Reading Assignment

Drake, Galileo's "Letter to the Grand Duchess Christina" (including the introduction)

Koestler, Part 5

Kuhn, Chapters 6 and 7

Langford, Chapters 3-6

Encyclopedia article on Galileo

 

Objectives

- To understand the criticisms of the telescope as a reliable instrument for science

- To become familiar with the problems in testing ideal laws

- To analyze the various positions taken by Galileo and his contemporaries concerning the proper relationship between science and religion

 

Key Concepts

- Irradiation or Adventitious Rays (as Galileo used the terms)

- Ideal Laws

- Necessary demonstrations (as Galileo used the phrase)

- Instrumentalism vs. Realism (as philosophers use these terms)

Discussion

 

Copernican theory was certainly a boon to astronomy. Even astronomers who did not believe it was true found it easier to make calculations using a heliocentric model. But as we have discussed in previous lessons, the hypothesis that the earth moved was inconsistent with Aristotelian physics. Thus the first order of business for any Copernican was the development of a new physics.

There were other objections to the new astronomy, however. It was inconsistent with various passages in the Bible. We will discuss the theologians' religious objections to the Copernican theory and Galileo's response to them shortly. But first let us look at some of the methodological and philosophical criticisms which anti- Copernican clerics raised.

Contrary to the impression Brecht's play may have given you, not all of Galileo's opponents were ignoramuses. Much of the best scholarly work of the time was done by churchmen. Although their opposition to Galileo was in large part religious and political, some of the arguments they produced were sound. We will look at their good objections first and then turn to Galileo's ignominious trial, which has often embarrassed Catholic intellectuals.

 

DOUBTS ABOUT THE TELESCOPE

 

The observations of the phases of Venus and the mountains of the moon, which led to the refutation of Ptolemaic astronomy and to the undermining of Aristotelian cosmology both relied on the existence of the telescope. If the telescope were shown to be an unreliable instrument for science, both observations would have to be thrown out.

Following are some of the reasons people opposed telescopic data. Some are better than others.

First of all, the telescope violated Aristotle's theory about which observations were reliable. (As you may realize by now, Aristotle had a theory about everything!) According to Aristotle, reliable observations can only be made with sense organs which are in their natural state. We do not trust the perceptions of a person who is drunk, or drugged, or feverish. If we press on our eyeball, we see sparkles, but these do not really exist outside of our minds--they are caused by the distortion of our vision. If we spin rapidly until we are dizzy, the world then appears to whirl around us, but this is a misperception caused by a temporary derangement of our sense organs.

The Aristotelian contemporaries of Galileo argued that lenses, and the telescope in particular, distort what we see. Images produced by a lens have colored fringes. They are sometimes inverted; often they are lengthened or warped as well as magnified. (Early lenses often were not perfectly spherical and none of them were corrected for chromatic aberration.)

Galileo had a response for this--all we need do is calibrate a lens or telescope by looking at familiar objects. We can then measure how much magnification is produced and we can correct for or ignore any distortions which the instrument introduces. (For example, we can use the telescope to read the time on a distant clock even though we may not be able to rely on it to tell us the color of the clock's hands.) When it comes to sizes and shapes, the telescope can perfect our vision, not distort it.

Unfortunately for Galileo, his opponents had a reply to his calibration proposal. When the telescope is used to view the moon, the image is magnified, just as we would expect. But when we look at the stars, they appear smaller through the telescope than they do with the naked eye! (If you have some binoculars, take a look for yourself tonight.) Furthermore, through the telescope, they don't twinkle as much.

The modern explanation for this phenomenon is quite complicated. I've never understood it fully--it has something to do with the light scattered by the earth's atmosphere which is cut out by the collimating effect of the telescope's tube. Needless to say, Galileo didn't really have a clue as to what was going on. He called the twinkles irradiation and claimed they were caused by adventitious rays which were somehow stripped off by the telescope. (Look up "irradiation" in the index of the Drake book and read the relevant passages.)

His opponents, steeped in Aristotelian cosmology, replied that just as the laws of motion are different for celestial and terrestrial bodies, so may the laws governing the behavior of celestial light be different from those of terrestrial light. Perhaps the telescope was reliable for viewing terrestrial objects; it certainly did not follow that it was reliable in the heavens.

Of course, astronomers continued to use the telescope and eventually even developed a detailed theory of how it worked. But it is important to realize that some of the doubts about its reliability during Galileo's time were legitimate, although perhaps not overriding. (Compare modern controversies about the use of lie detector evidence in courts.)

 

COMPLICATIONS ABOUT THE USE OF IDEAL LAWS IN SCIENCE

 

Although some of Aristotle's authoritarian followers may have had contempt for observational data, Aristotle himself was very concerned that his theories be consistent with empirical data. We have seen how his physics corresponded pretty well to our ordinary experience with moving objects. Things do stop moving unless pushed, feathers do fall more slowly than cannon balls, and so on.

According to Galileo's new theory of motion, however, a wagon set in motion would roll on forever and a feather would fall with the same acceleration as a hammer if conditions were ideal, i.e., if there were no friction or air resistance. But of course there always is! So how can we ever test Galileo's proposals against experience?

Scientists had always introduced minor idealizations into their laws--the law of the lever doesn't work if there's chewing gum on the fulcrum. But before Galileo, no one had proposed ideal laws in which the discrepancy between the ideal situation described in the law and the conditions which actually exist in ordinary experience was so large. Small wonder that Galileo's empiricist opponents accused him of being a rationalist,* of simply using his imagination to discover the laws of science.

In his Discorsi (which you recall was written after the trial) Galileo finally explained how to test-ideal laws. It is done by recording behavior in a variety of non-ideal conditions and then extrapolating to the ideal case. For example, to test the claim that all bodies fall at the same rate, one could compare the behavior of a wooden and iron ball in molasses, in water, and in air. As the viscosity of the medium decreases, their velocities get closer together. One can then reasonably claim that if there were no resisting medium, they would fall at the same rate. Of course, the extrapolation may later turn out to be false, but all science is fallible, whether it uses idealizations or not. (Remember those black swans in Australia.)

In the case of the ideal law for falling bodies, Galileo's extrapolation was correct, as Robert Boyle demonstrated later in the century after the invention of the vacuum pump. (On the first manned space flight to the moon, astronauts repeated the classic experiment by dropping a feather and a hammer in front of the TV camera. How gratified Galileo would have been to see his conjecture confirmed in front of millions of ordinary people!)

Ideal laws are indispensable for science, but it is easy to abuse them, either by not specifying what the sources of non-ideality are or by not performing the experiments which form the basis for extrapolation. For example, in Galileo's theory of the tides he was very vague about what might cause observed tidal behavior to deviate from what his theory predicted (it had something to do with the shape or depth of the seabed) and he made no attempt to observe the tides with seabeds of different depths, etc.-, in order to test his idealization. (Of course, life is short--and one scientist can't do everything.)

In summary then, Galileo made an important contribution to science by introducing the concept of an ideal law. But it is not surprising that his opponents were suspicious of this practice --extrapolation is risky and it is easy to be irresponsible in one's use of idealizations.

*The term they used was Platonist, but the approach is very similar to that which we called rationalist in the first lesson.

 

SOME IMPORTANT DISTINCTIONS

 

Before we turn to the theological opposition to Galileo and the Copernican theory, there are a few standard philosophical distinctions I would like to introduce. They will help us to analyze the controversy.

The first is what philosophers today often call the "is/ought" distinction. (It is also called the "descriptive/normative distinction.") In Galileo's time one distinguished "matters of fact" from "matters of faith and morals." Compare the following pairs of claims:

 

a.Incest is taboo in almost every society.
a'.Incest is always wrong.

 

b. Murder is found in every human society.

b'. Murder is never justified.

 

c. People value power.
c'. People ought not to value power so much.

 

d. There are PCBs in the Bloomington water supply.

d'. There shouldn't be PCBs in any city water supply.

In each case, the first sentence makes a factual claim, and so one could do a scientific investigation to see whether it is true. The second sentence makes a normative claim--it says what ought to be the case as opposed to what is the case. Most people believe that science cannot tell us what we ought to do in any ultimate sense. (Of course, science can tell us what PCBs do to our health, but it cannot tell us whether that risk is worth taking.)

Galileo believed that the Bible was a good guide to "ought" questions but not to "is" questions, which should be answered by scientific investigation. His opponents did not agree, although, as you will see, their exact position on the proper division of cognitive labor between science and religion is rather complex.

Both Galileo and his opponents allude to a second distinction that is harder to explain, partly because they weren't very- clear about it and partly because we think differently today. This is the distinction between scientific claims which are supported by necessary demonstrations and those which are only based on plausible or probable reasoning.

Today, since we know all scientific claims are fallible, we would say none of them can be demonstrated to be necessary truths. All we can do is to distinguish between more or less well-tested conjectures.

However, many scientists in Galileo's time (in fact most scientists who lived before the Einsteinian revolution) had more grandiose expectations about the degree of certainty which could be obtained in science.

The phrase necessary demonstration connotes not only certainty but also the feeling that things could not possibly be otherwise. For example, compare the following true claims:

 

a. My dog has at least four fleas.

b. My dog is less than 100 feet tall.

c. My dog is a mammal.

All the claims are true , but yet there seem to be important differences between them. For example, (c) is probably true by definition. The truth of (b) seems to rest on some very important realities about the world: if any dog were over 100 feet tall the whole history of evolution, the size of a dog's bones, its blood pressure, etc. would have to be very different. The truth of (a), on the other hand, seems to be more accidental. I may be very certain of its truth (here are the four fleas right in front of me), perhaps just as certain as I am about (b) and (c), yet I can easily imagine a world in which (a) were false, namely a world in which Fido wears a flea collar all his life.

Sometimes when Galileo's adversaries call for necessary demonstrations that the earth moves, they seem not just to be demanding proof that it is true, but also proof that it is necessarily true. But this is a doubly impossible demand. Of course, we can easily imagine a system in which a sun moves around an earth--this would not violate any laws of nature. Unfortunately, Galileo did not fully realize what an unrealistic challenge he would be taking on if he accepted his opponents' terms of combat. At times he nearly falls into the trap of claiming that he cannot only prove that the earth moves, but that it must move.

There is a third analytical distinction which may be useful in understanding this debate. In contemporary philosophy of science there are basically two views concerning the nature of scientific claims: the so-called realist and instrumentalist positions. (You will soon see that each of these terms is being used in a special sense, one which differs from the ordinary usage.) According to the realist position, good scientific theories are ones which correctly describe what the universe is really made of and how these constituents interact. Such theories explain the events which we observe around us. From the realist point of view, the aim of science is to produce true, explanatory theories.

According to the instrumentalist position, on the other hand, scientific theories should not be viewed as attempts to describe the world; it is incorrect to speak of them as being true or false. Rather they are formal instruments (or conceptual schemes) which enable us to organize our experience and make successful predictions. According to the instrumentalist, we should not ask (as the realist insists we must) whether Dalton's atomic theory (or the theory of quarks) is true or false --that is, whether there really are Daltonian atoms (or quarks) and whether what the theory says about them is correct. What we should ask is whether Daltonian atoms (or quarks) are convenient fictions. Do they provide a useful conceptual tool for the classification and correlation of experimental results? From the instrumentalist point of view, the aim of science is to produce economical formalisms that are useful instruments for prediction.

Often when there is a conflict between science and the Bible, the parties will try to resolve it either by taking an instrumentalist approach to science or by treating the Bible as metaphor.

 

YOU SHOULD NOW READ GALILEO'S LETTER TO THE GRAND DUCHESS (including Drake's introduction). The following comments may help you analyze the various positions which are discussed.

Notes on Galileo's "Letter to the Grand Duchess Christina"

(Most of Drake's introduction is optional. However, do read at least pages 167-171.)

This letter, "concerning the use of Biblical quotations in matters of science," was intended to be circulated among influential people. Galileo hoped to persuade the authorities not to ban the Copernican theory.

As there was no word scientist at this time, Galileo often speaks of philosophers or mathematicians in contexts where we would tend to speak of scientists or mathematical physicists. It is a bit confusing, however, because his Aristotelian opponents who are not much interested in experiments are also called philosophers.

There are a wide variety of different positions which one could take regarding the relationship between science and the Bible. Here are some of them:

 

If a statement in the Bible and a scientific statement conflict, then:

 

1.One should always reject the scientific claim because the Bible is always literally true.

 

2.If the scientific claim is proved beyond doubt, then one should reinterpret the Biblical claim--Nature and the Bible must agree. However, the Bible always takes priority and the scientist who disagrees with the Bible must prove that he or she is right.

3.The Bible is a better guide to the truth about matters of fact than is idle speculation. However, a well confirmed hypothesis (even if it is not proved) takes precedence over the Bible.

 

4.Scientists always completely ignore Biblical claims, because the Bible has no authority whatever on scientific matters. (It is the theologian who must resolve the inconsistency.)

As you read the "Letter," note which position is being discussed in each section.

Study Questions

1.Bring your chronological outline up to date.

2.Do the Review Questions at the end of Lecture VI. Ask your instructor about anything which is puzzling.

Written Assignment

1.Exercise A-4 in Chapter VI. (Reread pages 212-215 of the "Letter" before answering.)

2. a. Which of the four positions listed in my notes on the "Letter" does Galileo defend? (Or would you phrase it differently?) Does he slide back and forth between various positions in the course of the letter? If so, give quotations (including page numbers) illustrating each position which he adopts.

b.What was Cardinal Bellarmine's position? Give quotes to illustrate your summary.,

3.Does Galileo claim or hint that he has conclusive proof that the Copernican theory is correct? Is he cautious or bold on this matter? If bold, what is his evidence for saying Copernicus is correct? If cautious, why does he hold back?

4.Which of the following people in our story acted as if they
were realists (As defined above)? Which were instrumentalists? Or can you say? Defend your answer briefly:

Ptolemy, Copernicus, Osiander, Galileo, Tycho, Bellarmine.