“In a landscape where ‘post-truth’ and ‘alternative facts’ are part of our everyday vocabulary, this term might put some on the back foot – but the crucial difference between an imaginary fact and an alternative one is that the audience is fully aware [that the former] is a pretence.” Most of us are familiar with the concept in the form of “mockumentary” films and TV shows such as This Is Spinal Tap and The Office, but it’s now stretching into museums as well.