Even NIST Experts Disagree. – National Institute of Standards and Technology (.gov)”.
Bottom Line
The SI system remains a testament to thoughtful stewardship, allowing the public to use the system without noticing the underlying scientific improvements.
The Philosophy of Measurement
The International System of Units, commonly referred to as the metric system or SI, serves as the foundational framework for global science, commerce, and daily life. While many people perceive the current structure of seven base units as a fixed law of nature, the National Institute of Standards and Technology (NIST) notes that there is no inherent law of nature dictating how many units or constants should form the basis of our measurements. The selection of these units is ultimately a human decision rather than a scientific necessity. This philosophical distinction is central to ongoing discussions among metrologists regarding the ideal structure of the SI.
The Evolution and Structure of the SI System
The history of the metric system demonstrates that the number of base units has shifted over time to accommodate changing needs. For instance, the original Metre Convention signed in 1875 included only two units: the meter and the kilogram. It was not until 1970 that the current seven-unit system was formalized with the addition of the mole.
A group of physicists has proposed a reclassification system that splits the units into two distinct categories. Under this proposal, four units—the meter, kilogram, second, and ampere—would be considered true base units. The remaining three units, the candela, mole, and kelvin, would be categorized as scale-spanning units. These scale-spanning units are intended to translate tiny quantum-scale measurements into quantities that are more accessible at a human scale.
Other experts have proposed even more radical changes, suggesting that the number of base units could be reduced to three or even just one.
Practicality and Tradition in Metrology
The debate over the SI system often involves a tension between scientific purity and practical utility.
The mole is a prime example of a unit that is routinely used in essential fields such as pharmaceutical manufacturing and medical blood panels. Keeping these units as base units does not appear to cause harm, as the SI continues to work effectively for global commerce and everyday activities like measuring food, running races, or timing musical phrases.
Some have even suggested adding a new base unit, such as the radian for angular measurements. This proposal aims to clarify the difference between torque and work, both of which are currently measured in newton-meters. However, adding the radian would introduce complications, such as the need for new dimensional units to convert rotational power into linear power and the requirement for scientists to rewrite quantum physics textbooks and software.\n The verified publisher evidence does not establish broader claims regarding the specific timeline for these changes or which proposals will be adopted by international bodies.
Verified Source Evidence
This is the second installment in a two-part series about the SI, or metric system.
Even NIST Experts Disagree. – National Institute of Standards and Technology (.gov).
Source Licensing
- Source policy: NIST Copyrights and Disclaimers (https://www.nist.gov/copyrights-disclaimers). Source: National Institute of Standards and Technology (NIST). NIST endorsement or recommendation is not implied.
Sources
1 independent organization · 1 source document. Links open the original material.
- 1National Institute of Standards and Technology How Many Units Should Be in the Metric System? Even NIST Experts Disagree. - National Institute of Standards and Technology (.gov)
