Impossible Decision

An impossible decision on this Penrose Triangle…

The Penrose triangle, also known as the Penrose tribar, is an optical illusion that depicts a three-dimensional object that is physically impossible to construct.

An impossible Penrose Decision

The Penrose triangle, also known as the Penrose tribar, is an optical illusion that depicts a three-dimensional object that is physically impossible to construct.

The illusion is a two-dimensional drawing that is designed to create the impression of a triangular structure, but the angles of the lines are inconsistent with the laws of Euclidean geometry, making it impossible to construct in the real world.

Penrose Triangle
The Penrose Triangle Illusion

Table of Contents

How does the Penrose Triangle Illusion work?

The Penrose triangle works by exploiting the way the brain interprets the 2-dimensional image of a triangular structure, but with impossible angles and lines that are inconsistent with the laws of Euclidean geometry.

These impossible angles and lines create a visual illusion of depth and three-dimensionality that is impossible to construct in the real world.

The illusion works by playing with the viewer’s expectations about the relationships between the lines and angles of the object and the viewer’s sense of depth.

The brain uses cues such as perspective, shading, and past experiences to create a 3-dimensional perception of the image.

However, in the case of the Penrose triangle, the brain is unable to reconcile the conflicting information, creating the illusion of an impossible object.

The Penrose triangle illusion also highlights the concept of “perceptual set” which refers to the brain’s ability to focus on specific aspects of the image and ignore others depending on the context.

The brain tends to focus on the lines and angles that suggest depth and three-dimensionality, while ignoring the impossible angles and lines that would make the object impossible to construct in the real world.

Additionally, the concept of “top-down processing” comes into play as the brain uses prior knowledge to interpret the visual information coming from the eyes, and tries to make sense of the image with the information it has.

The brain is unable to reconcile the conflicting information in the Penrose triangle, creating the illusion of an impossible object.

Versions of the Penrose Triangle Illusion

The following are some alternate versions of the Penrose Triangle Illusion:

Penrose Triangle clored
From Wikimedia Commons



Penrose Triangle
From Wikimedia Commons



Penrose Triangle rainbow GIF
From Wikimedia Commons


Illusions like the Penrose Triangle Illusion

Paradox illusions are a type of optical illusion that involve images that appear to be self-contradictory or impossible. They typically involve the manipulation of visual cues such as size, shape, movement, and depth perception to create an image that appears to be impossible or defies our understanding of the physical world.

In general, these illusions work by exploiting the way the visual system processes information. The brain relies on certain cues, such as perspective, shading, and texture, to infer the 3D structure of an object. When these cues are manipulated in a certain way, the brain can be fooled into perceiving an impossible or self-contradictory image.

Some related illusions include the following:

The Rubin vase, also known as the Rubin face or the figure-ground vase, is a famous optical illusion in which the image of a vase can also be perceived as two faces in profile looking at each other.

Rubin Vase Classic Black and White


The duck-rabbit illusion is an optical illusion that is an image that can be perceived as either a duck or a rabbit depending on how the viewer looks at it.

Duck Rabbit Illusion

The Necker cube is an optical illusion that features a simple wireframe drawing of a cube. The cube appears to switch back and forth between two different orientations.

Necker Cube

The My Wife and My Mother-in-Law illusion is an optical illusion with an image of a young woman’s face that can also be perceived as an older woman’s face.

Wife and Mother In Law

The Schröder Staircase is an optical illusion that features a drawing of a staircase. The staircase appears to be either ascending or descending, depending on how the brain interprets the angles of the lines.

Schroeders_stairs
From Wikimedia Commons

The impossible cube is an optical illusion that depicts a three-dimensional object that is physically impossible to construct.

Impossible Cube Illusion


The impossible trident is a three-pronged impossible shape resembling a trident. It is usually depicted as a three-pronged fork with each prong appearing to be a continuation of the next, creating an impossible shape.

Impossible Trident
From Wikimedia Commons

The spinning dancer illusion is a visual illusion that depicts a silhouette of a dancer spinning clockwise or counterclockwise. The direction of the dancer’s spin can appear to change depending on the viewer’s perception

Spinning Dancer Gif
From Wikimedia Commons

The Monroe-Einstein illusion works by playing with the viewer’s expectations about the relationships between the features of the faces and the viewer’s sense of facial proportions.

Monroe-Einstein

Discovery of the Penrose Triangle Illusion

It was first created by the British mathematician and physicist Roger Penrose and his father Lionel Penrose, a psychiatrist and mathematician, in the 1950s.

Sir Roger Penrose is a renowned British mathematical physicist and Nobel laureate. He was born in 1931 and is still active today. He is known for his work in the fields of cosmology, general relativity, and quantum mechanics. He was awarded the Nobel Prize in Physics in 2020, jointly with Reinhard Genzel and Andrea Ghez, for his contributions to the understanding of the properties of black holes.

Penrose’s research has focused on the fundamental nature of space and time and the structure of the universe, he proposed new ways of understanding the Big Bang, black holes, and the nature of the universe itself. He has also been interested in the connection between physics and mathematics, particularly in the area of geometry. Penrose has written several books on these topics, which have been widely read and discussed by both scientists and the general public.

Penrose is also known for his work on the concept of “cosmic censorship” which is a theory that states that the singularities that occur in black holes are always hidden from the outside observer. He also developed new mathematical techniques, such as the Penrose diagram, which are used to describe the behavior of black holes and other singularities. Penrose is considered one of the most influential theoretical physicist of the 20th century and his work has had a significant impact on our understanding of the universe.

References and Resources

Check out our complete list of illusions.

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