Monday, March 14, 2011

The Geocentric Universe - Part 2

Early Greek Cosmology

Early Greek cosmology is dominated by several great thinkers. The foundations of philosophy and many mathematical principals would find their birth in this time. About the time 640 B.C, a movement known as the Ionic physical philosophy began. Thales of Miletos (620 – 547 B.C) is considered to be the founder of this school of thought. He sought to explain the world around us without resorting to any supernatural cause but instead to develop an explanation by naturalistic means.

Thales of Miletos

This break from old ideas of deities or other supernatural beings having control over terrestrial events would herald a new beginning in science. For the first time people began to try and solve problems in a mathematical or mechanical sense rather than resort to any supernatural explanation. From this school of thought many other philosophers arose, Anaximander was an early example.

Anaximander (610 – 546 B.C) considered the Earth to be one of many bodies in space and it was able to move free about space. According to Anaximander the Earth did not move as it had no reason to move, as it simply floated motionless in space. Many ideas at the time theorized that the Earth was held in place by some godly means. This again is a sign of the Greek thinking of moving away from any supernatural explanation and trying to solve it using mechanics and maths. Anaximander also theorized that all matter in the universe came from the one substance which he called apeiron (unlimited). This substance was transformed into all the different types of matter and eventually into what we know as Earth. From this idea arose his belief that the universe extending infinitely in time and space.

A student of Anaximander, Anaximenes (585 – 525 B.C) believed the Sun and the other heavenly bodies were globes of fire. He placed the Sun and the stars on a giant crystal sphere which rotated about the Earth. Anaximense also believed that the Universe was made of one substance, in his eyes he believed that air made up all of the matter. Anaximenes theorized that when air was compressed it got cold and so here on Earth it was compressed enough to become solid and cold just like rock or metal. In space it was allowed to expand and become hot at which point it became fire, this gave rise to the idea that the Sun and all the other points of light were spheres of fire. Another philosopher of this school of thought Anaxagoras (500 – 428 B.C), put forward the idea that the solar system formed from a spinning disc where all the most dense matter stayed near the centre and coalesced to form the planets and the Sun. He strongly augured that the Sun was a fiery ball and not deity, for this he was imprisoned. He also gave an explanation for solar ellipses, saying that the moon passed between the Earth and the Sun. This was the first time that a non supernatural explanation was put forward to explain this event.

The work started by the Ionian philosophers was continued and expanded upon. The separation of any godly explanation to terrestrial or celestial events was carried on by Pythagoras (c580 – 500 B.C). His belief was that all events and truth could be found within mathematics. To Pythagoras all events had an underlying explanation in number sequences or series. Pythagoras considered the Earth to be a sphere not a cylinder as Anaximander believed. Pythagoras like many before him believed the Earth was at the centre around which the other bodies revolved. This geocentric model made sense to the people at the time. Even though they separated science and the supernatural the egocentric tendency of humanity prevailed and they continued to place the Earth at the centre of the universe. It was not challenged until the theories of Aristarchus came forward.

Aristarchus (310 – 230 B.C) put forward the idea that the Earth rotates about the Sun and in doing so spins on its own axis. This he said explains the day/night cycle. For the first time the heliocentric model was given a voice. However this idea did not receive any support. Even though Greeks had begun to move away from the supernatural explanations there was still the idea that we were the centre. To move away from this would lessen the importance of man in the universe and this did not sit well with the Greek establishment. To put it simply Aristarchus was shouted down by the other philosophers at the time. Without any backing, his theory was lost to history. This set-back in cosmological theory cannot be under-stated. It would take almost 2000 years before this theory was challenged again.

Aristarchus's Heliocentric Model
The arguments against this theory to modern day observers seem almost ridiculous but without the idea of gravity and the vacuum of space these ideas would appear to make sense. The arguments said that if the Earth was indeed spinning on its own axis, then why were we not simply thrown off the surface as if we were on a merry-go round. Another pro-geocentric argument was that if we are orbiting the Sun why do we not feel a wind blowing against us as we move through space. At the time it was believed that space contained matter, be it a gas or liquid that the Earth floated in and as we passed through it we should feel its presence blowing against us. Looking at these arguments without the knowledge we have now it does appear to make some sense. Another point to note is that there was no hard evidence to prove Aristarchus’s theory and as such it was lost.

Aristarchus was also able to make estimates about the relative distances of the moon and the sun. He based a lot of this work on prior studies and theories of Eratosthenes. He too like Aristarchus was able to calculate relative distances. But too his credit he deduced the diameter of the Earth to a high degree of accuracy.

Eratosthenes's method for measuring the
diameter of the Earth, accurate to within 2% of the true value

At this time (c250 BC) the Ionian school of thought was in decline as was the Pythagorean brotherhood, this left the way open for a new school of thought which was lead by such philosophers like Plato and Aristotle. This movement and with the model developed by Ptolemy would hamper cosmology for centuries to come.

This would end the age of the true first scientific revolution. For the first time people began to seek answers to the bigger questions by looking to science rather than the heavens. Many great mathematicians and scholars of this age are still known to this day. Euclid and Archimedes are known to this day for their discoveries. As will be seen later in this essay the knowledge of the Greeks would remain static up to the second scientific revolution in Europe in the 1400’s. 

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