Is heaven real? Eben Alexander thinks so. He is a neurosurgeon who learned his craft at Duke and honed it at Harvard. In 2008 he fell into a coma, his brain infected by bacterial meningitis. He emerged from the coma with memories of a fantastical adventure, during which he rode on a butterfly beside an angelic blue-eyed girl into "an immense void, completely dark, infinite in size, yet also infinitely comforting." In Proof of Heaven (Simon and Schuster, 2012), his bestselling book about his experience, Alexander claims to have learned that "God and the soul are real and that death is not the end of personal existence but only a transition."

In a cover story he wrote for NEWSWEEK and in an interview with The New York Times, Alexander sounds intelligent and sincere but a tad short on self-doubt. Pulling his rank as a neurologist, he insists that what he experienced must have been "real," because during his coma his neo-cortex was completely "shut down" and "there is absolutely no way that I could have experienced even a dim and limited consciousness during my time in the coma, much less the hyper-vivid and completely coherent odyssey I underwent."

Absolutely no way? Really? As Martin Samuel, who heads Alexander's former department at Harvard, tells The Times, "There is no way to know, in fact, that his neo-cortex was shut down. It sounds scientific, but it is an interpretation made after the fact."

I understand why skeptics like biologist P.Z. Myers deride Alexander's claims as "bullshit," but I can't dismiss them so easily. I'm fascinated by mystical experiences, so much so that I wrote a book about them, Rational Mysticism (Houghton Mifflin, 2003), from which I've drawn some of the material that follows. Many people conclude, as Alexander did, that their experiences revealed Ultimate Reality, God, whatever. The problem is that different people discover radically different Absolute Truths.

In The Varieties of Religious Experience, more than a century old and still the best book ever written on mysticism, psychologist William James described experiences, like Alexander's, that revealed a loving, immortal spirit at the heart of existence. But James emphasized that some mystics have perceived absolute reality as terrifyingly alien, uncaring and meaningless. James called these visions "melancholic" or "diabolical." James himself had at least one such vision, a kind of cosmic panic attack.

One mystical expert I interviewed, German psychologist Adolf Dittrich, told me that mystical visions--whether induced by trauma, drugs, meditation, hypnosis, sensory deprivation or other means--fall into three broad categories, or "dimensions." Borrowing a phrase that Freud used to describe mystical experiences, Dittrich called the first dimension "oceanic boundlessness." This is the classic blissful experience reported by Alexander and many other mystics, in which you feel yourself dissolving into some benign higher power.

Dittrich labeled the second dimension "dread of ego dissolution." This is the classic "bad trip," in which your self-dissolution is accompanied not by bliss but by negative emotions, ranging from mild uneasiness to full-blown terror. You think you are going insane, disintegrating, dying, and all of reality may be dying with you. Dittrich's third dimension, "visionary restructuralization," consists of more explicit hallucinations, ranging from abstract, kaleidoscopic images to elaborate dream-like narratives. Dittrich referred to these three dimensions as "heaven, hell and visions."

During a drug trip in 1981, I experienced all three dimensions described by Dittrich. The trip occurred in early summer, just after I had finished my junior year of college. I had left my apartment in New York City to visit friends in suburban Connecticut. One of these friends, whom I'll call Stan, was a psychedelic enthusiast with an unusual connection: a chemist who investigated psychotropic drugs for a defense contractor in Research Triangle Park, North Carolina. The chemist had recently given Stan a thimble's worth of beige powder that was supposedly similar to LSD.*

One morning we each ingested about a matchhead-worth, a dose that Stan's friend had recommended. Within a half hour, I felt as though a volcano was erupting within me. Sitting on a lawn, barely holding myself upright, I told Stan that I feared I had taken an overdose. Stan, who for some reason was less affected by the compound, tried to calm me down. Everything would be fine, he said; I should just relax and go with the experience. As Stan murmured reassuringly, his eyeballs exploded from their sockets, trailed by crimson streamers.

That was my last contact with external reality for almost twenty-four hours. Stan and a couple of friends whose help he enlisted told me later that during this period I was completely unresponsive to them, although they could with some difficulty move me about. For the most part I lay or sat quietly, staring into space. Occasionally I flailed about, raving, grunting or emitting other peculiar sounds. For a while I stuck my arms out and hissed like a five-year-old boy pretending to be a jet-fighter: "Fffffffffffffff!" My expressions tended toward extremes: beatific, enraged, terrified, lewd. Occasionally I furiously clawed holes in the lawn. My eyes were for the most part wide open, the pupils dilated to the rim. My companions said I never seemed to blink, even when particles of dirt from my excavations were visible on my eyeballs.

Subjectively, I was immersed in a visionary phantasmagoria. I became an amoeba, an antelope, a lion devouring the antelope, an ape man squatting on a savannah, an Egyptian queen, Adam and Eve, an old man and woman on a porch watching an eternal sunset. At some point, I attained a kind of lucidity, like a dreamer who realizes he's dreaming. With a surge of power and exaltation, I realized that this is my creation, my cosmos, and I can do anything I like with it. I decided to pursue pleasure, pure pleasure, as far as it would take me. I became a bliss-seeking missile accelerating through an obsidian ether, shedding incandescent sparks, and the faster I flew, the brighter the sparks burned, the more exquisite was my rapture. This was probably when I was making the "fffffff" noise.

After eons of superluminal ecstasy, I decided that I wanted not pleasure but knowledge. I wanted to know why. I traveled backward through time, observing the births and lives and deaths of all creatures that have ever lived, human and non-human. I ventured into the future, too, watching as the Earth and then the entire cosmos was transformed into a vast grid of luminous circuitry, a computer dedicated to solving the riddle of its own existence. Yes, I became the Singularity! Before the term was even coined!

As my penetration of the past and future became indistinguishable, I became convinced that I was coming face to face with the ultimate origin and destiny of existence, which were one and the same. I felt overwhelming, blissful certainty that there is one entity, one consciousness, playing all the parts of this pageant, and there is no end to this creative consciousness, only infinite transformations.

At the same time, my astonishment that anything exists at all became unbearably acute. Why? I kept asking. Why creation? Why something rather than nothing? Finally I found myself alone, a disembodied voice in the darkness, asking, Why? And I realized that there would be, could be, no answer, because only I existed; there was nothing, no one, to answer me.

I felt overwhelmed with loneliness, and my ecstatic recognition of the improbability--no, impossibility--of my existence mutated into horror. I knew there was no reason for me to be. At any moment I might be swallowed up, forever, by this infinite darkness enveloping me. I might even bring about my own annihilation simply by imagining it; I created this world, and I could end it, forever. Recoiling from this confrontation with my own awful solitude and omnipotence, I felt myself disintegrating.

I awoke from this nightmarish trip convinced that I had discovered the secret of existence. There is a God, but He is not the omnipotent, loving God in Whom so many people have faith. Far from it. He's totally nuts, crazed with fear of his own existential plight. In fact, God created this wondrous, pain-wracked world to distract Himself from his cosmic identity crisis. He suffers from a severe case of multiple-personality disorder, and we are the shards of His fractured psyche. Since then, I have found hints of this theology in Gnosticism, the Kabbalah and the writings of Nietzsche, Jung and Borges.

So which mystical visions should we believe? The heavenly, blissful ones, like Alexander's, or the hellish ones, like mine? Or are both somehow true? The reasonable answer is: None of the above. The sensible, skeptical part of me knows that I was projecting my own fearful nihilism onto the universe, just as Alexander, a Christian, projected his yearnings. Our experiences were delusions brought about by aberrational brain states. The differences between our experiences—like the differences between our dreams--can be explained by our different backgrounds and personalities.

But another part of me is dissatisfied with this dismissal. My drug-induced visions possessed a mythical, archetypal quality that my dreams lack. The visions seemed not absurd and meaningless, like most of my dreams, but almost too meaningful. They seemed too artful—too laden with metaphorical and metaphysical significance—to be the products of my puny, personal brain. I felt as though I had left my individual mind behind and traveled into another, much more expansive realm. Alexander clearly feels the same way about his visions.

For the most part, I'm a hard-core materialist, but my experience—and those reported by Alexander and others—makes me suspect that our minds have untapped depths that conventional science cannot comprehend. And although I've reluctantly abandoned my neurotic-deity theology, I have an abiding sense of reality's profound weirdness and improbability. What William James said in Varieties still holds true:

"Our normal waking consciousness, rational consciousness as we call it, is but one special type of consciousness, whilst all about it, parted from it by the filmiest of screens, there lie potential forms of consciousness entirely different. We may go through life without suspecting their existence; but apply the requisite stimulus, and at a touch they are there in all their completeness... No account of the universe in its totality can be final which leaves these other forms of consciousness quite disregarded… [T]hey forbid our premature closing of accounts with reality."

Let me ask you skeptics this: If scientists invented a technology—a drug or brain-stimulating device--that could safely induce a mystical experience, wouldn't you seize that opportunity? Wouldn't you like to see heaven, even if you don't believe in it?

[*After hearing me describe this drug’s effects, Harvard psychologist John Halpern, an authority on psychedelics, guessed it was 3-quinuclidin-3-yl benzylate, otherwise known BZ, or an analog thereof. BZ is a potent hallucinogen developed as a chemical "incapacitant" by the U.S. Army in the 1950's. Although BZ was apparently never deployed, the Army stockpiled canisters of the drug through at least the early 1970's, when President Richard Nixon ordered the stockpiles destroyed. Whatever the drug I took was, I don't recommend it.]