4.5 Astro 1 Section 1 Professor Brandt

4.5 Astro 1 Section 1 Professor Brandt - Astro 1 Section 1...

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Astro 1 Section 1 Professor Brandt Monday April 5th 1999 Announcements: Lecture notes: Class 34 Lecture Title -- Will the Universe End with Ice or Fire? Review the three main pieces of evidence for the Big Bang 1. The expansion of the Universe 2. The Cosmic Microwave Background 3. Primordial Nucleosynthesis We have now extended our understanding of the Universe back to about three minutes after the Big Bang. Scientists think they understand things pretty reliably back to about three minutes after the Big Bang. At earlier times however things are less certain. We really don't have a totally satisfactory answer for example about why the Universe came into being. We have some good ideas but nothing totally compelling. Also we don't know know what happened before the Big Bang if anything at all. It is possible that there was simply nothing before the Big Bang since time and space had not yet come into being. We have already learned that a long time ago the Universe started expanding. By observing the redshifts of distant galaxies we know that it is still expanding today. A natural question to ponder is the distant future of the Universe. What will happen to the Universe on a very long timescale? Will it keep expanding like it is now forever? Or will it start to contract someday and shrink back down to a very small size? The Universe basically has 3 possible fates 1. It will keep expanding forever 2. It will ultimately stop expanding and contract again 3. It will expand forever but more and more slowly so that it essentially reaches a standstill
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To understand this in more detail we must first ask ourselves what might halt the expansion of the Universe? GRAVITY.
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4.5 Astro 1 Section 1 Professor Brandt - Astro 1 Section 1...

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