Alexander wept when he heard from Anaxarchus that there was an infinite number of worlds; and his friends asking him if any accident had befallen him, he returns this answer: “Do you not think it a matter worthy of lamentation that when there is such a vast multitude of them, we have not yet conquered one?” Plutarch
It was interesting to listen a scientist talking about the success of landing a small probe on the Titan moon. He said that we will learn how life was created, or how the atmosphere of the Earth was formed, whether extraterrestrial life exists or not. Why did he say this? Are we so stupid to believe this. Of course if some strange animal of Titan would appear in front of the camera of the probe then we could answer this question and not just because we see some structures formed possible by rivers. Did he try to justify the money spent for the mission? Who cares if there is extraterrestrial life and why should this knowledge change or revolutionize our life? Will this be a proof that God does not exist and life is formed just by the laws of nature and if the answer is no then will this be a proof that God exists? The only thing that will change is that we will know which of the two possibilities (are we alone in the universe: yes or no? ) is true. How can a small device answer such questions? It can just take some images, measure temperature, etc and one has only a few hours time for the measurements. Why did the scientist did not simple say that we did this just because Titan is there and more important for us is the challenge: can we go there and see how the Titan looks and do some experiments? Of course the scientist said this because he wanted to convince ordinary people and politicians that in order to answer this question we need much more expeditions until some day maybe we will find the answer. Whatever the scientist said I was happy that we have some information about this large moon of Saturn (or Kronos) and it is a success for the European Space Agency that the instruments and the device worked as planned after such a long period required to approach Saturn and Titan.
Only in the last years we have some indirect proofs that giant extraterrestrial planets exist. Is the idea of the existence of other planets and of the possibility of extraterrestrial life new?
And [we must suppose that] men have been formed and all the other animals that have life; and the men have settled cities and cultivated fields as with us, and sun and moon and the rest as with us; and the earth grows all sorts of produce for them, the most useful of which they gather into their houses and use. This is my account of the separating off, that it must have taken place not only where we live, but elsewhere also. Anaxagoras Translation from W.K.C. Guthrie, A History of Greek Philosophy, vol. 2, The Presocratic Tradition from Parmenides to Democritus (Cambridge: Cambridge Univ. Press, 1965), p. 314.
There are innumerable worlds of different sizes. In some there is neither sun nor moon, in others they are larger than in ours and others have more than one. These worlds are at irregular distances, more in one direction and less in another, and some are flourishing, others declining. Here they come into being, there they die, and they are destroyed by collision with one another. Some of the worlds have no animal or vegetable life nor any water. Democritus according to Hippolytus, Refutation of the Heresies I 13 2, in Diels and Kranz, Die Fragmente der Vorsokratiker, vol. 2, section 68 A 40, p. 94. Translation from Guthrie, A History of Greek Philosophy, vol. 2, p. 405.
τὸ μὲν πᾶν ἄπειρόν φησιν, ὡς προείρηται· τούτου δὲ τὸ μὲν πλῆρες εἶναι, τὸ δὲ κενόν, <ἃ> καὶ στοιχεῖά φησι. κόσμους τε ἐκ τούτου ἀπείρους εἶναι καὶ διαλύεσθαι εἰς ταῦτα. γίνεσθαι δὲ τοὺς κόσμους οὕτω· φέρεσθαι <κατὰ ἀποτομὴν ἐκ τῆς ἀπείρου> πολλὰ σώματα παντοῖα τοῖς σχήμασιν εἰς <μέγα κενόν>, ἅπερ ἀθροισθέντα δίνην ἀπεργάζεσθαι μίαν, καθ' ἣν προσκρούοντα καὶ παντοδαπῶς κυκλούμενα διακρίνεσθαι χωρὶς τὰ ὅμοια πρὸς τὰ ὅμοια. ἰσορρόπων δὲ διὰ τὸ πλῆθος μηκέτι δυναμένων περιφέρεσθαι, τὰ μὲν λεπτὰ χωρεῖν εἰς τὸ ἔξω κενόν, ὥσπερ διαττώμενα· τὰ δὲ λοιπὰ <συμμένειν> καὶ περιπλεκόμενα συγκατατρέχειν ἀλλήλοις καὶ ποιεῖν πρῶτόν τι σύστημα σφαιροειδές. Democritus
A infinite large universe and a great void. Rotating matter attracted and pieces that collide. The light bodies escape and the heavy parts form spherical systems. Sounds like a model of the creation of stars or planetary systems by gravitational forces according to Democritus who also discovered the atoms.
Not all shared the opinion of Aristotle that the Universe is finite. Strange is that Democritus not only proposed the existence of atoms, smallest not divisible units but also his opinion was that the Universe is infinite large and that there is not only one world but actually infinite. Strange also his idea that it is possible that identical worlds exists. He considered the Milky Way as the light of a large number of distant stars. Democritus was among the first to propose that the universe contains many worlds, some of them inhabited:
But what would you say, my dear friend, were you to hear them disputing, concerning ideal and incorporeal substances, and talking about finite and infinite? for this is a principal matter of contention between them; some confining all things within certain limits, others prescribing none. Some assert that there are many worlds, and laugh at those who affirm there is but one; whilst another, no man of peace, gravely assures us that war is the original parent of all things. Need I mention to you their strange opinions concerning the deities? One says, that number is a god;
In his Science Fiction Story, the first such known story, Lucian of Samosata in 160 AD describes the various opinions of ancient Greek natural philosophers.
Some assert that there are many worlds, and laugh at those who affirm there is but one
This was the opinion of Democritus, who held that there were infinite worlds in infinite space, according to all circumstances, some of which are not only like to one another, but every way so perfectly and absolutely equal, that there is no difference between them. Plutarch and Tully
whilst another, no man of peace, gravely assures us that war is the original parent of all things
Empedocles, of Agrigentum, a Pythagorean; he held that there are two principal powers in nature, amity and discord, and that "Sometimes by friendship, all are knit in one, Sometimes by discord, severed and undone."
One says, that number is a god;
Alluding to the doctrine of Pythagoras, according to whom, number is the principle most providential of all heaven and earth, the root of divine beings, of gods and demons, the fountain and root of all things; that which, before all things, exists in the divine mind, from which, and out of which, all things are digested into order, and remain numbered by an indissoluble series.
The ideas of Democritus were adopted by his followers, Metrodorus of Chios and Epicurus 341-270 BC. Epicurus who believed in atoms, in an infinite large world and in the evolution of the world writes in a letter to Herodotus:
...there are infinite worlds both like and unlike this world of ours. For the atoms being infinite in number...are borne far out into space. For those atoms.. have not been used up either on one worlds or on a limited number of worlds, nor on all the worlds which are alike, or on those which are different from these. So that there nowhere exists an obstacle to the infinite number of worlds.
He says also "we must believe that in all worlds there are living creatures and plants and other things we see in this world.." Epicurus used a similar argument as Archytas: If the universe is limited then it would be possible to go to the end and throw a spear further.
To consider the Earth as the only populated world in infinite space is as absurd as to assert that in an entire field of millet, only one grain will grow. Metrodorus of Chios, Source
Plutarch (Πλούταρχος) (46-120 AD), in On the Face That Can Be Seen in the Lunar Disk, compared the Moon to the Earth, upheld the idea of the plurality of worlds. Although he was surprised by the Moon's apparent lack of clouds that could be a result of the lack of water he considered that the dark areas probably to be seas. This was the reason of naming such a dark areas as a mare (sea).
Giordano Bruno (1548-1600 AD) revives Democritus' view that the Sun is one of an infinite number of stars. Even if he considered that the infinite spherical Universe is a manifestation of the greatness of God the Catholic Church was not happy with such ideas!
A question is if the infinite world could be created in finite time. If not then the Universe is infinite in time. Since the time is infinite then whatever event we choose there must be an infinite time have passed before this event.
Steven J. Dick, Life on Other Worlds: The 20th-Century Extraterrestrial Life Debate, Cambridge University Press 1998