Saturday, March 07, 2009

Pierre Duhem

"...but Thou hast ordered all things in measure, and number, and weight...."
[Wisdom 11:21]

Today is March 7, a very great day indeed. It is the day on which St. Thomas Aquinas died, and so is his real feast day (as still noted in the old calendar). But it is something more:
Pierre Duhem offered the last five volumes of his monumental opus as proof of the proposition that modern science “was born, so to speak, on March 7, 1277 from the decree issued by Monseigneur Étienne, bishop of Paris.” By this Duhem meant that the decree decisively reinforced, mainly at the University of Paris, a train of thought leading ultimately to the formulation of a new (classical) physics.
[Jaki, Science and Creation, note 52 to Chapter 10]
Ah (you say) - no wonder you are celebrating, Doctor! Truly right and just, proper and helpful - for all people to celebrate on this day, especially those of us who are reading these words by means of scientific technology.

But Doctor - (you go on to ask) Who is Pierre Duhem?

He was born in 1861, and died in 1916. He was a physicist specializing in thermodynamics, a brilliant man. When (from political motives) the college disapproved his doctoral dissertation in physics, he re-wrote it as a mathematical topic, and received his degree. He went on hikes in the Alps and made wonderful sketches - true art - of the scenes (Jaki has a volume of reprints: The Physicist as Artist.) Duhem was a very serious practicing Catholic, and he was also a great historian of science, making discoveries as important to us as any dozen merely scientific advances.

There is so much more to say about Duhem - his name appears in nearly every book by Father Jaki, and with good reason: not only his three-volume work on Leonardo da Vinci, but even more importantly, his ten volumes of Système du monde, which contain important research about the medieval origin of science. Jaki has two large volumes on Duhem, and another on Duhem's daughter Hélène, who fought censorship to get the last five volumes of her father's masterwork printed. It is very hard (at this moment) to produce a good summary of all this material - but Jaki has an excellent introduction, which gives the really important points of what happened, and I shall now quote it at length:
Pierre Duhem (1861-1916) was a French theoretical physicist educated in the Comtean perspective of intellectual history.The least objectionable aspect of that perspective was that no subject is properly understood until it is investigated in its historical development. So Duhem, a world authority on thermodynamics, began to write a history of the basic principles of mechanics. Very naturally he began with the Greeks (Archimedes in particular); he then wanted to go straight to Galileo, jumping about two thousand years. A very good Catholic, Duhem did not share the Comtean bias that there was nothing of importance in medieval philosophy and theology. But like all other Catholics of his time (and unfortunately like almost all Catholic intellectuals of our time), Duhem felt that there was no science to be looked for in the Middle Ages. While he studied the works of Galileo's immediate predecessors, he found an obscure reference to a certain Jordanus. The reference, which had just been noted by two historians of science among Duhem's contemporaries, was all the more enigmatic because in that message the mysterious Jordanus was credited with the discovery of the most fundamental law of mechanics, the law of virtual velocities.

What the two others did not do, although they were professional historians of science, Duhem did, and in a way which in the long run turned him into the most original historian of science of all times. Duhem undertook an intensive search for Jordanus, a search that ultimately led him to his heroic discovery of the origin of modern science in the Middle Ages. He expected anything but that. First Duhem was led from sixteenth-century printed books to the incunabula. Beyond that, there was a largely unexplored field of manuscripts written mostly in Latin shorthand, which varied from region to region and from century to century. No one was more surprised than Duhem on finding that Jordanus was part of the fourteenth-century Sorbonne, one of the great if not the greatest of medieval universities.

As always happens, one breakthrough quickly opened up a vast, unsuspected field. Within four or five years Duhem also found that the first intimations of Newton's first law of motion were also tied to the medieval Sorbonne. In two Sorbonne professors, Buridan and Oresme, who had been remembered only as curious figures in the history of philosophy, Duhem discovered two scientific geniuses. Most important, he discovered a very medieval reason for their historic breakthroughs in science. The reason was genuine, unadulterated Christian creed and theology.

The basis of Christian religion is belief in revelation as it is guaranteed by the teaching authority of the Church and codified in the various creeds. All the short and long creeds or credal formulas begin with the words: "I believe in God, the Father Almighty, Maker of Heaven and Earth." In other words, the Creed begins with the statement that the universe is a creation of God. In the beginning of the High Middle Ages, in the Fourth Lateran Council held in 1214, the Church also solemnly defined an age-old Christian conviction that the universe was created in time. By this, the Church meant that the past history of the universe was finite.

It was with such convictions that Buridan read Aristotle, for whom the universe was uncreated and therefore eternal. Thomas Aquinas and many other medievals before Buridan had also read Aristotle's statements that the universe was eternal. They all rejected it on the ground that it contradicted revelation. Buridan did the same but with a difference. Unlike Aquinas, a theologian with little interest in the scientific aspects of physical reality, Buridan was very much interested in them. Thus when Buridan claimed against Aristotle that the world had a finite past, he naturally thought about the physical manner in which the motion of the universe may have started.

The manner or way could not be the one which Aristotle proposed in terms of his pantheism. According to Aristotle, the universe moved, because its highest part, the sphere of the fixed stars, was in a sort of contact with the divine motor or the Prime Mover. It was through that eternal contact with the divine that, in Aristotle's opinion, the universe had been moving (rotating) since eternity and would keep moving forever.

Since Buridan the Christian had to postulate an absolute beginning for physical motion, it was practically impossible for him to keep that notion of contact as a source of motion. A universe created by God freely in time could not be imagined as being necessarily in contact with the divine. If no contact, then what? It is at that point that Buridan's genius asserted itself, a genius obviously motivated by his Christian convictions. He resorted to the idea of giving or imparting, an idea very much a part of the Christian notion of creation. Is not creation, which is an act of producing something out of nothing, a giving and imparting in the deepest possible sense? And was not God's giving something so solid and reliable as to stay with the thing to which it was given?

Thoughts like these must have been in the back of Buridan's mind as he made his statement about the beginning of all physical motion:
When God created the world, He moved each of the celestial orbs as he pleased, and in moving them He impressed in them impetuses which moved them without His having to move them any more except by the method of general influence whereby He concurs as a co-agent in all things which take place; ... these impetuses which He impressed in the celestial bodies were not decreased nor corrupted afterward, because there was no resistance which would be corruptive or repressive of that impetus.
The historical significance of that statement cannot be emphasized enough. It includes three all-important features. First, and the most obvious, is the statement's substantial equivalence to Newton's first law of motion. Since that law is the foundation of Newton's second and third laws, in Buridan's statement one has at hand the very basis of the science of physics. The importance of that science for modern life is well known. Much less known, and often not even suspected, is the medieval origin of that modernity.

The second feature to be noted about Buridan's statement is that it implies the notion of autonomous laws of nature. Once God gives motion to the universe, the universe keeps it and keeps acting in accordance with it. In other words, the proper idea of creation secures the notion of a nature acting consistently with the laws given to it. It is this consistency which is presupposed by all physicists as they do their research.

The third feature of the modernity of Buridan's medieval statement relates to the quantity of motion given to the universe. The idea was part of a broader notion about the universe, an idea which came straight out of the Book of Wisdom, one of the last books of the Old Testament. There the Creator is spoken of as one "who arranges everything according to measure, number, and weight." The phrase is not just another phrase from the Bible. Rather, as noted by Ernst Curtius, a foremost Protestant specialist on medieval literature, it was the most often quoted biblical passage during the Middle Ages. Such a phrase can readily form a climate of thought, which in fact it did. The efforts to treat processes quantitatively were numerous from the fourteenth century on. One of the results was the introduction of the art of latitudes, the forerunner of the use of coordinate systems.

In speaking about that phrase from the Bible, one must not picture medieval men, not even medieval scholars, as running around with Bibles in their pockets. Since Bibles were handwritten, they had to be relatively few and very expensive. Yet the medieval intellectuals knew their Bible very well because they were well instructed in catechism and in theology. The passages and stories of the Bible were part of a broad oral instruction. The quality of that instruction can be gathered from the fact that the medieval intellectual was a man with a drive which derived from the Bible's very first chapters. He was driven by a biblical sense of mission. He felt that God's words addressed to the first man and woman to "multiply and subdue the earth" were also addressed to him.
Jaki, The Only Chaos 38-40
All the quotes in the above are footnoted, but I omit them here. (Jaki's books are exemplars of high scholarship and vast and careful research.)
"When one is a Christian, when one does not believe in luck, when one believes in an appeal to Providence, a good wish is a prayer. Do not be astonished that my toast takes the form of a prayer. As you take your place at the banquet of life, I implore God to go along the tables often enough to notice the humble place where your modesty made you sit down and, taking you by the hand, tell you: My friend, move higher up."
[Pierre Duhem, a toast quoted in Jaki's Uneasy Genius: The Life and Work of Pierre Duhem]


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