Free Seven Brief Lessons on Physics by Carlo Rovelli

FIRST LESSON
    The Most Beautiful of Theories
    In his youth Albert Einstein spent a year loafing aimlessly. You don’t get anywhere by not “wasting” time—something, unfortunately, that the parents of teenagers tend frequently to forget. He was in Pavia. He had joined his family, having abandoned his studies in Germany, unable to endure the rigors of his high school there. It was the beginning of the twentieth century, and in Italy the beginning of its industrial revolution. His father, an engineer, was installing the first electricity-generating power plants in the Paduan plains. Albert was reading Kant and attending occasional lectures atthe University of Pavia: for pleasure, without being registered there or having to think about exams. It is thus that serious scientists are made.
    After this he registered at the University of Zurich and immersed himself in the study of physics. A few years later, in 1905, he sent three articles to the most prestigious scientific journal of the period, the
Annalen der Physik
. Each of these is worthy of a Nobel Prize. The first shows that atoms really exist. The second lays the first foundation for quantum mechanics, which I will discuss in the next lesson. The third presents his first theory of relativity (known today as “special relativity”), the theory that elucidates how time does not pass identically for everyone: two identical twins find that they are different in age if one of them has traveled at speed.
    Einstein became a renowned scientist overnight and received offers of employment from various universities. But something disturbed him: despite its immediate acclaim, his theory of relativity does not fit with what we know about gravity, namely, with how things fall. He came to realize this when writing an article summarizing his theory and began to wonder if the law of “universal gravity” as formulated by the father of physics himself, Isaac Newton, was in need of revision in orderto make it compatible with the new concept of relativity. He immersed himself in the problem. It would take ten years to resolve. Ten years of frenzied studies, attempts, errors, confusion, mistaken articles, brilliant ideas, misconceived ideas.
    Finally, in November 1915, he committed to print an article giving the complete solution: a new theory of gravity, which he called “The General Theory of Relativity,” his masterpiece and the “most beautiful of theories,” according to the great Russian physicist Lev Landau.
    There are absolute masterpieces that move us intensely: Mozart’s
Requiem
, Homer’s
Odyssey
, the Sistine Chapel,
King Lear
. To fully appreciate their brilliance may require a long apprenticeship, but the reward is sheer beauty—and not only this, but the opening of our eyes to a new perspective upon the world. Einstein’s jewel, the general theory of relativity, is a masterpiece of this order.
    I remember the excitement I felt when I began to understand something about it. It was summer. I was on a beach at Condofuri in Calabria, immersed in the sunshine of the Hellenic Mediterranean, and in the last year of my university studies. Undistracted by schooling, one studies best during vacations. I was studying with thehelp of a book that had been gnawed at the edges by mice because at night I’d used it to block the holes of these poor creatures in the rather dilapidated, hippie-ish house on an Umbrian hillside where I used to take refuge from the tedium of university classes in Bologna. Every so often I would raise my eyes from the book and look at the glittering sea: it seemed to me that I was actually seeing the curvature of space and time imagined by Einstein. As if by magic: as if a friend were whispering into my ear an extraordinary hidden truth, suddenly raising the veil of reality to disclose a simpler, deeper order. Ever since we discovered that Earth is round and turns like a mad spinning-top, we have understood that reality is not as it appears to us: every