{"id":2604,"date":"2023-09-30T10:45:04","date_gmt":"2023-09-30T09:45:04","guid":{"rendered":"https:\/\/perso.ens-lyon.fr\/ghys\/?p=2604"},"modified":"2023-09-30T10:46:00","modified_gmt":"2023-09-30T09:46:00","slug":"rene-thom-theoricien-des-catastrophes-a-lhonneur","status":"publish","type":"post","link":"https:\/\/perso.ens-lyon.fr\/ghys\/2023\/09\/30\/rene-thom-theoricien-des-catastrophes-a-lhonneur\/","title":{"rendered":"Ren\u00e9 Thom, th\u00e9oricien des catastrophes, \u00e0 l\u2019honneur"},"content":{"rendered":"\n<p><a href=\"https:\/\/www.lemonde.fr\/sciences\/article\/2023\/09\/27\/rene-thom-theoricien-des-catastrophes-a-l-honneur_6191211_1650684.html\">https:\/\/www.lemonde.fr\/sciences\/article\/2023\/09\/27\/rene-thom-theoricien-des-catastrophes-a-l-honneur_6191211_1650684.html<\/a><\/p>\n\n\n\n<h1 class=\"has-medium-font-size wp-block-heading\" style=\"font-style:normal;font-weight:600\">A l\u2019occasion du centenaire de la naissance du math\u00e9maticien, M\u00e9daille Fields&nbsp;1958, l\u2019Acad\u00e9mie des sciences et l\u2019Institut des hautes \u00e9tudes scientifiques lui ont rendu hommage. Etienne Ghys, \u00e9galement math\u00e9maticien, revient sur l\u2019h\u00e9ritage intellectuel de ce&nbsp;g\u00e9om\u00e8tre hors norme, dans sa \u00ab&nbsp;carte blanche&nbsp;\u00bb au \u00ab&nbsp;Monde&nbsp;\u00bb.<\/h1>\n\n\n\n<p><em>\u00ab&nbsp;Au moment o\u00f9 tant de savants calculent de par le monde, n\u2019est-il pas souhaitable que d\u2019aucuns, qui le peuvent, r\u00eavent&nbsp;?&nbsp;\u00bb<\/em>&nbsp;C\u2019est ainsi que se conclut le livre de Ren\u00e9 Thom (1923-2002)&nbsp;<em>Stabilit\u00e9 structurelle et morphogen\u00e8se<\/em>, \u00e9crit en&nbsp;1972. L\u2019auteur est l\u2019un des math\u00e9maticiens les plus influents du XX<sup>e<\/sup>&nbsp;si\u00e8cle. A l\u2019occasion du centenaire de sa naissance, deux colloques, \u00e0 l\u2019Acad\u00e9mie des sciences et \u00e0 l\u2019Institut des hautes \u00e9tudes scientifiques, viennent de revenir sur l\u2019h\u00e9ritage intellectuel de ce&nbsp;g\u00e9om\u00e8tre hors norme.<\/p>\n\n\n\n<p>Un r\u00eaveur, sans aucun doute. Lorsqu\u2019il pr\u00e9parait sa th\u00e8se, son mentor, Henri Cartan, avait le plus grand mal \u00e0 le canaliser. Il lui \u00e9crit par exemple&nbsp;:&nbsp;<em>\u00ab&nbsp;Abstenez-vous d\u2019\u00e9noncer des th\u00e9or\u00e8mes qui non seulement ne sont pas d\u00e9montr\u00e9s, mais dont l\u2019\u00e9nonc\u00e9 n\u2019a m\u00eame pas de sens clairement d\u00e9fini.&nbsp;\u00bb<\/em>&nbsp;Un coll\u00e8gue d\u2019Henri Cartan lui expliquera qu\u2019une bonne dizaine de math\u00e9maticiens pourraient fournir les d\u00e9monstrations manquantes, mais que seul Ren\u00e9 Thom \u00e9tait capable d\u2019imaginer de tels \u00e9nonc\u00e9s, incroyablement novateurs. La th\u00e8se sera soutenue en&nbsp;1951, et Ren\u00e9 Thom recevra la m\u00e9daille Fields en&nbsp;1958 pour ses d\u00e9couvertes dans le domaine de la topologie diff\u00e9rentielle, dont il est l\u2019un des pionniers. Cette m\u00e9daille le perturbera beaucoup. Il expliquera qu\u2019il pensait ne pas la m\u00e9riter, ce qui n\u2019est pas ce que pensent d\u2019ordinaire les m\u00e9daill\u00e9s.<\/p>\n\n\n\n<p>Il d\u00e9cida de prendre une autre direction, qu\u2019on pourrait qualifier de \u00ab&nbsp;plus appliqu\u00e9e&nbsp;\u00bb. Il postule qu\u2019en g\u00e9n\u00e9ral un syst\u00e8me (par exemple physique ou biologique) se trouve dans un \u00e9tat stable, et qu\u2019\u00e0 certains moments tr\u00e8s particuliers il passe par des situations qu\u2019il qualifie de \u00ab&nbsp;singuli\u00e8res&nbsp;\u00bb ou \u00ab&nbsp;catastrophiques&nbsp;\u00bb, en sautant tr\u00e8s rapidement d\u2019un domaine de stabilit\u00e9 \u00e0 un autre. Il s\u2019agissait donc de comprendre la nature de ces singularit\u00e9s, et ce sera la naissance de la&nbsp;\u00ab&nbsp;th\u00e9orie des catastrophes&nbsp;\u00bb, au succ\u00e8s immense dans les ann\u00e9es&nbsp;1970.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Une question de bord<\/h2>\n\n\n\n<p>Thom \u00e9tablit une liste de sept catastrophes \u00e9l\u00e9mentaires aux noms po\u00e9tiques&nbsp;: \u00ab&nbsp;pli&nbsp;\u00bb, \u00ab&nbsp;fronce&nbsp;\u00bb, \u00ab&nbsp;queue-d\u2019aronde&nbsp;\u00bb, \u00ab&nbsp;papillon&nbsp;\u00bb, \u00ab&nbsp;ombilic elliptique&nbsp;\u00bb, \u00ab&nbsp;parabolique&nbsp;\u00bb ou \u00ab&nbsp;hyperbolique&nbsp;\u00bb. Le math\u00e9maticien anglais Erik Christopher Zeeman \u00e9tend le champ d\u2019application \u00e0 des situations de plus en plus vari\u00e9es&nbsp;: \u00e9meutes dans les prisons, agressivit\u00e9 du chien, krach boursier,&nbsp;etc.<\/p>\n\n\n\n<p>Bien des critiques furent adress\u00e9es \u00e0 cette th\u00e9orie, et Thom les analysa avec s\u00e9rieux et en reconnut souvent la validit\u00e9. Par exemple, on lui reprocha de ne pas avoir tenu compte de l\u2019existence de dynamiques chaotiques (dont la th\u00e9orie se d\u00e9veloppait alors), ou encore d\u2019avoir construit un outil permettant de comprendre mais pas de pr\u00e9voir. Il remet en question la n\u00e9cessit\u00e9 d\u2019une validation exp\u00e9rimentale dans les sciences, ce qui ne fut pas sans engendrer des r\u00e9actions violentes, mais souvent justifi\u00e9es, de la part des biologistes. Son livre&nbsp;<em>Pr\u00e9dire&nbsp;n\u2019est pas expliquer<\/em>&nbsp;(1991) examine tous ces sujets avec honn\u00eatet\u00e9 et s\u00e9r\u00e9nit\u00e9.<\/p>\n\n\n\n<p>Aujourd\u2019hui, les concepts introduits par Thom, comme la stabilit\u00e9 structurelle, la g\u00e9n\u00e9ricit\u00e9 (le fait pour une propri\u00e9t\u00e9 de s\u2019appliquer au cas g\u00e9n\u00e9ral) ou la transversalit\u00e9, sont si importants qu\u2019ils sont entr\u00e9s dans le subconscient de tous les math\u00e9maticiens.<\/p>\n\n\n\n<p>Par la suite, il se tournera vers la philosophie d\u2019Aristote. Il s\u2019y reconna\u00eet dans bien des aspects, comme celui qui consiste \u00e0 d\u00e9finir un objet ou une id\u00e9e \u00e0 travers son bord. Sa th\u00e8se d\u00e9veloppait d\u00e9j\u00e0 une th\u00e9orie du \u00ab&nbsp;cobordisme&nbsp;\u00bb, et ses catastrophes ne sont que les travers\u00e9es du bord d\u2019un domaine de stabilit\u00e9.&nbsp;<em>\u00ab&nbsp;En v\u00e9rit\u00e9<\/em>,<em>&nbsp;<\/em>\u00e9crit-il,&nbsp;<em>il existe une r\u00e9elle unit\u00e9 dans ma r\u00e9flexion. Je ne la per\u00e7ois qu\u2019aujourd\u2019hui, apr\u00e8s y avoir beaucoup r\u00e9fl\u00e9chi, sur le plan philosophique. Et cette unit\u00e9, je la trouve dans cette notion de bord.&nbsp;\u00bb<\/em><\/p>\n\n\n\n<p>Les quatre derniers tableaux de Salvador Dali, en&nbsp;1983, sont des&nbsp;<em>Hommages \u00e0 Ren\u00e9 Thom<\/em>.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>https:\/\/www.lemonde.fr\/sciences\/article\/2023\/09\/27\/rene-thom-theoricien-des-catastrophes-a-l-honneur_6191211_1650684.html A l\u2019occasion du centenaire de la naissance du math\u00e9maticien, M\u00e9daille Fields&nbsp;1958, l\u2019Acad\u00e9mie des sciences et l\u2019Institut des hautes \u00e9tudes scientifiques lui ont rendu hommage. Etienne Ghys, \u00e9galement math\u00e9maticien, revient sur l\u2019h\u00e9ritage intellectuel de ce&nbsp;g\u00e9om\u00e8tre hors norme, dans sa \u00ab&nbsp;carte blanche&nbsp;\u00bb au \u00ab&nbsp;Monde&nbsp;\u00bb. \u00ab&nbsp;Au moment o\u00f9 tant de savants calculent de par le monde, n\u2019est-il &hellip; <a href=\"https:\/\/perso.ens-lyon.fr\/ghys\/2023\/09\/30\/rene-thom-theoricien-des-catastrophes-a-lhonneur\/\" class=\"more-link\">Continuer la lecture de <span class=\"screen-reader-text\">Ren\u00e9 Thom, th\u00e9oricien des catastrophes, \u00e0 l\u2019honneur<\/span> <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","ub_ctt_via":"","_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"episode_type":"","audio_file":"","cover_image":"","cover_image_id":"","duration":"","filesize":"","date_recorded":"","explicit":"","block":"","itunes_episode_number":"","itunes_title":"","itunes_season_number":"","itunes_episode_type":"","filesize_raw":"","footnotes":""},"categories":[57],"tags":[],"class_list":["post-2604","post","type-post","status-publish","format-standard","hentry","category-le-monde"],"featured_image_src":null,"author_info":{"display_name":"ghys","author_link":"https:\/\/perso.ens-lyon.fr\/ghys\/author\/ghys\/"},"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v25.4 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Ren\u00e9 Thom, th\u00e9oricien des catastrophes, \u00e0 l\u2019honneur - \u00c9tienne Ghys<\/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:\/\/perso.ens-lyon.fr\/ghys\/2023\/09\/30\/rene-thom-theoricien-des-catastrophes-a-lhonneur\/\" \/>\n<meta property=\"og:locale\" content=\"fr_FR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Ren\u00e9 Thom, th\u00e9oricien des catastrophes, \u00e0 l\u2019honneur - \u00c9tienne Ghys\" \/>\n<meta property=\"og:description\" content=\"https:\/\/www.lemonde.fr\/sciences\/article\/2023\/09\/27\/rene-thom-theoricien-des-catastrophes-a-l-honneur_6191211_1650684.html A l\u2019occasion du centenaire de la naissance du math\u00e9maticien, M\u00e9daille Fields&nbsp;1958, l\u2019Acad\u00e9mie des sciences et l\u2019Institut des hautes \u00e9tudes scientifiques lui ont rendu hommage. 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Etienne Ghys, \u00e9galement math\u00e9maticien, revient sur l\u2019h\u00e9ritage intellectuel de ce&nbsp;g\u00e9om\u00e8tre hors norme, dans sa \u00ab&nbsp;carte blanche&nbsp;\u00bb au \u00ab&nbsp;Monde&nbsp;\u00bb. \u00ab&nbsp;Au moment o\u00f9 tant de savants calculent de par le monde, n\u2019est-il\u2026","_links":{"self":[{"href":"https:\/\/perso.ens-lyon.fr\/ghys\/wp-json\/wp\/v2\/posts\/2604","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/perso.ens-lyon.fr\/ghys\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/perso.ens-lyon.fr\/ghys\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/perso.ens-lyon.fr\/ghys\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/perso.ens-lyon.fr\/ghys\/wp-json\/wp\/v2\/comments?post=2604"}],"version-history":[{"count":2,"href":"https:\/\/perso.ens-lyon.fr\/ghys\/wp-json\/wp\/v2\/posts\/2604\/revisions"}],"predecessor-version":[{"id":2606,"href":"https:\/\/perso.ens-lyon.fr\/ghys\/wp-json\/wp\/v2\/posts\/2604\/revisions\/2606"}],"wp:attachment":[{"href":"https:\/\/perso.ens-lyon.fr\/ghys\/wp-json\/wp\/v2\/media?parent=2604"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/perso.ens-lyon.fr\/ghys\/wp-json\/wp\/v2\/categories?post=2604"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/perso.ens-lyon.fr\/ghys\/wp-json\/wp\/v2\/tags?post=2604"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}