Chapter 2 - Cosmology

Abstract

The ancient skywatchers observed the patterns of the Sun and Moon. The cosmic alignment of Teotihuacán, Stonehenge, and the Great Pyramids of Giza is discussed. Physical motions in the cosmos and human invention of units of time are defined. The Chinese and Mayan calendars illustrate the gearlike structure between the units of time. Models of the Universe as circles rolling around circles developed by the Greeks are presented. The Renaissance Period saw the development of modern theories of the Universe. Copernicus showed that the motion of the planets was simplified if represented as concentric circles. The stellar observations of Brahe interpreted by Kepler showed that the orbits of planets were an ellipse. The careful observations of Galileo gave valuable information about the Sun and the Planets. Extending Galileo's studies on falling bodies, Newton developed three laws of motion that explained that the trajectories of celestial objects interacting through an inverse square law were conical sections: circle, ellipse, hyperbola, and parabola. Einstein eliminated the force of gravity with the introduction of the shape of spacetime in his Theory of General Relativity. Einstein's field equations led to solutions by Schwarzchild, Friedmann, de Sitter, and Lemaître, which gave further insight to the nature of the Universe. Eddington led a 1919 project to measure the bending of light and found that Einstein's theory fit the data better than that of Newton. The astronomical observations of Shapley, Hubble, and Baade showed how large the Universe is, galaxies exist outside of the Milky Way, and verified the prediction of Lemaître that the Universe was expanding.