PHSC
ChapterOnEvidenceForBigBang

ChapterOnEvidenceForBigBang - Unit 3 The Evidence for the...

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Unit 3 The Evidence for the Big Bang In this unit, we describe the evidence for the big bang and how the universe changed from its early beginnings into the one we have today. We will concentrate on the experimental evidence and how scientists interpret it. Each of the following three chapters covers a separate set of topics, but most of the ideas are interrelated. They are: Chapter 10: The Exploding Universe Chapter 11: Expanding Space-Time Chapter 12: Photons and Hydrogen in the Universe How we interpret the scientific clues in these chapters may seem complex at first, but I hope to de-mystify the whole process. The three primary pieces of evidence to explain are: 1. The galaxies in the universe : We observe about 100 billion galaxies in the universe and that they seem to be distributed evenly throughout. More importantly, we see that all of the distant galaxies are moving away from us. The farther away the galaxy, the faster it moves away. 2. The photons in the universe: Low-energy photons (microwaves) are uniformly distributed in all directions with a temperature of about 2.7 degrees above absolute zero (Kelvin). It is as if they are, or were, in thermal equilibrium.
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10 - 1 3. The atoms in the universe: About 91 percent of the atoms in the universe are hydrogen, while most of the rest are helium. There are precious few atoms of any other type. In Chapter 10, we discuss light from galaxies and how it leads us to the theory that we live in a universe that began with a big bang and has been expanding ever since. As the data can be misinterpreted to point away from a big-bang interpretation, we discuss how general relativity and expanding space-time come to the rescue in Chapter 11. In Chapter 12, we talk about the photons in the universe, known as the cosmic background radiation, and the fact that most of the atoms in the universe are hydrogen and helium. While many consider these last two pieces of evidence to be the most compelling, I find it hard to explain why they are evidence at all without tie together with the overall story of the universe’s evolution. Thus, we will explain them after our discussion of the expanding universe.
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10 - 2 Chapter 10 The Exploding Universe Before the 1920s, there was a small amount data that suggested that some of the light from “things out there” might be from galaxies beyond our own. However, the evidence was not convincing. Many scientists, including Einstein, thought our galaxy was the entire universe. Astronomer Edwin Hubble would soon prove otherwise. Armed with the most powerful telescope of its day, Hubble firmly established that there is a giant universe beyond the stars of our galaxy, the Milky Way. We now know that just as our Sun is only one of many stars, the Milky Way is just one of many galaxies.
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