In 1993, when a now-famous New Yorker cartoon appeared with the caption “On the Internet, no one knows you ‘re a dog,” it was already a clich that cyber-space is a magical place where the bodily limits and petty prejudices of the real world no longer hold. But the number of people who log on every day in search of like minds, novel experiences or safe sex continues to grow exponentially, proving that this is a clich with staying power.

Margaret Wertheim offers an explanation for the Internet’s appeal, and it goes way beyond the ideas of previous analysts such as MIT sociologist Sherry Turkle, whose 1997 book Life on the Screen interpreted the Net as a playground for our multiple selves. Cyberspace, Wertheim suggests, fills the spiritual vacuum Western science created when it demoted Heaven from a real celestial place-immaterial, yet inhabiting the same universe as ours-to a mere metaphor for the mystery of death.

That may sound like quite a feat for an artifact that is nothing more, after all, than a tangle of telephone wires, transistors, TV screens and transfer protocols. But Wertheim makes a remarkably convincing case for her thesis, by showing just how closely Western theology and cosmology have been tied to changing conceptions of space. Her tour starts with the Hell and Heaven of The Divine Comedy. When Dante placed these realms deep within the Earth and above the stars, respectively, he wasn’t being entirely fanciful, Wertheim asserts. God and sin, as the organizing principles of the medieval Christian cosmos, gave space an inherent “up” and “down,” making the sky above the stars the logical place for virtuous souls to reside.

But when Copernicus, Kepler and Galileo smashed the crystal spheres of Ptolemaic space and showed that the “heavenly bodies” are mere matter-subject to the same physical laws that apply on Earth-it signaled hard times ahead for the Christian idea of the soul. In the modern scientific worldview, Wertheim observes, “the whole of reality is taken up by physical space, and there is literally no place within this scheme for anything like a spirit or a soul to be.”

Clearly, however, billions still long to believe in an aspect of the self that exists apart from the body. Wertheim’s notion, argued with style and intelligence, is that the shared worlds created by the denizens of chat rooms, Usenet newsgroups, graphical virtual realities, or text-based multi-user domains (MUDs) provide the closest thing this world has to offer to genuine out-of-body experiences. On the Internet, in other words, the spirit-self can finally spread its figurative wings. Both dogs and gods are allowed.