No matter what the context, the basic idea of measurement is to enable quantitative comparison of one property or thing with another. The ability to numerically compare quantities may be considered one of the defining characteristics of a science: without measurement, there is only speculation.
This book contains a chapter on measurement because in the teaching of physics, the insights achieved as a result of studying measurements are often taught as secondary to insights derived from theoretical approaches to a subject. Indeed, I have attended entire lecture courses where no reference was made to a single measurement in the outside world. However, in practice it is exceedingly rare for physicists to proceed in such a fashion. The beliefs that physicists hold about the world are, in a sense, forced upon them by measurements. The results of measurements act as guides, and constraints, for developing explanatory ideas about the world. So familiarity with measurements and the way they are made is as important an aspect of physics as familiarity with (say) mathematics. Although a student might be forgiven for thinking otherwise, it is not mathematics but measurement, that makes physics a science rather than a philosophy.
This chapter is divided into four sections:
§3.2 Units: Measurement units are in some ways a most mundane subject. Units are the standard quantities which enable the quantitative comparison, of which I spoke above, to be realised. However in other ways things are not so simple.
§3.3 Key measurement techniques: Given the importance of measurement, the techniques used to carry out this process are of considerable interest. Here we look at some of the more common techniques. Throughout the twentieth century there has been astonishing progress in techniques driven by the availability of specific technological tools. Three trends stand out above all others: the exploitation of the phenomenal accuracy with which time may be measured; the use of digital voltmeters and the concept of a sensor; and most recently the use of lasers and opto-electronic techniques.
§3.4 Environments: In considering measurements of the properties of matter we are interested in how matter behaves in differing environments, for example high and low temperatures. In this section we see in rough terms how these environments are created.
§3.5 Uncertainty: All measurements have an associated uncertainty. In this section we mention the uncertainty associated with the extensive tabulations and graphs in this book.