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now to "Developments in
astronomy & physics: 1543-1687".English 233: Introduction to Western Humanities - Baroque & Enlightenment
From the time of the ancient Greeks, the job of explaining has been understood as "saving the appearances":
- In early astronomy, these data consist in observations of the relative spatial positions of the various heavenly phenomena (patches of light) upon the hemisphere of sky that arches over and around us.
We can logically divide this job of accounting for the way the world appears to us (via our senses) into several distinct phases. It is so crucial that we constantly keep these distinct in our mind that in what follows. Each plays is own unique role in the overall business of what we today sometimes call "doing" science.
- I'll use purple font for material about the specific Ptolemaic approach to explaining astronomical data, and
- red font for material about what's specific about the Copernican strategy for explaining these same data. I will use the same to highlight modifications of the Copernicus' original hypothesis that finally culminated in the full Newtonian picture of the cosmos. That is, features of Kepler's, Galileo's and Newton's work will appear in red because they are put forward within the general framework of the Copernican idea. (Nevertheless it is important to keep their ideas distinct in your mind from the aspects of Copernicus' own proposal that they departed from. Otherwise we cannot appreciate them as contributions towards the eventual victory of the basic Copernican innovation!)
(It is impossible to stress too much that the Ptolemaic and Copernican theories are different ways of explaining the same data, and that they differ not only from each other but from these data.)
A. The first task we might describe as taking stock of appearances. This itself actually involves several different operations.
1. initial, informal noticing of "how things are"
Before we are ever led to create an "astronomy," we will have turned our attention to the sky, which seems to arch over us like a huge bowl. In addition to birds and clouds, and the difference between day and night, we notice certain disks and dots of light, which show up repeatedly enough for us to tag them with names:
- There is a very bright disk that appears somewhere on the eastern horizon shortly after dawn, crosses the sky rising to a highpoint and then descending to somewhere on the western horizon shortly before dusk. English dubs it "the sun"; in Latin (the language in which astronomy was originally discussed in the European West) it is sol.
- Another something in the sky shows up sometimes as a disk, sometimes as a portion of a disk (ranging from a slivver to everything but a sliver). Sometimes it is not present during day or night; sometimes it is palely present during the day; sometimes it is brightly present in the night sky. In both cases, during a single given day or night it gradually changes its position in the sky with respect to the horizon). English names this "the moon"; Latin calls it luna.
- There are also dots that move across the sky during the night. (In English each is a "star," in Latin stella, in Greek, astro. Yet with almost all of these, their relative positions to each other do not change. That is, they stand to each other in such a way as to make stable patterns. If we are standing somewhere in the Middle East or Europe or North Africa or China, these constellations move together along an arc of an imaginary circle whose center would lie on a particular star directly north of us (the "North Star"). And these constellations themselves maintain their constant relative position to each other: they all move together in the course of a given night. On the other hand, there turn out to be a few dots that, on successive nights, are not in the same position with respect to the vast majority. These appearance wander through the others. This difference gets marked in the language: we distinguish these "erratic" dots (< Latin errare, "to wander", or "planets" (< Greek planein, "to wander") from the "fixed stars" that provide the stable background with reference to which we plot the planets' movement.
- Very important! Note that "planet" in this sense does not mean what it does in modern astronomy. It is a purely phenomenal term, meaning "those patches of light whose positions change with respect to those other patches of light (the fixed stars) who never change their positions with respect to each other."
2. recognition that "things might be otherwise" OR recognition of some incoherence in the overall picture of how things are: awareness that "things can't be in fact as they seem" (or as they are thought to be ).
This is necessary if there is going to be puzzlement. And puzzlement is essential: no one seeks explanation unless the facts of the situation are no longer taken for granted. Science is explanation; but explanation will not even be sought unless something very paradoxical happens -- unless for some reason the familiar comes to strike one as strange.
This is what Plato was getting at in the famous dictum that "in wonder is the beginning of philosophy." The term "philosophy" is a compound of two Greek words: philo-, meaning "the love of," and sophia, meaning "wisdom." Now there are many things that might be meant by "wisdom," but among them, for the Greeks, was an understanding of why things are as they are and (in the case of society as opposed to nature) what they should be. And "love of" here translates into "desire for," or "seeking of." "Philosophy," then, in this sense, boils down to "wanting and striving to understand." But wanting and striving for something testifies to a felt lack of that something. And that's where "wonder" comes in. To be in wonder in the face of a situation is to be conscious that there is something about it that can't be taken for granted, something that is not understood. So, to say that "philosophy begins in wonder" means that the search for understanding arises when we notice that there's something that we don't understand. This might seem like a platitude. But in fact most people go through most of their life without being puzzled by all sorts of things that, if we were notice certain things about them, or put them together in certain ways (think of them at the same time, rather than putting them in separate mental bins), would lead us to acknowledge that we don't know what's going on. Most people are not "philosophers" in the sense that the Greeks used the term, not because they don't have the answers but because they never see any reason to call things into question.
In the case of the phenomena associated with the heavens, we might eventually come to wonder "Why do these patches of light behave they way they do?" For instance:
- Why does the sun always move from east to west? Why doesn't it ever rise in the west and set in the east? Or, for that matter, why doesn't it ever rise in the north and set in the south, or vice versa?
- Why isn't the moon as bright as the sun?
- Why doesn't the moon follow, in the night, the same path across the night sky that the sun followed during the previous day?
- Why doesn't the sun change shape over time the way the moon does? Conversely: why does the moon change shape as it does, rather than present a constant disk, as does the sun?
- [What puzzlements might we frame concerning the behavior of the stars?]
3. keeping careful, deliberate records. These records need to be (1) systematic (comprehensive & regular) and (2) kept over some considerable stretch of time. This means they will have to be (3) written.
In the case of astronomy and physics, they will track with as much exactitude as possible
- fixity and motion
- patterns of behavior
Repetitions (recurrent patterns) we will formulate as generalizations. Our word "regularities" comes from the Latin word regula, which means "rule" (the Latin word for "king" -- rex -- comes from the same root). Our word "astronomy" comes from Greek astro ("star") + nomos ("law"). It is then only when the records we keep disclose that the celestial appearances we are recording are "regular" -- "follow some law" in their behavior -- that we are moving into "astronomy."
- parallax (the apparent displacement [or difference in apparent direction] of an object, as seen from two different points)
The Ptolemaic and Copernican models of the cosmos do not differ in the data that they seek to explain: those data are the same for each. (With the new observations made by the Danish astonomer Tycho Brahe (d. 1603), the data that will have to be explained by any theory starts to include elements that are more easily explained by one than the other.)
B. Next comes the task of "making sense of" the record of appearances: hypothesizing simpler patterns, and causal forces, "behind" the data.
In the case of astronomy, we have to do with two distinct "levels" of explanation.
1. Descriptive explanation asks
how do things really stand to each other in space (the "actual geometry of the system") such that, by virtue of projective geometry, they produce the array of appearances they do (the "geometry in the data") to an observer situated at the particular point within the system that we imagine ourselves to occupy?
Specifically, in astronomy, we have an observer situated at a particular point on the ground. He sees some heavenly bodies (the fixed stars) move in a certain constant way. He sees other heavenly bodies (the ancients called them the planets) which move in other ways. What actual situation in true space causes the pattern of paths of these bodies that we directly observe to look as they do to us?
The Ptolemaic and Copernican models of the cosmos differ with each other in how they seek to explain the same data.
For some important details in which these differ as descriptive explanation, see The appearances, Ptolemy's theory, Copernicus's theory.
After Tycho Brahe, the data become more complicated, so that the task of the various competing models becomes more challenging. Eventually, some models will be more successful in accomodating the total known data than others.
The Brahe model is a kind of hybrid between the new Copernican and the inherited Ptolemaic models: the earth is stationary at the center of the cosmos, and (in addition to the moon) the sun revolves around it. The rest of the planets, though, are conceived as circling the sun. Brahe proposed his model not as an improvement of the Copernican framework, but as an alternative to it. Accordingly, it represents a side-path from what eventually turns out to be the main lines of development (a side-path that turns out to be a dead end).
The Keplerian model is an important modification of the Copernican: It is Copernican insofar as the sun is the center of the cosmos, and the earth moves round it with a double mothion (the annual orbit and the daily rotation on its axis). The modification consists of the 3 Keplerian laws of planetary motion. (1) The orbits of the various planets and the moon no longer circular but elliptical. (2) Their motion about the "center" (now one of the focal points of an ellipse) is not constant, but varies: satellites speed up and slow down -- but still in a completely predictable way. And (3) the distances of the planets from the sun vary in a definite way -- described in the Third Law -- with the time it takes for them to complete their orbit around the sun. Kepler's laws, that is, explain why the bodies displayed to observers on this particular planet within the overall system look the way they do in the night sky, as recorded over time in the archives.
what innate (or "natural") properties of the bodies in question together with what extra intervening forces would produce the actual geometry of the system hypothesized in our descriptive explanation? That is, what would cause them to follow the paths in real space that they do (rather than paths that would show up differently in the appearances we register in our records of what we have seen)?
- An example of a physical hypothesis in the Ptolemaic picture is the crystalline spheres that were imagined to hold the planets in their circular orbits around the earth (these circular orbits themselves being descriptive hypotheses).
- The physical hypotheses that Newton brings to bear upon the Keplerian description are the famous 3 laws of motion plus the law of gravity. These principles explain why it is that the various satellites (the planets around the sun, the moon around the earth, the 4 then-known moons of Jupiter) behave in actual space as Kepler's 3 laws say they do.
3. Teleological explanation is of two sorts.
(1) One seeks to elucidate why something has the (material and formal) properties it exhibits, by pointing to the purposes it is designed to serve.
If, for example, one already knows (i.e., independently) that an object is made to be sat upon, one can investigate the particular ways in which the shape and arrangement of its materials fit it to be sat upon.
But if, on the other hand, one notices that the properties of an object collaborate in such a way that the object lends itself to being sat upon, one can (sometimes) soundly infer that the object exhibits those properties because they have been selected and arranged so as to make it something that can be sat upon.
(2) The other, that is, seeks to elucidate what the purposes are that something serves, by examining the properties (material and formal) it exhibits.
Now it happens that the period we are examining is one in which the very concept of what makes science science undergoes a profound change. One of these changes consists in this: At the beginning of the period, natural philosophers work from the assumption not only that Nature as a whole and in detail is artificial (since it is the product of an omnicient Creator), but that this same Creator has made known to mankind a good deal of this His purposes in creating the world in the first place. Hence those hypotheses about how the world is structured and operates that square with this knowledge of God's plan are more worthy of belief than those that do not (whether these outright contradict the received notions of God's purposes, or whether they just don't seem to have any connections at all with these, one way or the other). At the end of the period, natural philsophers (at least those in astronomy and physics) have reached the conclusion that knowledge of God's purposes does not contribute anything helpful to what science is concerned to discover, which is the exact mode of operation of the natural world. Hence it is both (a) unreliable to try to infer from what is known about God's purposes anything about the actual laws of operation of the cosmos (which is a question, rather, to be decided solely with reference to how well hypotheses about operation square with the data they are invoked to expalin, and (b) superfluous to try to infer from the way things are (phenomena, descriptive explanation of these, and physical explanations of these in turn) what the details must be of God's plan.
Between 1543 and 1687 -- i.e., in the 143 years between the publication of Copernicus's De Revolutionibus and Newton's Principia -- teleology goes from being an powerfully respected part of the overall enterprise of scientific explanation to banishment from the precincts of the two sciences that initially establish the modern prestige of the scientific enterprise.
Copernicus regarded the conformity of his hypothesis with received ideas of God's character and intentions as a major enhancement of its overall plausibility, over that of the Ptolemaic alternative. (Click here for details.)
Newton considered it a crowning merit of his physical explanation of Kepler's modification of the descriptive dimension of Copernicus's theory of the real structure and operation of the heavenly bodies (earth included) that it had no dependence on metaphysical, hence teleological, hence theological suppositions whatsoever. When his critics pointed to the fact that he had given no account of how material bodies can act at a distance (as his Law of Gravity postulates them to do), he pointed to this very fact as a virtue of his achievement: namely that, in explaining Kepler's description of the planetary motions, he had grounded these in a successful more general description of the way all matter in general behaves, without having recourse to supposed entities outside or behind nature itself. (Click here for details.)
[For a fuller discussion of the issues involved in this crucial shift, which redefined the very conception of science, work your way through the whole essay called "Teleology and Science".]
With these distinctions under our belt -- between description of phenomena and various orders of explanation of them -- , we are equipped to look in some detail at the process by which the old picture of the cosmos found itself increasingly in crisis and a new one developed capable in the end of commanding assent among the educated elite.
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