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Cosmology and the Universe Notes.pdf - Cosmology and the...

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Cosmology and the UniverseEhighschool AstronomyThe Nature of CosmologyCosmologyis the study of the structure, origin, and possible future of the universe. In simple terms, cosmologyis a study of how the universe began, how it is now, and how it will end. What is around me? Where did all ofthis--Earth, stars, planets, galaxies-- come from? Is the universe changing? These are just some of thefundamental questions even ancient cultures have addressed. In astronomy and in science, these are validquestions we try to answer using scientific measurements, observations, data, physics, and mathematics. Theseare also valid questions that religious studies also try to answer. However, it is important to understand thedifference between these two different ways of reasoning.In science, we are only allowed to draw conclusions about the universe based on what we can observe, measure,and calculate. However, in religion, we may draw conclusions based on religious texts and faith. It is moreimportant to understand that either way of answering these questions is valid, and one way of thinking about theuniverse does not necessarily mean the other is wrong. Religion and science are two separate ways of knowingthe universe. And because of the nature of this course, we will look at cosmology from a scientific perspective.In order to study the universe, we must operate under the cosmological principle. Thecosmological principleisthe assumption that the entire universe has roughly the same density and concentration of matter. An observer inanother galaxy would see roughly the same number of stars and galaxies that we observe. In addition, weassume that the basic laws of physics are the same throughout the universe. We must recognize that these arethe foundational assumptions upon which we lay the rest of our analysis.Observations of the universeBefore we begin talking about the beginning or the end of the universe, it is important to start with the mostbasic and fundamental observations. First and foremost, the most notable observation of the universe was madeby Edwin Hubble, and is since known asHubble's Law(v=Hd). Hubble observed that all galaxies showredshift, and more distant galaxies show higher degrees of redshift. In other words, we observe that the farthestgalaxies are have the greatest recessional velocities. This formula allows us to calculate the velocity of a galaxybased upon its distance from us (v=velocity, d=distance, and H=the Hubble constant, which is 70 km/sec/Mpc).These measurements imply that not only is the universe not static, but the universe is expanding. The Hubbleconstant is an observational constant that describes the rate of expansion of the universe. Based on Hubble'sLaw, astronomers estimate the radius of the universe to be approximately 16 billion light years. In addition,based on the work of Hubble, the age of the universe is estimated to be 14 billion years old.

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Term
Spring
Professor
Deirdre Daniels
Tags
Dark Energy, General Relativity, Big Bang, Redshift, Edwin Hubble, Physical cosmology

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