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The Universe Shouldn't Exist: Here's Why #science #universe
TL;DR
A tiny early-universe imbalance—about one extra matter particle per billion pairs—left enough matter to form all cosmic structures.
KEY POINTS
The matter–antimatter paradox
Fundamental physics predicts that matter and antimatter are created in equal amounts from energy. When they meet, they annihilate into radiation, implying the universe should have erased itself into pure energy shortly after its birth.
Observed imbalance
The visible universe is overwhelmingly composed of matter, with antimatter exceedingly rare. This asymmetry contradicts the expectation of perfect balance and remains one of cosmology’s central unsolved problems.
A one-in-a-billion surplus
Measurements of the cosmic microwave background indicate roughly a billion photons per matter particle today. Since annihilation of matter–antimatter pairs produces photons, this ratio implies that about one matter particle in a billion survived the early annihilation era.
Annihilation and survival
As the universe cooled, nearly all matter and antimatter pairs annihilated into radiation. The tiny excess of matter—just that one-in-a-billion fraction—remained and ultimately formed stars, galaxies, planets, and life.
Sakharov conditions
In 1967, physicist Andrei Sakharov proposed three requirements for generating this imbalance: processes that change the number of matter particles, slight differences in how matter and antimatter behave (CP violation), and conditions out of thermal equilibrium in the rapidly expanding early universe.
Frozen-in asymmetry
Rapid cosmic expansion and cooling prevented the slight bias from being erased. This “freeze-out” locked in the imbalance before reactions could restore symmetry, preserving the small matter surplus.
CONCLUSION
A minute asymmetry in the early universe—amplified by cosmic expansion—appears to explain why anything exists at all, though the precise mechanism behind this imbalance remains an open question in physics.
Full transcript
According to physics, the universe should have destroyed itself before stars, planets or humans ever existed. Where did the antimatter go? You see, from what we understand about physics and what we observe, every time that matter is created from energy, an equal amount of antimatter is also created at the same time. And when matter and antimatter combine, they annihilate each other back into energy. In fact, this is how quantum fluctuations work. So, how could we get a universe with only matter? What happened to all the antimatter? Shouldn't it have an equal amount of antimatter so that we end up back to a universe with only fluctuating fields and no matter at all? Well, this is an unresolved issue. But the leading hypothesis from physicists to explain this discrepancy is the following. Most of the antimatter annihilated with matter into radiation, but a tiny matter only excess survived. They estimate that this tiny proportion was about one particle out of a billion that survived. How do we know that it's one in a billion? Because we observe about a billion photons for every matter particle because two photons are created for every matter and antimatter particles that are annihilated. That one in a billion leftover is what built all the stars, planets, and matter that we observe in the universe. Now, you should ask, how the heck did that tiny imbalance occur? To end up with some matter left over, the early universe must have briefly violated some matter antimatter symmetry somewhere. In 1967, Andre Sakurov outlined a kind of recipe of how this could happen. This is now called the Sakarov conditions. To summarize, three things happened due to the conditions of the early universe which left a tiny extra bit of matter behind. First, some rare reactions could actually change how many matter particles existed. Second, the laws of physics are very slightly biased so that matter and antimatter don't behave exactly the same. It's like a bias coin that lands heads a tiny fraction of a percentage more than tails. And third, the universe was expanding and cooling so fast that this tiny bias froze in before it could be evened out. And as the cosmos cooled, nearly all the pairs annihilated, but that tiny surplus remained.