My friend Michael likes to tell about the time he was "abducted by aliens." Watch those quotation marks: They're part of the story.
He was bicycling along a country road in Nebraska in 1983, Michael says, when he became aware that a large, brightly lighted vehicle was following close behind him. Then, without his knowing quite how it happened, he found himself inside the vehicle where he was examined by strange creatures. About 90 minutes later, he was outside again with his bicycle.
"If I told you just that much," Michael asked, "What would you think?"
If I hadn't known he was leading up to something I suppose I might have thought, as polls show roughly half of Americans do, that aliens in spacecraft really do abduct human beings for mysterious experiments.
But Michael has a better explanation. At the time, he was participating in a transcontinental bike race, and he had been more than 80 hours without sleep. Hallucinations transformed his support crew into aliens straight out of the last sci-fi flick he'd seen, and their prosaic recreational vehicle into a hovering spacecraft.
His memories of the experience, Michael says, seem compellingly real, but he has good reason to know they aren't.
Does every "abduction by aliens" have the same origin in dreams or hallucinations? Polls notwithstanding, I think that's the only plausible answer.
But the implausible answer has plenty of fervent defenders, and among the best-known of them is John Mack, M.D., professor of psychiatry at Harvard Medical School. His book, "Abduction: Human Encounters with Aliens," centered on case histories of "experiencers" he has treated, incidentally set off a controversy that is testing the limits of academic freedom.
Mack's book is, to my reading, credulous and silly. It's embarrassing when someone with his very impressive credentials (among them a Pulitzer prize for a 1977 biography) commits in print such absurdities as "there may be some value in challenging our restricted epistemology and expanding our criteria for evaluating information to include the power or intensity with which something is felt and communicated."
Harvard apparently thought it was embarrassing too, and impaneled a committee to look into Mack's work. That's rare, as it should be. Most scholarly work that is created outside the mainstream of a discipline just dries up out there. But there are enough well-known examples of research that was ignored or ridiculed at first and later turned out to be prophetic that universities properly allow professors to fish for results anywhere they want to. The committee's response is expected soon.
I think Mack is more likely to prove a gull than a prophet, and it's not because I am resistant to the idea of intelligent life elsewhere in the universe. As a life-long reader of science fiction I'm delighted that the SETI project, the Search for Extra-Terrestrial Intelligence, is working to effect an introduction.
"It's hotly debated whether there are enough stars in the galaxy" for life to have developed elsewhere, said Tom McDonough, coordinator of the Planetary Society's SETI project, "but I'm an optimist."
But the evidence for the kind of alien intelligence Mack's subjects believe in is flaky, McDonough says. "Even garbage would help" as long as it was something tangible that couldn't have been made in any earthly way we know about yet.
Mack's approach to treating "experiencers" is primarily through hypnosis, and his book contains detailed descriptions of his regression sessions with 13 individuals selected from almost 80 who meet, he says, his "quite strict" criteria for abduction. Many of them recall frequent episodes, some going back to childhood.
I can well understand that it would be traumatic to believe you've been scooped up by aliens and subjected to painful and undignified experiments, some apparently involving an interspecies breeding program. But intensity of feeling is no guarantee of truth, and the logical argument amounts to begging the question — assuming what the investigator wants to prove, namely, that the fact that these unhappy people have obviously experienced something implies that what they have experienced is a real abduction.
These alien beings, wise beyond human imagining and appearing to possess "technologies thousands of years beyond us," seem oddly incompetent at getting themselves noticed. 
As Mack puts it disparagingly, the reigning cliché is "Why don't they land on the White House lawn?" and the answer, he says, "among those who take this phenomenon seriously is that the aliens do not dare to manifest themselves more directly. Government leaders would panic, might attack them, and surely would not know how to avoid scaring the rest of us."
Nonsense. At the very least, they could choose for abduction somebody important enough to do something about all the problems supposedly troubling the aliens. And besides, there's all that advanced technology that can stop cars and float people through walls.
There's also the fascinating fact that these interstellar intellectuals just happen to have exactly the same preoccupations as the investigator.
"For-profit business corporations, which impact every part of the globe, are perhaps the most powerful agents of planetary destruction that human beings have created," Mack says.
Perhaps he never heard of the Supreme Soviet, and the environmental destruction wrought by its demented economic plans. Think how much better off we'd have been if the aliens had nipped Lenin out of that railway car and prevented the Bolshevik revolution.
There's one telling passage, but its significance seems to have escaped the author.
"The United States leads the way in sheer numbers of abductions, with England and Brazil following behind," Mack tells us, "largely because of the availability of practicing hypnotists and therapists working with abductees in those countries."
Couldn't have said it better myself.