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Unformatted text preview: Chapter 2 Measurement 2.1 The Role of Measurement At the very center of physics is the essential role of experiment. Even the most carefully crafted theoretical system can only be valid if it agrees with experiment. Experiment is the process of careful observation of the world around us. In the process of performing experiments, in some cases, it is possible to control some parts of the activity of observation but that is not the important part of experiment. Experiment is the drawing of coherent information from a situation. In a sense, the idea of theory construction is to develop a method which can consistently bring into a concise set of statements the results of all possible experiments on a given system. In order to make consistent observations you have to make measure- ments. Measurement can be both qualitative and quantitative. Often times qualitative measurements can differentiate different ideas of how some pro- cess occurs. We will see this in the discussion of the foundations of quantum mechanics, see Chapter 7. Most of the time, however, to differentiate com- peting ideas based on what we see, our observations have to be quantitative. Actually when you think about it, even most qualitative observations are really just very rough quantitative assessments. The reddening of the sky at sunset says a great deal about how the atmosphere works. What do we mean by red in this case. A definite range of values in the wavelength of the light and thus a quantitative assessment. In this sense, all of physics is based on the process of measurement quantitative observation. In its simplest form, measurement is basically the comparison of two related things. Whenever a certain circumstance is seen, the caused sit- uation emerges. On both ends of this observation, measurements must be 37 38 CHAPTER 2. MEASUREMENT made to know what was set up and what was the result. Therefore, we must understand measurement if we want to understand physics. A process of measurement is basically a comparison of situations. This process is then formalized by using standards and comparing with these standards. This is best understood when we talk about length. The objects under consideration are separated. After some time, there appears to be a different separation. To quantify this set of events, we can find another separation that does not appear to be changing. An example of separated objects is two scratches on a rigid bar. Comparing the separations under consideration with the separation of the two scratches on the bar allows us to communicate the nature of the new separations. Of course, what is being measured is the length before and after. What most people miss in a discussion of length measurements is the fact that the process of measuring, the identification of a standard and a process is essentially the definition of length. The case of separation measurements is central to our study and available to our experience and that is the example that I will elaborate on...
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- Spring '07