Wait, what is… antimatter?

Somewhere in the Universe, there is an exact version of you. Same mass. Same shape. Same questionable fashion choices. But this version is... opposite somehow. Like a mirror image of you hidden in the depths of a faraway galaxy. Or at least... there should be. This doppelgänger would be made of antimatter, a staple of science fiction and crime novels (I'm looking at you, Dan Brown). Despite the reputation, it is very real, and we can even make it in our labs. Yet, for something that should be everywhere, it's exceedingly hard to find. So... wait, what is antimatter? In this article, we'll look at what it is, how it behaves, and why physicists believe there should be far more than we see.

The anti-Universe

Aside from being Hollywood's scapegoat — antimatter is an important scientific curiosity. Despite the way it sounds, it isn't some strange substance that breaks the rules of reality. It basically follows the same rules as matter — just with a few signs flipped.

Though it may sound basic, antimatter is simply the collective name for antiparticles. Every fundamental particle we know of has one: a twin with the same mass, but opposite charge*. The electron, for example, has a negatively charged antiparticle called the positron. The proton has the antiproton. The neutron has the antineutron.

Think of a photograph, where you have the regular image and its negative — a complete inversion of the original. Apply this idea to matter and antimatter and you're most of the way there.

Now, what would happen if you stacked a photograph and its negative together? All the detail washes out. So what would happen if you shook hands with your antimatter counterpart? Well… Angels and Demons got one thing right — a big ol’ explosion.

Well... almost. When a particle and its counterpart meet, they annihilate into a flash of pure energy**. This process is extremely efficient, converting all of their mass into energy. But at the scale of individual particles, that energy is tiny. For an electron and positron, it’s roughly equivalent to the energy of a tennis ball moving at just 0.000008 kilometres per hour.

This kind of annihilation happens all the time — so how did we ever notice it in the first place?

Discovering the opposite

Antimatter didn’t first show up in a lab. It appeared on paper.

In the early 20th century, physicists were trying to make sense of two very successful but very different ideas: quantum mechanics, the rule of the tiny and special relativity, the rule of the fast. But in 1928, Paul Dirac managed to unite these two in a single equation for the electron. This was massively successful — but came with a price.

When Dirac solved the equation, it didn't just describe electrons — it also described electrons with negative energy. This is an issue as if these states existed, electrons should immediately fall into them (like a ball rolling down a hill), and all matter would be completely unstable. And... you know, negative energy doesn't exist. Clearly something was wrong.

So Dirac proposed a strange solution. Imagine you're taking a bird's eye view of a completely full car park — every single space occupied. You wouldn't really notice any individual car, they all just blend into one another. However, if one space were suddenly empty — that absence would stand out immediately.

Dirac said the universe is the same — all the negative energy states are already filled, forming what became known as the Dirac sea. We don't see it — but if one of those states is missing, it would appear as a particle with positive energy and opposite charge***. For the electrons, this 'missing' electron would behave as a brand new particle: the positron. Our first piece of antimatter.

At the time, this was pure theory — no one had ever seen such a particle. But in 1932, whilst studying cosmic rays — high energy particles streaming in from space — Carl Anderson spotted something odd. A particle with the same mass as the electron, but curving the wrong way in a magnetic field. This could only mean one thing — the positron was real, and it had been found.

From that moment on, antimatter stopped being a mathematical curiosity and became a physical reality. Over time, physicists discovered antiparticles for protons, neutrons, and more. Every time a new particle appeared, its opposite followed close behind.

Where did all the antimatter go?

Most of particle physics is built on rules of symmetry. Under these rules, matter and antimatter should be created in perfectly equal amounts. And if that were the whole story, the universe would have been very short-lived — matter and antimatter would have met, annihilated, and left behind nothing but light. This is, to put it mildly, a problem.

Clearly, that didn't happen. The fact that our universe is made almost entirely of matter is known as the matter–antimatter asymmetry problem, and it’s one of the biggest open questions in modern physics. Somewhere in the early universe, something tipped the balance.

And this imbalance didn't need to be large. If the universe produced just one extra matter particle for every billion matter–antimatter pairs, those billion pairs could annihilate away — and the tiny leftover would still be enough to create every star, every planet and every person around us today.

Exactly how the universe managed this is... unclear. One particularly promising clue comes from something called CP violation, in which the laws of physics treats matter and antimatter slightly differently. If nature doesn't follow the rules of symmetry perfectly, even just by this tiny amount, that could be enough put antimatter on the back foot.

CP violation is just one piece of a much larger puzzle — on its own, it isn’t enough to explain why matter won. Instead, it forms part of a set of requirements known as the Sakharov conditions, which outline how the universe could generate an imbalance between matter and antimatter. What’s intriguing is that we’re seeing more and more particles exhibit this asymmetry. The universe is cheating slightly — and antimatter is the one paying the price.

But without that cheating, the universe might not be here at all.

Why anti-matters

Whilst antimatter might sound like an abstract curiosity with little connection to everyday life, we actually use it all the time. If you’ve ever had a PET scan, you’ve already benefited from antimatter. PET stands for positron emission tomography, and has become an invaluable tool in medical imaging — particularly in cancer diagnosis and research.

Antimatter has also been suggested as a potential fuel for the future. Pound for pound, it has the highest energy release of any fuel we know of. This makes it an exceptional candidate for propulsion in something like interstellar travel. However, producing and storing antimatter is extraordinarily difficult — so we might be waiting for this future for a while.

These are just a few examples of why antimatter matters beyond the equations. As research continues, it’s likely that new applications will emerge. And all of this comes on top of the sheer scientific achievement of creating and studying antimatter itself — including atoms like antihydrogen and antihelium, both of which have now been successfully observed.

Summary

Antimatter is not just sci-fi or locked in Hollywood films — it's a very real part of nature. Every particle we know has its evil twin waiting to annihilate it out of existence.

The real mystery isn't what antimatter is, but why we don't see more of it. The laws of physics as we understand them state that we should have equal amounts of both — but antimatter has clearly lost.

Studying antimatter isn't just an exercise in completeness — it's asking why we exist at all.