# 1: When size matters

## When size matters

As you may have noticed, scientists like to measure things, not just anything they can
get their hands on, but also lots of things that are too big to get their hands on,
and lots of things that are too small. For example:

### too small

rainforests

planets

solar systems

galaxies

universes

grains of pollen

blood cells

E. coli

enzymes

carbon atoms

electrons

When quoting numbers associated with sizes of these things we need a lot of digits. For example:

• The number of stars in our galaxy is roughly 100,000,000,000.
• The distance from here to the edge of the universe is roughly 94,608,000,000,000,000,000,000 km.

The problem is just as bad when we talk about small things:

• The diameter of a red blood cell is 0.000007 m.
• The mass of a carbon atom is 0.0000000000000000000000199 grams.

Obviously identifying the exact number of digits (mainly zeros in these examples) is difficult. A red blood cell with a diameter of 0.00007 m instead of 0.000007 m would be 10 times too big to fit through a capillary, yet it’s hard to tell the numbers apart by looking at them.

Of course one solution to this problem is to use specialised units. For example, we usually talk about the size of the universe in light-years, while we express the size of a red blood cell in micrometres. However, these different units make it hard to compare the sizes of things.