Robert Hatch

To understand these phenomena it is wise to begin with the simplest possible cases, and proceed gradually to the more complicated ones. Consider a body at rest, where there is no motion at all. To change the position of such a body it is necessary to exert some influence upon it, to push it or lift it, or let other bodies, such as horses or steam engines, act upon it. Our intuitive idea is that motion is connected with the acts of pushing, lifting or pulling. Repeated experience would make us risk the further statement that we must push harder if we wish to move the body faster. It seems natural to conclude that the stronger the action exerted on a body , the greater will be its speed. A four-horse carriage goes faster than a carriage drawn by only two horses. Intuition thus tells us that speed is essentially connected with action

It is a familiar fact to readers of detective fiction that a false clew muddles the story and postpones the solution. The method of reasoning dictated by intuition was wrong and led to false ideas of motion which were held for centuries. Aristotle’s great authority throughout Europe was perhaps the chief reason for the long belief in this intuitive idea. We read in the Mechanics, for two thousand years attributed to him:

The moving body comes to a standstill when the force which pushes it along can no longer so act as to push it.

The discovery and use of scientific reasoning by Galileo was one of the most important achievements in the history of human thought, and marks the real beginning of physics. This discovery taught us that intuitive conclusions based on immediate observations are not always to be trusted, for they sometimes lead to the wrong clues.

But where does intuition go wrong? Can it possibly be wrong to say that a carriage drawn by four horses must travel faster than one drawn by only two?

Let us examine the fundamental facts of motion more closely, starting with simple everyday experiences familiar to mankind since the beginning of civilization and gained in the hard struggle for existence.

Suppose that someone going along a level road with a pushcart suddenly stops pushing. The cart will go on moving for a short distance before coming to rest. We ask how is it possible to increase this distance? There are various ways such as oiling the wheels and making the road very smooth. The more easily the wheels turn, and the smoother the road, the longer the cart will go on moving. And just what has been done by the oiling and smoothing? Only this: the external influences have been diminished, both in the wheels and between the wheels and the road. This is already a theoretical interpretation of the observable evidence, and interpretation which is, in fact, arbitrary. One significant step further and we shall have the right clue. Imagine a road perfectly smooth, and wheels with no friction at all. Then there would be nothing to stop the cart, so that it would run forever. This conclusion is reached only by thinking of an idealized experiment, which can never be actually performed, since it is impossible to eliminate all external influences. The idealized experiment shows the clue which really formed the foundation of the mechanics of motion.

Comparing the two methods of approaching the problem we can say: the intuitive idea is–the greater the action the greater the velocity. Thus the velocity shows whether or not external forces are acting on a body. The new clue found by Galileo is: if a body is neither pushed, pulled, nor acted one any other way, or, more briefly, if no external forces act on a body, it moves uniformly, that is always with the same velocity along a straight in. Thus, the velocity does not show whether or not external forces are acting on a body. Galileo’s conclusion, the correct one, was formulated a generation later by Newton as the law of inertia. It is usually the first thing about physics which we learn by heart in school, and some of us my remember it:

Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon.

We have seen that this law of inertia cannot be derived directly from experiment, but only by speculative thinking consistent with observation. The idealized experiment can never be actually performed, although it leads to a profound understanding of real experiments.

From the variety of complex motions in the worlds around us we choose as our first example uniform motion. This is the simplest, because there are no external forced acting. Uniform motion can, however, never be realized; a stone thrown from a tower, a can pushed along a road can never move absolutely uniformly because we cannot eliminate the influence of external forces.

Aristotle and a reporter are seated on two chairs. Nearby stands a table with a couple of books on it.

Reporter: Professor Aristotle, it is a great honor for me that you have agreed to this interview. The world knows what a great philosopher and scientist you are, and we hope in this interview to learn something about your view of science and about the physics you have taught your disciples.

Aristotle: Thank you. That is very nice of you to be interested in my science. I will be more than happy to talk to you about sciences and physics, for all knowledge is a waste unless it is shared with others.

R: Sir, before we begin, could you tell us something about your personal life? About your parents and education, for example?

A: Frankly, I don’t remember much about my parents. After all, they both died while I was still a young boy. All I know is that my father was the personal physician of King Amyntas II of Macedon who, as you may remember, was the grandfather of the great Alexander.

R: I see…And you were also in touch with Alexander the Great, if I am not mistaken?

A: That is correct. In fact, for some years I was his tutor. And Alexander used  to send me the flora of many countries where he traveled during his conquests, for me to study.

R: Very interesting. And about your own education?

A: Well, I went to Athens when I was about 17 to study at the famous Academy of Plato. And I was part of the Academy till about my 37th year, when my Master Plato died. I left Athens then, but I returned after a decade or so. Now I began to teach in Athens. After several years, about twelve I think, during which I was honored and respected as a eminent scholar. I later left the place in voluntary exile,, and so it is that you see me here.

R: And what about your marriage, sir?

A: Young man, why should people be interested in the personal and private lives of so-called famous people? I am afraid I will not answer that question except to inform you that I married the daughter of the Aegean ruler hermias. Now let us pass on to matters more significant.

R: That is a good idea. Well, sir, tell me something about physics.

A: That I shall, very happily. But first do you know what is the meaning of the word physics?

R: I’m afraid, not precisely, sir.

A: In my language, Greek, physics means nature. And nature is that which grows and evolves. It is a dynamical process that is working towards an end.

R: Could you give me an example, sir?

A: Not one but many. The builder builds a house for people to live in; the doctor practices medicine to cure people; spiders, ants roots leaves, all have their function for specific goals. From the most sublime heavenly bodies to the most ordinary stones on the ground, everything has an ultimate end to fulfill.

R: I see . So things behave the way they do because they are striving to reach their respective goals.

A: That is correct. And this is what I call teleological behavior purpose-oriented behavior.

R: Does it mean that the cause of everything is to be found in its goad?

A: Yes and no. Because the word cause by itself has no meaning. There are, in fact, four different kinds of causes.

R: How is that?

A: Let me explain with an example. Consider this table here. What is the cause of this table?

R: I don’t know. Maybe somebody put it there.

A: True. But another person may say, wood is the cause of the table. Yet another may say it is the form of the wood which makes it a table. Yet another person may say it is the carpenter who made it a table. And, of course, as you say, the cause of the table is that somebody put it there for placing the books on it, maybe, that is with a well defined purpose. So you see, you can speak of the material cause of the table–the wood; the formal cause–the table form; the efficient cause; the carpenter, without whose efforts and expertise there could be no table; and finally, the final cause–the purpose to be served by the table.

R: So when we speak of the cause of something we must refer to which particular kind of cause we have in mind.

A: That is correct. Young man, you do learn things fast.

R: Thank you, sir. It is interesting that everything in the world has a well defined purpose. Does it mean that nature acts in a conscious way?

A: Not necessarily. The ends which natural objects and phenomena seek are within themselves, their inherent properties, as it were. It is true that in works of man the final cause is a conscious effort. In biological entities it is obvious also, but not due to any conscious effort. Thus it is clear that the purpose of the seed is to grow into another plant. But with the inanimate world this may not be always so clear.

R: Could you give me an example of some aspect of the physical world where there is a final cause?

A: Well, why do you think there is light?

R: I’m afraid I don’t know, sir.

A: Well, let me put it this way. What would happen if there was no light?

R: It would be dark.

A: Very good. Now you are already throwing some light on the subject. Now tell me, what would happen if there was total darkness?

R: I’m afraid I don’t see…

A: Correct. That is exactly it. If there is total darkness, you cannot see anything. Now can you tell me why there is light.

R: So that ia can see! Why didn’t I see that before?

A: Because, my friend, there was darkness inside of you. Now your mind has found light and it sees the cause. And in rejoices. For happy is the man who can see the cause of things.

R: Sir, you said that my mind saw the light. How does the mind see?

A: Oh, the mind can see in many ways , and its principal instruments in this is the logical faculty. It is by clearly understanding the powers and principles of logical thinking that we can hope to understand the world in which we live.

R: Sir, could you please tell me something about matter and motion? I read somewhere that these are important topics in you physics.

A: Of course they are. Some philosophers have simple answers to such profound questions. If you ask them, “What is matter?” they say, “No matter.” And to the question, “What is mind?” their answer is, “Never mind.” But I use this only at cocktail parties while drinking some olive liquor or chewing dates. But seriously, all matter is made up of four elements: Earth, Water, Air, and Fire, and their combinations.

R: You mean, all matter, except water, air, etc.

A: No, no, even water contains small quantities of earth, air and fire.

R: But how do we know that?

A: Because I have observed it, my friend. You see, many people think that I am only a speculative philosopher. They do not know that I have made many careful observation in my life. I have studied the embryos of chickens. I have classified plants and animals into different species, I have discovered that dolphins, though they live in water, give birth to their young like mammals. Well, to come to your question, I have found that whenever you boil some water, at the bottom of the vessel some earthy residue is always left over.

R: Very interesting. But what makes the boiling water leave the vessel and escape out?

A: Good question, very good question. By the way, do you know what is usually described as a good question?

R: I’m afraid not, sir.

A: One for which the teacher knows the answer. Well, coming back to the four elements, we must understand the fire and air are light, whereas earth and water are heavy. Hence the natural place for fire and air is up, and they tend to move in the upward direction. The natural place for earth and water is down. Hence…

R: They tend to move in the downward direction.

A: You see how simple logic is? Now consider the vessel of water. When I heat it, I am giving the water more of the fire element. Hence it tends to go upwards. It is precisely for the same reason that when you throw a stone upwards it falls back to the ground. The ground is the natural place f or earth which is what the stone is primarily made up of.

R: I see, everything seems to be falling into place.

A: That is a very intelligent remark. Indeed, my theory is the origin of that expression

R: And what about motion, Professor Aristotle. What is your theory of motion?

A: Before I answer that question I must explain that there are essentially two levels of physical reality. Here on our earth, in the region below the moon. This is the sublunary world. Here everything changes and decays. Nothing is the same for ever. Then there is the world above,m the heavens. There everything is perfect and incorruptible. Nothing ever changes or decays.

R: Is matter in the heavens also made up of the four elements?

A: No, not at all. Heavenly matter consists of an entirely different kind of element. This is the aether. Anaxagons has already suggested over a century ago that in the beginning everything was occupied by air and aether.

R: But where does this term “aether” come from?

A: Before I answer that, let me come back to you question about heavenly matter, this is endowed with permanent and perfect motion.

R: But what do you mean by perfect motion?

A: Well, you tell me. What is the perfect geometrical form?

R: The circle?

A: Quite right. Therefore it is that all heavenly bodies move a circular paths, they will do so for ever and for ever.

R: And here on earth?

A: Here motion, natural motion, is always along straight lines, and it will always come to a stop. In the heavens we have geometrical perfection. Indeed, it is because the sphere is the perfect geometrical form that the universe itself is spherical, and the universe is finite because it has a center: our earth.

R: Sir, I find all this very fascinating. Why didn’t I think of all this before?

A: Young man, one doesn’t think of things like this all of a sudden. It requires years of patient study and reflection. And occasionally you must observe things. Even matter which appears to be moving on and on, like a rolling stone from the top of a mountain, will eventually come to a stop. And we can conclude many things from this. The human mind is a truly marvelous thing. By using it properly we can learn a lot.

R: Sir, you said that natural motion in the sublunary world is always along a straight line. But what about a stone that is thrown at an angle to the horizontal? It seems to be moving along a curved path.

A: Aha! That’s what I call unnatural or violent motion. Such motions do exist as monsters and ill-formed creatures exist in the same world where normal animals live. But violent motion will also soon come to a stop.

R: Sir, what keeps bodies in motion?

A: I will answer your question with a simple experiment. You see this table, don’t you? Why?

R: Because there is light?

A: No, you have missed the point of my physics. You must always try to answer to question, “Why?” by looking for a purpose. The table is there because it can now be used for an experiment. Well, is the table at rest or in motion?

R: It is at rest.

A: Good. I admire your powers of observations. Now, how can you make it move?

R: By pushing it , I suppose.

A: Good. Push it and see what happens.

R: It moves!

A: What can you conclude?

R: You need to push a body to move it.

A: Or pull it.

R: Yes, a push or a pull is necessary for moving.

A: Now what happened when you stopped pushing?

R: The table stopped moving

A: Excellent. So can there be motion without push or pull?

R: Apparently not. Things move only so long as they are pushed or pulled.

A: Young man, you are quick. I wish all my students were like you.

R: Thank you, sir. But I find all this very exciting.

A: I am glad to hear that. You can learn nothing if you don’t get excited about it. And one cannot be enthusiastic and unhappy at the same time.

R: Professor Aristotle, you make me want to learn more and more. Now I am impatient to find out the answers to more questions.

A: Then you are on the right track. For curiosity is what keeps science going and growing. Somebody said it is also the mother of window shades.

R: (after a gentle laughter) Sir, I have one more question concerning motion. If a light stone and a heavy stone are dropped from the same height which of them will reach the ground first?

A: Let us see if we can answer this question together. To begin with, which of the stones has more earth in it?

R: The heavier one, no doubt.

A: Therefore, which of the stones will have a greater tendency to reach its natural position, namely the ground?

R: The heavier one.

A: Hence, which will reach the ground first?

R: The heavier one.

A: There you are. You have answered the question yourself but the simple application of logic. That, my friend, is the power of my system. By pure logic we can learn so much about the world around us.

R: Sir, the world owes you so much for the advancement of human knowledge. But what, in your opinion is knowledge?

A: My friend, that is an interesting question, but one that will require a great deal of time to answer. I will simply say this: When we know the cause on which a fact depends as the cause of the fact, and that the fact could not be otherwise, then we have knowledge of the fact. Such knowledge can be produced by the logical process of syllogism. In a syllogism you have premises and conclusions which follow from them. The premises themselves may be definitions, hypotheses, or axioms.

R: Sir, now you are getting too technical.

A: I was afraid of that. In any case, if you really wish to know more of these matters you should read my books.

R: Which are…

A: Which are many. But in particular you may wish to read my treatise on Physics and on the Heavens. In the first of these worlds I have discussed the principles of natural sciences, explanation in that science, motion and the infinite, place time, and void, classification of motions, continuity of motion, series of motions and eternity of motion. These are profound topics, and in this conversation I have barely touched on these ideas.

R: Sir, I thank you immensely for your time. I will try to read more of your works to understand your world view better.