A major theme throughout this book is that of science as a worldwide cooperative activity, a process, by which scientists, individually and collectively, seek to derive a commonly accepted explanation of the universe. The author recalls learning in the ninth grade that science was “classified (i.e., organized) knowledge,” only to have to discard that definition years later as the very active nature of science became apparent. To be sure, organized knowledge is one of the valuable products of science, but science is far more than a mere accumulation of facts and figures.

Science defies attempts at simple definition. Many—both professional scientists and others—who have sought to set forth an accurate description of the nature of science have found it necessary to devote entire volumes of elaborate discussion to the subject.² None has found it possible to give in a few sentences a complete and simple definition, although James B. Conant perhaps came close: “Science is an interconnected series of concepts and conceptual schemes that have developed as a result of experimentation and observation and are fruitful of further experimentation and observations.”³

On a casual reading, this definition may again appear to characterize science as a static collection of facts and figures. One must add to the definition the activity of scientists, their continuing exchange of information and ideas, and their penetrating criticism of new ideas, working hypotheses, and theories. A static mental construct alone is insufficient; one must include the process that constantly adds to, elaborates, and modifies the construct. All of this Conant—himself an eminently successful chemist—does actually include in what he is trying to convey in his brief definition, as is patent from the amplification he provides in the rest of his treatment. Indeed, the last clause of the quoted definition, requiring that the concepts and conceptual schemes of science be “fruitful of further experimentation and observations,” clearly implies the ongoing nature of science.

The difficulty of conveying in brief the nature of science, particularly to the layman, has led in exasperation to such statements as, “Science is what scientists do.” The circularity of this definition can be frustrating to one seriously trying to understand the subject—a legislator, for example, endeavoring to appreciate the significance of science for the country and his constituents, and to discern what science needs to keep it healthy and productive. Yet the definition suggests probably the best way of approaching the subject; that is, to tell just what it is that scientists do.

Scientists work together to develop a commonly accepted explanation of the universe. In this process, the scientist uses observation and measurement, imagination, induction, hypothesis, generalization and theory, deduction, test, communication, and mutual criticism in a constant assault on the unknown or poorly understood. Consider briefly each of these activities.

The scientist observes and measures. A fundamental rule of modern science is that its conclusions must be based on what actually happens in the physical world. To determine this the scientist collects experimental data. He makes measurements under the most carefully controlled conditions possible. He insists that the results of experiment and measurement be repeatable and repeated. When possible, he measures the same phenomenon in different ways, to eliminate any possible errors of method.

To experimental and observational results the scientist applies imagination in an effort to discern or induce common elements that may give further insight into what is going on. In this process he may discover relationships that lead him to formulate laws of action or behavior, such as Newton’s law of gravitation or the three fundamental laws of motion, or to make hypotheses, like Avogadro’s hypothesis that under the same pressures and temperatures, equal volumes of different gases contain equal numbers of molecules.^b It is not enough that these laws be expressed in qualitative terms; they must also be expressed in quantitative form so that they may be subjected to further test and measurement.

The scientist generalizes from the measured data and the relationships and laws that he has discerned to develop a theory that can “explain” a collection of what might otherwise appear to be unconnected or unrelated facts. In seeking generalization, the scientist requires that the new theory be broader than existing theory about the subject. If the new theory explains only what is already known and nothing more, it is of very limited value and basically unacceptable.

The new theory must predict by deduction new phenomena and new laws as yet unobserved. These predictions can then serve as guides to new experiments and observations. By taking predictions and working them together with other known facts and accepted ideas, the scientist can often deduce a result that can be put to immediate test either by observation of natural phenomena or by conducting a controlled experiment. Out of all the possible tests, the scientist attempts to choose those of such a clear-cut nature that a negative result would discredit the theory being tested, while a positive result would provide the strongest possible support for the theory.

In this connection, it must be emphasized that the scientist is not seeking “the theory,” the absolute explanation of the phenomena in question. One can never claim to have the ultimate explanation. In testing hypotheses and theories the scientist can definitely eliminate theories as unacceptable when the results of a properly designed experiment contradict in a fundamental way the proposed theory. In the other direction, however, the scientist can do no more than show a theory to be acceptable in the light of currently known facts and accepted concepts. Even a long-accepted theory may be incomplete, having been based on inadequate observations. With the continuing accumulation of new data, that theory may suddenly prove incapable of explaining some newly discovered aspect of nature. Then the old theory must be modified or expanded, or even replaced by an entirely new theory embodying new concepts. Thus, in his efforts to push back the frontiers of knowledge, the scientist is continually attempting to develop an acceptable “best-for-the-time-being” explanation of available data.

In all this process the scientist continually communicates with his colleagues through printed journals, in oral presentations, and in informal discussions, subjecting his results and conclusions to the close scrutiny and criticism of his peers. Ideally, observations and measurements are examined and questioned, and repeated and checked sufficiently to ensure their validity. Theories are compared against known observation and fact, against currently accepted ideas, and against other proposed theories. Acceptable standing in the growing body of scientific knowledge is achieved only through such a searching trial by ordeal.

One should hasten to add that this is not a process of voting on the basis of mere numbers. Even though the majority of the scientific community may be prepared to accept a given theory, a telling argument by a single perceptive individual can remove the theory from competition. Thus, the voting is carried out through a continuing exchange of argument and reasoned analysis. Those who have nothing to offer either pro or con in effect do not vote.

This process or activity called science has developed its rules, its body of tradition, from hard and telling experience. Recognizing that the scientific process cannot yield the absolute in knowledge, scientists have sought to substitute for the unattainable absolute the attainable utmost in objectivity. The scientific tradition wrings out of final results as much as possible of the personal equation by demanding that the individual subject his thoughts and conclusions to the uncompromising scrutiny of his skeptical peers.

The above are things that scientists do, and through the complex interchanges among scientists these activities amalgamate into what is called science. But at this point one must ask what factor distinguishes science from a number of other endeavors, Observation and measurement, imagination, induction, hypothesis, generalization and theory, deduction, test, communication, and mutual criticism are used in various combinations by the economist, the legislator, the social planner, the historian, and others who today in partial imitation of the scientists apply to their tasks and studies their concepts of what the scientific method is. The distinguishing factor is fundamental: underlying the pursuit of science is the basic assumption that, to the questions under investigation, nature has definite answers. Regardless of the philosophical dilemma that one can never be sure of having found the right answers, the answers are assumed to exist, their uniqueness bestowing on science a natural, intrinsic unity and coherence. In contrast one would hardly argue that societal, political, and economic problems have unique answers.

These latter problems are concerned with the human predicament, and the human equation enters not only into the search for answers, but into the very solutions themselves. Human invention and devising are necessary ingredients of the solutions achieved. In science, however, although imagination and invention are important elements of the discovery process, the human factor must ultimately be excluded from its findings, and to this end the scientific process is designed to eliminate as much personal bias and individual error as possible. This aspect gives science its appearance of objectivity and impersonality, while bestowing a universality that transcends political and cultural differences that otherwise divide mankind.

The reader is again cautioned not to be misled by oversimplification. One must not conclude from the above orderly listing of activities and processes of thought, either that they constitute a prescribed series of steps in the scientific process or that one can identify a single scientific method subscribed to and followed by all scientists. On the contrary, individual scientists have their individual insights, styles, and methods of research. Conant is emphatic on this point:

While there is no single scientific method, there is method, and each researcher develops his own sense of order and line of attack. And major elements of the various methods are sufficiently discernible that they can be identified. Indeed, there is enough of method to the profession to lead John Simpson, professor of physics at the University of Chicago, to assert that even the plodder, while he may never make brilliant contributions, can through systematic effort aid in the progress of science.

Nevertheless, the role of insight and perceptiveness is crucial. The application, however, cannot be equated with induction in the Baconian tradition.⁵ The inductive step from the singular to the general, while an important element in science, is far from routine. Often seemingly haphazard, this step calls into play inspiration, insight, intuition, imagination, and shrewd guesswork that are the hallmark of the productive researcher. Conant alluded to the elusive character of this phase of the scientific process: “Few if any pioneers have arrived at their important discoveries by a systematic process of logical thought. Rather, brilliant flashes of imaginative ‘hunches’ have guided their steps—often at first fumbling steps.”⁶

Each individual has his own devices for trying to discern from the particular what the general might be. Certainly the reasoner does not approach his task with no preconceptions. To the new data he adds other facts and data already known, and he calls into play previously accepted ideas that appear relevant. Whatever the method, the ultimate test is whether it works.

A continuing task of the space science manager was to assess progress in the program, and various criteria for measuring the worth of scientific accomplishments have been used. In this regard the author finds attractive a number of concepts provided by Thomas S. Kuhn.⁷

A scientist approaches a new situation or problem with a definite mental picture of how things ought to be, what processes should be operative, what kinds of results are to be expected from different experiments. This mental picture—which, with some leeway for differing points of view, he shares with scientific colleagues working in the same field—has developed over the years from experimentation and observation, hypothesizing, theorizing, and testing. It has stood the ordeal of searching tests and has proved its value in predicting new results and in integrating what is known of the field into a logically consistent, useful description of nature.

To this shared mental construct, Kuhn gives the name paradigm, a substantial extension of the usual meaning of the term. Thus, the ionosphericists share a paradigm, in which each knows—or at least agrees to accept—that there is an ionosphere in the upper reaches of the earth’s atmosphere consisting of electrons and positive and negative ions, varying in intensity, location, and character with time of day, season, and the sunspot cycle. He knows, or agrees, that most of the ionization and its variation over time are caused by solar radiation, and that the ionosphere has a complex array of solar-terrestrial interrelations. The ionosphere is affected by and affects the earth’s magnetic field. It has a profound influence on the propagation of many wavelengths in the radio frequency region of the electromagnetic spectrum and acts like a mirror reflecting waves of suitable wavelength, a phenomenon that before the advent of the communications satellite afforded the only means of round-the-world short-wave radio transmissions. To develop thoroughly the paradigm shared by ionospheric physicists would be a lengthy proposition,⁸ but the reader may find the above sufficiently suggestive.

As another example, solar physicists share a paradigm in which the sun is regarded as an average sort of star, about 10 billion years old and with some billions of years still to go before it evolves into a white dwarf. It originated as a condensation of dust and gases from a huge nebula and was heated by the gravitational energy released by the falling of the nebular material into the contracting solar ball until internal temperatures rose sufficiently to initiate nuclear burning of hydrogen, the major source today of the sun’s radiant energy. And so on.⁹ Workers in the field of solar studies understand each other, they have a common way of looking at things, they approach problems with a similar orientation.

Individual scientists usually share a number of paradigms with different colleagues. The paradigms of the upper atmosphere physicist and the ionosphericist overlap greatly. While an ionospheric investigator is applying his ionospheric paradigm to his work, he also has in the back of his mind that the laws of physics and chemistry must apply to the ionosphere, and when appropriate the ionospheric researcher brings to bear the paradigms of chemistry and modern physics. Likewise the solar physicist must constantly borrow from the para...