Ancient Cosmology: From Rationalism to Heliocentric Models
Rationalism and Empiricism
Rationalism and Empiricism: Empiricism and Rationalism made people rethink monism. If reality is one thing, then how can there be nothing, or motion, or how can anything be destroyed or created? If the real world is as Parmenides says, is this world not real? What is real?
Pythagoras
Pythagoras: Born c. 585 to 565 BCE on the island of Samos. He studied under Anaximander and founded a quasi-religious “brotherhood” influencing the Croton area of Southern Italy. This was a scientific mysticism where the one leads to the other. The basic belief was that all is one. He replaced the Ionian search for one substance with a search for numerical relationships between nature and life.
Philolaus
Philolaus: A famous Pythagorean. He proposed that the Earth revolves around the “central fire.” The Sun distributes heat and light to other luminaries. He also proposed an “antichton” or counter-Earth to account for the range of observed lunar eclipses. The counter-earth is not seen by earth observers because it rotates with the earth, hidden by the central fire. This was a religious and mathematical conception of the cosmos.
The Atomists
The Atomists (Leucippus and Democritus): They addressed the problem of change, attempting to reconcile all views into one. Leucippus (450-420 BCE, dates uncertain) proposed that change is not incompatible with the Eleatics’ ideal of immutable Being. He introduced the notion of the atom (Gk atomon). The world is composed of an infinite number of atoms moving aimlessly in the Void (space). They postulated a complementary science of Being (the atoms) and Non-being (the Void). Democritus (c. 460-370) described the origin of worlds. Atoms move randomly in all directions. Collisions between atoms occur, creating large vortices, or whirlpools, composed mainly of atoms. These filter atoms into similar qualities. As more atoms conglomerate into a whirlpool, worlds form. An infinite number of worlds form and decay, ours being only one of them.
Aristotle’s Cosmology
Aristotle’s view of cosmology and why his views lasted so long: Aristotle was born in 384 BCE in Stagira, Macedonia. His views lasted so long because his work was comprehensive and broad, covering politics, ethics, physics, biology, poetic theory, etc. His commonsense approach appealed to many. The Catholic Church appropriated his views. Thomas Aquinas in the 13th century based Christian faith and understanding of the universe on Aristotle. The Physical Structure of the Universe, according to Aristotle, had the Earth at the center. The Earth was spherical, not flat. The Universe (based on naked-eye observation) was divided into sublunar and superlunar regions. The order of planets was: Mercury, Venus, the Sun, Mars, Jupiter, Saturn, then the sphere of fixed stars equidistant from Earth. Superlunar objects were made of “ether,” a substance having unusual properties explaining why objects in heaven moved as they did. The size of the universe was not as large as we know today.
Eudoxus
Eudoxus: He proposed a geocentric model.
Heraclides of Pontus
Heraclides of Pontus: He discovered that the Earth rotated around its axis. He also proposed that the inner planets, Mercury and Venus, orbit the Sun, not the Earth. This led to the development of two competing views: Heliocentric (sun-centered) and Geocentric (earth-centered).
Aristarchus
Aristarchus and why his views were not more prominent: Born in Samos c. 310 BCE. Only one work survived: On the Sizes and Distances of the Sun and Moon. His discoveries included: the distance from Earth to the Sun is about 19 times the distance from Earth to the Moon; the diameter of the Sun is 6.8 times larger than the diameter of the Earth; and the diameter of the Moon is 0.36 times the diameter of the Earth. He proposed a heliocentric universe.
Ptolemaic System
Ptolemaic System: A geocentric model with 5 planets.
Copernicus’ Heliocentric System
Copernicus´Heliocentric system
- Sun at center (heliocentric)
- Uniform, circular motion, with almost no epicycles
- The Moon orbited the Earth, and the Earth orbited the Sun as another planet
- Planets and stars were still on fixed spheres, and stars did not move
- The daily motion of the stars resulted from the Earth’s spin
- The annual motion of the stars resulted from the Earth’s orbit
Tycho Brahe
Tycho Brahe
- Made extraordinary astronomical observations
- Opened space for an alternative conception of the universe
- Retained advantages of the Copernican system, but kept the Earth at the center
- The Tychonic system is mathematically equivalent to the Copernican system
- The telescope was not yet invented