One very common illusion employed in theaters, museums, shows and other venues is Pepper’s Ghost. The illusion is named after English scientist John H. Pepper who improved upon a previous ingenious but cumbersome illusion developed by inventor Henry Dircks in 1860. Pepper made the first demonstration of this illusion in 1862. The illusion relies on the fact that whereas light goes through most transparent glasses, a certain percentage of it is reflected by the surface of the glass. In the classical Peppers Ghost illusion, a glass is installed at an angle facing an audience. The audience can see with no problem the action taking place in the stage behind the glass. At some point an actor or an object is illuminated in a compartment that is located to the side of the glass in such a way that the light coming from the actor or object will bounce off the glass and appear to the audience to be coming from the stage as a ghostly apparition.
In the photo below, I use a window to generate a version of the Pepper’s Ghost illusion, where I seem to be within the tree outside as a ghostly apparition.
In the video I used an exhibit at the 2019 Prague Quadrennial. I manipulated the see-through and reflection qualities of the glass window of the exhibit as well as the proximity of my phone to the glass, to create a Peper’s Ghost illusion.
Note: the photo belongs to the author and can only be used with permission.
The folks of the YouTube channel brusspup demonstrate the “Crazy Nuts” illusion originally created by magician Jerry Andrus.
This illusion exploits the way our brain constructs perception of depth and volume using cues from lines, lighted and shaded surfaces, and knowledge of the geometry of known objects. The effect is similar to that shown in the photograph below of a section of a building at the Glenstone Museum in Potomac, Maryland. The photograph shows two walls joining at a midline which is away from the observer with a section of blue sky visible on top. Viewed this way, the illumination seems to come from the left. Thus, the right wall is more in the light, and the left wall is more in the shadow due to the angle. However, the photograph can also be seen as the edge of a tower with a blue top where the two walls join at a midline which protrudes towards the observer. Viewed this way, the illumination seems to come from the right.
The Glenstone Museum photograph belongs to the author and can only be used with permission.
Anamorphic illusions are images that require the viewer to see them from a certain vantage point in order for the image to not appear distorted. These illusions exploit the fact that our brain interprets reality based on spatial and geometrical cues. Some anamorphic images have elements that appear to be the same size when this is not the case. A common example of this type of images is the text of road markings which employ an anamorphic design because the driver views them from a very acute angle when approaching them.
A striking historical example of anamorphic images are the photos of soldiers forming patriotic symbols that photographers Arthur Mole and John Thomas took during world war I as part of a campaign to sell war bonds. In the photo below, 18,000 soldiers were assembled to form an image of the statue of liberty. The anamorphic character of the image is evidenced in the fact that 12,000 of those 18,000 men were required just to form the flame part of the stature’s image.
Using the right spatial and geometrical cues, two-dimensional images can be made to look three-dimensional as long as they are viewed from a specific vantage point. In the video below, the folks from the You Tube channel bursspup construct an amazing anamorphic illusion using lit candles.
The image of the human statue of liberty by Mole and Thomas is in the public domain.
As I’ve mentioned before, our brain does not perceive reality in a passive way, rather the brain interprets the information that our senses relay to it based on assumptions made from experience. The American scientist Adelbert Ames, Jr. exploited these assumptions to create some amazing illusions. The illusion of the Ames Window is shown in the video below by the folks from the Australian television program, Curiosity Show.
The illusion of the Ames Room is shown by psychologist Philip Zimbardo in the video below.
Science has discovered that we don’t perceive reality passively, but rather our brain employs certain assumptions that it uses to filter the information it obtains from our senses in order to construct a representation of the world around us. This fact can be exploited to create some amazing illusions as shown in the videos below.
The first is by psychologist, author, and magician Richard Wiseman who has a YouTube channel named, Quirkology. This illusion exploits the assumptions we make regarding the positioning of objects based on their size and location with respect to other objects.
The second video from the YouTube channel brusspup is based on the so called anamorphic illusions. These illusions are based on our sense of perspective and depend on the way you are looking at an object.
The above is, of course, just fun and games, but the important thing to realize is that we also filter the information relayed to our senses and employ assumptions to construct a representation of the world around us when engaging in complex behaviors such as befriending or loving people, defining our morality, following a religion, judging others, purchasing a product, or voting for a political candidate. And there is a wealth of information about this process that allows many people to create the equivalent of the illusions depicted in the videos above to influence and/or exploit these behaviors. The difference is that these people never reveal that they have created an illusion.
Scary isn’t it?
I filmed the video below from a train on my way to the town of Kutna Hora in the Czech Republic. The way the tracks seem to “travel” next to each other and then merge is really cool. This is due to the fact that the wooden blocks of the train tracks (called sleepers or ties) seem to be moving in the same direction that the train is moving even though in reality they are receding as the train moves forward. This effect is called "temporal aliasing", and it is the same effect that you see in the spokes of the rotating wheel of a wagon. In the case of the camera, this happens because it does not record reality in a continuous fashion. Rather the camera samples reality a number of times per second, and the samples are put together to generate the video. This is similar to how the old celluloid movies would generate the perception of motion from different successive frames each displaying different stages of a movement. If the sampling rate is not appropriate to record a moving object, the object will appear to move in a direction that is illusory, such as is the case of the wooden blocks in my video.
Whether the human eye/brain system takes samples of reality like a camera is controversial, and there is evidence both in favor and against this hypothesis. The interesting thing about my video is that I could not see this forward motion of the wooden blocks with my own eyes, because the blocks became a blur when the train was moving fast. I could only see it with the camera!
There is an amazing object called “Prince Rupert drop”. It is so called because a German nobleman, Prince Rupert, brought some of these tear shaped objects (they are also known as Bavarian Tears) to the King of England in 1660, who in turned them over his scientists for analysis.
What is exceptional about the Prince Rupert drops is that it combines great resistance to forces applied to the head of the drop along with a great fragility in the tail section of the drop where a small tear can produce an explosive disintegration of the whole drop. This derives from the way the drop is made. The Prince Rupert drop is basically a gob of molten glass that is dropped in water. The glass molecules on the surface of the drop cool rapidly creating a hard layer. This exterior hard layer is pulled in by the slowly cooling deeper layers in the center of the drop pushing the molecules in the exterior layer against each other. This gives rise to an interplay of compression forces in the outer layer along with tensile forces in the inner layers that is responsible for both the great strength and fragility of the Prince Rupert drop.
Destin from SmarterEveryDay gives an excellent visual explanation of this process in the video below where he also uses high-speed cameras to visualize the explosion of Prince Rupert drops.
You can also check Destin’s other video where he fires bullets at Prince Rupert drops!
The image below by Akiyoshi Kitaoka exploits the way the brain perceives reality to create the illusion of motion. The video underneath demonstrates that this perception is not unique to human beings. This indicates that there are similarities in the way nervous systems of related animals (humans and cats in this case) perceive reality.