In 2003, the phsycologists of Hertfordshire University, including Richard Wiseman assembled people in the concert hall in London. They had them listen to contemporary music, and meanwhile, they also played an etremely low-frequency noise using a seven-meter-long pipe. As a result, twenty-two percent of the audience reported that they experienced a strange feeling. Wiseman suggested that ghosts are hallucinations caused by such low-frequency noises. Can this theory be true?