READING #2



 

Aristotle and Geocentric Cosmology

Chris Impey

https://www.teachastronomy.com/textbook/Early-Astronomy/Aristotle-and-Geocentric-Cosmology/

 

[1] The earliest Greek thinkers developed the tools of geometry, allowing them to distinguish between apparent size and true size. These tools were used to determine the Earth's place in the universe. Aristotle (384-322 B.C.) was the most famous and influential Greek philosopher. He founded a school at Lyceum, near Athens, with a library, zoo, and lavish research equipment bought by his one-time pupil, Alexander the Great, who ruled Greece and conquered much of the Mediterranean world. Aristotle applied his prodigious brain to many subjects. He developed the rules of logic that are the basis of the scientific method. He wrote books on botany, anatomy, economics, politics, and meteorology. He is also responsible for a cosmological model that lasted for 2,000 years, even though it proved to be wrong!

 

[2] Aristotle and his colleagues made few new observations. In fact, they were painfully aware of the limitations of the human senses. They believed that the universe could be understood by the power of reason alone. This is truly audacious. We can see how far it is from the old idea that humans are subject to capricious and supernatural forces. The goal of these philosophers was to unify the diversity of the natural world with a few elegant ideas.

 

[3] For example, Democritus imagined the process of dividing a grain of sand in half again and again. He supposed that this could not go on forever and that there must be a must be a tiny indivisible unit of matter, much smaller than the eye could see. This is the idea of an atom. Empedocles imagined that nature was composed of only four primordial substances: earth, water, fire, and air. He proposed that all the material in the world is made of combinations of these four substances. This is the idea of elements. The Greeks did not have the tools to understand the microscopic world of the atom, but in their applications of logic and their search for simplicity they came up with some strikingly modern ideas.

 

[4] The earliest Greek thinkers developed the tools of geometry, allowing them to distinguish between apparent size and true size. These tools were used to determine the Earth's place in the universe. Aristotle (384-322 B.C.) was the most famous and influential Greek philosopher. He founded a school at Lyceum, near Athens, with a library, zoo, and lavish research equipment bought by his one-time pupil, Alexander the Great, who ruled Greece and conquered much of the Mediterranean world. Aristotle applied his prodigious brain to many subjects. He developed the rules of logic that are the basis of the scientific method. He wrote books on botany, anatomy, economics, politics, and meteorology. He is also responsible for a cosmological model that lasted for 2,000 years, even though it proved to be wrong!

 

[5] Aristotle and his colleagues made few new observations. In fact, they were painfully aware of the limitations of the human senses. They believed that the universe could be understood by the power of reason alone. This is truly audacious. We can see how far it is from the old idea that humans are subject to capricious and supernatural forces. The goal of these philosophers was to unify the diversity of the natural world with a few elegant ideas.

 

[6] For example, Democritus imagined the process of dividing a grain of sand in half again and again. He supposed that this could not go on forever and that there must be a must be a tiny indivisible unit of matter, much smaller than the eye could see. This is the idea of an atom. Empedocles imagined that nature was composed of only four primordial substances: earth, water, fire, and air. He proposed that all the material in the world is made of combinations of these four substances. This is the idea of elements. The Greeks did not have the tools to understand the microscopic world of the atom, but in their applications of logic and their search for simplicity they came up with some strikingly modern ideas.

 

[7] An alternative view came from Aristarchus (310-250 B.C.), who lived on the island of Samos off the coast of present-day Turkey. Living in the time just after Aristotle, he boldly proposed that the Earth and the planets orbited the Sun. This is a heliocentric cosmology. Few of his writings survive, but we have descriptions from other Greek authors. Think of the irony that Aristarchus was measuring the relative distances of a spherical Earth, Moon, and Sun, yet 1,000 years later, many Dark Age citizens of Europe still thought that the Earth was flat! This raises an important point. Why, in the history of science, do the correct ideas not always prevail? Usually, it has to do with a lack of compelling evidence. Aristarchus' followers couldn't prove that his hypothesis of an orbiting Earth was correct. Aristotle's followers couldn't prove that the Earth stood still. Aristotle argued that if Earth was really rushing through space, we should be able to detect its motion. This was considered a strong argument.

 

[8] We can recognize a powerful psychological reason for favoring a geocentric cosmology. Humans are intelligent enough to consider our place in the universe. The Greek philosophers were convinced that humans were the pinnacle of creation and therefore must be at the center of the universe. It was unthinkable for them to relegate the Earth to just another object flying through space. There is a natural resistance to displacing the Earth in its importance in the scheme of things. The discovery of the Earth's true place in a vast universe is a story that has unfolded throughout the history of astronomy.

 


 

Aristotle  (1955)

A. E. Taylor

Chapter III: First Philosophy ─ excerpts

 

[1] First Philosophy is defined by Aristotle as a "science which considers What Is simply in its character of Being, and the properties which it has as such." That there is, or ought to be, such a science is urged on the ground that every "special" science deals only with some restricted department of what is, and thus considers its subject-matter not universally in its character of being, or being real, but as determined by some more special condition. Thus, First Philosophy, the science which attempts to discover the most ultimate reasons of, or grounds for, the character of things in general cannot be identified with any of the "departmental" sciences. The same consideration explains why it is "First Philosophy" which has to disentangle the "principles" of the various sciences and defend them by dialectic against those who impugn them. It is no part of the duty of a geometer or a physicist to deal with objections to such universal principles of reasoning as the law of contradiction. They may safely assume such principles; if they are attacked, it is not by specifically geometrical or physical considerations that they can be defended. Even the " principles of the special sciences " have not to be examined and defended by the special sciences. They are the starting-points of the sciences which employ them; these sciences are therefore justified in requiring that they shall be admitted as a condition of geometrical, or physical, or biological demonstrations. If they are called in question, the defense of them is the business of logic.

 

[2] First Philosophy, then, is the study of "What Is simply as such," the universal principles of structure without which there could be no ordered system of knowable objects. But the word " is " has more than one sense. There are as many modes of being as there are types of predication. " Substances," men, horses, and the like, have their own specific mode of being— they are things; qualities, such as green or sweet, have a different mode of being— they are not things, but "affections" or "attributes" of things. Actions, again, such as building, killing, are neither things nor yet "affections" of things; their mode of being is that they are processes which produce or destroy things. First Philosophy is concerned with the general character of all these modes of being, but it is especially concerned with that mode of being which belongs to substances. For this is the most primary of all modes of being. We had to introduce a reference to it in our attempt to say what the mode of being of qualities and actions is, and it would have been the same had our illustrations been drawn from any other "categories." Hence the central and special problem of First Philosophy is to analyses the notion of substance and to show the causes of the existence of substances.

 

[3] Next, we have to note that the word "substance" itself has two senses. When we spoke of substance as one of the categories we were using it in a secondary sense. We meant by substances "horse," "mail," and the rest of the "real kinds" which we find in Nature, and try to reproduce in a scientific classification. In this sense of the word "substances" continuous advance towards the actual embodiment of a Form, or law of organization, in a Matter having the latent potentiality of developing along those special lines. When Aristotle is speaking most strictly he distinguishes the process by which a Form is realized, which he calls Energeia, from the manifestation of the realized Form, calling the latter Entelechy (literally "finished " or " completed " condition). Often, however, he uses the word Energeia more loosely for the actual manifestation of the Form itself, and in this he is followed by the scholastic writers, who render Energeia by actus or actus purus.

 

[4] One presupposition of this process must be specially noted. It is not an unending process of development of unrealized capacities, but always has an End in the perfectly simple sense of a last stage. We see this best in the case of growth. The acorn grows into the sapling and the sapling into the oak, but there is nothing related to the oak as the oak is to the sapling. The oak does not grow into something else. The process of development from potential to actual in this special case comes to an end with the emergence of the mature oak. In the organic world the end or last state is recognized by the fact that the organism can now exercise the power of reproducing its like. This tendency of organic process to culminate in a last stage of complete maturity is the key to the treatment of the problem of the "true end" of life in Aristotle's Ethics.

 

[5] The Four Causes.—The conception of the world involved in these antitheses of Form and Matter, Potential and Actual, finds its fullest expression in Aristotle's doctrine of the Four Causes or conditions of the production of things. This doctrine is looked on by Aristotle as the final solution of the problem which had always been the central one for Greek philosophy: What are the causes of the world-order? All the previous philosophies he regards as inadequate attempts to. formulate the answer to this question which is only given completely by his own system. Hence the doctrine requires to be stated with some fullness. We may best approach it by starting from the literal meaning of the Greek terms aitia, which Aristotle uses to convey the notion of cause. Aition is properly an adjective used as a noun, and means "that on which the legal responsibility for a given state of affairs can be laid."

 

[6] Similarly aitia, the substantive, means the " credit " for good or bad, the legal "responsibility," for an act. Now when we ask, " what is responsible for the fact that such and such a state of things now exists?" there are four partial answers which may be given, and each of these corresponds to one of the "causes." A complete answer requires the enumeration of them all. We may mention

(1) the smatter or material cause of the thing,

(2) the law according to which it has grown or developed, the form or formal cause,

(3) the agent with whose initial impulse the development began— the "starting-point of the process," or, as the later Aristotelians call it, the efficient cause,

(4) the completed result of the whole process, which is present in the case of human manufacture as a preconceived idea determining the maker's whole method of handling his material, and in organic development in Nature as implied in and determining the successive stages of growth— the end or final cause.

 


Chapter IV: Physics ─ excerpts

 

[7] There is no part of Aristotle's system which has been more carefully thought out than his Physics; at the same time, it is almost wholly on account of his physical doctrines that his long ascendancy over thought is so much to be regretted. Aristotle's qualifications as a man of science have been much overrated. In one department, that of descriptive natural history, he shows himself a master of minute and careful observation who could obtain unqualified praise from so great a naturalist as Darwin. But in Astronomy and Physics proper his inferiority in mathematical thinking and his dislike for mechanical ways of explaining facts put him at a great dis-advantage, as compared with Plato and Plato's Pythagorean friends. Thus his authority was for centuries one of the chief influences which prevented the development of Astronomy on right lines. Plato had himself both taught the mobility of the earth and denied correctly that the earth is at the center of the universe, and the " Copernican" hypothesis in Astronomy probably originated in the Academy. Aristotle, however, insists on the central position of the earth, and violently attacks Plato for believing in its motion.

 

[8] Even in the biological sciences Aristotle shows an unfortunate proneness to disregard established fact when it conflicts with the theories for which he has a personal liking. Thus, though the importance of the brain as the central organ of the sensory-motor system had been discovered in the late sixth or early fifth century by the physician Alcmaeon of Crotona, and taught by the great Hippocrates in the fifth and by Plato in the fourth century, Aristotle's prejudices in favor of the doctrines of a different school of biologists led him to revert to the view that it is the heart which is the center of what we now call the "nervous system."

 

[9] It is mainly on account of these reactionary scientific views that he was attacked in the early seventeenth century by writers like our own Francis Bacon, who found in veneration for Aristotle one of the chief hindrances to the free development of natural science. The same complaints had been made long before by critics belonging to the Platonic Academy. It is a Platonist of the time of Marcus Aurelius who sums up a vigorous attack on the Aristotelian astronomy by the remark that Aristotle never understood that the true task of the physicist is not to prescribe laws to Nature, but to learn from observation of the facts what the laws followed by Nature are.

 

[10] In determining the scope of Physics, we have to begin by considering what is the special characteristic of things produced by nature as contrasted with those that are produced by “art.” The obvious distinction, intimate by the very etymology of the word “Nature” (physis, connected with the concept of growing, of being born; “what is by nature” is born and grows, whereas what is the result of artifice is made. Hence Nature may be defined as the totality of things which have a source of motion internal to themselves. Nature comprises all beings capable of spontaneous change. Whatever you do does not change at all, or only changes in consequence of external influences, is excluded from Aristotle’s concept of Nature.

 

[11] As the fundamental fact everywhere present it Nature is “change, process, and motion.” Such motion requires space through which to move and time to move in, therefore the doctrine of space and time also forms a part of Aristotle’s conception of Physics. Aristotle knows nothing of the modern questions whether space and time are “real” or only “phenomenal,” whether they are “objective” or “subjective.” Just as he simply assumes that bodies are things that really exist, whether we happen to perceive them or not, so he assumes that the space and time in which they move are real features of the world that does not depend for its existence on our perceiving it.

 

[12] His treatment of space is singularly naïve. He conceives it as a sort of vessel, into which you can pour different liquids. Just as the same pot may hold first wine and then water, so, if you can say, “there was water here, but now there is air here,” this implies the existence of a receptacle which once held water, but now holds air. Hence the jungle pot may be called “a place that should be carried about.” Hence the “place” of a theme may be defined as the boundary, or inner surface, of the body which immediately surrounds the thing. It follows from this that there can be no empty space.

 

[13] In the last resort, “absolute space” is the actual surface of the outermost “heaven” which contains everything else in itself, but is not contained in any remoter body. Thus all things whatever our “in” this heaven, which itself is not “in” anything else. Thinking along these lines, Aristotle held that this outermost heaven must be a limited distance from us. Actual space is thus finite the sense that the volume of the universe could be expressed as a finite number of cubic miles or yards, though, since it must be “continuous,” it is infinitely divisible.

 

[14] His treatment of time is more thoughtful. Time is inseparably connected with movement or change. We only perceive that time has elapsed when we perceive the changes occurred. But time is not the same as change. For change is of different and incommensurate kinds, change of place, change of color, etc.  

 

The Continuous Motion and the “Spheres.”

[15] The continuous world-process depends upon the continuous movement set up in the universe as a whole by the presence of an everlasting and unchangeable “First Mover”─ God. From the self-sameness of God, it follows that this most universal of movement must be absolutely uniform. As the source of this movement is One, and the object moved is also one─ that is, the compass of “heaven,” the movement of the First Moved─ was immediately stimulated to motion by God’s presence to it, must be mechanically simple.

 

[16] Aristotle held, mistakenly, that there are two forms of movement which are simple and beyond analysis, motion in a straight line, and circular motion, or rotation, around an axis. He decides that the primary unbroken movement must be the rotation of the First Moved─ that is, the heaven containing the fixed stars around its axis. This is the only movement which could go on forever at a uniform rate and in the same sense. Starting with the conviction that the Earth is at rest at the center of the universe, he proceeds to account for the alternation of day and night as the effect of such a revolution of the whole universe around an axis passing through the center of the earth.