How every fact on this site was checked
137 facts. Each one is in our own words, each one has a source, and each one was checked against that source on 13 November 2026.
How we check
We read each source and wrote each fact in our own words. Our build stores the text of every source page, and for each fact it checks that the key words and figures, the “checks” in the table, really appear on the source page. If any check fails, the site does not build. Where good sources disagree, we show each version in a “Sources differ” box rather than picking one. Anything that is our own reading, rather than a sourced fact, is labelled Our opinion. The drawings are our own; the Escher prints are described in words only.
Known disagreements
- The title of the 1958 paper. “Impossible objects: a special type of visual illusion” (Escher museum, MathWorld) or “…a special type of illusion” (Michael Bach, the Illusions Index and the 2020 Journal of Imaging study, in their reference lists). We use the Escher museum’s wording.
- Who drew the impossible triangle first. Reutersvärd in 1934 (Escher museum, Illusions Index, MathWorld); the Penroses found it independently and published it in 1958. Michael Bach adds that Josef Albers (1931) and Hogarth (1754) made impossible pictures earlier still, and knows one from around 1025.
- Where Reutersvärd drew it. While sketching cubes in perspective (Escher museum), during a “long lecture” (MathWorld), or, by an anecdote the Illusions Index calls widely reported, in a Latin class.
- The cube in Belvedere. The Escher museum separates the Necker cube drawn on the floor from the impossible cube in the man’s hands; a 2020 study names the Necker cube as the impossible structure. Michael Bach says impossible figures are not the same thing as the Necker cube’s flipping.
- Whose idea the Perth sculpture is. A concept by Lionel and Roger Penrose “in 1954” (WA Government, 1999), devised by Sir Roger Penrose in the 1950s (local art trail), or the triangle “first articulated” by Reutersvärd (the makers, DENMAC).
- Where it stands. The roundabout at Royal Street, Brook Street and East Parade (WA Public Art Inventory) or Claisebrook Square (Illusions Index).
- When. Completed in November 1999 (DENMAC); unveiled on 5 November 1999 (WA Government).
- How many viewpoints. Two spots for the Perth sculpture (local art trail); one position for Richard Gregory’s 1968 wooden triangle (Illusions Index).
What we left out
- One encyclopaedia page on depth perception we fetched was a machine-written summary, so we did not use it.
- Michael Bach gives the Penroses’ paper two different volume numbers in two places; we follow the Escher museum’s volume 49.
- We found no official page for the Gotschuchen triangle, so we give only what its photo description says, and show no photo of it.
- The possible-or-impossible answers and the drawing steps are our own explanations, not quoted facts.
The log
| # | Fact | Source | Checks |
|---|---|---|---|
| 1 | Your brain builds a 3D model of the world from the flat image on the back of your eye. | Michael Bach, Optical Illusions & Visual Phenomena: Impossible objects | 1 passed |
| 2 | With an impossible object, every corner makes sense on its own. The trouble is that the corners combine viewpoints that can’t all be true at once. | Michael Bach, Optical Illusions & Visual Phenomena: Impossible objects | 1 passed |
| 3 | At the start of the 18th century the philosopher George Berkeley argued that we can’t see depth directly, because the image of anything on the retina is flat, like a painting. | Encyclopaedia Britannica: Space perception | 2 passed |
| 4 | Britannica notes that modern research does not back Berkeley’s idea that reasoning is the key to seeing depth; today’s theories mix inborn abilities with things we learn. | Encyclopaedia Britannica: Space perception | 2 passed |
| 5 | Psychologists also study how we know a cube has six sides when only three can be seen at once. | Encyclopaedia Britannica: Space perception | 1 passed |
| 6 | Even seeing a wire cube in a flat line drawing is an interpretation: many shapes could cast those same lines, but the brain picks a cube as the most likely answer. | Michael Bach, Optical Illusions & Visual Phenomena: Necker cube | 2 passed |
| 7 | Stare at a Necker cube and it suddenly flips between two orientations, typically every 3 to 5 seconds. | Michael Bach, Optical Illusions & Visual Phenomena: Necker cube | 1 passed |
| 8 | You can’t hold one version for long: after 10 seconds or so it flips again. Blinking can make it flip. | Michael Bach, Optical Illusions & Visual Phenomena: Necker cube | 2 passed |
| 9 | L. A. Necker was a Swiss mineralogist who came across the flip by chance while looking at a drawing of a cube-like crystal. He described it in 1832. | Michael Bach, Optical Illusions & Visual Phenomena: Necker cube | 3 passed |
| 10 | Michael Bach points out that an impossible figure is a different thing from the Necker cube’s flipping, though he finds his impossible version even less stable. | Michael Bach, Optical Illusions & Visual Phenomena: Necker cube | 2 passed |
| 11 | The “missing corner” cube can be seen three ways: a cube with a corner cut out, a small cube stuck on the front, or a cube sitting in the corner of a room. | Michael Bach, Optical Illusions & Visual Phenomena: “Missing corner” cube | 1 passed |
| 12 | Without stereo depth or clear lighting, all three readings are geometrically possible. | Michael Bach, Optical Illusions & Visual Phenomena: “Missing corner” cube | 1 passed |
| 13 | Cognitive scientists ask why we keep seeing an impossible figure as a real object even after we know it can’t exist. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible triangle | 1 passed |
| 14 | One standard answer is that parts of the visual system are “cognitively impenetrable”: knowing better doesn’t change what they output. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible triangle | 1 passed |
| 15 | Philosophers are interested because impossible figures seem to give us experiences with contradictory content. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible triangle | 1 passed |
| 16 | Researchers describe impossible structures as having odd geometry that isn’t obvious “pre-attentively”: within a single fixation of the eye, about 120 milliseconds. | Coltelli, Barsanti and Gualtieri: Unveiling the Secrets of Escher’s Lithographs, Journal of Imaging, 2020 (PubMed Central) | 1 passed |
| 17 | A 2020 study modelling the human retina argued that Escher’s secret was to place the clashing parts just outside the area the eye can check for 3D sense in one fixation. | Coltelli, Barsanti and Gualtieri: Unveiling the Secrets of Escher’s Lithographs, Journal of Imaging, 2020 (PubMed Central) | 1 passed |
| 18 | Mathematicians have studied impossible figures to model them for uses such as computer vision. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible triangle | 1 passed |
| 19 | The impossible triangle could only exist if the rules of Euclidean geometry were broken: its bottom bar is drawn both in front of and behind the top corner. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible triangle | 2 passed |
| 20 | Trace it from the top corner: one side seems to run away from you, the other towards you, yet they meet on the same level at the bottom. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible triangle | 1 passed |
| 21 | The Penrose triangle is also called the tribar, the impossible tribar or the impossible triangle. | Wolfram MathWorld: Penrose triangle | 3 passed |
| 22 | Lionel and Roger Penrose published it in the British Journal of Psychology, volume 49, in February 1958. | Museum Escher in The Palace: The OMG moment of Waterfall (12 October 2019) | 1 passed |
| 23 | The article was called “Impossible objects: a special type of visual illusion”. | Museum Escher in The Palace: Ascending and Descending (18 March 2018) | 1 passed |
| 24 | In the Escher museum’s words: the three right angles are normal, but they are joined up in an impossible way. | Museum Escher in The Palace: The OMG moment of Waterfall (12 October 2019) | 1 passed |
| 25 | Oscar Reutersvärd had drawn the shape earlier, though the Penroses didn’t know. | Museum Escher in The Palace: The OMG moment of Waterfall (12 October 2019) | 1 passed |
| 26 | The Penroses came up with the triple bar after Roger Penrose visited Escher’s one-man show at the Stedelijk Museum in 1954. | Museum Escher in The Palace: The OMG moment of Waterfall (12 October 2019) | 1 passed |
| 27 | MathWorld notes that Escher both inspired the triangle and later made it famous. | Wolfram MathWorld: Penrose triangle | 2 passed |
| 28 | The Illusions Index says Reutersvärd created it first and the Penroses discovered it independently and made it popular. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible triangle | 2 passed |
| 29 | Lionel Penrose (1898–1972) was a British psychiatrist, geneticist and mathematician; his son Roger was born in 1931. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible triangle | 2 passed |
| 30 | Roger Penrose was born on 8 August 1931 in Colchester, Essex. | Encyclopaedia Britannica: Roger Penrose | 1 passed |
| 31 | He later shared the 2020 Nobel Prize for Physics for his work on black holes. | Encyclopaedia Britannica: Roger Penrose | 1 passed |
| 32 | He also discovered Penrose tiling, a set of shapes that covers a flat surface without a repeating pattern. | Encyclopaedia Britannica: Roger Penrose | 2 passed |
| 33 | He was knighted in 1994. | Encyclopaedia Britannica: Roger Penrose | 1 passed |
| 34 | There are impossible figures with four sides and more, too. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible triangle | 1 passed |
| 35 | The idea stretches to many-sided barred shapes, including the “tribox”. | Wolfram MathWorld: Penrose triangle | 1 passed |
| 36 | In 1968 Richard Gregory made a wooden object that looks like a real impossible triangle from one position only; from anywhere else it is clearly three joined struts. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible triangle | 3 passed |
| 37 | Monument Valley, a 2014 game from Ustwo Games, is built around impossible figures. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible triangle | 1 passed |
| 38 | Oscar Reutersvärd was born in Stockholm in 1915. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 1 passed |
| 39 | He died on 2 February 2002. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 1 passed |
| 40 | The Escher museum calls him the archetypal father of the impossible figure. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 1 passed |
| 41 | The Illusions Index calls him the ‘father of the impossible figure’. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible triangle | 1 passed |
| 42 | In 1934, aged only 18, he drew an impossible triangle while sketching cubes in perspective. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 2 passed |
| 43 | MathWorld says he drew it in 1934 during a “long lecture”. | Wolfram MathWorld: Penrose triangle | 1 passed |
| 44 | The Illusions Index says it is anecdotally, but widely, reported that he made it in 1934 while doodling in a Latin class. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible triangle | 1 passed |
| 45 | A later colour lithograph of the first impossible triangle carries the title Opus 1. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 1 passed |
| 46 | He designed an impossible staircase in 1937. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 1 passed |
| 47 | His early discoveries stayed hidden for decades: Roger Penrose only found out in 1984 that Reutersvärd had drawn the triangle and the stairs first. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 2 passed |
| 48 | He always used the same isometric projection, where the lines of perspective stay parallel and never meet at a vanishing point. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 2 passed |
| 49 | He numbered his reproduced figures under the title ‘perspective japonaise’. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 1 passed |
| 50 | He drew thousands of them, plain, with no settings or decoration, unlike Escher, who hid his impossibilities in realistic scenes. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 2 passed |
| 51 | In 1950 a grant took him to Paris to study with the artist Fernand Léger. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 1 passed |
| 52 | He was professor of art history and art theory at Lund University from 1964 to 1981. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 1 passed |
| 53 | He also designed mazes, some built outdoors in Sweden. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 1 passed |
| 54 | Seeing what the Penroses and Escher were doing rekindled his own enthusiasm for impossible figures. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 1 passed |
| 55 | Sweden honoured him with a stamp in 1982. | Wolfram MathWorld: Penrose triangle | 1 passed |
| 56 | He wasn’t the first to fool the eye: William Hogarth (1697–1774) made an engraving in 1754 full of perspective tricks. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 1 passed |
| 57 | Giovanni Battista Piranesi hid similar tricks in the walls and stairs of his Carceri d’Invenzione prison scenes. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 2 passed |
| 58 | Michael Bach notes the first impossible object is often credited to Reutersvärd, but Josef Albers and Hogarth were clearly earlier. | Michael Bach, Optical Illusions & Visual Phenomena: Impossible objects | 2 passed |
| 59 | Bach lists Josef Albers’s “Rolled Wrongly” from 1931 and Hogarth’s Satire on False Perspective from 1754. | Michael Bach, Optical Illusions & Visual Phenomena: Impossible objects | 2 passed |
| 60 | The oldest impossible scene Bach knows is the Madonna and Child in the Pericope of Henry II, from around 1025, though he thinks that one was probably not on purpose. | Michael Bach, Optical Illusions & Visual Phenomena: Impossible objects | 2 passed |
| 61 | René Magritte painted an impossible scene too: “Carte blanche”, 1965. | Michael Bach, Optical Illusions & Visual Phenomena: Impossible objects | 1 passed |
| 62 | The Penroses’ 1958 article included a drawing and a 3D model of a continuous flight of stairs that seems to lead up, or down, for ever. | Museum Escher in The Palace: Ascending and Descending (18 March 2018) | 1 passed |
| 63 | Roger’s father Lionel, an expert in genetics and mathematics, built some models from Roger’s drawings. | Museum Escher in The Palace: Ascending and Descending (18 March 2018) | 1 passed |
| 64 | The Penrose stairs appear in Christopher Nolan’s 2010 film Inception. | Museum Escher in The Palace: Ascending and Descending (18 March 2018) | 1 passed |
| 65 | Lionel Penrose sent Escher their Christmas puzzle page, “Puzzles for Christmas”. | Museum Escher in The Palace: Ascending and Descending (18 March 2018) | 1 passed |
| 66 | The devil’s fork is also called the blivet; in his 1964 paper D. H. Schuster called it a “three-stick clevis”. | Michael Bach, Optical Illusions & Visual Phenomena: Impossible objects | 1 passed |
| 67 | Other names include the impossible fork, the devil’s pitchfork and the poiuyt. | Wolfram MathWorld: Impossible fork | 1 passed |
| 68 | The Illusions Index also calls it the impossible trident or the devil’s tuning fork. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible trident | 1 passed |
| 69 | At one end it seems to have three prongs; at the other, only two. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible trident | 1 passed |
| 70 | Schuster, an American psychologist, based it on an advertisement he saw in an aviation journal. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible trident | 1 passed |
| 71 | It was first published in The American Journal of Psychology in 1964. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible trident | 1 passed |
| 72 | Mad magazine made it a running joke, calling it the “poiuyt”: the third row of a keyboard typed from right to left. | Wolfram MathWorld: Impossible fork | 2 passed |
| 73 | In Mad, throughout the 1960s, the poiuyt stood for anything absurd or impossible. | Wolfram MathWorld: Impossible fork | 1 passed |
| 74 | Each prong looks normal; it is working out how they join that goes wrong. | Wolfram MathWorld: Impossible fork | 2 passed |
| 75 | Michael Bach’s way to draw one: start with six evenly spaced upright lines and give them “hats”, and you get three towers or a three-pronged fork. | Michael Bach, Optical Illusions & Visual Phenomena: Impossible objects | 2 passed |
| 76 | Cover the top, draw connecting curves at the bottom, and you get the bottom of a square bar bent into a U. | Michael Bach, Optical Illusions & Visual Phenomena: Impossible objects | 2 passed |
| 77 | Uncover the top and you see the two sensible readings don’t fit together. | Michael Bach, Optical Illusions & Visual Phenomena: Impossible objects | 1 passed |
| 78 | Bach’s impossible “contraption” also includes three “hexnuts” and a “Penrose frame”. | Michael Bach, Optical Illusions & Visual Phenomena: Impossible objects | 2 passed |
| 79 | The artist Roger Hayward worked the fork into a picture of Greek columns. | Wolfram MathWorld: Impossible fork | 1 passed |
| 80 | Of his three famous impossible prints, Escher invented the figure for Belvedere himself: an impossible cube. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 1 passed |
| 81 | Belvedere, Waterfall and Ascending and Descending are based on three impossible figures: a cube, a triangle and a staircase. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 1 passed |
| 82 | Escher told the Penroses he had the idea for Belvedere before he read their article. | Museum Escher in The Palace: Ascending and Descending (18 March 2018) | 1 passed |
| 83 | In Belvedere, a drawing of a Necker cube lies on the floor; the man on the bench holds an impossible cube. | Museum Escher in The Palace: Belvedere (20 May 2020) | 2 passed |
| 84 | A Necker cube is a cube drawn with all its edges showing, so you can’t tell which face is at the front. It can exist on paper; the man’s cube can’t. | Museum Escher in The Palace: Belvedere (20 May 2020) | 1 passed |
| 85 | A 2020 study instead names the Necker cube as the impossible structure in Belvedere. | Coltelli, Barsanti and Gualtieri: Unveiling the Secrets of Escher’s Lithographs, Journal of Imaging, 2020 (PubMed Central) | 1 passed |
| 86 | Escher also made a 1958 wood engraving of the same man with his impossible cube, Man with Cuboid. | Museum Escher in The Palace: Belvedere (20 May 2020) | 1 passed |
| 87 | Man with Cuboid is tiny: 64 × 64 mm. | EscherMath (Saint Louis University): Man with Cuboid | 1 passed |
| 88 | ‘Belvedere’ comes from the Latin for ‘beautiful view’: a tower or gallery added to a building for the view. | Museum Escher in The Palace: Belvedere (20 May 2020) | 1 passed |
| 89 | Escher said in a 1963 lecture that to show something impossible you must first deceive yourself, then your audience, so a casual viewer would not even notice. | Museum Escher in The Palace: Belvedere (20 May 2020) | 2 passed |
| 90 | The people in Belvedere wear clothes from the late Middle Ages. | Museum Escher in The Palace: Belvedere (20 May 2020) | 1 passed |
| 91 | The museum thinks the landscape is almost certainly Italian, perhaps the Abruzzo or Sicily. | Museum Escher in The Palace: Belvedere (20 May 2020) | 2 passed |
| 92 | M.C. Escher was born on 17 June 1898 in Leeuwarden, Netherlands, and died on 27 March 1972 in Laren. | Encyclopaedia Britannica: M.C. Escher | 1 passed |
| 93 | He did not excel at mathematics at school. | Encyclopaedia Britannica: M.C. Escher | 2 passed |
| 94 | He made some 450 lithographs, woodcuts and wood engravings, and about 2,000 drawings and sketches. | Encyclopaedia Britannica: M.C. Escher | 2 passed |
| 95 | He is sometimes called the “father of modern tessellations”. | Encyclopaedia Britannica: M.C. Escher | 1 passed |
| 96 | Belvedere is a lithograph from May 1958. | mcescher.com (the M.C. Escher Foundation and Company): List of works | 1 passed |
| 97 | Ascending and Descending is a lithograph from March 1960. | mcescher.com (the M.C. Escher Foundation and Company): List of works | 1 passed |
| 98 | Waterfall is a lithograph from October 1961. | mcescher.com (the M.C. Escher Foundation and Company): List of works | 1 passed |
| 99 | Escher finished Ascending and Descending on 18 March 1960. | Museum Escher in The Palace: Ascending and Descending (18 March 2018) | 1 passed |
| 100 | The Penrose article sparked the idea, and he started work in late 1959. | Museum Escher in The Palace: Ascending and Descending (18 March 2018) | 1 passed |
| 101 | In April 1960 he wrote to the Penroses to thank them for their invention. | Museum Escher in The Palace: Ascending and Descending (18 March 2018) | 1 passed |
| 102 | In a letter to his son Arthur, Escher described the staircase as a sealed ring, “like a snake eating its own tail”. | Museum Escher in The Palace: Ascending and Descending (18 March 2018) | 1 passed |
| 103 | In his own book, Escher imagined the people on the stairs as monks of some unknown sect, climbing for a few hours a day as a ritual duty. | Museum Escher in The Palace: Ascending and Descending (18 March 2018) | 2 passed |
| 104 | Two “recalcitrant individuals” refuse to take part. | Museum Escher in The Palace: Ascending and Descending (18 March 2018) | 1 passed |
| 105 | Waterfall’s water channel is built from three Penrose triple bars combined. | Museum Escher in The Palace: The OMG moment of Waterfall (12 October 2019) | 1 passed |
| 106 | He first sketched the building without water; the flowing water came later, to show the absurdity even better. | Museum Escher in The Palace: The OMG moment of Waterfall (12 October 2019) | 2 passed |
| 107 | Water always flows to the lowest point, but in Waterfall the lowest, furthest point is also the highest and nearest. The water falls and the cycle starts again: perpetual motion. | Museum Escher in The Palace: The OMG moment of Waterfall (12 October 2019) | 3 passed |
| 108 | A former curator called the second look at Waterfall “the fascinating OMG moment”: the water is flowing upwards. | Museum Escher in The Palace: The OMG moment of Waterfall (12 October 2019) | 2 passed |
| 109 | The museum suggests Waterfall is perhaps his most famous print of all. | Museum Escher in The Palace: The OMG moment of Waterfall (12 October 2019) | 2 passed |
| 110 | In a letter dated 30 November 1961 Escher wrote that the brand-new Waterfall was based on an idea from “the two Penroses”, adding that they mentioned his name in their article. | Museum Escher in The Palace: The OMG moment of Waterfall (12 October 2019) | 3 passed |
| 111 | Escher’s early Waterfall sketches also try out the impossible cube he had used for Belvedere. | Museum Escher in The Palace: The OMG moment of Waterfall (12 October 2019) | 2 passed |
| 112 | The International Congress of Mathematicians opened in Amsterdam on 2 September 1954. | Museum Escher in The Palace: International Congress of Mathematicians 1954 (2 September 2017) | 1 passed |
| 113 | Escher’s solo exhibition at the Stedelijk Museum ran from 27 August to 26 September 1954. | Museum Escher in The Palace: International Congress of Mathematicians 1954 (2 September 2017) | 1 passed |
| 114 | There Roger Penrose and the geometer Donald Coxeter first came across Escher’s work. | Museum Escher in The Palace: International Congress of Mathematicians 1954 (2 September 2017) | 2 passed |
| 115 | It was after seeing Escher’s Relativity at the exhibition that Penrose and his father published their article. | Museum Escher in The Palace: International Congress of Mathematicians 1954 (2 September 2017) | 1 passed |
| 116 | Of all his impossible buildings, Escher himself used the term for only three: Belvedere, Ascending and Descending and Waterfall. | Museum Escher in The Palace: Belvedere (20 May 2020) | 2 passed |
| 117 | Britannica: his mature style, after 1937, combined meticulous realism with puzzling optical illusions. | Encyclopaedia Britannica: M.C. Escher | 2 passed |
| 118 | Reutersvärd drew his own impossible version of Escher’s Cubic Space Division, where the front blocks don’t really touch. | Museum Escher in The Palace: Oscar Reutersvärd (6 February 2021) | 1 passed |
| 119 | In 2011 a German design student known as mcwolles built a wooden copy of Waterfall’s water path, which seems to run uphill. | Michael Bach, Optical Illusions & Visual Phenomena: The impossible waterfall | 3 passed |
| 120 | Bach explains one of its tricks: the shape only looks impossible from one single viewing angle. It is made of two Penrose triangles. | Michael Bach, Optical Illusions & Visual Phenomena: The impossible waterfall | 2 passed |
| 121 | Bach traces a chain of inspiration from the Penroses’ 1958 figure to Escher’s 1960 Ascending and Descending, and a letter exchange between them. | Michael Bach, Optical Illusions & Visual Phenomena: Hallucii, an “impossible” movie | 2 passed |
| 122 | The Impossible Triangle in East Perth, Western Australia, is by the artist Brian McKay and the architect Ahmad Abas. | DENMAC (the makers): The Impossible Triangle | 1 passed |
| 123 | It stands 13.5 metres high. | DENMAC (the makers): The Impossible Triangle | 1 passed |
| 124 | McKay and Abas submitted their design for the commission in 1997. | DENMAC (the makers): The Impossible Triangle | 1 passed |
| 125 | It was completed in November 1999. | DENMAC (the makers): The Impossible Triangle | 1 passed |
| 126 | Western Australia’s planning minister unveiled it on 5 November 1999. | Government of Western Australia: Unveiling of East Perth redevelopment’s latest piece of public art (media statement, 5 November 1999) | 1 passed |
| 127 | The minister said it can only be fully appreciated by moving around it to watch the shape change and the illusion appear. | Government of Western Australia: Unveiling of East Perth redevelopment’s latest piece of public art (media statement, 5 November 1999) | 1 passed |
| 128 | The minister’s statement called it an adaptation of a concept developed by Lionel and Roger Penrose in 1954. | Government of Western Australia: Unveiling of East Perth redevelopment’s latest piece of public art (media statement, 5 November 1999) | 1 passed |
| 129 | The makers say it was inspired by the Penrose triangle “first articulated” by Oscar Reutersvärd. | DENMAC (the makers): The Impossible Triangle | 1 passed |
| 130 | The local art trail says the triangle was devised by Sir Roger Penrose in the 1950s, and that there are only two spots from which it looks complete. | Trails WA: The Claisebrook Village Art Trail (PDF) | 2 passed |
| 131 | The local art trail calls it the 13.5 m landmark at the gateway to East Perth. | Trails WA: The Claisebrook Village Art Trail (PDF) | 1 passed |
| 132 | It was part of the East Perth Redevelopment Project, which turned 38 hectares of industrial land into a new suburb. | DENMAC (the makers): The Impossible Triangle | 1 passed |
| 133 | Its polished striations reflect sunlight and street light, changing look between sunrise and sunset. | DENMAC (the makers): The Impossible Triangle | 2 passed |
| 134 | The WA Public Art Inventory gives its location as the roundabout where Royal Street, Brook Street and East Parade meet. | WA Public Art Inventory: Penrose’s Impossible Triangle | 1 passed |
| 135 | The Illusions Index puts it in Claisebrook Square, and says it was chosen as the winning entry in a competition. | The Illusions Index (Centre for the Study of Perceptual Experience): Impossible triangle | 2 passed |
| 136 | A 4-metre Penrose triangle by the association Treffpunkt Physik stands in Gotschuchen, St. Margareten im Rosental, Austria. | Wikimedia Commons: file description of LargeTribarGotschuchenAustria.JPG (photo by Samo Kupper, Treffpunkt Physik) | 1 passed |
| 137 | Its beams don’t actually meet at the top. Only from one viewing angle do they seem to join. | Wikimedia Commons: file description of LargeTribarGotschuchenAustria.JPG (photo by Samo Kupper, Treffpunkt Physik) | 2 passed |