Poltergeist

Here's my take on a Poltergeist (derived from the German words poltern "to make noise" and geist "spirit", or Spuk, as modern Germans tend to call it), a type of spirit that is characterized by its propensity to interact with the physical world, especially present in European and North American collective imaginations. One of the first personalities to use this term was Martin Luther (1483-1546), the initiator of Protestantism, although according to him, the Poltergeist phenomenon could also be the work of the Devil himself. Many curious events – sometimes rationally explained, sometimes not – attributed to such spirits having occurred from the Middle Ages to the present day, the term has finally entered everyday language. However, the followers of parapsychology will have seized the subject since the end of the 19th century, gradually erasing the spiritualist hypothesis ; but we'll get to that later !

Poltergeists - as spirits, then - are known to be mischievous in nature, taking pleasure in surprising and terrorizing the living. They move furniture by making it levitate (or even dance...), produce more or less explicable sounds (percussion noises, squeaks, and spectral voices...), or violently throw objects such as plates or stones, aimed at the interior or the exterior of a house ; parapsychologist Ernest Bozzano reported (in his book "Haunting Phenomena") a case of "stone rain" that at times defied the laws of physics, but injured absolutely no one where it occured. These spirits even seem to be able to "transfer" their intangibility to objects they manipulate, to pass through walls in some cases. But sometimes, they can be more violent and dangerous, starting fires, and attacking the living, biting them, scratching them or lifting them from the ground. Most of the time, poltergeists seem to act in a "gratuitous" way, without seeking revenge for an injustice suffered during their lifetime (assuming that a disembodied spirit is the cause of the phenomenon) ; however, several "poltergeist attacks" that have been rationally explained were criminal acts that could not be more humane (notably at Cock Lane, London, in 1762, or at Séron, in the Hautes-Pyrénées, in 1979).
For the religious, these events are more often the work of demons than of strictly ghostly entities. According to Allan Kardec (1804-1869), founder of spiritualism, poltergeists constitute the sixth class of the third order, corresponding to "imperfect spirits", characterized by their strong attachment to the material world. The Vallée classification system (named after Jacques Vallée, a French ufologist born in 1939), on the other hand, classifies poltergeist "attacks" as type II anomalies (AN), concerning the physical effects, to which crop circles are also attached. Finally, folklorists tend to see poltergeists as nothing more than a variant of the misdeeds long attributed to fairies, goblins, and other similar beings.

Let us now look at the parapsychological and metapsychic hypotheses that emerged at the end of the 19th century. For parapsychologists, such phenomena are in no way the result of a spirit or any invisible entity. Their major theory - in particular carried by a certain William G. Roll (1926-2012) - is that it is rather uncontrolled psychokinetic/telekinetic effects, emanating from an unstable person, and not a haunting attached to a particular place. Similarly, Frank Podmore – another parapsychologist (1856-1910) – will have analyzed thousands of manifestations of this kind (listed by the Society for Psychical Research) to come to the conclusion that, in the majority of cases, a young and disturbed teenager in the middle of puberty was involved (more often a girl than a boy, though). This recalls the case of Enfield, England, in 1977, where young Janet Harper (then 11 years old) gave the impression of being the epicenter of paranormal phenomena worthy of a Poltergeist "attack", before confessing several frauds later on.
Whether they are frankly astute antics from teenagers, or young people manifesting unsuspected psychic powers worthy of a Stephen King novel, the choice is yours… Also – and I only mention this because how amusing it is - some French parapsychologists tried to create more "scientific" names to replace the word Poltergeist : thorybism (from the Greek thorubos, meaning "noise" or "trouble"), or even metakinetic metapsychorrhagia...