- Mary Todd Lincoln with the 'ghost' of her husband, taken by spirit photographer William H. Mumler. Mumler's photos are now considered hoaxes
Let’s round things up with the most perennial of spooky fascinations. Everyone loves a good ghost story. In fact, some polls suggest that about 50% of the UK public believe in ghosts. But what can science tell us about ghoulish phenomena?
Things we can’t see can have a huge influence on us. We’re affected in strange and unconscious ways by physical phenomena that we’re not even aware of. Whether it’s the environment around us or the state of our own mind, what we see is not always what’s really there.
Your mind really can play tricks on you. Normal function of the brain can be affected by both extreme physical or emotional stress, and by medical conditions such as stroke, epilepsy, cancer or migraine. Scientists have discovered that electrical stimulation of parts of brain can affect perception, causing us to experience spooky sensations or see shadow people around us.
Experiments by Michael Faraday in the 19th century demonstrated an effect known as the ideomotor response. This is where an individual, completely without conscious knowledge, performs minute muscular movements in accordance with preconceived ideas. So if you’re asked to imagine sucking a sweet, your mouth might salivate. Imagine tying shoelaces and your fingers might twitch.
This effect also accounts for ghostly phenomenon such as Ouija boards and some poltergeist activity. Perfectly honest and sane individuals can act unconsciously in response to suggestive clues and their perception of the situation.
Perhaps the most interesting scientific phenomenon commonly mistaken for paranormal activity is infrasound. People can't hear sounds lower than 20Hz – the human ear just can’t pick them up. But we can experience the sounds as tiny, imperceptible vibrations. These vibrations can cause a sense of panic or fear in the pit of your stomach. They can even vibrate the eyeballs so that we seem to see strange things that aren’t really there.
Infrasound has been uncovered as the culprit behind more than one supposedly haunted house. The vibrations caused by nearby traffic, a current of wind, or even a simple ceiling fan can all cause terrifying experiences that seem all too real.