Metrology

Political, philosophical and even religious impulses lie at the foundations of science and technology

In last month's column, we considered how standards of physical measurement can help to keep people honest in modern society. We also suggested that new measurement technologies can lead to new ways of healing, enhancing and protecting human lives, such as medical treatments and the global positioning system. Many recent advances have become possible only because scientists have continued to improve the precision of their measuring tools.  

Metrology, or the science of measurement, is an international effort involving scientific committees and delegations from dozens of countries. These groups maintain the Système Internationale d’Unités, which defines all of the units in today’s metric system. Their aim is to develop standards and calibration techniques that are reliable, fair and readily accessible at multiple locations throughout the world. Such efforts have become increasingly important as networks of manufacturing and trade have extended their global reach. 

The ’new’ kilo
This coming November, the world’s metric authorities will announce a major change that will redefine the kilogram. The metal cylinder whose mass has defined the kilogram for nearly 130 years will be retired in mid-2019. Metrologists will no longer have to travel to Paris, France, to compare their copies of that cylinder with the original. Until now, such a pilgrimage was a necessary step if you wanted to do a complete check on the calibrations of scales used in your local health clinic or grocery store. However, next-generation scales won’t rely on standard reference masses at all, and they will utilize a new definition of the kilogram in terms of a fundamental constant of nature – specifically, the Planck constant of quantum physics. 

The state of the art in the new devices is a seesaw-like contraption called a “Kibble balance.” In this balance, a coil of wire is attached to the bottom of a weighing pan and surrounded by magnets. The electric current in the wire is adjusted so that the magnetic force on the coil exactly cancels the gravitational force on the test object. The Kibble balance determines the mass of the object by measuring this current and a few other quantities very precisely.

This system ushers in a new era for metrologists, who will be able to set up primary calibration laboratories in their own countries. In addition, new variants of the Kibble balance will be capable of delivering precisely calibrated measurements in the one-gram range (which, perhaps surprisingly, has been an arduous and complicated operation up to this point).

De Standaard
At the heart of the movement to redefine the kilogram is a desire to abandon standards that are based on human-manufactured artifacts (like the metal cylinder in Paris), and to define measurement units in terms of fundamental constants of nature. This desire for objective and universally accessible standards has been discussed for roughly 250 years. It was what motivated the democratically minded scientists who first proposed the metric system around the time of the French Revolution. However, political agreement on this issue was not easily achieved through most of the nineteenth century, so metric principles were not inscribed into a lasting international treaty until the Metric Convention of 1875. 

Here we are reminded that political, philosophical and even religious impulses lie at the foundations of science and technology. Of course, agreeing on standards of physical measurement is only a small part understanding the norms and expectations that guide our behavior. This point was not lost on Abraham Kuyper, a guiding light in the tradition of Reformed Christianity. By the early 1870s, physical measurement standards had become a central concern in many industrializing activities, such as factory work, the construction of railways, and the stabilization of gold- and silver-based currencies. There was much talk of social standards as well, notably in the fields of education, government and medicine. This was a time when plans for the Metric Convention were taking shape, and when trends toward internationalism and secularization were gaining momentum. Perhaps we should not be surprised that the newspaper Kuyper launched in 1872 was called De Standaard, or that it pointed explicitly to the standard of Holy Scripture as the chief moral guide for understanding the many changing standards of the time. 

Author

  • Matthew is a professor at Calvin College and the chair of Calvin’s department of physics and astronomy.

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