Why didn’t matter and antimatter annihilate everything?

  The Antimatter Mystery in the Big Bang

We know from Einstein’s famous equation — E = mc² — that energy can turn into matter, and matter can turn back into energy. In the first few microseconds after the Big Bang, this is exactly what was happening: an extremely hot, dense soup of energy created particles and antiparticles in equal amounts.

But here’s the puzzle: if the universe started with equal amounts of matter and antimatter, why do we see only matter today? Antimatter seems to have vanished almost entirely, even though it should’ve annihilated all the matter in a giant cosmic fireball, leaving behind just energy.

Clearly, something tipped the scales.

The Need for Asymmetry

Physicists believe there must have been a tiny imbalance — maybe for every billion antimatter particles, there were a billion and one matter particles. That extra one in a billion is what survived after all the annihilations.

But how did this asymmetry arise?

 Enter CP Violation

One explanation involves a concept called CP violation. In simple terms, the laws of physics usually treat matter and antimatter as mirror opposites. But CP violation means that in certain rare interactions, matter behaves just a little bit differently than antimatter.

This tiny difference, observed in particles like kaons and B-mesons, could explain why more matter survived than antimatter — but current experiments show it’s not enough on its own.

 The Sakharov Conditions

In 1967, Russian physicist Andrei Sakharov outlined three conditions necessary for the universe to end up with more matter than antimatter:

1. Baryon number violation – Particles like protons must not always be conserved.

2. C and CP violation – There must be differences in how particles and antiparticles behave.

3. Departure from thermal equilibrium – The universe must have passed through out-of-balance conditions, like rapid expansion.

We know the early universe had the third condition. And we’ve observed a bit of CP violation. But we still don’t know enough about the first two.

 Where Are We Now?

Experiments at CERN, Fermilab, and KEK are trying to measure more CP violation in rare particle decays. The LHCb experiment, in particular, looks closely at how beauty quarks behave — they may hold more clues.

Meanwhile, some theories like leptogenesis suggest the imbalance may have started with neutrinos and later transferred to matter.

 So… Why Are We Here?

The truth is, we don’t yet fully understand why matter won. And that’s what makes this mystery so powerful. It’s not just about antimatter — it’s about why anything exists at all.

You, me, the stars, the galaxies — everything is made possible by a tiny tilt in nature’s scales.

And someday, we might finally know why the universe chose matter.

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