Jim al-Khalili, Pathfinders: the Golden Age of Arabic Science, Allen Lane: London, 2010 Jim al-Khalili, the author of Pathfinders: the Golden Age of Arabic Science, is a British national of Iraqi origin, a writer of popular science and a university teacher of physics. In his new book, based on a BBC television series, he draws on all three aspects of his identity, producing a book that is really almost three books in one. Pathfinders contains autobiographical material about the author's early life in Iraq, as well as background material on Abbasid history and society. It naturally also contains discussion of the author's real subject, which is the nature and achievements of "Arabic science," broadly speaking the scientific culture that flourished in lands recognising the authority of the Abbasid caliphate in Baghdad during the mediaeval period. Since, as al-Khalili points out, some western readers may be almost entirely ignorant of this civilisation's scientific achievements, Pathfinders often does not go much further than introduce the major figures and what is known about them. In doing so, al-Khalili can sometimes be frustrated either by the lack of evidence, particularly for earlier figures such as Jabir bin Hayyan (c.721-815), or by the need to explain complicated mathematical ideas, such as Ibn al-Haytham's (965-1039) work on conic sections. The tone is upbeat, with various figures, about whom little is sometimes known with any degree of certainty, being described as the most important physicist or greatest mathematician between the end of classical civilisation and the European renaissance. The book is media-friendly, presumably the result of its having started life as a television series, and the author has an apparent fondness for cliché. At the end of the day, as he is sometimes guilty of writing, such and such a figure deserves to be labeled a genius or a mastermind. Fortunately, in his more sober moments al-Khalili rejects this romantic vision of scientific work in favour of a focus not on individuals but instead on ideas and institutions. "Pathfinders" is one way of seeing the individuals written about in al-Khalili's book, but since little is known about many of them aside from lists of works, many of which are now lost, or from anecdotes in the works of later writers, it may be perilous to see them as heroic outliers. While a biographical approach was probably inevitable, given al-Khalili's need to introduce his readers not only to scientific ideas but also to an entire civilisation, the book is at its best when explaining the ideas themselves. Al-Khalili begins by describing the foundation of Abbasid Baghdad in the 8th century and the programme of translation of classical works of science and philosophy into Arabic that was begun with the support of the early Abbasid caliphs. A key figure here was Al-Ma'mun, the seventh caliph, al-Khalili stressing both Al-Ma'mun's desire to fashion an Arabic-speaking scientific culture that would draw upon the classical inheritance and the practical steps he took to create the institutions necessary for study and research. Thus, the famous bayt al-hikma, or house of wisdom, founded by Al-Ma'mun in 832, was designed to attract the best philosophical and scientific minds to Baghdad from the vast and polyglot empire now controlled by the Abbasids. Al-Khalili quotes Al-Ma'mun's famous "dream of Aristotle," recounted by the 10th-century bibliographer Ibn al-Nadim, in which the caliph saw the ancient Greek philosopher. One of the reasons why "books of philosophy and other ancient science became plentiful," Ibn al-Nadim explains, is because Al-Ma'mun "saw in a dream the likeness of a man white in colour, with a ruddy complexion, broad forehead, joined eyebrows, bald head, bloodshot eyes and good qualities." "Al-Ma'mun related, 'It was as though I was in front of him, filled with fear of him. Then I said, 'Who are you?' He replied, 'I am Aristotle.' Then I was delighted with him and said, 'O sage, may I ask you a question?' He said, 'Ask it.' Then I asked, 'What is good?' He replied, 'What is good in the mind.'" Immediately after this passage, Ibn al-Nadim explains that Al-Ma'mun then wrote to the Byzantine emperor in Constantinople asking for scientific manuscripts. While al-Khalili does his best not to get bogged down in the details, he cannot avoid giving a certain amount of background material on the intellectual debates of the time and particularly on the tensions between religious doctrine and rational enquiry. These are summed up in Al-Ma'mun's commitment to free philosophical enquiry, as expressed in the dream of Aristotle and his support for the translation movement, and the later reaction against it in the theological clampdown initiated by Al-Mutawakkil, Al-Ma'mun's successor as caliph. On the whole, al-Khalili's view is that while the translation movement and the spirit of intellectual enquiry that fostered it can be explained by the technological needs of the time -- knowledge of geometry was useful for engineering projects and astronomy was useful for calculating travel itineraries -- he also argues forcefully that it would be quite wrong to see the translation movement as basically derivative or as simply carrying the torch of the classical inheritance, ready for it to be picked up later in the European renaissance. Instead, the Abbasid Empire's "multicultural and multifaith tolerance...fostered a real sense of expectancy and optimism, and this would usher in a golden age of enlightenment and intellectual progress." While the translation movement itself was dedicated to the appropriation and recirculation of existing knowledge, Abbasid scientists and philosophers soon went beyond what they found in the materials they had inherited from classical civilisation, creating a new commitment to disinterested enquiry that al-Khalili identifies with the scientific method and its emphasis on critical experiment. Among the figures he discusses in the greatest detail are the mathematician al-Khwarizmi, the inventor of algebra, and the physicist Ibn al-Haytham, best known for his work on optics and the properties of light. Both writers, al-Khalili argues, took classical science significantly forward, in al-Khwarizmi's case essentially inventing a branch of mathematics unknown to classical authors, and in the case of Ibn al-Haytham setting out mathematical proofs for the behaviour of light that it was to take many centuries before they could be confirmed elsewhere. Working during the first half of the 9th century and apparently producing his major works in Baghdad during the reign of Al-Ma'mun, al-Khwarizmi's treatise al-mukhtasar fi hisab al-jabr wa-l-mukabala, from which the term algebra ( al-jabr ) derives, gives the rules for algebraic manipulation, allowing problems such as those having to do with the division of plots of land or with inheritance and taxes to be solved by algebraic means. Such practical applications were the immediate spur for al-Khwarizmi's investigations, but they did not exhaust them. For al-Khalili, what sets al-Khwarizmi apart is his having moved away from concrete cases towards genuine mathematical abstraction, most clearly in his treatment of whole numbers and fractions. While al-Khwarizmi did not develop a symbolic notation for the mathematical operations he describes, al-Khalili sees this as comparatively unimportant. "Al-Khwarizmi's text teaches algebra for the very first time as a separate discipline from either arithmetic or geometry." Regarding the second author described in detail, the slightly later Ibn al-Haytham, al-Khalili is on firmer ground as far as biographical source material is concerned. Whereas almost nothing is known of al-Khwarizmi's life or circumstances, this is less true of Ibn al-Haytham, born in around 965 in Basra in what is now Iraq and spending much of his life in Cairo, where he apparently worked as a copyist of scientific manuscripts. Like al-Khwarizmi before him, Ibn al-Haytham inherited much of the scientific thinking on the subjects that exercised him, in his case predominantly optics, from classical authors, and also like al-Khwarizmi he significantly built on and extended this inheritance. However, while al-Khwarizmi did this by inventing a new field of mathematics, Ibn al-Haytham chose instead to revolutionise the thinking in his field. Ibn al-Haytham's book kitab al-manazir, or book of optics, was important for reviewing, and rejecting, the views on light and vision held by the classical authors, a "confused mess," according to al-Khalili, of contradictory and undeveloped ideas. These ideas Ibn al-Haytham replaced with a properly physical and mathematical understanding of light, such that its behaviour could be studied in geometric terms as light rays are bent or refracted as they pass through different materials, such as lenses. In this way, Ibn al-Haytham put forward not only a new way of understanding vision, replacing the inchoate ideas of the classical authors, but also an entirely new method for studying light. Al-Khalili writes that it is this emphasis on method, studying light by experiment and giving mathematical descriptions of its behaviour, that gives Ibn al-Haytham "a stronger claim to the title of 'father of the scientific method' than either Francis Bacon or Descartes." A taste of his achievement can be had by considering "Alhazen's Problem," (Alhazen was a later European approximation of Ibn al-Haytham's name), which al-Khalili summarises "as the problem of finding the point of reflection on a concave mirror of a light source in order to reach a given point." Finding the angles on a flat surface, he says, "can easily be solved to make sure the angle of incidence is equal to the angle of reflection." However, "while the same law of reflection also holds for a curved reflector, the problem can no longer be solved using geometry. Instead, Ibn al-Haytham showed his readers that one must use and solve a difficult [fourth-degree] algebraic equation." Elsewhere in Pathfinders, al-Khalili discusses medicine and astronomy, as well as the later development of scientific thinking in Arab Spain, notably in the work of polymaths such as Ibn Rushd. He also comments on the aims and methods of his history of Arabic science and its connection to the history of science more generally, as well as possible reasons for the later decline in the scientific culture of the Arabs. On the first point, al-Khalili says that it is "natural and right when apportioning credit for scientific discoveries to probe issues relating to historical contingency, as well as political and social factors." In other words, context is all, and there is little point in getting lost in debates on whether Newton or Leibniz deserves credit for the invention of calculus. That being so, al-Khalili suggests that credit for mediaeval Arabic science is due to the character of Abbasid civilisation as a whole and to the cosmopolitan peace and prosperity that it introduced to much of Asia. He then considers suggested explanations for the later "slow decline in scientific progress and output in the Islamic world." The first of these is associated with "the move towards a more conservative interpretation of Islamic theology" exemplified in the works of the theologian Al-Ghazali, who sided with religious orthodoxy against "the incoherence of the philosophers." Al-Khalili rejects this idea, and he rejects, too, the notion that the 13th-century destruction of Abbasid civilisation at the hands of the Mongols dealt a body blow to Arabic science, since there were other centres of Arab civilisation, notably in Egypt and Arab Spain, that survived and prospered. Al-Khalili does not have much to say on this subject, but in a final chapter he turns to what he calls "science and Islam today," by which he means the state of scientific research and education in countries belonging to the Organisation of the Islamic Conference. These countries have little in common economically, since they include both some of the world's richest countries and also some of the poorest. Whereas scientific education is lavishly funded in the Gulf, it is often sadly lacking in Chad or Mauritania. Al-Khalili concludes Pathfinders by saying that "spending vast sums of money will not be enough to reignite and rebuild a scientific culture in the Muslim world...A scientific renaissance will not happen overnight and requires not only the political will but also the understanding of the meaning of both academic freedom and the scientific method itself." Reviewed by David Tresilian
