Reality Is Not What It Seems: The Journey to Quantum Gravity

by Carlo Rovelli

The incompleteness and the uncertainty of our knowledge, our precariousness, suspended over the abyss of the immensity of what we don’t know, does not render life meaningless: it makes it interesting and precious.

The world is a sequence of granular quantum events.

The world is not made up of tiny pebbles. It is a world of vibrations, a continuous fluctuation, a microscopic swarming of fleeting microevents.

The theory does not describe things as they “are”: it describes how things “occur,” and how they “interact with each other.” It doesn’t describe where there is a particle but how the particle shows itself to others. The world of existent things is reduced to a realm of possible interactions. Reality is reduced to interaction. Reality is reduced to relation.

Quantum mechanics does not describe objects: it describes processes and events that are junction points between processes.

But they remain mysterious: they do not describe physical systems, but only how physical systems interact with and affect one another.

At the extremely small scale of the quanta of space, the dance of nature does not develop to the rhythm kept by the baton of a single orchestral conductor: every process dances independently with its neighbors, following its own rhythm.

Space is a spin network whose nodes represent its elementary grains, and whose links describe their proximity relations. Spacetime is generated by processes in which these spin networks transform into one another, and these processes are described by sums over spinfoams. A spinfoam represents a history of a spin network, hence a granular spacetime where the nodes of the graph combine and separate.

The central point is rebellion against the renunciation of the desire to know. A declaration of faith in the comprehensibility of the world, a proud retaliation to those who remain satisfied with their own ignorance, who call “infinite” that which we don’t understand and delegate knowledge elsewhere.

The world isn’t, then, just a network of colliding atoms: it is also a network of correlations between sets of atoms, a network of real, reciprocal information between physical systems.

Any description of a system is therefore always a description of the information a system has about another system, that is to say, the correlation between the two systems.

It is always heat and only heat that distinguishes the past from the future.

We are always correlated with averages. Averages behave like averages: they disperse heat and, intrinsically, generate time.

A living organism is a system that continually re-forms itself in order to remain itself, interacting ceaselessly with the external world. Of such organisms, only those continue to exist that are more efficient at doing so, and therefore living organisms manifest properties that have suited them for survival. For this reason, they are interpretable, and we interpret them, in terms of intentionality, of purpose. The finalistic aspects of the biological world (this is Darwin’s momentous discovery) are therefore the result of the selection of complex forms effective in persisting. But the effective way of continuing to exist in a changing environment is to better manage correlations with the external world, that is to say, information: to collect, store, transmit, and elaborate information.

The world should not be understood as an amorphous ensemble of atoms—but rather as a game of mirrors, founded on the correlations between the structures formed by combinations of these atoms.

The answers given by science, then, are not reliable because they are definitive. They are reliable because they are not definitive. They are reliable because they are the best available today. And they are the best we have because we don’t consider them to be definitive, but see them as open to improvement. It’s the awareness of our ignorance that gives science its reliability. And it is reliability that we need, not certainty.