Physics 20083 - Current Questions
Covers material from the lecture on Wednesday, April 21.
Complete version of Study Guide #4 is here.
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- Explain why the density of matter in the Universe is related to how much Helium was present in the early Universe. Explain why the abundance of Helium (and other light elements) is a measure of the density of the Universe, independent of other measures of the density (such as counting galaxies in and dividing by a representative volume).
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- Explain how and why Astronomers hoped to use Hubble's Law as an independent method for estimating the density of the Universe. How would a high vs a low density (and a zero density) Universe compare on a Hubble law graph? Explain why they differ.
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- Explain how current observations of galaxy radial velocities and distances compare to the expectations of Hubble's Law under the influence of gravity. Explain why these observations lead us to believe that the Universe is accelerating away from us in all directions.
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- Explain what the Cosmological Constant is. Why did Einstein originally introduce the idea of a Cosmological Constant? Why was it later abandoned?