Discovery 2.2 - The Scientific Method

The Scientific Method

The earliest known models of the universe were based largely on imagination and mythology, and made little attempt to explain the workings of the heavens in terms of known earthly experience. However, history shows that some early scientists did come to realize the importance of careful observation and testing to the formulation of their theories. The success of their approach changed, slowly but surely, the way science was done and opened the door to a fuller understanding of nature.

As knowledge from all sources was sought and embraced for its own sake, the influence of logic and reasoned argument grew and the power of myth diminished. People began to inquire more critically about themselves and the universe. They realized that thinking about nature was no longer sufficient; looking at it was also necessary. Experiments and observations became a central part of the process of inquiry. To be effective, a theory—the framework of ideas and assumptions used to explain some set of observations and make predictions about the real world—must be continually tested. If experiments and observations favor it, a theory can be further developed and refined, but if they do not, it must be rejected, no matter how appealing it originally seemed.

The process is illustrated (very) schematically in the accompanying figure. This new approach to investigation, combining thinking and doing—that is, theory and experiment—is often known as the scientific method. It separates science from pseudoscience, fact from fiction.

Notice that there is no "end point" to the process depicted in the figure. A theory can be invalidated by a single wrong prediction, but no amount of observation or experimentation can ever prove it correct. Theories simply become more and more widely accepted as their predictions are repeatedly confirmed.

The notion that theories must be tested and may be proven wrong sometimes leads people to dismiss their importance. We have all heard the expression, "Of course, it’s only a theory," used to undermine an idea that someone finds unacceptable. Don’t be fooled by this abuse of the concept! Gravity (Section 2.7) is only a theory, but calculations based on it have guided human spacecraft throughout the solar system. Electromagnetism (Chapter 3) and quantum mechanics (Chapter 4) are theories too, yet they form the foundation for most of twentieth (and twenty-first) century technology.

In astronomy we are rarely afforded the luxury of performing experiments to test our theories, so observation becomes vitally important. The birth of modern science is usually associated with the Renaissance (and indeed, scientific inquiry can legitimately be said to have blossomed since the time of the Copernican revolution). However, one of the first documented uses of the scientific method in an astronomical context was performed by Aristotle (384–322 B.C.) nearly 25 centuries ago.

Aristotle noticed that, during a lunar eclipse, when Earth is positioned between the Sun and the Moon, it casts a curved shadow onto the Moon’s surface. The accompanying figure shows a series of photographs taken during a recent lunar eclipse. Earth’s shadow is indeed slightly curved. This is what Aristotle must have seen and recorded so long ago.

(G. Schneider)

Because the observed shadow seemed always to be an arc of the same circle, Aristotle concluded that Earth, the cause of the shadow, must be a sphere. On the basis of thishypothesis—this possible explanation of the observed facts—he then went on to predict that any and all future lunar eclipses would show that Earth’s shadow was curved, regardless of the orientation of our planet. That prediction has been tested every time a lunar eclipse has occurred. It has yet to be proved wrong. Aristotle was not the first person to argue that Earth is round, but he was apparently the first to offer evidence of it using the lunar-eclipse method.

The reasoning procedure Aristotle used forms the basis of all scientific inquiry today. Observation, theory, and testing are the cornerstones of the scientific method, a technique whose power will be demonstrated again and again throughout our text. Scientists throughout the world today use an approach that relies heavily on testing ideas. They gather data, form a working hypothesis that explains the data, then proceed to test the implications of the hypothesis using experiment and observation. Eventually, one or more "well-tested" hypotheses may be elevated to the stature of physical laws and come to form the basis of a theory of even broader applicability. The new predictions of the theory will in turn be tested, as scientific knowledge continues to grow.

Experiment and observation are integral parts of the process of scientific inquiry. Untestable theories, or theories unsupported by experimental evidence, rarely gain any measure of acceptance in scientific circles. Used properly over a period of time, this rational, methodical approach enables us to arrive at conclusions that are mostly free of the personal bias and human values of any one scientist. The scientific method is designed to yield an objective view of the universe we inhabit.

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