III. Hypotheses, Models, Theories and LawsInphysics and other science disciplines, the words "
hypothesis,""model," "theory"
and "law" have differentconnotations in relation to the stage of acceptance or knowledge about a groupof phenomena.An hypothesisis a limited statement regarding cause and effect in specific situations; italso refers to our state of knowledge before experimental work has beenperformed and perhaps even before new phenomena have been predicted. To take anexample from daily life, suppose you discover that your car will not start. Youmay say, "My car does not start because the battery is low." This isyour first
hypothesis. You may then check whether the lights were left on, orif the engine makes a particular sound when you turn the ignition key. Youmight actually check the voltage across the terminals of the battery. If youdiscover that the battery is not low, you might attempt another hypothesis("The starter is broken"; "This is really not my car.")The wordmodel is reserved for situations when it is known that the hypothesishas at least limited validity. A often-cited example of this is the Bohr modelof the atom, in which, in an analogy to the solar system, the electrons aredescribed has moving in circular orbits around the nucleus. This is not anaccurate depiction of what an atom "looks like," but the modelsucceeds in mathematically representing the energies (but not the correctangular momenta) of the quantum states of the electron in the simplest case,the hydrogen atom. Another example is Hook's Law (which should be called Hook'sprinciple, or Hook's model), which states that the force exerted by a massattached to a spring is proportional to the amount the spring is stretched. Weknow that this principle is only valid for small amounts of stretching. The"law" fails when the spring is stretched beyond its elastic limit (itcan break). This principle, however, leads to the prediction of simple harmonicmotion, and, as a model of the behavior of a spring, has been versatilein an extremely broad range of applications.A scientifictheory or law represents an hypothesis, or a group of related hypotheses,which has been confirmed through repeated experimental tests. Theories inphysics are often formulated in terms of a few concepts and equations, whichare identified with "laws of nature," suggesting their universalapplicability. Accepted
scientific theories and laws become part of our understandingof the universe and the basis for exploring less well-understood areas ofknowledge. Theories are not easily discarded; new discoveries are first assumedto fit into the existing theoretical framework. It is only when, after repeatedexperimental tests, the new phenomenon cannot be accommodated that scientistsseriously question the theory and attempt to modify it. The validity that weattach to scientific theories as representing realities of the physical worldis to be contrasted with the facile invalidation implied by the expression,"It's only a theory." For example, it is unlikely that a person willstep off a tall building on the assumption that they will not fall, because"Gravity is only a theory."Changesin scientific thought and theories occur, of course, sometimes revolutionizingour view of the world (Kuhn, 1962). Again, the key force for change is thescientific method, and its emphasis on experiment. IV. Are there circumstances in which the Scientific Method is notapplicable?Thereare, of course, circumstances when one cannot isolate the phenomena or when onecannot repeat the measurement over and over again. In such cases the resultsmay depend in part on the history of a situation. This often occurs in socialinteractions between people. For example, when a lawyer makes arguments infront of a jury in court, she or he cannot try other approaches by repeatingthe trial over and over again in front of the same jury. In a new trial, thejury composition will be different. Even the same jury hearing a new set ofarguments cannot bpected to forget what they heard before. V. ConclusionThescientific method is intricately associated with science, the process of humaninquiry that pervades the modern era on many levels. While the method appearssimple and logical in description, there is perhaps no more complex questionthan that of knowing how we come to know things. In this introduction, we haveemphasized that the scientific method distinguishes science from other forms ofexplanation because of its requirement of systematic experimentation. We havealso tried to point out some of the criteria and practices developed byscientists to reduce the influence of individual or social bias on scientificfindings. Further investigations of the scientific method and other aspects ofscientific practice may be found in the references listed below.