Q. Does Judaism accept the possibility of other worlds?
A. We constantly make a distinction between olam hazeh – this world – and olam haba – the World to Come. But I don’t think this is what you are asking. Your question is more likely to be whether we believe that there are or could be worlds other than the earth we live on.
From a theological point of view the answer is, “Why not?” Our concern, our sphere of activity, is this world, but there is no tenet of Judaism that insists that this is the only world.
The Book of Judges (5:23) speaks of an inhabited place called Maroz, which the Talmud (Mo’ed Katan 16a) identifies as a planet. The Talmud (Avodah Zarah 3b) also speaks about eighteen thousand worlds which God inspects by night.
What the word “world” means in this context is not spelt out. The Midrash (B’reshit Rabbah 3:9) says that God made a number of other worlds before settling on this one and saying, “This one pleases Me: those did not please Me”.