From quarks to galaxies: how the universe's matter formed

0:00How did the matter in our universe form?

0:03It began with the big bang, about 13.8 billion years ago, extremely hot and dense.

0:11Since then, it has expanded and cooled; this bar runs from hot to cold.

0:17In the first second, particles called quarks joined in threes to make protons and neutrons.

0:24At one second it was about 10 billion kelvin. Zero kelvin is the coldest possible.

0:31In the first few minutes, at about 1 billion kelvin, some protons and neutrons fused, or joined, into helium nuclei, the centres of atoms.

0:42Lone protons are hydrogen nuclei. By mass, there was about 3 parts hydrogen to 1 part helium.

0:50At about 380,000 years and 3000 kelvin, electrons joined nuclei to make neutral atoms, with no overall charge.

1:00Light stopped bouncing off free electrons and could travel freely.

1:05Within a few hundred million years, below 100 kelvin, gravity pulled gas into the first stars and galaxies, huge groups of stars.

1:15Inside stars, fusion makes heavier elements, like carbon, oxygen and iron.

1:22Big stars explode and scatter these elements. About 4.6 billion years ago, the Sun and Earth formed from that gas and dust.

1:32A common mistake is thinking every element came from the big bang.

1:37It made almost only hydrogen and helium; heavier elements came later, mostly from stars.

1:44As it cooled, matter built up: protons and neutrons, nuclei, atoms, stars and planets.