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Telescopes and space missions

Telescopes and space missions

The Galileo affair

02 Mar 2009

Maurice Finocchiaro discusses the lessons and the cultural repercussions of Galileo’s telescopic discoveries

Telescopic vision

In June 1609 Galileo Galilei heard about an optical instrument invented in Holland the year before, consisting of an arrangement of lenses that magnified images three to four times. Despite not having a prototype in his possession, he was soon able to duplicate the instrument, mostly by trial and error. He was also able to increase its magnifying power first to nine, then to 20, and, by the end of the year, to 30. Moreover, rather than merely exploiting the instrument for practical applications on Earth, he started using it to make systematic observations of the heavens to learn new truths about the universe.

Within three years Galileo had made several startling discoveries. He discovered that the Moon had a rough surface full of mountains and valleys. He saw that innumerable other stars existed in addition to those visible with the naked eye. He found that the Milky Way and the nebulae were dense collections of large numbers of individual stars. The planet Jupiter had four moons revolving around it at different distances and with different periods. The appearance of the planet Venus, in the course of its orbital revolution, changed regularly from a full disc, to half a disc, to crescent, and back to a half and a full disc, in a manner analogous to the phases of the Moon. And the surface of the Sun was dotted with dark spots that were generated and dissipated in a very irregular fashion and had highly irregular sizes and shapes, like the clouds above the Earth; while they lasted, these spots moved in such a way as to imply that the Sun rotated on its axis with a period of about one month.

Many of these discoveries were also made independently by others; for example, lunar mountains were also seen by Thomas Harriot in England, and sunspots by Christoph Scheiner in Germany. However, no-one understood their significance as well as Galileo. Methodologically, the telescope implied a revolution in astronomy, in so far as it was a new instrument for the gathering of new kinds of data, vastly transcending the previous reliance on naked-eye observation. Substantively, these discoveries provided a crucial, although not conclusive, confirmation of the Copernican hypothesis of the Earth’s motion. To understand the latter, some background is needed.

The Copernican revolution

In 1543 Copernicus had published a book elaborating a world system the key point of which was that the Earth rotates on its own axis daily and revolves around the Sun yearly. Copernicus’s accomplishment was to give a new argument supporting an old idea that had been almost universally rejected since the ancient Greeks. He demonstrated that the known facts about heavenly motions could be explained in quantitative detail if the universe is a heliocentric system where the Earth revolves around the Sun (the geokinetic hypothesis); and that this explanation was more coherent (and simpler and more elegant) than the geostatic account.

However, the Copernican revolution required much more than this argument. The geokinetic hypothesis had to be supported not only with new theoretical arguments, but also with new observational evidence. The telescope provided such novel evidence. For example, lunar mountains and sunspots showed that there were significant similarities between the Earth and the heavenly bodies. This refuted the traditional doctrine of the Earth–heaven dichotomy; and so it became possible for the Earth to be a planet, i.e. located in “heaven”. The satellites of Jupiter showed that it was physically possible for one body to revolve around another, while the latter revolved around a third; and hence it became possible for the Earth to revolve around the Sun while the Moon revolved around the Earth. And the phases of Venus proved the heliocentricity of its orbit, thus confirming this particular element of the Copernican system.

Moreover, the Earth’s motion had to be not only constructively supported with new arguments and evidence, but it also had to be critically defended from a host of powerful old and new objections. These objections were based on astronomical observation, Aristotelian physics, scriptural passages and traditional epistemology. For example, according to Aristotelian physics, the natural state of bodies was rest and a constant force was needed to keep a body in motion; thus, supposedly, bodies on a rotating Earth could not fall vertically, as they are seen to do. And according to the scriptural passage in Joshua 10:12–13, God miraculously stopped the diurnal motion of the Sun to prolong daylight, so that Joshua could lead the Israelites to victory before nightfall. Galileo answered the astronomical objections by showing that the observational consequences implied by Copernicanism were indeed visible with the telescope, although still invisible with the naked eye. He answered the physical objections by articulating a new physics centred on the principles of conservation and composition of motion. And he answered the biblical objections by arguing that Scripture is not a scientific authority, and so scriptural passages should not be used to invalidate astronomical claims that are proved or provable.

Finally, the defence of heliocentrism required not only the destructive refutation of these objections, but also the appreciative understanding of their strength. Galileo was keen on this, and so in his writings we find the anti-Copernican arguments stated more clearly and incisively than in the works of advocates of geocentrism.

However, Galileo also realized that his case in favour of Copernicanism was not absolutely conclusive or decisive. Some counter-evidence remained, since, for example, his telescope failed to reveal an annual parallax of the fixed stars.

In short, Galileo’s key contribution to the Copernican revolution was to elaborate a successful (although not definitive) defence of Copernicanism that stressed argumentation and observation judiciously guided by the ideals of critical-mindedness, open-mindedness and fair-mindedness.

Galileo’s trial

As is well known, however, Galileo’s efforts were hindered by the Catholic Church. In fact, the trial of Galileo can be interpreted as a series of ecclesiastic attempts to stop him from defending Copernicus. In 1616 the Church’s department of book censorship decreed that the geokinetic doctrine was contrary to Scripture, and this decree amounted to a general prohibition on defending Copernicanism from scriptural objections. Furthermore, Cardinal Robert Bellarmine warned Galileo to cease defending the Earth’s motion — a warning that amounted to a personal prohibition on defending Copernicus from an astronomical, scientific and philosophical point of view. In 1633, after a formal trial, the Inquisition condemned Galileo as a suspected heretic for defending the geokinetic hypothesis and denying the astronomical authority of Scripture. He had done these things implicitly, indirectly and probably in his Dialogue on the Two Chief World Systems, Ptolemaic and Copernican (1632), which was a critical discussion, examining the arguments on both sides, showing that the geokinetic arguments were stronger than the geostatic ones, implying that Copernicanism was probably true, and thus defending it in that sense.

The condemnation of Galileo in turn generated a more protracted, complex and polarized controversy that is still ongoing. However, I believe these complexities can be simplified, without oversimplification.

At first, various questions were raised about the physical reality of the Earth’s motion; but gradually, historians of science established incontrovertibly that Galileo was right on this issue. As this realization emerged, questions began to be raised about whether his supporting reasons, arguments and evidence had been correct; that is, whether he had been right for the wrong reasons. This is an instructive issue, but Galileo’s reasoning can be defended from this criticism. For some time, he was also criticized for his hermeneutical principle that Scripture was not a scientific authority; but history vindicated Galileo in this regard too, at least from the viewpoint of the official position of the modern Catholic Church, which was promulgated in 1893 by Pope Leo XIII in the encyclical Providentissimus Deus. However, before this theological vindication, the myth spread that Galileo had been condemned for being a bad theologian, namely for preaching and practising the use of Scripture to support astronomical claims (i.e. the opposite of what he actually did); it took the whole 19th century before this myth was dispelled. In any case, on the hermeneutical issue too, it is important to check the correctness of his argument to justify that Scripture is not a scientific authority; although this Galilean reasoning has been the target of many objections, I believe it can be defended from them.

As it became increasingly clear that Galileo could not be validly convicted of being a bad scientist, a bad theologian or a bad logician, he started being blamed for other reasons. Some authors began to stress the legal situation, charging that he was guilty of disobeying the Church’s 1616 admonition regarding Copernicanism. However, if this admonition is interpreted as a prohibition on mere discussion, the existence of such a special injunction is undermined by the record of the trial proceedings, first published in 1867–1878. These records include only one document stating that Galileo was forbidden to even discuss the topic, but this document is highly irregular in several respects, whereas there are several more reliable relevant documents that say nothing about such a strict prohibition, although they should have mentioned it if it had occurred. On the other hand, if the admonition is taken as a prohibition on defending Copernicanism, nobody denies its existence, but the issue reduces to whether such a prohibition was legitimate, and if it was, whether Galileo’s defence was scientifically and logically fair and valid.

Finally, there is the issue of whether Galileo should be credited or blamed for helping us understand that science and religion are in conflict or that they are in harmony, as the case may be. The resolution of this issue requires that we admit three crucial things. First, the original affair featured an historical conflict between those who affirmed and those who denied that Copernicanism contradicted Scripture; and the irony is that it was Galileo who denied the conflict and the Church officials who advocated it. Second, the original affair epitomized more the conflict between cultural conservation and innovation than the conflict between science and religion; this is the case because there were many clergymen who sided with Galileo and many scientists who sided with the Church, which means that there was an internal split within both the Church and science. Third, in the subsequent four centuries the original affair was usually perceived (rightly or wrongly) as epitomizing the conflict between science and religion; thus, the most essential feature of the subsequent controversy is indeed the science versus religion conflict.

The two cultures

The controversy shows no signs of abating to this date. This is obvious not only from the recent rehabilitation efforts by the Catholic Church, but also from the recent anti-Galilean critiques by left-leaning social critics.

For example, in 1942, the tricentennial of Galileo’s death, there was the first partial and informal rehabilitation. In the years that followed, this was done by several clergymen who held the top positions at the Pontifical Academy of Sciences, the Catholic University of Milan, the Pontifical Lateran University in Rome, and the Vatican Radio. They published accounts of Galileo as a Catholic hero who upheld the harmony between science and religion, who had the courage to advocate the truth in astronomy even against the Catholic authorities of his time, and who had the religious piety to retract his views outwardly when the 1633 trial proceedings made his obedience necessary.

In 1979 Pope John Paul II began a further informal rehabilitation of Galileo that was not concluded until 1992. In two speeches to the Pontifical Academy of Sciences, and in other statements and actions, the pope admitted that Galileo’s trial was not merely an error but also an injustice. The pope also declared that Galileo was theologically right about scriptural interpretation, as against his ecclesiastical opponents; that even pastorally speaking, his desire to disseminate novelties was as reasonable as his opponents’ inclination to resist them; and that he provides an instructive example of the harmony between science and religion.

At about the same time that Galileo was being rehabilitated by various Catholic officials and institutions, he became the target of unprecedented criticism on the part of various representatives of secular culture. It was an unexpected reversal of roles, with his erstwhile enemies turning into friends and his former friends becoming enemies. These critics elaborated what might be called social and cultural criticism of Galileo; that is, they tried to blame Galileo by holding him personally or emblematically responsible for such things as the abuses of the industrial revolution, the social irresponsibility of scientists, the atomic bomb, and the rift between the two cultures. They were mostly leftwing writers. Chief among them were the German playwright Bertolt Brecht, whose play Galileo, written in 1938, became a classic of 20th-century theatre; Arthur Koestler, who wrote the 1958 bestselling book The Sleepwalkers: A History of Man’s Changing Vision of the Universe; and Paul Feyerabend, the Austrian-born philosopher, who advanced his version of social criticism in a book entitled Against Method, first published in 1975.

These developments have not been properly assimilated yet. For example, the Catholic “rehabilitations” tend to be either unfairly criticized (even by Catholics) or uncritically accepted (even by non-Catholics). And the left-leaning social critiques tend to be summarily dismissed by practising scientists, whose professional identity is thereby threatened, or dogmatically advocated by self-styled progressives, who seem not to have learned much from Galileo and to want to turn the clock back to pre-Galilean days. I believe this controversy is likely to continue for the foreseeable future.

Nevertheless, I believe I have devised a framework that paves the way for coming to terms with the controversy and eventually resolving it. In my approach, one interprets the controversy in terms of arguments for and against the rightness of Galileo’s condemnation; one displays towards these arguments the same attitude that Galileo displayed towards the arguments for and against the Earth’s motion; and the key elements of this Galilean attitude (labelled critical-mindedness, open-mindedness and fair-mindedness) are to know and understand the arguments against one’s own view and appreciate their strength before refuting them. In short, my overarching thesis is that today, in the context of the Galileo affair and the controversies over science versus religion and over institutional authority versus individual freedom, the proper defence of Galileo should have the reasoned, critical, open-minded and fair-minded character that was also displayed by his own defence of Copernicus.

These are some of the cultural repercussions and lessons of the telescopic discoveries that Galileo began making in 1609. And such are, in part, the challenges and opportunities of the quatercentenary of their occurrence.

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