It’s said that we’re all made of star stuff, but how is that star stuff itself made? Harry Cliff explains
Harry Cliff is a particle physicist at Cambridge working on the Large Hadron Collider and the author of Space Oddities (2024)
Everything we can see in the world around us is made of atoms. But where did those atoms come from? It’s a question that’s fascinated natural philosophers and scientists for centuries, and is one we’re still learning more about today.
At the start of the 18th century, Isaac Newton declared that atoms had probably been created by God at the beginning of time. He believed that atoms were indestructible, “no ordinary power being able to divide what God had made one in the first creation”.
However, in the first decades of the 20th century, physicists found that they could break atoms apart in the lab using powerful, albeit earthly, forces, which eventually led to the realisation that every atom in the periodic table is made of just three subatomic particles: electrons, protons and neutrons.
The discovery of atomic substructure opened up the possibility that atoms themselves had been created out of these basic constituents. But how?
Every atom has the same structure, a tiny positively charged nucleus orbited by negatively charged electrons. The nucleus itself is made of positively charged protons and electrically neutral neutrons bound together by the strong nuclear force, and crucially it is the number of protons in the nucleus that determines whether an atom is, say, carbon, oxygen or uranium.
Raw materials
Hydrogen is the simplest atom, a single proton orbited by a single electron, and most of the hydrogen we see in the Universe today was created shortly after the Big Bang. It is the obvious candidate for the raw material from which all the heavier elements are made.
The next simplest atom is helium, whose nucleus is made of two protons and two neutrons. However, combining hydrogen together to make helium is far from easy.
Protons are positively charged, and so exert an enormous repulsive force on each other when they come close together. For two protons to fuse, they have to get within around 10-15 metres of each other – a distance comparable to the size of the protons themselves – at which point the attractive strong nuclear force begins
