SAY THIS ABOUT ASSERTIONS THAT ALIENS have been, are or will soon be landing on Earth: at least a scenario like that of ""Independence Day'' would not violate any laws of nature. In contrast, claims in other fringe realms, such as telepathy and psychokinesis, are credible only if you ignore a couple or three centuries of established science. That alone does not mean that the claims reflect self-deception or hoaxes, as skeptics assert. But it does mean that the standard for accepting the claims is higher than it is for, say, accepting that aspirin reduces a man's risk of a second heart attack. As Cornell University astronomer Carl Sagan puts it, ""extraordinary claims require extraordinary evidence.'' Here are the experiments that offer the best evidence of paranormal phenomena -- and some of the objections to their conclusions:
Telepathy. Strap half a Ping-Pong ball over each eye. Cover your ears with headphones and lose yourself in the white noise. You are now supposedly in an ideal state to receive another person's thoughts. To probe for the existence of telepathy, experiments have a ""sender'' in an isolated room look at a randomly selected ""target'' (magazine ad, art print, movie clip) for 30 minutes or so. Then the experimenter, ignorant of the target, shows the ""receiver,'' in another room, that image plus three decoys. The receiver rates how closely each image matches her thoughts during the isolation period. By chance alone the receiver should score a hit one time in four, for a 25 percent success rate. In a 1985 analysis of 28 studies from several labs, the late Charles Honorton of the University of Edinburgh calculated a combined hit rate of 35 percent. A run of 354 sessions by Honorton, reported in 1994, yielded 32 per- cent. And a recent run at Edinburgh, using arts students, got a nearly 50 percent hit rate.
Was it telepathy? Someexperiments failed to take into account that people hearing white noise think about water more often than sex (or so they say); if beaches appear more often as a target than couple in bed, a high hit rate would reflect this tendency, not telepathy. Also, receivers tend to choose the first or last image shown them; unless the experimenter makes sure that the target does not appear in the first or last place more often than decoys do, the hit rate would be misleadingly high.
Skeptic Ray Hyman of the University of Oregon found that, in the Edinburgh runs, video targets that were used just once or twice had hit rates of about chance, while those appearing three or more times yielded a ""telepathic'' 36 percent. How come? A video clip run through a player several times may look different from one never played for the sender; a canny receiver would choose a tape that looked ""used'' over one that didn't. Also, of the 28 studies Honorton analyzed in 1985, nine came from a lab where onetime believer Susan Blackmore of the University of the West of England had scrutinized the experiments. The results are ""clearly marred,'' she says, by ""accidental errors'' in which the experimenter might have known the target and prompted the receiver to choose it. Researchers have been hoodwinked before. Says magician James (The Amazing) Randi, ""I can go into a lab and fool the rear ends off any group of scientists.''
Psychokinesis. The most credible experiments in whether mind can affect matter come from the Princeton Engineering Anomalies Research laboratory, founded by rocket engineer Robert Jahn in 1979. (In response, Princeton stripped Jahn of his deanship.) In Jahn's experiment, an electrical diode produces, at random, equal numbers of positive and negative electric pulses. The machine also counts how often the pulses alternate: plus-minus-plus-minus. Then a volunteer concentrates on making more, or fewer, pulses match this pattern. After more than 14 million trials, Jahn has found a persistent effect: in every 1,000 trials, subjects somehow produce one more or one fewer match than predicted by chance. The odds that this is a statistical fluke are 1 in 5,000. In a similar vein, Dean Radin and colleagues at the University of Nevada, Las Vegas, tapping into the local resources, found that of the five days with huge slot-machine payouts, four came on days with a full moon, when psychic powers supposedly soar. The odds on that happening by chance are 2 in 1,000.
That's worth further study. But it means little until independent labs replicate it. As for Jahn's results, there are a couple of puzzles. First, one of the subjects, rumored to be on Jahn's staff, is responsible for half of the successes even though he was in just 15 percent of the trials. Second, some peculiarities in how the machine behaved suggest that the experimenters might have ignored negative data. Jahn says this is virtually impossible. But other labs, using Jahn's machine, have not obtained his results.
Researchers plead that paranormal phenomena are extremely subtle. For instance, explains psychologist Daryl Bem of Cornell University, if the hit rate for telepathy is 34 percent, then an experiment with the typical 30 sessions has less than 1 chance in 6 of finding the effect.
UFOs. The possibility that intelligent life exists far beyond our own has grown more plausible in just the last year, thanks to the discovery of the first planets (seven) orbiting other suns. Sure, the existence of extraterrestrials requires more than a habitable rock orbiting a stable star. But other demands -- that life begin and evolve, that a civilization arise and send emissaries to distant worlds -- are looking more likely, too. Biologists hot on the trail of how a soup of molecules sprang to life, for instance, suspect the process isn't that difficult. Says astronomer Frank Drake of the University of California, Santa Barbara, ""It's widely accepted in the scientific community that there are other civilizations.''
But do UFOs come from such a civilization? Witness accounts are not proof. Photos come closer. But Joe Nickell of the Committee for the Scientific Investigation of Claims of the Paranormal, a group of skeptical scientists who check out UFO sightings, spoon bendings and similar claims, has amassed a catalog of ordinary explanations for UFO photos. A blister in the emulsion can create a round object in the photo, for instance. And computers make perpetrating UFO hoaxes as easy as counterfeiting the old $100 bill. Says Drake, ""There is not one accepted fact that would lead one to conclude UFOs are extraterrestrials.''
Believers are right in complaining that their results are subjected to more scrutiny, and after-the-fact nitpicking, than those in any other field. But then, no other field makes such extraordinary claims.