There is considerable speculation both in science and science fiction as to why the observable universe is apparently almost entirely matter, whether other places are almost entirely antimatter instead, and what might be possible if antimatter could be harnessed, but at this time the apparent asymmetry of matter and antimatter in the visible universe is one of the greatest unsolved problems in physics

It is now thought that symmetry was broken in the early universe during a period of baryogenesis, when matter-antimatter symmetry was violated. Standard Big Bang cosmology tells us that the universe initially contained equal amounts of matter and antimatter