Cosmology: Understanding the Evolution of the Universe
CoSMOLOGY UNDERSTANDING THE EVOLUTION OF THE UNIVERSE The first great age of scientific cosmology began in Greece in the 6th century BCE when the Pythagoreans introduced the concept of a spherical Earth In approximately 170 CE one predominant theory espoused by the Greek culture and Ptolemy of Alexandria in par ticular was a geocentric one This theory was based upon the concept that the Earth was at the center of the universe A number of scientists and deep thinkers offered a variety of theories over the ensuing years Of particular significance was 16th century astronomer Nicolaus Copernicus who ushered in the second great age of cos mology when he developed the heliocentric concept of the solar system which placed the Sun at the center with Earth and the other planets continually orbiting it Albert Einstein one of the most brilliant scientists of the 2oth century is another individual who contributed much to our understanding of cosmology At the top of the list was his approach to thinking about time matter space energy and gravity He pub lished his revolutionary theory of relativity in 1916 which marked the beginning of the third great age of cosmology The most popular answer to the question about how our universe came to be is known 10
INTRODUCTION as the big bang theory Proponents of this the ory believe that between 13 and 14 billion years ago from an infinitely hot incredibly tiny supercondensed state the universe exploded Then in a moment following this event the universe began expanding For the following billions of years the expansion continued but at a slower pace Over thousands of years the intensely hot energy mixture of the early universe began to cool down After millions of years gas stars and galaxies were formed And in about 8 to 10 billion years our solar system including Earth appeared Many other notable figures made substan tial contributions to the world of cosmology in the 20th and 21st centuries They include Edwin Hubble Georges Lemaitre Aleksandre Friedmann George Gamow Edward Teller Hans Bethe Arno Penzias Alan Guth and George Smoot among others Current areas of research in cosmology include the nature of dark matter dark energy antimatter and more After reading this book you will see that while much about the nature and evolution of the universe remains to be discovered the works of many individuals over the centuries have gone a long way toward answering some of our most fundamental questions 11
CHAPTER 1 EARLY UNDERSTANDING NN hroughout recorded history human kind has asked big questions about the universe How large is it Is it finite or does space go on forever How old is it or has it always been here and will it last forever Where in the universe are we the center Or does it even have a center Is the universe fundamentally chaotic or orderly If it is ordered is this order constant through time Or is it perhaps evolving decaying still being created or going through cycles of cre ation and destruction The quest to find answers to such ques tions about the origin history and future of the universe and its structure and order is called cosmology This word in fact comes from the Greek word kosmos mean ing order and the world ANCIENT IDEAS Until the last few centuries these ques tions remained the province of religion and 12
EARLY UNDERSTANDING philosophy Different cultures and traditions at different times offered a wide variety of answers As for our place in the universe a com mon view was the geocentric one that Earth is at the center This model was developed in detail by the ancient Greeks culminating with the elaborate theory of Ptolemy of Alexandria in about 150 CE The Pythagoreans 5th century BCE were responsible for one of the first Greek astro nomical theories Believing that the order of the cosmos is fundamentally mathematical they held that it is possible to discover the har monies of the universe by contemplating the regular motions of the heavens Theorizing that all the heavenly bodies including the Earth and Sun revolve around a central fire they constructed the first physical model of the solar system Subsequent Greek astron omy derived its character from a comment ascribed to Plato in the 4th century BCE who is reported to have instructed the astronomers to save the phenomenal in terms of uniform circular motion That is to say he urged them to develop predictively accurate theories using only combinations of uniform circular motion As a result Greek astronomers never regarded their geometric models as true or as being physical descriptions of the machinery 13
