In this blog, I would like to introduce Aristotle’s model of the universe. The cosmic theory from Aristotle is clearly wrong from the view of modern science. However, before modern astronomy was developed, Aristotle’s ideas about our world dominated people’s belief for thousands of years. It was embraced by scholars, philosophers, and religious leaders as a foundation for their principles.
In Aristotle’s cosmology, the universe is made up by multiple celestial spheres. Earth is located at the center of the universe. Same as his teacher Pluto, Aristotle also believes that the universe is constructed by basic elements. However, Aristotle thinks that besides the four basic elements, which are earth, fire, air and water, there exists one extra dominating element, called aether. In his view of the world, the universe contains two realms, the terrestrial realm and the celestial realm. The former one naturally covers the internal celestial sphere. The entire amount of fire, water, earth, and air makes up the terrestrial sphere. According to Aristotle, we can discover from natural observation that these four basic elements undergo transformations and interactions. Thus, this characteristic determines that all things in the terrestrial realm are material and perishable.
On the other hand, the outer celestial sphere is made up of only one element, aether. Aristotle states that aether is ungenerated, unalterable, and indestructible. The features of aether leads to Aristotle’s conclusion that all stars in the outer sphere are made up by aether. They are eternal and without a beginning, so does the universe itself. Being similar to Pluto, Aristotle’s model demonstrates his worship to circular motions. He considers stars in the heaven doing perfect circular motions around Earth. For him, circle represents perfectness and fulfillment to the natural purpose of the universe.
Aristotle’s cosmology was viewed as undoubtable truth throughout the most history of humanity. One important reason is that his cosmology was created based on his physics, and his physical theory was tightly connected to the very basis of his philosophy. In past time, people readily found Aristotle’s ideas correct, because many of his thoughts were quite intuitive if people just take into consideration of their senses and their daily observations to the nature. More crucially, there was no advanced scientific tools to prove that Aristotle was incorrect. A key loophole of Aristotle’s geocentric model was the existence of stellar parallax. Nevertheless, no competitive telescope was invented to successfully observe stellar parallax until 1838.