Cosmos: Chapter 1 - The Shores of the Cosmic Ocean
In this chapter, Sagan uses the metaphor of space as a "cosmic ocean" and Earth as the shore upon which we stand looking out across that ocean. He notes how we have "waded a little out to sea, enough to dampen our toes or, at most, wet our ankles." In this way, he describes how relatively little we have yet explored into space and how much of what is out there is still unknown to us.
This chapter is organized into two parts. In the first part, Sagan orients our view of the universe from the cosmic perspective. That is, he encourages us to view our Earth, solar system and galaxy from the outside looking in rather than from the inside looking out. To do this, he leads us through a journey on what he calls in the television series a "ship of the imagination." This is an imaginary ship, much like the starship Enterprise of Star Trek fame, which can move at many times the speed of light. We begin the journey at a point halfway between the Earth and the edge of the known universe -- 8 billion light years from Earth -- and end the journey back here on our home planet. As we move along Sagan is our tour guide, pointing out various items of interest, of which there are many. He gives brief descriptions of galaxies and galaxy clusters, quasars, pulsars, supernovae, black holes, stars, planets, moons and comets. Throughout this journey, he gives us a feel for the size of the space we are travelling through and the objects we are encountering. In classic Sagan-speak, the words "million", "billion" and "trillion" are used repeatedly. For example,
"There are some hundred billion galaxies, each with, on the average, a hundred billion stars. In all the galaxies there are perhaps as many planets as stars, 10e11 x 10e11 = 10e22, ten billion trillion."
Sagan speculates that, based on these overwhelming numbers and the fact that organic molecules are commonly found throughout the Cosmos, the odds are extremely small that Earth is the only place where life has emerged.
"In the face of such overpowering numbers, what is the likelihood that only one ordinary star, the Sun, is accompanied by an inhabited planet? Why should we, tucked away in some forgotten corner of the Cosmos, be so fortunate? To me, it seems far more likely that the universe is brimming over with life. But we humans do not yet know. We are just beginning our explorations."
In the second part of the chapter, Sagan takes us back to the early days of recorded human history, when we first began to systematically question the nature of our world. Specifically, he describes the Library of the city of Alexandria in Egypt which existed for 600 years beginning around 300 B.C. We learn that this library at that time contained all the recorded knowledge of the ancient world. In Sagan's words, it was "the first true research institute in the history of the world ... the brain and glory of the greatest city on the planet ... a citadel of human consciousness ... and a beacon on our journey to the stars." Sagan mentions several important people who worked there, including
"the astronomer Hipparchus, who mapped the constellations and estimated the brightness of the stars; Euclid, who brilliantly systematized geometry, ... Dionysius of Thrace, the man who defined the parts of speech (nouns, verbs, etc.), ... Herophilus, the physiologist who firmly established that the brain rather than the heart is the seat of intelligence; Heron of Alexandria, inventor of gear trains and steam engines and the author of Automata, the first book on robots; Apollonius of Perga, the mathematician who demonstrated the forms of the conic sections -- ellipse, parabola and hyperbola ... Archimedes, the greatest mechanical genius until Leonardo da Vinci; and the astronomer and geographer Ptolemy, who compiled much of what is today the pseudoscience of astrology: his Earth-centered universe held sway for 1,500 years, a reminder that intellectual capacity is no guarantee against being dead wrong."
Sagan gives a fascinating account of how a man named Eratosthenes, around 200 B.C., accurately deduced the circumference of the Earth based on the length of shadows cast by sticks on the same day in different parts of Egypt. (If two objects hundreds of miles apart cast shadows of different lengths at the same time, you can use Euclidean geometry to compute the circumference of the sphere on which they rest -- the Earth -- knowing only the length of the shadows and objects and the distance between the objects.) Of this achievement, Sagan says, "Eratosthenes' only tools were sticks, eyes, feet and brains, plus a taste for experiment. ... He was the first person accurately to measure the size of a planet."
Sagan concludes the chapter by describing how sad and tragic it is that the Library of Alexandria and the half-million books that it contained were destroyed around 400 A.D. when the ancient Egyptian civilization collapsed. Of this event, which marked the beginning of the Dark Ages, Sagan says,
"We know, for example, that there was on the library shelves a book by the astronomer Aristarchus of Samos, who argued that the Earth is one of the planets, which like them orbits the Sun, and that the stars are enormously far away. Each of these conclusions is entirely correct, but we had to wait nearly two thousand years for their rediscovery. If we multiply by a hundred thousand our sense of loss for this work of Aristarchus, we begin to appreciate the grandeur of the achievement of classical civilization and the tragedy of its destruction."
Tom |
