Measurement and Measurement Error

PHYS 1313 S06
Prof. T.E. Coan
Version: 16 Jan ’06

Introduction

Physics makes both general and detailed statements about the physical universe and these statements are organized in such a way that they provide a model or a kind of coherent picture about how and why the universe works the way it does. These sets of statements are called “theories” and are much more than a simple list of “facts and figures” like you might find in an almanac or a telephone book (even though almanacs and telephone books are quite useful). A good physics theory is far more interested in principles than simple “facts.” Noting that the moon appears regularly in the night sky is far less interesting than understanding why it does so.

We have confidence that a particular physics theory is telling us something interesting about the physical universe because we are able to test quantitatively its predictions or statements about the universe. Indeed, all physics (and scientific) theories have this “put up or shut up” quality to them. For something to be called a physics “theory” in the first place, it must be falsifiable and therefore must make quantitative statements about the universe that can be then quantitatively tested. These tests are called “experiments.” The statement, “My girlfriend is the most charming woman in the world,” however true it may be, has no business being in a physics theory because it simply cannot be quantitatively tested. If the experimental measurements are performed correctly and the observations are inconsistent with the theory, then at least some portion of the theory is wrong and needs to be modified. Yet, consistency between the theoretical predictions and the experimental observations never decisively proves a theory true. It is always possible that a more comprehensive theory can be developed