Christmas traditionally presents scientists, archaeologists and shopkeepers with the perfect opportunity to play party-pooper by picking over the time-honoured story of events in a Bethlehem stable that we imbibed with our mother's milk, replacing it with their own unauthorised and often unholy version.
Astrologers, for instance, have long enjoyed identifying comets and shooting stars that may just have been the one to guide the three (although historians now say probably only one) kings from the east, but most of their theories would involve moving the date of Christ's birth to anywhere between 6BC and 10AD. Such an adjustment is, however, minor compared to the leap of faith required by those, like the writer A N Wilson, who say that pilgrims gathering in Bethlehem on 25 December have been duped. They should be asking for their money back because Jesus, this school of thought suggests, was born in the Galilean metropolis of Sepphoris. Hence no shepherds, no manger, no cattle a-lowing. Moreover, his earthly father was a well-heeled manufacturer, not a poor carpenter. And as for Mary - let's just say she wasn't all that she seemed.
We would appear to have reached the point at which all "religious" Christmas cards could be happily consigned to the waste bin on the grounds that they are peddling a lie. Yet there is a danger of believers and unbelievers alike becoming too attached to the historical truth of the details. Richard Harries, who doubles as the Bishop of Oxford and the bishop of Radio 4, has earned the ire of the literalist Widdecombe tendency for his remarks about how we should regard such well-known events as the Christmas story as important, profound and enduring myths - but myths none the less.
He and others - remember David Jenkins, the former bishop of Durham? - have tried to say that organised religion has to realise that it can be enhanced by myths. This remains an unpopular view in the churches, though, especially at a time when fundamentalists around the globe are drawing the crowds with messages that seek to confirm the black-and-white truth of every claim made in the holy book.
Of all the many layers of myth involved with the Christmas story, the core idea of God in His heaven directing such a sequence of events is perhaps the hardest to scrutinise by any known criteria. The concept of heaven and, by association, eternal life, is certainly the one that is best insulated against the encroachments of the scientists. They may have proved long ago that it was not the Devil who causes earthquakes, or angels crying that makes it rain, but as no one has ever come back from the dead - at least in a situation more verifiable than that of a medium's front parlour - to tell us what it is or isn't like, heaven still remains a possibility.
And such is human nature that the alternative, for most of us, is simply too awful to contemplate. Not hell - that was written off years ago by the churches, along with limbo and purgatory, as too embarrassingly medieval to mention - but rather, the nothingness that scientists predict but cannot prove will await us.
The arrogant, selfish, self-absorbed part of us all cannot quite believe that our own death will be the end. We cannot, surely to God we cannot, just vanish in a split second.
As such, heaven remains religion's last bestselling point - and the reason why people begin to drift back to church attendance as soon as the OAP bus pass looms on the horizon. Since we cannot suck it and see until it is too late to report back any feelings of disappointment, heaven remains nothing more than a glorious but untried promise, something that is so finely attuned to our own desires and needs that it has been with humankind from the start.
Indeed, the notion of heaven predates alphabets, philosophy and organised religion. From the time when the first Neanderthal widow or widower sat next to the lump of dead protein that had been his or her mate and realised that something had to be done about the smell, we have wondered what comes next. The assumption has always been that there should be something. So when that body was put in a cave or a ditch or on to a fire, or pushed over a ledge into a ravine, the one left behind looked into the void that was left and felt emptiness and abandonment. Thus arose the myths and traditions and literatures, the shamans, the soothsayers, the priests, the popes, the poets, the writers and dramatists who would attempt to provide the answer.
Organised religion offers two basic varieties of heaven. The first is the place where we spend eternal solitude with God alone, somewhere so utterly beyond our imagination that it is impossible to picture. All earthly relationships - spouses, parents, children - are as nothing in this place, and the body and bodily pleasures are exchanged for a vaguely defined inner peace. This is pre-eminently the domain of figures such as the medieval mystics; Mechthild of Magdeburg, for instance, saw erotic visions of a heaven where every soul had a love affair with God. But it is also the vision of heaven most often espoused by the modern church. No less a figure than Pope John Paul II pronounced in 1999 that heaven was a "blessed community" which was "neither abstraction nor physical place".
Set against this vague whiteness, the second version is much more tangible, familiar and easy to plot. It is the domain of angels and wings, clouds and harps, and allows for some overlap between heaven and earth, and hence for relationships outside the central bond with God. In the one and only conversation I ever had with my mother about death, she told me that her own image of heaven was of a welcoming committee of my great-aunts greeting their sister with, "Well, Annie, what took you so long?" This is the flip side of Jean-Paul Sartre's acid remark in Huis clos that "hell is other people".
Both these approaches offered by the churches are appealing - depending on whether it is comfort, freedom from fear or the search for another dimension beyond the banalities of earthly life that is prompting the seeker. Throughout history and across the range of religious creeds, opinion has vacillated between the two positions on heaven - one theocentric (or based on God) and the other anthropocentric (focused on the human). We have never quite made up our minds.
So the New Testament, for example, speaks of heavenly liturgies, bodies that are but spirit, and of an angelic, celibate lifestyle in the hereafter. In the same theocentric vein, Saint Augustine spoke of death as the "flight in solitude of the Solitary". The Protestant reformers, the Puritans and the Jansenists all embraced the God-centred view of heaven.
Yet, alongside this trend, there has been a parallel one which insists on creating heaven in the image of a spruced-up earth. So in the second century, Irenaeus of Lyons, taking his lead from the Book of Revelation, with its description of heaven as a rebuilt Jerusalem, held that the chosen would, for a thousand years after their death, inhabit what was in effect a renewed earth. Later, in Renaissance times, theologians joined with humanists and artists in humanising heaven. Borrowing from the Golden Age and the Isles of the Blest found in classical mythology, they fashioned an environment where men and women met, played, kissed and caressed against a pastoral backdrop. This was the Garden of Eden reborn.
Nearer our own time, the writings of Emanuel Swedenborg, the 18th-century Swedish scientist turned religious guru, influential but today much neglected, gave the earth-linked heaven a modern makeover. His Heaven and Hell, part of a body of works known as Heavenly Arcana, which in their time were much read and remarked upon, described the author's encounter with angels as he moved between the spirit world and the material world.
It was an image to inspire 19th-century Romantics and 20th-century film-makers alike. This is a place of music, dancing, good health, self-congratulation and plenty; it is the world of Fra Angelico's Last Judgement, Luca Signorelli's Coronation of the Elect and William Blake's The Meeting of a Family in Heaven. This heaven is where, according to its greatest chronicler, Dante, in his Paradiso, the "Great Light shines in three circles"; where, as Charles Kingsley wrote, "marital love will be without oscillation, even at the same glorious full tide of delight", and where, in Steven Spielberg's Always, Audrey Hepburn dwells in a green glade.
The question of heaven, like that of Christmas from which it inexorably follows, is complex. The key is to understand what the details are trying to convey, without getting too wrapped up with what actually did or didn't happen 2,001 years ago in the Holy Land. To play that game is to fall into the seductive trap of science - namely, the belief that everything can be put to the test, be proven or disproven, and then reduced to a series of propositions that can be expressed in mathematical symbols. It certainly doesn't make for Christmas cards that you would want to put on your mantelpiece. If those happy family scenes from the stable are trying to convey the question mark that, like it or not, hovers over all our eternal fates, then I, for one, am happy to give them house room.
Peter Stanford is currently researching and writing a travellers' guide to heaven as a companion volume to his The Devil: a biography, which is published by Arrow in paperback