{"id":1571,"date":"2025-11-24T00:28:30","date_gmt":"2025-11-23T22:28:30","guid":{"rendered":"https:\/\/www.lbscience.org\/en\/2025\/11\/19\/%d7%91%d7%a2%d7%95%d7%9c%d7%9d-%d7%94%d7%93%d7%99%d7%a1%d7%a7-discworld-%d7%a9%d7%9c-%d7%98%d7%a8%d7%99-%d7%a4%d7%a8%d7%90%d7%a6%d7%98-%d7%94%d7%93%d7%99%d7%a1%d7%a7-%d7%94%d7%95%d7%90\/"},"modified":"2025-11-26T03:58:43","modified_gmt":"2025-11-26T01:58:43","slug":"why-does-water-fall-off-discworld","status":"publish","type":"post","link":"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/","title":{"rendered":"Why Does Water Fall Off Discworld?"},"content":{"rendered":"

Terry Pratchett\u2019s Discworld (which also appears in mythologies and other stories) is a captivating realm that attracts millions of geeks from all over the world. The structure of this world is familiar to every fan of the series\u2014the world is a disc resting on four elephants, and they, in turn, stand on a turtle, and the turtle sails through the universe.<\/span><\/p>\n

Discworld is not a standard world in several respects. One of its features, for example, is that its sun revolves around it. The way the sun moves hints us toward a historical discovery presented here for the first time.<\/span><\/p>\n

First, we must remember a few things. The first is that many of the laws of physics we know operate similarly in Discworld. For example\u2014gravity. Gravity works: things fall. Rincewind, the cowardly wizard, is afraid, among other things, of the ground (not of heights\u2014of the ground, because it is the ground that kills you). Water at the edge of Discworld pours in one direction, just as \u201cdown\u201d works everywhere else.<\/span><\/p>\n

From this we can infer that gravity operates similarly to our world. If so, Kepler\u2019s laws, which describe the motion of celestial objects, also apply in Discworld. Kepler formulated three laws [1, 2], and the one that interests us is the first\u2014every planet\u2019s orbit around its sun is an ellipse, and the sun is located at one of the foci of that ellipse. When Kepler formulated it, he was interested in the planets of our solar system and noticed that they move around the Sun in ellipses with the Sun at one focus. This law can be generalized to the motion of any small body around a large body\u2014a small body will move in an ellipse with the large body located at one of the foci of the ellipse. Note, the smaller body will never pass in front of the larger body; it will always orbit it.<\/span><\/p>\n

In Discworld the sun moves around the world. When it passes beneath the disc (or, more accurately, on the uninhabited side of the disc that faces the turtle) it passes between the turtle and the elephants. It is even mentioned that sometimes an elephant has to lift a foot so that the sun will not collide with it.<\/span><\/p>\n

What do we deduce from this information? First, that the elephants are the massive body. They possess the greatest mass and attract both the world and the turtle. Second, the turtle has a small, negligible mass\u2014it is probably mostly hollow. Otherwise, the sun\u2019s orbit would be different and would not pass between the turtle and the elephants.<\/span><\/p>\n

This also explains why water spills off the edge of Discworld \u201cdownward\u201d. The directions \u201cup\u201d and \u201cdown\u201d are determined mainly by gravity, and the elephants pull the water toward themselves from the edge of the disc. In fact, the disc stands on the elephants and the turtle lies upside-down on the elephants. Perhaps this is why the world drifts through the universe\u2014maybe the turtle is trying to flip over because it is tired of lying on its back.<\/span><\/p>\n

Hebrew editing: Shir Rosenblum-Man
\nEnglish editing: Elee Shimshoni<\/p>\n

\n

References:<\/b><\/p>\n

    \n
  1. A list of stories in which the world sails through the universe on a turtle<\/a><\/li>\n
  2. Orbits in Space: Part I<\/span><\/a><\/li>\n
  3. Orbits in Space: Part 2<\/span><\/a><\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"

    Terry Pratchett\u2019s Discworld (which also appears in mythologies and other stories) is a captivating realm that attracts millions of geeks from all over the world. The structure of this world is familiar to every fan of the series\u2014the world is a disc resting on four elephants, and they, in turn, stand on a turtle, and […]<\/p>\n","protected":false},"author":30,"featured_media":1574,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[3,12,7],"tags":[],"class_list":["post-1571","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-astronomy","category-engineering","category-physics"],"acf":[],"yoast_head":"\nWhy Does Water Fall Off Discworld? - Little, Big Science<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Why Does Water Fall Off Discworld? - Little, Big Science\" \/>\n<meta property=\"og:description\" content=\"Terry Pratchett\u2019s Discworld (which also appears in mythologies and other stories) is a captivating realm that attracts millions of geeks from all over the world. The structure of this world is familiar to every fan of the series\u2014the world is a disc resting on four elephants, and they, in turn, stand on a turtle, and […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/\" \/>\n<meta property=\"og:site_name\" content=\"Little, Big Science\" \/>\n<meta property=\"article:published_time\" content=\"2025-11-23T22:28:30+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2025-11-26T01:58:43+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.lbscience.org\/en\/wp-content\/uploads\/sites\/3\/2025\/11\/en_meme-1.jpeg\" \/>\n\t<meta property=\"og:image:width\" content=\"2400\" \/>\n\t<meta property=\"og:image:height\" content=\"1350\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/jpeg\" \/>\n<meta name=\"author\" content=\"\u05d5\u05d9\u05e7\u05d8\u05d5\u05e8 \u05e6\u05f3\u05e8\u05e0\u05d5\u05d1\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"\u05d5\u05d9\u05e7\u05d8\u05d5\u05e8 \u05e6\u05f3\u05e8\u05e0\u05d5\u05d1\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"3 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/\",\"url\":\"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/\",\"name\":\"Why Does Water Fall Off Discworld? - Little, Big Science\",\"isPartOf\":{\"@id\":\"https:\/\/www.lbscience.org\/en\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/#primaryimage\"},\"image\":{\"@id\":\"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/#primaryimage\"},\"thumbnailUrl\":\"https:\/\/www.lbscience.org\/en\/wp-content\/uploads\/sites\/3\/2025\/11\/en_meme-1.jpeg\",\"datePublished\":\"2025-11-23T22:28:30+00:00\",\"dateModified\":\"2025-11-26T01:58:43+00:00\",\"author\":{\"@id\":\"https:\/\/www.lbscience.org\/en\/#\/schema\/person\/f86a2a941e7541e6ab47da8f45a3aed7\"},\"breadcrumb\":{\"@id\":\"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/\"]}]},{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/#primaryimage\",\"url\":\"https:\/\/www.lbscience.org\/en\/wp-content\/uploads\/sites\/3\/2025\/11\/en_meme-1.jpeg\",\"contentUrl\":\"https:\/\/www.lbscience.org\/en\/wp-content\/uploads\/sites\/3\/2025\/11\/en_meme-1.jpeg\",\"width\":2400,\"height\":1350},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/www.lbscience.org\/en\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"Why Does Water Fall Off Discworld?\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\/\/www.lbscience.org\/en\/#website\",\"url\":\"https:\/\/www.lbscience.org\/en\/\",\"name\":\"Little, Big Science\",\"description\":\"\",\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\/\/www.lbscience.org\/en\/?s={search_term_string}\"},\"query-input\":{\"@type\":\"PropertyValueSpecification\",\"valueRequired\":true,\"valueName\":\"search_term_string\"}}],\"inLanguage\":\"en-US\"},{\"@type\":\"Person\",\"@id\":\"https:\/\/www.lbscience.org\/en\/#\/schema\/person\/f86a2a941e7541e6ab47da8f45a3aed7\",\"name\":\"\u05d5\u05d9\u05e7\u05d8\u05d5\u05e8 \u05e6\u05f3\u05e8\u05e0\u05d5\u05d1\",\"image\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\/\/www.lbscience.org\/en\/#\/schema\/person\/image\/\",\"url\":\"https:\/\/secure.gravatar.com\/avatar\/03ac9e7541cc22ee9e99b39c692b3b03?s=96&d=mm&r=g\",\"contentUrl\":\"https:\/\/secure.gravatar.com\/avatar\/03ac9e7541cc22ee9e99b39c692b3b03?s=96&d=mm&r=g\",\"caption\":\"\u05d5\u05d9\u05e7\u05d8\u05d5\u05e8 \u05e6\u05f3\u05e8\u05e0\u05d5\u05d1\"},\"description\":\"\u05de\u05e8\u05e6\u05d4 \u05d1\u05db\u05d9\u05e8 \u05d1\u05de\u05d7\u05dc\u05e7\u05d4 \u05dc\u05d4\u05e0\u05d3\u05e1\u05ea \u05de\u05db\u05d5\u05e0\u05d5\u05ea, \u05d4\u05de\u05db\u05dc\u05dc\u05d4 \u05d4\u05d0\u05e7\u05d3\u05de\u05d9\u05ea \u05dc\u05d4\u05e0\u05d3\u05e1\u05d4 \u05d1\u05e8\u05d0\u05d5\u05d3\u05d4 \u05d1\u05db\u05e8\u05de\u05d9\u05d0\u05dc. \u05d5\u05d9\u05e7\u05d8\u05d5\u05e8 \u05d4\u05d5\u05d0 \u05d3\u05d5\u05e7\u05d8\u05d5\u05e8 \u05dc\u05d4\u05e0\u05d3\u05e1\u05ea \u05d0\u05d5\u05d5\u05d9\u05e8\u05d5\u05e0\u05d0\u05d5\u05d8\u05d9\u05e7\u05d4 \u05d5\u05d7\u05dc\u05dc, \u05de\u05ea\u05de\u05d7\u05d4 \u05d1\u05e9\u05e8\u05d9\u05e4\u05d4, \u05de\u05e0\u05d5\u05e2\u05d9\u05dd, \u05de\u05db\u05e0\u05d9\u05e7\u05ea \u05d6\u05d5\u05e8\u05de\u05d9\u05dd \u05d5\u05e1\u05d9\u05de\u05d5\u05dc\u05e6\u05d9\u05d5\u05ea. \u05e2\u05d5\u05e8\u05da \u05de\u05d3\u05e2\u05d9 \u05d1\\\"\u05de\u05d3\u05e2 \u05d2\u05d3\u05d5\u05dc, \u05d1\u05e7\u05d8\u05e0\u05d4\\\".\",\"url\":\"https:\/\/www.lbscience.org\/en\/author\/victorc\/\"}]}<\/script>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"Why Does Water Fall Off Discworld? - Little, Big Science","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/","og_locale":"en_US","og_type":"article","og_title":"Why Does Water Fall Off Discworld? - Little, Big Science","og_description":"Terry Pratchett\u2019s Discworld (which also appears in mythologies and other stories) is a captivating realm that attracts millions of geeks from all over the world. The structure of this world is familiar to every fan of the series\u2014the world is a disc resting on four elephants, and they, in turn, stand on a turtle, and […]","og_url":"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/","og_site_name":"Little, Big Science","article_published_time":"2025-11-23T22:28:30+00:00","article_modified_time":"2025-11-26T01:58:43+00:00","og_image":[{"width":2400,"height":1350,"url":"https:\/\/www.lbscience.org\/en\/wp-content\/uploads\/sites\/3\/2025\/11\/en_meme-1.jpeg","type":"image\/jpeg"}],"author":"\u05d5\u05d9\u05e7\u05d8\u05d5\u05e8 \u05e6\u05f3\u05e8\u05e0\u05d5\u05d1","twitter_card":"summary_large_image","twitter_misc":{"Written by":"\u05d5\u05d9\u05e7\u05d8\u05d5\u05e8 \u05e6\u05f3\u05e8\u05e0\u05d5\u05d1","Est. reading time":"3 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"WebPage","@id":"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/","url":"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/","name":"Why Does Water Fall Off Discworld? - Little, Big Science","isPartOf":{"@id":"https:\/\/www.lbscience.org\/en\/#website"},"primaryImageOfPage":{"@id":"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/#primaryimage"},"image":{"@id":"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/#primaryimage"},"thumbnailUrl":"https:\/\/www.lbscience.org\/en\/wp-content\/uploads\/sites\/3\/2025\/11\/en_meme-1.jpeg","datePublished":"2025-11-23T22:28:30+00:00","dateModified":"2025-11-26T01:58:43+00:00","author":{"@id":"https:\/\/www.lbscience.org\/en\/#\/schema\/person\/f86a2a941e7541e6ab47da8f45a3aed7"},"breadcrumb":{"@id":"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/#breadcrumb"},"inLanguage":"en-US","potentialAction":[{"@type":"ReadAction","target":["https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/"]}]},{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/#primaryimage","url":"https:\/\/www.lbscience.org\/en\/wp-content\/uploads\/sites\/3\/2025\/11\/en_meme-1.jpeg","contentUrl":"https:\/\/www.lbscience.org\/en\/wp-content\/uploads\/sites\/3\/2025\/11\/en_meme-1.jpeg","width":2400,"height":1350},{"@type":"BreadcrumbList","@id":"https:\/\/www.lbscience.org\/en\/2025\/11\/24\/why-does-water-fall-off-discworld\/#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/www.lbscience.org\/en\/"},{"@type":"ListItem","position":2,"name":"Why Does Water Fall Off Discworld?"}]},{"@type":"WebSite","@id":"https:\/\/www.lbscience.org\/en\/#website","url":"https:\/\/www.lbscience.org\/en\/","name":"Little, Big Science","description":"","potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/www.lbscience.org\/en\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-US"},{"@type":"Person","@id":"https:\/\/www.lbscience.org\/en\/#\/schema\/person\/f86a2a941e7541e6ab47da8f45a3aed7","name":"\u05d5\u05d9\u05e7\u05d8\u05d5\u05e8 \u05e6\u05f3\u05e8\u05e0\u05d5\u05d1","image":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/www.lbscience.org\/en\/#\/schema\/person\/image\/","url":"https:\/\/secure.gravatar.com\/avatar\/03ac9e7541cc22ee9e99b39c692b3b03?s=96&d=mm&r=g","contentUrl":"https:\/\/secure.gravatar.com\/avatar\/03ac9e7541cc22ee9e99b39c692b3b03?s=96&d=mm&r=g","caption":"\u05d5\u05d9\u05e7\u05d8\u05d5\u05e8 \u05e6\u05f3\u05e8\u05e0\u05d5\u05d1"},"description":"\u05de\u05e8\u05e6\u05d4 \u05d1\u05db\u05d9\u05e8 \u05d1\u05de\u05d7\u05dc\u05e7\u05d4 \u05dc\u05d4\u05e0\u05d3\u05e1\u05ea \u05de\u05db\u05d5\u05e0\u05d5\u05ea, \u05d4\u05de\u05db\u05dc\u05dc\u05d4 \u05d4\u05d0\u05e7\u05d3\u05de\u05d9\u05ea \u05dc\u05d4\u05e0\u05d3\u05e1\u05d4 \u05d1\u05e8\u05d0\u05d5\u05d3\u05d4 \u05d1\u05db\u05e8\u05de\u05d9\u05d0\u05dc. \u05d5\u05d9\u05e7\u05d8\u05d5\u05e8 \u05d4\u05d5\u05d0 \u05d3\u05d5\u05e7\u05d8\u05d5\u05e8 \u05dc\u05d4\u05e0\u05d3\u05e1\u05ea \u05d0\u05d5\u05d5\u05d9\u05e8\u05d5\u05e0\u05d0\u05d5\u05d8\u05d9\u05e7\u05d4 \u05d5\u05d7\u05dc\u05dc, \u05de\u05ea\u05de\u05d7\u05d4 \u05d1\u05e9\u05e8\u05d9\u05e4\u05d4, \u05de\u05e0\u05d5\u05e2\u05d9\u05dd, \u05de\u05db\u05e0\u05d9\u05e7\u05ea \u05d6\u05d5\u05e8\u05de\u05d9\u05dd \u05d5\u05e1\u05d9\u05de\u05d5\u05dc\u05e6\u05d9\u05d5\u05ea. \u05e2\u05d5\u05e8\u05da \u05de\u05d3\u05e2\u05d9 \u05d1\"\u05de\u05d3\u05e2 \u05d2\u05d3\u05d5\u05dc, \u05d1\u05e7\u05d8\u05e0\u05d4\".","url":"https:\/\/www.lbscience.org\/en\/author\/victorc\/"}]}},"_links":{"self":[{"href":"https:\/\/www.lbscience.org\/en\/wp-json\/wp\/v2\/posts\/1571","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.lbscience.org\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.lbscience.org\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.lbscience.org\/en\/wp-json\/wp\/v2\/users\/30"}],"replies":[{"embeddable":true,"href":"https:\/\/www.lbscience.org\/en\/wp-json\/wp\/v2\/comments?post=1571"}],"version-history":[{"count":11,"href":"https:\/\/www.lbscience.org\/en\/wp-json\/wp\/v2\/posts\/1571\/revisions"}],"predecessor-version":[{"id":1716,"href":"https:\/\/www.lbscience.org\/en\/wp-json\/wp\/v2\/posts\/1571\/revisions\/1716"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.lbscience.org\/en\/wp-json\/wp\/v2\/media\/1574"}],"wp:attachment":[{"href":"https:\/\/www.lbscience.org\/en\/wp-json\/wp\/v2\/media?parent=1571"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.lbscience.org\/en\/wp-json\/wp\/v2\/categories?post=1571"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.lbscience.org\/en\/wp-json\/wp\/v2\/tags?post=1571"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}