The question you're referring to relates to the mystery of why there is more matter than antimatter in the universe, a phenomenon known as the baryon asymmetry. According to our current understanding, during the early stages of the universe, matter and antimatter were produced in nearly equal amounts. However, when matter and antimatter particles come into contact, they annihilate each other, converting their mass into energy.
The fact that there is more matter than antimatter today suggests that there was an imbalance in the initial conditions of the universe. This imbalance, which is still not fully understood, allowed a small excess of matter to survive the annihilation process.
One of the leading explanations for this asymmetry is a process called baryogenesis. Baryogenesis involves violations of certain fundamental symmetries, known as CP-violation (charge conjugation and parity violation), which can lead to the creation of more matter than antimatter.
During the early moments of the universe, as it went through a phase known as the electroweak epoch, these CP-violating processes may have occurred, generating a tiny excess of matter over antimatter. Subsequently, as the universe expanded and cooled, this excess of matter remained while most of the antimatter annihilated with the remaining matter.
It is important to note that the precise mechanisms and details of baryogenesis are still an active area of research and not fully understood. Scientists continue to explore theoretical models and conduct experiments to better comprehend the origin of the matter-antimatter asymmetry.
Regarding the size of the universe, the asymmetry in matter and antimatter doesn't directly impact its scale. The expansion of the universe is driven by the cosmological principle and the influence of various energy components, such as dark energy. The relative abundance of matter and antimatter within the universe does not affect its overall size or expansion rate.