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vision of the universe was made by his fellow Englishman Edmond Halley (1656–1742). Using Newton’s laws and historical records, Halley was able to work out the orbit of the comet that now bears his name and to predict its reappearance in the sky. When the comet was “recovered” on Christmas Day, 1758, the event powerfully underscored the idea of the clockwork universe. Not only could Newton’s scheme explain things that were already known, it could make reliable predictions about events that had yet to occur.
    Today, with the advent of quantum mechanics and the field of complex chaotic systems, scientists’ ideas about the clockwork universe have changed. The universe is still, in the modern view, governed by simple laws, but these laws do not always allow us to make the kind of straightforward predictions about the future that Newton envisioned. Nevertheless, much of the Newtonian mind-set survives in modern science.
THE SCIENTIFIC METHOD
    Newton’s development of the clockwork universe was the first, classic example of the scientific method in use. The method depends on a constant interplay of observation and theory; observations lead to new theories, which guide more experiments, which help to modify the existing theories.
    In Newton’s case, some of the observations and experiments were recorded by Galileo, others by Kepler. In each case, the cycle of observation, theory, test-against-new-observations was repeated until the investigators achieved a complete understanding of the phenomenon being studied. Newton, as we pointed out, incorporated these understandings into his sweeping theory of motion, and then his new theory was used to make many predictions like the projected reappearance of Halley’s comet. Only after many such tests was the theory accepted by scientists.
    The scientific method does not require researchers to be unbiased observers of nature. Scientists almost always have a theory in mind when they perform an experiment. But the method does require that scientists be willing to change their views about nature when the data demand it.
    Newton provided a model for the development of modern science in many ways. He was the first to use the scientific method, and he was the first to show that scientific theories can develop by incorporation rather than revolution.
    When Kepler published his laws of planetary motion, he swept aside the old ideas about the solar system. This was a revolutionary change—the old notions were seen to be wrong and were abandoned. When Newton published his work, however, he showed that all of Kepler’s laws could be derived from universal gravitation and the laws of motion. His work, then, incorporatesKepler’s and expands upon it, but does not invalidate it. In the same way, Newton was able to derive Galileo’s conclusions, in corporating them into the same theoretical framework that ac commodated the description of the planets. This has proved to be a common occurrence in science. When Albert Einstein produced the theory of general relativity, our current best theory of gravitation, it incorporated Newton, Kepler, and Galileo, and when some future theoretical physicist produces the final unified field theory, it will likely incorporate Einstein.
    Despite what you read in sensationalistic headlines, true revolutions are rare in mature sciences.
SCIENTISTS
    The universe seems far too complex to comprehend all at once, so the classic scientific approach is to examine well-defined pieces of our surroundings, one at a time. The universe can be divided into an infinite number of “systems,” which are nothing more than parcels of matter and energy Each parcel, which can contain almost anything from a single spinning subatomic particle to an entire galaxy, is fair game for scientific study. Astronomers probe stars and the solar system. Chemists investigate systems containing carefully selected groups of atoms. Geologists study minerals or mountain ranges. Biologists