Importance and research background of measurement uncertainty
In scientific research and actual measurement work, accurately evaluating the quality of measurement results is a crucial task. The concept of measurement uncertainty was born precisely to accomplish this task. Guide 25 jointly issued by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) clearly stipulates that each certificate or report issued by a laboratory must include a description of the evaluation of the uncertainty of calibration or test results. This fully reflects the important position of measurement uncertainty in the field of measurement. When we present measurement results, according to actual needs, we should also provide the corresponding measurement uncertainty at the same time, so as to make the measurement results more scientific and reliable. This article will elaborate in detail on the entire process from the uncertainty principle to the wide - spread application of measurement uncertainty from the perspective of historical development.
The proposal of the uncertainty principle
In 1927, the outstanding German physicist Heisenberg (Heisenberg·Werner, 1901 - 1976) proposed the epoch - making uncertainty relation. In the microscopic world, when we try to measure the position of a particle, we will find that there is an uncertain range, which we denote as ΔX. Meanwhile, there is also an uncertain range for the particle's momentum, denoted as ΔP. Heisenberg found that the product of ΔP and ΔX is always greater than a specific value, which can be expressed mathematically as ΔP·ΔX≥h/2. Here, h is specially defined, h = h/2π, where h is the Planck constant, and its value is equal to 6.626×10 - 34 joule - second. The Planck constant is a key constant in quantum mechanics, and its existence profoundly reflects the quantum characteristics of the microscopic world.
The connotation of the uncertainty principle
The physical phenomenon revealed by the uncertainty relation is of profound significance. If we want to measure the momentum of an object extremely precisely, that is, let ΔP approach 0, then according to the uncertainty relation, the position of the object will become very uncertain, that is, ΔX approaches infinity. Conversely, if we try to measure the position of the object precisely, then its momentum will become highly uncertain. This phenomenon is not limited to that between position and momentum. Similar uncertainty relations also exist between energy and time, as well as between angular momentum and angular displacement. In fact, the uncertainty relation is a principle of universal significance. In classical mechanics, such a relation exists between all conjugate dynamic variables. This shows that the uncertainty principle is an objective law of the material world, which fundamentally breaks the cognitive model of microscopic particles in classical mechanics. In classical mechanics, we always think that we can simultaneously and precisely know the exact position and the definite value of momentum of a microscopic particle. However, the uncertainty principle tells us that this is impossible in the microscopic world. For the description of the position of a microscopic object, we can only use a probabilistic approach, saying that it has a certain probability of being in a certain position. In the space where a microscopic particle may appear, there is a distribution of position probability, and this distribution follows the laws of statistical physics.
Early Dilemmas in the Use of the Uncertainty Concept
After Heisenberg proposed the uncertainty relation (also known as the indeterminacy relation), the term "uncertainty" has gradually been used by many scholars. However, in the early stage, this concept was not clearly and precisely defined, and its meaning was rather vague. Starting from 1970, the metrological departments of various countries also began to use uncertainty to evaluate measurement results one after another. But due to the lack of unified standards and specifications, there were a large number of debates regarding the classification, processing, and expression of uncertainty. Different institutions and scholars adopted a wide variety of usage methods, and the entire field presented a rather chaotic situation. This chaotic situation has brought great difficulties to the mutual utilization of measurement results among countries, and has also made the comparison of measurement results among countries extremely inconvenient, seriously affecting the smooth progress of scientific research and international cooperation.
Unification of uncertainty evaluation standards
In order to solve the problems arising in the use of uncertainty, in 1980, on the basis of extensively soliciting opinions from various countries, the International Bureau of Weights and Measures put forward the uncertainty proposal INC - 1 (1980). This proposal basically provided a complete description of uncertainty and laid the foundation for subsequent standardization work. By 1993, seven important international organizations, including the International Organization for Standardization, jointly issued the "Guide to the Expression of Uncertainty in Measurement" (referred to as the "ISO Guide"). The release of this guide was of milestone significance as it established a unified international standard for the evaluation and expression of uncertainty. Since then, the research and application of uncertainty have entered a brand - new stage, enabling measurement work worldwide to have a unified specification and basis in uncertainty evaluation.
Definition and evaluation method of measurement uncertainty
The definition of measurement uncertainty is as follows: It is a parameter associated with the measurement result, and its function is to characterize the dispersion of the values reasonably attributed to the measurand. The parameter used to characterize the dispersion can be the standard deviation, a given multiple of the standard deviation, or the half - width of the interval at a certain confidence level. This is the latest definition with strong operability. When actually evaluating the measurement uncertainty, we classify the standard uncertainties of the components of the measurement result into Type A and Type B for evaluation. By combining these two types of uncertainties, the combined standard uncertainty can be obtained. Once the combined standard uncertainty is obtained, the uncertainty, an important parameter characterizing the measurement result, can be smoothly calculated. Such an evaluation method makes the calculation of measurement uncertainty more scientific, accurate, and standardized.