How Galileo Proved which Ideas were False
During his lifetime Galileo Galilei demonstrated several accepted ideas, about the physical world, of the ancient Greek philosophers, to be false. Three of these ideas were: Bodies fall at a constant rate. Bodies twice as heavy fall twice as fast. The earth stands still while the rest of the universe revolves about it.
In 1974, Richard Feynman stated:
“During the Middle Ages there were all kinds of crazy ideas, such as that a piece of rhinoceros horn would increase potency. Then a method was discovered for separating the ideas—which was to try one to see if it worked, and if it didn’t work, to eliminate it. This method became organized, of course, into science.” (Caltech commencement address given in 1974)
Today, there is no doubt that each of the three ancient Greek ideas are absolutely false. But today, how would you demonstrate to a doubter that each was absolutely false? I ask this question because, if you could not simply describe some experimental observation, available to Galileo, that absolutely refuted each of these ideas known to be false, how could you begin to test any idea not yet proven to be wrong?
If we read Dialogues Concerning Two New Sciences, we will discover that even the simplest of these three false ancient ideas to test by experiment and thereby proven to be false would not be willingly accepted by one of the characters created by Galileo. About this, Galileo had Salviati state (as translated by Henry Crew and Alfonso de Salvio , 1914):
“I greatly doubt that Aristotle ever tested by experiment whether it be true that two stones, on weighing ten times as much as the other, if allowed to fall, at the same instant, from a height of, say, 100 cubits, would so differ in speed that when the heavier had reached the ground, the other would not have fallen more than 10 cubits.”
To which Simplicio, the doubter, replied: “His language would seem to indicate that he had tried the experiment, because he says: We see the heavier; now the word see shows he had made the experiment.”
To which Sagredo responded:
“But I, Simplicio, who have made the test can assure you that a cannon ball weighing one or two hundred pounds, or even more, will not reach the ground by as much as a span ahead of a musket ball weighing only half a pound, provided both are dropper from a height of 200 cubits.”
Now, somewhat recently I had an email conversation with a person, who questioned if Galileo had ever done the experiment which Sagredo described because of the weights of the cannon ball and musket ball and the height of 200 cubits were unrealistic.
Thus, he seemed to claim that Galileo lied, or mislead, just as Aristotle had. Except there is one observable difference between these two cases. Galileo reported what anyone doing a similar experiment, using more realistic bodies and height could observe whereas no one could ever observe what Aristotle suggested by the word, see, he had seen.
However, after Sagredo’s comment, Salviati immediately states:
“But, even without further experiment, it is possible to prove clearly, by means of a short and conclusive argument, that a heavier body does not move more rapidly than a lighter one provided both bodies are of the same material and in short such as those mentioned by Aristotle. But tell me, Simplicio, whether you admit that each falling body acquires a definite speed fixed by nature, a velocity which cannot be increased or diminished except by the use of force [violenza] or resistance.”
Here I must admit that for too long I had missed the possibility that Galileo was moving on to the second false idea: bodies fall at a constant rate. I had missed the possibility that Galileo was setting up Simplico, who immediately replied:
“There can be no doubt that one and the same body moving in a single medium has a fixed velocity which is determined by nature and which cannot be increased except by the addition of momentum [impeto] or diminished except by some resistance which retards it.”
About twenty pages later Simplico states:
“The previous experiments, in my opinion, left something to be desired: but now I am fully satisfied.” And immediately Salviati reviews: “The facts set forth by me up to this point and, in particular, the one which shows that difference of weight, even when very great, is without effect in changing the speed of falling bodies, so that as far as weight is concerned they all fall with equal speed: this idea is, I day, so new, and at first glance so remote from fact, that if we do not have the means of making it just as clear as sunlight, it had better not be mentioned; but having once allowed it to pass my lips I must neglect no experiment or argument to establish it.”
Now, given this review, I have to question my previously stated opinion that twenty pages earlier Galeleo was moving on to the second false idea. The key words, upon which I now focus to understand Galileo’s objective, are: “I must neglect no experiment or argument to establish it.”
To which Sagredo responded:
“Not only this but also many other of your views are so far removed from the commonly accepted opinions and doctrines that if you were to publish them you would stir up a large number of antagonists; for human nature is such that men do not look with favor upon discoveries—either of truth or fallacy—in their own field, when made by others than themselves. They call him an innovator of doctrine, an unpleasant title, and by subterranean mines they seek to destroy structures which patient artisans have built with customary tools. But as for ourselves who have no such thoughts, the experiments and arguments which you have thus far adduced are fully satisfactory; however if you have any experiments which are more direct or any arguments which are more convincing we will hear them with pleasure.”
So for another twenty pages of the First Day, Galileo had Salviati oblige Sagredo’s request as the three characters continued to interact with each other.
Later, Third Day, Galileo had Sagredo remark:
“You present these recondite matter with too much evidence and ease; this great facility makes them less appreciated than they would be had they been presented in a more abstruse manner. For, in my opinion, people esteem more lightly that knowledge which they acquire with so little labor than that acquired through long and obscure discussion.” To which Salviati responded: “If those who demonstrate with brevity and clearness the fallacy of many popular beliefs were treated with contempt instead of gratitude the injury would be quite bearable; but on the other hand it is very unpleasant and annoying to see men, who claim to be peers of anyone in a certain field of study, take for granted certain conclusions which later are quickly and easily shown by another to be false. I do not describe such a feeling as one of envy, which usually degenerates into hatred and anger against those who discover such fallacies; I would call it a strong desire to maintain old errors, rather than accept newly discovered truths. This desire at times induces them to unite against these truths, although at heart believing in them, merely for the purpose of lowering the esteem in which certain others are held by the unthinking crowd.”
There are two principal reasons (purposes) for this essay. One is that I, a scientist and an instructor of chemistry, had never read on portion of Crew and de Salvio’s translation of Dialogues Concerning Two New Sciences until near the end of my teaching career when I was near 55 years of age. Hence, I had never assigned my students to read at least a portion of Galileo’s forbidden book.
This I consider to have been a serious mistake. I cannot believe that I would not have been a better science student and a better science instructor if I had read Crew and de Salvio’s 1914 translation of Dialogue Concerning Two New Sciences. Hence, I consider that every science teacher, instructor, professor would be better teachers, instructors, professors if they would read this book and their students would be better students if they were required to read at least some portions of it.
The second is the practice of Galileo’s sciences has become so corrupted that even doubting the validity of an established scientific idea is considered to be anti-science. A doubter is considered a denier. It is seems critically important that those who call a doubter a denier see that they give evidence of the human natural which resisted Galileo’s attempt to refute false ideas by experiment (observation) and to substitute the wrong ideas with ideas tested by experiment (observation).
It is very important to thoughtfully consider:
“No amount of experimentation can ever prove me right; a single experiment can prove me wrong.” (Albert Einstein)
Until most all scientists recognize the truth of Einstein’s statement, it will continue to be difficult work to prove an idea wrong because of the human nature referred to by Galileo. For it, too, has been an easily observed fact of certain sciences which, at times past, did not follow Galileo’s lead.
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