{"id":1182,"date":"2023-10-22T16:40:50","date_gmt":"2023-10-22T16:40:50","guid":{"rendered":"https:\/\/www.brendanmyers.net\/blog\/?p=1182"},"modified":"2023-10-22T17:49:56","modified_gmt":"2023-10-22T17:49:56","slug":"spacetime-and-the-limits-of-human-knowledge","status":"publish","type":"post","link":"https:\/\/www.brendanmyers.net\/blog\/2023\/10\/spacetime-and-the-limits-of-human-knowledge\/","title":{"rendered":"Spacetime and the limits of human knowledge"},"content":{"rendered":"\n<p>Last night, while doing some math research for fun (and isn&#8217;t that just like me?), I found out that the universe is flat.<\/p>\n\n\n\n<p>By which I mean: the geometry of space-time has now been measured. It&#8217;s within 0.4% of flat-Euclidean, as per expectations arising from our current best theory of the Big Bang.<\/p>\n\n\n\n<p>Some of you reading this might be tempted to reply with &#8220;Yeah, kid, we already know. Nice of you to catch up!&#8221;<\/p>\n\n\n\n<p>But we *didn&#8217;t* know. We only assumed. Until some astronomers figured out an ingenious way to measure it. Here&#8217;s how:<\/p>\n\n\n\n<p>&#8211; Take the expected size of quantum fluxuations in the early universe, given what we know of the first few attoseconds after the Big Bang.<\/p>\n\n\n\n<p>&#8211; Extrapolate to the current age of the universe.<\/p>\n\n\n\n<p>&#8211; Look for signs of those fluxuations in the cosmic microwave background. Measure their angular width.<\/p>\n\n\n\n<p>&#8211; Compare measurement to prediction.<\/p>\n\n\n\n<p>And the winner is: flat-Euclidean, not spherical, and not hyperbolic. Within the margin of error.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large is-style-default\"><a href=\"https:\/\/www.brendanmyers.net\/blog\/wp-content\/uploads\/2023\/10\/guillermo-ferla-QfLm-2AiJ_M-unsplash-scaled.jpg\"><img decoding=\"async\" loading=\"lazy\" width=\"1024\" height=\"668\" src=\"https:\/\/www.brendanmyers.net\/blog\/wp-content\/uploads\/2023\/10\/guillermo-ferla-QfLm-2AiJ_M-unsplash-1024x668.jpg\" alt=\"\" class=\"wp-image-1183\" srcset=\"https:\/\/www.brendanmyers.net\/blog\/wp-content\/uploads\/2023\/10\/guillermo-ferla-QfLm-2AiJ_M-unsplash-1024x668.jpg 1024w, https:\/\/www.brendanmyers.net\/blog\/wp-content\/uploads\/2023\/10\/guillermo-ferla-QfLm-2AiJ_M-unsplash-300x196.jpg 300w, https:\/\/www.brendanmyers.net\/blog\/wp-content\/uploads\/2023\/10\/guillermo-ferla-QfLm-2AiJ_M-unsplash-768x501.jpg 768w, https:\/\/www.brendanmyers.net\/blog\/wp-content\/uploads\/2023\/10\/guillermo-ferla-QfLm-2AiJ_M-unsplash-1536x1002.jpg 1536w, https:\/\/www.brendanmyers.net\/blog\/wp-content\/uploads\/2023\/10\/guillermo-ferla-QfLm-2AiJ_M-unsplash-2048x1337.jpg 2048w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/a><\/figure>\n\n\n\n<p>This isn&#8217;t the last word: in the future, some new method might be devised, or a more accurate measurement might be made.<\/p>\n\n\n\n<p>But here&#8217;s the point that kept me up all night.<\/p>\n\n\n\n<p>In a spherical universe, human mortality and the speed of light prevents us from being able to explore all the universe in a single human lifetime. But supposing both those barriers are overcome*, it may be possible for someone to know all that there is to know. For however far you travel in any direction, you always end up back where you began. You&#8217;d always get back home. Science and philosophy could some day end.<\/p>\n\n\n\n<p>But our current best science says we live in a flat-Euclidean universe, where, if the limits of mortality and the speed of light were overcome*, you could explore as much of the universe as you like, and always return home. (Aside: this is also true of a hyperbolic universe.)<\/p>\n\n\n\n<p>And that felt like a comforting thought.<\/p>\n\n\n\n<p>But at the same time, I also troubled. For it also means the limits of our potential knowledge might correspond 1:1 to the limits of our tolerance for fear of the unknown. Anything might be out there. The curvature of spacetme won&#8217;t protect us.<\/p>\n\n\n\n<p>The above doesn&#8217;t account for dark energy and the accelerating expansion of spacetime. But the correspondence there is that: the further you travel from home, the harder it is to get back. You&#8217;d need more energy to return home than you needed to reach your furthest distant point: for in the time it took to travel that far, the line behind you &#8220;stretched&#8221;, and got longer. The limits of our potential for knowledge might correspond 1:1 to the limits of our tolerance for loneliness.<\/p>\n\n\n\n<p>A few years ago, I studied the math of that, and of the likelihood that some day all matter and energy will be eaten by black holes. That also gave me a few nights of existential dread.<\/p>\n\n\n\n<p>The point is here much like my earlier remarks about the <a href=\"https:\/\/www.brendanmyers.net\/blog\/2023\/09\/the-fermi-paradox-is-personal\/\">Fermi Paradox<\/a>. <strong>Claims about cosmology correspond to claims about the human condition.<\/strong> I&#8217;ve been thinking a lot about those correspondences lately, and wondering if anyone out there feels the same.<\/p>\n\n\n\n<p>*Footnote: those barriers probably won&#8217;t be overcome, except perhaps in science fiction.<\/p>\n\n\n\n<p>Link: <a href=\"https:\/\/www.nature.com\/articles\/35010035\">A flat Universe from high-resolution maps of the cosmic microwave background radiation<\/a> <\/p>\n\n\n\n<p>Link: <a href=\"https:\/\/wmap.gsfc.nasa.gov\/\">Wilkinson Microwave Anisotropy Probe<\/a><\/p>\n\n\n\n<p>[Image: Guillermo Ferla, unsplash dot com.]<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Last night, while doing some math research for fun (and isn&#8217;t that just like me?), I found out that the universe is flat. By which I mean: the geometry of space-time has now been measured. It&#8217;s within 0.4% of flat-Euclidean, &hellip; <a href=\"https:\/\/www.brendanmyers.net\/blog\/2023\/10\/spacetime-and-the-limits-of-human-knowledge\/\">Continue reading <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":"","_links_to":"","_links_to_target":""},"categories":[23],"tags":[],"_links":{"self":[{"href":"https:\/\/www.brendanmyers.net\/blog\/wp-json\/wp\/v2\/posts\/1182"}],"collection":[{"href":"https:\/\/www.brendanmyers.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.brendanmyers.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.brendanmyers.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.brendanmyers.net\/blog\/wp-json\/wp\/v2\/comments?post=1182"}],"version-history":[{"count":0,"href":"https:\/\/www.brendanmyers.net\/blog\/wp-json\/wp\/v2\/posts\/1182\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.brendanmyers.net\/blog\/wp-json\/wp\/v2\/media?parent=1182"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.brendanmyers.net\/blog\/wp-json\/wp\/v2\/categories?post=1182"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.brendanmyers.net\/blog\/wp-json\/wp\/v2\/tags?post=1182"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}