Celebrated on May 20th each year to commemorate the signing of the Meter Convention, which took place in 1875 in Paris with the participation of 17 states, including Sweden, the aim was to establish a unified measurement system worldwide. This led to the adoption of the International System of Units (SI), which plays a fundamental role in our modern society, essential for research, technological advancement, and production.

"Historically, we've had various arbitrary measurements such as inches, ells, and feet, and even today, there are other units besides seconds, meters, and kelvin used in countries like the USA and the UK, as well as in our construction industry," says Kerstin Ramser, Professor of Experimental Mechanics at Luleå University of Technology. "Standardizing units allows us to take precise measurements and compare them internationally. As students, researchers, and citizens, we can find a common ground and fairly compare different things."

Promoting Sustainable Development

A unified system of measurement plays a crucial role in promoting global communication, collaboration, and development. Its universality and standardization make it a vital resource for addressing global challenges and encouraging sustainable development. It has provided a unified basis for researchers to work from.

"It would be difficult to easily compare different results if everyone used different measurement systems. To compare research conducted with different units, a reliable conversion table would be needed, which brings us back to standardization. SI units are our common ground," says Kerstin Ramser.

The International System of Units also plays a crucial role in the global transition to sustainability. By using SI units as a reference point, communities, businesses, and policymakers can better understand their environmental impact, streamline resource usage, and work towards common sustainability goals.

"For example, we can examine how combustion processes can be improved and the conversion of carbon dioxide into other products can be studied meticulously, while also investigating weather phenomena and their impact on the environment. We can also improve production lines, which brings economic benefits, and we have the means to measure progress in processes or the transformation of toxic substances into useful products," explains Kerstin Ramser.

Existentially Important

In her own research, Kerstin Ramser utilizes spectroscopy, among other techniques, where visible light is split into its various colors with nanometer precision.

"With spectroscopy, we can measure how molecules' bonds vibrate, done in the unit of inverse centimeters. This somewhat odd unit was determined about a hundred years ago because it provided nice integers. In our research, we can also use interferometry to measure phase differences, i.e., the difference in length between two light waves hitting a detector after traveling different paths, with nanometer precision. Through this, we can calculate differences in refractive index and thus the density of different materials."

For her and many other researchers, metrology is not just a tool but directly decisive for their research.

"With the help of metrology, coupled with, for example, laser light or X-rays, we can perform extremely accurate measurements in terms of energy, time, and length units. Two of our SI units, time, and length, are measured using light, which is the most important tool in our lab. It is existentially important for us to have precise metrological measurement methods."

A recent example of metrology is the world's adoption of a new definition of the kilogram in 2019, where Margareta Groth, now the head of the Department of Engineering Sciences and Mathematics at Luleå University of Technology, played a significant role.

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• Experimental mechanics