Free A Brief Guide to the Great Equations by Robert Crease Page A

closed off from our own, whose events disclose to us much about our world. The equation
F
=
ma
is the ‘soul’ of that world, as Wilczek wrote, serving to define its structure, and part and parcel of every event that takes place in it.
    This is why
F
=
ma
is not as straightforward as it appears. When we learn it we are learning more than we think. We are inheriting the entire journey that led up to it.

Interlude
THE BOOK OF NATURE
    Philosophy is written in this grand book, the universe, which stands continually open to our gaze. But the book cannot be understood unless one first learns to comprehend the language and read the letters in which it is composed. It is written in the language of mathematics, and its characters are triangles, circles, and other geometrical figures without which it is humanly impossible to understand a single word of it; without these, one wanders about in a dark labyrinth.
– Galileo,
The Assayer
    In 1623, Galileo crafted a famous image that is still often cited by scientists. Nature, he wrote, is a book written in ‘the language of mathematics’, and if we cannot understand that language, we are doomed to wander about as if ‘in a dark labyrinth.’
    Like other metaphors, this one is both true and untrue; it is insightful but it may be misleading if taken literally. It captures our sense that nature’s truths are somehow imposed on us – that they are already imprinted in the world – and underlines the key role played by mathematics in expressing those truths. But Galileo devised the image for a specific purpose. Taken out of its historical context and placed in ours, the image can be dangerously deceptive.
    The idea of a book of nature did not begin with Galileo. For centuries it had been an accepted part of religious doctrine thatthe world contained two fundamental books. Nature, the first book, is full of signs that reveal a deeper meaning when interpreted according to scripture, the second book, which supplies the ultimate meaning or syntax of nature’s signs. Understanding involved reading the books together, going back and forth between what one finds in the world and what one reads in scripture. As Peter Harrison has pointed out in his book
The Bible, Protestantism, and the Rise of Natural Science
, reading the Bible was once considered part and parcel of studying nature, and it is therefore wrong to equate serious Bible reading with literalism and antiscientific behaviour as we often do today.
    During the Renaissance, however, scholars came to appreciate more keenly that the truths of nature were not always easy to discern. Rather, such truths were often cleverly encoded in nature and so required a special training to unlock. Meanwhile, the Protestant Reformation brought about changes in the understanding of texts, emphasizing the truths in them that were exact and self-contained rather than symbolic or allegorical.
    Galileo, building on these scientific and religious changes, then appropriated the ‘two books’ image for his own purposes, transforming its meaning.
    For in 1623, Galileo was in a jam. His troubles had begun 10 years earlier, when a student of his had discussed his work at the Pisan court, and a participant noted the apparent conflict between scripture and Galileo’s scientific claims, especially regarding the motion of the earth. Meanwhile, the authorities were threatening to put
De Revolutionibus
, by his intellectual ally Copernicus, on the official index of forbidden books for similar reasons. Worried for himself and for other scientists, Galileo wrote a letter to the Grand Duchess Christina about the connection between science and scripture. In that letter, he appealed to the traditional image that God reveals himself to humanity in two books, nature and scripture. Hesuggested that both books express eternal truths and are compatible because they have the same Author – God is saying the same thing in two different ways.
    Yet Galileo’s novel crafting of