- Cosmological theories describe the physical structure of the universe. For cosmology in the Bible, see creation . -In the Talmud According to R. Simeon b. Yoḥai, the earth and the heavens are like "a pot with a cover." This "cover" is the raki'a, the firmament. "The darkness of the firmament is that of a journey of 50 years. While the sun in the sky passes this journey of 50 years, a man can walk four miles." The distance between the firmament and the earth is the equivalent of a journey of 500 years (TJ, Ber. 1:1, 2c). The firmament is composed of water and the stars of fire, but they dwell harmoniously together (TJ, RH 2:5,58a). The heavens (shamayim) are an admixture of fire and water (esh and mayim) or made wholly of water (Sham mayim; Ḥag. 12a). Indeed, "the Holy One, blessed be He, took all the waters of the sea and with half He made the firmament and the other half the ocean. The firmament is like a pool, and above it is an arch" (Gen. R. 4:4 and 5). The earth is of the same thickness as the firmament (Gen. R. 4:5). Once every 1,656 years the firmament shakes on its foundations (Gen. R. 38:6). There is however more than one firmament; according to R. Judah, there are two, according to Resh Lakish, seven (Ḥag. 12b). The sun and the moon are situated in the second firmament (Gen. R. 6:6). The above-quoted view of R. Simeon b. Yoḥai would imply that the world is wholly enclosed by the firmament. R. Joshua was also originally of the same opinion, that the world was "like a tent" enclosed on all sides, but later he came round to the view of R. Eliezer that it is like an exedra, closed on three sides only, but open on the north side, and it is from this opening that the north wind comes (BB 25b). Originally the sun and the moon were both of the same size but God, realizing that "two kings cannot wear one crown," diminished the size of the moon. Thus what were originally "the two great luminaries" became "the greater luminary" and "the lesser luminary" of Genesis 1:16 (Ḥul. 60b). Eclipses of the sun are a sign of God's anger or displeasure (Suk. 29a). Beneath the earth is the abyss (tehom). There is a cavity which descends from the Holy of Holies to the abyss. (Louis Isaac Rabinowitz) -In Medieval Jewish Philosophy In medieval philosophy there were four types of cosmological theories: the Aristotelian-Ptolemaic, the neoplatonic, the Kalām theory, and the theory of the infinite universe. ARISTOTELIAN-PTOLEMAIC The medieval version of the Aristotelian-Ptolemaic cosmology asserts that the universe is a finite sphere whose center is the earth, around which nine other concentric spheres – the moon, the sun, the various planets, the stars, and the diurnal sphere – rotate. These spheres form a compact whole in which there are no gaps, or an inner vacuum, and around which there is nothing. The earth and the heavenly spheres differ in their composition. The latter are made up of a single element, ether, whose homogenous nature is free from change other than locomotion. The earth is composed of four elements, earth, water, air, and fire, whose continual transmutations make terrestrial substances subject to generation and corruption. Each of these moving spheres has a "soul," or internal moving force, which is set in motion by corresponding incorporeal substances, the Separate Intelligences. (According to some, "soul" and "intellect" are different aspects of the incorporeal substance.) According to maimonides , these incorporeal substances are identical with the angels (Maimonides, Guide of the Perplexed, 2:6). The ultimate source of motion is God, the Prime Mover, who "moves" the universe insofar as He is the most perfect substance, and therefore the object of love of all other substances (Aristotle, Metaphysics, 7:7; Maimonides, Guide 1:72; 2:1). NEOPLATONIC Medieval neoplatonic cosmology employs several Aristotelian notions but tries to overcome the terrestrial-celestial dichotomy inherent in the Aristotelian theory. Indeed, in some neoplatonic philosophies there is a decidedly pantheistic or monistic tendency (cf. the Christian philosopher Scotus Erigena). solomon ibn gabirol is the most neoplatonic of the medieval Jewish philosophers. In attempting to demonstrate the essential unity of the universe he applied the Aristotelian form-matter framework to every part of the universe except God and the Divine Will. The result of this extension is that every level of being that emanates from God (see emanation ) exhibits a common universal matter and universal form. Each level of being, however, is further characterized by a specific material nature and a particular formal structure. In this way both homogeneity and diversity are accounted for. Typical of monistic cosmologies, Gabirol's system tends to be static: the emanation of the lower stages of being from God is described in non-temporal terms. The origin of the universe, as well as motion, is explained by Ibn Gabirol as the effect of God's will, which seems to serve as the mediating link between God and the universe. KALĀM The Kalām cosmology employs the model of a universe consisting of atoms in a vacuum. These indivisible particles combine, separate, and recombine, forming the universe by these movements. The Kalām version of atomism differs from its Greek antecedents in that it rejects any notion of an infinite magnitude (Maimonides, Guide, 1:73). Atomism had virtually no impact upon the mainstream of Jewish philosophy, although a number of Karaite philosophers accepted its doctrines (see atomism ). Abu al-Barākāt Ḥibat Allah of Baghdad was a profound atomist but he had no influence upon Jewish thought, probably because of his conversion to Islam in his late years. Indeed, the most important Jewish representative of the Kalām, saadiah gaon , was not an atomist. INFINITE UNIVERSE – CRESCAS One aspect of classical atomism, however, is found in the cosmology of Ḥasdai Crescas . His philosophy constitutes a vigorous critique of Aristotle's physics and cosmology. Crescas reverts to the atomistic hypothesis of an infinite vacuum in which our universe, and perhaps others, are located. (The possibility of a plurality of universes is also found in rabbinic literature, but is rejected by Maimonides and other medieval Aristotelians; cf. Gen. R. 3; Maimonides, Guide, 2:30). Although Crescas does not explicitly introduce atoms into his physics, his theory of matter exhibits atomistic aspects. For example, unlike Aristotle, Crescas sees matter as requiring no external principle for its motion: bodies have a natural tendency to move. Consequently, Crescas eliminates the artificial system of intelligences as causes of motion. Finally, he rules out the distinction between the composition of the earth and the heavens in favor of the notion of a common matter characteristic of all bodies celestial and terrestrial. In several important respects Crescas' cosmology anticipates some ideas of Galileo and Newton. (Seymour Feldman) -BIBLIOGRAPHY: Aristotle, Physics and On the Heavens; Munk, Mélanges; Maimonides, Guide of the Perplexed, ed. and tr. by S. Pines (1963); H.A. Wolfson, Crescas' Critique of Aristotle (1929); idem, in: PAAJR, 11 (1941), 105–63; A.C. Crombie, Medieval and Early Modern Science, 1 (1959), index; Hyman, in: Congrès International de Philosophie Médiévale, La filosofia della natura nel Medioevo (1966), 209–18. ADD. BIBLIOGRAPHY: J. Dillon, "Ibn Gabirol: The Sage among the Schoolmen," in: L.E. Goodman (ed.), Neoplatonism and Jewish Thought (1992), 77–110; P. Duhem, Medieval Cosmology (1985); I. Efros, The Problem of Space in Jewish Medieval Philosophy (1917); S. Feldman, "Platonic Themes in Gersonides' Cosmology," in: Salo W. Baron Jubilee Volume (1975), 383–405; G. Freudenthal, "Cosmogonie et physique chez Gersonide," in: REJ, 145 (1986), 295–314; L.E. Goodman, "Maimonidean Naturalism," in: Neoplatonism in Jewish Thought (1992): 157–94; A. Hyman, "From What Is One and Simple Only What Is One and Simple Can Come to Be," in: L.E. Goodman (ed.), Neoplatonism in Jewish Thought (1992), 111–36; T. Rudavsky, "Philosophical Cosmology in Judaism," in: Early Science and Medicine (1997), 149–84; N. Samuelson, "The Role of the Elements and Matter in Gersonides' Cosmogony," in: G. Dahan (ed.), Gersonide en son temps (1991), 199233; H. Wolfson, Crescas' Critique of Aristotle (1929).
Encyclopedia Judaica. 1971.