Looking Inside the Atom

The existence of atoms had been recognized in antiquity around 400 BC, when the Greek philosopher Democritus first proposed the idea that everything is composed of atoms which are physically indivisible. The word atom means “indivisible” and was coined by Greek philosophers. Conclusive evidence of the existence of molecules and atoms was provided by Scottish scientist Robert Brown, who observed in 1827 the random motion of particles suspended in a fluid (a liquid or a gas) resulting from their collision with the quick atoms or molecules in the liquid or gas. This phenomenon is now known as Brownian motion.

Eighteen centuries before Brown’s observation, the Roman poet Lucretius had written a remarkable poem describing Brownian motion as follows: “Observe what happens when sunbeams are admitted into a building and shed light on its shadowy places. You will see a multitude of tiny particles mingling in a multitude of ways… their dancing is an actual indication of underlying movements of matter that are hidden from our sight… It originates with the atoms which move of themselves. Then those small compound bodies that are least removed from the impetus of the atoms are set in motion by the impact of their invisible blows and in turn cannon against slightly larger bodies. So, the movement mounts up from the atoms and gradually emerges to the level of our senses, so that those bodies are in motion that we see…