School of international studies and law Coventry University
Almost everybody I know has some kind of ghost story to tell. I do not have anything against ghost stories - I still get spooked myself on occasions - but I do think that scientists should be interested in what causes apparitions, rather than simply pooh-poohing them.
After I and my colleague Tony Lawrence linked the ghostly occurrences in our laboratory to a low-frequency standing wave emitted by a faulty extractor fan, we realised that the presence of infrasound at or about 19 Hertz may explain apparitions. With the fan off, it felt as if we had gone from an enclosed, muggy room, which made the hairs on the back of your neck stand on end, to one filled with butterflies and babbling brooks.
We recently decided to test our theory in a 14th-century "haunted" cellar in Coventry. A couple of white witches had visited the site and were convinced that it was occupied by the ghost of an unwelcoming old lady. I must admit I did experience a little twinge as I stepped inside the doorway, but I felt safe in my knowledge that ghosts are mainly infrasound - sound-like waves with frequencies below the audible limit of 20Hz.
We attached a precision sound-level meter, sensitive to frequencies down to 1Hz, to a spectrum analyser and were astonished when it recorded a level of 38 decibels and infrasound at 19Hz frequency - the same ranges that caused apparitions to appear in our lab.
Other research has shown that only a minority of the population is sensitive to the effects of infrasound. Witness the differing reactions of an American couple to the Coventry cellar - while he was quite happy to enter the cellar, his wife refused to even cross the threshold.
Philosophically speaking, I would never discourage anyone from telling a ghost story, but as a scientist I will always look for a cross-reference to something else. Some people can become ill if they live close to the seashore or airports, both sources of infrasound, so it appears that we can link infrasound's presence to physical health. It would be interesting to see if it can also be linked to sick building syndrome.
To verify our results in the cellar, we asked a young female colleague to accompany us. We told her that if we did see a ghost, she would have to bring out all the technical kit. I and my colleague would have already legged it!
* Interview by Jennifer Currie