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An infinite universe (unbounded metric space) means that there are points arbitrarily far apart: for any distance d, there are points that are of a distance at least d apart. A finite universe is a bounded metric space, where there is some distance d such that all points are within distance d of each other.
The first non-geocentric model of the universe was proposed by the Pythagorean philosopher Philolaus (d. 390 BC), who taught that at the center of the universe was a "central fire", around which the Earth, Sun, Moon and planets revolved in uniform circular motion.
A cyclic model (or oscillating model) is any of several cosmological models in which the universe follows infinite, or indefinite, self-sustaining cycles. For example, the oscillating universe theory briefly considered by Albert Einstein in 1930 theorized a universe following an eternal series of oscillations, each beginning with a Big Bang and ending with a Big Crunch; in the interim, the ...
Heavenly motions are uniform, eternal, and circular or compounded of several circles (epicycles). The center of the universe is near the Sun. Around the Sun, in order, are Mercury, Venus, the Earth and Moon, Mars, Jupiter, Saturn, and the fixed stars. The Earth has three motions: daily rotation, annual revolution, and annual tilting of its axis.
Aristotle proposed a geocentric model of the universe in De Caelo. The Earth is the center of motion of the universe, with circular motion being perfect because Earth was at the center of it. There can be only one center of the universe, and as a result there are no other inhabited worlds within it besides Earth.
The physical universe is defined as all of space and time [a] (collectively referred to as spacetime) and their contents. [10] Such contents comprise all of energy in its various forms, including electromagnetic radiation and matter, and therefore planets, moons, stars, galaxies, and the contents of intergalactic space.
The Earth and the Heavens form a unit within infinite "waters of chaos"; the Earth is flat and circular, and a solid dome (the "firmament") keeps out the outer "chaos"-ocean. Eleatic cosmology: Parmenides (c. 515 BCE) Finite and spherical in extent The Universe is unchanging, uniform, perfect, necessary, timeless, and neither generated nor ...
The change from circular orbits to elliptical planetary paths dramatically improved the accuracy of celestial observations and predictions. Because the heliocentric model devised by Copernicus was no more accurate than Ptolemy's system, new observations were needed to persuade those who still adhered to the geocentric model.