Critical mass

摘要

The protests that took place on the streets of London on the eve of the G20 summit in April lived up to many people's expectations. Around 2000 protestors turned up, and were heavily marshalled by police. There was a bit of trouble, but the police tactics - specifically, the decision to corral the entire crowd into a small area near the Bank of England, an approach known as "kettling" -kept a lid on the violence.rnThat, at least, is the official version of events, and it reflects a belief about crowds that is shared by police, governments and to a large degree the general public across the world: that they are hotbeds of trouble and must be contained. Trouble is seen as especially likely when something goes wrong at a large gathering. Under such circumstances, the expectation is that the crowd will lose its head and all hell will break loose.