In anticipation of the Royal Academy’s postponed Marina Abramović retrospective, and the days when we can get up close and personal with strangers once more, here’s a look back at Abramović and Ulay’s 1977 performance, Imponderabilia. It saw the then-lovers stand facing each other, totally nude, in the doorway of an exhibition of their work in Bologna. To get in, you had to squeeze by them. The duo were intrigued to see how entrants would respond: would they avoid or instigate skin contact? Which artist would they choose to face to pass through? Most faced Abramović, as it turned out, including the two police officers who came to shut it down after just ninety minutes.