The expansion of the universe is indeed a concept supported by various lines of observational evidence. According to the prevailing cosmological model known as the Big Bang theory, the universe began with a tremendous release of energy and has been expanding ever since. This expansion is often visualized as the motion of galaxies moving away from each other.
However, it is important to note that the expansion of the universe does not mean that everything in space is moving away from each other at a great speed in the traditional sense of objects moving through space. Rather, it refers to the expansion of the very fabric of space itself. The metric of space is expanding, causing galaxies to move apart from each other. Think of it as the stretching of space between galaxies, rather than galaxies themselves moving through space.
Despite this expansion, galaxies, stars, and other matter exist and play vital roles in the universe. The formation and existence of galaxies and stars are a result of gravitational forces at work. Gravity acts as an attractive force, causing matter to clump together over time. In the early universe, slight density fluctuations in the distribution of matter led to regions with slightly higher densities, which attracted more matter through gravity. Over billions of years, these dense regions grew and eventually formed galaxies.
Within galaxies, stars are formed through the gravitational collapse of gas and dust clouds. Gravity pulls matter together, compressing it until the conditions for nuclear fusion are reached, leading to the ignition of a star. Stars, in turn, produce energy through various processes, including nuclear fusion, and contribute to the chemical enrichment of the universe by synthesizing heavier elements.
So, while the expansion of the universe may cause galaxies to move apart, it does not negate the existence and importance of galaxies, stars, and other matter within the universe. These structures and objects are a result of the interplay between gravitational forces and other fundamental physical processes.