It’s another of those “grey areas” between science fiction and fantasy, although some people, readers and writers alike, have some especially (yes, pun — of sorts) strong opinions about which side of the line it falls on.
P is for psionics.
Coined by John W. Campbell to mean “engineering of the mind,” the term comes from psi (psyche, or mind) and the ending -onics (from electronics). Campbell believed that principles of engineering could be applied to the mind and that so-called paranormal abilities could be studied and made to work reliably. Campbell wrote about psionics not as a pseudo-science or a way to shove magic into a science fiction story, but as a way to explore and embrace human potential.
Quantum physics acknowledges psionics to some degree. The mind of the observer can alter a scientific test on a fundamental level. Read about experiments to determine whether light is waves or particles, and you may become a believer in psionics. (Short version for the impatient: If the experimenter believes that light is a wave, the experiment shows that it is a wave; if the experimenter believes that light is a particle, the exact same experiment shows that light is a particle.)
But what is psionics?
As said above, psionics seeks to use science and engineering to unlock hidden potential within the human mind. Throughout history, there have been reports of strange phenomenon, miracles, and superhuman feats. What if the stories were true, at least in part?
Telepathy, empathy, precognition, extra-sensory perception and a host of other possible abilities… Duke University (ever heard of Zener cards?) conducted years of research, as did the US military and Soviet Russia. China claims to have succeeded in producing individuals who can perform a host of seemingly miraculous feats.
The evidence to date for such things is inconclusive, but not entirely against their existence, either. (Do not talk to me about the work of professional debunkers. Lying and/or falsifying evidence to “prove” that something does not exist is bad science, and is doing the cause of logic and rationality no favors.) There is enough evidence to warrant further study. It has moved beyond the realm of conjecture and into the realm of hypothesis testing. It may be possible.
Isn’t that enough for science fiction?
A few things to keep in mind, though, for any author who wants to write about characters with psionic abilities…
First, whether you believe in it or not makes no difference, but there are agreed-upon terms for this kind of stuff, and using those terms incorrectly in fiction is not going to win you any points with readers who’ve been reading about psions (the term for characters with psionic abilities) ever since they first picked up an Andre Norton novel at the age of ten. Don’t have your telepathic character able to move things with her mind unless she is also a telekinetic. (It’s a bit like calling a creature an extra-terrestrial when it isn’t from any place off the Earth, and hasn’t even been to such a place. Seriously, don’t be that writer. Or that mad scientist.)
Second (and this is more just-my-opinion than the other one), please don’t use psionics as a cheap substitute for also-cheap over-the-top magic. (Unless you’re writing superhero fiction, in which case it’s great. Sometimes just giving a name to something, even if it’s nothing but hand waving, makes it seem more reasonable — and interesting.)
Third, the word psion has quite different connotations from the word psychic (although some people would argue that they mean the same thing and that it doesn’t matter anyway since it’s all fictional). The former fits rather well in at least some science fiction; the latter is definitely a fantasy term. Chose accordingly.