The poltergeist phenomenon is probably the most difficult explanatory challenge that the would-be skeptic has to face. It has been reported in many countries for hundreds of years and the manifestations are remarkably constant over different times and cultures. To put it all down to misperception or misreporting will hardly do, so it must be hoaxing, mustn't it? But it's difficult to sustain this view after reading Gauld's and Cornell's scholarly book, which leaves one in an uncomfortable no-man's land of uncertainty.
A poltergeist (German for "noisy spirit") is an "entity" which typically moves objects, throws things about, and may cause damage of various kinds. Witnesses are seldom injured, although they may be. Sometimes stranger phenomena allegedly occur, including levitation of people as well as objects and the mysterious appearance or disappearance of various objects. There is some overlap with more "conventional" hauntings but on the whole poltergeists and hauntings seem to be different kinds of phenomena.
The book begins with the famous Mompesson case, which dates from the 17th century. Though it is old it is very fully documented, and Mompesson, the central figure in the story, was nobody's fool and had nothing to gain from describing the events he witnessed—indeed, much the reverse. Other early cases are also discussed and analysed, as well as modern ones. Gauld and Cornell have themselves investigated some of these. Perhaps the most remarkable concerned the inexplicable production of large quantities of water in a house; this was extensively investigated by experts in heating and plumbing, who were utterly baffled; the experts' report is quoted in full.
In all, the authors list 500 cases and present a computer analysis of some of them. They even conducted experiments on a house that was due to be demolished to see whether violent shaking, almost strong enough to shake the building to pieces, could reproduce the displacement of small objects (it has been suggested by sceptics that slight earthquakes might be responsible), but no such displacement occurred. They discuss all the possible explanations that have been advanced for poltergeists and conclude that hoaxing, although it was certainly present in some instances, does not account for all the phenomena. In other words, they think there is something paranormal at work.
But what kind of paranormal thing? Are poltergeists produced by living people under some kind of stress (a popular theory), or are they discarnate spirits, or the spirits of the dead? The authors conclude, very tentatively, that most cases are due to living people but that there may possibly be a few that are due to discarnate entities of some kind.
I have to say I found this an unsettling book. I count myself a rationalist and I would much prefer to think that the whole poltergeist business was nonsense and could be dismissed out of hand. But Gauld and Cornell are not gullible fools and the detailed evidence they provide is very difficult to shrug off. Gauld, in particular, is a writer who inspires a lot of confidence (see his other books reviewed at this site). Moreover, the authors have a lot of first-hand experience of the matter and I have none. I therefore have to keep an open mind about it, but, if they are right, the world must be a much stranger place than we rationalists like to think it is.