# 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

What ends up happening is that we need a lot of zero's to express these sizes. For example:

# stars in our galaxy = 100,000,000,000 (roughly)

distance from here to the edge of the universe:
94,608,000,000,000,000,000,000 km (roughly!)

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

diameter of a red blood cell = 0.000007 m

mass of a carbon atom = 0.0000000000000000000000199 grams

Obviously these are numbers that are hard to deal with. 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 - and hard to remember how many zeros there are supposed to be in the first place!

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