The Order of Time

by Carlo Rovelli

Even the words that we are speaking now thieving time has stolen away, and nothing can return. (I, 11)

And yet things are somewhat more complicated than this. Reality is often very different from what it seems. The Earth appears to be flat but is in fact spherical. The sun seems to revolve in the sky when it is really we who are spinning. Neither is the structure of time what it seems to be: it is different from this uniform, universal flowing. I discovered this, to my utter astonishment, in the physics books I read as a university student: time works quite differently from the way it seems to.

Because the mystery of time is ultimately, perhaps, more about ourselves than about the cosmos. Perhaps, as in the first and greatest of all detective novels, Sophocles’ Oedipus Rex, the culprit turns out to be the detective. Here, the book becomes a fiery magma of ideas, sometimes illuminating, sometimes confusing. If you decide to follow me, I will take you to where I believe our knowledge of time has reached: up to the brink of that vast nocturnal and star-studded ocean of all that we still don’t know.

The source of Rilke’s “eternal current” is nothing other than this. Appointed a university professor at just twenty-five years old; received at court by the emperor at the apex of his success; severely criticized by the majority of the academic world, which did not understand his ideas; always precariously balanced between enthusiasm and depression: the “dear sweet chubby one,” Ludwig Boltzmann, will end his life by hanging himself. He does so at Duino, near Trieste, while his wife and daughter are swimming in the Adriatic. The same Duino where, just a few years later, Rilke will write his Elegy.

Ten years before understanding that time is slowed down by mass,21 Einstein had realized that it was slowed down by speed.22 The consequence of this discovery for our basic intuitive perception of time is the most devastating of all. The fact itself is quite simple. Instead of sending the two friends from the first chapter to the mountains and the plains, respectively, let’s ask one of them to stay still and the other one to walk around. Time passes more slowly for the one who keeps moving.

There is our past: all the events that happened before what we can witness now. There is our future: the events that will happen after the moment from which we can see the here and now. Between this past and this future there is an interval that is neither past nor future and still has a duration: fifteen minutes on Mars; eight years on Proxima b; millions of years in the Andromeda galaxy. It is the expanded present.28 It is perhaps the greatest and strangest of Einstein’s discoveries. The idea that a well-defined now exists throughout the universe is an illusion, an illegitimate extrapolation of our own experience.29 It is like the point where the rainbow touches the forest. We think that we can see it—but if we go to look for it, it isn’t there.

For centuries, we have divided time into days. The word “time” derives from an Indo-European root—di or dai—meaning “to divide.” For centuries, we have divided the days into hours.37 But for most of those centuries, however, hours were longer in the summer and shorter in the winter, because the twelve hours divided the time between dawn and sunset: the first hour was dawn, and the twelfth was sunset, regardless of the season, as we read in the parable of the winegrower in the Gospel according to Matthew.38 Since, as we say nowadays, during summer “more time” passes between dawn and sunset than during the winter, in the summer the hours were longer, and the hours were shorter in wintertime.

In other words, Newton recognizes that a kind of “time” exists that measures days and movements: the one treated by Aristotle (relative, apparent, and common). But he also contends that, in addition to this, another time must exist: “true” time that passes regardless, independently of things and of their changes. If all things remained motionless and even the movements of our souls were to be frozen, this time would continue to pass, according to Newton, unaffected and equal to itself: “true” time. It’s the exact opposite of what Aristotle writes.

So, who is right: Aristotle or Newton? Two of the most acute and profound investigators of nature that the world has ever seen are proposing two opposite ways of thinking about time. Two giants are pulling us in opposite directions.46 Time is only a way of measuring how things change, as Aristotle would have it—or should we be thinking that an absolute time exists that flows by itself, independently of things? The question we should really be asking is this: Which of these two ways of thinking about time helps us to understand the world better? Which of the two conceptual schemes is more efficient?

Clocks, for Newton, are devices that seek, albeit in a manner that is always imprecise, to follow this equal and uniform flowing of time. Newton writes that this “absolute, true, and mathematical” time is not perceptible. It must be deduced, through calculation and observation, from the regularity of phenomena. Newton’s time is not the evidence given to us by our senses: it is an elegant intellectual construction. If, my dear cultivated reader, the existence of this Newtonian concept of time which is independent of things seems to you simple and natural, it’s because you encountered it at school. Because it has gradually become the way in which we all think about time. It has filtered through school textbooks throughout the world and ended up becoming our common way of understanding time. We have turned it into our common sense. But the existence of a time that is uniform, independent of things and of their movement that today seems so natural to us is not an ancient intuition that is natural to humanity itself. It’s an idea of Newton’s.

The synthesis between Aristotle’s time and Newton’s is the most valuable achievement made by Einstein. It is the crowning jewel of his thought.

The idea that time could be granular, that there could be minimal intervals of time, is not new. It was defended in the seventh century by Isidore of Seville in his Etymologiae, and in the following century by the Venerable Bede in a work suggestively entitled De Divisionibus Temporum (“On the Divisions of Time”). In the thirteenth century, the great philosopher Maimonides writes: “Time is composed of atoms, that is to say of many parts that cannot be further subdivided, on account of their short duration.”53 The idea probably dates back even further: the loss of the original texts of Democritus prevents us from knowing whether it was already present in classical Greek atomism.54 Abstract thought can anticipate by centuries hypotheses that find a use—or confirmation—in scientific inquiry.

You got to deep-six your wristwatch, you got to try and understand, The time it seems to capture is just the movement of its hands . . .57 Let’s enter the world without time.

O gentlemen, the time of life is short . . . And if we live, we live to tread on kings. Shakespeare, Henry IV, Part I (act 5, scene 2) When Robespierre freed France from monarchy, Europe’s ancien régime feared that the end of civilization itself was nigh. When the young seek to liberate themselves from an old order of things, the old are afraid that all will founder. But Europe was able to survive perfectly well, even without the king of France. The world will go on turning, even without King Time.

We can think of the world as made up of things. Of substances. Of entities. Of something that is. Or we can think of it as made up of events. Of happenings. Of processes. Of something that occurs. Something that does not last, and that undergoes continual transformation, that is not permanent in time. The destruction of the notion of time in fundamental physics is the crumbling of the first of these two perspectives, not of the second. It is the realization of the ubiquity of impermanence, not of stasis in a motionless time.

The difference between things and events is that things persist in time; events have a limited duration. A stone is a prototypical “thing”: we can ask ourselves where it will be tomorrow. Conversely, a kiss is an “event.” It makes no sense to ask where the kiss will be tomorrow. The world is made up of networks of kisses, not of stones.

On closer inspection, in fact, even the things that are most “thinglike” are nothing more than long events. The hardest stone, in the light of what we have learned from chemistry, from physics, from mineralogy, from geology, from psychology, is in reality a complex vibration of quantum fields, a momentary interaction of forces, a process that for a brief moment manages to keep its shape, to hold itself in equilibrium before disintegrating again into dust, a brief chapter in the history of interactions between the elements of the planet, a trace of Neolithic humanity, a weapon used by a gang of kids, an example in a book about time, a metaphor for an ontology, a part of a segmentation of the world that depends more on how our bodies are structured to perceive than on the object of perception—and, gradually, an intricate knot in that cosmic game of mirrors that constitutes reality. The world is not so much made of stones as of fleeting sounds, or of waves moving through the sea.

What works instead is thinking about the world as a network of events. Simple events, and more complex events that can be disassembled into combinations of simpler ones. A few examples: A war is not a thing, it’s a sequence of events. A storm is not a thing, it’s a collection of occurrences. A cloud above a mountain is not a thing, it is the condensation of humidity in the air that the wind blows over the mountain. A wave is not a thing, it is a movement of water, and the water that forms it is always different. A family is not a thing, it is a collection of relations, occurrences, feelings. And a human being? Of course it’s not a thing; like the cloud above the mountain, it’s a complex process, where food, information, light, words, and so on enter and exit. . . . A knot of knots in a network of social relations, in a network of chemical processes, in a network of emotions exchanged with its own kind.

The words of Anaximander quoted in the first chapter of this book invited us to think of the world “according to the order of time.” If we do not assume a priori that we know what the order of time is—if we do not, that is, presuppose that it is the linear and universal order that we are accustomed to—Anaximander’s exhortation remains valid: we understand the world by studying change, not by studying things. Those who have neglected this good advice have paid a heavy price for it. Two of the greats who fell into this error were Plato and Kepler, both curiously seduced by the same mathematics.

Gone is the whiteness of snow— green returns in the grass of the fields, in the canopies of trees, and the airy grace of spring is with us again. Thus time revolves, the passing hour that steals the light brings a message: immortality, for us, is impossible. Warm winds will be followed by cold. (IV, 7)

Usually, we call “real” the things that exist now, in the present. Not those which existed once, or may do so in the future. We say that things in the past or the future “were” real or “will be” real, but we do not say they “are” real. Philosophers call “presentism” the idea that only the present is real, that the past and the future are not—and that reality evolves from one present to another, successive one. This way of thinking no longer works, however, if the “present” is not defined globally, if it is defined only in our vicinity, in an approximate way. If the present that is far away from here is not defined, what “is real” in the universe? Diagrams such as the ones that we have seen in previous chapters depict an entire evolution of spacetime with a single image: they do not represent a single time but all times together:

Let’s return to the question with which we began: What “is real”? What “exists”? The answer is that this is a badly put question, signifying everything and nothing. Because the adjective “real” is ambiguous; it has a thousand meanings. The verb “to exist” has even more. To the question “Does a puppet whose nose grows when it lies exist?” it is possible to reply: “Of course it exists! It’s Pinocchio!”; or: “No, it doesn’t, it’s only part of a fantasy dreamed up by Carlo Collodi.” Both answers are correct, because they are using different meanings of the verb “exist.” There are so many different usages of the verb, different ways in which we can say that a thing exists: a law, a stone, a nation, a war, a character in a play, the god (or gods) of a religion to which we do not belong, the God of the religion to which we do belong, a great love, a number. . . . Each one of these entities “exists” and “is real” in a sense different from all the others.

Einstein coins this phrase when his friend Michele Besso dies. Michele has been his dearest friend, the companion of his thinking and discussions since his days at the University of Zurich. The letter in which Einstein writes the phrase is not directed at physicists or philosophers. It is addressed to Michele’s family, and in particular to his sister. The sentences that come before it read: Now he [Michele] has departed from this strange world a little ahead of me. That means nothing. It is not a letter written to pontificate about the structure of the world, it’s a letter written to console a grieving sister. A gentle letter, alluding to the spiritual bond between Michele and Albert. A letter in which Einstein also confronts his own suffering at the loss of his lifelong friend; and in which, evidently, he is thinking about his own approaching death. A deeply emotional letter, in which the illusoriness and the heartrending irrelevance to which he alludes do not refer to time as understood by physicists. They are prompted by the experience of life itself. Fragile, brief, full of illusions. It’s a phrase that speaks of things that lie deeper than the physical nature of time. Einstein died on April 18, 1955, one month and three days after the death of his friend.

The second ingredient on which our identity is based is the same as for the chariot. In the process of reflecting the world, we organize it into entities: we conceive of the world by grouping and segmenting it as best we can in a continuous process that is more or less uniform and stable, the better to interact with it. We group together into a single entity the rocks that we call Mont Blanc, and we think of it as a unified thing. We draw lines over the world, dividing it into sections; we establish boundaries, we approximate the world by breaking it down into pieces. It is the structure of our nervous system that works in this way. It receives sensory stimuli, elaborates information continuously, generating behavior. It does so through networks of neurons, which form flexible dynamic systems that continuously modify themselves, seeking to predict109—as far as possible—the flow of information intake. In order to do this, the networks of neurons evolve by associating more or less stable fixed points of their dynamic with recurring patterns that they find in the incoming information, or—indirectly—in the procedures of elaboration themselves. This is what seems to emerge from the very lively current research on the brain.110 If this is so, then “things,” like “concepts,” are fixed points in the neuronal dynamic, induced by recurring structures of the sensorial input and of the successive elaborations. They mirror a combination of aspects of the world that depends on recurrent...

It’s a rationalistic a posteriori reflection on the first stage of the process in which Descartes had articulated a state of doubt: logic dictates that if someone doubts something, they must have thought about it. And that if they can think, then they must exist. It is substantially a consideration made in the third person, not in the first, however private the process. The starting point for Descartes is the methodical doubt experienced by a refined intellectual, not the basic experience of a subject.)

But there is a third ingredient in the foundation of our identity, and it is probably the essential one—it is the reason this delicate discussion is taking place in a book about time: memory. We are not a collection of independent processes in successive moments. Every moment of our existence is linked by a peculiar triple thread to our past—the most recent and the most distant—by memory. Our present swarms with traces of our past. We are histories of ourselves, narratives. I am not this momentary mass of flesh reclined on the sofa typing the letter a on my laptop; I am my thoughts full of the traces of the phrases that I am writing; I am my mother’s caresses, and the serene kindness with which my father calmly guided me; I am my adolescent travels; I am what my reading has deposited in layers in my mind; I am my loves, my moments of despair, my friendships, what I’ve written, what I’ve heard; the faces engraved on my memory. I am, above all, the one who a minute ago made a cup of tea for himself. The one who a moment ago typed the word “memory” into his computer. The one who just composed the sentence that I am now completing. If all this disappeared, would I still exist? I am this long, ongoing novel. My life consists of it.

Augustine’s exposition of the idea is quite beautiful. It is based on our experience of music. When we listen to a hymn, the meaning of a sound is given by the ones that come before and after it. Music can occur only in time, but if we are always in the present moment, how is it possible to hear it? It is possible, Augustine observes, because our consciousness is based on memory and on anticipation. A hymn, a song, is in some way present in our minds in a unified form, held together by something—by that which we take time to be. And hence this is what time is: it is entirely in the present, in our minds, as memory and as anticipation.

Proust finds a limitless space and an incredible throng of details, fragrances, considerations, sensations, reflections, re-elaborations, colors, objects, names, looks, emotions . . . all within the folds of the brain between the ears of Marcel. This is the flow of time familiar from our experience: it is inside there that it nestles, inside of us, in the utterly crucial presence of traces of the past in our neurons.

The Buddha summed this up in a few maxims that millions of human beings have adopted as the foundations of their lives: birth is suffering, decline is suffering, illness is suffering, death is suffering, union with that which we hate is suffering, separation from that which we love is suffering, failure to obtain what we desire is suffering.124 It’s suffering because we must lose what we have and are attached to. Because everything that begins must end. What causes us to suffer is not in the past or the future: it is here, now, in our memory, in our expectations. We long for timelessness, we endure the passing of time: we suffer time. Time is suffering.

Perhaps God has many more seasons in store for us— or perhaps the last is to be this winter that guides back the waves of the Tyrrhenian Sea to break against the rough pumice cliffs. You must be wise. Pour the wine and enclose in this brief circle your long-cherished hope. (I, 11)

In the third part of the great Indian epic the Mahābhārata, a powerful spirit named Yaksa asks the oldest and wisest of the Pandava, Yudhistira, what is the greatest of all mysteries. The answer given resounds across millennia: “Every day countless people die, and yet those who remain live as if they were immortals.”128

Our fear of death seems to me to be an error of evolution. Many animals react instinctively with terror and flight at the approach of a predator. It is a healthy reaction, one that allows them to escape from danger. But it’s a terror that lasts an instant, not something that remains with them constantly. Natural selection has produced these big apes with hypertrophic frontal lobes, with an exaggerated ability to predict the future. It’s a prerogative that’s certainly useful but one that has placed before us a vision of our inevitable death, and this triggers the instinct of terror and flight. Basically, I believe that the fear of death is the result of an accidental and clumsy interference between two distinct evolutionary pressures—the product of bad automatic connections in our brain rather than something that has any use or meaning. Everything has a limited duration, even the human race itself. (“The Earth has lost its youthfulness; it is past, like a happy dream. Now every day brings us closer to destruction, to desert,” as Vyasa has it in the Mahābhārata.129) Fearing the transition, being afraid of death, is like being afraid of reality itself; like being afraid of the sun. Whatever for?

So what really drives us? It is difficult to say. Perhaps we do not know entirely. We recognize motivations in ourselves. We give names to these motivations, and we have many of them. We believe that we share some of them with other animals; others only with humankind—and others still with smaller groups to which we see ourselves as belonging. Hunger and thirst, curiosity, the need for companionship, the desire to love, being in love, the pursuit of happiness, the need to fight for a position in the world, the desire to be appreciated, recognized, and loved; loyalty, honor, the love of God, the thirst for justice and liberty, the desire for knowledge . . .

Carlo Rovelli, an Italian theoretical physicist, is the head of the quantum gravity group at the Centre de Physique Théorique of Aix-Marseille Université. He is one of the founders of the loop quantum gravity theory and author of the international bestseller Seven Brief Lessons on Physics, Reality Is Not What It Seems, and The Order of Time. Rovelli lives in Marseille, France.