'A remarkable conspiracy': Why is matter neutral? Physicist Frank Close explores the mystery in a new book

An artist's 3D rendering of an atom — In his new book, Frank Close explores the mystery of why subatomic particles balance each others' charges.

(Image credit: Rost-9D via Getty Images)

Since the discovery of the proton and the electron in the 20th century, a mystery persists at the core of the atom: Despite belonging to completely different particle families and being radically different in size, the charges of these two particles completely balance each other out — enabling a universe where gravity dominates. But why?

To explore the clues, Live Science sat down with Frank Close, an author and emeritus professor of particle physics at Oxford University, to discuss his new book "Charge" (Oxford University Press, 2024). In it, Close traces out the conundrum through a concise history of particle physics, including the strong, weak and electromagnetic forces that operate over short distances, the discovery of the Higgs boson, and the hints of a yet-to-be-discovered grand unified theory.

Why is it that, every breath you take, your hair doesn't stand on end, given that you're breathing in a billion billion billion atoms of oxygen and nitrogen in the air, each of which has got all this electricity in it? The negative charge on the electrons of all these atoms is triflingly small, but there are so many of them together that a single breath is like breathing in roughly 15,000 coulombs — that's enough to spark 1,000 bolts of lightning.

It's the puzzle at the heart of the book. If we had this discussion a century ago, the only particles that were known were the negatively charged electrons and the positively charged protons. I would probably have told you that I don't know quite what charge is, but it is something that you can take away or add and that in the case of the electron it's had it removed and the proton has had it added.

The problem is that we now know much more. In the 1960s we discovered that the proton has a structure, it's made up of things called quarks. Up quarks have two thirds of positive charge, and down quarks negative charge of one third. The simplest way to make a proton is out of three quarks — two up quarks and one down. If you want to make a [neutrally charged] neutron you use two down quarks and one up.

FC: Quarks carry another sort of charge, which we call color. This color charge occurs in three different varieties: red, blue and green. They're not real colors, but there are three of them and they follow the same rules as electrostatic charges — with like charges repelling and unlike ones attracting. So it's this 'threeness' of the color charges that help them clump powerfully to form the proton. The fact that each of them, on average, carries one-third electrical charge is what makes the conspiracy work.

We know from very precise experiments over the last 30 or 40 years that, as you go to higher energies at the Large Hadron Collider, that the relative strength of these [fundamental] forces does change slightly. If you extrapolate that, it means that at some unimaginably high energy these three forces [the strong force via color charge, the electromagnetic force via electrostatic charge, and the weak force via the W and Z bosons] have roughly the same strength.

Ben Turner is a U.K. based writer and editor at Live Science. He covers physics and astronomy, tech and climate change. He graduated from University College London with a degree in particle physics before training as a journalist. When he's not writing, Ben enjoys reading literature, playing the guitar and embarrassing himself with chess.