How do atoms form? A physicist explains where the atoms that make up everything come from

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How do atoms form? – Joshua, age 7, Shoreview, Minnesota

Richard Feynman, a famous theoretical physicist who won the Nobel Prize, said that if he could pass on just 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, because everything is made of mass.

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

What is an atom?

An atom consists of a heavy center called the nucleus, made of particles called protons and neutrons. An atom has lighter particles called electrons that can be thought of as orbiting 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 total charge.

Now most atoms in the universe are of the two simplest types: hydrogen, which has one proton, zero neutrons, and one electron; and helium, which has two protons, two neutrons and two electrons. Of course, there are many other atoms on Earth 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.

When were the first atoms formed?

Most of the hydrogen and helium atoms in the universe formed about 400,000 years after the Big Bang, which is the name for when scientists think the universe began about 14 billion years ago.

Why were they created at that time? Astronomers know from observing distant exploding stars that the size of the universe has expanded since the Big Bang. When hydrogen and helium atoms were first formed, the universe was about a thousand times smaller than it is today.

And based on their knowledge of physics, scientists believe that the universe was much hotter when it was smaller.

Before then, the electrons had too much energy to settle into orbits around the hydrogen and helium nuclei. So the hydrogen and helium atoms could only form after the universe had cooled to about 5,000 degrees Fahrenheit (2,760 degrees Celsius). For historical reasons, this process is misleadingly called recombination; combination would be more descriptive.

The helium and deuterium nuclei, a heavier form of hydrogen, formed even earlier, just a few minutes after the Big Bang, when temperatures exceeded 556 million degrees Celsius. Protons and neutrons can collide to form such nuclei only at very high temperatures.

Scientists believe that almost all ordinary matter in the universe is made up of about 90% hydrogen atoms and 8% helium atoms.

How do heavier atoms form?

So the hydrogen and helium atoms were formed during recombination, when the lower temperature allowed electrons to fall into orbits. But you, me and almost everything on Earth are made of much more massive atoms than just hydrogen and helium. How are these atoms made?

The surprising answer is that heavier atoms are made in stars. Making atoms with different protons and neutrons stuck together in the nucleus requires the kind of high-energy collisions that occur in very hot places. The energy required to form a heavier nucleus must be great enough to overcome the repulsive electrical force that positive charges, such as two protons, feel against each other.

Protons and neutrons also have another property – a bit like a different kind of charge – that is strong enough to bind them together once they can get very close together. This property is called the strong force, and the process that sticks these particles together is called fusion.

Scientists believe that most elements, from carbon to iron, are fused in stars more massive than our sun, where temperatures can exceed 556 million degrees Celsius – the same temperature the universe was when it was just a few minutes old.

But even in hot stars, elements heavier than iron and nickel will not form. These require extra energy, because the heavier elements can break into pieces more easily.

In a dramatic event called a supernova, the inner core of a massive star suddenly collapses after running out of fuel for combustion. During the powerful explosion that causes this collapse, elements heavier than iron can form and be thrown into the universe.

Astronomers are still figuring out the details of other fantastic stellar events that form larger atoms. Colliding neutron stars, for example, can release enormous amounts of energy – and elements such as gold – on the way to forming black holes.

To understand how atoms are made, you just need to learn a little general relativity, plus some nuclear, particle, and atomic physics. But to make matters even more complicated, there are other things in the universe that don’t seem to be made of normal atoms at all: dark matter. Scientists are investigating what dark matter is and how it can form.

Hello, curious children! Do you have a question that you would like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Tell us your name, age and the city where you live.

And since curiosity knows no age limit – adults, let us know what you’re wondering too. We won’t be able to answer all questions, but we will do our best.

This article is republished from The Conversation, an independent nonprofit organization providing facts and trusted analysis to help you understand our complex world. It was written by: Stephen L. Levy, Binghamton University, State University of New York

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Stephen L. Levy receives funding from the National Science Foundation and the National Institutes of Health. He is affiliated with CyteQuest, Inc.