THE SI SYSTEM – THE LANGUAGE OF MEASUREMENT FOR THE WHOLE WORLD

Lead

 

Metre, second, kilogram or kelvin — we all know these units, but rarely think about how they are created or why they have the same value everywhere. The International System of Units (SI) is humanity’s agreement that there should be one universal language of measurement.

 

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After centuries of diverse and confusing measures, today almost the entire world uses the International System of Units — SI. It is the foundation that connects science, industry, and everyday life.

 

The SI consists of seven base units:

• metre (m)– length
  • kilogram (kg) – mass
  • second (s) – time
  • ampere (A) – electric current
  • kelvin (K) – temperature
  • mole (mol) – amount of substance
  • candela (cd) – luminous intensity

(Visual 1: Symbolic representation of the seven SI base units with their associated fundamental constants / Source: Public domain)

 

All other quantities — such as speed, pressure, energy or power — are derived from these base units. For example, the tesla (T), the unit of magnetic flux density named after Nikola Tesla, is derived from the kilogram, second and ampere:

1 T = 1 kg / (s² · A).

(Visual 2: Modern magnetic resonance imaging device achieving a magnetic flux density of 3 T / Source: Photo by Ildar Sagdejev, Wikimedia Commons)

 

Since 2019, none of the base units are defined by physical objects, but by fundamental constants of nature: the speed of light, the Planck constant, the Avogadro number, and others. This means they can be reproduced anywhere in the world, without risk of the original standard being damaged or lost.

(Visual 3: “Timeline of the Universe — From the Big Bang to Today” (visualisation) / Source: NASA’s Goddard Space Flight Center, Visualisation Studio)

 

The SI is not only a technical agreement — it is also a cultural phenomenon. It allows scientists, engineers, and traders across the world to speak the same language of numbers.