Note
to students: Chapter 1 of The Foundations of Modern Cosmology
is recommended reading.
Consider the following:
In the days before cities, before electric lights, the sky,
on a clear, moonless night, might
be the cabinet of some celestial jeweler, displaying glittering points of
light on a field of black velvet. A faint, irregular band meanders
overheard, like a river of cosmic milk, bisected by a path of shadows.
On any particular night,
noticeable bright stars might stand out among the others; on subsequent
evenings, an observant watcher would find that these wandering lights had
shifted their positions against the backdrop of stars. As the seasons
change, so does the sky; some groups of stars visible in summer disappear
during the winter, whereas others remain above the horizon all year. In
the morning, the Sun appears on the eastern horizon. It climbs upward into
the sky, then descends, and vanishes beneath the western horizon. As the
Sun disappears, the stars rise, retracing the Sun's motion from east to
west across the sky. The Moon rises as well, but keeps its own schedule,
independent of the stars. At times, the Moon appears as a silvery disk
marked with gray splotches; the imaginative may see a man, a rabbit, or
even a beetle in the face of the Moon. At other times, the Moon shows us a
crescent, or half its disk. Sometimes, it never appears at all.
Some, like the Romantics, declare that modern science has removed
the wonder from the sky, that understanding a phenomenon somehow
takes away its beauty. It is not science that is at fault but
rather an inability of some step away from their myopic view and
behold the Universe in all its magnificient glory. For despite
all the rhetoric to the contrary, human beings are still held
in awe by the marvel that is the sky, the wonder which is now
magnified manifold by the extraordinary discoveries of modern
astronomy. The Milky Way retains its subtle grandeur, but
but now we know that this band of diffuse light is the combined glow
of some of the billions of stars filling the unimaginably huge galaxy
in which we live, an awesome contemplation on a dark evening.
The heavens still pose many questions to those who take the time to ponder them, from the casual "What are the stars? What makes the Sun rise?" to the profound "How did it all begin? Was there a beginning at all, or have the heavens and Earth existed forever? Will the universe come to an end? What is the nature of the universe, and what role do humans play in it?"
Many of these questions puzzled the ancients;
some of the old mysteries have long since been resolved while modern
astronomy has deepened some and added new ones.
Most people have heard such expressions as "the big bang" and "expanding space." They may be aware that astronomers debate whether the universe is "open" or "closed," infinite or finite, eternal or doomed. But what does it mean to say that the universe expands? Is the universe really expanding? Into what? When astronomers say that most of the mass of the universe is "missing," what do they mean? Where could it have gone? What are space and time, and why does time move in only one direction? What is the big bang? How did elements originate? What happens to stars when they die? What is a black hole? What will be the ultimate fate of our Sun and even of the universe itself? Were there other universes before this one, and will others follow ours?
These questions fall within the realm of cosmology, the study of the
Universe. Today, we regard cosmology as a modern science, but
cosmological yearnings have been part of humanity throughout history. All
cultures have a cosmology, for such questions have been asked by all
peoples for as long as we have wondered at the stars. The explanations
have varied from culture to culture, and from time to time, but all seek to
impose an order upon the cosmos, to make it accessible to the human mind.
This is just as true of scientific as of prescientific cosmologies.
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