response to his question about how this would occur given many problems in society, I had little response. He suggested that once a minimal amount of people reach a stage of heightened awareness harmony with nature and society, change would accelerate. Unexpected events - loosely termed emergent phenomena in physics circles - would start to happen. It was an insight I had not previously thought of. 

It would be nice to hear others explain their view on the importance of critical mass to cultural/social/spiritual change. What are some examples you have found relevant? Why is a critical mass necessary for social change? Take the topic where you deem fit.