In the first half of the 19th century the theory of evolution was mired in conjecture until Charles Darwin and Alfred Russel Wallace compiled a body of evidence and posited a mechanism—natural selection—for powering the evolutionary machine.
The theory of continental drift, proposed in 1915 by Alfred Wegener, was not accepted by most scientists until the 1960s, with the discovery of midoceanic ridges, geomagnetic patterns corresponding to continental plate movement, and plate tectonics as the driving motor.
Data and theory. Evidence and mechanism. These are the twin pillars of sound science. Without data and evidence, there is nothing for a theory or mechanism to explain. Without a theory and mechanism, data and evidence drift aimlessly on a boundless sea.
For more than a century, claims have been made for the existence of psi, or psychic phenomena. In the late 19th century organizations such as the Society for Psychical Research were begun to employ rigorous scientific methods in the study of psi, and they had world-class scientists in support, including none other than Wallace (Darwin was skeptical). In the 20th century psi periodically appeared in serious academic research programs, from Joseph B. Rhine's experiments at Duke University in the 1930s to Daryl J. Bem's research at Cornell University in the 1990s.
In January 1994, for example, Bem and his late University of Edinburgh parapsychologist colleague Charles Honorton published "Does Psi Exist? Replicable Evidence for an Anomalous Process of Information Transfer" in the prestigious review journal Psychological Bulletin. Conducting a meta-analysis of dozens of published experiments, the authors concluded that "the replication rates and effect sizes achieved by one particular experimental method, the ganzfeld procedure, are now sufficient to warrant bringing this body of data to the attention of the wider psychological community." (A meta-analysis is a statistical technique that combines the results from studies to look for an overall effect, even if the results from the individual studies are insignificant; the ganzfeld procedure places the "receiver" in a room with Ping-Pong ball halves over the eyes and headphones over the ears playing white noise and the "sender" in another room psychically transmitting visual images.)
Despite the evidence for psi (subjects had a hit rate of 35 percent, when 25 percent was predicted by chance), Bem and Honorton lamented that "most academic psychologists do not yet accept the existence of psi, anomalous processes of information or energy transfer (such as telepathy or other forms of extrasensory perception) that are currently unexplained in terms of known physical or biological mechanisms."
Until psi finds its Darwin, it will continue to drift on the fringes of science.
Why don't scientists accept psi? Bem has a stellar reputation as a rigorous experimentalist and has presented statistically significant results. Aren't scientists supposed to be open to changing their minds when presented with new data and evidence? The reason for skepticism is that we need replicable data and a viable theory, both of which are missing in psi research.
Data. The meta-analysis and ganzfeld techniques have been challenged. Ray Hyman of the University of Oregon determined that there were inconsistencies in the experimental procedures used in different ganzfeld experiments (which were lumped together in Bem's meta-analysis as if they used the same procedures). He also pointed out flaws in the target randomization process (the sequence in which the visual targets were sent to the receiver), resulting in a target-selection bias. Richard Wiseman of the University of Hertfordshire in England conducted a meta-analysis of 30 more ganzfeld experiments and found no evidence for psi, concluding that psi data are nonreplicable.