At the moment of the Big Bang, the incredibly hot, impossibly dense mass known as the universe exploded to create every particle of matter that now surrounds us. Here’s the problem: the way physicists understand it, the processes that formed those first particles should have produced an equal number of antiparticles, thereby annihilating all matter and effectively canceling everything out.
But they didn’t. That has left physicists scratching their heads for decades trying to ask this most basic question: why does anything exist at all?
Heads, You Win
Every particle in the Standard Model — the theory that describes the tiniest building blocks of the universe — has what’s known as an antiparticle. Antiparticles have the exact same mass as their sister particles, but an opposite electric charge. For example, take a familiar particle like the electron, which has a negative charge. Its antiparticle is called the positron, and it has (you guessed it) a positive charge. Most antiparticles don’t get their own names the way the positron does; the others just slap “anti-” in front to become the anti-neutron or the anti-muon. Still others are their own antiparticles: the photon doesn’t have a charge, so the photon and the anti-photon are the same thing. Since particles are what make up matter, antiparticles are what make up antimatter.
When antimatter and matter interact, the result is catastrophic. The two particles annihilate each other, leaving behind a burst of pure energy. (In fact, the reaction is so pure and efficient that the writers of “Star Trek” decided to power the starship Enterprise with antimatter). But when a particle of matter is created the way it was at the beginning of the universe, it’s always paired with its antimatter particle. Physicists have made this happen in the lab, in fact, and watched as particles and their antiparticles “oscillate” millions of times per second before they decay into another particle, one that’s either matter or antimatter. At the beginning of the universe, this decay should have happened in a 50/50 ratio: half into matter, half into antimatter. And as you now know, 50 percent matter plus 50 percent antimatter means zero percent universe.
CERN explains this using a coin analogy: a coin spinning on a table can land on heads or tails, but you can’t call it heads or tails until it actually lands. If you spin a whole lot of coins, you should expect that roughly half will land on heads and half will land on tails. Same goes for the oscillating particles. But in the early universe, something changed the odds, and we don’t know what that something was. It was as if a magic marble rolled along the table and made most of the coins land on heads.
Two Steps Forward, Two Steps Back
So what was it? Why did we get more matter than antimatter? Why is matter even a thing? To find out, physicists are trying to find the tiniest, subtlest differences between matter and antimatter. If a difference exists, it could explain why one got a leg up on the other in the early universe.