Entrance to paradise has, of course, always been notoriously difficult, and the Tate's is no exception. The show's catalogue is fuller of signifiers, paradigms and italicised quotations - one essay cites references in English, French, German, Latin and Greek - than a Sorbonneful of structuralists. This is problematical, and for two reasons. First, the catalogue to "Heaven" is so deeply impenetrable that you may find yourself longing for hell: a place, presumably, where people use short English words. Second, the Tate's catalogue calls the existence of Heaven into doubt. If there were a benign deity, would it have allowed Mr and Mrs Derrida to have had young Jacques?
All of which is a shame, because "Heaven" is actually that rare thing, an exhibition with an intellectual thesis behind it. The trouble is that unless you are familiar with the collected works of Georges Bataille, you may never know what that thesis is. Translated into mere English, it seems to run as follows. In the late 20th century, the need that led men to imagine a transcendent place peopled by immortals - ie, a heavenful of angels - has been satisfied instead by fantasies about icons of popular culture. The point of what I take to be the Tate's thesis is that the impulse behind the two sets of fantasisings remains unchanged, namely a wish to transform ourselves into something greater than ourselves. The end result may be different, but the act of apotheosis is the same: ergo, any contemporary art that plays with ideas of popular culture is actually religious art. It is, in fact, the art of heaven.
Neat, no? Well, yes, only too much so. You could say that transformation - mimesis, we used to call it - is what art has always been about. "Heaven" is like that ad that challenges you to find three reasons why the tube train in which you are sitting is like amazon.com. If you cast your definitions wide enough, they can be made to cover anything. If you are a Tate curator, this means you can include everyone from Jeff Koons to Katja Kloft in your show and watch the punters roll in.
This is not to say that "Heaven" is full of any old iron. It isn't. The show is packed with A-list goodies, such as Ron Mueck babies and Chapman- brothers war models. Most of these have been seen before, although some exhibits - notably Tony Oursler's extraordinary video, Separation, which projects a human head into a glass vitrine - are new. The question, though, is whether all these things hang together as a cohesive show and, if so, whether that show has anything to do with heaven.
The answer is yes and no, in that order. There is a unifying voice behind "Heaven", but it is not that of thwarted religious impulse. Rather, the show is notable for its fascination with the flesh, for its entirely self- centred obsession with - its celebration of - mortality.
Perhaps it is all to do with some millennarian sense of rebirth, but the word that springs most obviously to mind in describing the work in "Heaven" (and I do not mean it pejoratively) is "childish". Take the room containing the Chapmans and Muecks. The thing that strikes you is its curious sense of scale. Mueck's Big Babies are horrifyingly enormous; by contrast, the Chapman twins' miniaturise Goya's Disasters of War series into a battle of toy soldiers, magnifying their monstrousness in the process. Like children, we are in a world where things are either disproportionately large (because of our own smallness) or small (because they are toys). The work in "Heaven" is childlike both in its iconography and in the sensations it instils in the viewer.
Upstairs, the kindergarten continues. Koons's sculpture of Michael Jackson is a childish portrait: kitsch, in this context, is a symbol of traduced innocence. Wang Fu's sculptures of sleeping children, Unter den Sternen, also nibbles away at the innocence of childhood by exploring the overlap between sleep and the Freudian unconscious. Like many works in this show, Mariko Mori's blown-up photograph of a Japanese indoor beach, Empty Dream, uses the artistry of children - bright colours, mythical images - to examine adult fantasies. (Spot the mermaids on Mori's beach and you think: but mermaids are mythical. Then it occurs to you that the landscape they inhabit - waves, sand and sky - is itself a manmade myth.) Katja Kloft's Col. 228, a room covered in pink satin villi, takes regression to its biological extreme by turning one corner of the Tate's top floor into a womb.
In the end, it doesn't do to be too po-faced about "Heaven". Like most of the exhibits in it, the Tate's show is knowingly jokey. You can't help feeling, though, that there is also something singular and serious going on, and that it might have been interesting to know what it was. Preferably in English.
`Heaven: An Exhibition That Will Break Your Heart': Tate Gallery Liverpool (0151 702 7400) to 27 Feb