Physics: A Window on the Universe

8 Aug 2011

Physics a Window on the Universe

Physics a Window on the Universe

What makes physics so exciting is that you will be involved in thinking about how the universe works and why the universe behaves as it does. When asked to de?ne science, Albert Einstein once replied, science is nothing more than re?nement of everyday thinking. If you substitute physics for science in Einsteins de?nition, just what is the re?nement he is referring to? Using the language of mathematics to construct models and theories, physics attempts to explain and predict interactions between matter and energy. In physics, the search for the nature of these relationships takes us from the submicroscopic structure of the atom to the super macroscopic structure of the universe. All endeavours in physics, however, have one thing in common; they all aim to formulate fundamental truths about the nature of the universe.
Your challenge will be to develop a decision making process for yourself that allows you to move from Einsteins everyday thinking to his re?nement of everyday thinking. This re?nement, the systematic process of gathering
data through observation, experimentation, organizing the data, and drawing conclusions, is often called scienti?c inquiry. The approach begins with the process of hypothesizing. A good scientist tries to ?nd evidence that is not supported by a model.
If contradictory evidence is found, the model was inadequate. Throughout the textbook, you will ?nd scienti?c
misconceptions highlighted in the margins. See if your current thinking involves some of these misconceptions. Then, by exploring physics through experimentation throughout the course, develop your own understanding.

How did our present understanding of the universe begin? What was the progress over the centuries before present time? The thinking that we know about started with Artistotle.

Two Models from Aristotle
Over 2300 years ago, two related models were used as the basis for explaining why objects fall and move as they do. Aristotle (384328 B.C.E.) used one model to account for the movement of objects on Earth, and a second model (see the diagram opposite) for the movement of stars and planets in the sky. We do not accept these models today as the best interpretation of movement of objects on Earth and in space. However, at the time they were very intelligent ways to explain these phenomena as Aristotle observed them.

Aristotle and Motion
The model for explaining movement on Earth was based on a view advanced by the Greeks, following Aristotles thinking. Aristotle accepted the view of Empedocles (492435 B.C.E.) that everything is made of only four elements or essences earth, water, air, and ?re. All objects were assumed to obey the same basic rules depending on the essences of which they were composed. Each essence had a natural place in the cosmic order. Earths position is at the bottom, above that is water, then air and ?re. According to this model, every object in the cosmos is composed of varous
amounts of these four elements. A stone is obviously earth. When it is dropped, a stone falls in an attempt to return to its rightful place in the order of things. Fire is the uppermost of the essences.
When a log burns, the ?re it trapped from the sun while it was growing is released and rises back to its proper place. Everything ?oats, falls, or rises in order to return to its proper place in the world, according to Aristotle. These actions were classi?ed as natural motions. When an object experiences a force, it can move in directions other than the natural motions that return them to their natural position. A stone can be made to move horizontally or upward by exerting a force in the desired direction. When the force stops so does the motion.
The model for explaining movement in the sky was somewhat different. Greek astronomers knew that there were two types of stars, the ?xed stars and the planets (or wanderers), as well as the Sun and the Moon. These objects seemed not to be bound by the same rules as objects formed of the other essences. They moved horizontally across the sky without forces acting on them.

The Greeks placed them in a ?fth essence of their own. All objects in this ?fth essence were considered to be perfect. The Moon, for example, was assumed to be a perfect sphere. Aristotles model assumes that perfect crystal, invisible spheres existed, supporting the celestial bodies.
Later, when Ptolemy (87150 C.E.) developed his Earth-centred universe model, he used this idea as a base and expanded upon it to include wheels within wheels in order to explain why planets often underwent retrograde (backward) motion. A single spherical motion could explain only the motions of the Sun and the Moon.
To European cultures, Aristotles two models were so successful that for almost 2000 years people accepted them without question. They remained acceptable until challenged by the revolutionary model of Copernicus (14731543) and the discoveries of Galileo Galilei (15641642).
Galileo and Scienti?c Inquiry
In 1609, using a primitive telescope (Figure 1.2), Galileo observed that the Moons surface was dotted with mountains, craters, and valleys; that Jupiter had four moons of its own; that Saturn had rings; that our galaxy (the Milky Way) comprised many more stars than anyone had previously imagined; and that Venus, like the Moon, had phases. Based on his observations, Galileo felt he was able to validate a revolutionary hypothesis one advanced previously by Polish astronomer Nicolaus Copernicus which held that Earth, along with the other planets in the Solar System,
actually orbited the Sun.
What the Greeks had failed to do was test the explanations based on their models. When Galileo observed falling bodies he noted that they didnt seem to fall at signi?cantly different rates. Galileo built an apparatus to measure the rate at which objects fell, did the experiments, and analyzed the results. What he found was that all objects fell essentially at the same rate. Why had the Greeks not found this? Quite simply, the concept of testing their models by experim entation was not an idea they found valuable, or perhaps it did not occur to them.
Since Galileos time, scientists the world over have studied problems in an organized way, through observation, systematic experimentation, and careful analysis of results. From these analyses, scientists draw conclusions, which they then subject to additional scrutiny in order to ensure their validity. As you progress through this course, keep the following ideas about theories, models, and observations in mind. Use them to stimulate your own thinking, and questioning about current ideas.

Thinking about Science, Technology, Society and the Environment
In the middle of the twentieth century, scienti?c progress seemed to go forward in leaps and bounds. The presence of ?gures like Albert Einstein gave science in general, and physics in particular, an almost mystical aura. Too often physics was seen as a pure study isolated from the real world. Contrary to that image, science is now viewed as part of the world and has the same responsibilities, perhaps even greater, to the world as any other form of endeavour. Everything science does has a lasting impact on the world. Part of this course is to explore the symbiotic relationship that exists between science, technology, society and the environment (STSE).
To many people, science and technology are almost one and the same thing. There is no doubt that they are very closely related. New discoveries in science are very quickly picked up by technology and vice versa. For example, once thought of as a neat but rather impractical discovery of physics, the laser is a classic example of how science, technology, society, and the environment are inseparable. The lasers involvement in our lives is almost a daily occurrence. Technology has very quickly re?ned and improved its operation. Today, laser use is widespread.
Supermarket scanners, surveying, communications, holography, metal cutters, surgery, and the simple laser pointer are just a few examples of the innovations that technology has found for the laser. Clearly it would be impossible to separate the importance of science and technology to society. Figure 1.3 on the following page shows just a sfew of the many applications of physics in todays world.
Often the same developments have both positive and negative impacts. Our societys ever increasing demand for energy has strained our environment to its limits. Society, while demanding more and more energy, has also demanded that science and technology ?nd alternate sources of energy. This has led to the technological development of nuclear, solar, wind, hydro, geothermal, and fossil fuel as energy sources. Societys and the environments relationship with science and technology seems to be a two-edged sword.

Thinking Scienti?cally
Knowledge begins with observations and curiosity. Scientists organize their thinking by using observations, models, and theories, as summarized below.

Theory
A theory is a collection of ideas, validated by many scientists, that ?t together to explain and predict a particular natural phenomenon. New theories often grow out of old ones, providing fresh, sometimes radical ways of looking at the universe. One such example, still in the process of development, is the GUT, or Grand Uni?ed Theory, being
sought by researchers across the different ?elds of physics. Through the GUT, physicists hope one day to be able describe all physical phenomena in the universe by using the same set of laws.
Observations
An observation is information gathered by using one or more of the ?ve senses. Observations may yield a variety of explanations, as participants in the same event often report different things. It takes hundreds of observations of a single phenomenon to develop a theory. There are two kinds of observations that can be made. The ?rst are qualitative, which describe something using words: A feather is falling slowly to the ground. The second are quantitative, which describe something using numbers and units: The rock fell at 2 m/s.
Model
A model is a representation of phenomena and can come in a variety of forms, including a list of rules, pencil lines on a piece of paper, an object that can be manipulated, or a mathematical formula. An observation may be explained using more than one model; however, in most cases, one model type is more effective than others.


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