The expansion of the universe and the dynamics of individual galaxies are two separate phenomena governed by different mechanisms.
The expansion of the universe is a broad-scale phenomenon observed on the largest cosmic scales. It refers to the overall increase in the distance between galaxies as space itself expands. This expansion is described by the theory of general relativity. The expansion of the universe is not driven by gravity but rather by a property of space itself called dark energy. Dark energy is a hypothetical form of energy that is thought to permeate all of space and contribute to its expansion.
On the other hand, the motion of individual galaxies within the universe is primarily governed by the gravitational interactions between them. Gravitation plays a crucial role in determining the behavior of galaxies. The gravitational attraction between galaxies can cause them to cluster together, form galaxy groups or clusters, and even merge over time.
It is important to note that the expansion of the universe does not directly affect the gravitational interactions within individual galaxies. The expansion acts on the large-scale structure of the universe, while gravity operates on smaller scales, such as within galaxies.
The differences in size, shape, mass, and rotation speed of galaxies arise from a variety of factors, including their initial conditions, interactions with neighboring galaxies, and the distribution of matter and dark matter within them. These factors contribute to the diverse range of observed galaxy properties.
So, while the expansion of the universe and gravitational dynamics coexist, they operate on different scales and are influenced by different factors. The expansion of the universe does not depend on the specific characteristics of individual galaxies but rather on the overall properties of space itself.