The building blocks of life: how atoms form in extreme heat

Most of the universe is made up of hydrogen and helium atoms, which came into being after the big bang cooled down a little. Heavier atoms are formed during high-energy collisions in stars. By Stephen L Levy

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Richard Feynman, a famous theoretical physicist who won the Nobel Prize, said that if he could pass on only one piece of scientific information to future generations, it would be that all things are made of atoms.

Understanding how atoms form is a fundamental and important question, since they make up everything with mass.

The question of where atoms come from requires a lot of physics to be answered completely - and even then, physicists like me only have good guesses to explain how some atoms are formed.

What is an atom?

An atom consists of a heavy centre, called the nucleus, made of particles called protons and neutrons. An atom has lighter particles called electrons that you can think of as orbiting around the nucleus.

The electrons each carry one unit of negative charge, the protons each carry one unit of positive charge, and the neutrons have no charge. An atom has the same number of protons as electrons, so it is neutral - it has no overall charge.

Now, most of the atoms in the universe are the two simplest kinds: hydrogen, which has one proton, zero neutrons and one electron; and helium, which has two protons, two neutrons and two electrons. Of course, on Earth there are lots of atoms besides these that are just as common, such as carbon and oxygen, but I'll talk about those soon.

An element is what scientists call a group of atoms that are all the same, because they all have the same number of protons.

The first atoms form