'Now'

Thousands of years ago, all these basic queries were treated as secondary, for the primary concern seemed well in hand: Earth was presumed to be the stable hub of the Universe. After all, the Sun, Moon, and stars all appear to revolve around our planet. It was natural to conclude, not knowing otherwise, that home and selves were special. This centrality led to a feeling of security or at least contentment—a belief that the origin, maintenance, and fate of the Universe were governed by something more than natural, something supernatural. The ancients thought deeply and well, but not much more. Logic was paramount; empiricism less so. Their efforts nonetheless produced such notable endeavors as myth, religion, and philosophy. Eventually, yet only a few hundred years ago, the idea of Earth’s centrality and the reliance on supernatural beings were shattered. During the Renaissance, humans began to inquire more critically about themselves and the Universe. They realized that thinking about Nature was no longer sufficient. Looking at it was also necessary. Experiments became a central part of the process of inquiry. To be effective, ideas had to be tested experimentally, either to refine them if data favored them or to reject them if they did not. The scientific method was born—probably the most powerful technique ever conceived for the advancement of factual information. Modern science had arrived. Today, all natural scientists throughout the world employ the scientific method. Normally it works like this: First, gather some data by observing an object or event, then propose an idea to explain the data, and finally test the idea by experimenting with Nature. Those ideas that pass the tests are selected, accumulated, and conveyed, while those that don’t are discarded—a little like the evolutionary events described on this Web site. In that way, by means of a selective editing or pruning of ideas, scientists discriminate between sense and nonsense. We gain an ever-better approximation of reality. Not that science claims to reveal the truth—whatever that is—just to gain an increasingly accurate model of Nature.

Researchers now sense that the cutting edge of knowledge resembles a thinning haze rather than a sharp boundary. The research front resembles the “fog of war,” meaning that scientific work is hardly ever crystal clear in real time, while the work is underway. Rather, the intellectual landscape is often revealed only later, after the subjective confusion has abated and a certain objective reality has emerged. That’s because the enterprise of science is now advancing rapidly, acquiring new information at a phenomenal rate and requiring novel interdisciplinary ventures to put it straight. Less than a hundred years ago we didn't understand how stars shine, how heredity works, that the Universe is filled with galaxies, or even that it had a definite beginning. Furthermore, much of science as a "work in progress" involves the human condition, which ensures many false starts and occasional botched logic among the many valid, proven ideas. As a fair assessment, we might say that a pencil sketch of the answers to some of the most basic questions is now at hand, but that many specifics are yet wanting.

Nothing, however, has been more revolutionary than the idea that this entire universe is in a state of constant change, as planets, stars and galaxies are born and die. This story of the life of the universe, and our place in it, is known as cosmic evolution. Although the idea has roots in the 19th century, and was occasionally invoked in the first half of the 20th century by astronomers such as George Ellery Hale, it really came into its own only in the Space Age. Already in 1958, in his classic book Of Stars and Men, Harvard College Observatory Director Harlow Shapley wrote that the Earth is "on the outer fringe of one galaxy in a universe of millions of galaxies. Man becomes peripheral among the billions of stars in his own Milky Way; and according to the revelations of paleontology and geochemistry he is also exposed as a recent, and perhaps an ephemeral manifestation in the unrolling of cosmic time."

One hundred years ago most astronomers considered the universe to be about 3600 light years in extent, less than a billion years old, and with our solar system near its center. Astronomers today have seen objects 13 billion light years away in a universe 13.7 billion years old containing hundreds of billions of galaxies. We are peripherally located in one of those galaxies, known as the Milky Way.