During a January week in 2012, around 700,000 English-speaking Facebook users were chosen, without their knowledge or consent, to be emotional lab rats. The researchers found that if you tweak what people see in their Facebook news feed – the scrolling information on your page –to suppress or heighten certain emotive words, readers’ emotions will shift to match.

It’s not only emotions Facebook can nudge. It can make you vote, too. On the US presidential election day in 2010 it offered one group a graphic with a link to find nearby polling stations, along with a button that would let you announce that you’d voted, and the profile photos of six “friends” who had already done so. Users shown that page were 0.39% more likely to vote than those in the control group who hadn’t seen the link, button or photos.

The researchers reckoned they’d mobilised 60,000 voters and that the ripple effect caused 340,000 extra votes.