Wait, what is… an electron?

We all know what an electron is, right? There are around 100 billion billion billion* inside your body right at this moment. They are those tiny, negative balls whizzing around atoms like planets around the Sun. They're the reason that atoms bond, metals shine and your brain even works. Without electrons, there'd be no chemistry, no electricity, and no WiFi for me to upload this for you to read. But... wait, what is an electron? We talk about electrons like we know them, but what are they really?

The Humble Electron

Let's start with something everyone knows — an electron is tiny, and it's negative. Electrons were the first subatomic particles ever discovered and, as far as we know, they don't have any size — like a point. No smaller parts, no structure — just an intrinsic piece of reality. This is the definition of a fundamental particle — not made of anything else, it just... is.

Physicists class the electron as a lepton, meaning it's part of a family of particles that don't feel the strong nuclear force (which keeps protons and neutrons together) but feel all the others**. Electrons have a charge of -1, and a mass so small it would take roughly 1 septillion of them to make up the mass of an ant. And yet, despite this tiny size, electrons impact the lives of all of us.

Electrons also have an evil twin, positrons, which are identical in every way except charge — they're positive, +1. When the two meet they annihilate, leaving no trace except for a flash of pure energy — a possibility you might remember from the plot of Dan Brown's Angels and Demon. The positron was the world's first example of antimatter, but we'll leave that for another time.

However, we didn't alway know these basic facts. 150 years ago, suggesting anything could be smaller than an atom was ludicrous — until a strange glow in a glass tube indicated something more.

Discovering the Electron

In the late 1800s, physicists knew about electricity, but were unsure what it was made of.

They accepted it contained positive and negative parts, and some believed these themselves had fundamental components — like little particles of electricity. They named these electrons, but it was widely accepted that they must be bound up tight inside an atom. You couldn't possibly see these individually.

At a similar time, physicists were also debating the nature of cathode rays, which caused an odd glow to appear on the inside of a glass tube. This only occurred when an electric current was applied across a tube with all of the air taken out of it. By putting the rays in electric and magnetic fields, scientists worked out their charge to mass ratio — finding they were made of particles almost 2,000 times smaller than a hydrogen atom. And thus, the first subatomic particle was discovered!

This discovery was made by a British scientist called J. J. Thomson in 1897. Originally, he called them corpuscles, but eventually changed the name to match with the particles of electric charge: electrons. Thomson predicted (correctly) that they were small parts of an atom, modelled like a plum pudding: the negative charged “currants”, electrons, embedded in the positive “pudding”. Of course, we now know this is incorrect, and that the atom is made of a positive centre with electrons surrounding it, but the first step had been taken.

For decades we pictured electrons as tiny dots circling atoms like moons. However, the 20th Century had something else in store for us. Physicists began probing electrons in new ways — not with vacuum tubes, but with beams and slits.

The Quantum Electron

Imagine firing a gun at a metal sheet with one slit cut into it. The bullets that make it through will leave the shape of a single band on a wall behind. Cut two slits, and you'd expect two bands on the wall. What if instead, you saw a wave-like pattern of bright and dark spots, as if the bullets behaved as a wave.

Well, that's exactly what happens with electrons: one slit, they behave like tiny bullets; two slits, they behave like a wave — this is the Double-Slit Experiment. “Okay.”, you're thinking, “Perhaps the different electrons are interfering with each other and bouncing off one another”. Perfectly reasonable... but electrons have something to say about that. Even if you fire electrons one at a time through the two slits, you still see the wave-like behaviour — it's as if the electrons are bouncing and interfering with themselves, as though one electron is going through both the slits at the same time. Yeah, quantum physics is strange.

But that's not all. If you watch the electron and which gap it goes through, the wave-like behaviour disappears! It behaves just like a bullet would. The mere act of observation changes the way the electron travels. One way physicists describe this is with the wavefunction — a cloud of probabilities that change once you have more information.

In reality, the electrons don't have definite paths... or even positions. One electron exists as this cloud of probability — where it could be here, there, or in your neighbour Carol's cup of tea. We can only say where we are likely to find it. The entire field of quantum physics can be attributed to trying understand how electrons behave. They truly are everywhere all at once — until you look at them, that is.

Summary

From cathode rays to quantum theory, electrons have shaped our views on the universe for over a century. They power our computers, influence every chemical reaction, and even stop our feet from falling through the Earth. They were the first thing we discovered beyond the “impenetrable” atom, and yet have never lost their significance.

So, what is an electron? It’s a wave, a particle, a field — and the reason you can read these words right now.