Galileo’s Dialogue concerning the Two Chief World Systems (1632), which argues for the superiority of the heliocentric Copernican over the geocentric Ptolemaic system, is a classic straw man argument. By 1632, astronomers had all but abandoned the Ptolemaic system, which had become untenable in the light of the evidence from telescopes for more than 20 years, which showed, for example, that Mercury and Venus orbited the sun. By that late stage, the majority of astronomers had adopted the geo-heliocentric model, such as that of Tycho Brahe, which had all the planets (other than earth) orbiting the sun, and the sun and the moon in orbit around the earth. Adapted to include a rotating earth, it was indistinguishable from the Copernican system on the basis of empirical observations of our ‘solar system’ from the vantage point of a terrestrial observer.
The Tychonic system was still highly regarded until the end of the seventeenth century when Newton’s discovery of principles of gravitation, and their application to the solar system, caused it to be abandoned as an explanation of reality, though it continues to this day as an elegant method for generating the terrestrial observer’s view of the motions of heavenly bodies in our solar system, for example in planetarium projectors.
So, Galileo was incapable of making a case in favour of Copernican heliocentrism over against the majority view of Tychonic geo-heliocentrism based on observation of the sun, moon and planets, and he could not do so based on physical principles as he rejected the idea of gravitation beyond the earth’s atmosphere and had never bothered to read up on Kepler’s laws of planetary motion, which had been sitting on his bookshelf for over 20 years. He also believed that no practicable terrestrial experiments could establish whether the earth was in motion, for he says in his foreword “all experiments practicable upon the earth are insufficient measures for proving its mobility, since they are indifferently adaptable to an earth in motion or at rest.” Thus he deliberately contrived to make his case using the artifice of a straw man argument, with not even a mention of the then chiefest of the world systems, the Tychonic model.
That method of argument, putting up the discredited and disproved Ptolemaic system as his straw man, was bad enough. But labouring to advance a fanciful ‘proof’ for the motion of the earth (which we will later see he actually knew was refutable), Galileo claimed support in the terrestrial phenomenon of the tides, having dismissed the truth (since it could not serve his purpose) that the attraction of the moon was of primary importance. He put mention of the argument for the moon’s attraction into the mouth of Simplicio, the feeble apologist for Aristotle and Ptolemy, whose name also connotes ‘simpleton’ in Italian, simply to shoot it down:
There are many who refer the tides to the moon, saying that this has a particular dominion over the water. Lately a certain prelate has published a little tract wherein he says that the moon, wandering through the sky, attracts and draws up toward itself a heap of water which goes along following it…
To which Galileo’s alter ego in the Dialogue, Salviati, the learned apologist for Copernicus, cuts in with
Please, Simplicio, spare us the rest; I do not think there is any profit in spending the time to recount them, let alone the words to refute them. If you should give assent to any of these or to similar triflings, you would be wronging your own judgment.
No attempt to deal with the argument – just a put down. And later:
But among all the great men who have philosophized about this remarkable effect, I am more astonished at Kepler than at any other…[who has] lent his ear and his assent to the moon’s dominion over the waters, to occult properties, and to such puerilities.
Once again, there is no engagement with the argument, but instead a disgraceful put down of one of the greatest astronomers and scientists of all time. Kepler had recently died, so was unable to defend himself against the charge of assenting to puerilities. And the charge of having ‘lent his ear to occult properties’ such as gravitation was completely below the belt in Kepler’s personal situation since his great aunt had been burned at the stake as a witch, and Kepler had lost his own mother shortly after her being incarcerated and threatened with torture on similar charges. But still, Galileo was a nasty piece of work, who also played the religious hatred card when it suited him, tossing out epithets such as ‘heretic’ and ‘heresiarch’ against Protestants who were better at science than he.
Pope Urban VIII, an able mathematician and patron of the sciences, had quite rightly disagreed with Galileo’s line of reasoning that the tides proved the motion of the earth, and held that they were no proof at all. He had even granted Galileo six private audiences and had insisted that his own objections be included in the Dialogue, i.e. that Galileo’s argument for the tides was not compelling, and that the Creator was well able to order secondary causes in a way yet to be discovered and understood so as to cause the tides, without relying on the motion of the earth around the sun.
Indeed, Galileo’s argument, which in the foreword he describes as an ‘ingenious speculation’, was fallacious: the tides did not prove the motion of the earth around the sun, and nor did Galileo’s argument prove the tides: his argument was internally inconsistent, and logically led to the conclusion that tides would not occur at all. Urban was absolutely right to discern that, as was Kepler in attributing the tides to the attraction of the moon: the natural agency for the tides is gravitational attraction in the earth-moon system, which would only be intellectually apprehended in mathematical form towards the end of the century.
Faced with the demand to insert this ‘spoiler’ against his particularly fanciful ‘clincher’ (having dismissed the true explanation of the tides as occult puerilities not worthy of refutation), Galileo committed an act of gross stupidity and affront. One would have expected Urban’s reservations to be placed in the Dialogue in the mouth of the fair-minded interlocutor Sagredo, the representative of the intelligent, astute scholar, who was not credulous and and was sensibly sceptical – like Urban, in fact. But Galileo had spent his whole career thus far trying to make others look stupid, or plagiarizing their work, or claiming priority for their discoveries, in order to promote himself, and had made a whole host of enemies along the way. He was now about to get his comeuppance. Urban had been his friend and supporter, but for no longer. Unable to pass up an opportunity to poke fun, Galileo left the Pope’s justifiable reservations about his contrived ‘proof’ of the motion of the earth to the very end, putting them into the mouth of Simplicio, the dim-witted dullard, whom he had contrived throughout the Dialogue to lose all the arguments, make an utter fool of himself, and be the butt of all the put downs. By the end of the book, the reader would know that anything Simplicio said was to be treated with contempt. So Galileo put the Pope’s argument into his mouth:
I maintain that your explanation of the tides is neither true nor conclusive, and that… God by his infinite power and wisdom might confer the reciprocal motion of the oceans in some other way than by making the containing vessel move…[and] beyond the apprehension of our intellect…this being so, it would be excessive boldness for anyone to limit and restrict the Divine power and wisdom to some particular fancy of his own.
And to Sagredo, the fair-minded interlocutor, he gave the jaw-dropping put down to Urban’s reservations, the irony dripping off the page with undisguised sarcasm:
What admirable and angelic doctrine! And so well in accord with another doctrine, also Divine, which, while granting us the liberty to debate about the constitution of the universe (perhaps so that the working of the human mind will not become attenuated or grow lethargic), adds that we cannot discover the work of His hands.
Such impious sarcasm is likely to get the hackles up on any pious person. Quite understandably, Urban was personally offended, and enraged, and forever maintained that Galileo had tricked him. And so he had. Yet Galileo got off pretty lightly, in the circumstances.
But did Galileo himself hold to the Copernican system that is contrived to come out on top throughout this straw man contest? After publication he affirmed under oath his own personal conviction that
I have neither held nor defended the opinion of the earth’s motion and sun’s stability; on the contrary…Copernicus’s reasons are invalid and inconclusive. (April 10, 1633)
However, the very foreword in the Dialogue ‘To the discerning reader’ states
I have taken the Copernican side in the discourse…striving by every artifice to represent it as superior to supposing the earth motionless.
So, was this just artifice, some form of rhetorical and intellectual sport? Was he, for the sheer thrill of it, ‘taking side’ in something that he did not himself believe? He would portray it as such, for in testimony under oath in April 30, 1633 he confirmed that
I freely confess that…a reader, unaware of my intention, would have had reason to form the opinion that the arguments for the false side [N.B. Galileo here means Copernicanism]…were so stated as to be capable of convincing because of their strength. In particular, two arguments, one based on sunspots and the other on the tides, are presented favourably to the reader as being strong and powerful…I inwardly and truly did and do hold them to be inconclusive and refutable…I resorted to that natural gratification everyone feels for his own subtleties and for showing himself to be cleverer than the average man, by finding ingenious and apparent considerations of probability even in favour of false propositions…My error then was – and I confess it – one of vain ambition, sheer ignorance, and culpable negligence.
So, did a heliocentric model better than Copernicus’ attract him? Did he have any better ideas for a world system? Apparently not, for he categorically states:
I still hold Ptolemy’s opinion as actually true and certain, namely the immovability of the earth and the motion of the sun.
In regard to my writing of the Dialogue now published, I did not write thus because I held Copernicus’s opinion to be true…I do not hold the opinion of Copernicus, and I have not held it. (June 21, 1633)
What could be clearer, especially since these are not extracts from some supposed ‘recantation’? They are not a form a words that he was forced to sign, but are his own testimony, under oath, and in his own words. And why mention old Ptolemy at all? Either Galileo was a troublemaking heliocentrist who committed perjury on multiple occasions, thus compounding his offensive behaviour (as most historians maintain, as did the Roman Catholic church) or he was a troublemaking crypto-geocentrist and no worthy champion of heliocentrism at all. Let the reader decide. But a martyr for science and free speech he was not. Further demonstration of Galileo’s disingenuousness and duplicity, and the false legends of history about him, will have to await another post, but suffice to say that Galileo was a persistent troublemaker and plagiarist who could have spared himself and others a good deal of bother had he been able to tame his impetuous folly and unbridled arrogance. As Rodney Stark has pointed out, his insufferable arrogance and recklessness ‘placed the whole scientific enterprise itself in jeopardy’.