How Einstein Proved that Atoms Existed. And How You Will Too

In 1905, 26 year old Einstein had his miracle year. During that year he made several brilliant theoretical breakthroughs that changed the world, the most famous being relativity and gravitation. However, one calculation that Einstein did, and which you will repeat and understand, will fascinate us in this post series.

In 1827 a botanist named Robert Brown was looking at pollen grains under a microscope, he observed them floating in water, they were not standing still, they were jiggling around moving in all sorts of random directions. Being a Biologist, Brown naturally assumed they were alive, but being a good scientist he decided to test that hypothesis: He proved himself wrong by putting sand grains instead of pollen grains and discovered that they also had this weird motion, while floating in perfectly still water! This type of motion is now called “Brownian Motion”.

So where does Einstein come in, and more importantly where do you come in?

Well, I’ll start with Einstein. He was able to show that this type of random motion happened, in a perfectly still cup of water, because “still water” was made of

Simulation of Brownian motion

molecules that are moving in an extremely chaotic way. Before you think this is not too cool, remember that at that time people were not even sure that atoms existed! We take them granted now :)
so basically genius Einstein calculated the force on a pollen grain floating in water. Then, by watching how pollen grain moved around in still water, you can determine the size of water molecules that are hitting them.

Pause for a second and appreciate how cool this is. We humans, starting in a jungle not knowing anything about the world, were able to build microscopes and determine that everything in the universe is made up of atoms. One botanist watching pollen grains and one genius using pen and paper were able to prove the existence of atoms and to determine some of their properties.

I think everybody should be able to appreciate this, and I want to share this thought with many people. This is were you come in, I want to create a series of posts to guide you through this calculation in a project based format.

By project based, I mean you will be doing the calculations and experiments in guided way. It also means that you will only learn things as you need them. Traditionally people teach you an entire course of calculus that you don’t get apply to anything you care about. Here we will do the opposite, we start with something you care about, like proving that atoms exist, and then we will learn along the way anything that we need to apply, like basic integration for example.

If this series comes out like I envision it in my head, it will feel like a game to you. You will start with a goal in mind and then clear level after level, feeling like you are winning along the way. Of course this will not be easy but it will be engaging to everyone. So if you like challenging games, this should be the coolest game you play: understanding the universe!

Who is this for?


Well nothing is for everybody, but, this series of posts is for anybody who wants to understand how our world works. If you want to get a feeling of how physicists understand the world then this series will provide you with that understanding. You might be an English major, an entrepreneur or a mechanical engineer, this is fun and incredibly useful for all humans.