CHAPTER 1

Aristotle's (384-322 B.C.) writings dominated western knowledge for nearly 2000 years. Prior to the fifteenth century some aspects of the pervasive order in nature had been noticed, but the order that was recognized in nature was largely imposed by human reasoning alone, without reference to observations or experiment. Systematic observations and experimentation as a way of understanding nature did not begin in western Europe until the fifteenth and sixteenth centuries. Danish scientists Sophia Brahe and her brother Tycho were among the first to record accurate positions of the planets in the sky in the late sixteenth century. Aided by Johannes Kepler they compiled a catalog of their measured planetary positions which extended over several decades. This catalog constituted the most accurate set of uniform data on the positions of the planets relative to the reference background of stars as a function of time.

Kepler spent decades of his life analyzing these planetary positions, searching for inherent patterns and trends in the data. After twenty years, Kepler summarized the patterns he found in the planetary positional data into three general laws of planetary motion:

1. Planets move around the sun in orbits with shapes of ellipses.

2. The radius vectors extending from the Sun to any planet sweeps out equal areas in equal time intervals.

3. The cube of the semi-major axis of a planet orbit equals the square of its period of revolution around the sun.

These are called Kepler's Laws because they are generalizations of patterns which Kepler noticed in the data. Remember Kepler was only working with positions of planets measured against the background stars as a function of time. His laws specify no cause for the changes in positions as a function of time.

Galileo Galili is commonly regarded as one of the first scientists in history, because he was the first to utilize methods for understanding how nature works that are recognized as appropriate by scientists today. Early in the seventeenth century Galileo pioneered the basic method of doing science by simply observing how nature behaved, performing enough carefully designed experiments that he could make generalizations based on reasoned conclusions drawn from his observational and experimental data. This approach to constructing knowledge about nature marks the beginnings of modern science. Galileo was first to train a telescope on the moons of Jupiter and discover that they were orbiting that planet. This was an extremely important discovery in the context of 17th century Europe, because the concept that the Earth and planets orbited the Sun had been introduced by Nikolai Copernicus at the end of 16th century, and met with resistance from people unfamiliar with the value to the scientific method. The Brahe's, Kepler, Copernicus, Galileo and Newton are considered pioneers of modern science, and with a handful of other enlightened people in the 16th and 17th centuries laid the foundations for science as we know it and do it today.

While a student at Cambridge University in England in the mid sixteenth century, Isaac Newton became intrigued by motions of objects and what causes motion. Newton lived about 50 years after Kepler, and thus inherited this immense body of complex and superbly accurate planetary observations made by the Brahes and Kepler. Newton also inherited Kepler's three laws of planetary motion.

Faced with the enormous complexities of the Brahe's observations, Newton must have felt overwhelmed initially by the detail. In fact other scientists of the day also had access to these observations as well as Kepler's laws, yet other brilliant minds missed the opportunity to make the monumental discovery that revolutionized all of science. What did Newton do right?

He asked the right questions which were: 1) What were the positions of the planets in the past and what will the planetary positions be at any time in the future? 2) What causes the planets to move around the sun, and not in straight line paths?

There were a myriad of other valid scientific questions he could have posed, such as: How did the planets form? What causes planets to rotate? Why do some planets have moons and others do not? He may have wondered about these interesting and valid scientific questions, but he did not hone in on them, and become mired in the details of pursuing answers to questions for which we even today have no scientific answers. Newton was sufficiently reflective and creative to recognize the important few questions to ask about motion which might be answerable. Because he succeeded in posing and in answering questions 1) and 2) above, Newton discovered some of the most fundamental laws in the history of science, namely Newton's Laws of Motion and Newton's Theory of Gravitation. Posing the important, answerable question which can be tested by scientific experiment is key to making major discoveries and advances in science.

Newton spent the bulk of his life pursuing the answers to the first two questions. In answering them, he needed to make no more planetary observations, nor perform additional Earth-based experiments. He began with Galileo's Law of Inertia inferred from careful experiments with moving objects on Earth. Galileo generalized the results of his experiments on motions of objects in a Law of Inertia: If nothing is acting on an object and it is moving with constant speed, then the object will continue to move forever in a straight line. Newton made an immensely creative connection when he realized that Galileo's Law of Inertia must also apply to the motions of the planets.

But Kepler had demonstrated from his detailed studies of the planetary positions that planets do not move in straight lines. Newton posed the important scientific question: Why do the planets not move in straight lines? This was the key insightful question that led to a law so fundamental that science was reshaped forever, by Newton's Theory of Universal Gravitation. The basis of major advances in science is posing the key question at the right time, and a creative idea that makes unexpected links among diverse phenomena.

Newton's Theory of Gravitation attributed a force of attraction between any two objects, such as a planet and the Sun, to an inherent property of the two objects. Newton found that the strength of the attractive force between the two objects depended not only on the masses of the two objects but on their separation. Newton's Theory of Gravitation is a theory because it not only embodies the concepts of all three of Kepler's laws, but it also identifies a cause for the motions. A theory is more powerful, but not necessarily more (or less) immutable than a law.

The time has to be right for great discoveries such as the laws of motion and the theory of gravitation to be found. But the right question must be posed to get the process started in the right direction. The same applies to learning science by doing it. A question must be posed for which a feasible experiment can be designed to test the model you have proposed to explain the phenomenon under consideration. Breakthroughs like Newton's and Galileo's are extremely rare in science. Most of the fabric of science has been patched together from tiny bits and pieces, over the past three centuries collectively by scientists working alone and collaboratively.

One of the most remarkable aspects of science is that scientists have tested the theories and laws discovered on Earth and discovered that scientific theories apply throughout the vast reaches of the Universe. In every case where a law or theory has been tested, scientists have found that it applies throughout the Universe. A scientific theory is not the last word, however, it is only the best current description of how nature works. The job of a scientist involves continuous testing and revising or changing the current theories and laws. Scientific knowledge is continually being built and refined. Only very rarely is an entirely new theory such as Newton's discovered.

All science builds on previous knowledge. Science is manifested in a common framework called scientific laws and theories. These laws and theories represent the current best reasoned consensus of scientists about the rules that govern how nature works. Scientists continually revise and change these laws and theories based on their new experimental results. This body that constitutes scientific laws and theories provides the basic framework for doing science. The framework is continuously being improved and updated through scientific experimentation, commonly called scientific research. The laws and theories on which science is based represent our collective current best knowledge of the rules by which nature functions. This framework of scientific laws transcends the discipline boundaries of biology, geology and physics, and applies to all natural phenomena.

Theories continually undergo refinement based on improved scientific experiments. Occasionally old theories must be discarded when new ones are discovered. Newton's Theory of Gravitation has been phenomenally successful in predicting the positions of planets and stars for times in the past and the future, and remains an accurate description of the attractive force among all objects. Note that Newton's Theory of Gravitation does not incorporate an explanation of what gravity is. You could navigate a spacecraft to Mars using Newton's Laws of Motion and his Theory of Gravitation, without knowing what causes the attractive force between objects that we call gravity.

But at the turn of the twentieth century Albert Michelson and Morley performed an experiment that demonstrated a fundamental inconsistency with Newton's laws of motion and his theory of gravitation, and once again caused an upheaval in physical science. Michelson and Morley discovered that the speed that light travels is constant regardless of the motion of either the light source or the observer of the light source. Thus in 1900 because this new experiment on the speed of light had been performed, and two scientists had interpreted their experimental results using a new model for the speed of light, the basic time-tested Newtonian theory of motion needed to be either modified or replaced.

In 1915, aware of the profound meaning of the Michelson-Morley experimental results, Albert Einstein made a highly creative yet completely unexpected link between gravity and light that led to an improved and dramatically different theory of gravitation, now called Einstein's Theory General Relativity. Because scientists require irrefutable experimental evidence before accepting any new theory, and the observational data to support the theory of general relativity were not overwhelmingly convincing, the scientific community did not accept general relativity as an improved theory of gravitation until many years after Einstein's death in the 1950's.

General relatively, however, is today recognized by most scientists to be an improved theory of gravitation because it can more accurately describe the motions of objects caused by their mutual gravitational interactions than Newton's theory. Of interest to the scientific community, but not required to qualify as a theory, general relativity specifies a cause for the attraction among objects.

The basic postulates of general relativity are that matter curves space and objects follow that curvature in space. The theory of general relativity is a truly creative concept which connects unexpected ideas. Now generally accepted by scientists, general relativity has advanced our knowledge of gravity and our ability to predict the paths of stars and planets a gigantic step. Like any successful new theory, general relativity can be used in all cases where Newton's laws of motion and gravitation once applied, and can explain additional phenomena which could not previously be explained such as the bending of light and the slowing of time near massive objects and black holes.

We do not yet know whether there is any connection between the seemingly different phenomena of light, gravity, electricity and magnetism. Einstein sought a theory to link these phenomena into a grand unified theory, but failed. We do not know if these phenomena can be linked, but if they are, the theory which links them could be rightly called the "theory of everything", since these four concepts, light, gravity, electricity and magnetism, pertain to the most basic phenomena associated with the physical sciences. The theories that form the basis of physical science constitute the underpinnings of all branches of science. The present set of laws and theories which constitute the framework for physical science, undergo continual testing through experiment, and are constantly being modified and refined.

Doing science can take the form of mundane refinements and verifications of existing laws and theories, or of great advances in the conceptual framework of science. The great leaps forward occur when a discovery (usually unanticipated) is made or a creative mind links two seemingly unrelated phenomena in an unexpected way. Unfortunately the great advances in science are usually unpredictable, occur sporadically and are extremely rare. The key to making discoveries that lead to the rare, but major advances in science is a creative mind that recognizes links between apparently unassociated phenomena.

You should be aware that by far the most common advances in scientific knowledge are minute in comparison to the contributions of Newton and Einstein. Also finding a model that explains or predicts a phenomenon in nature only very rarely leads to a new law or theory. Nonetheless, the excitement of discovering a pattern or trend in experimental data, not previously noticed, drives scientists in their endeavor to complete our understanding of nature's patchwork fabric which was initiated in the sixteenth century.

Hopefully, in Doing Science you, too, will experience the flavor and excitement of doing scientific research. Exploring the unknown has always been an enjoyable adventure for humans. The rewards in science come from the rare moments of creative insights. Nature has infinite variety, and all humans have the potential to be very creative. Take time to reflect on the patterns you observe. They may gel into a single pattern. When inventing hypothesis to explain what you see in your experiments, feel free to be creative. You should always think of several alternative hypotheses, testable by experiment. Based on any of your hypotheses you should be able to plan an experiment which will test whether that hypothesis is correct. Be alert, creative and observant, and you will be amazed by what you can learn from careful observations and thoughtful reasoning about the way nature works.

The purpose of this text is for you to learn from your own experiences and experiments some of these fundamental theories that comprise the common framework called physical laws. This framework has been painstakingly constructed by scientists from careful observation, experimentation and dialog over the past 300 years. Here you will learn the basic laws of science by actually doing science.

How is Science Done?

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Last modified 9 Aug 1997
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