Lecture #5: Some History (Ch. 4)

I. Pythagorus (500 BC) -- a leading proponent of the idea that the mysteries of the universe were accessible to human reason II. Aristotle (350 BC) -- the leading reasoner, who argued for a certain philosophical perfection in the heavens: perfect spheres, moving in perfect circles, with the Earth at the center III. Aristarchus (250 BC) -- reasoned that it was easier to explain the motions of the heavens by making the Earth rotate, not the heavens, and also to make the Earth revolve about the Sun! That was almost 2000 years before Copernicus. -- if he was right, why was his idea rejected by the Greeks? Two key reasons: it didn't agree with Aristotle and Plato, who argued on philosophical grounds that the Earth had to be immovable and at the center, and also it didn't agree with the simple observational fact that the stars don't appear to move in the sky over the course of the year, which they'd have to do if the Earth orbited the Sun (this effect is called parallax-- it's why you have two eyes.) But they never dreamed how far away the stars were! IV. Hipparchus (150 BC) -- the first great observer, he discovered that the celestial pole precesses every 26,000 years. We now know this is because the Earth's axis precesses, which means traces out a cone, that goes between Polaris and Vega-- this means that in 13,000 years, or half a precession cycle (so in the year 15000 AD), Vega will be the North star, and in 28000 AD, it will be back to Polaris. -- his careful observations proved that Aristotle couldn't be quite right about the perfect circles, but he found a way to introduce a new level of complexity to the model that still used circles that were offset a little. III. Ptolemy (150 AD) -- wrote a book later called the Almagest (the greatest), which laid out the central ideas of the geocentric model -- put Hipparchus' ideas into a precise and accurate model of the solar system, which had the Earth at the center and a very complicated series of circles. It worked fairly well and lasted for 14 centuries, and was totally wrong. But it was good science because it was based on observations, it made predictions, and it was falsifiable. That it took so long to falsify is merely a measure of how good it was! IV. Copernicus (1500 AD) -- wrote de Revolutionibus, claiming that the Earth "revolved" around the Sun, not the other way around -- his model had inaccuracies that were comparable to Ptolemy, so the real point is the revolutionary idea that the Earth is a planet like the others, and is a lot easier to set in motion that the entire heavens V. Bruno (1600 AD) -- was a heretic burned at the stake by the Inquisition for teaching that not only did the Earth orbit the Sun but all stars were distant suns that had planets orbiting them, and probably had life on those planets -- he was not really a scientist because he did not have observations to back up his claims, and some of his beliefs were rather flaky, but he was an idea person who thought "outside the box" and was way ahead of his time in some of his thinking (and paid an awful price) VI. Galileo (1610 AD) -- is considered one of the founders of the scientific method -- he combined careful observations, both in the laboratory and using his telescope to look into space, with deep thinking -- he reasoned that questions about the motions of objects in the sky should be a matter of experiment rather than religious belief: he felt the right approach was to just look, and be as objective as possible, ready to discard any past idea that doesn't stand up -- using this approach, he discovered the law of inertia and the fact that all objects fell at the same rate, if you could neglect air resistance -- his astronomical discoveries were even more significant, in that his telescope found several key clues that the Earth did indeed orbit the Sun: (1) he saw craters on the Moon (so the Moon was an imperfect planet like Earth- so the Earth was not so special) (2) he saw moons orbiting Jupiter (so planets could move and yet still carry moons with them, and the Earth could not be the center of all orbits) (3) he saw that Venus went through phases, so must orbit the Sun (Ptolemy had Venus always between the Earth and the Sun) (4) he saw sunspots (so the Sun is also not a perfect object) (5) he saw that the Milky Way was composed of many stars very far away (so if the stars could be that far away, it explains why we don't see parallax as the Earth moves) -- he wrote the "Dialog of Two World Systems" to explain why Copernicus was right and Ptolemy (which had been adopted by the church) was wrong -- all this brought him into direct conflict with the Catholic Church, whose power was based on the idea that faith, not observation, was the path to truth -- in 1992, the Catholic church admitted it was an error for the Inquisition to force Galileo to recant his ideas. It is also illuminating to read Pope John Paul II's words: "A tragic mutual incomprehension has been interpreted as the reflection of a fundamental opposition between science and faith". This points out that umderstanding the different goals of science and religion can help avoid conflict between them. The proper domain of religion is what is personal and unable to be demonstrated or predicted; the proper domain of science is what is objective and able to be demonstrated or predicted.