In films such as A Matter of Life and Death, Heaven Can Wait, Field of Dreams, Truly Madly Deeply or The Lovely Bones, cinema has used the afterlife as a convenient narrative contrivance. Hereafter is different. It expects us to take the idea seriously; indeed it preaches it as a manifest truth. To emphasise the veracity of its spooky goings-on, it purloins real events such as the 2004 tsunami and the 7 July London bombings, and even subtitles its foreigners. Not to worry, it assures us cheeringly, death isn't, after all, the end.

Of course, there's a market for such stuff. People seem to find it impossible to accept that one day their existence will cease. Perhaps they find it even harder to accept that their departed loved ones are lost to them forever. Anyway, the idea of a life after death, to be enjoyed in some Elysium or Valhalla but otherwise not too different from its sublunary counterpart, has been among the most widespread and persistent of human beliefs.

The Abrahamic religions have found the promise of an afterlife one of their most effective selling points: today it continues to console not just Islamist martyrs but many millions of ordinary churchgoers. Though 19th-century science overthrew much outlandish scriptural dogma, the doctrine of the hereafter triumphantly survived. Even among those who renounced God, there were many who refused to let it go. They just transferred their patronage to the burgeoning army of psychics who continue to offer access to the Other Side through defiantly secular channels. In Britain today, more than half of the population apparently believe in some kind of afterlife.

Yet, much more than the idea of an intelligent Creator, the concept is perplexing, both cosmologically and logically. Even its most eminent evangelisers find it difficult to explain to the satisfaction of enquirers. Jesus was once asked which of a serial widow's seven deceased spouses would be her husband for eternity. According to Matthew's Gospel, the Son of God felt obliged to respond that in the world to come we "neither marry nor are given in marriage, but are like angels in heaven".

If for you, only the matrimonial lifestyle could deliver heavenly bliss, this news may disappoint. It might get the rest of us wondering which of our own cherished earthly practices will prove out of bounds to a quasi-angel. That's the trouble with the hereafter. On closer examination, most of its virgins turn out to be raisins. Such versions of it as might make any kind of sense fail to meet our requirements. Unsurprisingly, contemporary theologians prefer to avoid the subject.

Inevitably, Hereafter's eager advocacy of its eponymous fancy turns out to be counter-productive. A deceased little boy saves his brother from catching a train that's about to be blown up. That's great, but if those who've passed on enjoy such powers, they could damn well use them a bit more often.

One of the film's characters writes a book which proves that the afterlife exists. Apparently, mysterious conspiratorial forces have been suppressing the truth for unexplained reasons. We're not told much about the book's contents, but the evidence on which it relies seems to be drawn largely from near-death, out-of-body experiences. We get to see what one of these looks like. It's not very enticing. If that's the afterlife, you might well conclude, then perhaps you'd rather not bother.

Though Eastwood directed this unlikely exercise and Steven Spielberg cleared its path, it was conceived, a bit surprisingly, by Peter Morgan, the begetter of Frost/Nixon and The Queen. How did that come about? Morgan had lost a friend in an accident. "He died so suddenly. So violently. It made no sense. His spirit was still so alive around us. At his funeral I was probably thinking what everyone else was: 'Where has he gone?'"

Morgan went on to write Hereafter because he wanted to ask how it's possible that "we can be so close to somebody, know everything about them, share everything with them, and then they're gone and suddenly we know nothing". It's a question many have asked before and many will ask again. Unfortunately, the answer isn't necessarily what we might wish it to be.

When he'd finished his therapeutic script, Morgan dropped it into a drawer, where it stayed happily undisturbed for several years. It's a pity it didn't remain there.