Aristotle's Model of the Universe

Aristotle's Model of the Universe

It is important to point out that Aristotle used his theory of violent motion to develop a model for the Universe. Aristotle, and philosophers before him, knew that the night sky experienced many different cycles: day and night, monthly phases of the moon and the yearly cycle of the Sun (seasons). Thus they thought the celestial objects must be on perfect crystalline spheres (the circle and sphere were thought to be perfect shapes that repeated in space, with no beginning or end).Aristotle thought that the Earth was at the center of the Universe since it could not move. He reasoned that if it did move, all the water in the ocean and air in the sky would be left behind. He also could not imagine a force which could violently push the Earth through space. All other objects in the heavens moved on crystalline spheres where the Earth would be the center of the sphere. Aristotle developed one of the first geocentric (Earth centered) models of the Universe. Ptolemy later improved on the model by placing the planets on epicycles while keeping the Earth at the center. This model survived until the Renaissance, when Copernicus proposed the Heliocentric (Sun centered) model of the Universe.

Heliocentric Model

Copernicus is often credited for starting the Renaissance with his Heliocentric model of the Universe.Copernicus became interested in astronomy after studying mathematics. He was fascinated with Ptolemy's geocentric model of the Universe and tried to create a simpler method to calculate the positions of the planets. Copernicus did not initially think that the Earth orbited the Sun. He just found the mathematical calculations for planetary positions easier if all objects went in circles around the Sun rather than the Earth. Seeing how successful and simple this heliocentric model was, he soon came to realize that it must be true. To have the Earth go around the Sun violated Aristotle's theory of violent motion since the Earth must move to orbit the Sun.

It also violated church teaching since the Vatican supported the ideas that the Earth was the center of the Universe where all objects would orbit the Earth. The church believed that humans were made in God's image, and were therefore the most important beings in the Universe. Thus they must be the center of the Universe and the Earth must therefor also be located at the center of the Universe.

In the diagram below we see the Universe as believed by Copernicus. It is impoertant to note that Copernicus kept many of the features from Aristotle's and Ptolemy's models including the circular orbits and the outer sphere of stars. The model also shows the six known planets at the time, Mercury (closest to the Sun), Venus, Earth, Mars, Jupiter and Saturn (outer most planet). The Moon was known to orbit the Earth and is not shown in the diagram.

Model of the Solar SystemGalileo did not invent the Heliocentric model of the Solar system, rather he presented the experimental evidence that supported this model. Using the telescope, Galileo made observations of four celestial objects. While these observations did not directly show that the Earth orbited the Sun, these observations did demonstrate that much of the Greek theories of the heavens were wrong.Unfortunately the Roman Catholic church was disturbed by his support of the heliocentric model. The Vatican had Galileo brought before the Inquisition twice for teaching Copernicus' model (outlawed by the church earlier). While Galileo was cleared during the first interview, during the second interrogation the Inquisition threatened to find Galileo guilty of heresy. Being a devout catholic, Galileo feared excommunication which would have prevented him from receiving a Christian burial. According to Galileo's beliefs, he would not have been able to enter heaven and thus he would be condemned to eternal damnation in hell. Galileo recanted his support for the heliocentric model and was kept under house arrest for most of the remainder of his life. The Vatican has since, albeit posthumously, apologized to Galileo and has stated that the

It all began with Philosophy - Although science owes its roots to many different cultures, one culture in particular has had the greatest influence on science (and all other academic disciplines): the ancient Greeks. The ancient Greeks were the first to attempt to understand the world around them using logic and reasoning...what we call philosophy. Thales of Mellitus, is credited with being the first ancient Greek philosopher who started the tradition of explaining the world around us in a physical rather than mystical approach. Other famous Greek philosophers included Pythagorus, Socrates, Plato, Archimedes and Plato. The philosophers of the ancient Greek world emphasized the power of mathematics and used geometry to gain a better understanding of the Universe. As you will see, the Greeks were able to use simple measurements and geometrical principles to measure the size of the Earth, Moon and Sun and the distances between these bodies. Today scientists still express scientific understanding in terms of mathematical relationships using equations.

Galileo, the father of Modern Science - A simple but effective definition for philosophy might be "Philosophy is the search for understanding or knowledge". Science was once known as natural philosophy because it used logical principles from philosophy to understand the natural world. It is important, however, to stress that the ancient Greek philosophers were not scientists because they did not use the experiment to test their ideas. Today science has become much more than just a search for understanding.

After the fall of the ancient Greeks and the Roman empire, and prior to the Renaissance a few European philosophers began to come to the conclusion that the laws of nature could be better understood through the use of experiments. During the Renaissance, Galileo performed experiments with motion that forever changed the way we looked at the Universe. More significantly, Galileo also changed the way we studied nature by popularizing the experiment and the scientific method. He used induction (a logical conclusions from experiments) rather than deduction to prove his ideas. Prior to Galileo, European academics continued in the classical tradition of Greek philosophy and accepted the findings of the Greek philosophers as truths. The great philosopher Aristotle had proposed that heavier object should fall faster than lighter objects, because the heavier objects contained more material. He arrived at this conclusion using observations and a simple chain of logic known as deduction, but never tested his idea using an experiment. Galileo, however, did not just rely on logic. He set up a series of controlled