{"id":12967,"date":"2017-01-25T15:30:59","date_gmt":"2017-01-25T23:30:59","guid":{"rendered":"http:\/\/www.preposterousuniverse.com\/blog\/?p=12967"},"modified":"2017-01-25T15:30:59","modified_gmt":"2017-01-25T23:30:59","slug":"what-happened-at-the-big-bang","status":"publish","type":"post","link":"https:\/\/preposterousuniverse.com\/blog\/2017\/01\/25\/what-happened-at-the-big-bang\/","title":{"rendered":"What Happened at the Big Bang?"},"content":{"rendered":"<p>I had the pleasure earlier this month of giving a plenary lecture at <a href=\"https:\/\/aas.org\/meetings\/aas229\">a meeting of the American Astronomical Society<\/a>. Unfortunately, as far as I know they don&#8217;t record the lectures on video. So here, at least, are the slides I showed during my talk. I&#8217;ve been a little hesitant to put them up, since some subtleties are lost if you only have the slides and not the words that went with them, but perhaps it&#8217;s better than nothing.<\/p>\n<p><iframe loading=\"lazy\" src=\"\/\/www.slideshare.net\/slideshow\/embed_code\/key\/pC28l1efeNfg0e\" width=\"595\" height=\"485\" frameborder=\"0\" marginwidth=\"0\" marginheight=\"0\" scrolling=\"no\" style=\"border:1px solid #CCC; border-width:1px; margin-bottom:5px; max-width: 100%;\" allowfullscreen> <\/iframe> <\/p>\n<div style=\"margin-bottom:5px\"> <strong> <a href=\"\/\/www.slideshare.net\/seanmcarroll\/what-we-dont-know-about-the-beginning-of-the-universe\" title=\"What We (Don&#x27;t) Know About the Beginning of the Universe\" target=\"_blank\">What We (Don&#x27;t) Know About the Beginning of the Universe<\/a> <\/strong> from <strong><a target=\"_blank\" href=\"\/\/www.slideshare.net\/seanmcarroll\">Sean Carroll<\/a><\/strong> <\/div>\n<p>My assigned topic was &#8220;What We Don&#8217;t Know About the Beginning of the Universe,&#8221; and I focused on the question of whether there could have been space and time even before the Big Bang. Short answer: sure there could have been, but we don&#8217;t actually know.<\/p>\n<p>So what I did to fill my time was two things. First, I talked about different ways the universe could have existed before the Big Bang, classifying models into four possibilities (see Slide 7):<\/p>\n<ol>\n<li><strong>Bouncing<\/strong> (the universe collapses to a Big Crunch, then re-expands with a Big Bang)<\/li>\n<li><strong>Cyclic<\/strong> (a series of bounces and crunches, extending forever)<\/li>\n<li><strong>Hibernating<\/strong> (a universe that sits quiescently for a long time, before the Bang begins)<\/li>\n<li><strong>Reproducing<\/strong> (a background empty universe that spits off babies, each of which begins with a Bang)<\/li>\n<\/ol>\n<p>I don&#8217;t claim this is a logically exhaustive set of possibilities, but most semi-popular models I know fit into one of the above categories. Given <a href=\"https:\/\/www.preposterousuniverse.com\/blog\/2009\/01\/14\/from-eternity-to-here-the-origin-of-the-universe-and-the-arrow-of-time\/\">my own way of thinking<\/a> about the problem, I emphasized that any decent cosmological model should try to explain why the early universe had a low entropy, and suggested that the <a href=\"https:\/\/www.preposterousuniverse.com\/blog\/2004\/10\/27\/the-arrow-of-time\/\">Reproducing models<\/a> did the best job.<\/p>\n<p>My other goal was to talk about how thinking quantum-mechanically affects the problem. There are two questions to ask: is time emergent or fundamental, and is Hilbert space finite- or infinite-dimensional. If time is fundamental, the universe lasts forever; it doesn&#8217;t have a beginning. But if time is emergent, there may very well be a first moment. If Hilbert space is finite-dimensional it&#8217;s necessary (there are only a finite number of moments of time that can possibly emerge), while if it&#8217;s infinite-dimensional the problem is open.<\/p>\n<p>Despite all that we don&#8217;t know, I remain optimistic that we are actually making progress here. I&#8217;m pretty hopeful that within my lifetime we&#8217;ll have settled on a leading theory for what happened at the very beginning of the universe.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>I had the pleasure earlier this month of giving a plenary lecture at a meeting of the American Astronomical Society. Unfortunately, as far as I know they don&#8217;t record the lectures on video. So here, at least, are the slides I showed during my talk. I&#8217;ve been a little hesitant to put them up, since [&hellip;]<\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[28,35],"tags":[],"class_list":["post-12967","post","type-post","status-publish","format-standard","hentry","category-science","category-time"],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/posts\/12967","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/comments?post=12967"}],"version-history":[{"count":3,"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/posts\/12967\/revisions"}],"predecessor-version":[{"id":12970,"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/posts\/12967\/revisions\/12970"}],"wp:attachment":[{"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/media?parent=12967"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/categories?post=12967"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/tags?post=12967"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}