The statement that the mass of a trillion galaxies was once smaller than an atom is not a logical assertion but rather an illustrative comparison used to emphasize the immense expansion of the universe over time. It is not meant to be taken literally.
In the early stages of the universe, shortly after the Big Bang, the universe was incredibly dense and hot. However, it is important to note that galaxies as we know them today did not exist during that time. The formation of galaxies took place over billions of years through the process of cosmic evolution.
During the early universe, matter was in the form of a hot, dense plasma composed of particles such as protons, neutrons, and electrons. As the universe expanded and cooled down, these particles began to come together under the influence of gravity, forming structures like galaxies, stars, and planets.
The comparison of the mass of a trillion galaxies to that of an atom is meant to highlight the incredible expansion and transformation that has occurred in the universe over billions of years. It showcases the vast scale and dynamic nature of the cosmos. However, it is not a precise representation of the actual physical state of the universe at any specific point in time.