Baryon asymmetry facts for kids
In physical cosmology, the baryon asymmetry problem, also known as the matter asymmetry problem or the matter–antimatter asymmetry problem, is the observed imbalance in baryonic matter (the type of matter experienced in everyday life) and antibaryonic matter in the observable universe.
The Big Bang should have produced equal amounts of matter and antimatter. Since this does not seem to have been the case, it is likely some physical laws must have acted differently or did not exist for matter and antimatter.
There is as of yet no theory to explain the phenomenon. As they said in a 2012 research paper, "The origin of matter remains one of the great mysteries in physics."
Baryon asymmetry Facts for Kids. Kiddle Encyclopedia.