Why Is There More Matter Than Antimatter?

Nobody knows yet. Our best physics says the Big Bang should have made matter and antimatter in equal amounts. The two destroy each other on contact, so the universe should now hold little but leftover light. Instead, it is full of stars, planets and people. According to CERN, the best explanation so far is that some unknown process left a tiny surplus of matter: about one extra particle for every billion particles of antimatter. Everything we see is made of that leftover.

The known laws of physics do treat matter and antimatter a little differently. But the difference they allow is far too small to explain why we are here. That makes this one of the biggest open questions in science.

What is antimatter?

Antimatter is real, not science fiction. In 1928, the British physicist Paul Dirac wrote an equation for the electron that had two kinds of solutions. One described the electron as expected. The other seemed to describe a particle with negative energy. Physicists came to read it as an “anti-electron”: a twin with the same mass but the opposite electric charge. In 1932, Carl Anderson spotted that twin, the positron, in cloud chamber tracks left by cosmic rays. It was the first antiparticle proven by experiment.

Today we know every kind of matter particle has an antimatter partner. When a particle meets its partner, both vanish in a burst of energy. That is called annihilation. In nature, antimatter shows up only as single particles made in nuclear reactions or cosmic-ray collisions. CERN makes it on purpose to study it, but only in tiny amounts. If its “Antimatter Factory” ran non-stop for a whole year, all the antiprotons it made would light a 100-watt bulb for only about five seconds.

If the Big Bang made both, why are we still here?

Picture a bank ledger. In the hot early universe, every time a particle of matter was written in, a particle of antimatter was written in beside it. When they met, both entries were crossed out. At the end, the balance should be zero. Yet the universe ended up with a small amount left over.

We can measure how much. Scientists compare the number of particles of ordinary matter with the number of particles of light left from the early universe. Two separate methods, one using the cosmic microwave background (the oldest light we can see) and one using the mix of the lightest elements, agree beautifully. In a perfectly balanced universe, that ratio would be about a billion times smaller. The first light elements could not have been made, and stars and galaxies could not have formed. To learn how those leftover atoms later built stars and planets, see where our atoms came from.

What would it take to tip the balance?

In 1967, the physicist Andrei Sakharov listed three conditions that any explanation must meet. In plain words, as explained by Symmetry magazine:

1. The balance must be able to change. Normally, matter and antimatter are made and destroyed only in matched pairs. Some process must be able to break that pattern and change the total count of matter minus antimatter. Physicists call this baryon number violation. (Baryons are particles like protons and neutrons.)
2. Nature must play favorites. Matter and antimatter must follow slightly different rules. Physicists call this C and CP violation.
3. There must be a one-way street. The universe must change quickly enough that reactions cannot simply run backward and undo the surplus. Physicists call this a departure from thermal equilibrium.

Think of a game that starts 0–0. For one team to end up ahead, points must be possible, the rules must slightly favor one side, and the final whistle must blow before the other side can catch up.

What have experiments found so far?

The second condition is real. In the 1960s, physicists first saw matter and antimatter follow slightly different rules in a family of particles called mesons. For decades after that, experiments saw the effect clearly only in mesons.

In 2025, CERN’s LHCb experiment saw the same kind of difference in baryons for the first time. The team studied more than 80,000 decays of a heavy cousin of the proton. It found a small but clear imbalance, about 2.45 percent, between how often the particle and its antimatter twin decayed in one particular way. The result passed the strict statistical test physicists require to claim an observation, not just a hint.

Other CERN teams test whether antimatter is a perfect mirror of matter. The ALPHA experiment makes and traps antihydrogen, the simplest anti-atom. It has measured antihydrogen’s properties to 12 significant digits. A separate experiment, BASE, has compared the charge-to-mass ratio of protons and antiprotons to 11 digits. In 2023, ALPHA showed that antihydrogen falls down, not up, within the precision of the test, about 20 percent. Apart from those small differences in how some particles decay, antimatter so far looks like a near-perfect mirror of matter.

What do we still not know?

We do not know what created the surplus. The Standard Model, physics’ best theory of particles, does include matter–antimatter differences. But CERN says the amount it predicts is many orders of magnitude (many powers of ten) too small to explain the universe. The model also falls short on the third condition. A key change happened in the early universe when basic particles first gained mass. For a Higgs boson with the mass we have measured, the Standard Model says that change was smooth, not the sudden, one-way event that would be needed.

So something new is probably involved. One idea, called leptogenesis, uses very heavy relatives of the neutrino. Another, called electroweak baryogenesis, adds new particles that would make that early change sudden and violent. Both are serious proposals. Neither is confirmed.

A brief aside: why is there anything at all?

People sometimes put this physics puzzle as “why is there something rather than nothing?” But it is narrower than that. It asks why matter won out, given a universe that already has energy and laws. The bigger question, why anything exists at all, is beyond science. It involves philosophy and belief, and science can inform it but not settle it. The philosopher Martin Heidegger called it the most fundamental question in philosophy, as the Stanford Encyclopedia of Philosophy notes.

Thoughtful people answer it differently. One perspective, argued by Gottfried Leibniz and developed by many philosophers and theologians, holds that everything needs a sufficient reason, and that the chain of reasons points to a necessary being, God. Another perspective, voiced by the philosopher Bertrand Russell, holds that the universe may simply exist as a brute fact, with no deeper explanation needed. Both views are laid out in the encyclopedia’s entry on the cosmological argument. They are perspectives, not evidence. For more, see whether science can decide if God exists.

What would change the answer?

Several clear results would move this question forward:

• A new source of matter–antimatter difference, larger than the Standard Model allows, found at the LHC or in other precision experiments.
• Signs that the early change was violent, such as a new Higgs-like particle, or a faint hum of gravitational waves that a future space observatory called LISA could detect. Our guide to how we hear gravitational waves explains the idea.
• Any measured difference between how matter and antimatter behave, including in gravity. ALPHA and other teams aim to make their tests far more precise.

Until then, the honest answer is that we are made of a leftover no one can yet explain. That is not a gap to hide. It is one of the best questions a curious person can carry. What would you want to measure first?