Seven Brief Lessons on Physics

by Carlo Rovelli

Because science shows us how to better understand the world, but it also reveals to us just how vast is the extent of what is still not known.

The first lesson is dedicated to Albert Einstein’s general theory of relativity, the “most beautiful of theories.” The second to quantum mechanics, where the most baffling aspects of modern physics lurk. The third is dedicated to the cosmos: the architecture of the universe that we inhabit; the fourth to its elementary particles. The fifth deals with quantum gravity: the attempts that are under way to construct a synthesis of the major discoveries of the twentieth century. The sixth is on probability and the heat of black holes. The final section of the book returns to ourselves and asks how it is possible to think about our existence in the light of the strange world described by physics.

FIRST LESSON The Most Beautiful of Theories

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 quan...

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...

employment from various universities. But something disturbed him: despite its immediate acclaim, his theory of relativity does not fit with what we know a...

“The General Theory of Relativity,” his masterpiece and the “most beautiful of theories,” according to the great Russian physicist Lev Landau.

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 time we glimpse a new aspect of it, it is a deeply emotional experience. Another veil has fallen.

numerous leaps forward in our understanding that have succeeded one another over the course of history, Einstein’s is perhaps unequaled. Why?

move through space and that space is a great empty container, a large box that enclosed the universe, an immense structure through which all objects run true until a force obliges their trajectory to curve.

Michael Faraday and James Maxwell, had added a key ingredient to Newton’s cold world: the electromagnetic field. This field is a real entity that, diffused everywhere, carries radio waves, fills space, can vibrate and oscillate like the surface of a lake,

the gravitational field is not diffused through space; the gravitational field is that space itself. This is the idea of the general theory of relativity. Newton’s “space,” through which things move, and the “gravitational field” are one and the same thing.

momentous simplification of the world: space is no longer something distinct from matter—it is one of the “material” components of the world.

The sun bends space around itself, and Earth does not turn around it because of a mysterious force but because it is racing directly in a space that inclines, like a marble that rolls in a funnel. There are no mysterious forces generated at the center of the funnel; it is the curved nature of the walls that causes the marble to roll. Planets circle around the sun, and things fall, because space curves.

The result of Riemann’s thesis was that the properties of a curved space are captured

object, which we know today as Riemann’s curvature

Einstein wrote an equation that says that R is equivalent to the energy of matter. That is to say: space curves where there is matter. That is it. The equation fits into half a line, and there is nothi...