The question of what protons or neutrons are made up of has an apparently simple answer: quarks and gluons. However, when it comes to atoms’ third component, electrons, the answer is not as easy.
That’s because, as far as we know, electrons are fundamental particles. In other words, they have no smaller components. That’s not something that can be absolutely proven, but it’s certainly what the available evidence suggests. This raises the much more difficult question of what is the composition of a fundamental particle, and how does it differ between electrons and others?
The word “atom” comes from the Greek for “unable to be cut”, based on the philosopher Democritus’s reasoning that matter must be composed of something so small it could not be further divided. Twenty-three centuries later, we discovered that the objects we called atoms were not in fact atoms in Democritus’s sense, having at least two, and aside from hydrogen, three, smaller components.
Once the composition of protons and neutrons was revealed, it was easy to suspect that this was a case of “turtles all the way down”; we would keep discovering smaller and smaller particles that made up each level we discovered. Indeed, some might have considered it arrogant to think they were part of the generation to have discovered the true fundamental particles.
However, electrons have resisted this sort of infinite regression; 125 years after their discovery, there is no sign of anything smaller within them. Attempts to find some component particles involve both smashing electrons against other electrons and seeing if they release anything, and trying to find internal structure at very high energies. Neither approach has revealed anything inside.
In the meantime, we learned that electrons, like everything that small, are both particles and waves.
Some hypothetical component particles have been proposed for electrons, but the physics they rely on doesn’t fit as well with what we see as the Standard Model of Particle Physics. Although the Standard Model is generally thought not to be a complete description of reality, with particles not included within it suspected to exist, the fundamental nature of the electron is not one of the aspects that attracts widespread doubts.
Given how much lighter electrons are than the particles of an atomic nucleus, it’s not so surprising they’re not made up of anything lighter.
So, if electrons have no smaller particles to compose them, is there some sort of indivisible material from which they are formed, some electronia, perhaps?
This is the point where it becomes hard to visualize (even for people who don’t have aphantasia). Rather than having some type of matter to make them up, physicists describe fundamental particles as an excitation of a field. In a rare effort to assist understanding, in the case of the electron, this is known as the electron field.
Interactions of this field with other fields give electrons their properties. For example, it is the Higgs field that gives particles, including electrons, their mass.
Describing something as an excitation of a field isn’t a very satisfying answer for non-physicists. Unfortunately, or perhaps fortunately, the universe doesn’t really do things for the sake of our satisfaction, and it’s the best description we have.
