Seven Brief Lessons on Physics

Milky Way 

“Physics opens windows through which we see far into the distance. What we see does not cease to astound us. We realize that we are full of prejudices and that our intuitive image of the world is partial, parochial, inadequate.”

Carlo Rovelli is an Italian theoretical physicist and writer who has worked in Italy and the USA. His work is mainly in the field of quantum gravity, where he is among the founders of the loop quantum gravity theory. He has also worked in the history and philosophy of science. Seven Brief Lessons on Physics is a short read based on a series of articles he published in “Sole 24 Ore.”


Is about Einstein's general theory of relativity. Space is not empty, but composed of particles of some kind. The sun bends space around itself, and the planets circle around the sun because they follow the curve of space (like marbles that roll around a funnel.) This explains the 'force of gravity' that prevents the planets from flying off into the galaxy.

Einstein's major breakthrough was to realize that Newton's gravitational field is not a field at all but is space-time itself:

Within this equation there is a teeming universe. And here the magical richness of the theory opens up into a phantasmagorical succession of predictions that resemble the delirious ravings of a madman, but which have all turned out to be true.

Special theory of relativity — The faster you move, the slower time passes. This would be really obvious if you could travel at the speed of light. 


Quantum mechanics laws do not describe what happens to a physical system but only how one physical system affects another.

The energy of a field is distributed in 'quanta', or packets of energy, like electrons in an electrical field. But quanta only exist when they're interacting with something else, so they bleep in an out of existence. Quanta move randomly so we can't know where they'll manifest themselves.


In the Big Bang theory and the architecture of the cosmos he talks about many other wonders revealed by Einstein's theory combined with many of the tools of modern physics such as radio telescopes and particle detectors.

Our sun is one star among billions of stars in the galaxy, there are billions of galaxies. There may even be more than one universe, but we don't know.


Particles tells us how the findings of quantum mechanics led to an explosion of understanding of the building blocks of the cosmos in the postwar years. The universe is teeming with quarks and electrons, Higgs bosons and neutrinos. The culmination of all this progress was the Standard Model of particle physics, essentially a kind of periodic table which lists all known particles and their properties.

Unlike general relativity the Standard Model is incomplete. Many of the particles' parameters are poorly understood, and the model itself is incompatible with general relativity. We have much more to discover in fundamental physics.


Quantum gravity is about the marriage of general relativity theory where he universe is a continuous curved space, and quantum mechanics, where the universe is composed of particles that bleep in and out of existence. Even though they work well, the two theories contradict each other. Physicists are trying to merge the ideas in a field of study called 'loop quantum gravity.'

One combined theory suggests that space is not continuous but made up of infinitesimally small 'grains of space' called loops somewhat connected like a chain link fence. This theory has repercussions incompatible with the reality of time, it needs a lot more of work.


Is about probability, time, and the heat of Black Holes. The notion of time is elusive and has been the subject of much debate among physicists. Rovelli points out, though, that heat distinguishes the past from the future. As time goes by, heat passes from things that are hotter to things that are colder (for example, a teaspoon heats up in hot tea.) The science of heat is called thermodynamics.

We don't know what happens to a gravitational field when it heats up, but a clue might be found in a black hole — a collapsed star with a gravitational field so strong that nothing (not even light) can escape. Black holes are hot — in essence hot spots of space-time. They combine quantum mechanics, general relativity, and thermodynamics. Eventually scientists might be able to use black holes to reveal the true nature of time.


In ourselves Rovelli talks about the ultimate entity that allows us to figure all this out — the human brain. If humans are composed of ephemeral particles, the same stuff as the rest of the universe, where do we get our sense of ourselves, of being conscious and making decisions. Scientists studying the brain are trying to shed light on this.

“We are made of the same stardust of which all things are made, and when we are immersed in suffering or when we are experiencing intense joy, we are being nothing other than what we can’t help but be: a part of our world.”

One of the most poetic passages in Seven Brief Lessons on Physics deals with the tension between our desire to explain phenomena through storytelling and our thirst for knowledge and learning, which ignites out imagination:

“When we talk about the big bang or the fabric of space, what we are doing is not a continuation of the free and fantastic stories that humans have told nightly around campfires for hundreds of thousands of years. It is the continuation of something else: of the gaze of those same men in the first light of day looking at tracks left by antelope in the dust of the Savannah—scrutinizing and deducting from the details of reality in order to pursue something that we can’t see directly but can follow the traces of. In the awareness that we can always be wrong, and therefore ready at any moment to change direction if a new track appears; but knowing also that if we are good enough we will get it right and will find what we are seeking. This is the nature of science.

The confusion between these two diverse human activities—inventing stories and following traces in order to find something—is the origin of the incomprehension and distrust of science shown by a significant part of our contemporary culture. The separation is a subtle one: the antelope hunted at dawn is not far removed from the antelope deity in that night’s storytelling.

The border is porous. Myths nourish science, and science nourishes myth. But the value of knowledge remains. If we find the antelope, we can eat.”