We love to be dazzled or scared, and the "Haunted Mansion", "Phantom Manor" and "The Twilight Zone Tower of Terror" attractions at Disney resorts do just that. In the Haunted Mansion, as you walk along an elevated mezzanine, ghosts dance and dart around a haunted ballroom.
This effect isn't a modern computer generated image (CGI), but rather an effect that goes back 500 years. In 1584, the Neapolitan scholar Giambattista della Porta wrote Magia Naturalis (Natural Magic), which described an illusion that he entitled, "How we may see in a Chamber things that are not."
The effect della Porta described is created by placing a piece of glass, sheet of Plexiglass or plastic film at an angle between an audience and a room. The angled glass reflects a second room that is offstage — either to the side of the stage, or above or below it. This second room is often called a "blue room", and it is a mirror-image of the first room.
When the blue room is dim, there is no reflection, but when that room is lit, its reflection appears on the glass, and when the audience looks at the first room, they see a composite image comprised of the first room and the reflection of the second room.
In these diagrams, the red square is the audience's field of view, and the green square is the sheet of glass. In the first image, the blue room is darkened so nothing is being reflected. In the second diagram, the blue room is lit, and the glass displays its reflection.
Professor Pepper and the Ghost Become Entwined
A year after Queen Victoria began her reign in 1837, the Royal Polytechnic Institute opened in London. It was a showcase for invention and ingenuity that hosted public lectures and displayed a diving bell, model railway, and photographic exhibitions.
In 1848, chemist John Henry Pepper joined the institute. Pepper was known as a science performer whose demonstrations included mechanics, pneumatics, optics, heat, electricity, magnetism, chemistry, and astronomy. His electromagnetic induction experiments were particularly spectacular.
In 1862, the inventor Henry Dircks set up a booth at the Institute to display his implementation of della Porta's effect. Dircks had tried without success to sell the idea to theaters, who found it too expensive to implement. When Pepper first saw it, he knew immediately it could be modified to make it less expensive to incorporate into theaters.
The effect made its debut at a performance of Charles Dickens's The Haunted Man in 1862, and from then on, the effect came to be called "Pepper's Ghost."
Pepper's Ghost Today
Today, Pepper's Ghost is used at "The House at Haunted Hill" Halloween attraction in Woodland Hills, California, the "Mystery Lodge" exhibit at Knott's Berry Farm in Buena Park, California, and the "Ghosts of the Library" exhibit at the Abraham Lincoln Presidential Library and Museum in Springfield Illinois.
At Universal Studios Florida's attraction "The Hogwarts Express," guests entering "Platform 93/4" disappear into a brick wall when viewed by those farther back in the queue. Pepper's Ghost also shows up in museums, including the ghost of John McEnroe at the Wimbledon Lawn Tennis Museum, and the ghost of the Eighth Duke of Marlborough at Blenheim Palace.
And, if you thought that politicians were particularly smart giving long speeches seemingly without notes, think again. The teleprompter is a modern implementation of Pepper's ghost.
Perhaps the most poignant uses of Pepper's Ghost have been at the 2012 Coachella Valley Music and Arts Festival and 2014 Billboard Music Awards. At Coachella, a Pepper's ghost version of the deceased rapper Tupac Shakur joined rappers Dr. Dre and Snoop Dogg onstage to perform "Hail Mary" and "2 of Amerikaz Most Wanted." The effect was created by a high resolution image projected onto a sheet of glass, then that image was reflected onto a Mylar screen.
During the Billboard Music Awards on May 18, 2014, Pepper's Ghost was used to create the illusion of deceased pop star Michael Jackson performing the song "Slave to the Rhythm" from Jackson's posthumous Xscape album.
Pepper's Ghost and the Ghost Pepper
Finally, don't confuse Pepper's Ghost with the ghost pepper. Also known as the Bhut Jolokia, in 2007 Guinness World Records certified it as the world's hottest chili pepper, with a Scoville Heat Units (SHUs) rating of more than 1 million. In the last several years, the ghost pepper has been superseded by the Infinity pepper in 2011, the Naga Viper and the Trinidad Moruga scorpion in 2012, and the Carolina Reaper on August 7, 2013.