The number of atoms in the universe is generally considered to be constant. Atoms are not created or destroyed in ordinary chemical reactions or physical processes. The law of conservation of mass states that matter cannot be created or destroyed, only transformed from one form to another.
However, it is important to note that in certain high-energy environments, such as nuclear reactions or particle accelerators, atoms can be broken apart or fused together, resulting in the creation of new elements or isotopes. These processes occur in very specific conditions and are not part of everyday occurrences.
In the normal course of events, the atoms that make up the universe have been around since the early moments of the universe's existence, undergoing various transformations and combinations to form the matter we observe today. So, while atoms can be rearranged and combined in different ways, the total number of atoms in the universe remains constant.