Gravity: With effects this special, how can we tell outer space from CGI?

If the moon landings were taking place now, people would be rightly suspicious

Sandra Bullock and George Clooney in Gravity (Warner Bros)

By now, you will probably have seen the posters proclaiming “Gravity” as one of the best films ever made. In the advance publicity for the film which opens next week, they've not been parsimonious with the superlatives, and one of my friends - a highly respected figure in Britain's movie industry - told me a few weeks ago that it was an outstanding piece of work, and not to be missed.

So, laden with expectation, I went to a charity screening of the film the other night. It is, no doubt, a film like no other, a 3D extravaganza that, indeed, takes you to another dimension. It is an assault on the senses. It is a powerfully crafted mix of fantasy and reality. And it certainly has a very different texture from almost every other film you'll see these days. In synopsis, it's the story of an American space mission that goes wrong, and the struggle of the two astronauts, an experienced space hand played by George Clooney and a rookie scientist played by Sandra Bullock, to find their way back to earth, or, more specifically, to middle America.

No need for a spoiler alert, but the unfolding of the story is just one of the ways in which "Gravity" fails to conform strictly to Hollywood type. Another is that you never get actually to see Clooney: the voice is unmistakeable but he only appears in full space suit with mask. This is not the case with Ms Bullock, who is to be seen for long periods in tight T-shirt and undercrackers, allowing viewers to marvel not only at this journey to the furthest frontiers of man's discovery, or to glory in the awe-inspiring stillness and dream-like quality of space, but to imagine how much work you have to do to maintain a body like that at the age of 49.

We are told that the only thing that's real in the film are the actors: everything else is computer-generated imagery. I did wonder whether this extended to Ms Bullock's physiognomy, but we'll let that pass. Equally, I've never actually been to space, but it looked pretty authentic to me. The ability to create the illusion of reality is, of course, a stock in trade for Hollywood, and now, with the advance in technology, anything in the world (or beyond it) can be realised by a few clever people in front of computer screens.

When George Clooney rhapsodises about seeing the sun rise from space, I totally believed what I was seeing. Which led me to wonder this: what if the moon landings had only just happened? We're all aware of the conspiracy theorists who are adamant that the Apollo 11 mission was created in a movie studio, the ultimate piece of advertising for American hegemony. And that was in an era when computers were in their infancy. Hard to imagine it could be faked. But now? A bit of airbrushing on one of the astronauts would be the least of it. Surely, if the landings were taking place now, people would assume that the whole thing had been cooked up by a CGI studio in LA. However, the clinching argument would be this: it must be real, because it would look much better if it wasn't.