CINXE.COM

<!DOCTYPE html> <html lang="en"> <head><script type="text/javascript" src="/_static/js/bundle-playback.js?v=HxkREWBo" charset="utf-8"></script> <script type="text/javascript" src="/_static/js/wombat.js?v=txqj7nKC" charset="utf-8"></script> <script>window.RufflePlayer=window.RufflePlayer||{};window.RufflePlayer.config={"autoplay":"on","unmuteOverlay":"hidden"};</script> <script type="text/javascript" src="/_static/js/ruffle/ruffle.js"></script> <script type="text/javascript"> __wm.init("https://web.archive.org/web"); __wm.wombat("http://light2015blog.org:80/2015/05/13/discovering-the-most-ancient-cosmic-light/","20150515192850","https://web.archive.org/","web","/_static/", "1431718130"); </script> <link rel="stylesheet" type="text/css" href="/_static/css/banner-styles.css?v=S1zqJCYt" /> <link rel="stylesheet" type="text/css" href="/_static/css/iconochive.css?v=3PDvdIFv" />  <meta charset="UTF-8"> <meta name="viewport" content="width=device-width"> <title>Discovering the most ancient cosmic light | International Year of Light Blog</title> <link rel="profile" href="http://gmpg.org/xfn/11"> <link rel="pingback" href="http://light2015blog.org/xmlrpc.php"> <script src="https://web.archive.org/web/20150515192850js_/https://r-login.wordpress.com/remote-login.php?action=js&host=light2015blog.org&id=66139115&t=1431718129&back=http%3A%2F%2Flight2015blog.org%2F2015%2F05%2F13%2Fdiscovering-the-most-ancient-cosmic-light%2F" type="text/javascript"></script> <script type="text/javascript"> /* <![CDATA[ */ if ( 'function' === typeof WPRemoteLogin ) { document.cookie = "wordpress_test_cookie=test; path=/"; if ( document.cookie.match( /(;|^)\s*wordpress_test_cookie\=/ ) ) { WPRemoteLogin(); } } /* ]]> */ </script> <link rel="alternate" type="application/rss+xml" title="International Year of Light Blog » Feed" href="https://web.archive.org/web/20150515192850/http://light2015blog.org/feed/"/> <link rel="alternate" type="application/rss+xml" title="International Year of Light Blog » Comments Feed" href="https://web.archive.org/web/20150515192850/http://light2015blog.org/comments/feed/"/> <link rel="alternate" type="application/rss+xml" title="International Year of Light Blog » Discovering the most ancient cosmic light Comments Feed" href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/13/discovering-the-most-ancient-cosmic-light/feed/"/> <script type="text/javascript"> /* <![CDATA[ */ function addLoadEvent(func){var oldonload=window.onload;if(typeof window.onload!='function'){window.onload=func;}else{window.onload=function(){oldonload();func();}}} /* ]]> */ </script> <link rel="stylesheet" id="all-css-0" href="https://web.archive.org/web/20150515192850cs_/https://s0.wp.com/_static/??-eJx9j90OgjAMhV/IORWCV8ZnmVudg5Y2rAvh7QUSY/wJdz0n35eT2lGM516hV0vFCJaY+mwzJYRJBm7B62fa+5x39r+GqYNsW1BxvjNr+sFvyPEtcIwQuKi5MyKPdkwhwubGAOgUghHO+pW2NM8DzD2J04UgCMkBAs3YlkbSvKzlfMx/rTNXuhzr6lA1zak+t0/e0Xo9" type="text/css" media="all"/> <link rel="stylesheet" id="motif-fonts-css" href="//web.archive.org/web/20150515192850cs_/http://fonts.googleapis.com/css?family=Droid+Serif%3A400%2C400italic%2C700%2C700italic%7CDroid+Sans%3A400%2C700&subset=latin" type="text/css" media="all"/> <link rel="stylesheet" id="all-css-2" href="https://web.archive.org/web/20150515192850cs_/https://s1.wp.com/_static/??-eJyFjt0KwjAMRl/ImqlTvBGfZStZzWiT0h+Gb2+1CBVx3oQv5JzwweKVFk7ICVxW3mZDHMEgY6By+BG3OsYNNG66ocMIPo/gJNEEMd0t/seIdUXV4rW4L6HphE5mqrNiBFx+vJq9w5pvUJQVPSQS/ljUZAcKa2rA0Yop0UChmvUpXd1l1x+6vjvvj6f5AZfOfhs=" type="text/css" media="all"/> <link rel="stylesheet" id="print-css-3" href="https://web.archive.org/web/20150515192850cs_/https://s0.wp.com/wp-content/mu-plugins/global-print/global-print.css?m=1387483371g" type="text/css" media="print"/> <link rel="stylesheet" id="all-css-4" href="https://web.archive.org/web/20150515192850cs_/https://s2.wp.com/_static/??-eJxljNEKwjAMRX/IGB0V9UH8lm6taaRNS5Ox358DhYFP9zycc3FpMFWxKIZlhpZnYlFsVQ1e2XNHTb6z0G+Pk+oBd5WlWKJicki5jj7/CbvbhQNFU/woXwbqHMBLgMxqW/ssj7Mbrre7G06X9wrk2DpI" type="text/css" media="all"/> <script type="text/javascript"> /* <![CDATA[ */ var LoggedOutFollow = {"invalid_email":"Your subscription did not succeed, please try again with a valid email address."}; /* ]]> */ </script> <script type="text/javascript" src="https://web.archive.org/web/20150515192850js_/https://s2.wp.com/_static/??-eJyFkOsKwjAMhV/IrHgZ+Ed8lm3NSmpv9mLRp7dzU3COCSVN0u8ckrLsgEynEsfAZDnXhP4+XZUMG7YGgCbhm4iVJvOGO2simjiw2rakEFJA34jSK0a9XeCcDVFjCAVaeP0eicyNMP/FJEbXdBfwGOjx49oqK8CpJMgEVnKB3KYIvVXKZpaJC4xzjU4fhUdVluYwzD2rVlSj7esTxxTapB1M65z1aXvYHesS6r18Au8tmLQ="></script> <link rel="stylesheet" id="all-css-0" href="https://web.archive.org/web/20150515192850cs_/https://s2.wp.com/wp-content/mu-plugins/highlander-comments/style.css?m=1377793621g" type="text/css" media="all"/>  <link rel="EditURI" type="application/rsd+xml" title="RSD" href="https://light2015blogdotorg.wordpress.com/xmlrpc.php?rsd"/> <link rel="wlwmanifest" type="application/wlwmanifest+xml" href="https://s1.wp.com/wp-includes/wlwmanifest.xml"/> <link rel="prev" title="The Midnight Run // European Tour 2015" href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/12/the-midnight-run-european-tour-2015/"/> <link rel="next" title="Let there be light – Inside and outside" href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/14/let-there-be-light-inside-and-outside/"/> <meta name="generator" content="WordPress.com"/> <link rel="canonical" href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/13/discovering-the-most-ancient-cosmic-light/"/> <link rel="shortlink" href="https://web.archive.org/web/20150515192850/http://wp.me/p4tvNV-ln"/> <link rel="alternate" type="application/json+oembed" href="https://web.archive.org/web/20150515192850/https://public-api.wordpress.com/oembed/1.0/?format=json&url=http%3A%2F%2Flight2015blog.org%2F2015%2F05%2F13%2Fdiscovering-the-most-ancient-cosmic-light%2F&for=wpcom-auto-discovery"/><link rel="alternate" type="application/xml+oembed" href="https://web.archive.org/web/20150515192850/https://public-api.wordpress.com/oembed/1.0/?format=xml&url=http%3A%2F%2Flight2015blog.org%2F2015%2F05%2F13%2Fdiscovering-the-most-ancient-cosmic-light%2F&for=wpcom-auto-discovery"/>  <meta property="og:type" content="article"/> <meta property="og:title" content="Discovering the most ancient cosmic light"/> <meta property="og:url" content="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/13/discovering-the-most-ancient-cosmic-light/"/> <meta property="og:description" content="The Universe has not always been the sparkling mix of stars and galaxies we live in and observe today. In fact, in its first few minutes, it was an extremely hot and dense jumble of light and parti..."/> <meta property="article:published_time" content="2015-05-13T08:00:07+00:00"/> <meta property="article:modified_time" content="2015-05-07T14:32:28+00:00"/> <meta property="article:author" content="http://light2015blog.org/author/light2015/"/> <meta property="og:site_name" content="International Year of Light Blog"/> <meta property="og:image" content="https://web.archive.org/web/20150515192850im_/https://light2015blogdotorg.files.wordpress.com/2015/05/fig2_holmdelhornantenna.jpg"/> <meta property="og:image" content="https://web.archive.org/web/20150515192850im_/https://light2015blogdotorg.files.wordpress.com/2015/05/fig1_cosmic_timeline.jpg"/> <meta property="og:locale" content="en_US"/> <meta name="twitter:site" content="@IYL2015"/> <meta name="twitter:image" content="https://web.archive.org/web/20150515192850im_/https://light2015blogdotorg.files.wordpress.com/2015/05/fig1_cosmic_timeline.jpg?w=240"/> <meta name="twitter:card" content="summary"/> <meta name="twitter:creator" content="@IYL2015"/> <meta property="article:publisher" content="https://www.facebook.com/WordPresscom"/> <link rel="shortcut icon" type="image/x-icon" href="https://web.archive.org/web/20150515192850im_/http://s2.wp.com/i/favicon.ico?m=1405977958g" sizes="16x16 24x24 32x32 48x48"/> <link rel="icon" type="image/x-icon" href="https://web.archive.org/web/20150515192850im_/http://s2.wp.com/i/favicon.ico?m=1405977958g" sizes="16x16 24x24 32x32 48x48"/> <link rel="apple-touch-icon-precomposed" href="https://web.archive.org/web/20150515192850im_/http://s0.wp.com/i/webclip.png?m=1391188133g"/> <link rel="openid.server" href="http://light2015blogdotorg.wordpress.com/?openidserver=1"/> <link rel="openid.delegate" href="http://light2015blogdotorg.wordpress.com/"/> <link rel="search" type="application/opensearchdescription+xml" href="https://web.archive.org/web/20150515192850/http://light2015blog.org/osd.xml" title="International Year of Light Blog"/> <link rel="search" type="application/opensearchdescription+xml" href="https://web.archive.org/web/20150515192850/https://wordpress.com/opensearch.xml" title="WordPress.com"/> <meta name="application-name" content="International Year of Light Blog"/><meta name="msapplication-window" content="width=device-width;height=device-height"/><meta name="msapplication-task" content="name=Subscribe;action-uri=http://light2015blog.org/feed/;icon-uri=http://s2.wp.com/i/favicon.ico"/><meta name="msapplication-task" content="name=Sign up for a free blog;action-uri=http://wordpress.com/signup/;icon-uri=http://s2.wp.com/i/favicon.ico"/><meta name="msapplication-task" content="name=WordPress.com Support;action-uri=http://support.wordpress.com/;icon-uri=http://s2.wp.com/i/favicon.ico"/><meta name="msapplication-task" content="name=WordPress.com Forums;action-uri=http://forums.wordpress.com/;icon-uri=http://s2.wp.com/i/favicon.ico"/><meta name="title" content="Discovering the most ancient cosmic light | International Year of Light Blog on WordPress.com"/> <meta name="description" content="The Universe has not always been the sparkling mix of stars and galaxies we live in and observe today. In fact, in its first few minutes, it was an extremely hot and dense jumble of light and particles that has been expanding and cooling down ever since. Likewise, our understanding of the Universe and its…"/> <style type="text/css" id="motif-header-css"> .site-title, .site-description { clip: rect(1px, 1px, 1px, 1px); position: absolute; } </style> <style type="text/css" id="custom-background-css"> body.custom-background { background-color: #ffffff; } </style> <style type="text/css" id="syntaxhighlighteranchor"></style> <style type="text/css" id="custom-colors-css"> .site-title a, .site-description { color: #333333;} .main-navigation a { color: #FFFFFF;} .main-navigation a:hover, .main-navigation ul :hover > a,.main-navigation ul ul :hover > a, .main-navigation li.current_page_item a, .main-navigation li.current-menu-item a, .main-navigation li.current_page_ancestor a, .main-navigation li.current-menu-ancestor a { color: #FFFFFF;} .main-navigation ul ul li { border-top-color: #FFFFFF;} .main-navigation ul ul ul li { border-top-color: #FFFFFF;} .footer-widget-area { color: #979797;} .footer-widget-area .widget ul > li, .footer-widget-area .widget ol > li, .footer-widget-area .widget_calendar table, .footer-widget-area .widget_calendar td { border-color: #999999;} .footer-widget-area .search-field { background-color: #999999;} body { background-color: #ffffff;} .main-navigation, .footer-widget-area { background-color: #2e2e2e;} .main-navigation ul ul { background-color: #343434;} .main-navigation ul ul ul { background-color: #3A3A3A;} .entry-title, .entry-title a { color: #666666;} .entry-title a:hover { color: #666666;} .entry-meta, .entry-meta a, .featured-post { color: #6B6B6B;} .entry-meta a:hover { color: #8E8E8E;} button,html input[type="button"],input[type="reset"],input[type="submit"] { color: #ea2e25;} button:hover,html input[type="button"]:hover,input[type="reset"]:hover,input[type="submit"]:hover { background-color: #ea2e25;} a { color: #DA1F15;} a:hover { color: #EA2E25;} .page-links a { color: #D01E14;} .page-links a:hover { background-color: #ea2e25;} .post-navigation a,.paging-navigation a { color: #D01E14;} .post-navigation a:hover,.paging-navigation a:hover { background-color: #D01E14;} .comment-navigation a { color: #ea2e25;} .comment-navigation a:hover { background-color: #ea2e25;} </style> <link rel="stylesheet" id="custom-css-css" type="text/css" href="https://web.archive.org/web/20150515192850cs_/https://s1.wp.com/?custom-css=1&csblog=4tvNV&cscache=6&csrev=7"/> </head> <body class="single single-post postid-1325 single-format-standard custom-background mp6 typekit-enabled customizer-styles-applied not-multi-author highlander-enabled highlander-light custom-colors"> <div id="page" class="hfeed site"> <header id="masthead" class="site-header" role="banner"> <div class="site-branding"> <div class="site-image"> <a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/" title="International Year of Light Blog" rel="home" class="header-image-link"> <img src="https://web.archive.org/web/20150515192850im_/http://light2015blogdotorg.files.wordpress.com/2014/10/iyl2015blogbanner1.jpg" width="1140" height="316" alt=""/> </a> </div> <h1 class="site-title"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/" title="International Year of Light Blog" rel="home">International Year of Light Blog</a></h1> </div> <nav id="site-navigation" class="main-navigation" role="navigation"> <h1 class="menu-toggle">Menu</h1> <div class="screen-reader-text skip-link"><a href="#content" title="Skip to content">Skip to content</a></div> <div class="menu-main-container"><ul id="menu-main" class="menu"><li id="menu-item-243" class="menu-item menu-item-type-custom menu-item-object-custom menu-item-home menu-item-243"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/">Home</a></li> <li id="menu-item-242" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-242"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/about-iyl/">About IYL 2015</a></li> </ul></div> </nav> </header> <div id="content" class="site-content"> <div id="primary" class="content-area"> <main id="main" class="site-main" role="main"> <article id="post-1325" class="post-1325 post type-post status-publish format-standard hentry category-48041 category-anniversaries category-astronomy category-may tag-cosmic-light tag-cosmic-microwave-background-radiation tag-nobel-prize tag-penzias tag-wilson"> <header class="entry-header"> <h1 class="entry-title">Discovering the most ancient cosmic light</h1> <div class="entry-meta"> <span class="date"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/13/discovering-the-most-ancient-cosmic-light/" title="Permalink to Discovering the most ancient cosmic light" rel="bookmark"><time class="entry-date published" datetime="2015-05-13T08:00:07+00:00">May 13, 2015</time><time class="updated" datetime="2015-05-07T14:32:28+00:00">May 7, 2015</time></a></span><span class="author vcard"><a class="url fn n" href="https://web.archive.org/web/20150515192850/http://light2015blog.org/author/light2015/" title="View all posts by light2015">light2015</a></span> <span class="comments-link"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/13/discovering-the-most-ancient-cosmic-light/#respond">Leave a comment</a></span> </div> </header> <div class="entry-content"> <p>The Universe has not always been the sparkling mix of stars and galaxies we live in and observe today. In fact, in its first few minutes, it was an extremely hot and dense jumble of light and particles that has been expanding and cooling down ever since. Likewise, our understanding of the Universe and its evolution has changed dramatically over time, with the current picture of cosmic history emerging from an exciting progression of theoretical and experimental investigations throughout the past century. In particular, this year we celebrate the anniversary of two milestones in the build-up of modern cosmology: the general theory of relativity, presented by Einstein in November 1915, which allowed scientists to study the effect of gravity on cosmic scales, and the discovery of the most ancient light in the history of the Universe, the cosmic microwave background (CMB) radiation, announced in May 1965, exactly fifty years ago.</p> <div data-shortcode="caption" id="attachment_1327" style="width: 675px" class="wp-caption aligncenter"><a href="https://web.archive.org/web/20150515192850/https://light2015blogdotorg.files.wordpress.com/2015/05/fig1_cosmic_timeline.jpg"><img class="size-large wp-image-1327" src="https://web.archive.org/web/20150515192850im_/https://light2015blogdotorg.files.wordpress.com/2015/05/fig1_cosmic_timeline.jpg?w=665&h=477" alt="A visual representation of almost 14 billion years of cosmic history: the CMB was emitted when the Universe was only about 400,000 years old. Credit: NASA/WMAP" width="665" height="477"/></a><p class="wp-caption-text">A visual representation of almost 14 billion years of cosmic history: the CMB was emitted when the Universe was only about 400,000 years old. Credit: NASA/WMAP</p></div> <p><span id="more-1325"></span></p> <p><b>A chance discovery</b></p> <p>The CMB is a relic of the light that filled the early cosmos, almost 14 billion years ago. It can still be observed today across the entire sky, but not with the naked eye, as it shines at much longer wavelengths than those of visible light, in the domain of microwaves. Finding the CMB was crucial to settling the debate that was going on in the 1950s and early 1960s among cosmologists. At the time, the community was mainly divided in two factions: on one side, those who supported an expanding Universe that started hot and dense and then cooled down; on the other, those who believed in a stationary Universe, whose properties are the same not only when averaged on large spacial scales, but also over time. Interestingly, the name “big bang” that is now universally used to refer to the former theory was coined by Fred Hoyle, one of the scientists who devised the latter. The decisive event in this scientific dispute, the discovery of the CMB, happened by pure chance.</p> <p>It was 1964, when Arno Penzias and Robert Wilson, two radio astronomers working for the Bell Telephone Laboratories in Holmdel, New Jersey (USA), first detected this curious signal. They were scanning the sky with an antenna that had been built, a few years before, to perform satellite communications experiments at microwave wavelengths. Penzias and Wilson were planning to use this very sensitive antenna for radio astronomy, to observe long-wavelength light emitted by celestial sources in our Galaxy. However, anywhere they pointed in the sky, they seemed to detect a slightly higher signal than expected: the sky appeared to be filled with a uniform background “noise” corresponding to a temperature of about 3 degrees Kelvin (K). Penzias and Wilson considered all possible sources of this nuisance to their data, but without success.</p> <div data-shortcode="caption" id="attachment_1328" style="width: 606px" class="wp-caption aligncenter"><a href="https://web.archive.org/web/20150515192850/https://light2015blogdotorg.files.wordpress.com/2015/05/fig2_holmdelhornantenna.jpg"><img class="size-full wp-image-1328" src="https://web.archive.org/web/20150515192850im_/https://light2015blogdotorg.files.wordpress.com/2015/05/fig2_holmdelhornantenna.jpg?w=665" alt=" The 15 meter Holmdel horn antenna at the Bell Telephone Laboratories, used by Penzias and Wilson to detected the CMB on 20 May 1964. Credit: Wikipedia public domain (Great Images in NASA)"/></a><p class="wp-caption-text">The 15 meter Holmdel horn antenna at the Bell Telephone Laboratories, used by Penzias and Wilson to detected the CMB on 20 May 1964. Credit: Wikipedia public domain (Great Images in NASA)</p></div> <p><b>From the stars to the Universe</b></p> <p>What the two Bell Laboratories astronomers did not know at the time was that, about fifteen years before and for completely different reasons, three physicists had contemplated the existence of just such a background. These are George Gamow, Ralph Alpher and Robert Herman, who were studying the origin of chemical elements in the Universe around 1948 (1). The nuclear reactions that take place in the interior of stars, turning hydrogen into helium and releasing copious amounts of energy, had been discovered only a decade earlier, and the three physicists were looking at them in detail, trying to explain the abundance of the different chemical elements that are observed in the present Universe. In a series of papers published between 1948 and 1949, they suggested that the nuclei of elements heavier than hydrogen might have formed in the early Universe, as long as it had been a sufficiently hot and dense place in the first couple of minutes of its existence.</p> <p>As a side remark, in one of these papers, Alpher and Herman noted that, had the Universe been so hot early on – about one billion degrees – to allow these nuclear fusion processes, then a relic of this primordial heat must have survived until present time. Due to cosmic expansion, however, the hot light that pervaded the ancient Universe would have become increasingly colder, reaching a temperature only a few degrees above absolute zero, between 1 and 5 K (2).</p> <p><b>It all comes together</b></p> <p>Following similar lines of thought, a group of cosmologists at Princeton University were investigating this “big bang” origin of the Universe in the early 1960s. Their scientific leader, Robert Dicke, had developed a sensitive type of microwave receiver during the second world war and, at the end of the conflict, he had tried to use it to seek cosmic microwaves in the sky. He later set on this search again, together with Peter Roll and David Wilkinson, who built a new receiver specially to look for the CMB, and with James Peebles, a theoretical physicist who was studying the cosmological consequences of finding such a signal. However, by 1965 the Princeton group had not detected anything. But as the news about their search spread, eventually making their way to the Bell Laboratories, Penzias and Wilson realised the significance of the mysterious signal of 3 K they had found across the sky only a few months before.</p> <p>Finally, the search was over. The discovery of the CMB was announced by two papers, published in the May 1965 issue of the Astrophysical Journal: one by Dicke, Peebles, Roll and Wilkinson, outlining the implications of a microwave background for the history of the Universe; the other by Penzias and Wilson, describing their experimental detection (3).</p> <p>Finding the CMB represented a triumph for the “big bang” description of the Universe: the fossil microwave light, observed to have roughly the same temperature across the sky, could not be easily explained in the alternative model, the steady-state cosmos. In 1978, Penzias and Wilson would be awarded the Nobel Prize in Physics for their discovery (4).</p> <p>But that was not the end: in fact, the detection of the CMB was only the beginning of the era of observational cosmology, setting into motion a long series of increasingly accurate experiments and ever finer theoretical calculations. About fifty years later, this body of research has led to our current cosmological view, consisting of a Universe that is not only expanding from the early hot big bang state but also appears to be dominated by two mysterious components, the dark matter and the dark energy.</p> <p>The story of the past fifty years of studying the most ancient cosmic light will follow in a coming post next week. Stay tuned!</p> <p><strong>Notes</strong></p> <p>1 – In fact, the first published paper on this series is by R. A. Alpher, H. Bethe and G. Gamow, “The Origin of Chemical Elements”, Physical Review, Vol. 73, Issue 7, Pages 803-804. The addition of Hans Bethe to the author list was a famous pun by Gamow, who wanted the sequence of author names to resemble the first three letters of the Greek alphabet: alpha, beta, gamma. Bethe is one of the physicists who discovered the nuclear reactions that power the stars, but he was apparently unaware that his name had been added by Gamow to this paper.</p> <p>2 – R. A. Alpher & R. C. Herman, “Remarks on the Evolution of the Expanding Universe”, 1949, Physical Review, Vol. 75, N. 7</p> <p>3 – R. H. Dicke, P. J. E. Peebles, P. G. Roll and D. T. Wilkinson, “Cosmic black-body radiation”, 1965, Astrophysical Journal, Vol. 142, Page 414; A. A. Penzias & R. W. Wilson, “A measurement of excess antenna temperature at 4080 Mc/s”, 1965, Astrophysical Journal, Vol. 142, Page 419</p> <p>4 – <a href="https://web.archive.org/web/20150515192850/http://www.nobelprize.org/nobel_prizes/physics/laureates/1978/" target="_blank">http://www.nobelprize.org/nobel_prizes/physics/laureates/1978/</a></p> <hr/> <p><strong><a href="https://web.archive.org/web/20150515192850/https://light2015blogdotorg.files.wordpress.com/2015/05/cmignone.jpg"><img class="alignright size-medium wp-image-1326" src="https://web.archive.org/web/20150515192850im_/https://light2015blogdotorg.files.wordpress.com/2015/05/cmignone.jpg?w=200&h=300" alt="cmignone" width="200" height="300"/></a>Claudia Mignone</strong> (<a href="https://web.archive.org/web/20150515192850/https://twitter.com/claudiascosmos" target="_blank">@claudiascosmos</a>) is an astrophysicist and science writer with a passion for science and telling stories about it. Originally from Salerno, in the south of Italy, she studied astronomy and cosmology in Bologna and Heidelberg (Germany). After having scrutinised the Universe’s expansion during her PhD, she became a full-time communicator of the wonders of astronomy, first as a science journalism intern at the European Southern Observatory and later as a science writer for the European Space Agency. She is based at ESA/ESTEC, in the Netherlands, where she has been writing space science stories for the past five years.</p> <div id="jp-post-flair" class="sharedaddy sd-like-enabled sd-sharing-enabled"><div class="sharedaddy sd-sharing-enabled"><div class="robots-nocontent sd-block sd-social sd-social-icon-text sd-sharing"><h3 class="sd-title">Share this:</h3><div class="sd-content"><ul><li class="share-twitter"><a rel="nofollow" class="share-twitter sd-button share-icon" href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/13/discovering-the-most-ancient-cosmic-light/?share=twitter" title="Click to share on Twitter" id="sharing-twitter-1325"><span>Twitter</span></a></li><li class="share-facebook"><a rel="nofollow" class="share-facebook sd-button share-icon" href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/13/discovering-the-most-ancient-cosmic-light/?share=facebook" title="Share on Facebook" id="sharing-facebook-1325"><span>Facebook</span></a></li><li class="share-google-plus-1"><a rel="nofollow" class="share-google-plus-1 sd-button share-icon" href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/13/discovering-the-most-ancient-cosmic-light/?share=google-plus-1" title="Click to share on Google+" id="sharing-google-1325"><span>Google</span></a></li><li class="share-end"></li></ul></div></div></div><div class="sharedaddy sd-block sd-like jetpack-likes-widget-wrapper jetpack-likes-widget-unloaded" id="like-post-wrapper-66139115-1325-555648f2005da" data-src="//web.archive.org/web/20150515192850oe_/http://widgets.wp.com/likes/#blog_id=66139115&post_id=1325&origin=light2015blogdotorg.wordpress.com&obj_id=66139115-1325-555648f2005da" data-name="like-post-frame-66139115-1325-555648f2005da"><h3 class="sd-title">Like this:</h3><div class="likes-widget-placeholder post-likes-widget-placeholder" style="height:55px"><span class="button"><span>Like</span></span> <span class="loading">Loading...</span></div><span class="sd-text-color"></span><a class="sd-link-color"></a></div> <div id="jp-relatedposts" class="jp-relatedposts"> <h3 class="jp-relatedposts-headline"><em>Related</em></h3> </div></div> </div> <footer class="entry-meta"> <span class="categories-links"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/2015/" rel="category tag">2015</a>, <a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/anniversaries/" rel="category tag">Anniversaries</a>, <a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/astronomy/" rel="category tag">Astronomy</a>, <a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/2015/may/" rel="category tag">May</a></span><span class="tags-links"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/tag/cosmic-light/" rel="tag">Cosmic Light</a>, <a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/tag/cosmic-microwave-background-radiation/" rel="tag">Cosmic Microwave Background Radiation</a>, <a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/tag/nobel-prize/" rel="tag">Nobel Prize</a>, <a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/tag/penzias/" rel="tag">Penzias</a>, <a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/tag/wilson/" rel="tag">Wilson</a></span> </footer> </article> <nav role="navigation" id="nav-below" class="post-navigation"> <h1 class="screen-reader-text">Post navigation</h1> <div class="nav-previous"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/12/the-midnight-run-european-tour-2015/" rel="prev"><span class="meta-nav">←</span> The Midnight Run // European Tour 2015</a></div> <div class="nav-next"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/14/let-there-be-light-inside-and-outside/" rel="next">Let there be light – Inside and outside <span class="meta-nav">→</span></a></div> </nav> <div id="comments" class="comments-area"> <div id="respond" class="comment-respond"> <h3 id="reply-title" class="comment-reply-title">Leave a Reply <small><a rel="nofollow" id="cancel-comment-reply-link" href="/web/20150515192850/http://light2015blog.org/2015/05/13/discovering-the-most-ancient-cosmic-light/#respond" style="display:none;">Cancel reply</a></small></h3> <form action="https://web.archive.org/web/20150515192850/http://light2015blog.org/wp-comments-post.php" method="post" id="commentform" class="comment-form" novalidate> <input type="hidden" id="highlander_comment_nonce" name="highlander_comment_nonce" value="3b5394fe87"/><input type="hidden" name="_wp_http_referer" value="/2015/05/13/discovering-the-most-ancient-cosmic-light/"/> <input type="hidden" name="hc_post_as" id="hc_post_as" value="guest"/> <div class="comment-form-field comment-textarea"> <label for="comment">Enter your comment here...</label> <div id="comment-form-comment"><textarea id="comment" name="comment" title="Enter your comment here..."></textarea></div> </div> <div id="comment-form-identity"> <div id="comment-form-nascar"> <p>Fill in your details below or click an icon to log in:</p> <ul> <li class="selected" style="display:none;"> <a href="#comment-form-guest" id="postas-guest" title="Guest"> <span></span> </a> </li> <li> <a href="#comment-form-load-service:WordPress.com" id="postas-wordpress" title="WordPress.com"> <span></span> </a> </li> <li> <a href="#comment-form-load-service:Twitter" id="postas-twitter" title="Twitter"> <span></span> </a> </li> <li> <a href="#comment-form-load-service:Facebook" id="postas-facebook" title="Facebook"> <span></span> </a> </li> <li> </ul> </div> <div id="comment-form-guest" class="comment-form-service selected"> <div class="comment-form-padder"> <div class="comment-form-avatar"> <a href="https://web.archive.org/web/20150515192850/https://gravatar.com/site/signup/" target="_blank"> <img src="https://web.archive.org/web/20150515192850im_/http://1.gravatar.com/avatar/ad516503a11cd5ca435acc9bb6523536?s=25&d=identicon&forcedefault=y&r=G" alt="Gravatar" width="25" class="no-grav"/> </a> </div> <div class="comment-form-fields"> <div class="comment-form-field comment-form-email"> <label for="email">Email <span class="required">(required)</span> <span class="nopublish">(Address never made public)</span></label> <div class="comment-form-input"><input id="email" name="email" type="email" value=""/></div> </div> <div class="comment-form-field comment-form-author"> <label for="author">Name <span class="required">(required)</span></label> <div class="comment-form-input"><input id="author" name="author" type="text" value=""/></div> </div> <div class="comment-form-field comment-form-url"> <label for="url">Website</label> <div class="comment-form-input"><input id="url" name="url" type="text" value=""/></div> </div> </div> </div> </div> <div id="comment-form-wordpress" class="comment-form-service"> <div class="comment-form-padder"> <div class="comment-form-avatar"> <img src="https://web.archive.org/web/20150515192850im_/https://s2.wp.com/wp-content/mu-plugins/highlander-comments/images/wplogo.png" alt="WordPress.com Logo" width="25" class="no-grav"/> </div> <div class="comment-form-fields"> <input type="hidden" name="wp_avatar" id="wordpress-avatar" class="comment-meta-wordpress" value=""/> <input type="hidden" name="wp_user_id" id="wordpress-user_id" class="comment-meta-wordpress" value=""/> <input type="hidden" name="wp_access_token" id="wordpress-access_token" class="comment-meta-wordpress" value=""/> <p class="comment-form-posting-as pa-wordpress"><strong></strong> You are commenting using your WordPress.com account. <span class="comment-form-log-out">( <a href="javascript:HighlanderComments.doExternalLogout( 'wordpress' );">Log Out</a> / <a href="#" onclick="javascript:HighlanderComments.switchAccount();return false;">Change</a> )</span></p> </div> </div> </div> <div id="comment-form-twitter" class="comment-form-service"> <div class="comment-form-padder"> <div class="comment-form-avatar"> <img src="https://web.archive.org/web/20150515192850im_/http://1.gravatar.com/avatar/ad516503a11cd5ca435acc9bb6523536?s=25&d=identicon&forcedefault=y&r=G" alt="Twitter picture" width="25" class="no-grav"/> </div> <div class="comment-form-fields"> <input type="hidden" name="twitter_avatar" id="twitter-avatar" class="comment-meta-twitter" value=""/> <input type="hidden" name="twitter_user_id" id="twitter-user_id" class="comment-meta-twitter" value=""/> <input type="hidden" name="twitter_access_token" id="twitter-access_token" class="comment-meta-twitter" value=""/> <p class="comment-form-posting-as pa-twitter"><strong></strong> You are commenting using your Twitter account. <span class="comment-form-log-out">( <a href="javascript:HighlanderComments.doExternalLogout( 'twitter' );">Log Out</a> / <a href="#" onclick="javascript:HighlanderComments.switchAccount();return false;">Change</a> )</span></p> </div> </div> </div> <div id="comment-form-facebook" class="comment-form-service"> <div class="comment-form-padder"> <div class="comment-form-avatar"> <img src="https://web.archive.org/web/20150515192850im_/http://1.gravatar.com/avatar/ad516503a11cd5ca435acc9bb6523536?s=25&d=identicon&forcedefault=y&r=G" alt="Facebook photo" width="25" class="no-grav"/> </div> <div class="comment-form-fields"> <input type="hidden" name="fb_avatar" id="facebook-avatar" class="comment-meta-facebook" value=""/> <input type="hidden" name="fb_user_id" id="facebook-user_id" class="comment-meta-facebook" value=""/> <input type="hidden" name="fb_access_token" id="facebook-access_token" class="comment-meta-facebook" value=""/> <p class="comment-form-posting-as pa-facebook"><strong></strong> You are commenting using your Facebook account. <span class="comment-form-log-out">( <a href="javascript:HighlanderComments.doExternalLogout( 'facebook' );">Log Out</a> / <a href="#" onclick="javascript:HighlanderComments.switchAccount();return false;">Change</a> )</span></p> </div> </div> </div> <div id="comment-form-googleplus" class="comment-form-service"> <div class="comment-form-padder"> <div class="comment-form-avatar"> <img src="https://web.archive.org/web/20150515192850im_/http://1.gravatar.com/avatar/ad516503a11cd5ca435acc9bb6523536?s=25&d=identicon&forcedefault=y&r=G" alt="Google+ photo" width="25" class="no-grav"/> </div> <div class="comment-form-fields"> <input type="hidden" name="googleplus_avatar" id="googleplus-avatar" class="comment-meta-googleplus" value=""/> <input type="hidden" name="googleplus_user_id" id="googleplus-user_id" class="comment-meta-googleplus" value=""/> <input type="hidden" name="googleplus_access_token" id="googleplus-access_token" class="comment-meta-googleplus" value=""/> <p class="comment-form-posting-as pa-googleplus"><strong></strong> You are commenting using your Google+ account. <span class="comment-form-log-out">( <a href="javascript:HighlanderComments.doExternalLogout( 'googleplus' );">Log Out</a> / <a href="#" onclick="javascript:HighlanderComments.switchAccount();return false;">Change</a> )</span></p> </div> </div> </div> <div id="comment-form-load-service" class="comment-form-service"> <div class="comment-form-posting-as-cancel"><a href="javascript:HighlanderComments.cancelExternalWindow();">Cancel</a></div> <p>Connecting to %s</p> </div> </div> <script type="text/javascript"> var highlander_expando_javascript = function(){ var input = document.createElement( 'input' ), comment = jQuery( '#comment' ); if ( 'placeholder' in input ) { comment.attr( 'placeholder', jQuery( '.comment-textarea label' ).remove().text() ); } // Expando Mode: start small, then auto-resize on first click + text length jQuery( '#comment-form-identity' ).hide(); jQuery( '#comment-form-subscribe' ).hide(); jQuery( '#commentform .form-submit' ).hide(); comment.css( { 'height':'10px' } ).one( 'focus', function() { var timer = setInterval( HighlanderComments.resizeCallback, 10 ) jQuery( this ).animate( { 'height': HighlanderComments.initialHeight } ).delay( 100 ).queue( function(n) { clearInterval( timer ); HighlanderComments.resizeCallback(); n(); } ); jQuery( '#comment-form-identity' ).slideDown(); jQuery( '#comment-form-subscribe' ).slideDown(); jQuery( '#commentform .form-submit' ).slideDown(); }); } jQuery(document).ready( highlander_expando_javascript ); </script> <div id="comment-form-subscribe"> <p class="comment-subscription-form"><input type="checkbox" name="subscribe" id="subscribe" value="subscribe" style="width: auto;" tabindex="6"/> <label class="subscribe-label" id="subscribe-label" for="subscribe" style="display: inline;">Notify me of new comments via email.</label></p><p class="post-subscription-form"><input type="checkbox" name="subscribe_blog" id="subscribe_blog" value="subscribe" style="width: auto;" tabindex="7"/> <label class="subscribe-label" id="subscribe-blog-label" for="subscribe_blog" style="display: inline;">Notify me of new posts via email.</label></p></div> <p class="form-submit"><input name="submit" type="submit" id="comment-submit" class="submit" value="Post Comment"/> <input type="hidden" name="comment_post_ID" value="1325" id="comment_post_ID"/> <input type="hidden" name="comment_parent" id="comment_parent" value="0"/> </p><p style="display: none;"><input type="hidden" id="akismet_comment_nonce" name="akismet_comment_nonce" value="1e1cc117ff"/></p> <input type="hidden" name="genseq" value="1431718130"/> <p style="display: none;"><input type="hidden" id="ak_js" name="ak_js" value="143"/></p> </form> </div> <div style="clear: both"></div> </div> </main> </div> <div id="secondary" class="widget-area sidebar-widget-area" role="complementary"> <aside id="search-2" class="widget widget_search"><form role="search" method="get" class="search-form" action="https://web.archive.org/web/20150515192850/http://light2015blog.org/"> <label> <span class="screen-reader-text">Search for:</span> <input type="search" class="search-field" placeholder="Search …" value="" name="s" title="Search for:"/> </label> <input type="submit" class="search-submit" value="Search"/> </form></aside><aside id="text-3" class="widget widget_text"> <div class="textwidget">Interested in becoming a contributor? <a href="https://web.archive.org/web/20150515192850/mailto:jorge.rivero@eps.org?subject=IYL Blog Contributor"> Email us</a> today.</div> </aside><aside id="blog_subscription-2" class="widget widget_blog_subscription"><h1 class="widget-title"><label for="subscribe-field">Follow Blog via Email</label></h1> <form action="https://web.archive.org/web/20150515192850/https://subscribe.wordpress.com/" method="post" accept-charset="utf-8" id="subscribe-blog"> <p>Enter your email address to follow this blog and receive notifications of new posts by email.</p> <p>Join 12,630 other followers</p> <p><input type="text" name="email" style="width: 95%; padding: 1px 2px" placeholder="Enter your email address" value="" id="subscribe-field"/></p> <p> <input type="hidden" name="action" value="subscribe"/> <input type="hidden" name="blog_id" value="66139115"/> <input type="hidden" name="source" value="http://light2015blog.org/2015/05/13/discovering-the-most-ancient-cosmic-light/"/> <input type="hidden" name="sub-type" value="widget"/> <input type="hidden" name="redirect_fragment" value="blog_subscription-2"/> <input type="hidden" id="_wpnonce" name="_wpnonce" value="b5cb2fb878"/> <input type="submit" value="Follow"/> </p> </form> </aside><aside id="facebook-likebox-2" class="widget widget_facebook_likebox"><h1 class="widget-title"><a href="https://web.archive.org/web/20150515192850/https://www.facebook.com/pages/Light-2015/710660098979023">Like IYL2015 On Facebook!</a></h1><iframe src="https://web.archive.org/web/20150515192850if_/https://www.facebook.com/plugins/likebox.php?href=https%3A%2F%2Fwww.facebook.com%2Fpages%2FLight-2015%2F710660098979023&width=200&height=432&colorscheme=light&show_faces=true&stream=false&show_border=false&header=false&force_wall=false" scrolling="no" frameborder="0" style="border: none; overflow: hidden; width: 200px; height: 432px; background: #fff"></iframe></aside><aside id="twitter_timeline-2" class="widget widget_twitter_timeline"><h1 class="widget-title">Follow IYL2015 on Twitter!</h1><a class="twitter-timeline" data-widget-id="461232390451363840" data-theme="light" data-link-color="#f96e5b" data-border-color="#e8e8e8" data-chrome="noheader transparent" data-tweet-limit="2" width="225" height="400" lang="EN">My Tweets</a></aside></div> </div> <div id="tertiary" class="widget-area footer-widget-area" role="complementary"> <div class="first footer-widgets"> <aside id="search-2" class="widget widget_search"><form role="search" method="get" class="search-form" action="https://web.archive.org/web/20150515192850/http://light2015blog.org/"> <label> <span class="screen-reader-text">Search for:</span> <input type="search" class="search-field" placeholder="Search …" value="" name="s" title="Search for:"/> </label> <input type="submit" class="search-submit" value="Search"/> </form></aside> <aside id="recent-posts-2" class="widget widget_recent_entries"> <h1 class="widget-title">Recent Posts</h1> <ul> <li> <a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/15/in-time-of-light/">An electronic oratorio for James Clerk Maxwell</a> </li> <li> <a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/14/let-there-be-light-inside-and-outside/">Let there be light – Inside and outside</a> </li> <li> <a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/13/discovering-the-most-ancient-cosmic-light/">Discovering the most ancient cosmic light</a> </li> <li> <a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/12/the-midnight-run-european-tour-2015/">The Midnight Run // European Tour 2015</a> </li> <li> <a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/11/ibn-al-haytham-optics-ii-life-and-achievements/">Ibn Al Haytham Optics II – Life and Achievements</a> </li> </ul> </aside> </div> <div class="second footer-widgets"> <aside id="archives-4" class="widget widget_archive"><h1 class="widget-title">Archives</h1> <ul> <li><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/05/">May 2015</a> (13)</li> <li><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/04/">April 2015</a> (26)</li> <li><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/03/">March 2015</a> (26)</li> <li><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/02/">February 2015</a> (24)</li> <li><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2015/01/">January 2015</a> (26)</li> <li><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2014/12/">December 2014</a> (1)</li> <li><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2014/11/">November 2014</a> (3)</li> <li><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2014/10/">October 2014</a> (1)</li> <li><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2014/09/">September 2014</a> (3)</li> <li><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2014/08/">August 2014</a> (5)</li> <li><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2014/07/">July 2014</a> (3)</li> <li><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2014/06/">June 2014</a> (1)</li> <li><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2014/05/">May 2014</a> (1)</li> <li><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/2014/04/">April 2014</a> (1)</li> </ul> </aside> </div> <div class="third footer-widgets"> <aside id="categories-4" class="widget widget_categories"><h1 class="widget-title">Categories</h1> <ul> <li class="cat-item cat-item-1173184"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/2014/">2014</a> (1) </li> <li class="cat-item cat-item-48041"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/2015/">2015</a> (112) </li> <li class="cat-item cat-item-2214"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/region-specific/africa/">Africa</a> (2) </li> <li class="cat-item cat-item-8055"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/region-specific/america/">America</a> (1) </li> <li class="cat-item cat-item-54804"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/anniversaries/">Anniversaries</a> (7) </li> <li class="cat-item cat-item-51790"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/2015/april/">April</a> (26) </li> <li class="cat-item cat-item-177"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/art/">Art</a> (13) </li> <li class="cat-item cat-item-1612"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/region-specific/asia/">Asia</a> (8) </li> <li class="cat-item cat-item-4003"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/astronomy/">Astronomy</a> (14) </li> <li class="cat-item cat-item-6641479"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/country-overview/">Country Overview</a> (3) </li> <li class="cat-item cat-item-1098"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/culture/">Culture</a> (4) </li> <li class="cat-item cat-item-780"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/development/">Development</a> (8) </li> <li class="cat-item cat-item-1342"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/education/">Education</a> (2) </li> <li class="cat-item cat-item-247384435"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/efficient-lighting-2/">Efficient Lighting</a> (8) </li> <li class="cat-item cat-item-41009"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/einstein/">Einstein</a> (1) </li> <li class="cat-item cat-item-4328"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/region-specific/europe/">Europe</a> (5) </li> <li class="cat-item cat-item-61306"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/2015/february/">February</a> (23) </li> <li class="cat-item cat-item-534415"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/founding-partners/">Founding Partners</a> (8) </li> <li class="cat-item cat-item-988887"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/fresnel/">Fresnel</a> (1) </li> <li class="cat-item cat-item-227617"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/gender-balance/">Gender Balance</a> (1) </li> <li class="cat-item cat-item-100405"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/gender-equality/">Gender Equality</a> (1) </li> <li class="cat-item cat-item-54"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/general/">General</a> (29) </li> <li class="cat-item cat-item-337"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/health/">Health</a> (6) </li> <li class="cat-item cat-item-2151584"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/ibn-al-haytham/">Ibn Al Haytham</a> (2) </li> <li class="cat-item cat-item-315463075"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/iyl-2015-events/">IYL 2015 Events</a> (25) </li> <li class="cat-item cat-item-41381"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/2015/january/">January</a> (26) </li> <li class="cat-item cat-item-1420882"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/light-design/">Light Design</a> (8) </li> <li class="cat-item cat-item-275716"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/light-pollution/">Light Pollution</a> (5) </li> <li class="cat-item cat-item-64621"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/2015/march/">March</a> (27) </li> <li class="cat-item cat-item-67579"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/maxwell/">Maxwell</a> (2) </li> <li class="cat-item cat-item-64623"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/2015/may/">May</a> (13) </li> <li class="cat-item cat-item-50"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/medical/">Medical</a> (3) </li> <li class="cat-item cat-item-1099"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/nature/">Nature</a> (4) </li> <li class="cat-item cat-item-2033034"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/nautre/">Nautre</a> (1) </li> <li class="cat-item cat-item-22119"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/2014/november/">November</a> (1) </li> <li class="cat-item cat-item-35028238"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/optics-2/">Optics</a> (16) </li> <li class="cat-item cat-item-13925"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/outreach/">Outreach</a> (5) </li> <li class="cat-item cat-item-35788940"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/photonics-2/">Photonics</a> (37) </li> <li class="cat-item cat-item-11979"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/quantum-mechanics/">Quantum Mechanics</a> (3) </li> <li class="cat-item cat-item-54510309"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/region-specific/">Region Specific</a> (15) </li> <li class="cat-item cat-item-31827"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/sponsors/">Sponsors</a> (13) </li> <li class="cat-item cat-item-6"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/technology/">Technology</a> (28) </li> <li class="cat-item cat-item-1"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/uncategorized/">Uncategorized</a> (3) </li> <li class="cat-item cat-item-1509201"><a href="https://web.archive.org/web/20150515192850/http://light2015blog.org/category/vision-2/">Vision</a> (3) </li> </ul> </aside> </div> </div> <footer id="colophon" class="site-footer"> <div class="site-info" role="contentinfo"> <a href="https://web.archive.org/web/20150515192850/https://wordpress.com/?ref=footer_blog">Blog at WordPress.com</a>. <span class="sep"> | </span> <a href="https://web.archive.org/web/20150515192850/https://wordpress.com/themes/motif/" title="Learn more about this theme">The Motif Theme</a>. </div> </footer> </div>  <script type="text/javascript"> !function(d,s,id){ var js,fjs=d.getElementsByTagName(s)[0],p=/^http:/.test(d.location)?'http':'https'; if(!d.getElementById(id)){ js=d.createElement(s); js.id=id;js.src=p+"://platform.twitter.com/widgets.js"; fjs.parentNode.insertBefore(js,fjs); } }(document,"script","twitter-wjs"); </script> <script type="text/javascript" src="//web.archive.org/web/20150515192850js_/http://0.gravatar.com/js/gprofiles.js?ver=201520x"></script> <script type="text/javascript"> /* <![CDATA[ */ var WPGroHo = {"my_hash":""}; /* ]]> */ </script> <script type="text/javascript" src="https://web.archive.org/web/20150515192850js_/https://s2.wp.com/wp-content/mu-plugins/gravatar-hovercards/wpgroho.js?m=1380573781g"></script> <script> //initialize and attach hovercards to all gravatars jQuery( document ).ready( function( $ ) { if (typeof Gravatar === "undefined"){ return; } if ( typeof Gravatar.init !== "function" ) { return; } Gravatar.profile_cb = function( hash, id ) { WPGroHo.syncProfileData( hash, id ); }; Gravatar.my_hash = WPGroHo.my_hash; Gravatar.init( 'body', '#wp-admin-bar-my-account' ); }); </script> <div style="display:none"> </div> <script type="text/javascript"> /* <![CDATA[ */ var HighlanderComments = {"loggingInText":"Logging In\u2026","submittingText":"Posting Comment\u2026","postCommentText":"Post Comment","connectingToText":"Connecting to %s","commentingAsText":"%1$s: You are commenting using your %2$s account.","logoutText":"Log Out","loginText":"Log In","connectURL":"https:\/\/web.archive.org\/web\/20150515192850\/https:\/\/light2015blogdotorg.wordpress.com\/public.api\/connect\/?action=request","logoutURL":"https:\/\/web.archive.org\/web\/20150515192850\/https:\/\/light2015blogdotorg.wordpress.com\/wp-login.php?action=logout&_wpnonce=aff8538616","homeURL":"https:\/\/web.archive.org\/web\/20150515192850\/http:\/\/light2015blog.org\/","postID":"1325","gravDefault":"identicon","enterACommentError":"Please enter a comment","enterEmailError":"Please enter your email address here","invalidEmailError":"Invalid email address","enterAuthorError":"Please enter your name here","gravatarFromEmail":"This picture will show whenever you leave a comment. Click to customize it.","logInToExternalAccount":"Log in to use details from one of these accounts.","change":"Change","changeAccount":"Change Account","comment_registration":"","userIsLoggedIn":"","isJetpack":"0","text_direction":"ltr"}; /* ]]> */ </script> <script type="text/javascript" src="https://web.archive.org/web/20150515192850js_/https://s2.wp.com/_static/??/wp-content/js/jquery/jquery.autoresize.js,/wp-content/mu-plugins/highlander-comments/script.js?m=1424115551j"></script> <div id="bit" class="loggedout-follow-normal"> <a class="bsub" href="javascript:void(0)"><span id="bsub-text">Follow</span></a> <div id="bitsubscribe"> <h3><label for="loggedout-follow-field">Follow “International Year of Light Blog”</label></h3> <form action="https://web.archive.org/web/20150515192850/https://subscribe.wordpress.com/" method="post" accept-charset="utf-8" id="loggedout-follow"> <p>Get every new post delivered to your Inbox.</p> <p id="loggedout-follow-error" style="display: none;"></p> <p class="bit-follow-count">Join 12,630 other followers</p> <p><input type="email" name="email" value="Enter your email address" onfocus="this.value=(this.value=="Enter your email address") ? "" : this.value;" onblur="this.value=(this.value=="") ? "Enter your email address" : this.value;" id="loggedout-follow-field"/></p> <input type="hidden" name="action" value="subscribe"/> <input type="hidden" name="blog_id" value="66139115"/> <input type="hidden" name="source" value="http://light2015blog.org/2015/05/13/discovering-the-most-ancient-cosmic-light/"/> <input type="hidden" name="sub-type" value="loggedout-follow"/> <input type="hidden" id="_wpnonce" name="_wpnonce" value="b5cb2fb878"/><input type="hidden" name="_wp_http_referer" value="/2015/05/13/discovering-the-most-ancient-cosmic-light/"/> <p id="bsub-subscribe-button"><input type="submit" value="Sign me up"/></p> </form> <div id="bsub-credit"><a href="https://web.archive.org/web/20150515192850/https://wordpress.com/?ref=lof">Build a website with WordPress.com</a></div> </div> </div> <script type="text/javascript"> window.WPCOM_sharing_counts = {"https:\/\/web.archive.org\/web\/20150515192850\/http:\/\/light2015blog.org\/2015\/05\/13\/discovering-the-most-ancient-cosmic-light\/":1325}; window.WPCOM_jetpack = false; window.WPCOM_site_ID = 66139115; </script> <script type="text/javascript"> jQuery(document).on( 'ready post-load', function(){ jQuery( 'a.share-twitter' ).on( 'click', function() { window.open( jQuery(this).attr( 'href' ), 'wpcomtwitter', 'menubar=1,resizable=1,width=600,height=350' ); return false; }); }); </script> <script type="text/javascript"> jQuery(document).on( 'ready post-load', function(){ jQuery( 'a.share-facebook' ).on( 'click', function() { window.open( jQuery(this).attr( 'href' ), 'wpcomfacebook', 'menubar=1,resizable=1,width=600,height=400' ); return false; }); }); </script> <script type="text/javascript"> jQuery(document).on( 'ready post-load', function(){ jQuery( 'a.share-google-plus-1' ).on( 'click', function() { window.open( jQuery(this).attr( 'href' ), 'wpcomgoogle-plus-1', 'menubar=1,resizable=1,width=480,height=550' ); return false; }); }); </script> <iframe src="https://web.archive.org/web/20150515192850if_/http://widgets.wp.com/likes/master.html?ver=20141028#ver=20141028&mp6=1" scrolling="no" id="likes-master" name="likes-master" style="display:none;"></iframe> <div id="likes-other-gravatars"><div class="likes-text"><span>%d</span> bloggers like this:</div><ul class="wpl-avatars sd-like-gravatars"></ul></div> <script type="text/javascript"> //<![CDATA[ var jetpackLikesWidgetQueue = []; var jetpackLikesWidgetBatch = []; var jetpackLikesMasterReady = false; function JetpackLikespostMessage( message, target ) { if ( "string" === typeof message ){ try{ message = JSON.parse( message ); } catch(e) { return; } } pm( { target: target, type: 'likesMessage', data: message, origin: '*' } ); } function JetpackLikesBatchHandler() { var requests = []; jQuery( 'div.jetpack-likes-widget-unloaded' ).each( function( i ) { if ( jetpackLikesWidgetBatch.indexOf( this.id ) > -1 ) return; jetpackLikesWidgetBatch.push( this.id ); var regex = /like-(post|comment)-wrapper-(\d+)-(\d+)-(\w+)/; var match = regex.exec( this.id ); if ( ! match || match.length != 5 ) return; var info = { blog_id: match[2], width: this.width }; if ( 'post' == match[1] ) { info.post_id = match[3]; } else if ( 'comment' == match[1] ) { info.comment_id = match[3]; } info.obj_id = match[4]; requests.push( info ); }); if ( requests.length > 0 ) { JetpackLikespostMessage( { event: 'initialBatch', requests: requests }, window.frames['likes-master'] ); } } function JetpackLikesMessageListener( event ) { if ( "undefined" == typeof event.event ) return; if ( 'masterReady' == event.event ) { jQuery( document ).ready( function() { jetpackLikesMasterReady = true; var stylesData = { event: 'injectStyles' }; if ( jQuery( 'iframe.admin-bar-likes-widget' ).length > 0 ) { JetpackLikespostMessage( { event: 'adminBarEnabled' }, window.frames[ 'likes-master' ] ); stylesData.adminBarStyles = { background: jQuery( '#wpadminbar .quicklinks li#wp-admin-bar-wpl-like > a' ).css( 'background' ), isRtl: ( 'rtl' == jQuery( '#wpadminbar' ).css( 'direction' ) ) }; } if ( !window.addEventListener ) jQuery( '#wp-admin-bar-admin-bar-likes-widget' ).hide(); stylesData.textStyles = { color: jQuery( '.sd-text-color').css( 'color' ), fontFamily: jQuery( '.sd-text-color' ).css( 'font-family' ), fontSize: jQuery( '.sd-text-color' ).css( 'font-size' ), direction: jQuery( '.sd-text-color' ).css( 'direction' ), fontWeight: jQuery( '.sd-text-color' ).css( 'font-weight' ), fontStyle: jQuery( '.sd-text-color' ).css( 'font-style' ), textDecoration: jQuery( '.sd-text-color' ).css('text-decoration') }; stylesData.linkStyles = { color: jQuery( '.sd-link-color' ).css('color'), fontFamily: jQuery( '.sd-link-color' ).css('font-family'), fontSize: jQuery( '.sd-link-color' ).css('font-size'), textDecoration: jQuery( '.sd-link-color' ).css('text-decoration'), fontWeight: jQuery( '.sd-link-color' ).css( 'font-weight' ), fontStyle: jQuery( '.sd-link-color' ).css( 'font-style' ) }; JetpackLikespostMessage( stylesData, window.frames[ 'likes-master' ] ); JetpackLikesBatchHandler(); jQuery( document ).on( 'inview', 'div.jetpack-likes-widget-unloaded', function() { jetpackLikesWidgetQueue.push( this.id ); }); }); } if ( 'showLikeWidget' == event.event ) { jQuery( '#' + event.id + ' .post-likes-widget-placeholder' ).fadeOut( 'fast', function() { jQuery( '#' + event.id + ' .post-likes-widget' ).fadeIn( 'fast', function() { JetpackLikespostMessage( { event: 'likeWidgetDisplayed', blog_id: event.blog_id, post_id: event.post_id, obj_id: event.obj_id }, window.frames['likes-master'] ); }); }); } if ( 'clickReblogFlair' == event.event ) { wpcom_reblog.toggle_reblog_box_flair( event.obj_id ); } if ( 'showOtherGravatars' == event.event ) { var $container = jQuery( '#likes-other-gravatars' ); var $list = $container.find( 'ul' ); $container.hide(); $list.html( '' ); $container.find( '.likes-text span' ).text( event.total ); jQuery.each( event.likers, function( i, liker ) { $list.append( '<li class="' + liker.css_class + '"><a href="' + liker.profile_URL + '" class="wpl-liker" rel="nofollow" target="_parent"><img src="' + liker.avatar_URL + '" alt="' + liker.name + '" width="30" height="30" style="padding-right: 3px;" /></a></li>'); } ); var offset = jQuery( "[name='" + event.parent + "']" ).offset(); $container.css( 'left', offset.left + event.position.left - 10 + 'px' ); $container.css( 'top', offset.top + event.position.top - 33 + 'px' ); var rowLength = Math.floor( event.width / 37 ); var height = ( Math.ceil( event.likers.length / rowLength ) * 37 ) + 13; if ( height > 204 ) { height = 204; } $container.css( 'height', height + 'px' ); $container.css( 'width', rowLength * 37 - 7 + 'px' ); $list.css( 'width', rowLength * 37 + 'px' ); $container.fadeIn( 'slow' ); var scrollbarWidth = $list[0].offsetWidth - $list[0].clientWidth; if ( scrollbarWidth > 0 ) { $container.width( $container.width() + scrollbarWidth ); $list.width( $list.width() + scrollbarWidth ); } } } pm.bind( 'likesMessage', function(e) { JetpackLikesMessageListener(e); } ); jQuery( document ).click( function( e ) { var $container = jQuery( '#likes-other-gravatars' ); if ( $container.has( e.target ).length === 0 ) { $container.fadeOut( 'slow' ); } }); function JetpackLikesWidgetQueueHandler() { var wrapperID; if ( ! jetpackLikesMasterReady ) { setTimeout( JetpackLikesWidgetQueueHandler, 500 ); return; } if ( jetpackLikesWidgetQueue.length > 0 ) { // We may have a widget that needs creating now var found = false; while( jetpackLikesWidgetQueue.length > 0 ) { // Grab the first member of the queue that isn't already loading. wrapperID = jetpackLikesWidgetQueue.splice( 0, 1 )[0]; if ( jQuery( '#' + wrapperID ).hasClass( 'jetpack-likes-widget-unloaded' ) ) { found = true; break; } } if ( ! found ) { setTimeout( JetpackLikesWidgetQueueHandler, 500 ); return; } } else if ( jQuery( 'div.jetpack-likes-widget-unloaded' ).length > 0 ) { // Grab any unloaded widgets for a batch request JetpackLikesBatchHandler(); // Get the next unloaded widget wrapperID = jQuery( 'div.jetpack-likes-widget-unloaded' ).first()[0].id; if ( ! wrapperID ) { // Everything is currently loaded setTimeout( JetpackLikesWidgetQueueHandler, 500 ); return; } } if ( 'undefined' === typeof wrapperID ) { setTimeout( JetpackLikesWidgetQueueHandler, 500 ); return; } var $wrapper = jQuery( '#' + wrapperID ); $wrapper.find( 'iframe' ).remove(); if ( $wrapper.hasClass( 'slim-likes-widget' ) ) { $wrapper.find( '.post-likes-widget-placeholder' ).after( "<iframe class='post-likes-widget jetpack-likes-widget' name='" + $wrapper.data( 'name' ) + "' height='22px' width='68px' frameBorder='0' scrolling='no' src='" + $wrapper.data( 'src' ) + "'></iframe>" ); } else { $wrapper.find( '.post-likes-widget-placeholder' ).after( "<iframe class='post-likes-widget jetpack-likes-widget' name='" + $wrapper.data( 'name' ) + "' height='55px' width='100%' frameBorder='0' src='" + $wrapper.data( 'src' ) + "'></iframe>" ); } $wrapper.removeClass( 'jetpack-likes-widget-unloaded' ).addClass( 'jetpack-likes-widget-loading' ); $wrapper.find( 'iframe' ).load( function( e ) { var $iframe = jQuery( e.target ); $wrapper.removeClass( 'jetpack-likes-widget-loading' ).addClass( 'jetpack-likes-widget-loaded' ); JetpackLikespostMessage( { event: 'loadLikeWidget', name: $iframe.attr( 'name' ), width: $iframe.width() }, window.frames[ 'likes-master' ] ); if ( $wrapper.hasClass( 'slim-likes-widget' ) ) { $wrapper.find( 'iframe' ).Jetpack( 'resizeable' ); } }); setTimeout( JetpackLikesWidgetQueueHandler, 250 ); } JetpackLikesWidgetQueueHandler(); //]]> </script> <script type="text/javascript" src="https://web.archive.org/web/20150515192850js_/https://s1.wp.com/wp-content/mu-plugins/akismet-3.0/_inc/form.js?m=1404442431g"></script> <script type="text/javascript"> /* <![CDATA[ */ var JetpackEmojiSettings = {"base_url":"https:\/\/web.archive.org\/web\/20150515192850\/http:\/\/s0.wp.com\/wp-content\/mu-plugins\/emoji\/twemoji\/"}; /* ]]> */ </script> <script type="text/javascript"> /* <![CDATA[ */ var sharing_js_options = {"lang":"en","counts":"1"}; /* ]]> */ </script> <script type="text/javascript" src="https://web.archive.org/web/20150515192850js_/https://s0.wp.com/_static/??-eJyNzU0SgjAMBeALWYLj78bxLLUUSGnTDE1Bb29d6Oi4gNVb5HsvMLMykcSSgEvQ2AmN5Xvl0ga+TtLbYBNwvkGIgu3Lkp6w04KR1ug0ICuPNKg2mpxUi58nSMbnphQKMzGEMqFGy/5RBfzbDlmxzx1SAhuiQ5D5Jxe9s8LaDGqdXlIck6jWaxwh9XpE6t5ZStdw2e539fl4quuDewLdAIbF"></script> <script type="text/javascript"> // <![CDATA[ (function() { try{ if ( window.external &&'msIsSiteMode' in window.external) { if (window.external.msIsSiteMode()) { var jl = document.createElement('script'); jl.type='text/javascript'; jl.async=true; jl.src='/wp-content/plugins/ie-sitemode/custom-jumplist.php'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(jl, s); } } }catch(e){} })(); // ]]> </script> <script type="text/javascript"> var skimlinks_pub_id = "725X584219" var skimlinks_sitename = "light2015blogdotorg.wordpress.com"; </script> <script type="text/javascript" src="https://web.archive.org/web/20150515192850js_/http://s.skimresources.com/js/725X1342.skimlinks.js"></script><script src="//web.archive.org/web/20150515192850js_/http://stats.wp.com/w.js?46" type="text/javascript" async defer></script> <script type="text/javascript"> _tkq = window._tkq || []; _stq = window._stq || []; _tkq.push(['storeContext', {'blog_id':'66139115','blog_tz':'0','user_lang':'en','blog_lang':'en','user_id':'0'}]); _stq.push(['view', {'blog':'66139115','v':'wpcom','tz':'0','user_id':'0','post':'1325','subd':'light2015blogdotorg'}]); _stq.push(['extra', {'crypt':'UE40eW5QN0p8M2Y/RE1oVEcmQyVLQXJDYWRsdW1Ycy55SXZNSzk0YUdmY2wsS2FbYy1peTNMNWxbNX45YmhUSWxUOGFscE0vbW5tQkxZbzlsczVsXSV4YytWbTMsWEFpL0ddfG80LnN8OHJuLiY2S3wyQ1UxR3g1P21mdU8sKzElVFZxZjI9Skl+MC0/RVREYVVObXEzakplcklEUC4yYm9OSmhualFDJUc5VFBJWWdpUkVWdGIxc0hYUThvSmMzcU9GcE0lenhZLXolLHlqdWcseXMta3FLTHRmY242TEFWP25MczJNSHxvPVZzU24/LHZnSHB4YUdPTlMzZ1pwMFddR1prVWU2Ml1LUmdJVkIlLHAuRTFZQVRnZmRwN2pvaX4/W2hWUHx2K3NDL3Q0fCssTEdiSiZDbk5Wdm9VTUdvLGgyZl9pTVtTSHBtblE='}]); _stq.push([ 'clickTrackerInit', '66139115', '1325' ]); </script> <noscript><img src="https://web.archive.org/web/20150515192850im_/http://pixel.wp.com/b.gif?v=noscript" style="height:0px;width:0px;overflow:hidden" alt=""/></noscript> <script> if ( 'object' === typeof wpcom_mobile_user_agent_info ) { wpcom_mobile_user_agent_info.init(); var mobileStatsQueryString = ""; if( false !== wpcom_mobile_user_agent_info.matchedPlatformName ) mobileStatsQueryString += "&x_" + 'mobile_platforms' + '=' + wpcom_mobile_user_agent_info.matchedPlatformName; if( false !== wpcom_mobile_user_agent_info.matchedUserAgentName ) mobileStatsQueryString += "&x_" + 'mobile_devices' + '=' + wpcom_mobile_user_agent_info.matchedUserAgentName; if( wpcom_mobile_user_agent_info.isIPad() ) mobileStatsQueryString += "&x_" + 'ipad_views' + '=' + 'views'; if( "" != mobileStatsQueryString ) { new Image().src = document.location.protocol + '//web.archive.org/web/20150515192850/http://pixel.wp.com/g.gif?v=wpcom-no-pv' + mobileStatsQueryString + '&baba=' + Math.random(); } } </script> </body> </html>