Seven Brief Lessons on Physics

by Carlo Rovelli

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

Einstein wrote an equation which says that R is equivalent to the energy of matter. That is to say: space curves where there is matter.

All of this is the result of an elementary intuition: that space and gravitational field are the same thing.

Both protons and neutrons are made up of even smaller particles which the American physicist Murray Gell-Mann named ‘quarks’, inspired by a seemingly nonsensical word in a nonsensical phrase in James Joyce’s Finnegans Wake: ‘Three quarks for Muster Mark!’

Quantum mechanics and experiments with particles have taught us that the world is a continuous, restless swarming of things; a continuous coming to light and disappearance of ephemeral entities. A set of vibrations, as in the switched-on hippy world of the 1960s. A world of happenings, not of things.

There are no nouns, only verbs

The difference between past and future only exists when there is heat. The fundamental phenomenon that distinguishes the future from the past is the fact that heat passes from things that are hotter to things that are colder.

The images which we construct of the universe live within us, in the space of our thoughts. Between these images – between what we can reconstruct and understand with our limited means – and the reality of which we are part, there exist countless filters: our ignorance, the limitations of our senses and of our intelligence. The very same conditions that our nature as subjects, and particular subjects, imposes upon experience.

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. Our knowledge consequently reflects the world. It does this more or less well, but it reflects the world we inhabit. This communication between ourselves and the world is not what distinguishes us from the rest of nature.