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Plurality From Ancient Times to the 18th Century

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(Previous Page) Introduction: Final Essay on Extraterrestrial Life                     


Plurality From Ancient Times to the 18th Century


      The earliest mentions of plurality are from Atomism and the Ancient Greeks. The Atomists were natural philosophers who believed that the universe was infinite in space and matter. These atoms formed the world and the life we see through spontaneous, random, accidental and purposeless collisions. By this logic, atoms could also reproduce life elsewhere, by the same mechanism. In addition, these atoms were the smallest parts of matter and therefore indivisible. From these atheistic views, the idea of plurality was born. The Atomists were the first people with documented ideas about plurality. This documentation would begin a debate that continues today, and is at the very core of the discussion over extraterrestrial life. 


     Around 460-370 B.C., Greek philosophers and atomists Democritus and Leucippus published their ideas on pluralism, ideas Epicurus and Lucretius that would develop further.  Because they believed that everything consisted of atoms and the universe was full of chance collisions of these atoms, it followed that, in an infinite universe, other worlds must exist.  As it was written in 99-55 B.C., "it is in the highest degree unlikely that this earth and sky is the only one to have been created and that all those particles are accomplishing nothing" (Lucretius, The Nature of the Universe, pp. 6-8 in Michael J. Crowe).  This is the basis for the “principle of plenitude” idea (discussed later in this essay) that continues to crop up throughout the history of the pluralism debate.


     The pluralists did have to deal with a counter argument, however. Aristotle's argument was anti-pluralist in nature. He believed in geocentricism, which placed Earth in the center of the universe. If Earth were the center, it would be impossible to have another center, thus negating the argument for plurality. Only one center could exist, and that center was Earth. He supported this idea with his theory of natural motion, which stated that every object has a natural motion towards the center of the Earth. The natural motion of "heavy objects" is down, while up is the natural motion for "light objects." This is explained by how fire and smoke rise into the sky, while heavier objects fall towards the Earth when dropped. Natural motion supports his belief of geocentricism because the natural motion for celestial matter is circular; the planets and the sun will orbit around the assumingly nonmoving Earth. Aristotle believed that the universe only expanded until it reached the "fixed stars" so if all other celestial bodies orbited around the Earth, than Earth must be the center of the universe. His ideas dominated throughout the medieval period due to their compelling Deistic and "common sense" theories, and they influenced others such as Aquinas and Oresmene. Although the anti-pluralist mindset was most common throughout this period, the 16th century saw a paradigm shift with the onset of the Enlightenment and the Scientific Revolution.


     The early church fathers in the first and second century came up with the idea of a sequence of worlds in time. This way there would not necessarily be more than one center at one time. In Summa Theologica, Thomas Aquinas contemplates the idea of multiple worlds; after providing three objections to Aristotle's anti-pluralist view, he also refutes pluralism by providing in turn replies for each of his previous objections. His first objection is that God has the power to create many worlds, and since he creates nothing without a purpose, he would create many worlds with the same purpose for creating Earth. He replies, "the world is one because all things must be arranged in one order and to one end" (Crowe, p. 19).  His second objection states that God would have created many worlds because many are better than one. His response to this is that if more worlds were better than one, God would have created an infinite number of worlds, an idea inconsistent with cosmology, which believed that the universe was finite. Aquinas's final pluralistic idea is that nothing prevents the existence of multiple worlds. He counterattacks this with the idea that "the world is composed of the whole of its matter. For it is not possible for there to be another earth, since every earth would naturally be carried to this central one" (Crowe, p. 20).     


      Teleology, the study of a purpose or reason, and Christianity played a major role in the denial of plurality. Religious arguments used theological statements and beliefs but had little proof or evidence to support the claims that extraterrestrials did not exist.  Thomas Paine, in 1794, published Age of Reason, Part I, an extremely popular extended argument that accepting extraterrestrial life entails rejecting Christianity and its central doctrines of the divine incarnation and redemption.  Using knowledge that had derived from the Enlightenment regarding the immensity of our universe, he believed that the two were simply incompatible because God cannot send Jesus to die on an infinite number of worlds, constantly dying.  It would lead to absurdity.  In order to maintain any sense of credibility, he made it known that religion had to be “consistent with the ever-existing world of God that we behold in his works”, or in other words, what we have come to know about the world through science (Paine, The Age of Reason, p. 229 in Michael J. Crowe).


     Nicolas Copernicus also had a great effect on the extraterrestrial life debate.  In 1543, Copernicus proposed in his book, On the Revolutions of the Celestial Orbs, that it was possible for the Earth not to be the center of the universe.  Up until this point of time, it had been almost unanimously believed that the universe was centered around our planet.  In this work, Copernicus stated that he believed that the Earth was not the center of the universe, that in fact the Earth revolved around the sun and that the sun was just an ordinary star.  He did not know this was a fact, but he concluded that this was the best possibility based on his observations. This theory was one of the most important developments in the history of science, and this development significantly shifted the nature of the debate on otherworldly life.  Eventually, this led to the thought that there may indeed be other earths, since there are other stars and therefore there could possibly be planets around some of them.  Once again, after an extended period of belief in a geocentric universe, the Principle of Plenitude pops up, as it does throughout the debate (see Part 6: The Principle of Plentitude later in this essay for more information).  


     In the 17th century, Isaac Newton's work further supported Copernicus's ideas. Newton was able to show that an undiscovered force, gravity, was governing the movements of the astrological bodies in the universe.  He showed that all bodies have a gravitational attraction to all other bodies based on their masses and distances from one another.  Gravity operated as a force-at-a-distance instead of through actual contact and since Newton's work showed that gravity worked equivalently on Earth and throughout the solar system, it united terrestrial and extraterrestrial physics into one comprehensive formula.  This contributed to the concept of universal physical law, from which scientists could infer properties of other planets and eliminate the mystic of a special Earth that was separate from the rest of the solar system and universe. 


     Upon the end of the 18th century, the model of the solar system was almost complete and astronomers and philosophers began to turn their attention from the solar system to the surrounding astronomy. They began looking at the stars and the structure of the universe. During this century, the nebulae theory was created due to the technological advancement of telescopes. This theory stated that only some of the clusters of stars within the sky could be resolved into single stars. The others were too large, too far away, and too close together to resolve with the technology at the time. The other main astronomical theory to originate in this century was that the shape of the Milky Way in the night sky is an optimal effect from its disc-like nature. Astronomers and philosophers like Immanuel Kant, Thomas Wright and Johann Lambert created their own theories with this idea as their basis.


     Although Wright was the first to suggest the disk theory of the Milky Way, Kant theories were more popular and are still popular in the 21st century. With his theory, Kant envisioned a nebula with clouds of space dust and other matter swirling around and pulling together to create the sun and its planets. This theory gave an explanation for the planets moving in the same direction. Due to the presence of other nebulas throughout the universe, Kant was a believer of the theory of multiverse because he thought the other nebulas were other universes like the Milky Way. Kant's theories of extraterrestrials were also very interesting. As a great believer in plurality, his theory was that the exterrestrials become more and more moral as the distance between the sun increases. Thus this creates a positive relationship between the distance of the sun and the amount of moral perfection an inhabbitant attains.


     As scientists and astronomers continued to discover more about our solar system and universe, the public was becoming absorbed in the discussion of plurality.  Writers and philosophers began to publish popular works about plurality in order to explain and elaborate on contemporary ideas that were shaping the understanding of our universe.  One writer was Bernard Le Bovier De Fontenelle, who published a very popular work called Conversations of the Plurality of Worlds in 1686. Fontenelle wrote from the perspective of a philosopher describing contemporary ideas with a charming countess.  The philosopher uses analogy to describe the likelihood that life inhabits the moon, even though we cannot see signs to indicate this.  He compared it to someone looking at a city from a very far distance and not being able to see life, even though the city is crawling with life.  More specifically, he wrote that "since the Sun, which is now immovable, hath left off being a planet, and the Earth, which turns round him, is now become one, you will not be surprised when you hear that the Moon is an Earth too and that she is inhabited as ours is” (Crowe pg. 74). Examples of popular non-scientific work such as this show that the public not only accepted Copernicanism and plurality, but they were truly a popular phenomenon.


(Next Page) Part 2: The 19th Century

Comments (1)

Peter Ramberg said

at 10:33 am on Dec 7, 2008

Maybe the previous page links could go at the very top of the page, above the tile (in regular font).

This page looks very good. I wouldn't add more, except maybe a little bit about eighteenth century astronomy. Also some more dates would be useful for the reader to keep track of when things are happening.

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