📏 Measuring the world

Units, like metres, grams or seconds, give everyone the exact same way to measure something, so a measurement means the same thing no matter who takes it or where they are in the world. Without shared units, numbers alone would not tell you much, "five" does not mean anything until you know five of what. Units of measurement used to be based on things like a king's foot, which is exactly why they eventually needed to be made the same everywhere.

Scientists use powerful microscopes that can zoom in far beyond what our eyes alone can see, letting them look at things as small as individual cells or even tinier building blocks called molecules. The most powerful microscopes can actually let scientists see individual atoms, the tiny building blocks that make up everything around us. To measure things this small, scientists also use tiny units far smaller than a millimetre, since a normal ruler simply cannot capture something that small.

For huge distances, like the space between stars, scientists use special units, like light-years, which measure how far light travels in a year instead of using metres, because the numbers would otherwise be far too enormous to write out easily. A single light-year is about nine and a half trillion kilometres, which is why scientists needed a whole new kind of unit just to measure space. Choosing the right unit for the job, tiny units for tiny things and giant units for giant things, is a key part of how measuring actually works.

The metric system, based on units like metres and grams, is popular because it uses simple multiples of ten to switch between sizes, which makes it much easier to calculate and share measurements across different countries. Only a handful of countries in the world still do not use the metric system as their main system of measurement, which can make it tricky when sharing scientific results internationally. Because the metric system is used almost everywhere in science, it lets researchers from very different countries compare their results without confusion.