Penrose triangle

Last updated

Penrose triangle Penrose-dreieck.svg
Penrose triangle

The Penrose triangle, also known as the Penrose tribar, the impossible tribar, [1] or the impossible triangle, [2] is a triangular impossible object, an optical illusion consisting of an object which can be depicted in a perspective drawing. It cannot exist as a solid object in ordinary three-dimensional Euclidean space, although its surface can be embedded isometrically (bent but not stretched) in five-dimensional Euclidean space. [3] It was first created by the Swedish artist Oscar Reutersvärd in 1934. [4] Independently from Reutersvärd, the triangle was devised and popularized in the 1950s by psychiatrist Lionel Penrose and his son, the mathematician and Nobel Prize laureate Roger Penrose, who described it as "impossibility in its purest form". [5] It is featured prominently in the works of artist M. C. Escher, whose earlier depictions of impossible objects partly inspired it.

Contents

Description

A rotating Penrose triangle model to show illusion. At the moment of illusion, there appears to be a pair of purple faces (one partially occluded) joined at right angles, but these are actually parallel faces, and the partially occluded face is internal, not external. Penrose-triangle-4color-rotation.gif
A rotating Penrose triangle model to show illusion. At the moment of illusion, there appears to be a pair of purple faces (one partially occluded) joined at right angles, but these are actually parallel faces, and the partially occluded face is internal, not external.

The tribar/triangle appears to be a solid object, made of three straight beams of square cross-section which meet pairwise at right angles at the vertices of the triangle they form. The beams may be broken, forming cubes or cuboids.

This combination of properties cannot be realized by any three-dimensional object in ordinary Euclidean space. Such an object can exist in certain Euclidean 3-manifolds. [6] A surface with the same geodesic distances as the depicted surface of the tribar, but without its flat shape and right angles, are to be preserved, can also exist in 5-dimensional Euclidean space, which is the lowest-dimensional Euclidean space within which this surface can be isometrically embedded. [3] There also exist three-dimensional solid shapes each of which, when viewed from a certain angle, appears the same as the 2-dimensional depiction of the Penrose triangle on this page (such as – for example – the adjacent image depicting a sculpture in Perth, Australia). The term "Penrose Triangle" can refer to the 2-dimensional depiction or the impossible object itself.

If a line is traced around the Penrose triangle, a 4-loop Möbius strip is formed. [7]

Depictions

A 3D-printed version of the Reutersvard Triangle illusion Penrosetrianglemodel.jpg
A 3D-printed version of the Reutersvärd Triangle illusion

M.C. Escher's lithograph Waterfall (1961) depicts a watercourse that flows in a zigzag along the long sides of two elongated Penrose triangles, so that it ends up two stories higher than it began. The resulting waterfall, forming the short sides of both triangles, drives a water wheel. Escher points out that in order to keep the wheel turning, some water must occasionally be added to compensate for evaporation. A third Penrose triangle lies between the other two, formed by two segments of waterway and a support tower. [8]

Sculptures

See also

Related Research Articles

<span class="mw-page-title-main">Euclidean geometry</span> Mathematical model of the physical space

Euclidean geometry is a mathematical system attributed to ancient Greek mathematician Euclid, which he described in his textbook on geometry, Elements. Euclid's approach consists in assuming a small set of intuitively appealing axioms (postulates) and deducing many other propositions (theorems) from these. Although many of Euclid's results had been stated earlier, Euclid was the first to organize these propositions into a logical system in which each result is proved from axioms and previously proved theorems.

<span class="mw-page-title-main">M. C. Escher</span> Dutch graphic artist (1898–1972)

Maurits Cornelis Escher was a Dutch graphic artist who made woodcuts, lithographs, and mezzotints, many of which were inspired by mathematics. Despite wide popular interest, for most of his life Escher was neglected in the art world, even in his native Netherlands. He was 70 before a retrospective exhibition was held. In the late twentieth century, he became more widely appreciated, and in the twenty-first century he has been celebrated in exhibitions around the world.

<span class="mw-page-title-main">Surface (topology)</span> Two-dimensional manifold

In the part of mathematics referred to as topology, a surface is a two-dimensional manifold. Some surfaces arise as the boundaries of three-dimensional solid figures; for example, the sphere is the boundary of the solid ball. Other surfaces arise as graphs of functions of two variables; see the figure at right. However, surfaces can also be defined abstractly, without reference to any ambient space. For example, the Klein bottle is a surface that cannot be embedded in three-dimensional Euclidean space.

<span class="mw-page-title-main">Möbius strip</span> Non-orientable surface with one edge

In mathematics, a Möbius strip, Möbius band, or Möbius loop is a surface that can be formed by attaching the ends of a strip of paper together with a half-twist. As a mathematical object, it was discovered by Johann Benedict Listing and August Ferdinand Möbius in 1858, but it had already appeared in Roman mosaics from the third century CE. The Möbius strip is a non-orientable surface, meaning that within it one cannot consistently distinguish clockwise from counterclockwise turns. Every non-orientable surface contains a Möbius strip.

<span class="mw-page-title-main">Impossible object</span> Type of optical illusion

An impossible object is a type of optical illusion that consists of a two-dimensional figure which is instantly and naturally understood as representing a projection of a three-dimensional object but cannot exist as a solid object. Impossible objects are of interest to psychologists, mathematicians and artists without falling entirely into any one discipline.

<span class="mw-page-title-main">Torus</span> Doughnut-shaped surface of revolution

In geometry, a torus is a surface of revolution generated by revolving a circle in three-dimensional space one full revolution about an axis that is coplanar with the circle. The main types of toruses include ring toruses, horn toruses, and spindle toruses. A ring torus is sometimes colloquially referred to as a donut or doughnut.

<span class="mw-page-title-main">Impossible cube</span> 2D drawing of impossible 3D object

The impossible cube or irrational cube is an impossible object invented by M.C. Escher for his print Belvedere. It is a two-dimensional figure that superficially resembles a perspective drawing of a three-dimensional cube, with its features drawn inconsistently from the way they would appear in an actual cube.

<span class="mw-page-title-main">Hyperbolic geometry</span> Non-Euclidean geometry

In mathematics, hyperbolic geometry is a non-Euclidean geometry. The parallel postulate of Euclidean geometry is replaced with:

<span class="mw-page-title-main">Tessellation</span> Tiling of a plane in mathematics

A tessellation or tiling is the covering of a surface, often a plane, using one or more geometric shapes, called tiles, with no overlaps and no gaps. In mathematics, tessellation can be generalized to higher dimensions and a variety of geometries.

<span class="mw-page-title-main">Penrose stairs</span> Impossible object

The Penrose stairs or Penrose steps, also dubbed the impossible staircase, is an impossible object created by Oscar Reutersvärd in 1937 and later independently discovered and made popular by Lionel Penrose and his son Roger Penrose. A variation on the Penrose triangle, it is a two-dimensional depiction of a staircase in which the stairs make four 90-degree turns as they ascend or descend yet form a continuous loop, so that a person could climb them forever and never get any higher. This is clearly impossible in three-dimensional Euclidean geometry but possible in some non-Euclidean geometry like in nil geometry.

<i>Reptiles</i> (M. C. Escher) 1943 lithograph by M. C. Escher

Reptiles is a lithograph print by the Dutch artist M. C. Escher first printed in March 1943. It touches on the theme found in much of his work of mathematics in art.

<i>Waterfall</i> (M. C. Escher) Lithograph print by M. C. Escher

Waterfall is a lithograph by the Dutch artist M. C. Escher, first printed in October 1961. It shows a perpetual motion machine where water from the base of a waterfall appears to run downhill along the water path before reaching the top of the waterfall.

<span class="mw-page-title-main">Oscar Reutersvärd</span> Swedish artist (1915–2002)

Oscar Reutersvärd was a Swedish graphic artist, who in 1934 pioneered the art of 3D drawings that may initially appear feasible, yet cannot be physically constructed. He is sometimes described as "the father of the impossible figure", although there are much older examples, e.g. Hogarth's Satire on False Perspective.

<span class="mw-page-title-main">Four-dimensional space</span> Geometric space with four dimensions

Four-dimensional space (4D) is the mathematical extension of the concept of three-dimensional space (3D). Three-dimensional space is the simplest possible abstraction of the observation that one needs only three numbers, called dimensions, to describe the sizes or locations of objects in the everyday world. For example, the volume of a rectangular box is found by measuring and multiplying its length, width, and height. This concept of ordinary space is called Euclidean space because it corresponds to Euclid's geometry, which was originally abstracted from the spatial experiences of everyday life.

<span class="mw-page-title-main">Parallel projection</span> Projection of a 3D object onto a plane via parallel rays

In three-dimensional geometry, a parallel projection is a projection of an object in three-dimensional space onto a fixed plane, known as the projection plane or image plane, where the rays, known as lines of sight or projection lines, are parallel to each other. It is a basic tool in descriptive geometry. The projection is called orthographic if the rays are perpendicular (orthogonal) to the image plane, and oblique or skew if they are not.

<span class="mw-page-title-main">Rhombille tiling</span> Tiling of the plane with 60° rhombi

In geometry, the rhombille tiling, also known as tumbling blocks, reversible cubes, or the dice lattice, is a tessellation of identical 60° rhombi on the Euclidean plane. Each rhombus has two 60° and two 120° angles; rhombi with this shape are sometimes also called diamonds. Sets of three rhombi meet at their 120° angles, and sets of six rhombi meet at their 60° angles.

In mathematics, a Riemannian manifold is said to be flat if its Riemann curvature tensor is everywhere zero. Intuitively, a flat manifold is one that "locally looks like" Euclidean space in terms of distances and angles, e.g. the interior angles of a triangle add up to 180°.

<span class="mw-page-title-main">Differential geometry of surfaces</span> The mathematics of smooth surfaces

In mathematics, the differential geometry of surfaces deals with the differential geometry of smooth surfaces with various additional structures, most often, a Riemannian metric.

<span class="mw-page-title-main">Mathematics and art</span> Relationship between mathematics and art

Mathematics and art are related in a variety of ways. Mathematics has itself been described as an art motivated by beauty. Mathematics can be discerned in arts such as music, dance, painting, architecture, sculpture, and textiles. This article focuses, however, on mathematics in the visual arts.

<span class="mw-page-title-main">Binary tiling</span> Tiling of the hyperbolic plane

In geometry, the binary tiling is a tiling of the hyperbolic plane, resembling a quadtree over the Poincaré half-plane model of the hyperbolic plane. It was first studied mathematically in 1974 by Károly Böröczky.

References

  1. Pappas, Theoni (1989). "The Impossible Tribar". The Joy of Mathematics: Discovering Mathematics All Around You. San Carlos, California: Wide World Publ./Tetra. p. 13.
  2. Brouwer, James R.; Rubin, David C. (June 1979). "A simple design for an impossible triangle". Perception . 8 (3): 349–350. doi:10.1068/p080349. PMID   534162. S2CID   41895719.
  3. 1 2 Zeng, Zhenbing; Xu, Yaochen; Yang, Zhengfeng; Li, Zhi-bin (2021). "An isometric embedding of the impossible triangle into the Euclidean space of lowest dimension" (PDF). In Corless, Robert M.; Gerhard, Jürgen; Kotsireas, Ilias S. (eds.). Maple in Mathematics Education and Research: 4th Maple Conference, MC 2020, Waterloo, Ontario, Canada, November 2–6, 2020, Revised Selected Papers. Springer International Publishing. pp. 438–457. doi:10.1007/978-3-030-81698-8_29. ISBN   9783030816988.
  4. Ernst, Bruno (1986). "Escher's impossible figure prints in a new context". In Coxeter, H. S. M.; Emmer, M.; Penrose, R.; Teuber, M. L. (eds.). M. C. Escher Art and Science: Proceedings of the International Congress on M. C. Escher, Rome, Italy, 26–28 March, 1985. North-Holland. pp. 125–134. See in particular p. 131.
  5. Penrose, L. S.; Penrose, R. (February 1958). "Impossible objects: a special type of visual illusion". British Journal of Psychology . 49 (1): 31–33. doi:10.1111/j.2044-8295.1958.tb00634.x. PMID   13536303.
  6. Francis, George K. (1988). "Chapter 4: The impossible tribar". A Topological Picturebook. Springer. pp. 65–76. doi:10.1007/978-0-387-68120-7_4. ISBN   0-387-96426-6. See in particular p. 68, where Francis attributes this observation to John Stillwell.
  7. Gardner, Martin (August 1978). "Mathematical Games: A Möbius band has a finite thickness, and so it is actually a twisted prism". Scientific American . 239 (2): 18–26. doi:10.1038/scientificamerican1278-18. JSTOR   24960346.
  8. M. C. Escher: The Graphic Work. Taschen. 2000. p. 16. ISBN   9783822858646.
  9. Федоров, Ю. (1972). "Невозможное-Возможно". Техника Молодежи. 4: 20–21.