{"id":376367,"date":"2021-12-04T13:00:44","date_gmt":"2021-12-04T10:00:44","guid":{"rendered":"https:\/\/en.buradabiliyorum.com\/what-we-think-we-know-we-dont\/"},"modified":"2021-12-04T13:00:44","modified_gmt":"2021-12-04T10:00:44","slug":"what-we-think-we-know-we-dont","status":"publish","type":"post","link":"https:\/\/buradabiliyorum.com\/en\/what-we-think-we-know-we-dont\/","title":{"rendered":"#what we think we know, we don\u2019t"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_84 counter-hierarchy ez-toc-counter ez-toc-custom ez-toc-container-direction\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<label for=\"ez-toc-cssicon-toggle-item-6a298db65a84a\" class=\"ez-toc-cssicon-toggle-label\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #dd3333;color:#dd3333\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #dd3333;color:#dd3333\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/label><input type=\"checkbox\"  id=\"ez-toc-cssicon-toggle-item-6a298db65a84a\" checked aria-label=\"Toggle\" \/><nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/buradabiliyorum.com\/en\/what-we-think-we-know-we-dont\/#What_is_a_black_hole\" >What is a black hole?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/buradabiliyorum.com\/en\/what-we-think-we-know-we-dont\/#New_black_holes\" >New black holes<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/buradabiliyorum.com\/en\/what-we-think-we-know-we-dont\/#New_understandings\" >New understandings<\/a><\/li><\/ul><\/nav><\/div>\n<p>&#8220;<strong>#what we think we know, we don\u2019t<\/strong>&#8221;<\/p>\n<div>It took <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/www.pbs.org\/wgbh\/aso\/databank\/entries\/dp15ei.html\">Albert Einstein 10 years to find the equations of general relativity<\/a>, but <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/arxiv.org\/abs\/physics\/9912033\">German astrophysicist Karl Schwarzschild only needed a few months to solve them<\/a>. Schwarzschild\u2019s solution describes the gravity of an isolated, spherical and unchanging object \u2014 the enigmatic black hole \u2014 but it was not understood for many years.<\/p>\n<p>Black holes helped to explain new astronomical discoveries, becoming essential ingredients of astrophysics. <a href=\"https:\/\/buradabiliyorum.com\/en\/category\/sciencee\/\" data-internallinksmanager029f6b8e52c=\"5\" title=\"Science\" target=\"_blank\" rel=\"noopener\">Science<\/a> regarded <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/science.nasa.gov\/astrophysics\/focus-areas\/black-holes\/\">black holes as abstractions until the 1960s<\/a>. The recent experimental discovery of gravitational waves has changed our understanding of what black holes are.<\/p>\n<p>In 2016, the LIGO-Virgo collaboration detected <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/theconversation.com\/gravitational-waves-discovered-the-universe-has-spoken-54237\">gravitational waves generated by two merging black holes<\/a>, opening a new era of astronomy celebrated by the 2017 Nobel Prize in physics.<\/p>\n<p>In 2019, the <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/theconversation.com\/first-black-hole-photo-confirms-einsteins-theory-of-relativity-115167\">Event Horizon Telescope<\/a> released an image of the supermassive black hole in the nearby galaxy M87. The following year, the Nobel Prize in physics recognized <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/www.nobelprize.org\/prizes\/physics\/2020\/press-release\/\">the trailblazing theoretical black hole studies of Roger Penrose and the observational ones by Andrea Ghez and Reinhard Genzel<\/a>.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"What_is_a_black_hole\"><\/span>What is a black hole?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>The notion of black hole reflected in popular science hinges on the idea of event horizon \u2014 this is when the velocity needed to escape the gravitational pull of the black hole exceeds the speed of light. Whatever falls into the event horizon is lost forever.<\/p>\n<p>The Schwarzschild radius is the radius of the event horizon, <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/astronomy.swin.edu.au\/cosmos\/S\/Schwarzschild+Radius\">and is proportional to the mass of the black hole<\/a>. But Schwarzschild\u2019s definition has a pitfall: it requires us to know that nothing will emerge from the black hole. This means that the black hole must be monitored forever to know that nothing exits. In practice, this is impossible.<\/p>\n<p>Another mathematical solution to Einstein\u2019s equations <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/doi.org\/10.1139\/p05-063\">describes the formation of a black hole through the collapse of a spherical shell of light<\/a>. An event horizon forms at its centre, expands outwards, <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/doi.org\/10.1103\/PhysRevD.52.7053\">meets the infalling shell of light at the Schwarzschild radius where it stops<\/a> \u2014 <em>et voil\u00e0!<\/em> \u2014 a black hole is formed.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"New_black_holes\"><\/span>New black holes<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Perfectly isolated or unchanging black holes do not exist. Real-world black holes are surrounded by disks orbiting them, stellar winds and dark matter, all of which produce infalling matter that increases their masses.<\/p>\n<p>Black holes often exist in pairs, spiraling closer and closer to each other and emitting gravitational waves until they merge into a larger black hole, the horizon changing in time, dramatically so at the merger.<\/p>\n<figure class=\"align-center zoomable\">\n<p><figure class=\"post-image post-mediaBleed aligncenter\"><a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/www.jpl.nasa.gov\/images\/two-black-holes-on-way-to-becoming-one-artists-concept\"><img decoding=\"async\" loading=\"lazy\" sizes=\"auto, (min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px\" alt=\"Two black holes surrounded by yellow and orange flames spiraling into each other. Image via NASA\" width=\"600\" height=\"338\" class=\"js-lazy\" src=\"https:\/\/images.theconversation.com\/files\/435166\/original\/file-20211201-15-1deuifg.jpeg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip\" srcset=\"https:\/\/images.theconversation.com\/files\/435166\/original\/file-20211201-15-1deuifg.jpeg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=600&amp;h=338&amp;fit=crop&amp;dpr=1 600w, https:\/\/images.theconversation.com\/files\/435166\/original\/file-20211201-15-1deuifg.jpeg?ixlib=rb-1.1.0&amp;q=30&amp;auto=format&amp;w=600&amp;h=338&amp;fit=crop&amp;dpr=2 1200w, https:\/\/images.theconversation.com\/files\/435166\/original\/file-20211201-15-1deuifg.jpeg?ixlib=rb-1.1.0&amp;q=15&amp;auto=format&amp;w=600&amp;h=338&amp;fit=crop&amp;dpr=3 1800w, https:\/\/images.theconversation.com\/files\/435166\/original\/file-20211201-15-1deuifg.jpeg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;h=424&amp;fit=crop&amp;dpr=1 754w, https:\/\/images.theconversation.com\/files\/435166\/original\/file-20211201-15-1deuifg.jpeg?ixlib=rb-1.1.0&amp;q=30&amp;auto=format&amp;w=754&amp;h=424&amp;fit=crop&amp;dpr=2 1508w, https:\/\/images.theconversation.com\/files\/435166\/original\/file-20211201-15-1deuifg.jpeg?ixlib=rb-1.1.0&amp;q=15&amp;auto=format&amp;w=754&amp;h=424&amp;fit=crop&amp;dpr=3 2262w\"\/><noscript><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/images.theconversation.com\/files\/435166\/original\/file-20211201-15-1deuifg.jpeg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip\" alt=\"Two black holes surrounded by yellow and orange flames spiraling into each other. Image via NASA\" width=\"600\" height=\"338\" class=\"\" srcset=\"https:\/\/images.theconversation.com\/files\/435166\/original\/file-20211201-15-1deuifg.jpeg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=600&amp;h=338&amp;fit=crop&amp;dpr=1 600w, https:\/\/images.theconversation.com\/files\/435166\/original\/file-20211201-15-1deuifg.jpeg?ixlib=rb-1.1.0&amp;q=30&amp;auto=format&amp;w=600&amp;h=338&amp;fit=crop&amp;dpr=2 1200w, https:\/\/images.theconversation.com\/files\/435166\/original\/file-20211201-15-1deuifg.jpeg?ixlib=rb-1.1.0&amp;q=15&amp;auto=format&amp;w=600&amp;h=338&amp;fit=crop&amp;dpr=3 1800w, https:\/\/images.theconversation.com\/files\/435166\/original\/file-20211201-15-1deuifg.jpeg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;h=424&amp;fit=crop&amp;dpr=1 754w, https:\/\/images.theconversation.com\/files\/435166\/original\/file-20211201-15-1deuifg.jpeg?ixlib=rb-1.1.0&amp;q=30&amp;auto=format&amp;w=754&amp;h=424&amp;fit=crop&amp;dpr=2 1508w, https:\/\/images.theconversation.com\/files\/435166\/original\/file-20211201-15-1deuifg.jpeg?ixlib=rb-1.1.0&amp;q=15&amp;auto=format&amp;w=754&amp;h=424&amp;fit=crop&amp;dpr=3 2262w\"\/><\/noscript><\/a><figcaption><a rel=\"nofollow noopener\" target=\"_blank\" href=\"#\" data-url=\"https:\/\/twitter.com\/intent\/tweet?url=https%3A%2F%2Feditorial.thenextweb.com%2Fspace%2F2021%2F12%2F04%2Fblack-holes-what-we-think-we-know-we-dont-syndication%2F&amp;via=thenextweb&amp;related=thenextweb&amp;text=Check out this picture on: Two black holes surrounded by yellow and orange flames spiraling into each other. Image via NASA\" data-title=\"Share Two black holes surrounded by yellow and orange flames spiraling into each other. Image via NASA on Twitter\" data-width=\"685\" data-height=\"500\" class=\"post-image-share popitup\" title=\"Share Two black holes surrounded by yellow and orange flames spiraling into each other. Image via NASA on Twitter\"><i class=\"icon icon--inline icon--twitter--dark\"\/><\/a>Two black holes surrounded by yellow and orange flames spiraling into each other. Image via NASA<\/figcaption><\/figure>\n<\/p>\n<\/figure>\n<p>The <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/doi.org\/10.1103\/PhysRevX.6.041015\">2016 LIGO\/Virgo gravitational waves<\/a> originated in the spectacular merger of two black holes. By the time these waves reached Earth, they were weaker than the ambient noise and could only be identified by matching theoretical templates of the expected signal to the data.<\/p>\n<p>Large banks of templates are generated in computer simulations that obviously cannot run forever, as would be necessary if the black hole was characterized by the eternal event horizon. Instead, simulations use the <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/theconversation.com\/grey-is-the-new-black-hole-is-stephen-hawking-right-22481\">apparent horizon<\/a>, characterized by the property that nothing can escape from it <em>now<\/em>.<\/p>\n<p><a href=\"https:\/\/buradabiliyorum.com\/en\/category\/download-scripts-themes-apps\/\" data-internallinksmanager029f6b8e52c=\"9\" title=\"Download Scripts &amp; Themes &amp; Apps\" target=\"_blank\" rel=\"noopener\">App<\/a>arent horizons have played a crucial role in the newly born <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/doi.org\/10.1103\/PhysRevLett.116.241103\">gravitational wave astronomy<\/a>, but are surprisingly little known.<\/p>\n<p>Black holes change because they live in an <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/theconversation.com\/explainer-the-mysterious-dark-energy-that-speeds-the-universes-rate-of-expansion-40224\">expanding universe<\/a>. Theoretical physicist Stephen Hawking predicted that all black holes <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/www.vox.com\/science-and-health\/2018\/3\/14\/17119320\/stephen-hawking-hawking-radiation-explained\">radiate energy due to quantum mechanics<\/a>, which makes them shrink. Although negligible for practical purposes, this radiation is unavoidable in principle.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"New_understandings\"><\/span>New understandings<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Our understanding of black holes is based on the mathematical definition of horizon. The apparent horizon <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/arxiv.org\/abs\/gr-qc\/0508107v2\">is defined by the behavior of light rays in its vicinity<\/a>: rays cannot escape (and since nothing moves faster than light, nothing escapes) <em>at the present moment<\/em>.<\/p>\n<p>But how light rays behave depends on the observer describing them using mathematical simulations. Since, in relativity, time and space depend on the observer, the location where rays stop and the present time are different for different observers. So, the apparent horizon itself depends on the observer.<\/p>\n<p>The very existence of the black hole has come to depend on the observer, while the old event horizon was universal.<\/p>\n<p>The mathematics expressing the new black hole concept tells us that, even in Schwarzschild\u2019s case, <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/arxiv.org\/abs\/gr-qc\/0511017v3\">certain observers exist<\/a> according to whom there is no apparent horizon and, therefore, no black hole! Admittedly, these mathematical observers are very artificial. All natural observations (those that occur through observing the actual behavior of a black hole) that perceive the Schwarzschild geometry as spherical, agree on <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/arxiv.org\/abs\/1610.05822v1\">the existence and location of the apparent horizon<\/a>.<\/p>\n<p>Scientists have finally detected gravitational waves from black holes but had to change the way they understand them. The essence of black hole theory is now different.<!-- Below is The Conversation's page counter tag. Please DO NOT REMOVE. --><img decoding=\"async\" loading=\"lazy\" style=\"border: none !important; box-shadow: none !important; margin: 0 !important; max-height: 1px !important; max-width: 1px !important; min-height: 1px !important; min-width: 1px !important; opacity: 0 !important; outline: none !important; padding: 0 !important; text-shadow: none !important;\" alt=\"The Conversation\" width=\"1\" height=\"1\" class=\"js-lazy\" src=\"https:\/\/counter.theconversation.com\/content\/172816\/count.gif?distributor=republish-lightbox-basic\"\/><!-- End of code. If you don't see any code above, please get new code from the Advanced tab after you click the republish button. The page counter does not collect any personal data. More info: https:\/\/theconversation.com\/republishing-guidelines --><\/p>\n<p><noscript><img decoding=\"async\" loading=\"lazy\" style=\"border: none !important; box-shadow: none !important; margin: 0 !important; max-height: 1px !important; max-width: 1px !important; min-height: 1px !important; min-width: 1px !important; opacity: 0 !important; outline: none !important; padding: 0 !important; text-shadow: none !important;\" src=\"https:\/\/counter.theconversation.com\/content\/172816\/count.gif?distributor=republish-lightbox-basic\" alt=\"The Conversation\" width=\"1\" height=\"1\" class=\"\" srcset=\"\"\/><\/noscript><\/p>\n<p><em>This article by <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/theconversation.com\/profiles\/valerio-faraoni-1288886\">Valerio Faraoni<\/a>, Professor, Physics &amp; Astronomy, <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/theconversation.com\/institutions\/bishops-university-3310\">Bishop\u2019s University<\/a>, is republished from <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/theconversation.com\">The Conversation<\/a> under a Creative Commons license. Read the <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/theconversation.com\/our-understanding-of-black-holes-has-changed-over-time-172816\">original article<\/a>.<\/em><\/p>\n<\/div>\n<p><script async src=\"\/\/platform.twitter.com\/widgets.js\" charset=\"utf-8\"><\/script><\/p>\n<blockquote><p><strong><span style=\"color: #ff6600;\">If you liked the article, do not forget to share it with your friends. Follow us on\u00a0<span style=\"color: #ff0000;\"><a style=\"color: #ff0000;\" href=\"https:\/\/news.google.com\/publications\/CAAqBwgKMLG0nwswvr63Aw\" target=\"_blank\" rel=\"nofollow noopener noreferrer\">Google News<\/a><\/span>\u00a0too, click on the star and choose us from your favorites.<\/span><\/strong><\/p><\/blockquote>\n<blockquote>\n<p style=\"text-align: center;\">For forums sites go to <span style=\"color: #ff9900;\"><a style=\"color: #ff9900;\" href=\"https:\/\/forum.buradabiliyorum.com\/\" target=\"_blank\" rel=\"noopener\">Forum.BuradaBiliyorum.Com<\/a><\/span><\/strong>\n<\/p><\/blockquote>\n<blockquote>\n<p style=\"text-align: center;\"><strong>If you want to read more like this article, you can visit our <span style=\"color: #ff9900;\"><a style=\"color: #ff9900;\" href=\"https:\/\/en.buradabiliyorum.com\/technology\/\" target=\"_blank\" rel=\"noopener\">Technology category.<\/a><\/span><\/strong><\/p>\n<\/blockquote>\n<p><span style=\"color: black;\"><a style=\"color: #ff9900;\" href=\"https:\/\/thenextweb.com\/news\/black-holes-what-we-think-we-know-we-dont-syndication\" target=\"_blank\" rel=\"noopener\">Source<\/a><\/span><\/p>\n","protected":false},"excerpt":{"rendered":"<p>&#8220;#what we think we know, we don\u2019t&#8221; It took Albert Einstein 10 years to find the equations of general relativity, but German astrophysicist Karl Schwarzschild only needed a few months to solve them. Schwarzschild\u2019s solution describes the gravity of an isolated, spherical and unchanging object \u2014 the enigmatic black hole \u2014 but it was not&#8230;<\/p>\n","protected":false},"author":1,"featured_media":376368,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"fifu_image_url":"https:\/\/img-cdn.tnwcdn.com\/image\/tnw?filter_last=1&fit=1280,640&url=https:\/\/cdn0.tnwcdn.com\/wp-content\/blogs.dir\/1\/files\/2021\/12\/Black-hole-confusion-hed.jpg&signature=2ef8881ab77884fe8c1b129f80cdde2b","fifu_image_alt":"","footnotes":""},"categories":[18],"tags":[],"class_list":["post-376367","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-technology"],"_links":{"self":[{"href":"https:\/\/buradabiliyorum.com\/en\/wp-json\/wp\/v2\/posts\/376367","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/buradabiliyorum.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/buradabiliyorum.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/buradabiliyorum.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/buradabiliyorum.com\/en\/wp-json\/wp\/v2\/comments?post=376367"}],"version-history":[{"count":0,"href":"https:\/\/buradabiliyorum.com\/en\/wp-json\/wp\/v2\/posts\/376367\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/buradabiliyorum.com\/en\/wp-json\/wp\/v2\/media\/376368"}],"wp:attachment":[{"href":"https:\/\/buradabiliyorum.com\/en\/wp-json\/wp\/v2\/media?parent=376367"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/buradabiliyorum.com\/en\/wp-json\/wp\/v2\/categories?post=376367"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/buradabiliyorum.com\/en\/wp-json\/wp\/v2\/tags?post=376367"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}