(bright music) (glass clacking) (coffee machine hissing) (liquid sloshing) - [Narrator] Ah, that's better.

Okay, now that I've had some coffee, let's run that back.

(liquid sloshing) (booming) What's going on in that cup of coffee?

It might seem boring, but the closer you look, the more complex and surprising it becomes.

(coffee machine hissing) First off, there are trillions upon trillions of molecules in the air around that coffee and those hot vapors rising off the cup carry more than a thousand different types of molecules.

A few dozen of those contribute to coffee's one of a kind aroma.

Pyrazine has an earthy smell.

Methylpropanal is fruity and spicy.

There's vanillin, you can probably guess what that smells like.

Methional smells like a baked potato.

Methanethiol is the odor of cabbage or garlic, thanks to a sulfur group which also shows up in the smells of rotten eggs and skunk spray.

Most of those molecules are made when the beans are roasted.

The heat of roasting provides the energy to convert coffee's bitter chlorogenic acid into all these other compounds, making a richly flavorful, fragrant, and just awesome beverage.

Many chemical reactions require some energy to get going, even the ones that release energy like combustion.

After all, spending energy is how we make things happen.

Cars drive, legs walk, and coffee brews, which brings me to caffeine, which is probably the reason why most of us drink coffee anyway.

The story of caffeine is also a story of evolution.

Plants didn't evolve caffeine to help us get through 9:00 AM meetings.

Like so many of the molecules plants make, caffeine, which is actually pretty bitter on its own, is a chemical weapon that can disable or even kill insects that threaten plants.

But citrus plants use caffeine a different way.

Thanks to caffeine's memory boosting and ever so slightly addictive kick, it helps bees and other pollinators remember the citrus flowers they visit.

That gives those plants an advantage in spreading their genetic material which is, evolutionarily speaking, what life is all about.

So caffeine doesn't just give you that pleasant morning buzz, you can also thank it for your orange juice.

But back to our own brains, caffeine blocks the nerve receptors that signal the brain that it's time to sleep.

That's what helps us power through our bedtime.

And speaking of energy, watch that milk swirl and blend with the coffee.

You're looking at diffusion, the process of particles moving from an area where there is a lot of the same stuff to an area where there isn't.

Diffusion is how breathing keeps us alive.

Oxygen diffuses from air into our bloodstream in the lungs, and from capillaries into our cells throughout the body.

The way the milk moves here is driven by a few things.

It falls due to the force of gravity, pulling it down from the carton and into the mug.

But then its motion through the coffee is disrupted by the stickiness of milk and coffee molecules interacting.

That and the walls of the mug help set up those swirling eddies.

Convection is at play here too.

Colder, denser milk sinks to the bottom of the warmer, less dense coffee.

This causes the same kind of loops of motion that happen in liquified rock far beneath the Earth's surface.

It's this motion that keeps our planet geologically active.

But even in the absence of any of these phenomena, milk and coffee would eventually mix anyway.

The particles of milk and little undissolved coffee grounds dance, thanks to Brownian motion.

That's the random movement of particles as they crash and collide off of one another.

Studying this dance was one of the clues that Einstein used to prove the existence of atoms.

This spontaneous process of mixing follows the second law of thermodynamics, that entropy or disorder increases over time.

Your coffee and milk go from two separate substances to a mixture, which is less ordered because it's made of two things all mixed up together.

This disorder increase is even more obvious with the sugar, which goes from a solid crystalline state where each molecule is locked in a pattern to a dissolve form with sugar molecules all over the place.

And so it goes with the rest of the universe, rocks crumble to dust, ice melts, and your place just keeps on getting messier.

Left to itself for long enough, the entire universe will one day reach a state of maximum disorder, a bit like this milk and coffee.

What are we getting at here?

From the largest scale to the smallest, chemistry is everywhere.

And once you see it, you'll never look at the world the same way again.

(gentle upbeat music)