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How Physics Can Overthrow A Dictatorship


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer

Hong Kong protests

Millions of people in Hong Kong are the latest non-violent campaigners against repressive governments. Social scientists are trying to use physics analogies to estimate their chances of winning the reforms they seek. samuelwong/Shutterstock

Many times in recent decades the world has watched transfixed as protestors in authoritarian states face down heavily armed state forces, up to and including tanks. Sometimes they win, liberating their nation. Sometimes it ends in streets running with blood. If the protest organizers could identify the features leading to success, the world would be a better place. Two social scientists think the answer may lie in adopting Newton's laws of motion, perhaps proving the claim that other fields have “physics envy”.

Harvard's Professor Erica Chenoweth has co-authored influential studies showing movements that manage to get more than 3.5 percent of the population actively involved in the struggle for democracy to succeed. Naturally, these activists always have much wider support among people unable or afraid to take to the streets. Nevertheless, Chenoweth and Dr Margherita Belgioioso of Burnel University, London, wondered how such a modest minority can achieve such great things, and turned to the tools of their trade.


The language of physics has been incorporated into democracy campaigns so much we barely consider references to protest “movements”, campaign “momentum” or even “revolution”. Chenoweth and Belgioioso wondered if these are more than mere analogies and might follow similar laws.

Physical momentum equals mass times velocity. If a campaign's mass is the number of people involved, then perhaps its velocity is just as important. In Nature Human Behavior, Chenoweth and Belgioioso define a campaign's velocity as the number of events held in a week, including nonviolent demonstrations, strikes, and boycott campaigns. They used a database of every attempt to overthrow an African dictator between 1990 and 2014 to test the theory the proportion of the national population participating multiplied by the number of events held would serve as a good predictor of success.

“Although studies have shown that large numbers of participants increase the chances of movement success,” the paper argues, “The impact of participation on the effectiveness of civil resistance movements is often based on reported peak participation, rather than dynamic ebbs and flows of participation.” Getting 10 percent of a nation's population onto the streets once may demonstrate broad support, but seldom works if it's not sustained.

Unsurprisingly, there is a strong correlation between movement momentum and the successful overthrow of a ruler. The authors created seven models to harness this in predicting movements' success, adding in various other factors they thought might prove relevant, such as population size and average wealth. They found these work much better than the simple 3.5 percent engagement threshold, despite the public attention Chenoweth's earlier work has attracted.


Interestingly, violent protests don't seem to boost the chances of removing dictators, although they didn't lower them either. Instead, these movements succeeded when their displays of support swayed the military, police or key players in the ruling coalition to change sides.


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