cosmology - These notes cover part of the material that...

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Unformatted text preview: These notes cover part of the material that will appear on the last exam: Friday Dec. 7. Chapters 26 and 27. COSMOLOGY AND THE EARLY UNIVERSE [Note: these notes and the lectures cover chapters 26 and 27 together, with topics discussed in a somewhat different order than in the textbook. References to textbook sections and pages and figures are given below. These notes will be of most benefit if you have already read chapters 26 and 27. This material is probably the most difficult, and also the most interesting, of the entire course, so you will have to read very carefully. Because of the amount of the material, I will not test you on the Discovery or More Precisely sections of your text for these two chapters, but I suggest that you read them anyway.] The diagram below illustrates what we will be interested in from an observational point of viewwe want to see the universe in the distant past by looking far away. At first we only want to observe more and more distant galaxies (to get the Hubble constant), count up all the matter we can see (and cant) see in order to find what kind of space-time we live in, but we end by probing times when the universe was only 100,000 yr old (the cosmic background radiation), and even a few minutes old (the formation of deuterium and helium, whose abundance cant be explained by formation in stars). Then (ch. 27) we try to go back to extremely small times, finding that the spacetime of the universe probably underwent a fantastic but theoretically sound inflation when it was only a tiny fraction of a second old. Finally, as we try to understand the stages of the universe that are inaccessible to present-day physics (quantum-gravity), we will enounter strong suggestions that a viable theory may be one in which the universe has many more dimensions than three, and even more speculative things. The Expanding Universe: The Big Bang [Sec. 26.2] Hubbles law : velocity = H x distance expanding universe . Now can ask: How big is the universe that we can see? When did it begin? How will it end? These are questions of cosmology , questions about the universe as a whole. Although there have been other contenders over the years (the cold big bang and the steady state cosmology) well see that only the hot big bang theory (and only a particular form of it: inflationary dark matter big bang) accounts for the observations, and does so very convincingly, but at the expense of introducing two entities whose nature is completely unknown: dark matter (already known) and dark energy. How long since all galaxies (and everything else) were in the same place? Time = distance/velocity = d/(H x d) = 1/H ~ 15 billion years This is when the big bang must have occurred; i.e. it is the age of the universe....
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This note was uploaded on 04/20/2008 for the course AST 301 taught by Professor Harvey during the Fall '07 term at University of Texas at Austin.

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cosmology - These notes cover part of the material that...

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