{"id":538,"date":"2018-06-14T19:18:44","date_gmt":"2018-06-14T19:18:44","guid":{"rendered":"https:\/\/sites.krieger.jhu.edu\/class\/?page_id=538"},"modified":"2019-09-17T09:40:26","modified_gmt":"2019-09-17T13:40:26","slug":"the-big-questions","status":"publish","type":"page","link":"https:\/\/sites.krieger.jhu.edu\/class\/science\/the-big-questions\/","title":{"rendered":"The Big Questions"},"content":{"rendered":"

CLASS was motivated by several big questions about how the universe began, questions which brought our project to where it is today.<\/span><\/p>\n

How did the universe evolve?<\/strong><\/span><\/p>\n

In the popular imagination, the Big Bang Theory describes an event at the beginning of the universe (sometimes literally imagined as the \u201cbang\u201d of an explosion) from which the universe is born.\u00a0In physics, the Big Bang Theory describes not the\u00a0beginning<\/em>\u00a0of the universe (much less a \u201cbang\u201d) but rather the\u00a0evolution<\/em>\u00a0of the universe.<\/span><\/p>\n

During the first half of the 20th century,\u00a0Edwin Hubble<\/span><\/a>\u00a0and other scientists demonstrated that the\u00a0universe is expanding<\/em>. In its basic essence, the Big Bang Theory is the theory of the expanding universe. <\/span><\/p>\n

What does \u201cthe expanding universe\u201d imply? <\/strong><\/span><\/p>\n

According to the Big Bang Theory, a given volume in the universe is literally growing in size. The distances between objects in the universe that are not bound to each other grow with time. Correspondingly, the matter (e.g., atoms), light and other \u201cstuff\u201d inside that volume are becoming\u00a0less dense\u00a0<\/em>with time. Therefore, we can infer that the density of the universe was higher in the past. The heat in the universe also grows more diffuse with time causing an ever decreasing temperature.\u00a0<\/span><\/p>\n

What is the Cosmic Microwave Background (CMB) radiation?<\/strong><\/span><\/p>\n

Long ago, the universe was very hot \u2014 so hot that it glowed with high energy radiation. After much expansion, this glow is measured today as microwaves called the Cosmic Microwave Background (CMB) and its existence was a prediction of the Big Bang Theory. <\/span><\/p>\n

Thus the announcement of the\u00a0discovery of the CMB<\/span><\/a>\u00a0in 1965 was a pivotal triumph of the Big Bang Theory. The\u00a0Wilkinson Microwave Anisotropy Probe (WMAP)<\/span><\/a>\u00a0satellite measured the age of the universe to be 13.77 billion years. The CMB originated just 375,000 years after the beginning.<\/span><\/p>\n

What actually happened at the \u201cbeginning\u201d of the universe?<\/strong><\/span><\/p>\n

We still don\u2019t know the answer to this, but an idea called \u201cInflation<\/strong>\u201d may answer this question. The Big Bang Theory successfully describes the evolution and cooling of the universe over billions of years. Within the Big Bang evolution framework, tiny initial \u201cprimordial\u201d density fluctuations grew under gravity to become the structure of the universe (e.g., galaxies and their stars) we see today. But the Big Bang Theory does not explain the origin of these primordial fluctuations \u2014 it does not explain the true beginning. Inflation theory completes the picture by describing how the initial state of the universe was established by a rapid expansion at the very beginning, stretching random submicroscopic\u00a0quantum fluctuations<\/span><\/a>\u00a0into\u00a0primordial density fluctuations \u2014 the seeds of cosmic structure<\/span><\/a>.\u00a0 Quoting physicist Brian Greene, \u201cGalaxies are nothing but quantum mechanics writ large across the sky.\u201d<\/span><\/p>\n

The figure below, taken from the\u00a0<\/span>WMAP website<\/em><\/span><\/a>,\u00a0<\/span>illustrates this history of the expanding universe:<\/span><\/p>\n

\"\"
The Big Bang Theory describes the expansion history of the universe, illustrated here with a timeline from left to right, by an expanding volume filled with matter and other forms of energy. At the far left, I<\/strong>nflation\u00a0Theory<\/strong> describes a rapid expansion of space at the beginning of the universe during which microscopic quantum fluctuations in density and the fabric of space-time grew to macroscopic cosmological size. From these primordial cosmological fluctuations (at the left of the figure) grew galaxies and other cosmic structures (at the right). After Inflation slows, the expansion that can be explained by the Big Bang Theory takes over.<\/figcaption><\/figure>\n\n

Discover how these questions translated into the specific goals of the CLASS project today…<\/em><\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

CLASS was motivated by several big questions about how the universe began, questions which brought our project to where it is today. How did the universe evolve? In the popular imagination, the Big Bang Theory describes an event at the beginning of the universe (sometimes literally imagined as the \u201cbang\u201d of an explosion) from which […]<\/p>\n","protected":false},"author":47,"featured_media":0,"parent":394,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"footnotes":""},"class_list":["post-538","page","type-page","status-publish","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/sites.krieger.jhu.edu\/class\/wp-json\/wp\/v2\/pages\/538","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sites.krieger.jhu.edu\/class\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sites.krieger.jhu.edu\/class\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sites.krieger.jhu.edu\/class\/wp-json\/wp\/v2\/users\/47"}],"replies":[{"embeddable":true,"href":"https:\/\/sites.krieger.jhu.edu\/class\/wp-json\/wp\/v2\/comments?post=538"}],"version-history":[{"count":5,"href":"https:\/\/sites.krieger.jhu.edu\/class\/wp-json\/wp\/v2\/pages\/538\/revisions"}],"predecessor-version":[{"id":956,"href":"https:\/\/sites.krieger.jhu.edu\/class\/wp-json\/wp\/v2\/pages\/538\/revisions\/956"}],"up":[{"embeddable":true,"href":"https:\/\/sites.krieger.jhu.edu\/class\/wp-json\/wp\/v2\/pages\/394"}],"wp:attachment":[{"href":"https:\/\/sites.krieger.jhu.edu\/class\/wp-json\/wp\/v2\/media?parent=538"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}