If all the antimatter in the universe were to combine with all the regular matter, it would result in a process called annihilation. When matter and antimatter come into contact, they annihilate each other, releasing a tremendous amount of energy.
Annihilation occurs because matter and antimatter are composed of particles with opposite charges. For example, an electron (matter) has a negative charge, while its corresponding antiparticle, the positron (antimatter), has a positive charge. When an electron and a positron meet, they can annihilate each other, resulting in the production of energy in the form of gamma-ray photons.
If all matter and antimatter in the universe were to collide and annihilate, an enormous amount of energy would be released, potentially leading to a cataclysmic event. The exact consequences would depend on the scale and conditions of the annihilation. However, it is important to note that the current understanding of the universe indicates that there is an asymmetry between matter and antimatter, with matter being more prevalent. This is known as the matter-antimatter asymmetry problem and is an active area of research in physics.
It is also worth mentioning that our current knowledge and understanding of the universe may not be complete, and there may be other factors or phenomena that could influence the behavior of matter and antimatter.