---
title: "History of the extraterrestrial life debate"
chunk: 2/4
source: "https://en.wikipedia.org/wiki/History_of_the_extraterrestrial_life_debate"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:31:38.469760+00:00"
instance: "kb-cron"
---

The Greeks discussed as well the possible existence of other worlds, but did not consider the planets as such. In their view, the celestial sphere was a part of Earth and other potential worlds would have their own ones. There was consensus that the world was made of the four classical elements, earth, water, fire and air. From there, they had two opposite ideas: Atomists thought that all existence was composed by atoms, small and indivisible pieces of the four elements, and Aristotelians thought that the four elements were exclusive to Earth and that the universe was made of a fifth one, the Aether. The atomist view would allow the existence of other worlds, as the processes that created Earth may happen elsewhere as well. Although very few of their writings were preserved, it is known that early atomists Leucippus and Democritus thought that atoms should create other worlds the same way Earth was created. Epicurus said in his "Letter to Herodotus" that "There are infinite worlds both like and unlike this world of ours... we must believe that in all worlds there are living creatures and plants and other things we see in this world".
Aristotle and Plato opposed the idea of a plurality of worlds. Plato reasoned that there could be a single heaven, and that if there were several worlds the universe would be composite, eventually falling into dissolution and decay. Aristotle thought that the earth element would tend to fall to the center of the universe and fire to rise away from it, under that logic the existence of other worlds would not be possible. He also thought that Aether moves in circles, and for that reason the universe could not be spatially infinite. Aristotle also rejected the plurality of universes, or heavens, arguing that the universe has a Prime Mover that started it all. If there were more than one universe then there would be more than one Prime Mover, and he considered that idea to be impossible. This idea may be influenced by his theological views, as well as his views about physics and cosmology. He concluded that "The world must be unique... There cannot be several worlds".
The Greek ideas and debates expanded across the ancient world, beyond Greece. Epicureanism spread across the Roman Empire, with proponents such as Lucretius with his book De rerum natura. Alexander the Great made a series of military campaigns that expanded the Greek Macedonian Empire to the Middle East, founding the city of Alexandria in Egypt, which would house the Library of Alexandria which was eventually destroyed. Baghdad became a hub of learning and trade during the Islamic Golden Age. Many Islamic scholars studied at the Library and cited or translated the work of the Greek authors, which did not get completely lost. They were also in contact with Hindu scholars from India, who were in turn influenced by the Chinese works and discoveries. Thus, Baghdad created a synthesis of the combined works of Ancient Greece, India, China, and their own scholars. This knowledge spread across the Byzantine Empire, and finally returned to Europe when many scholars escaped from the fall of Constantinople.

== Christianity ==

The views of the atomists fell under religious scrutiny when Christianity became a prominent religion. All Church Fathers who made mention of the idea of the plurality of worlds dismissed it as a heresy. The only exception was Origen, who did not believe in many worlds existing at the same time, but rather in worlds that may exist before and after Earth. He developed this idea to explain God's apparent lack of purpose and activities before creating the world. Augustine of Hippo rejected this idea, proposing that time only manifests in the motion of the material, which means that there was no time "before" the creation because time itself started with it. Thomas Aquinas discussed it in his Summa Theologica: according to John 1:10 "the world was made by Him", with "world" in singular, which would mean only one. A single world would also mean order, in contrast with the plurality of words held by atomists, who would believe in chance rather than in an "ordaining wisdom" creating it all. He cited the Aristotlean thought in his support; On the Heavens had been translated to Latin by Gerard of Cremona a few years before. He also considered that, as God was only one, he would create only one world to mirror his own perfection. However, the ideas of Aquinas were banned by the Condemnation of 1277: they considered that God was being analyzed in a very rational way, and that they were close to suggesting that God could not do certain things, such as creating infinite worlds. In the following years several scholars discussed the plurality of worlds and maintained that it was not a theological impossibility, even if they rejected it for other reasons.
William Vorilong was likely the first author to discuss the death and resurrection of Christ in the context of the plurality of worlds. He reasoned that if there were people on other worlds they would not be living in sin, because they would not descend from Adam and Eve, but they would still live by virtue of God. He assumed that the death of Christ would surely redeem the people of other worlds just as it did for humans on Earth, and did not consider fitting that God would repeatedly manifest at each different world.

== Copernican revolution ==