In 1917, Albert Einstein examined the implications of his general theory of relativity, focusing on the cosmological aspects of the universe. At that time, the prevailing belief among astronomers was that the universe was limited to our Milky Way galaxy, which contained around 100 billion stars, existing in a vast emptiness.
This perspective reflected the limited understanding of the cosmos during that era, as scientists had yet to discover the existence of other galaxies. Einstein's work laid the groundwork for a more complex view of the universe that would emerge in the following decades.