Near the end of Tansy Davies’ new 9/11 opera, an ENO/Barbican co-production, there is a lovely episode where two dancers, one earthbound and one aerial, perform a serene duet. One is the “falling man”, the icon of that day; the woman on the ground keeps him from falling to earth, supports him in the air, battles to reverse time and horror. An ethereal soundtrack of harp and strings reinforces the message that hope and humanity can be salvaged from unspeakable things, and for a brief moment you understand that art can create a worthy response to evil.That is one of very few moments in the work that has the slightest authenticity, thanks largely to choreographer Kim Brandstrup. For the rest, Davies and her librettist, Nick Drake, have produced something utterly vapid and c