Picture the whole universe — every star, every galaxy, every empty stretch of space. Now imagine all of it is made of tiny building blocks called elements. There are about a hundred kinds. And one of them is so common it makes everything else look rare. Its name is hydrogen.

Hydrogen is the simplest thing there is. One little center, called a proton, with one even tinier electron buzzing around it. That's the whole recipe. Nothing in the universe is built more simply than this.

Why is hydrogen everywhere? Because it was first. About 13.8 billion years ago, the universe was a hot, crowded soup. As it cooled, the very first atoms snapped together — and almost all of them were hydrogen.

So hydrogen had a huge head start. Long before there were planets or people, the young universe was basically one enormous ocean of hydrogen gas, drifting in the dark.

Then gravity got to work. It gathered the hydrogen into giant clumps, squeezing them tighter and tighter until they grew hot enough to burst into light. Those glowing balls of squeezed hydrogen are what we call stars.

Here's the wonderful part. Stars are still mostly hydrogen, burning it for fuel. Our own Sun is a giant hydrogen furnace. So even the things made of hydrogen are made of mostly hydrogen!

There's a runner-up, too. Inside stars, hydrogen slowly fuses into the next-simplest element, helium — the same stuff that fills floaty party balloons. Helium is second-most-common, but it's still far behind. Hydrogen wins by a landslide.

If you scooped up every atom in the universe and lined them up, about nine out of every ten would be hydrogen. Heavier stuff — the carbon in you, the oxygen you breathe, the iron in the ground — are the rare guests at a party hydrogen has been throwing for billions of years.

So the most common element isn't gold, or oxygen, or anything fancy. It's the smallest, simplest, oldest one of all. The universe is, more than anything else, an enormous sea of hydrogen — quietly lighting up the stars.