The artist’s Royal Academy retrospective revives her 1977 live work in which visitors pass through a naked couple in a doorway – and reveal something of themselves In 1977, in a gallery in Bologna, the artist Marina Abramović and her lover and collaborator, Ulay, stood naked in a narrow doorway, staring intently at one another, as the public squeezed between them. Last week Imponderabilia, as the…