What is the problem?
Every particle has a counterpart with the opposite charge. When they meet, the pair disappears, turning into radiation. In the hot early universe, such pairs were constantly being created and destroyed, and under symmetric laws, the final result should have been zero.
- Pairs are created
- Pairs annihilate
- Radiation should remain
- But matter remained
The scale of the imbalance is estimated like this: for every billion pairs that annihilated each other, there was about one extra matter particle. Everything we see around us, including stars and ourselves, is what's left of this tiny excess.
What would be needed
The conditions under which an imbalance could arise were formulated long ago. The laws of nature would need to behave slightly differently toward matter and antimatter, processes would need to exist that change their amounts, and all of this would need to happen out of equilibrium.
The first condition has been partially met: experiments with some particles do show a small difference in behavior. The problem is that the difference found is nowhere near enough: it is millions of times smaller than what is needed to produce the observed imbalance.
The asymmetry has been measured reliably, but its cause has not been found
That is where the estimate comes from. The fact that matter remained is beyond doubt: we are made of it. But the explanation is missing, and this is one of the major unsolved problems in physics.
Where scientists are looking
Researchers are exploring several directions: looking for stronger differences in the behavior of particles and antiparticles, studying neutrinos, which may behave unusually, and searching for new heavy particles that decayed in the early universe with an imbalance.
They are also testing a much simpler possibility: what if antimatter exists somewhere, just in other regions? So far, this has not been confirmed: at the boundary between such regions, there would be powerful radiation from annihilation, but none has been seen.
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Sources
- The conditions necessary for matter to prevail were formulated by Andrei Sakharov in 1967. The symmetry violation observed in known processes is not sufficient to explain the asymmetry