Aristotles Conception of the Universe

The great philosopher Aristotle (384-322 B.C.) adopted the homocentric model of the universe and thoroughly integrated it into his philosophical system, showing its relationship to physics and metaphysics. (Metaphysics is that branch of philosophy that deals with the nature of reality.) He considered the universe as being spherical in shape and divided into two worlds, the astronomical (or heavenly) world and the sublunar world. The sublunar world was made up of four prime substances earth,...

Appearance of the Heavens

Kinetic Energy Imagas

If a time exposure photograph of the night sky is taken over a period of a few hours, the result will be as shown in Fig. 2.3. During the time that the camera shutter is open, the positions of the various stars in the sky change, the paths of their apparent motions being traced by arc-like streaks, just as photographs of a city street at night show streaks of light from the headlights of passing automobiles. If the camera shutter is left open for 24 hours (and if somehow the Sun could be turned...

Ptolemys Refined Geocentric Model

These modifications culminated some 1800 years ago, about the year 150, when the Hellenistic astronomer Claudius Ptolemy, in Alexandria, Egypt, published an extensive treatise, The Great Syntaxis, on the calculations of the motions of the Sun, Moon, and planets. With the decline of secular learning accompanying the collapse of the Roman Empire, this work was temporarily lost to the Western world. It was translated into Arabic, however, and eventually reintroduced into Europe under the title of...

Greek Science and Numerology

According to tradition, the recognition of mathematics as a subject worthy of study in its own right, regardless of its utility for practical matters, was achieved some 2600 years ago by Thales, who lived on the Asiatic coast of the Aegean Sea. Some time later the followers of Pythagoras (who lived in one of the Greek colonies that had been established in Italy) proclaimed that the entire universe was governed by numbers. The numbers they referred to were integers (whole numbers) or ratios of...

Newtonian Mechanics

We are now ready to discuss the contributions of Isaac Newton (1642-1727) to the science of mechanics. His work presents fairly complete answers to the questions first raised by Aristotle, which have been the subject of this chapter. In fact, Newton's work represents one of the greatest contributions made by an individual to human understanding of the physical universe. It is difficult to overestimate the impact of his work on Western thought, as we will discuss further below. He developed a...

Pythagorean Mysticism

Both Tycho Brahe and Galileo Galilei used a relatively modern approach to scientific problems. Brahe insisted on the importance of systematic, extensive, and accurate collection of data. Galileo was not content simply to make observations, but recognized the necessity to alter experimental conditions in order to eliminate extraneous factors. Both men were very rational and logical in their approach to their work. Copernicus, on the other hand, and Kepler (of whom more will be said later) even...

Competing Models of the Universe

Many ancient civilizations developed models of the universe. The Egyptians, for example, believed the universe to be like a long rectangular box, with the Earth being a slightly concave floor at the bottom of the box and the sky being a slightly arched iron ceiling from which lamps were hung. There were four mountain peaks supporting the ceiling, and they were connected by ranges of mountains, behind which flowed a great river. The Sun was a god who traveled in a boat along this river and, of...