For thousands of years it was believed that our Universe was finite. In 1920, The Great Debate, also called the Shapley-Curtis Debate happened in Washington where Shapley argued that our Milky Way was the only galaxy in the Universe and Curtis argued that there were many other galaxies in the Universe but none of the opponents had any concrete evidence to prove their respective theories. However, in 1929 Edwin Hubble provided observational evidence from which he concluded that there was millions of galaxies in the Universe beside our Milky Way Galaxy. And in the process of discovering, he also found out that our Galaxy was in fact expanding! The public formation of the Great Debate influenced the ways ideas were presented and it ultimately lead to the trajectory of the Debate. This paper argues why Shapley believed that there is only one Galaxy and how Edwin Hubble proved him wrong with his discovery of the expanding Universe. From this discovery, we came to realize that at some point in the past, our Universe was very small, probably a tiny dot, then after the Big Bang, it started expanding. This was a big discovery, which changed the history of Physics. At the end, the paper also discusses - if our Universe will continue to expand or is there a limit?
Expansion of the Universe
Firstly, it is important to understand what we understand by the Expansion of the Universe. It means that the galaxies outside our own galaxy are moving away from us and the ones that are farther apart are moving even faster. Therefore it means that no matter where we are, all the other galaxies are moving away from us. And if it continues to do so, after a time, these galaxies would expand to infinity. We still have very little knowledge about the other galaxies since they are all moving away from us. A famous analogy to explain the Expansion of the Universe in a simplistic way would be the example of an expanding balloon. Imagine a balloon with a large number of dots marked on its surface. When you blow the balloon, it inflates that is the distances between the dots increase the same way as the distances between the galaxies. 1(Eddington, 1933)
It is important to understand that when the Great Debate happened in the 1920 , the general view of the public and the scientific community was that there is only one Universe. There was doubts regarding its size and scale but it was mostly believed that the Universe was finite. It was not until 1929, that it was officially confirmed that the Universe was expanding. Today, we are aware about a great deal of information about our cosmic world due to the invention and innovation of many new technologies. But it makes an individual ask themselves now - under what circumstances did Shapley develop his theories of the Universe? What observations did he make? Why did he argue so strongly against the idea of external galaxies and an infinite Universe? What evidence did he have? We will discuss in this paper why Shapley believed...