Science: Key to Comprehending the Cosmos

Scientists strive to understand how nature works. Engineers, in turn, use the discoveries scientists make to craft the myriad high-tech products that surround us. As technology advances, so does our ability to make even deeper discoveries about space, time, matter, and energy, and the relationships between them.

Driven by the needs of national security, military equipment, and space exploration, among other things, scientific research and its engineering applications have had a profound impact on our lives, providing us with ever-improving computer technology, cell phones, GPS (global positioning systems), and innumerable medical advances and devices, to name just a few things. This spiral of understanding and application began centuries ago. In this chapter we begin by examining the nature of science and then use science to discover how gravity keeps planets and other objects orbiting the Sun and how gravity also keeps moons orbiting their respective planets.

2-1 Science is both a body of knowledge and a process of learning about nature

Science is actually two things. First, it is a body of knowledge that we acquire through observations and experiments. The details of the motions of the Moon, the planets, and the Sun on the celestial sphere, described in Chapter 1, are examples of that knowledge. While nature can be discussed descriptively, as it is for the most part in this book, science also provides mathematical equations that quantify the effects being studied.

Second, science is a process for gaining more knowledge in a way that ensures that the information can be tested and thereby accepted by everyone. Science as a process is also called the scientific method, which describes how scientists ideally go about observing, explaining, and predicting physical reality. The scientific method (Figure 2-1) can begin in a variety of places, but most often it starts by people making observations or doing experiments. For example, the observation that planets move along the celestial sphere, while stars remain fixed on it, demanded explanation. If a theory exists that purports to explain previous observations, new observations or experimental results are compared with the predictions of the theory. If the new data and old theory are not consistent, then a hypothesis that modifies or replaces the existing explanation is proposed. (If no theory explains observations or experimental results, a new hypothesis is proposed to explain them.) Hypotheses on related topics that make accurate predictions are incorporated together as a scientific theory (often just called a theory).

An interesting counterexample to beginning a scientific inquiry with observations or experiments is the discovery of a particle called the Higgs boson. This particle is what causes matter to have mass, which in turn allows matter to interact gravitationally, among other things. In 1964, Scottish physicist Peter Higgs (1929–), along with other scientists, predicted the existence of this particle based on powerful equations that describe the properties of matter. Based on this prediction, experiments were run to discover the Higgs boson. Scientists believe that it was observed in July 2012, at the Large Hadron Collider in Switzerland.

In everyday conversation, a theory is an idea based on common sense, intuition, or deep-seated personal beliefs. Such theories neither originate in equations nor do they usually lead to rigorous predictions. The word theory in science has a very different meaning. A scientific theory is an explanation of observations or experimental results that can be described quantitatively (that is, in terms of equations) and tested formally. The mathematical description used in a scientific theory is considered a model of the real system. For example, Newton’s theory (or, in earlier usage, law) of gravitation is written as an equation that predicts how bodies attract each other. (The word gravity is often used as shorthand for gravitation, and both are used in this book.)

As just noted, to be considered scientific, a theory must make testable predictions that can be verified by making new observations or doing new experiments. Testing is a crucial aspect of the scientific method, which also requires that the theory accurately forecast the results of new observations in its realm of validity. Newton’s law of gravitation predicts that the Sun’s gravitational force makes the planets move in elliptical orbits, and it predicts how long it should take each planet to orbit the Sun. As we will see shortly, observations have confirmed most of these predictions.

One important theme in science is to look for patterns that allow seemingly unrelated events or activities to be explained by one theory. For example, Newton observed that the Moon’s motion around Earth had the same behavior as the motion of a flying cannonball. Indeed, if you fired a cannonball fast enough, it would orbit Earth just as the Moon does. He hypothesized that they were both responding to Earth’s gravitational attraction, which led to his successfully applying the same equations to describe their motions. The motion of the planets around the Sun, he found, could also be described by the same equations. One theory. Three applications. Very satisfying! It is worth noting that Newton’s theory of gravity has since been applied successfully to myriad other situations.

As another example, we see billions upon billions of objects in the universe. It would be virtually impossible to study all of them separately so that we could come up with detailed descriptions of each one. Fortunately, individual theories explaining each object are not necessary. Scientists overcome this problem by noting that many of the bodies in space appear similar to each other. By categorizing them suitably and then applying the scientific method to these groups of objects, we form a few theories that describe many objects and how they have evolved. These few theories can then be tested and refined as necessary. Such groupings of objects have proven invaluable, and they give us insights into the structure and organization of billions of stars and galaxies that are, indeed, very similar to one another.

Often several competing theories describe the same concepts with the same accuracy. In such cases, scientists choose the simplest one—namely, the theory that contains the fewest unproven assumptions. That basic tenet, formally expressed by the philosopher and Franciscan friar William of Occam (c. 1288–c. 1347), is known as Occam’s razor. Indeed, the Sun-centered cosmology as refined by Johannes Kepler, which we are about to explore, was appealing because it made the same predictions within a simpler model than did the earlier Earth-centered cosmology. Remember Occam’s razor.

Scientists who develop new or more accurate models are going where no person has gone before. Many of them find this process of discovery as satisfying as an artist does in creating a masterpiece, an athlete breaking a world record, or an astronaut going into space.

For a theory to be considered scientific, it must be potentially possible to disprove it. For example, Newton’s law of gravitation can be tested and potentially disproven by observations and thus qualifies as a scientific theory. The idea that Earth was created in 6 days cannot be tested, much less disproved. It is not a scientific theory, but rather a matter of faith.

If the predictions of a theory are inconsistent with observations, the theory is modified, applied in more limited circumstances, or discarded in favor of a more accurate explanation. For example, Newton’s law of gravitation is entirely adequate for describing the motion of an apple falling to Earth, the flight of a soccer ball, or the path of Earth orbiting the Sun; however, it is inaccurate in describing the orbit of Mercury around the Sun or the behavior of matter in the vicinity of very dense concentrations of matter, like black holes. In these cases, Newton’s law of gravitation is replaced by Einstein’s theory of general relativity, which describes gravitational behavior more accurately and over a much wider range of conditions than Newton’s law, but at the cost of much greater mathematical complexity.

Some scientific theories, like Newton’s theory of gravity, have immediate applications, but many do not reveal their value to society for years or even decades. The underlying science for the ubiquitous flat screen used in virtually all TVs and computers these days, for example, was developed by 1964, but only became commercially available in 1995. The more we understand how nature works, the more we will eventually be able to control it.

While the vast majority of scientists carefully and scrupulously follow the rules of scientific research, we acknowledge that some experiments are run poorly. Some scientists have ignored experimental data or observations that do not mesh with cherished beliefs or have even fudged data or stolen data from Emil Rupp (1898–1979), who collaborated with Einstein, among others, is one such scientist. Virtually all of these over-sights and misdeeds are eventually discovered because most theories and their predictions are tested by several independent researchers.

The scientific method can be summarized in six words: observe, hypothesize, predict, test, modify, simplify. I urge you to watch for applications of the scientific method throughout this book. Our first encounter with it is the discovery that Earth orbits the Sun.