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TAMU ASTR 101 - Lecture27

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Copyright © 2009 Pearson Education, Inc. Chapter 16 Dark Matter, Dark Energy, and the Fate of the UniverseCopyright © 2009 Pearson Education, Inc. End of Term • Final midterm – 8am 16 Dec • Essay due 16 Dec on Turnitin.com • Final homework is extra-credit. It will replace your worse (or missed) homework. • It has been fun teaching you. I hope you have enjoyed this review of astronomyCopyright © 2009 Pearson Education, Inc. 17.3 The Big Bang and Inflation Our goals for learning: • What aspects of the universe were originally unexplained by the Big Bang theory? • How does inflation explain these features of the universe? • How can we test the idea of inflation?Copyright © 2009 Pearson Education, Inc. What aspects of the universe were originally unexplained by the Big Bang theory?Copyright © 2009 Pearson Education, Inc. Mysteries Needing Explanation 1. Where does structure come from? 2. Why is the overall distribution of matter so uniform? 3. Why is the density of the universe so close to the critical density? 4. Why are there no magnetic monopoles?Copyright © 2009 Pearson Education, Inc. Mysteries Needing Explanation 1. Where does structure come from? 2. Why is the overall distribution of matter so uniform? 3. Why is the density of the universe so close to the critical density? An early episode of rapid inflation can solve all three mysteries!Copyright © 2009 Pearson Education, Inc. How does inflation explain these features of the universe?Copyright © 2009 Pearson Education, Inc. Inflation can make structure by stretching tiny quantum ripples to enormous sizes. These ripples in density then become the seeds for all structure in the universe.Copyright © 2009 Pearson Education, Inc. How can microwave temperature be nearly identical on opposite sides of the sky?Copyright © 2009 Pearson Education, Inc. Regions now on opposite sides of the sky were close together before inflation pushed them far apart.Copyright © 2009 Pearson Education, Inc. The overall geometry of the universe is closely related to total density of matter and energy. Density = Critical Density > Critical Density < CriticalCopyright © 2009 Pearson Education, Inc. The inflation of the universe flattens the overall geometry like the inflation of a balloon, causing overall density of matter plus energy to be very close to critical density.Copyright © 2009 Pearson Education, Inc. How can we test the idea of inflation?Copyright © 2009 Pearson Education, Inc. Patterns of structure observed by WMAP show us the “seeds” of the universe.Copyright © 2009 Pearson Education, Inc. Observed patterns of structure in the universe agree (so far) with the “seeds” that inflation would produce.Copyright © 2009 Pearson Education, Inc. “Seeds” Inferred from CMB • Overall geometry is flat — Total mass + energy has critical density • Ordinary matter ~4.6% of total • Total matter is ~28% of total — Dark matter is ~23% of total — Dark energy is ~72% of total • Age of 13.7 billion yearsCopyright © 2009 Pearson Education, Inc. “Seeds” Inferred from CMB • Overall geometry is flat — Total mass + energy has critical density • Ordinary matter ~4.6% of total • Total matter is ~28% of total — Dark matter is ~23% of total — Dark energy is ~72% of total • Age of 13.7 billion years In excellent agreement with observations of present-day universe and models involving inflation and WIMPs!Copyright © 2009 Pearson Education, Inc. What have we learned? • What aspects of the universe were originally unexplained by the Big Bang theory? — The origin of structure, the smoothness of the universe on large scales, the nearly critical density of the universe • How does inflation explain these features of the universe? — Structure comes from inflated quantum ripples. — Observable universe became smooth before inflation, when it was very tiny. — Inflation flattened the curvature of space, bringing the expansion rate into balance with the overall density of mass-energy.Copyright © 2009 Pearson Education, Inc. What have we learned? • How can we test the idea of inflation? — We can compare the structures we see in detailed observations of the microwave background with predictions for the “seeds” that should have been planted by inflation. — So far, our observations of the universe agree well with models in which inflation planted the “seeds.”Copyright © 2009 Pearson Education, Inc. 17.4 Observing the Big Bang for Yourself Our goals for learning: • Why is the darkness of the night sky evidence for the Big Bang?Copyright © 2009 Pearson Education, Inc. Why is the darkness of the night sky evidence for the Big Bang?Copyright © 2009 Pearson Education, Inc. Olbers’ Paradox 1. infinite 2. unchanging 3. everywhere the same then stars would cover the night sky. If the universe wereCopyright © 2009 Pearson Education, Inc. Olbers’ Paradox 1. infinite 2. unchanging 3. everywhere the same then stars would cover the night sky. If the universe wereCopyright © 2009 Pearson Education, Inc. The night sky is dark because the universe changes with time. As we look out in space, we can look back to a time when there were no stars.Copyright © 2009 Pearson Education, Inc. The night sky is dark because the universe changes with time. As we look out in space, we can look back to a time when there were no stars.Copyright © 2009 Pearson Education, Inc. What have we learned? • Why is the darkness of the night sky evidence for the Big Bang? — If the universe were eternal, unchanging, and everywhere the same, the entire night sky would be covered with stars. — The night sky is dark because we can see back to a time when there were no stars.Copyright © 2009 Pearson Education, Inc. Some Final Thoughts • Is there a beginning to time? • Is the Universe compactified? • String TheoryCopyright © 2009 Pearson Education, Inc. String Theory • (lots of handwaving here)Copyright © 2009 Pearson Education, Inc. String Theory ICopyright © 2009 Pearson Education, Inc. String Theory II 11 dimensions - 6 compactified = 5 dimensions 4 dimensional “branes” in a 5-D universe Forces are little loops 100500 universes = the landscapeCopyright © 2009 Pearson Education, Inc. Chapter 18 Life in the UniverseCopyright © 2009 Pearson


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TAMU ASTR 101 - Lecture27

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