The previous chapter may have given you, dear reader, the impression of being shown round three different rooms in the house of nature-knowledge. First of all you visited the kitchen, then the best room and then the playroom. In each room the furniture was very different. Each mode of nature-knowledge differed not only in its outcomes but also in its style of reasoning, in its handiwork (if any were involved) and in its exploration of ways and means to counter what Newton called ‘fansying’. In other words, each of the three worked largely in its own way, and the high walls separating ‘Athens’ from ‘Alexandria’, which we first encountered with the ancient Greeks, were still standing unscathed. Although in Europe, together with a third mode of nature-knowledge, they had gone through a revolutionary transformation, hardly any effort had as yet been made to end their mutual isolation. It is true that we have encountered a few individuals, especially Huygens and the young Newton, who were involved in both realist-mathematical nature-knowledge and exploratory, fact-finding experiment. But for each mode they wore, as it were, a different hat. They behaved in the one quite differently from in the other and in each they followed prevailing practices and styles of thought (which they seized upon to make some splendid discoveries).

And yet it was also these two, Huygens and the young Newton, together with Boyle and Hooke, who managed to some extent to break down the walls separating different modes of nature-knowledge or at least to make sizable breaches in them.

BARRIERS BROKEN DOWN

Three aspects to this breaching of the walls should be noted. There is the political and religious background which we might call ‘the spirit of Westphalia’. Then, within each of the three modes of revolutionary nature-knowledge there are certain recurring themes which more or less incidentally lend themselves to crossover. One such theme is the making of measurements, the other is thinking in terms of moving particles. Finally, there is the unprecedented fact itself of crossing the boundaries between distinct modes of nature-knowledge. It takes the form of two new, and again revolutionary, transformations. For certain specific subjects such as impact, circular motion, light and chemical reactions it proves possible to merge the practices and styles of reasoning current in two distinct modes of nature-knowledge.

Does it matter whether we characterise what happened in seventeenth-century nature-knowledge as a revolution, or refrain from using that loaded term?

In one sense, of course not. ‘Revolution’ is just a word, with changing meanings which up to a point we may determine ourselves.

Nevertheless, we have in the course of this book come across several criteria that might help us to decide whether or not it makes good historical sense to keep speaking of ‘The Scientific Revolution of the seventeenth century’.

A VERITABLE REVOLUTION?

Take for starters the vast contrast between the state of nature-knowledge in 1600 and that one century later. It is vast in terms of reining in ‘fansy’ which we discussed at length when exploring the different ways in which the seventeenth-century pioneers of a radically new conception of the natural world sought to confirm the validity of their conclusions without resorting, as in the past, to hoary dogmatic certainties or conversely lapsing into all-encompassing sceptical doubt. In realist-mathematical science, the interaction between mathematics and experiment appeared to offer the prospect of a progression of often valid, sometimes wrong, but as a rule well-testable conclusions. In exploratory-experimental science, numerous artful devices were tried out to pin nature down in all its capricious unpredictability; at the end of the century, Newton made the criteria for this even more demanding. In short, nature-knowledge in the seventeenth century served, as it were, as a laboratory for finding out how to probe specific truth claims (whether made by oneself or by anyone else) in a spirit of methodical distrust. It goes a little too far perhaps to follow Popper here without more ado and ascribe ‘falsifiability’ to the pursuit of nature-knowledge in the seventeenth century, yet an implicit sense of human fallibility and a determination to make it operative (that is the new thing) are clearly taking over as the century proceeds.

The contrast between 1600 and 1700 is also vast in terms of substantive content. The Earth turns. Our blood circulates. The air that we breathe has weight. A void space can be created. Objects that are attracted by the Earth fall to the ground with uniform acceleration. White light is composed of all the colours of the rainbow. Unequal cross-sections of a river discharge equal quantities of water in equal periods of time.

If we had been born a couple or more centuries ago, there is a good chance that we would have been poor, very poor indeed. Our lives would have been spent working on the land, with little or no prospect of change. We would produce large families, but few of our children would outlive us. In any case, we ourselves wouldn't expect to live much beyond about 45. We would call a hovel our home, and heat it in winter with whatever sticks of wood that we were able to collect. Other comforts would have to be paid for either in kind or with the few pennies we had managed to save. Apart from everyday conversation, crying children and the noise of poultry and livestock, we would have lived amidst silence, interrupted on occasion by a thunderclap, communal song, the drums and trumpets of passing soldiers, maybe a lonely church bell tolling every so often. Most of us would have believed without question in the literal existence of spirits or gods or one God as the guiding or even the all-determining power in life and even more so after death.

In short, we would have been living in what is sometimes called the Old World, as distinct from the modern New World which you and I inhabit and which has made us rich and next year may make us richer still. Ours is a world where goods are readily available everywhere; however many we may own today we can always obtain newer and more up-to-date versions of them tomorrow. We are living longer and we are dying of mostly different diseases. Noise surrounds us wherever we go. We are parents of a few carefully planned and properly vaccinated children, who are likely to live even longer than we will. Many of those among us who still regularly go to church are no longer inclined to take the texts recited there in their literal sense. Our everyday behaviour is oriented towards this life – however hard we may try we find it difficult to imagine what life after death might possibly be like. When we travel we usually reach our destination by air, rail or motor car within hours instead of after days or weeks on horseback or on board a pitching barque, more concerned about tailbacks or punctures than ambush by pirates or robbers.

Kepler and Galileo, Beeckman and Descartes, Bacon, Gilbert, Harvey and van Helmont were each in their own way pioneers who, with their revolutionary transformations around 1600, were far in advance of the foot soldiers they had left behind. Even if we leave out of further consideration the profound ideological problems attached to their work, one would still have expected the three prevailing modes of nature-knowledge to survive for some time as if nothing much had happened in the intervening period. The surprising thing is that when you look back from around 1700 you find how little remained of these ‘old’ modes of nature-knowledge. In the first half of the seventeenth century there were still many who practised mathematical nature-knowledge in the old, hyper-abstract manner of Archimedes, of Euclid and of Ptolemy's Almagest. This was particularly true of planetary theory and the study of light and vision. When, between 1600 and 1625, Harriot, Snel and Descartes each discovered the law of refraction first found by Ibn Sahl, it still fitted almost seamlessly within the tradition. And in so far as a generation of astronomers after Kepler could approve of his results at all, they were as a rule still handled in tried and trusted fashion as fictional aids to model building of the usual kind. By the end of the century, this has all been swept away and ‘Alexandria-plus’ is the order of the day. This involves what I have called Ptolemy's bridge building as well. Ptolemy had ingeniously sought to inject elements of the real world in current, highly abstract mathematical accounts of the propagation of light (updated in the eleventh century by Ibn al-Haytham), of musical consonance (updated in the sixteenth century by Zarlino) and of planetary trajectories. As realist-mathematical science expands beyond Kepler and Galileo, all this begins to be replaced with almost brand-new physical theories in the former two cases, concurrent with the speedy demise (at least among astronomers) of belief in horoscopes or in any planetary influences at all. When in December 1659 Huygens is invited by a daughter of the late stadhouder (whom his father had served as secretary) to inspect her nativity and cast her horoscope, he knows that he cannot refuse, but he asks his fellow astronomer Boulliau to do it for him.

In 1608, Hans Lippershey, a Dutch optician, placed a concave and a convex lens a certain distance apart and enclosed them inside a tube. With the concave lens held up to the eye, distant objects looked larger and nearer, and you could even see things too far away for the naked eye. News of the invention spread quickly and reached Padua in the summer of 1609. The professor of mathematics, Galileo, was one of only two people (Thomas Harriot was the other) to whom it occurred to point the tube with lenses at the skies.

Galileo's idea was far from obvious. We at present take it for granted that the natural world is full of things which are invisible to the naked eye, from the cells in our bodies to the star-studded Milky Way set in infinite space. To observe such things one needs instruments, of a kind that did not then exist. The instruments which did exist were able to support observations and calculations – Tycho Brahe had refined them to the highest degree – but they did nothing but give greater precision to the recorded properties of objects already known. Nobody could have guessed that the Milky Way, that misty veil lying across the night sky, would on closer inspection dissolve into millions of stars. Nobody could have suspected that Jupiter is orbited by moons, that there are strange appendages on both sides of Saturn or that the surface of the Moon is studded with craters and valleys. All these facts were discovered by Galileo, and their repercussions would extend much further than the immediate sensation they caused throughout Europe when he published them in 1610 in a concise, matter-of-fact and spectacularly illustrated treatise entitled Sidereus nuncius (‘The Starry Messenger’). They were also to have a number of important repercussions for Galileo himself.

In the first place, they gave him the opportunity to get away from Padua. The previous eighteen years of experimenting, reasoning and checking had laid the foundations for a radically new mode of realist-mathematical nature-knowledge. He was entirely convinced of its superiority over any current philosophy of nature. He now saw himself as a ‘mathematical philosopher’. Not that this was a recognised social role: there were mathematicians and there were philosophers, but in between yawned a wide gulf.

Around 1600 the Scientific Revolution broke out. Or, to put it more precisely, a revolution occurred within each of the three modes of nature-knowledge that had flowered during the previous one and a half centuries. But the great paradox of the Scientific Revolution is that the one that underwent the most radical change was the most oriented towards the past. Against all those well-grounded expectations of our trend-watcher, ‘Alexandria’ turned out not to be nearing the end of its potential for development but really formed the inner core of a fundamental transformation into a largely new mode of nature-knowledge that I shall here call ‘Alexandria-plus’. And those responsible for this revolutionary transformation were the same Johannes Kepler and Galileo Galilei who a few years earlier had largely failed in their attempts, undertaken with greater boldness than ever before, to enrich ‘Alexandria’. It is through their doing that the time bomb which for half a century had quietly been ticking away in Copernicus’ book now suddenly exploded.

KEPLER AND GALILEO: FROM ‘ALEXANDRIA’ TO ‘ALEXANDRIA-PLUS’

Kepler and Galileo never met. One lived in the German-Austrian part of the Habsburg Empire (Graz, Prague, Linz) while the other lived in Italy (Pisa, Padua, Florence). They did exchange a few letters, and Kepler was keen to continue the correspondence, but Galileo held him at arm's length except for the one occasion when he urgently needed Kepler's help. Not only were their characters very different but also their methods and the core problems to which they dedicated their respective careers. What they had in common was intellectual brilliance and a deeply felt need to make mathematics deal with the real world. Kepler derived that desire from Ptolemy, who in his own way had taken some steps in the same direction. For Kepler its urgency was rooted in his conviction that, as Copernicus had argued in Book I half a century earlier, the Earth really is a planet and really does rotate on its axis each day and revolve around the Sun every year. Only, with Copernicus this idea, even if supported in Book I by several arguments, was hard to reconcile with the detailed models that he produced in Books II–VI in the time-honoured ‘save the phenomena’ style of the Almagest.

The natural world around us looks both impressive and mysterious. In the past, controlling it in times of drought or plague required magical incantations, while real understanding came via the world of the gods. Take the Iliad or the Odyssey: the angry voice of Zeus (Jupiter) is heard in a thunderstorm; volcanic eruptions and earthquakes are caused by Hephaestus (Vulcan) hammering on his anvil; if rain should fall while the Sun is shining, Iris hurries to place a rainbow in the heavens. In the pantheons of other civilisations it was much the same if with different names. But such explanations still left open the possibility of penetrating more deeply into specific phenomena. The Babylonians, for instance, produced strikingly accurate predictions of the positions of the Moon, stars and planets by systematically tracking their movements through the night sky. The Polynesians, by sophisticated observation of subtle changes in cloud formations and bird flight, were able to navigate their canoes accurately over hundreds of miles of ocean.

Among the civilisations that developed such specialised nature-knowledge, two took a further decisive step. They were the Greeks in the sixth century BC and the Chinese at about the same time. Both ceased appealing to explanations of the Zeus/Iris type, and came up with a very different picture of the natural world. They did not abandon their belief in gods and the spirit world, but they no longer attributed the myriad of natural events to divine action. Instead, they posed certain principles of natural order and established certain explanatory schemata that enabled them to understand and chart the whole of the natural world from a few fundamental points of view.

There are of course many ways of doing this, and just as one can choose between eating with a knife and fork or with chopsticks, or writing with letters or characters, so one can choose between different ways of approaching natural phenomena and breaking them down into manageable portions. Accordingly, how the Greeks chose to approach and order the natural world turned out to be very different from how the Chinese did essentially the same thing. The Chinese approach relied primarily on observation and focused on practical use. In the second century, Zhang Heng attempted to detect regularity in the occurrence of earthquakes in order to find a way of predicting them.

I shall chart the successive transplantations of Greek nature-knowledge by way of a metaphor. Or, rather, let us extend in a literal sense our image of transplantation. Imagine that in Greece a flowering shrub, an oleander for example, has been sown and carefully cultivated. Centuries later the nursery goes bankrupt. The administrators (in this case the rulers and scholars of Byzantium) are not particularly concerned whether the plant has withered or not but luckily it can survive for centuries without water. However, if it is to recover fully, cuttings will have to be taken and it will certainly need repotting. Also, customers will need well-tilled land in which the cuttings can take root, as well as compost to help it to blossom.

On three occasions, a customer did come to the door and, in each case, his land had been thoroughly ploughed and prepared. However, the ploughing had been done by warfare.

Warfare is obviously horrendous for the many who throughout history have been its victims. Daily routine is lost and nobody's life is safe. But, by turning everything on its head, war also creates space for change. Such change can be large-scale and at times even creative. We have seen how in the Greek world the conquests of Alexander the Great led to the founding of a cultural centre where certain pre-Socratic ideas were systematically developed into a mathematical mode of nature-knowledge.

The creative potential of warfare is evident on each occasion that cuttings are taken from Greek nature-knowledge and planted elsewhere. The first customer who came to the nursery was a caliph, some way down the family line of the prophet Mohammed. His name was al-Mansur and he came to power around the Islamic year 140 (or c. 760 AD, according to the Christian calendar which I shall keep using for the sake of convenience). His accession had not been straightforward. His family had engineered a coup and had won the civil war that ensued. He justified the coup on the grounds that he was a descendant of the prophet's uncle Abbas, and the dynasty that he founded is known accordingly as the Abbasid Caliphate. Determined to make a fresh start, he began by founding a new capital city of Baghdad on the model of Alexandria. The similarity went much further than its grid street plan.