To Explain the World: The Discovery of Modern Science

by Steven Weinberg

  It is revealing that, whatever the influence of al-Tusi and Ibn al-Shatir on Copernicus, their work was not followed up among Islamic astronomers. In any case, the Tusi couple and the planetary epicycles of Ibn al-Shatir were means of dealing with the complications that (though neither al-Tusi nor al-Shatir nor Copernicus knew it) are actually due to the elliptical orbits of planets and the off-center location of the Sun. These are complications that (as discussed in Chapters 8 and 11) equally affected Ptolemaic and Copernican theories, and had nothing to do with whether the Sun goes around the Earth or the Earth around the Sun. No Arab astronomer before modern times seriously proposed a heliocentric theory.

  Observatories continued to be built in Islamic countries. The greatest may have been an observatory in Samarkand, built in the 1420s by the ruler Ulugh Beg of the Timurid dynasty founded by Timur Lenk (Tamburlaine). There more accurate values were calculated for the sidereal year (365 days, 5 hours, 49 minutes, and 15 seconds) and the precession of the equinoxes (70 rather than 75 years per degree of precession, as compared with the modern value of 71.46 years per degree).

  An important advance in medicine was made just after the end of the Abbasid period. This was the discovery by the Arab physician Ibn al-Nafis of the pulmonary circulation, the circulation of blood from the right side of the heart through the lungs, where it mixes with air, and then flows back to the heart’s left side. Ibn al-Nafis worked at hospitals in Damascus and Cairo, and also wrote on ophthalmology.

  These examples notwithstanding, it is hard to avoid the impression that science in the Islamic world began to lose momentum toward the end of the Abbasid era, and then continued to decline. When the scientific revolution came, it took place only in Europe, not in the lands of Islam, and it was not joined by Islamic scientists. Even after telescopes became available in the seventeenth century, astronomical observatories in Islamic countries continued to be limited to naked-eye astronomy13 (though aided by elaborate instruments), undertaken largely for calendrical and religious rather than scientific purposes.

  This picture of decline inevitably raises the same question that was raised by the decline of science toward the end of the Roman Empire—do these declines have anything to do with the advance of religion? For Islam, as for Christianity, the case for a conflict between science and religion is complicated, and I won’t attempt a definite answer. There are at least two questions here. First, what was the general attitude of Islamic scientists toward religion? That is, was it only those who set aside the influence of their religion who were creative scientists? And second, what was the attitude toward science of Muslim society?

  Religious skepticism was widespread among scientists of the Abbasid era. The clearest example is provided by the astronomer Omar Khayyam, generally regarded as an atheist. He reveals his skepticism in several verses of the Rubaiyat:14

  Some for the Glories of the World, and some

  Sigh for the Prophet’s Paradise to come;

  Ah, take the Cash, and let the Credit go,

  Nor heed the rumble of a distant Drum!

  Why all the Saints and Sages who discuss’d

  Of the two Worlds so learnedly, are thrust

  Like foolish Prophets forth; their Words to Scorn

  Are scatter’d, and their mouths are stopt with Dust.

  Myself when young did eagerly frequent

  Doctor and Saint, and heard great argument

  About it, and about: but evermore

  Came out by the same door as in I went.

  (The literal translation into English is of course less poetic, but expresses essentially the same attitude.) Not for nothing was Khayyam after his death called “a stinging serpent to the Shari’ah.” Today in Iran, government censorship requires that published versions of the poetry of Khayyam must be edited to remove or revise his atheistic sentiments.

  The Aristotelian Ibn Rushd was banished around 1195 on suspicion of heresy. Another physician, al-Razi, was an outspoken skeptic. In his Tricks of the Prophets he argued that miracles are mere tricks, that people do not need religious leaders, and that Euclid and Hippocrates are more useful to humanity than religious teachers. His contemporary, the astronomer al-Biruni, was sufficiently sympathetic to these views to write an admiring biography of al-Razi.

  On the other hand, the physician Ibn Sina had a nasty correspondence with al-Biruni, and said that al-Razi should have stuck to things he understood, like boils and excrement. The astronomer al-Tusi was a devout Shiite, and wrote about theology. The name of the astronomer al-Sufi suggests that he was a Sufi mystic.

  It is hard to balance these individual examples. Most Arab scientists have left no record of their religious leanings. My own guess is that silence is more likely an indication of skepticism and perhaps fear than of devotion.

  Then there is the question of the attitude of Muslims in general toward science. The caliph al-Mamun who founded the House of Wisdom was certainly an important supporter of science, and it may be significant that he belonged to a Muslim sect, the Mutazalites, which sought a more rational interpretation of the Koran, and later came under attack for this. But the Mutazalites should not be regarded as religious skeptics. They had no doubt that the Koran is the word of God; they argued only that it was created by God, and had not always existed. Nor should they be confused with modern civil libertarians; they persecuted Muslims who thought that there was no need for God to have created the eternal Koran.

  By the eleventh century, there were signs in Islam of outright hostility to science. The astronomer al-Biruni complained about antiscientific attitudes among Islamic extremists:15

  The extremist among them would stamp the sciences as atheistic, and would proclaim that they lead people astray in order to make ignoramuses, like him, hate the sciences. For this will help him to conceal his ignorance, and to open the door to the complete destruction of science and scientists.

  There is a well-known anecdote, according to which al-Biruni was criticized by a religious legalist, because the astronomer was using an instrument that listed the months according to their names in Greek, the language of the Christian Byzantines. Al-Biruni replied, “The Byzantines also eat food.”

  The key figure in the growth of tension between science and Islam is often said to be al-Ghazali (Algazel). Born in 1058 in Persia, he moved to Syria and then to Baghdad. He also moved about a good deal intellectually, from orthodox Islam to skepticism and then back to orthodoxy, but combined with Sufi mysticism. After absorbing the works of Aristotle, and summarizing them in Inventions of the Philosophers, he later attacked rationalism in his best-known work, The Incoherence of the Philosophers.16 (Ibn Rushd, the partisan of Aristotle, wrote a riposte, The Incoherence of the Incoherence.) Here is how al-Ghazali expressed his view of Greek philosophy:

  The heretics in our times have heard the awe-inspiring names of people like Socrates, Hippocrates, Plato, Aristotle, etc. They have been deceived by the exaggerations made by the followers of these philosophers—exaggerations to the effect that the ancient masters possessed extraordinary intellectual powers; that the mathematical, logical, physical and metaphysical sciences developed by them are the most profound; that their excellent intelligence justifies their bold attempts to discover the Hidden Things by deductive methods; and that with all the subtlety of their intelligence and the originality of their accomplishments they repudiated the authority of religious laws: denied the validity of the positive contents of historical religions, and believe that all such things are only sanctimonious lies and trivialities.

  Al-Ghazali’s attack on science took the form of “occasionalism”—the doctrine that whatever happens is a singular occasion, governed not by any laws of nature but directly by the will of God. (This doctrine was not new in Islam—it had been advanced a century earlier by al-Ashari, an opponent of the Mutazalites.) In al-Ghazali’s Problem XVII, “Refutation of Their Belief in the Impossibility of a Departure from the Natural Course of Events,” one reads:

  In ou
r view, the connection between what are believed to be the cause and the effect [is] not necessary. . . . [God] has the power to create the satisfaction of hunger without eating, or death without the severance of the head, or even the survival of life when the head has been cut off, or any other thing from among the connected things (independently of what is supposed to be its cause). The philosophers deny this possibility; indeed, they assert its impossibility. Since the inquiry concerning these things (which are innumerable) may go to an indefinite length, let us consider only one example—viz., the burning of a piece of cotton at the time of its contact with fire. We admit the possibility of a contact between the two which will not result in burning, as also we admit the possibility of a transformation of cotton into ashes without coming into contact with fire. And they reject this possibility. . . . We say that it is God who—through the intermediacy of angels, or directly—is the agent of the creation of blackness in cotton; or of the disintegration of its parts, and their transformation into a smouldering heap or ashes. Fire, which is an inanimate thing, has no action.

  Other religions, such as Christianity and Judaism, also admit the possibility of miracles, departures from the natural order, but here we see that al-Ghazali denied the significance of any natural order whatsoever.

  This is hard to understand, because we certainly observe some regularities in nature. I doubt that al-Ghazali was unaware that it was not safe to put one’s hand into fire. He could have saved a place for science in the world of Islam, as a study of what God usually wills to happen, a position taken in the seventeenth century by Nicolas Malebranche. But al-Ghazali did not take this path. His reason is spelled out in another work, The Beginning of Sciences,17 in which he compared science to wine. Wine strengthens the body, but is nevertheless forbidden to Muslims. In the same way, astronomy and mathematics strengthen the mind, but “we nevertheless fear that one might be attracted through them to doctrines that are dangerous.”

  It is not only the writings of al-Ghazali that bear witness to a growing Islamic hostility to science in the Middle Ages. In 1194 in Almohad Córdoba, at the other end of the Islamic world from Baghdad, the Ulama (the local religious scholars) burned all medical and scientific books. And in 1449 religious fanatics destroyed Ulugh Beg’s observatory in Samarkand.

  We see in Islam today signs of the same concerns that troubled al-Ghazali. My friend the late Abdus Salam, a Pakistani physicist who won the first Nobel Prize in science awarded to a Muslim (for work done in England and Italy), once told me that he had tried to persuade the rulers of the oil-rich Persian Gulf states to invest in scientific research. He found that they were enthusiastic about supporting technology, but they feared that pure science would be culturally corrosive. (Salam was himself a devout Muslim. He was loyal to a Muslim sect, the Ahmadiyya, which has been regarded as heretical in Pakistan, and for years he could not return to his home country.)

  It is ironic that in the twentieth century Sayyid Qutb, a guiding spirit of modern radical Islamism, called for the replacement of Christianity, Judaism, and the Islam of his own day with a universal purified Islam, in part because he hoped in this way to create an Islamic science that would close the gap between science and religion. But Arab scientists in their golden age were not doing Islamic science. They were doing science.

  10

  Medieval Europe

  As the Roman Empire decayed in the West, Europe outside the realm of Byzantium became poor, rural, and largely illiterate. Where some literacy did survive, it was concentrated in the church, and there only in Latin. In Western Europe in the early Middle Ages virtually no one could read Greek.

  Some fragments of Greek learning had survived in monastery libraries as Latin translations, including parts of Plato’s Timaeus and translations around AD 500 by the Roman aristocrat Boethius of Aristotle’s work on logic and of a textbook of arithmetic. There were also works written in Latin by Romans, describing Greek science. Most notable was a fifth-century encyclopedia oddly titled The Marriage of Mercury and Philology by Martianus Capella, which treated (as handmaidens of philology) seven liberal arts: grammar, logic, rhetoric, geography, arithmetic, astronomy, and music. In his discussion of astronomy Martianus described the old theory of Heraclides that Mercury and Venus go around the Sun while the Sun goes around the Earth, a description praised a millennium later by Copernicus. But even with these shreds of ancient learning, Europeans in the early Middle Ages knew almost nothing of the great scientific achievements of the Greeks. Battered by repeated invasions of Goths, Vandals, Huns, Avars, Arabs, Magyars, and Northmen, the people of Western Europe had other concerns.

  Europe began to revive in the tenth and eleventh centuries. The invasions were winding down, and new techniques improved the productivity of agriculture.1 It was not until the late thirteenth century that significant scientific work would begin again, and not much would be accomplished until the sixteenth century, but in the interval an institutional and intellectual foundation was laid for the rebirth of science.

  In the tenth and eleventh centuries—a religious age—much of the new wealth of Europe naturally went not to the peasantry but to the church. As wonderfully described around AD 1030 by the French chronicler Raoul (or Radulfus) Glaber, “It was as if the world, shaking itself and putting off the old things, were putting on the white robe of churches.” For the future of learning, most important were the schools attached to cathedrals, such as those at Orléans, Reims, Laon, Cologne, Utrecht, Sens, Toledo, Chartres, and Paris.

  These schools trained the clergy not only in religion but also in a secular liberal arts curriculum left over from Roman times, based in part on the writings of Boethius and Martianus: the trivium of grammar, logic, and rhetoric; and, especially at Chartres, the quadrivium of arithmetic, geometry, astronomy, and music. Some of these schools went back to the time of Charlemagne, but in the eleventh century they began to attract schoolmasters of intellectual distinction, and at some schools there was a renewed interest in reconciling Christianity with knowledge of the natural world. As remarked by the historian Peter Dear,2 “Learning about God by learning what He had made, and understanding the whys and wherefores of its fabric, was seen by many as an eminently pious enterprise.” For instance, Thierry of Chartres, who taught at Paris and Chartres and became chancellor of the school at Chartres in 1142, explained the origin of the world as described in Genesis in terms of the theory of the four elements he learned from the Timaeus.

  Another development was even more important than the flowering of the cathedral schools, though not unrelated to it. This was a new wave of translations of the works of earlier scientists. Translations were at first not so much directly from Greek as from Arabic: either the works of Arab scientists, or works that had earlier been translated from Greek to Arabic or Greek to Syriac to Arabic.

  The enterprise of translation began early, in the middle of the tenth century, for instance at the monastery of Santa Maria de Ripoli in the Pyrenees, near the border between Christian Europe and Ummayad Spain. For an illustration of how this new knowledge could spread in medieval Europe, and its influence on the cathedral schools, consider the career of Gerbert d’Aurillac. Born in 945 in Aquitaine of obscure parents, he learned some Arab mathematics and astronomy in Catalonia; spent time in Rome; went to Reims, where he lectured on Arabic numbers and the abacus and reorganized the cathedral school; became abbot and then archbishop of Reims; assisted in the coronation of the founder of a new dynasty of French kings, Hugh Capet; followed the German emperor Otto III to Italy and Magdeburg; became archbishop of Ravenna; and in 999 was elected pope, as Sylvester II. His student Fulbert of Chartres studied at the cathedral school of Reims and then became bishop of Chartres in 1006, presiding over the rebuilding of its magnificent cathedral.

  The pace of translation accelerated in the twelfth century. At the century’s start, an Englishman, Adelard of Bath, traveled extensively in Arab countries; translated works of al-Khwarizmi; and, in Natural Questions, reported on
Arab learning. Somehow Thierry of Chartres learned of the use of zero in Arab mathematics, and introduced it into Europe. Probably the most important twelfth-century translator was Gerard of Cremona. He worked in Toledo, which had been the capital of Christian Spain before the Arab conquests, and though reconquered by Castilians in 1085 remained a center of Arab and Jewish culture. His Latin translation from Arabic of Ptolemy’s Almagest made Greek astronomy available to medieval Europe. Gerard also translated Euclid’s Elements and works by Archimedes, al-Razi, al-Ferghani, Galen, Ibn Sina, and al-Khwarizmi. After Arab Sicily fell to the Normans in 1091, translations were also made directly from Greek to Latin, with no reliance on Arabic intermediaries.

  The translations that had the greatest immediate impact were of Aristotle. It was in Toledo that the bulk of Aristotle’s work was translated from Arabic sources; for instance, there Gerard translated On the Heavens, Physics, and Meteorology.

  Aristotle’s works were not universally welcomed in the church. Medieval Christianity had been far more influenced by Platonism and Neoplatonism, partly through the example of Saint Augustine. Aristotle’s writings were naturalistic in a way that Plato’s were not, and his vision of a cosmos governed by laws, even laws as ill-developed as his were, presented an image of God’s hands in chains, the same image that had so disturbed al-Ghazali. The conflict over Aristotle was at least in part a conflict between two new mendicant orders: the Franciscans, or gray friars, founded in 1209, who opposed the teaching of Aristotle; and the Dominicans, or black friars, founded around 1216, who embraced “The Philosopher.”