We are interested in science as part of intellectual history. We are not, therefore, concerned whether Galileo’s theories are correct or not in terms of the scientific conception of truth, however mistrustful we might be of such a way of thinking about truth. Nor do we need do pay attention to the specifics of Galileo’s theories, as though we were studying physics, though does not mean that details of his interpretations of nature will be of no concern at all. Rather, what matters to us is how, as non-scientists, our conception of the world has completely changed because of Galileo’s achievements. We live in a completely different world view because of the rise of experimental science in the 16th and 17th centuries, and this has profoundly altered the way we view nature. Galileo’s name, therefore, marks an epochal change in our history, and the present cannot be understood without it.
Before, however, we discuss what it is that is so important about Galileo, let us first say a few things about ‘intellectual history’ or the ‘history of ideas’, which we began to talk about last week. First of all, and perhaps most importantly, what do we mean by history? The fundamental basis of history must be time, for if we were not temporal beings; that is, had a sense of our own past, present and future, then our history as such would not have a meaning for us. Thus, we can talk about this history of rocks, but it unclear that rocks have a history for themselves. Likewise, we can talk about the history of lions, but they themselves do not have their own history.
The time of history is not the same as clock time, though it can be measured by clock time (we say that such and such an historical event happened at such a date and such a time), because it is our own experience of time that is the basis of clock time, and not clock time the basis of our experience of time. Human beings were already historical, have a sense of their own lives and death, and their place in the sweep of generations, long before clock time became the representation of lived time. If we first of all did not live in time, then there would be no calendars and clocks to measure it.
What do we mean by the past of history? It cannot mean just what once happened in the present and now has disappeared into past only to be retrieved in the present like a fish pulled out of the river gasping for air on the bank. In some sense, isn’t the past ahead of us rather than in front of us? Heidegger in Being and Time speaks of there being two meanings of history (1962, pp.424–55). One is the positivism of the past, which marches under the banner of the words of the famous German historian Ranke, who raised the study of history to a proper science, wie es eigentlich gewesen (the past as it actually was). The other, far more difficult to understand, and the sense of history that Heidegger will argue for, is the past as the possibility of the future. He asks what makes something preserved in a museum historical. We are not just speaking of statues and artefacts, but all the kinds of things the historian works with: letters, diaries, memoirs, eye witness accounts, government archives, treaties, and so on. For the positivist, these are the facts of history, and what makes history more than fables and myths. Heidegger does not dispute the reality of these documents nor their importance to the scientific study of history, but he asks a more difficult question: what is the ‘pastness’ of the past? Why, when I hold them in my hand, do I say they belong to the past. What is the status of these past artefacts as past, even though they belong to the present, since I holding these documents in my hands now?
What is at stake here is what we mean by truth, for it is the authenticity of these past documents (that they really belong to the past) that legitimate history and make it different from myth or storytelling. The historian isn’t interested merely in the fact that the battle of Waterloo happened on the 18th of June 1818, but that such an event can be verified by real witness accounts that have been written down and stored in archive. Just as clock time is derivate of lived time, since if human beings did not live in time, then we wouldn’t have clocks, so Heidegger thinks there is a fuller experience of history on which this narrower conception, however important and interesting it is, must rest. Why would we be interested in preserving this past, and why are some pasts more significant than others, since there are pasts that are absolutely lost, and some pasts that now that interest us (the pasts or women and the marginal, for example) that did not interest us before?
Heidegger answer is that the past matters to us because of our present. We can only interpret the past from the vantage point of the present, but this means we see the past in terms of our future. The truth of history is not the collection of supposedly true facts about the past, but how life can be breathed into them so that these lost documents might be retrieved and their burning embers illuminate our world in a new light. We study history because it reveals the present, but in so doing it shines a light forward into our future.
When we come to read Galileo, then, we are not interested in it as a dead object that has nothing to say about our present or our future, but precisely the opposite. The world we live in now is the world picture of Galileo, and the dangers of the future precisely spring out of this future. What is at the heart of Galileo’s projection of nature is mathematics. ‘The book of nature,’ he famously said, is written in the language of mathematics’. Nature was not understood, as it was by the Ancient Greeks, and in the Medieval period, inspired as it was by the writings of Aristotle and other Greek philosophers, as made up of qualities, but as a quantity. What we see, colours, shapes, sizes and sounds, is not what is.
The ancient Greek word for nature is φύσις. Rather than suggesting a mathematical homogenous reality, φύσις is related to the verb φύω, which means to ‘grow, produce or engender’. In latter medical texts of that period, φύσις began to mean not just the process of something (growing, producing, engendering, and so on), but the nature of something, what it is be that thing (Hadot 2004, pp.39–52). It is this notion of φύσις that we find in the works of Plato and Aristotle and which are passed down to our European heritage through the Islamic scholars by the 12th century. It is this intellectual world that is being rejected by Galileo’s hypothesis. Here nature becomes something very different, and its transformation is something that we still live with today.
It is in the next lecture that we shall investigate this transformation metaphysically and not just scientifically (for it is really Descartes who systematises Galileo’s approach and he understands more fully that it requires a whole different way of looking at nature). At this point we only want to describe generally how such a conception of nature is very different from before. It is no longer seen as a living being, but as a machine. It is the machine model of nature that opens it up to mathematisation. It is not that Galileo first sees nature mathematically and then subsequently understands it as a physical quantity, it is because he see nature as machine, whose parts can be explained purely physically, that it is open to the descriptive power of mathematics. It is this physical mathematical model that is still the basis of our modern physics, and affects the way that all view nature and ourselves. The aim of the new science of nature is to uncover those hidden mechanisms behind appearances using the new instruments (like Galileo’s telescope) and technologies, and constructing experiments through which they might be described mathematically.
What is at the heart of the new mechanical, physical, and mathematical model of nature is the belief that reality is homogenous. It is homogeneity of physical reality that is the real revolution of Galileo’s world view. For previously to Galileo, both in Ancient Greek thought, and in the monotheistic faiths, nature was heterogeneous and not homogeneous. Thus, the universe was divided into two distinct spheres, the physical and intelligible in Plato, which was then repeated in Aristotle’s double world view in the difference between the sublunary world and the heavenly spheres. The theistic division of the world into the earthly and heavenly was easily overlaid on top of these philosophical distinctions, such that in the long Scholastic period the one reinforced the other.
From the perspective of the Church, then, especially since there was no empirical proof for Galileo’s Copernicanism, since it was only a hypothesis, the judgement against Galileo was clearly justified. For it overthrew an image of nature that had existed for millennia. What this homogeneity of nature implied (as Spinoza knew only too well), was not that God did not exist, but that there was no unique place for man in the universe. As Freud remarked, the Copernican hypothesis was a blow to man’s pride, not God’s, since God was required to set such a nature in motion, but man certainly wasn’t (1973, pp.284–5). The universe is made of an infinite homogeneous matter, in which there are infinite stars and infinite planets, some no doubt inhabited by beings who equally mistakenly thought they were at the centre of the universe, but who quite obviously were not, just as man isn’t. That later on God dropped out of the model (‘we no longer need this hypothesis,’ as Laplace famously remarked), should not obscure the fact that it was the disappearance of man that led to the disappearance of God, and not the other way around.
You have to read The Dialogue of the Two Chief World Systems with a healthy scepticism (which of course is always the way you should read) (Galilei & Finocchiaro 2008, pp.190–271). Galileo presents the Copernican system as though it were merely an mathematical hypothesis (which is how Copernicus himself understood it), whereas he believed he already had empirical proof that such a motion was real (he even argued erroneously that it was an explanation of the tides on the earth). What you have to understand is what the motion of the earth implied, however much it went against common sense, and why his opponents, who he represents as slaves to their learning and their books, rather than earnest observational study of nature (though it was his theories rather than his observations that were the source for his own hypothesis), were so adamantly against his views. Because to see the earth as in motion meant that there no difference between the earth and the other planets, and thus there was nothing at all distinctive about it.
As he writes at the very beginning of the second day, ‘Independent Mindedness and Aristotle’s Authority’, the traditional view was that the heavenly spheres were ‘ingenerable, indestructible, unchangeable and inert’, whereas the earth was the opposite of this, ‘elemental, generable, degradable, and changeable (Galilei & Finocchiaro 2008, p.193). Galileo’s argument was that there was no difference between the earth and rest of the universe because they were made of one and the same substance, and that the earth is the same as the planet Jupiter, which is clearly moving. It is important to note that Galileo does not get Simplicus (who represents all those who reject the heliocentric view) as not disagreeing with this hypothesis by putting forward a different one, but saying that it disagrees with the authority of Aristotle. Galileo is thereby opposing two different practices of science. One in which observation and theory is fundamental (though he probably overplays the observation, since he already entertained the hypothesis and constructed the experiments to prove them), and the other, traditional and hidebound by the interpretation of texts. The former, Galileo asserts, would have been more attractive to Aristotle than the latter, even though they claim to speak in his name, since he too was a scientist, and if he had looked through Galileo’s telescope would have agreed with him and not his opponents.
If we are going to reject Aristotle, he continues, we do not need another author. The only authority we need is our own senses. Our discussion as proper philosophers should be about the ‘sensible world and not a world on paper’ (Galilei & Finocchiaro 2008, p.201). As we shall see next week, however, it is precisely this world that we cannot see.
 He did not actually say this. The quotation is a gloss of a passage in The Assayer. ‘Philosophy is written in this all-encompassing book that is constantly open before our eyes, that is the universe; but it cannot be understood unless one first learns to understand the language and knows the characters in which it is written. It is written in mathematical language, and its characters are triangles, circles, and other geometrical figures; without these it is humanly impossible to understand a word of it, and one wanders around pointlessly in a dark labyrinth’ (Galilei & Finocchiaro 2008, p.183).
 For the Liddell and Scott entry for φύσις, see http://tinyurl.com/3a4fsaf. And for φύω, see http://goo.gl/oeZ43f.