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Scientific content in Jewish sources.


The overlap between science and Torah is still the subject of a great deal of discussion. (See, for example, AVIEZER 1990; BODENHEIMER 2012-2013.) In these areas of overlap, one would expect mutual compatibility, as two different approaches to the truth. In this paper I shall present eight examples of science in the Torah, ranging from concepts known in the ancient world to concepts discovered or developed in the modern age. Torah refers not only to the Five Books of Moses and Scripture, but also to the Oral Tradition. The Talmud tells us that Scripture and the Oral Law were given at Sinai and complement each other (TALMUD Brakhot 5a on EXODUS 24:12). With regard to the Talmud, Shmuel Ha'Nagid distinguishes between halakhah and aggadah. The former, he holds, is law and must be accepted totally; with regard to the latter, we are obligated to accept only that which is plausible (see Mevo Ha'Talmud for definitions of aggadetah and hilkhatah, found in most Babylonian editions of the Talmud between tractates Brakhot and Shabbat). The Talmudic examples here relate to halakhic issues. Some present straightforward literal meanings as understood by classical Biblical commentators.

The general approach adopted here is that of Nahmanides, described in his introduction to the book of Genesis. After discussing the concept of Torah from Sinai, Nahmanides suggests that the Creation and the forces of nature were all described or given to Moses and written in the Torah in some form either explicitly, or through hints, or numerology, or in the forms of the letters, or the "crowns" (tagim) above letters. Nahmanides quotes the description in the Talmud Rosh Hashanah 21b of the fifty categories (shearim) of knowledge created in the world, of which forty-nine were given to Moses. Nahmanides suggests that the creation of the universe therefore involved fifty categories of knowledge. He suggests as possible examples materials or minerals, vegetation, animals, and mankind. He further suggests that the category not given to Moses involved knowledge of the Creator, which cannot be given to those whom He created. The numbers involved, fifty and forty-nine, are hinted at in the Torah, for example, with regard to the counting of the omer and the counting of years until the Jubilee. Nahmanides maintains that King Solomon's knowledge of the strengths and medicinal properties of herbs and his ability to communicate with birds and animals were all obtained from the Torah.

Below are eight specific examples which can illustrate Nahmanides' view that science exists in the Torah in the form of the above she'arim. The examples involve concepts rather than a "handbook" of numerical values. (The Torah is not, of course, a handbook of science.) To these can be added examples such as the shape of the Earth (JERUSALEM TALMUD, Avodah Zarah, Chap. 3, halakhah 1, and ISAIAH 40:22) and the Jewish calendar, which have been discussed elsewhere. Nahmanides' concept of conversion of energy and mass also has been discussed elsewhere.



A discussion is held in the Talmud Pesahim 94a concerning the distance a person can walk in one day. The discussion continues with a statement by Rava that the Earth is 6,000 parsah, and the width of Heaven is 1,000 parsah. The Talmud says that the former is tradition, and the latter is reasoning.

A parsah is equal to four mil. A mil is approximately one kilometer, so that the distance considered is approximately 24,000 kilometers. The Talmud then quotes Rabbi Yehudah, who says that a normal walking distance is forty mil during the day, plus four mil from dawn to sunrise, and four mil from sunset to the coming out of the stars. The Talmud infers from this that the time from dawn to sunrise and from sunset to the coming out of the stars are each one tenth of the duration of a day (a ratio of four to forty mil), equal to 1.2 hours or 72 minutes, assuming a twelve-hour day as at the spring and autumnal equinoxes (tikufatNisan and tikufat Tishrei). As the discussion continues, eventually the Talmud refutes separately each of Rava's statements, with the conclusion that both statements are refuted. However, Rava's tradition of 6,000 parsah or 24,000 kilometers can be explained to be in accord with scientific measurement of the circumference of the Earth. The explanation is that the 24,000 kilometers represent the arc length of that part of the Earth in which there is sunlight. This arc length must be divided into two components--one of direct illumination and one of indirect illumination. The former represents those areas in which the sun can be seen directly. Here the time of day is between sunrise and sunset. Indirect solar illumination is in areas which are in transition from night to day (between dawn and sunrise) and from day to night (between sunset and darkness). Rabbi Yehudah indicates that the arc of each transition region is one tenth of that over which there is direct sunlight and, according to Rava's tradition, the sum of all three arcs is approximately 24,000 kilometers. This means the arc over which there is direct sunlight, which is half the circumference of the Earth, is 20,000 kilometers. The two transition arcs are then one tenth of that, or 2,000 kilometers each, yielding an arc of 24,000 kilometers over which there is some sort of sunlight. The meter is defined historically such that the Earth's average circumference is 40,000 kilometers. However, the purpose of the discussion in the Talmud is not to teach us the circumference of the Earth. (1)

The significance of the position of Rabbi Yehudah concerning the transition time from day to night and night to day being one tenth of the day at the equinox (tikufat Nisan and tikufat Tishrei) is demonstrated by the Tosafot, who ruled that the halakhah is according to Rabbi Yehudah. This is the ruling accepted in the Shulhan Arukh, Orah Hayyim 261:2, although there is a difference of opinion between the Tosafot and the Vilna Gaon as to how these 1.2 temporal hours are composed. This halakhic statement of Rabbi Yehudah is basic to my explanation above of the circumference of the Earth in accordance with Rava's tradition.


The prohibition given in Exodus 22:30 against eating treifah refers to animals that would die within twelve months because of an internal or external blemish conforming to the definitions of treifah (TALMUD Hulin 42a, 57b-58a). There is some question as to whether the implication is a literal twelve months (PRI HADASH on Shulhan Arukh, Yoreh Deah 57:18), or thirteen months for a leap year (SIFTEI KOHEN on Shulhan Arukh, Yoreh Deah 57:18), or 365 days (solar year, PITHEI TSHUVAH on Shulhan Arukh, Yoreh Deah 57:18). The Talmudic discussion implies that it is essential for the animal in question to be capable of surviving the various changes in seasonal conditions such as heat and cold that occur during a normal year in order for it to not be considered treifah (TALMUD Hulin 57b-58a). Consistent with the concept that the kashrut of permissible animals is associated with life, and treifah with death (ibid., based on LEVITICUS 11:2), if the animal in question is female then the ability to become pregnant is sufficient for the animal not to be considered treifah even before the "twelve month" trial period has passed (SIFTEI KOHEN on Shulhan Arukh Yoreh Deah 57:18). Such criteria for determining whether or not an animal is treifah can be applied only in cases of doubt. (See Arukh Ha'Shulhan, Yoreh Deah 57:78 for a list of examples.) If there is a conflict of opinion, the clear halakhic criteria take precedence over "twelve month" or pregnancy criteria (SIFTEI KOHEN on Shulhan Arukh, Yoreh Deah 57:18). Even if medical opinion is that under certain conditions a non-treifah animal will not survive for the "twelve month" period, we do not add such conditions to those for which an animal is considered treifah (MAIMONIDES, Mishneh Torah, Shehitah 10:12-13). Similarly, even if modern medical opinion is that some or all of the treifot listed by the Talmud Sages are conditions under which animals can live rather than die, we still do not change the list of treifot (ibid.). We neither add nor detract from the halakhic list of treifot, no matter what medical opinion may be (MEIRI on TALMUD Hulin 57b-58a). The association of death with treifah does not necessarily apply for all animals with a given treifah condition (Siftei Kohen on Shulhan Arukh, Yoreh Deah 57:18). It is recognized that some animals considered treifah can survive for "twelve months" (ibid.).

Nevertheless, the "twelve month" criterion supports the connection of the laws of treifot to the above concepts of life and death (LEVIN and BOYDEN, 1969).


Kirchhoff's Law of Thermal Radiation (1860) states that the radiant emission and the absorption of a material body in thermodynamic equilibrium are equal (SIEGEL and HOWELL, 1983). This stems from conservation of energy and implies that the radiant energy emitted by the surface of a body is equal to that absorbed by it when the body is in thermodynamic equilibrium with its surroundings. If an object is heated, it absorbs energy and becomes hot. If the heating process is stopped, that object does not remain hotter than its surroundings but cools until it reaches thermodynamic equilibrium with the surroundings. If the ambient temperature remains unchanged, the energy gained by the object equals the energy lost (ibid.). Such surface effects are analogous to the Talmudic concept of kevolo kakh polto (TALMUD Pesahim 30a, 74a), which is the basis of koshering utensils which have absorbed a forbidden substance. The utensil must be heated to at least that temperature at which the forbidden ingredient was absorbed in order for that ingredient to be released or "emitted." By then immersing the object in cold water, the forbidden ingredient is removed.

The koshering process can be understood physically from surface physics as follows. Molecules inside a given material usually have identical molecules around them, and chemical bonds can be formed between them. However, molecules on the surface do not have identical molecules in the outward direction with which to form bonds, since the outward direction involves a different material--usually air. Hence, the surface molecules usually form weaker bonds with ambient external molecules such as oxygen, nitrogen, water vapor, and so on, since there are no identical molecules in the outward direction with which to form bonds. When an object is heated, such bonds can be broken, and if a forbidden ingredient is located on the surface, it can form bonds with the surface atoms of the utensil. The forbidden ingredient is thus adsorbed onto the surface. (2) To kosher the utensil, its surface must be heated to at least that temperature at which the forbidden ingredient was adsorbed in order for such bonds to be broken and the forbidden ingredient to be released. By immersing the utensil in cold water, the forbidden ingredient is removed from the surface so that it cannot be re-adsorbed elsewhere in the utensil.

The koshering process can be explained by analogy to the concepts which comprise Kirchhoff's Law. As in the previous examples, this does not mean that the Talmud Sages knew infrared or surface physics, but rather that analogous concepts are contained in the Torah in the form of kevolo kakh polto (ibid.) rather than Kirchhoff's Law. The latter deals with absorption and emission of radiant energy; the former can be explained in terms of adsorption and emission of "forbidden" substances which also depend on energy.


Talmud Niddah 31b states that if a woman reaches satisfaction (mazraat) first, if she conceives the child will be male; if her male partner reaches satisfaction first, the child if conceived will be female. This is based on Leviticus 12:2 in which the words ki tazria appear to be superfluous. This particular Talmudic concept is now known as an important factor in gender determination (RORVIK and SHETTLES, 1970; and Shettles and Rorvik, 2006). The biological explanation is the following. Y chromosome sperm, which produce males, are of different physiological structure than X chromosome sperm, which produce females. The male-producing sperm have a smaller "head" but larger tail, thus making them less rugged with a shorter lifetime, but faster than the female-producing sperm. If the female partner reaches satisfaction first, her medium is more favorable in alkalinity to the sperm and the faster male-producing sperm with their longer tails are more likely to reach the egg first. However, if it is the male partner who reaches satisfaction first, the medium in which the sperm have to travel is more acidic, which is detrimental to the less rugged male-producing sperm, thus making it more likely that the female-producing sperm will reach the egg first. In the latter case, a girl child is more likely to result. Reliability of this phenomenon is about 75-90 percent. (SHETTLES 1970; and SHETTLES and RORVIK 2011). It is not infallible because of statistical variations, e.g., some males have sperm that is more abundantly male or female, rather than half and half. (The author has been informed by physicians that they actually use this insight of the Talmud in advising their patients.) This medical discovery had to wait until the 1960s when discovery of the different physiological features of the X and Y chromosome sperm became better understood. Differing lifetimes of both types of sperm further limit reliability. This method of choosing the sex of babies, known as the Shettles method, is also therefore dependent on the accuracy of prediction of ovulation time.

The Whelan method has also been suggested as a way to choose the gender of babies. It contradicts the Shettles method in many aspects, especially the timing of copulation with regard to ovulation. However, reliability is only about 56-68 percent, which is much closer to the natural 50 percent probability range (WHITTLE and RODECK, 2006).

Again, the Torah is not a biology textbook. Nevertheless, this is an example of a law of nature clearly described in the Torah.


Ecclesiastes 1:6 tells us that winds blow in cyclonic patterns: "The wind blows to the south and turns to the north; round and round it goes, ever returning on its course." Although today cyclonic wind patterns are seen easily in satellite photos, they were not confirmed until Benjamin Franklin discovered them about 200 years ago. This understanding is the literal meaning of this verse according to the major classical commentators Rashi, Ibn Ezra, and Radak. It is attributed in the Talmud Bava Batra 25b to Rabbi Yehoshua and in Midrash Yalkut Shimoni to Rabbi Eliezer, both of whom consider how wind directions change in a cyclonic pattern according to the position of the sun in the spherical envelope of the sky surrounding the world (Rabbeinu Hananel on TALMUD Bava Batra 25b).


An expression describing G-d's majesty used in Rosh Hashanah hymns extolling the Creation of the universe, is toleh erets al belimah. This is from Job 26:7 where, according to commentators such as Rashi, Metsudat Zion, and Ibn Ezra, belimah is composed of the two words beli mah, which together mean "nothing," i.e., G-d suspends (toleh) the Earth on nothing" (YALKUT SHIMONI 913). Commentaries on the Rosh Hashanah prayer book explain belimah similarly. Although homiletical teachings have been suggested, the literal meaning (according to Metsudat David and Metsudat Zion) is that the Earth is suspended in space with nothing to support it. This is the description given by the traditional Targum translation. The verse describes how, indeed, the Earth appears in space from afar. In the Midrash, Rabbi Abahu uses the word belimah (beli mah) to refer to G-d Who conceals Himself (k'eilu aino) while supporting the world.


In 1839 Matthew Maury noticed that Psalm 8:9 describes paths of the sea (orhot yamim). Up to that time sailors had not yet charted ocean currents nor used them to navigate. Maury understood the potential advantages of such currents for navigation. His landmark book The Physical Geography of the Sea, published in 1855, is considered a milestone in the beginning of oceanography. He understood the significance of the phrase "paths of the sea" literally, and then looked to find ocean currents and streams. His understanding of this verse is actually the literal meaning according to the Targum, Ibn Ezra, Metsudat David, and Radak, all of whom specifically describe man as building ships which pass through paths of the sea.


Ecclesiastes 1:7 describes how rivers run into the sea but the sea is never full. Classical Biblical commentators on this verse explain the reason as being the evaporation-condensation cycle, and connect it to Amos 5:8, in which G-d is described as "calling the water of the sea and pouring it upon the face of the Earth." Ibn Ezra, Radak, and Metsudat David agree that evaporation is the literal meaning of these verses. The commentaries distinguish between saltwater and sweet water, i.e., even over the sea, water is evaporated ("called"), but only sweet water forms clouds. Actually this idea comes from the midrashim in Ecclesiastes Rabati 1:13 and Yalkut Shimoni 967, based on a discussion reported between Rabbi Yehoshua and Rabbi Eliezer. The evaporation-condensation cycle is also described by the Targum on Genesis 1:2.


These eight examples of science in the Torah can be understood to support the view of Nahmanides that the Creation and the forces of nature were all described or given to Moses and written in the Torah either explicitly or implicitly. The Torah, of course, is not a science textbook. In this regard, it is interesting to note that Rabbi Yehudah Ha'Nasi did not hesitate to admit in a discussion on a certain scientific topic that the wise men of the nations of the world are correct and those of Israel incorrect (TALMUD Pesahim 94b). Furthermore, the fact that certain natural phenomena are described clearly in the Talmud does not mean that the Talmud Sages understood their scientific implications, but rather that these teachings were transferred from generation to generation as part of our Oral Tradition.


Aviezer, N. 1990. In the Beginning. Brooklyn, NY: Ktav.

Bodenheimer, J.S. 2012-2013. "Our Sages' Knowledge of Nature." B'Or HaTorah. vol. 22, pp. 125-136.

Kopeika, N.S. 1998. A System Engineering Approach to Imaging. Bellingham, WA: SPIE Optical Engineering Press, pp. 135-137.

Levin, S.I., and E.A. Boyden. 1969. The Kosher Code of the Orthodox Jew. NewYork: Hermon Press.

Rorvik, D.M., and L.B. Shettles. 1970. Your Baby's Sex: Now You Can Choose. New York: Dodd, Mead and Co.

Shettles, L.B. 1970. "Factors Influencing Sex Ratios" Intl. J. Gynecology and Obstetrics. Sep 1970, vol. 8, no. 5, pp. 643-647.

Shettles, L.B., and D.M. Rorvik. 1970. How to Choose the Sex of Your Baby. New York: Broadway Books.

Siegel, R., and J.R. Howell.1983. Thermal Radiation Heat Transfer. 2nd edition. New York: Hemisphere.

Whittle, M.J., and C.H. Rodeck. 2006. How to Choose the Sex of Your Baby: The Method Best Supported by Scientific Evidence. New York: Random House.

Presented at the Moshiach and Science Conference of the RYAL Institute in Beersheva, 14 Iyar 5773.

(1.) Editor's note: The great Talmudic scholar and philosopher, the Maharal (1520-1609 C.E.) makes a fundamental point regarding this particular Talmudic source and others: "Do not think that this measure of the world is a physical measure, for you must know that the Rabbis did not consider such things at all, because matters that do not pertain to the essence of the world and its essential truth they did not discuss at all ... This measure of 6,000 given by the Sages is only an abstraction of essence and spirituality, not a material measure" Beer Ha'Golah, part 6, chap. 4. Other rabbinical sources make similar comments. However, the author is suggesting that Rava's tradition, although rejected by the Talmud itself, can be explained in accordance with modern knowledge.

(2.) Editor's note: Adsorption is the adhesion of atoms, ions or molecules onto a material surface, from a gas, liquid, or dissolved solid. This process creates a film of the adsorbed substance on the surface of the material, to which the author's explanation applies. In contrast, absorption is a process in which the external substance penetrates into the bulk of the material, to which the author's explanation does not properly apply.

Professor N. S. Kopeika

Natan (Norman) Kopeika was born in Baltimore, MD, and raised in Philadelphia, PA. He obtained BSc, MSc, and PhD degrees in electrical engineering from the University of Pennsylvania, specializing in electro-optics. While preparing for his doctorate, he studied privately towards rabbinic ordination (Yoreh Yoreh), finishing requirements for both before coming on aliyah with his family in 1972.

He joined Ben-Gurion University of the Negev in 1973 and reached the rank of professor in 1987. He has chaired both the Departments of Electrical and Computer Engineering (1989-92) and Electro-optical Engineering (1998-2005). He is the author of about 190 papers in international professional journals, about 150 conference papers, and two books on electro-optics. He has supervised about fifty graduate student dissertations. His areas of specialization include imaging theory and systems, atmospheric optics, effects of ambient environment on semiconductor device surface states and device properties, interactions of electromagnetic waves with plasma, and thermal and millimeter wave imaging. In 1999, he and his former student and present colleague Professor Shlomi Arnon were recipients of the Thomson Prize from the IEE (UK). Since 1994 Professor Kopeika is the incumbent of the Reuven and Frances Feinberg Chair in Electro-optics at BGU. He has been a Fellow of SPIE since 2000.

He married Miriam Sirota in 1966. They have three children and eight grandchildren, with two of the families living in Beersheva and one in Otniel.

For the past several years, he has served as spiritual leader of the historic Hadassah Synagogue in downtown Beersheva, founded and named in 1948 after the medical convoy massacred on Mount Scopus.
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Author:Kopeika, N.S.
Publication:B'Or Ha'Torah
Article Type:Critical essay
Geographic Code:1USA
Date:Jan 1, 2014
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