The Great Debate (or, My universe is bigger than yours.)

We are bounded in a nutshell of Infinite space: Blog Post #16, History #1: The Great Debate (or, My universe is bigger than yours.)

In the early 20^th century, astronomers Harlow Shapley and Heber D. Curtis began a discussion on the overall structure of the universe, essentially. Each posited different views on how the universe was constructed and the role of galaxies in it.

Harlow Shapley

Shapley postulated that the entire universe was the Milky Way Galaxy, one huge structure in the order of tens of thousands of light years across, and the farthest objects were globular clusters and the mysterious spiral nebulae. Shapley also believed our solar system is one that revolves around the galactic center, placing the Sun somewhere in the mid distance of the radius if our galaxy. He evidenced these claims with the measurements done with the Wilson telescope and how the data was analyzed and interpreted to mean how the light collected and the rate at which the image was processed evidenced a distance closer than what later experiments would prove. He also relied on the early understanding of Cepheid variables and misinterpreted their distance in finding out how far away the so called spiral nebulae were, although Cepheid data did lead him to make correct observations regarding the general order of the size of the galaxy.

Heber D. Curtis

On the other hand, Heber D. Curtis thought of a completely different system for the universe as a whole. He came to understand that the universe was made up of many galaxies, which could actually be the spiral nebulae that were routinely observed.  Using the data from telescopes around the world, Curtis saw that the spirals were definitely extra galactic objects, because of the fact of how small he believed the Milky Way to be and the observations of the spirals’ physical properties resembling many qualities already found in the Milky Way. He evidenced these claims by undermining the possibility that the spirals could be nebulae, citing many facts like spectrum analysis and luminosity distribution as reasons why there is no tenable way the spirals could maintain a shape and structure within a galaxy. He further postulates his “Island Universe Theory” where many spirals exist in the universe and we are one of many evidenced by how a galaxy like Andromeda would need to be extremely far away for it to be seen as it is, were it the size of our galaxy, and thus its speed at which it heads towards us makes more sense than if it were a “small” nebulae inside the galaxy. However, Curtis also posited that he also interpreted the data from the Cepheids that Shapley and other astronomers used, and found his to result in a smaller Milky Way Galaxy, and as such the solar system is closer to the enter, and quite near it according to his measurements.

Nevertheless, both of these men were right and wrong, about different aspects of their theories. In the mid 1920’s, Dr. Hubble searched for and found more conclusive evidence for the nature of the universe, employing measurements of Cepheid variables and other distance modulus to discover key attributes of the universe. He saw not only that the universe is actively expanding, but also how there were a seemingly infinite number of galaxies, as per Curtis’s theory, within our corner of the universe where the oldest light has gotten to us. Later on, experiments and observations of clusters and light absorption rates proved that the Milky Way is quite larger, in the same order of magnitude as Shapley’s hypothesis, and that we are inside one of the arms midway between the center and outer bounds of the galaxy. Essentially, they both won, they both contributed to the development of a general understanding of the composition of the universe (including hints of “invisible objects” that play into the mechanisms of the galaxy), and furthering the way astronomical would be interpreted for decades and now almost a century since their great debate.

Reference: http://apod.nasa.gov/diamond_jubilee/debate_1920.html