There are more atoms in a single glass of water than there are glasses of water in all the world’s oceans combined — and if you marked every atom in one glass, dumped it into the sea, and waited for the oceans to mix completely, every glass of water on Earth would contain several thousand of those marked atoms

The arithmetic is one of the oldest and most reliable demonstrations in physics, and the conclusion is one of the harder facts about the size of atoms to actually believe. A standard 250-millilitre glass of water contains roughly 25 trillion trillion atoms, written as 2.5 × 10²⁵, accounting for the three atoms in each water […]