16 Theory of knowledge

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1 THEORY OF KNOWLEDGE 16 Theory of knowledge The task is not to see what has never been seen before, but to think what has never been thought before about what you see everyday. Erwin Schrodinger Introduction In the Theory of knowledge course you will be asked to analyse and discuss the different ways of knowing and areas of knowledge. Physics is one of the areas of knowledge that you have been introduced to, but what makes it different from other subjects such as art or languages? In this chapter we will look at the way that you gain knowledge in physics, so that you can compare this with the ways of knowing in your other subjects. What is the role of imagination in physics? Can physics be beautiful? Is physics all logic and maths or is there a place for feelings? Are these particle physics equations beautiful? Can you use your imagination to work out what they represent? Is this sunset more beautiful to people who understand Einstein s theory of general relativity? Is this what an atom looks like? If we knew what it was we were doing, it would not be called research, would it? Albert Einstein The secret of genius is to carry the spirit of childhood into maturity. T. H. Huxley 550 M16_IBPH_SB_HIGGLB_4426_U16.indd /6/10 13:49:43

2 The scientific method The scientific method is the way that physicists work to invent new theories and to discover new laws, and it is also the way that you will have been working in the practical program. There are actually many variations to this process and many exceptions, where new theories have come about without following any strict procedure. However, to make things simple, we will consider just one four-step version. 1 Observation Physics is all about making models to help us understand the universe. Before we can make a model, we must observe what is happening. In physics, the observations are often of the form How does one thing affect another? Galileo makes observations using a telescope. 2 Hypothesis Having made an observation, the next step is to use your knowledge to develop an idea of what is causing the event you have observed. What factors cause this thing to happen and what factors are not involved? Having made a hypothesis, it is possible to predict the outcome of a change in one of the variables. 3 Experiment All experiments are conducted to test hypotheses. The experiment is designed to test the hypothesis. It is important to change only the quantity that you think is responsible for the event you must keep the other variables constant. If the experiment does not prove the hypothesis then you must go back to the observations and think of a new one (this is often helped by the outcome of the experiment). If the experiment supports the hypothesis then you can go on to the next step. Franklin s lightning experiment. If Franklin had had a full understanding of electricity, he wouldn t have done this. He was lucky that the kite did not get struck by lightning, and in fact many people died repeating this experiment. 4 Theory If experiment supports the hypothesis, you can make a theory that relates the variables involved. A theory is a set of related statements that can be used to make predictions and explain observations. 551 M16_IBPH_SB_HIGGLB_4426_U16.indd /6/10 13:49:47

3 THEORY OF KNOWLEDGE Example the simple pendulum Observation A student watches a simple pendulum swinging and wonders what factors affect the frequency of the swing. Hypothesis The student hadn t studied the motion of the pendulum so used his intuition to come up with an idea related to the mass of the bob. He thought that since the bigger mass had more weight, then the force pulling it down would be greater, causing it to swing faster. So the hypothesis was that the frequency of the bob was proportional to the mass of the bob. Experiment An experiment was carried out measuring the frequency of bobs with different mass. The length of the string, the height of release and all other variables were kept constant. The result showed that there was no change; the hypothesis was therefore wrong. Back to observations On observing the pendulum further, the student noticed that if its length were increased, it appeared to swing more slowly. This led to a second hypothesis and the process continued. Theories must be falsifiable For a theory to be accepted it must be possible to think of a way that it can be proved wrong. For example: Newton s gravitational theory would be proved wrong if an object with mass was seen to be repelled from the Earth. However, the theory that the Earth is inhabited by invisible creatures with eyes on each finger is not falsifiable since you cannot see the creatures to tell if they have eyes on their fingers or not. Occam s razor A razor is a strange name for a principle. Its name arises because it states that a theory should not contain any unnecessary assumptions it should be shaved down to its bare essentials. This is the same as the KIS principle keep it simple. For example, a theory for gravitational force could be that there is a force between all masses that is proportional to the product of their mass and is caused by invisible creatures with very long arms. The last bit about the invisible creatures is unnecessary so can be cut out of the theory (using Occam s razor). There are children playing in the street who could solve some of my top problems in physics, because they have modes of sensory perception that I lost long ago. Robert Oppenheimer Just a theory If someone says The theory of special relativity is just a theory, what do they mean? The use of the word theory in the English language can cause some problems for scientists. The word is sometimes used to mean that something isn t based on fact. For instance, you could say that you have a theory as to why your friend was annoyed with you last night. In physics, a theory is based on strong experimental evidence. Serendipity Discoveries aren t always made by following a rigorous scientific method sometimes luck plays a part. Serendipity is the act of finding something when you were looking for something else. For example, someone could be looking for their car keys but find their sunglasses. There are some famous examples of this in physics. 552

4 Hans Christian Oersted discovered the relationship between electricity and magnetism when he noticed the needle of a compass moving, during a lecture on electric current. Arno A. Penzias and Robert Woodrow Wilson discovered radiation left over from the Big Bang, whilst measuring the microwave radiation from the Milky Way. They at first thought their big discovery was just annoying interference. These serendipitous discoveries were all made by people who had enough knowledge to know that they had found something interesting. If they weren t expert physicists, would they have realized that they had discovered something new? Previous knowledge When you do practical work for the IB diploma, is the principle behind what you are doing the same as that used by leading physicists working in research departments of universities around the world? What you are doing is using the knowledge learnt in class to develop your hypothesis. You should find out that, if you apply your knowledge correctly, your experiment will support your hypothesis. At the cutting edge of science, the scientists are developing new theories so the experiment is used to test the theory, not to test if they have applied accepted theory correctly. To find a new way of relating quantities requires imagination, but what you are being asked to do in your physics lab is to use accepted theory and not to use imagination. How can students trained to apply strict physical laws be expected to make imaginative new theories? Paradigm shifts Hans Christian Oersted experimenting with magnets and current after a chance observation. A paradigm is a set of rules that make up a theory that is accepted by the scientific community. Having completed this course, you will have accepted certain paradigms. We see and interpret the world by virtue of paradigms and theories. Newtonian mechanics is a paradigm we apply Newton s laws of motion to balls, electrons, planes and cars. The theory works well and is accepted by the scientific community. The way we treat almost everything as a particle is another paradigm. This paradigm is so entrenched in the way that we think that it is almost impossible to think of matter not being made of particles. How could you have a gas that was continuous? Before anyone thought of matter being made of particles, this wouldn t have been a problem, but now it is. To change your way of thinking requires a big leap of imagination, and this is called a paradigm shift. Throughout the development of physics there have been many paradigm shifts. Copernicus In 1543, when Copernicus suggested that the Sun was the centre of the solar system, it went against a theory that had been accepted for over a thousand years. Furthermore, it not only went against scientific theory it went against common sense, for how can we be going around the Sun when we are quite obviously standing still? It required a totally new way of thinking to accept this new idea. At the time the evidence was not strong enough to be convincing and the old paradigm remained. It was not until Galileo provided more evidence and later Newton developed an explanation, that the shift took place. 553

5 THEORY OF KNOWLEDGE Einstein s theory of relativity Before Einstein, it was accepted that time is the same everywhere, the length of a body is the same as measured by everyone and the mass of a body is constant. Einstein showed that time, length and mass all depend on the relative velocity of two observers. After this discovery it wasn t possible to carry on as if nothing had happened; what was required was a new way of thinking and a new set of laws. However, when a paradigm shift takes place, the old laws don t suddenly become obsolete they just obtain limits. Newtonian mechanics is still fine when relative velocities are much less than the speed of light, and that is why it is still included in physics courses such as this. The next paradigm shift Will there be another paradigm shift? Can physics advance without one? Because there have been paradigm shifts in the past, does that mean that there has to be another one to advance physics further? In 1900 Lord Kelvin famously said There is nothing new to be discovered in physics now, all that remains is more and more precise measurement. He was certainly wrong. Does that mean that if someone said the same thing today they d also be wrong? One problem is that, as students go through the process of education, they get entrenched in the ways of thinking of their teachers, so the leap in imagination to make that new paradigm shift becomes bigger and bigger as time goes on. Use of language In physics, we use language in a very precise way; every time a quantity is named, it is given a specific definition. For example velocity means one thing and one thing only, the rate of change of displacement. In normal use of language, words can mean more than one thing; this is often used in jokes, poems and literature but not in physics. Sometimes the other meanings of a word can lead to confusion. Potential energy sounds like a body could possibly have energy but it actually means the energy a body has owing to its position. Electron spin sounds like the electron is actually a little ball spinning; a spinning charge would indeed have the properties exhibited by the electron; however these properties do not arise because it s spinning. To get around this problem, physicists sometimes use words that can t be confused with other meanings, who would think that a charm quark was actually charming, for instance? The battleship and a bucket of water Can a battleship float in a bucket of water? To solve this problem, you use Archimedes principle that tells you that a body will float if it displaces it own weight of water. You might therefore conclude that the ship can t float in a bucket of water, because it has to displace (move out of the way) its own weight of water and there isn t that much water in the bucket. However, this is a misinterpretation of the theory. What Archimedes meant is that, when a boat is floating, if you filled the space in the water taken up by the boat with water, then it would be the same weight as the boat. This still might not make sense that s why physicists use so many diagrams. This demonstrates again how important it is to understand the language. 554

6 Opinions If you see a painting, read a book or watch the news on the television, you will probably formulate some opinion about it. In many subjects that you study you are actively encouraged to formulate opinions and discuss them in class. For example, you could think the painting here is beautiful or you could think that it is horrible. Either way is fine, because it s your opinion and you can have whatever opinion you like when it comes to such things. a) c) b) Can you have an opinion in physics? Is it OK to say that in your opinion Newton was wrong when he said that force was proportional to rate of change momentum and that you think that they are independent? In physics, opinions don t count for much, although they can sometimes be the beginning of the formulation of a testable hypothesis. Figure 16.1 a) Bucket with a bit of water. b) Large object floating in bucket. The bucket is now almost full because the object is taking the place of the water. The object displaces the water. c) Archimedes says that the weight of fluid displaced equals the weight of the object. So this amount of water will have the same weight as the object. Laws All truths are easy to understand once they are discovered; the point is to discover them. Galileo Galilei How much water do you need to float this huge oil tanker? In Physics we use the term law quite a lot; for example, Newton s laws of motion, the law of conservation of energy and Ohm s law. The laws are generalized descriptions of observations that are used to solve problems and make predictions. If we want to know what height a ball will reach when thrown upwards, then we can use the law of conservation of energy to find the answer. When you use a law to solve a problem, you have a solid foundation for your solution. If someone were to disagree with your solution then they are disagreeing not only with you, but the law (assuming you applied it correctly). Laws sometimes give easy answers to difficult problems. If someone comes to you with a design of a machine that is 100% efficient, you don t need to study the details, because you can simply apply the second law of thermodynamics and say it won t work. Universal laws Some of the laws in physics are called universal laws; for example, Newton s universal law of gravitation. A universal law applies to the whole universe, but it is possibly naïve (or arrogant) to think that we can write laws that apply to the whole universe, when we can only make measurements from one very small part of it. Today, scientists are more modest in their claims and accept that there are probably parts of the universe that do not behave in the same way as things in our solar system. 555

7 THEORY OF KNOWLEDGE Sense and perception Physics is based on observation and observations are made with our senses. This was certainly true hundreds of years ago but today, although the information finally arrives into our brain via our senses, the observation itself is often done via some instrument. Copernicus had difficulty convincing anyone about his theory that the planets orbited the Sun, because he didn t have any convincing observations. He had predicted that Venus would have phases like the Moon, but couldn t observe this. Galileo used the telescope to observe that Venus did indeed have phases like the Moon. At first, this was still not accepted, since people didn t trust the telescope they wanted to see it with their own eyes. Galaxy cluster MS The red part of this image is radio, the blue X-ray and the yellow is light. You could never see this. Seeing is believing? Deceptive pictures A camera operates on the same physical principle as the human eye. Visible light is reflected from an object and focused by a lens onto a screen. It is reasonable to think that a picture is a good record of what we see. Using digital technology, it is now possible to recreate pictures from light that we can t see. Is this seeing? Can we say that we have seen a distant galaxy when we look at a picture constructed from radio waves? Can we say that we have seen the face of a flea when the picture was constructed from the diffraction pattern of electrons? The face of a flea. Can you really say that this is what it looks like since you can never see it directly? Can you see a hidden face in this picture? Apparently those with physical brains take a long time. See below for a hint. During the IB physics course you will have been asked to make observations and devise research questions; is this easier when you have studied the topic already or when it s something totally new? When you already know what you are supposed to be looking for, it is often easier to get started. However, if you have no preconceived ideas, you might have more chance of spotting something new. Hint: look between 3 o clock and 5 o clock. 556 M16_IBPH_SB_HIGGLB_4426_U16.indd /6/10 13:49:55

8 The Moon illusion <Photo 1614> Have you ever noticed that the Moon looks bigger when it s close to the horizon? If you know some physics, you might have thought of an explanation. Maybe it s due to the refraction of the light by the atmosphere, or the elliptical orbit of the Moon causing it to sometimes be closer to the Earth. These theories would be based on the observation that you have made using your senses. However, if you were actually to measure the size of the Moon you d find that it doesn t change as it moves from overhead to the horizon; it s an illusion. Physical theories are based on measurement not perception. Imagination Have you made use of your imagination during this course? Maybe not, but it is important that physicists have imagination, as Einstein famously said; I am enough of an artist to draw freely upon my imagination. Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world. Without imagination, the huge leaps that have brought about the paradigm shifts in the way we perceive the world would never have been made. In learning basic physics, following rules tends to be emphasized more than using imagination, but at the cutting edge it is imagination that enables scientists to forge their way forward. Children use their imagination all the time when playing. What happens to this skill in later life? 557 M16_IBPH_SB_HIGGLB_4426_U16.indd /6/10 13:49:59

9 THEORY OF KNOWLEDGE Physics or intuition? One of the problems with studying physics is that we all live in the physical world and have all seen how bodies interact. We all know that if you drop something it falls to Earth and if you push someone on a swing they will move back and forth. These observations give us a feeling for what is going to happen in other instances; we call this feeling intuition, the ability to sense or know what is going to happen without reasoning. In physics, we create models to help give a reason for what is happening. This all works fine until intuition gives us a different answer to the laws of physics. Here s an example: Consider a metal bar floating in space, where the gravitational field strength is zero. If you apply two forces to the bar as shown in Figure 16.2, what happens? Intuition will probably tell you that the bar will rotate about point A. This is because if you do this yourself that is what will happen. However that answer is wrong. Let s now apply Newton s laws of motion to the problem. Newton s first law states that a body will remain at rest or with uniform motion in a straight line unless acted upon by an unbalanced force. The forces in this example are balanced, so the centre of mass of the bar (B) will not move. We can see however that the turning effect (torque) of these forces is not balanced, so the rod will turn. If the rod turns but point B doesn t move, then the rod must turn about B. And that is what happens. The reason for the difference in these two predictions is that this rod is not in a gravitational field. When we try to do this with a rod on Earth, there are other forces acting. Intuition was wrong; physics was right. The laws of physics can tell you what happens even if you can t do it or see it yourself. 100N A 100N Figure 16.2 What happens when the bar experiences these forces? Peer review One of the strengths of modern scientific practice is that every new discovery goes through a rigorous process of peer review. Before a theory is published, it is sent to other scientists working in the same field. They give feedback to the research team before the theory is published. In this way mistakes can be spotted and problems ironed out. It also gives the possibility for other groups working in the same field to think of experiments that could be conducted to prove the theory wrong. Scientists are continually looking for ways to prove theories wrong, so when a theory is accepted by the scientific community one can be sure that it has been rigorously tested. B It doesn t matter how beautiful your theory is, it doesn t matter how smart you are. If it doesn t agree with experiment, it s wrong. Richard Feynman There are many hypotheses in science which are wrong. That s perfectly all right; they re the aperture to finding out what s right. Carl Sagan The most exciting phrase to hear in science, the one that heralds new discoveries, is not Eureka! (I found it!) but That s funny... Isaac Asimov 558

10 Ethics and physics Ethics is the study of right and wrong. It is sometimes not easy to decide when a course of action is right or wrong, and in these cases, it is useful to have a moral code or set of guidelines to refer to. In physics, there are two areas where ethical considerations are important; 1 The way physicists work in relation to other physicists; for example, they shouldn t copy each other s work or make up data. 2 The way their actions affect society; for example, physicists shouldn t work on projects that will endanger human life. Whether a particular piece of research is ethical or not can be difficult to determine, especially when you do not know what the results of the experiment might lead to. Should Rutherford have performed his experiments in nuclear physics, since the discovery of the nucleus led to the discovery of the atom bomb? Can it be ethical to work in the weapons industry? Who should decide whether a piece of research is carried out, physicists or governments? If you left your body to science, would it be OK if it were used to test car seat belts? How about if it were used to test how far different types of bullets penetrate flesh? Is it ethical to spend billions to carry out an experiment to test someone s hypothesis? 559