A poltergeist is a paranormal phenomenon which consists of events alluding to the manifestation of an imperceptible entity. Such manifestation typically includes inanimate objects moving or being thrown about, sentient noises (such as impaired knocking, pounding or banging) and, on some occasions, physical attacks on those witnessing the events.
Since no conclusive scientific explanation of the events exists up to this day, poltergeists have traditionally been described in folklore as troublesome spirits or ghosts which haunt a particular person, hence the name. Such alleged poltergeist manifestations have been reported in many cultures and countries including the United States, Japan, Brazil, Australia, and all European nations, and the earliest recorded cases date back to the 1st century.
Poltergeist activity has often been believed to be the work of malicious ghosts. According to Alan Kardec, the founder of Spiritism, poltergeists are manifestations of disembodied spirits of low level, belonging to the sixth class of the third order. They are believed to be closely associated with the elements (fire, air, water, earth).
In parapsychology, Nandor Fodor proposed that poltergeist disturbances were caused by human agents suffering from some form of emotional stress or tension. William G. Roll studied 116 different poltergeist cases and found that the agents were often children or teenagers, and supposed that recurrent neuronal discharges resulting in epileptic symptoms may cause recurrent spontaneous psychokinesis (RSPK), which would affect the person's surroundings. The case of the Rosenheim Poltergeist, where none of the disturbances could be explained via physical means, was suggested to be caused by psychokinetic forces.
Poltergeist disturbances that have not been traced to fraud have been attempted to be explained scientifically. David Turner, a retired physical chemist, suggested that ball lighting, another phenomenon, could cause inanimate objects to move erratically. Some skeptics propose that poltergeist activity might be caused by simpler phenomena such as static electricity, electromagnetic fields, ultrasound, infrasound, or ionized air. Hallucinations, like the sounds of bells or footsteps, may be caused by carbon monoxide poisoning.