Parapsychology is the supposedly scientific study of paranormal phenomena involving the human mind. This includes such things as psychokinesis, clairvoyance, and telepathy. The goal is to apply the rigors of the scientific method to the world of the paranormal.
In practice, it is a pseudoscience due to sloppy practice (poorly designed experiments, poor controls if any, small sample sizes, ill-defined terms and procedures, bad blinding), its perennial lack of verifiable positive results, bias against publication of negative results or disconfirmation of positive results, that parapsychologists who continue to get negative results get gently pushed out of the field and that it contradicts extremely well-understood and verified known science.
Parapsychology provides useful teachable examples of compelling ideas that nevertheless can’t possibly be right, and how such wishful thinking persists well past mere physical impossibility.
“Psi” is the ill-defined term for the force or phenomenon thought to underpin parapsychology. According to the Parapsychological Association, there is psi-gamma (paranormal cognition; extrasensory perception) and psi-kappa (paranormal action; psychokinesis). The term “psi” also applies to survival of death. Of course, it doesn’t matter to those constructing this detailed taxonomy that none of this has ever been demonstrated to exist. Parapsychologists such as Dean Radin and Charles Tart claim that psi is real, but is non-physical in basis and does not operate according to known scientific laws — but has (somehow) nevertheless been proven by science in repeatable experiments (that have not been repeated). No consistent theory of psi (or parapsychology in general) exists even within the field.
The most famous example of parapsychological research is probably the Princeton Engineering Anomalies Research Lab (PEAR). PEAR attempted to prove that human thought could manipulate the functioning of machines. They used devices designed to generate random phenomena, and then had subjects focus on disrupting that random pattern. They claimed to have shown that the experimental group of subjects focusing on disruption made the machine perform non-randomly in the direction the person was focusing. However, review of their procedures and data puts that conclusion into serious doubt, with effect being inversely proportional to sample size.
Joseph B. Rhine, a professor at Duke University in the mid-20th century, did extensive work on parapsychology and was substantially responsible for the field’s sloppiness in protocol design, happily throwing away negative results. Rhine and his colleague Karl Zener designed a special deck of cards containing five visually distinct shapes for use in telepathy and clairvoyance experiments, but also seemed blind to the consistent failure of experiments done under proper controls.
Daryl J. Bem’s “Feeling the Future: Experimental Evidence for Anomalous Retroactive Influences on Cognition and Affect” achieved some notice in 2010. In this paper, Bem wrote up an experimental run which showed effects of statistical significance … while not mentioning years of runs that didn’t. Amongst much other sloppiness, he also started from his data and worked back to a hypothesis.
The field of parapsychology is filled with deception, fraud and tricks. Whilst some parapsychologists have exposed the tricksters, many in the field seem to accept them as genuine evidence for the paranormal. Dean Radin’s book The Conscious Universe: The Scientific Truth of Psychic Phenomena (2009) contains many errors and promotes discredited experiments with poor controls as genuine scientific evidence for psi. Randi’s Prize: What Sceptics say about the Paranormal: Why they are Wrong and Why it Matters (2010) by Robert McLuhan describes itself as documenting “the truth of the paranormal” and debunking the skeptics, but contains falsehoods on almost every page. McLuhan even dedicates an entire chapter (over 40 pages) to the mediumship of Eusapia Palladino and concludes she was genuine; when in reality she had been exposed in every country she was investigated in as using conjuror’s tricks.
Not everything studied within parapsychology is the result of fraud or tricks. Paranormal phenomena have naturalistic explanations resulting from psychological and physical factors that give humans the impression of paranormal activity. Phenomena such as mediumship, precognition, out-of body experiences and psychics can be explained by psychology without recourse to the supernatural: cognitive biases, anomalous psychological states, dissociative states, hallucinations, personality factors, developmental issues and the nature of memory.
The big problem with parapsychology as a field is that science is all of a piece. Thus, physics is consistent with chemistry, biology and so on; any inconsistency is a serious problem. So the question is not “what knowledge can we derive on the assumption that we know nothing?” but “what knowledge can we derive given what we know already?”
Basic physics leaves it not looking good for parapsychology as a field in any way. Sean Carroll points out that both human brains and the spoons they try to bend are made, like all matter, of quarks and leptons; everything else they do is emergent properties of the behaviour of quarks and leptons. And the quarks and leptons interact through the four forces: strong, weak, electromagnetic and gravitational. Thus, parapsychology would work either through one of the four known forces or through a new force — and any new force with range over 1 millimetre must be at most a billionth the strength of gravity or it will have been captured in experiments already done. So either it’s electromagnetism, gravity or something weaker than gravity.
This leaves no force that could possibly account for psychokinesis, for example. Telepathy would require a new force much weaker than gravity that is not subject to the inverse square law, and also a detector in the brain evolved to use it for signaling. Precognition, the receipt of information transmitted back in time, would violate quantum field theory. (Unless you warp spacetime sufficiently closely around a black hole or something.)
What this means is that these ideas have pretty much no chance of being right even before we test them directly.
Allan Crossman suggests that parapsychology can serve as the control group for science itself: a field using the methods of science but where the null hypothesis is always true. If they come up with positive results (as they occasionally do), this shows where the methods of science need improving.
This does have the philosophical problem that it would require dismissing out of hand any positive results, rather than properly evaluating them as merely ridiculously unlikely. Fortunately, this is unlikely to be a practical problem while well-designed tests show no positive results, and the only tests showing any positive results tend to exhibit the experimental design and file-drawer skills so popular in the field.