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We No Longer Live in the World of Talmudic Rabbis. What’s a Modern Jew to Do?

In the Bible, the rabbis had the most accurate possible description of the world—a flawed and limited cosmology

Adam Kirsch
October 01, 2013
(Photoillustration Tablet Magazine; original photo San Diego Air & Space Museum Archive/Flickr)

Literary criticAdam Kirschis readinga page of Talmud a day, along with Jews around the world.

Just about every page of Talmud I read makes clear to me that the rabbis lived in a different world than we do. But this week’s Daf Yomi reading showed that this was true in the most literal sense: The world, for the rabbis, was not our planet Earth, a small blue planet orbiting the Sun in the vastness of empty space. To them, as to all educated people of their time, the Earth was the center of the universe, surrounded by a series of concentric spheres, the outermost of which was studded with stars. “The Jewish Sages,” according to Pesachim 94b, “say the celestial sphere is stationary, and the constellations revolve in their place within the sphere.” In this they differed from the Gentile sages, who “say the entire celestial sphere revolves, and the constellations are stationary within the sphere.”

This is a surprising moment in the Talmud—perhaps a unique one, in my reading so far—because of the way it takes seriously the opinion of non-Jewish authorities. Most of the time, the Talmud is discussing Jewish law, and on that subject, naturally, Gentiles have nothing to say; the rabbis themselves are the chief authority on what God expects from the Jews. When non-Jews do appear in the Talmud, they are usually mentioned in a spirit of hostility and fear—as when, in Tractate Eruvin, the rabbis advised a Jew not to live alone among non-Jews, lest he be murdered.

But when it comes to matters of astronomy and cosmology, there is no reason in principle why a Gentile should not be better informed than a Jew. Indeed, the rabbis lived among cultures, Greek and Babylonian, which had invented the study of the stars and which raised speculation about the nature of the universe to a high art. At least some of the Jewish sages recognized this and were even willing to defer to the Gentiles on questions of astronomy.

In Pesachim 94a, for instance, Yehuda HaNasi, the great sage who compiled the Mishnah and who is referred to simply as “Rabbi,” argued in favor of the Jewish view, that the constellations revolved within their sphere. But Rav Acha bar Ya’akov “strongly objects” to Rabbi’s position—something that he would surely never dare to do if it were a question of Jewish law. Perhaps, Rav Acha says, the constellations are fixed within the outermost sphere of the universe, and the whole sphere itself rotates “like the pivot of a door.” Just as a door swings around its pivot, so the celestial sphere could swing around the Earth, carrying the stars with it. In that case, the Gentile cosmologists would be correct and the Jewish ones wrong.

Indeed, in the next stage of the discussion, we find Yehuda HaNasi himself coming down in favor of a non-Jewish theory. Ancient cosmology agreed that the Earth was covered by a firmament in the form of a dome—an idea reflected in the Creation account in Genesis, where God divides the waters above the firmament from those below. The Jewish Sages, we read this week, imagined this firmament as opaque. During the day, the sun travels from east to west below the firmament, so we can see its light. But at night, the sun returns from west to east by traveling above the firmament, which blocks its light, making nighttime dark.

This explains how the sun gets back to its starting-point in the east every morning. But there is also another possible explanation, the one that was offered by “the sages of the nations of the world.” This is that at night the sun continues its rotation around the bottom of the globe, traveling “beneath the earth,” but still in an east-to-west direction, until it reaches the east again in the morning. Yehuda HaNasi himself, it turns out, agreed with this theory: “And the statement of the sages of the nations of the world appears to be more accurate than our statement,” he conceded. The reason he gives is that, at night, subterranean springs are warm, which could only mean that they are being warmed by the sun as it passes beneath the Earth.

At another point in this discussion, Rava offers a figure for the size of the Earth: It is 6,000 parasangs, which translates to roughly 15,000 miles. But Rava never says whether he means this is the diameter of the Earth or the circumference, and in either case he is wrong; the diameter is about 8,000 miles at the equator, while the circumference is close to 25,000 miles. Other rabbis challenge his figures, but their reasoning is just as erroneous. One sage argues that, wherever you stand in the inhabited part of the Earth—for of course the rabbis knew nothing about the Western Hemisphere or Australia—a given star will always be in the same direction relative to the observer. If a star is in the western part of the sky from the point of view of someone in Babylonia, for instance, it will also be in the western part of the sky from the point of view of someone in Rome. This is taken to prove that the inhabited part of the world “rests under one star,” and since there are thousands of stars in the sky, the whole globe must be thousands of times larger than the inhabited zone.

Another baraita gives ratios: “The size of Egypt was four hundred parasangs by four hundred parasangs, and Egypt is one-sixtieth of the size of Cush, and Cush is one-sixtieth of the world.” By this reckoning, the surface of the Earth would be 576 million square parasangs, or 1.44 billion square miles (the correct figure is 200 million square miles). But the baraita doesn’t stop there. Earth, it continues perplexingly, is only one-sixtieth the size of the Garden of Eden, and the Garden of Eden is one-sixtieth the size of Eden, and Eden is one-sixtieth the size of Gehenna. I’m far from certain exactly what this is supposed to mean—how could the Garden of Eden, which in Genesis is a place on Earth, be so much larger than the Earth itself? The Talmud seems to be speaking in mystical terms here, and Rava’s sober attempt to figure out the size of the Earth has given way to cosmological fantasy.

Indeed, this whole discussion in Chapter Nine of Tractate Pesachim is a good demonstration of how premodern science was non-empirical. It relied on established authorities and abstract reasoning rather than actual measurement and experiment. A small but telling example comes when the rabbis are trying to figure out how far an average person can walk in the time between dawn and sunrise. The question has cosmological implications, because the rabbis are trying to work out a ratio between the distance traveled by a person and the distance traveled by the sun in the same period of time.

The easiest way to answer the question would be to get an average person and tell him to start walking. But of course this is not the way the rabbis approach things. Rather, Ulla cites a passage from Genesis, in which Lot flees Sodom at dawn and by sunrise had come to Zoar. The distance from Sodom to Zoar, according to Rabbi Chanina, is five mil (a mil is a quarter of a parasang); ergo, five mil is the distance a man can walk between dawn and sunrise. (Unless, of course, Lot was walking unusually fast, as a later rabbi will argue.) This combination of hearsay and biblical citation appears more trustworthy to the rabbis than anything they could find out on their own. To us, this seems deeply unscientific; to them, it was the natural method of problem-solving, since in the Bible they had the most accurate possible description of the world.

All of this cosmology comes into the Talmudic discussion in a typically indirect way. Chapter Nine of Tractate Pesachim deals primarily with the institution of the Second Pesach, which Moses explains in the Book of Numbers. The Passover sacrifice is supposed to be held on the 14th of the month of Nissan. But, the law says, anyone who is unable to make the sacrifice on that day, because he is ritually impure or because he is “on a journey far away,” is allowed to make it the following month, on the 14th of Iyyar.

This raises the question of how you define “a journey far away.” How far away from Jerusalem do you have to be in order to be exempt from the obligation of traveling there on Passover? The traditional answer, according to the Mishna on Pesachim 93b, is “anywhere from the city of Modi’in and beyond.” Modi’in lay 15 mil from Jerusalem, therefore 15 mil is taken as the definition of a distant journey. This leads to a discussion of how long it would ordinarily take a person to walk that distance, which leads in turn to the broader debate about the size of the Earth and the constitution of the heavens. As always, it is the most practical questions that lead the rabbis to the most abstract speculations.

The rabbis were no more mistaken about the nature of the universe than everyone else in their time, and for a long time afterwards. But it is impossible to avoid wondering whether the religion that fit their universe still fits our own, which is so much vaster and more chaotic, and where the role of humanity seems so much smaller and less significant. We may dismiss the rabbis’ cosmology while holding on to their laws and ethics, of course, as many modern Jews do. But I wonder whether theory and practice aren’t too closely entwined for such a neat separation. We no longer live in the rabbis’ world; how can we help living differently in our own?


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Adam Kirsch is a poet and literary critic, whose books include The People and the Books: 18 Classics of Jewish Literature.

Adam Kirsch is a poet and literary critic, whose books include The People and the Books: 18 Classics of Jewish Literature.