Poltergeist is a term for a supposed spirit or ghost that manifests by moving and influencing inanimate objects (rather than through visible presence or vocalization). Stories featuring poltergeists typically focus heavily on raps, thumps, knocks, footsteps, and bed-shaking, all without a discernable point of origin or physical reason for occurrence. Many accounts of poltergeist activity detail objects being thrown about the room, furniture being moved, and even people being levitated. A few poltergeists have even been known to speak (The Bell Witch, 1817; Gef the Talking Mongoose, 1931). Most classic poltergeist stories originate in England, though the word itself is German.
Poltergeist phenomena are a focus of study within parapsychology. Parapsychologists define poltergeist activity as a type of uncontrolled psychokinesis. Recurrent Spontaneous Psychokinesis (RSPK) is a phrase suggested by parapsychologist William G. Roll to denote poltergeist phenomena.
Poltergeist activity tends to occur around a single person called an agent or a focus. Focuses are often, but not limited to, pubescent children. Almost seventy years of research by the Rhine Research Center (Raleigh-Durham, NC USA) has led to the hypothesis among parapsychologists that the "poltergeist effect" is a form of psychokinesis generated by a living human mind (that of the agent). According to researchers at the Rhine Center, the "poltergeist effect" is the outward manifestation of psychological trauma. Skeptics believe that the phenomena are hoaxes perpetrated by the agent. Indeed, many poltergeist agents have been caught by investigators in the act of throwing objects. A few of them later confessed to faking. However, parapsychologists investigating poltergeists think that most occurrences are real, and the agents cheat only when they are subsequently caught cheating. The longevity and consistency between poltergeist stories (the earliest one details the raining of stones and bed shaking in ancient Egypt) has left the matter open for debate within the parapsychology community.
Another version of the poltergeist is the "wrath version." When a person dies in a powerful rage at the time of death, that person is believed by some to come back to fulfill that vengeance. In some cases, the vengeance is too strong to let go or forgive, and the metaphysical ghost becomes a poltergeist, in which the newly formed ghost can affect solid objects, and in some cases are deadly. According to yet another opinion, ghosts and poltergeists are "recordings." When there is a powerful emotion, sometimes at death and sometimes not, a recording is believed to be embedded into the fabric of time, and this recording will continue to play over and over again until the energy embedded disperses.
Some people theorize that poltergeists are caused by the Hutchison effect.
William Roll, Hans Bender and Harry Price are perhaps three of the most famous poltergeist investigators in the annals of parapsychology. Harry Price investigated Borley Rectory which is widely regarded as "the most haunted house in England."
Some scientists propose that all poltergeist activity that they cannot trace to fraud has an explained physical explanation such as static magnetic/electric fields, ultra and infra sound, static electric charging and ionised air. In some cases such as the Rosenheim poltergeist case, the physicist F. Karger from the Max-Planck-Institut für Plasmaphysik and G. Zicha from the Technical University of Munich found neither none of these effects present, and psi proponents claim that no evidence of fraud was ever found, even after a sustained investigation from the police force and CID, though criminologist Herbert Schäfer quotes a detective watching the agent pushing a lamp when she thought nobody was looking.
But according to the two physicists this did not rule out what they called "short duration forces" or the case that the effects that they were looking for were not constant, but only happening at the time of the phenomena, which was witnessed by Hans Bender, the police force, the CID, reporters, and the physicists present and the phenomena such as the rotation of a picture and swinging lamps were captured on video (which was one of the first times any poltergeist activity has been captured on film) and strange sounds that sounded electrical in origin were recorded. The claims were aired in a documentary in 1975 in a series called "Leap in the Dark".