This article originally appeared in the Jewish Free Press, Calgary

Over the Rainbow *

Living in a region known for its rapid changes of weather, where severe rainstorms are followed quickly (or even overlapped) by bright sunshine, we are privileged to witness rainbows with uncommon frequency. Some of us might still recall the explanation that we learned in our high school science classes: rainbows arise from the process of refraction of sunlight through the droplets of water that remain in the air after the storm. We may even have attempted to reproduce that process for a science fair with the help of lawn sprinklers and lamps.

The appearance of rainbows would therefore appear to be an invariable process that takes place whenever there is a convergence of the necessary conditions: moisture in the air, sunlight, and an eye that is capable of viewing it from the appropriate angle.

This provokes a serious problem when we compare it with what seems to be the Torah's explanation for the origin of rainbows. After the flood that wiped out the sinful humans of Noah's time, God reassured the survivors that he would never again bring upon them a flood of such proportions. This pledge was then given symbolic representation by the creation of a rainbow that would henceforth appear in the heavens after rain showers, as if to remind the Almighty of his commitment. If we take the words at face value, they seem to be saying that prior to the great deluge there were no rainbows and that God did not introduce them until the time of Noah.

This premise was extremely problematic to Jewish commentators who took their science seriously, and it provoked many questions. Were the laws of light refraction in force before the flood? During the ten generations between the creation and Noah, what happened when the sun shone after a rainshower? The essence of science (and of the creator who produced them) is that its laws are eternally valid and reproducible, so it is inconceivable that God would change the rules in mid-play?

These questions vexed the illustrious philosopher, exegete and talmudist Saadiah Gaon in the tenth century, and he dealt with them in a terse comment. Where Scripture has God declaring "I set my bow in the cloud and it shall be a token of a covenant between me and the earth," Sa'adia stresses that the operational verb should be translated in the past tense (exploiting an ambiguity of biblical grammar) as "I have set my bow in the cloud." That is to say: the rainbow has existed since the six days of the creation, but it shall henceforth function as a token of the divine covenant. According to this reading, it is not the behaviours of light, moisture or their interactions that have changed, but the religious meaning that is to be attached to those physical laws.

Even among rationalist exegetes, not everyone was willing to accept Saadiah's reading of the verse. Rabbi Abraham Ibn Ezra took issue with it, and insisted that the verb should be read in the present tense: "behold I am setting the bow now in the cloud." He nonetheless alluded to the scientific theories advanced by the Greek scholars that rainbows are generated by sunlight, and he did not claim that the laws of physics or optics were altered in any way.

It is quite true that Greek philosophers and natural scientists were fascinated to the phenomenon of rainbows, and made ambitious attempts to provide scientific explanations that would account for their diverse and mystifying features. The most influential theory was that of Aristotle as he formulated it in his "Meteorology" and other works. He was not yet aware of light refraction, so his explanation focused instead on the reflection of the sun's rays on water particles whose distribution through the air or clouds causes them to function as virtual flat surfaces. Aristotle also sought explanations for the sequence of the rainbow's colours. He discerned three "primary colours"—red, green and violet—that he believed fell in a hierarchical sequence extending from light to dark. Those early scientists were particularly intrigued by the phenomenon of double rainbows; and they sought an explanation for why the order of the colours was reversed in the second rainbow. Aristotle also toiled hard, though not quite successfully, to calculate the relative angles of the sun, moisture and observer’s position that coalesce to produce different perspectives for viewing the differing arcs of the rainbows.

Similar studies were undertaken by medieval Jewish scientists liker Rabbi Levi ben Gerson (Gersonides, Ralbag). Advances were also being made by Muslim and Christian scientists like Ibn al-Haytham, al-Farisi and Theodoric of Freiberg. The science was so impressive that even a mystic like Rabbi Moses Nahmanides (Ramban) who often took Maimonides to task for his reluctance to believe in miracles (that is, divine suspensions of the laws of nature), conceded here that we must accept the Greek science and, in the spirit of Saadiah, posit that rainbows had existed before the flood.

Ibn Ezra, on the other hand, believed that though the laws of physics might have remained unchanged since creation, God did introduce some changes in the specific material conditions that prevail after the flood. Changes of that sort are certainly within the power of the Almighty and they do not fundamentally impair the foundations of the science. He claimed that the creator strengthened the light of the sun which—so he seems to assume—had not hitherto been powerful enough to produce rainbows. (We must bear in mind that Ibn Ezra's pre-Copernican sun revolving around the Earth was a considerably smaller body than the heliocentric giant that we have come to acknowledge.)

Ibn Ezra went so far as to explain that the essential conditions for producing rainbows—sunlight shining on clouds or water particles—are continually in operation, and it is only the limitations of the human perspective that prevent us from seeing them at all times. God, however, can behold them at all times, so that they serve him as an eternal token or "reminder" of his covenant with the human species.

This last theme was developed in impressive depth by Don Isaac Abravanel who understood it as a source of consolation for humanity: even though we are not always able to see the rainbow from down here, we may rest assured that God above can see it and will always remember his promise not to inflict a second deluge. Unlike the days of Noah’s flood, when forty days of uninterrupted cloud prevented us from ever catching a glimpse of the sun, God will periodically thin out the cloud cover sufficiently to allow humans to behold the sun’s image.

Once again we see how, by shining their intellectual lights on a challenging text from the Bible, Jewish scholars have provided a metaphoric prism that allows us to appreciate the brilliant and variegated hues of their scientific and spiritual learning.

This article and many others are now included in the book

Chronicles and Commentaries
Chronicles and Commentaries

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  • First Publication:
    • The Jewish Free Press, Calgary, October 12, 2012, p. 13.
  • For further reading:
    • Klein-Braslavy, Sara. “Gersonides’ Use of Aristotle’s Meteorology in his Accounts of some Biblical Miracles.” Aleph-Historical Studies in Science & Judaism 10, no. 2 (2010): 241–313.
    • Lee, Raymond L. The Rainbow Bridge: Rainbows in Art, Myth, and Science. University Park, PA: Pennsylvania State University Press, 2001.
    • Langermann, Y. Tzvi. “Acceptance and Devaluation: Nahmanides’ Attitude Towards Science.” Journal of Jewish Thought and Philosophy 1, no. 2 (1992): 223–245.
    • Meiron, Eyal. “Mathematical and Physical Optics in Medieval Jewish Scientific Thought.” In Science in Medieval Jewish Cultures, edited by Gad Freudenthal, 476–510. New York: Cambridge University Press, 2011.
    • Sayili, Aydin M. “The Aristotelian Explanation of the Rainbow.” Isis 30, no. 1 (1939): 65–83.
    • Tirosh-Rothschild, Hava. “Kabbalah and Science in the Middle Ages: Preliminary Remarks.” In Science in Medieval Jewish Cultures, edited by Gad Freudenthal, 476–510. New York: Cambridge University Press, 2011.