• from another aspect of space-time, in effect another dimension. from this dimension in space but not in time. Some form of time travel may not be impossible, only unlikely and probably very energy-intensive. For example, if we could convert a human being into some sort of energetic medium — say light or radio waves — then place a reconverter 100,000 light years from earth, a person could step through a door here, feel as if he had come out the other side instantaneously, then step back and find that he was 200,000 years in the future. A cumbersome time machine, but it would work. We cannot assume that time travel is out of the question.

• from within us. I keep returning to this hypothesis because I find it so endlessly interesting and at its core so compelling. I suppose the idea that the gods we create would turn out to be real because we created them has a certain ironic appeal to a modern intellectual.

• a side effect of a natural phenomenon. We know so little about how magnetism and extra-low frequencies of all kinds affect the human organism. Perhaps there are natural electromagnetic anomalies that trip a certain hallucinatory wire in the mind, causing many different people to have experiences so similar as to seem to the result of encounters with the same physical phenomena.

• an aspect of the human species. We have a very ancient tradition of afterlife. The respect with which Neanderthals buried their dead in the Middle East more than thirty thousand years ago suggests that this belief may actually predate our own species.

Maybe we do have an afterlife, but not quite in the way tradition suggests. Maybe you and I are larvae, and the "visitors" are human beings in the mature form. Certainly, we are consuming our planet's resources with at least the avidity of caterpillars on a shrub.

Ancient astronomers of India believed that the Siddhas (human beings who have attained perfection) revolved between the clouds and the moon, having been transformed into a lighter, less material state.

Maybe the ancient and revered concept of human spiritual transformation relates to the emergence of the adult from the larva.

In our society transformation has a bad name, having been associated with various meditation fads and instant success groups. But real transformation has nothing to do with gaming a better life in this world; deliverance does not involve trying to use Buddhist chanting techniques to acquire a new Mercedes, nor is salvation a side effect of Fundamentalist healing services. Transformation for a Zen monk, a Moslem sufi, a Catholic, or a Jehovah's Witness is the same: It is a matter of delivering one's self into the possession of God. Meister Eckhart puts it very well when he says, "We must become as clear glass through which God can shine." But this involves giving up the "self," which feels just like dying.