Carlo Rovelli Time Quotes

In his youth Albert Einstein spent a year loafing aimlessly. You don't get anywhere by not 'wasting' time- something, unfortunately, that the parents of teenagers tend frequently to forget.

This is time for us. Memory. A nostalgia. The pain of absence. But it isn't absence that causes sorrow. It is affection and love. Without affection, without love, such absences would cause us no pain. For this reason, even the pain caused by absence is in the end something good and even beautiful. Because it feeds on that which gives meaning to life.

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.

The atoms of our body, as well, flow in and away from us. We, like waves and like all objects, are a flux of events; we are processes, for a brief time monotonous

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.

The ability to understand something before it’s observed is at the heart of scientific thinking.

If I ask whether two events—one on Earth and the other on Proxima b—are happening “at the same moment,” the correct answer would be: “It’s a question that doesn’t make sense, because there is no such thing as ‘the same moment’ definable in the universe.” The “present of the universe” is meaningless.

All of the sons of Adam are part of one single body, They are of the same essence. When time afflicts us with pain In one part of that body All the other parts feel it too. If you fail to feel the pain of others You do not deserve the name of man.

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.

There are frontiers where we are learning, and our desire for knowledge burns. They are in the most minute reaches of the fabric of space, at the origins of the cosmos, in the nature of time, in the phenomenon of black holes, and in the workings of our own thought processes. Here, on the edge of what we know, in contact with the ocean of the unknown, shines the mystery and the beauty of the world. And it’s breathtaking.

It is entropy, not energy, that keeps stones on the ground and the world turning.

But it isn’t absence that causes sorrow. It is affection and love. Without affection, without love, such absences would cause us no pain. For this reason, even the pain caused by absence is, in the end, something good and even beautiful, because it feeds on that which gives meaning to life.

Nature is our home, and in nature we are at home. This strange, multicoloured and astonishing world which we explore – where space is granular, time does not exist, and things are nowhere – is not something that estranges us from our true selves, for this is only what our natural curiosity reveals to us about the place of our dwelling. About the stuff of which we ourselves are made.

We inhabit time as fish live in water. Our being is being in time.

Before Newton, time for humanity was the way of counting how things changed. Before him, no one had thought it possible that a time independent of things could exist. Don't take your intuitions and ideas to be 'natural': they are often the products of the ideas of audacious thinkers who came before us.

Temporality is profoundly linked to blurring. The blurring is due to the fact that we are ignorant of the microscopic details of the world. The time of physics is, ultimately, the expression of our ignorance of the world. Time is ignorance.

Things change only in relation to one another. At a fundamental level, there is no 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.

This is the disconcerting conclusion that emerges from Boltzmann’s work: the difference between the past and the future refers only to our own blurred vision of the world. It’s a conclusion that leaves us flabbergasted: is it really possible that a perception so vivid, basic, existential—my perception of the passage of time—depends on the fact that I cannot apprehend the world in all of its minute detail? On a kind of distortion that’s produced by myopia? Is it true that, if I could see exactly and take into consideration the actual dance of millions of molecules, then the future would be “just like” the past?

Past and future are different from each other. Cause precedes effect. Pain comes after a wound, not before it. The glass shatters into a thousand pieces, and the pieces do not re-form into a glass. We cannot change the past; we can have regrets, remorse, memories. The future instead is uncertainty, desire, anxiety, open space, destiny, perhaps. We can live toward it, shape it, because it does not yet exist. Everything is still possible... Time is not a line with two equal directions: it is an arrow with different extremities.

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.

As human beings, we live by emotions and thoughts. We exchange them when we are in the same place at the same time, talking to each other, looking into each other's eyes, brushing against each other's skin. We are nourished by this network of encounters and exchanges. But, in reality, we do not need to be in the same place and time to have such exchanges. Thoughts and emotions that create bonds of attachment between us have no difficulty in crossing seas and decades, sometimes even centuries, tied to thin sheets of paper or dancing between the microchips of a computer. We are part of a network that goes far beyond the few days of our lives and the few square meters that we tread. This book is also a part of that weave...

I believe that our species will not last long. It does not seem to be made of the stuff that has allowed the turtle, for example, to continue to exist more or less unchanged for hundreds of millions of years, for hundreds of times longer, that is, than we have even been in existence. We belong to a short-lived genus of species. All of our cousins are already extinct. What's more, we do damage. The brutal climate and environmental changes that we have triggered are unlikely to spare us.

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)

Things” in themselves are only events that for a while are monotonous

I remember a little girl... But how can that be... Once I was that little Resi, and then one day I became an old woman? ...If God wills it so, why allow me to see it? Why doesn't he hide it from me? Everything is a mystery, such a deep mystery... I feel the fragility of things in time. From the bottom of my heart, I feel we should cling to nothing. Everything slips through our fingers. All that we seek to hold on to dissolves. Everything vanishes, like mist and dreams... Time is a strange thing. When we don't need it, it is nothing. Then, suddenly, there is nothing else. It is everywhere around us. Also within us. It seeps into our faces. It seeps into the mirror, runs through my temples... Between you and I it runs silently, like an hourglass. Oh, Quin Quin. Sometimes I feel it flowing inexorably. Sometimes I get up in the middle of the night and stop all the clocks...

How long is forever?” asks Alice. “Sometimes, just one second,” replies the White Rabbit. There are dreams lasting an instant in which everything seems frozen for an eternity.

The world, particles, light, energy, space, and time—all of this is nothing but the manifestation of a single type of entity: covariant quantum fields.

Children grow up and discover that the world is not as it seemed from within the four walls of their homes. Humankind as a whole does the same.

For everything that moves, time passes more slowly.

I do not fear death. I fear suffering. And I fear old age, though less so now that I am witnessing the tranquil and pleasant old age of my father. I am afraid of frailty, and of the absence of love. But death does not alarm me. It did not scare me when I was young, and I thought at the time that this was because it was such a remote prospect. But now, at sixty, the fear has yet to arrive. I love life, but life is also struggle, suffering, pain. I think of death as akin to a well-earned rest.

A moving object therefore experiences a shorter duration than a stationary one: a watch marks fewer seconds, a plant grows more slowly, a young man dreams less. For a moving object, time contracts.

We are the products of a long selection process of chemical, biological, and cultural structures that at different levels have interacted for a long time in order to shape the funny process that we are.

The entire evolution of science would suggest that the best grammar for thinking about the world is that of change, not of permanence. Not of being, but of becoming.

The world is not a collection of things, it is a collection of events.

Newton’s mechanics, Maxwell’s equations, quantum mechanics, and so on, tell us how events happen, not how things are.

Every day countless people die, and yet those who remain live as if they were immortals.

Time, as Aristotle suggested, is the measure of change;

Scientific answers are not definitive: they are, almost by definition, the best ones that we have at any given time. Consider

The notion of “the present” refers to things that are close to us, not to anything that is far away. Our “present” does not extend throughout the universe. It is like a bubble around us.

The heat of black holes is like the Rosetta stone of physics, written in a combination of three languages- quantum, gravitational, and thermodynamic- still awaiting decipherment in order to reveal the true nature of time.

A precious miracle that the infinite play of combinations has unlocked for us, allowing us to exist. We may smile now. We can go back to serenely immersing ourselves in time - in our finite time - to savoring the clear intensity of every fleeting and cherished moment of the brief circle of our existence.

If things fall, it is due to this slowing down of time. Where time passes uniformly, in interplanetary space, things do not fall. They float, without falling. Here on the surface of our planet, on the other hand, the movement of things inclines naturally toward where time passes more slowly, as when we run down the beach into the sea and the resistance of the water on our legs makes us fall headfirst into the waves. Things fall downward because, down there, time is slowed by the Earth.

Those who defend this way of thinking about reality—eternalism—frequently cite Einstein, who in a famous letter writes: For people like us who believe in physics the distinction between past, present and future is only a stubbornly persistent illusion.

An elementary structure of the world is emerging, generated by a swarm of quantum events, where time and space do not exist. Quantum fields draw together space, time, matter, and light, exchanging information between one event and another. Reality is a network of granular events; the dynamic that connects them is probabilistic; between one event and another, space, time, matter, and energy melt into a cloud of probability.

Time is information we don't have. Time is our ignorance.

Our “present” does not extend throughout the universe. It is like a bubble around us.

Physics does not describe how things evolve "in time" but how things evolve in their own times, and how "times" evolve relative to each other.

As human beings, we live by emotions and thoughts. We exchange them when we are in the same place at the same time, talking to each other, looking into each other’s eyes, brushing against each other’s skin. We are nourished by this network of encounters and exchanges. But, in reality, we do not need to be in the same place and time to have such exchanges. Thoughts and emotions that create bonds of attachment between us have no difficulty in crossing seas and decades, sometimes even centuries, tied to thin sheets of paper or dancing between the microchips of a computer. We are part of a network that goes far beyond the few days of our lives and the few square meters that we tread. This book is also a part of that weave. . .

None of the pieces that time has lost (singularity, direction, independence, the present, continuity) puts into question the fact that the world is a network of events. On the one hand, there was time, with its many determinations; on the other, the simple fact that nothing is: things happen.

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.

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.

Time opens up our limited access to the world. Time, then, is the form in which we beings, whose brains are made up essentially of memory and foresight, interact with the world: it is the source of identity.

And it seems to me that life, this brief life, is nothing other than this: the incessant cry of these emotions that drive us, that we sometimes attempt to channel in the name of a god, a political faith, in a ritual that reassures us that, fundamentally, everything is in order, in a great and boundless love—and the cry is beautiful. Sometimes it is a cry of pain. Sometimes it is a song.

The entropy of a system depends explicitly on blurring. It depends on what I do not register, because it depends on the number of indistinguishable configurations. The same microscopic configuration may be of high entropy with regard to one blurring and of low in relation to another.

Change is ubiquitous. Only: elementary processes cannot be ordered along a common succession of instants. 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 neighbours, following its own rhythm. The passing of time is intrinsic to the world, it is born of the world itself, out of the relations between quantum events which are the world and which themselves generate their own time.

Fearing the transition, being afraid of death, is like being afraid of reality itself; like being afraid of the sun. Whatever for?

Time passes more slowly for the one who keeps moving.

Don’t take your intuitions and ideas to be “natural”: they are often the products of the ideas of audacious thinkers who came before us.

The mystery of time has always troubled us, stirring deep emotions. So deep as to have nourished philosophies and religions.

But the world is a quantum one, and gelatinous spacetime is also an approximation.

Wonder is the source of our desire for knowledge,1 and the discovery that time is not what we thought it was opens up a thousand questions.

There is no preferred direction of time without heat.

But there are not just two times. Times are legion: a different one for every point in space. There is not one single time; there is a vast multitude of them.

The events of the world do not form an orderly queue, like the English. They crowd around chaotically, like Italians.

we understand the world by studying change, not by studying things.

Our fear of death seems to me to be an error of evolution.

Abstract thought can anticipate by centuries hypotheses that find a use—or confirmation—in scientific inquiry.

Aristotle is the first we are aware of to have asked himself the question “What is time?,” and he came to the following conclusion: time is the measurement of change.

We long for timelessness, we endure the passing of time: we suffer time. Time is suffering.

Scientists are not immune from talking nonsense.

For a hypothetically supersensible being, there would be no “flowing” of time: the universe would be a single block of past, present, and future.

You don’t get anywhere by not ‘wasting’ time – something, unfortunately, which the parents of teenagers tend frequently to forget.

I chose as my supervisor a professor who allowed me to continue to study what I wanted.

Time is our ignorance.

Let’s begin with a simple fact: time passes faster in the mountains than it does at sea level.

A science that closes its ears to philosophy fades into superficiality; a philosophy that pays no attention to the scientific knowledge of its time is obtuse and sterile.

But this does not imply that we cannot or must not trust our own thinking. To the contrary: our own thinking is the best tool we have for finding our way in this world. Recognizing its limitations does not imply that it is not something to rely upon. If instead we trust in “tradition” more than in our own thinking, for instance, we are only relying on something even more primitive and uncertain than our own thinking. “Tradition” is nothing else than the codified thinking of human beings who lived at times when ignorance was even greater than ours.

Such is time, and because of this we are fascinated and troubled by it in equal measure-and perhaps because of this, too, dear reader, my brother, my sister, you are holding this book in your hands. Because it is nothing but a fleeting structure of the world, an ephemeral fluctuation in the happening of the world, that which is capable of giving rise to what we are: beings made of time. That to which we owe our being, giving us the precious gift of our very existence, allowing us to create the fleeting illusion of permanence that is the origin of all our suffering.

It is in order to escape this anxiety that we have imagined the existence of “eternity,” a strange world outside of time that we would like to be inhabited by gods, by a God, or by immortal souls.

Things are transformed one into another according to necessity, and render justice to one another according to the order of time. “According to the order of time” (κατὰ τὴν τοῦ χρόνου τάξιν). From

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.

Perhaps the rivers of ink that have been expended discussing the nature of the “continuous” over the centuries, from Aristotle to Heidegger, have been wasted. Continuity is only a mathematical technique for approximating very finely grained things. The world is subtly discrete, not continuous. The good Lord has not drawn the world with continuous lines: with a light hand, he has sketched it in dots, like the painter Georges Seurat.

The entropy of the world in the far past appears very low to us. But this might not reflect the exact state of the world: it might regard the subset of the world' s variables with which we, as physical systems, have interacted. It is with respect to the dramatic blurring produced by our interactions with the world, caused by the small set of macroscopic variables in terms of which we describe the world, that the entropy of the universe was low.

The world is in a ceaseless process of change. The entire evolution of science would suggest that the best grammar for thinking about the world is that of change not of permanence, not of being but of becoming. 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 undergoes continual transformation that is not permanent in time.

It follows that the notion of certain configurations being more particular than others (twenty-six red cards followed by twenty-six black, for example) makes sense only if I limit myself to noticing only certain aspects of the cards (in this case, the colors). If I distinguish between all the cards, the configurations are all equivalent: none of them is more or less particular than others.18 The notion of “particularity” is born only at the moment we begin to see the universe in a blurred and approximate way.

There is no “truer” time; there are two times and they change relative to each other. Neither is truer than the other. But there are not just two times. Times are legion: a different one for every point in space. There is not one single time; there is a vast multitude of them.

A science that closes its ears to philosophy fades into superficiality; a philosophy that pays no attention to the scientific knowledge of its time is obtuse and sterile. It betrays its own deepest roots, which are evident in the etymology of philosophy: the love of knowledge.

(Even the attribution of the idea to Descartes seems wrong to me: Cogito ergo sum is not the first step in the Cartesian reconstruction, it is the second. The first is Dubito ergo cogito. The starting point of the reconstruction is not a hypothetical a priori that is immediate to the experience of existing as a subject. 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.

Physics opens windows through which we see far into the distance. What we see does not cease to astonish us. We realize that we are full of prejudices and that our intuitive image of the world is partial, parochial, inadequate. Earth is not flat; it is not stationary. The world continues to change before our eyes as we gradually see it more extensively and more clearly. If we try to put together what we have learned in the twentieth century about the physical world, the clues point toward something profoundly different from our instinctive understanding of matter, space, and time.

Is the daily spectacle of a revolving universe “illusory”? No, it is real, but it doesn’t involve the cosmos alone. It involves our relation with the sun and the stars. We understand it by asking ourselves how we move. Cosmic movement emerges from the relation between the cosmos and ourselves.

But it is not only space that curves: time does too. Einstein predicts that time on Earth passes more quickly at higher altitude, and more slowly at lower altitude. This is measured, and also proves to be the case. Today we have extremely precise clocks, in many laboratories, and it is possible to measure this strange effect even for a difference in altitude of just a few centimeters. Place a watch on the floor and another on a table: the one on the floor registers less passing of time than the one on the table. Why? Because time is not universal and fixed; it is something that expands and shrinks, according to the vicinity of masses: Earth, like all masses, distorts spacetime, slowing down time in its vicinity. Only slightly—but two twins who have lived respectively at sea level and in the mountains will find that, when they meet up again, one will have aged more than the other

We can see the world without time: we can perceive with the mind’s eye the profound structure of the world where time as we know it no longer exists—like the Fool on the Hill who sees the Earth turn when he sees the setting sun. And we begin to see that we are time. We are this space, this clearing opened by the traces of memory inside the connections between our neurons. We are memory. We are nostalgia. We are longing for a future that will not come. The clearing that is opened up in this way, by memory and by anticipation, is time: a source of anguish sometimes, but in the end a tremendous gift.

[S]ong, as Augustine observed, is the awareness of time. It is time. It is the hymn of the Vedas that is itself the flowering of time. In the Benedictus of Beethoven’s Missa Solemnis, the song of the violin is pure beauty, pure desperation, pure joy. We are suspended, holding our breath, feeling mysteriously that this must be the source of meaning. That this is the source of time. Then the song fades and ceases. “The silver thread is broken, the golden bowl is shattered, the amphora at the fountain breaks, the bucket falls into the well, the earth returns to dust.” And it is fine like this. We can close our eyes, rest. This all seems fair and beautiful to me. This is time.

In the elementary equations of the world,13 the arrow of time appears only where there is heat.* The link between time and heat is therefore fundamental: every time a difference is manifested between the past and the future, heat is involved. In every sequence of events that becomes absurd if projected backward, there is something that is heating up.

In The Order of Time, physicist and author Carlo Rovelli sums up this dynamic beautifully: "It isn't absence that causes sorrow. It is affection and love. Without affection, without love, such absences would cause us no pain. For this reason, even the pain caused by absence is, in the end, something good and even beautiful, because it feeds on that which gives meaning to life.

There is no secure, unquestionable basis upon which we can find knowledge. Each time we have deluded ourselves into believing we have discovered the definitive theory of the world, we have played fools. Similarly, each time we have thought we have found the final secret to certainty, the secure point of departure for knowledge, we have later been forced to realize we were wrong.

Empowered by new conceptual tools and by mathematics, Einstein writes the equations which describe Democritus’s void and finds for its ‘certain physics’ a colourful and amazing world where universes explode, space collapses into bottomless holes, time slows down in the vicinity of a planet, and the boundless expanses of interstellar space ripple and sway like the surface of the sea

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.

Hold on tight, because we are about to take off. “NOW” MEANS NOTHING What is happening “now” in a distant place? Imagine, for example, that your sister has gone to Proxima b, the recently discovered planet that orbits a star at approximately four light-years’ distance from us. What is your sister doing now on Proxima b? The only correct answer is that the question makes no sense. It is like asking “What is here, in Beijing?” when we are in Venice.

In the elementary equations of the world,13 the arrow of time appears only where there is heat.* The link between time and heat is therefore fundamental: every time a difference is manifested between the past and the future, heat is involved. In every sequence of events that becomes absurd if projected backward, there is something that is heating up. If I watch a film that shows a ball rolling, I cannot tell if the film is being projected correctly or in reverse. But if the ball stops, I know that it is being run properly; run backward, it would show an implausible event: a ball starting to move by itself. The ball’s slowing down and coming to rest are due to friction, and friction produces heat. Only where there is heat is there a distinction between past and future. Thoughts, for instance, unfold from the past to the future, not vice versa—and, in fact, thinking produces heat in our heads. . . .

Too often scientists sell hypothetical theories to the large public, as if they were established theories. I have seen this often done, for instance, with string theory. I think this is a great mistake, because it questions the credibility itself of science. We scientists live out of public money and it is our duty to be fully honest in reporting what we know and what we do not know. We are paid to dream, but we must not sell our dreams for established realities.

If LISA is launched, it should be able to see not only the gravitational waves produced by stars and black holes but also the diffuse background of primordial gravitational waves generated at a time close to the Big Bang. These waves should tell us about the quantum bounce. In the subtle irregularities of space, we should be able to find traces of events that took place fourteen billion years ago, at the origin of our universe, and confirm our deductions on the nature of space and time.

I believe that our species will not last long. It does not seem to be made of the stuff that has allowed the turtle, for example, to continue to exist more or less unchanged for hundreds of millions of years, for hundreds of times longer, that is, than we have even been in existence. We belong to a short-lived genus of species. All of our cousins are already extinct. What’s more, we do damage. The brutal climate and environmental changes that we have triggered are unlikely to spare us. For Earth they may turn out to be a small irrelevant blip, but I do not think that we will outlast them unscathed—especially since public and political opinion prefers to ignore the dangers that we are running, hiding our heads in the sand. We are perhaps the only species on Earth to be conscious of the inevitability of our individual mortality. I fear that soon we shall also have to become the only species that will knowingly watch the coming of its own collective demise, or at least the demise of its civilization.

A mechanism in the box opens the small window on the right for an instant, allowing a photon to escape at some precise time. By weighing the box, it is possible to deduce the energy of the released photon. Einstein hoped that thus would create difficulties for quantum mechanics, which predicts that time and energy cannot both be precisely determined. Bohr replied, mistakenly, that the way out of the difficulty required Einstein's general relativity, and Einstein, mistakenly, accepted Bohr's reply. The correct response to Einstein, that Bohr was unable to find but is clear today, is that the position of the escaping photon and the weight of the box remain tied to each other ("correlated") even if the photon is already far away.

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. As before, the two friends experience different durations: the one who moves ages less quickly, his watch marks less time passing; he has less time in which to think; the plant he is carrying takes longer to germinate, and so on. For everything that moves, time passes more slowly.

The entropy of the world in the far past appears very low to us. But this might not reflect the exact state of the world: it might regard the subset of the world’s variables with which we, as physical systems, have interacted. It is with respect to the dramatic blurring produced by our interactions with the world, caused by the small set of macroscopic variables in terms of which we describe the world, that the entropy of the universe was low. This, which is a fact, opens up the possibility that it wasn’t the universe that was in a very particular configuration in the past. Perhaps instead it is us, and our interactions with the universe, that are particular. We are the ones who determine a particular macroscopic description. The initial low entropy of the universe, and hence the arrow of time, may be more down to us than to the universe itself. This is the basic idea.

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.

And it seems to me that life, this brief life, is nothing other than this: the incessant cry of these emotions that drive us, that we sometimes attempt to channel in the name of a god, a political faith, in a ritual that reassures us that, fundamentally, everything is in order, in a great and boundless love—and the cry is beautiful. Sometimes it is a cry of pain. Sometimes it is a song. And song, as Augustine observed, is the awareness of time. It is time. It is the hymn of the Vedas that is itself the flowering of time.131 In the Benedictus of Beethoven’s Missa Solemnis, the song of the violin is pure beauty, pure desperation, pure joy. We are suspended, holding our breath, feeling mysteriously that this must be the source of meaning. That this is the source of time. Then the song fades and ceases. “The silver thread is broken, the golden bowl is shattered, the amphora at the fountain breaks, the bucket falls into the well, the earth returns to dust.”132 And it is fine like this. We can close our eyes, rest. This all seems fair and beautiful to me. This is time.

The idea of thermal time reverses this observation. That is to say, instead of inquiring how time produces dissipation in heat, it asks how heat produces time. Thanks to Boltzmann, we know that the notion of heat comes from the fact that we interact with averages. The idea of thermal time is that the notion of time, as well, comes from the fact that we interact only with averages of many variables.* As long as we have a complete description of a system, all the variables of the system are on the same footing; none of them act as a time variable. That is to say, none is correlated to irreversible phenomena. But as soon as we describe the system by means of averages of many variables, we have a preferred variable that functions like common time. A time along which heat dissipates. The time of our everyday experience. Hence time is not a fundamental constituent of the world, but it appears because the world is immense, and we are small systems within the world, interacting only with macroscopic variables that average among innumerable small, microscopic variables. We, in our everyday lives, never see a single elementary particle, or a single quantum of space. We see stones, mountains, the faces of our friends—and each of these things we see is formed by myriads of elementary components. We are always correlated with averages. Averages behave like averages: they disperse heat and, intrinsically, generate time.

first theory of relativity (known today as “special relativity”), the theory that elucidates how time does not pass identically for everyone:

The expanded present is the set of events that are neither past nor future: it exists, just as there are human beings who are neither our descendants nor our forebears.

If the present has no meaning, then what “exists” in the universe? Is not what “exists” precisely what is here “in the present”?

Even the distinction between present, past, and future thus becomes fluctuating, indeterminate. Just as a particle may be diffused in space, so, too, the differences between past and future may fluctuate: an event may be both before and after another one.

If by “time” we mean nothing more than happening, then everything is time. There is only that which exists in time.

As human beings, we live by emotions and thoughts. We exchange them when we are in the same place at the same time, talking to each other, looking into each other’s eyes, brushing against each other’s skin. We are nourished by this network of encounters and exchanges. But, in reality, we do not need to be in the same place and time to have such exchanges. Thoughts and emotions that create bonds of attachment between us have no difficulty in crossing seas and decades, sometimes even centuries, tied to thin sheets of paper or dancing between the microchips of a computer. We are part of a network that goes far beyond the few days of our lives and the few square meters that we tread.

We often say that causes precede effects and yet, in the elementary grammar of things, there is no distinction between “cause” and “effect.

NOW” MEANS NOTHING

WHAT HAPPENS WHEN NOTHING HAPPENS?

If more gently than Orpheus who moved even the trees you were to pluck the zither the life-blood would not return to the vain shadow . . . Harsh fate, but its burden becomes lighter to bear, since everything that attempts to turn back is impossible. (I, 24) WHERE DOES THE ETERNAL CURRENT COME FROM?

For the same reason that apples grow in northern Europe, where people drink cider, and grapes grow in the south, where people drink wine; or that I was born where people happen to speak my native language; or that the sun which warms us is at the right distance from us—not too close and not too far away. In all these cases, the “strange” coincidence arises from confusing the causal relations: it isn’t that apples grow where people drink cider, it is that people drink cider where apples grow. Put this way, there is no longer anything strange about it.

Bertrand Russell noted this in a famous article, writing emphatically that “The law of causality . . . is a relic of a bygone age, surviving, like the monarchy, only because it is erroneously supposed to do no harm.

Happy and master of himself is the man who for every day of his life can say: “Today I have lived; tomorrow if God extends for us a horizon of dark clouds or designs a morning of limpid light, he will not change our poor past he will do nothing without the memory of events that the fleeting hour will have assigned to us.

Things are transformed one into another according to necessity, and render justice to one another according to the order of time.

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

The nature of time is perhaps the greatest remaining mystery. Curious threads connect it to those other great open mysteries: the nature of mind, the origin of the universe, the fate of black holes, the very functioning of life on Earth. Something essential continues to draw us back to the nature of time.

Why do we remember the past and not the future? Do we exist in time, or does time exist in us? What does it really mean to say that time “passes”? What ties time to our nature as persons, to our subjectivity? What am I listening to when I listen to the passing of time?

Dances of love intertwine such graceful girls lit by the moon on these clear nights. (I, 4) THE SLOWING DOWN OF TIME

Perhaps poetry is another of science's deepest roots: the capacity to see beyond the visible.

Thinking of the world as a collection of events, of processes, is the way that allows us to better grasp, comprehend, and describe it.

La capacidad de comprender antes de ver constituye el corazón del pensamiento científico.

The proposal is not well received, because people are attached to local time. In 1883, a compromise is reached with the idea of dividing the world into time zones, thereby standardizing time only within each zone. In this way, the discrepancy between twelve on the clock and local midday is limited to a maximum of about thirty minutes. The proposal is gradually accepted by the rest of the world and clocks begin to be synchronized between different cities.

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.

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)

It is hard to take in the idea that an electron behaves in such a bizarre way. It is even more difficult to digest that this is also the way time and space behave.

This may seem like an abstruse mental problem. But modern physics has made it into a burning issue, since special relativity has shown that the notion of the “present” is also subjective. Physicists and philosophers have come to the conclusion that the idea of a present that is common to the whole universe is an illusion and that the universal “flow” of time is a generalization that doesn’t work. When his great Italian friend Michele Besso died, Einstein wrote a moving letter to Michele’s sister: “Michele has left this strange world a little before me. This means nothing. People like us, who believe in physics, know that the distinction made between past, present and future is nothing more than a persistent, stubborn illusion.

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.

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.

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.

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.)

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.

There is no single time: there is a different duration for every trajectory; and time passes at different rhythms according to place and speed. It is not directional; the difference between past and future does not exist in the elementary euqations of the world; its oritentation is merely a contigent aspect that appears when we look at things and neglect the details. In this blurred view, the past of the universe was in a curioysly “particular” state. The notion of the “present” does not work; in the vast universe there is nothing that we can resonably call “present”. The substratum that determines the duration of time is not an independent entity, different from the others that make up the world; it is an aspect of a dynamic field. It jumps, fluactuates, materializies only by interacting, and is not to be found beneath a minimum scale.

a meaning determined by where, how, when, and by whom

So black holes emit heat, like a stove, and Hawking computed their temperature. Radiated heat carries away energy. As it loses energy, the black hole gradually loses mass (mass is energy), becoming ever lighter and smaller. Its horizon shrinks. In the jargon we say that the black hole “evaporates.” Heat emission is the most characteristic of the irreversible processes: the processes that occur in one time direction and cannot be reversed. A stove emits heat and warms a cold room. Have you ever seen the walls of a cold room emit heat and heat up a warm stove? When heat is produced, the process is irreversible. In fact, whenever the process is irreversible, heat is produced (or something

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.

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.

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.

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.

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)

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.

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.

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 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.

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.

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.

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:

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 structures of the world and on their relevance in their interactions with us. This is what a chariot consists of. Hume would have been pleased to know about these developments in our understanding of the brain.

time passes faster in the mountains than it does at sea level.

We suddenly remember that it's not the sun that's moving, but the Earth that's spinning and we see with the unhinged eye of the mind our entire planet, and ourselves with it, rotating backwards, away from the sun. We are seeing with "mad eyes" like those of Paul McCartney's Fool on the Hill. The crazed vision that sometimes sees further than our blurry customary eyesight.

Within the reflections in a glass of water, there is an analogous tumultuous life made up of the activities of a myriad of molecules. Many more than there are living beings on Earth.

I am this long ongoing novel. My life consists of it. It is memory that solders together the processes scattered across time of which we are made. In this sense, we exist in time. It is for this reason that I am the same person today as I was yesterday. To understand ourselves means to reflect on time. But to understand time, we need to reflect on ourselves.

The possibility of predicting something in the future obviously improves our chances of survival, and consequently, evolution has selected the neural structures that allow it. We are the result of this selection. This being between past and future events is central to our mental structure. This, for us, is the flow of time.

This is the flow of time familiar from our experience. It is inside there that it nestles. Inside of us. The utterly crucial presence of traces of the past in our neurons. Proust could not be more explicit on this matter. Writing in the first book, "Reality is formed only by memory" and memory in its turn is a collection of traces-an indirect product of the disordering of the world.

Time is a strange thing. When we don't need it, it is nothing. Then suddenly, there is nothing else. It is everywhere around us. Also, within us. It seeps into our faces. It seeps into the mirror, runs through my temples. Between you and I it runs silently like an hourglass.

But it is still not enough to allow us to explain ourselves clearly to ourselves. We're not even clear about what it means to understand. We see the world, and we describe it. We give it an order. We know little of the actual relation between what we see of the world and the world itself. We know that we are myopic-we barely see a tiny window of the vast electromagnetic spectrum emitted by things. We do not see the atomic structure of matter nor the curvature of space. We see a coherent world that we extrapolate from our interaction with the universe, organized in simplistic terms that our devastatingly stupid brain is capable of handling. We think of the world in terms of stones, mountains, clouds and people and this is the world for us. About the world independent of us, we know a good deal without knowing how much this good deal is.

Our thinking is prey to its own weakness. But even more so, to its own grammar. It takes only a few centuries for the world to change from angels, devils and witches, to atoms and electromagnetic waves. It takes only a few grams of mushrooms for the whole of reality to dissolve before our eyes, before reorganizing itself into a surprisingly different form. It only takes the experience of spending time with a friend who has suffered a serious schizophrenic episode, a few weeks with us, struggling to communicate, to realize that delirium is a vast piece of theatrical equipment with the capacity to stage the world. And that it is difficult to find arguments to distinguish it from those great collective deliriums of ours that are the foundations of our social and spiritual life and of our understanding of the world.

What makes it so—that I am Carlo—and that my hair and my nails and my feet are considered part of me, as well as my anger and my dreams, and that I consider myself to be the same Carlo as yesterday, the same as tomorrow; the one who thinks, suffers, and perceives?

The idea that a well-defined now exists throughout the universe is an illusion, an illegitimate extrapolation of our own experience.

ature is our home, and in nature we are at home. This strange, multicoloured and astonishing world which we explore – where space is granular, time does not exist, and things are nowhere – is not something that estranges us from our true selves, for this is only what our natural curiosity reveals to us about the place of our dwelling. About the stuff of which we ourselves are made. 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.

Nature is our home, and in nature we are at home. This strange, multicoloured and astonishing world which we explore – where space is granular, time does not exist, and things are nowhere – is not something that estranges us from our true selves, for this is only what our natural curiosity reveals to us about the place of our dwelling. About the stuff of which we ourselves are made. 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.

Where time passes uniformly, in interplanetary space, things do not fall.

But it is not only space that curves: time does too. Einstein predicts that time on Earth passes more quickly at higher altitude, and more slowly at lower altitude.

For the first time in the history of mankind, an experiment is made. Experimental science begins with Galileo.

Thus, it is possible to measure time by simply counting the oscillations of a pendulum. It seems such an obvious idea, but it took Galileo to find it; it had not occurred to anyone before him. So it goes, with science.

Newton asserts explicitly in his book that we can’t ever measure the true time t, but if we assume that it exists, we can set up an efficient framework to describe nature.

(…) funciona, en cambio, concebir el mundo como una red de eventos: unos más simples, y otros más complejos, que a su vez se pueden descomponer en combinaciones de eventos más simples (…) Una familia no es una cosa: es un conjunto de relaciones, acontecimientos y sentimientos. ¿Y un ser humano? Por supuesto que no es una cosa: es un proceso complejo, en el que como en la nube sobre la montaña entra y sale aire, pero también comida, información, luz, palabras, etc. Un nodo de nodos en una red de relaciones sociales, en una red de procesos químicos, en una red de emociones que se intercambian con el prójimo.

La diferencia entre cosas y eventos es que las cosas permanecen en el tiempo. Los eventos, en cambio, tienen una duración limitada. Un prototipo de “cosa” es una piedra: podemos preguntarnos dónde estará mañana. Mientras que un beso es un “evento”: no tiene sentido preguntarse adónde habrá ido el beso mañana. El mundo está hecho de redes de besos, no de piedras

Times are legion: a different one for every point in space. There is not one single time; there is a vast multitude of them. The time indicated by a particular clock measuring a particular phenomenon is called ‘proper time’ in physics. Every clock has its proper time. Every phenomenon that occurs has its proper time, its own rhythm.

Then, at Miletus, at the beginning of the fifth century before our era, Thales, his pupil Anaximander, Hecataeus and their school find a different way of looking for answers. This immense revolution in thought inaugurates a new mode of knowledge and understanding, and signals the first dawn of scientific thought. The Milesians understand that by shrewdly using observation and reason, rather than searching for answers in fantasy, ancient myths or religion – and, above all, by using critical thought in a discriminating way – it is possible to repeatedly correct our world view, and to discover new aspects of reality which are hidden to the common view. It is possible to discover the new. Perhaps the decisive discovery is that of a different style of thinking, where the disciple is no longer obliged to respect and share the ideas of the master but is free to build on those ideas without being afraid to discard or criticize the part that can be improved. This is a novel middle way, placed between full adherence to a school and generic deprecation of ideas. It is the key to the subsequent development of philosophical and scientific thinking: from this moment onwards, knowledge begins to grow at a vertiginous pace, nourished by past knowledge but at the same time by the possibility of criticism, and therefore of improving knowledge and understanding. The dazzling incipit of Hecataeus’s book of history goes to the heart of this critical thinking, including as it does the awareness of our own fallibility: ‘I wrote things which seem true to me, because the accounts of the Greeks seem to be full of contradictory and ridiculous things.’ According to legend, Heracles descended to Hades from Cape Tenaro. Hecataeus visits Cape Tenaro, and determines that there is in fact no subterranean passage or other access to Hades there – and therefore judges the legend to be false. This marks the dawn of a new era. This new approach to knowledge works quickly and impressively. Within a matter of a few years, Anaximander understands that the Earth floats in the sky and the sky continues beneath the Earth; that rainwater comes from the evaporation of water on Earth; that the variety of substances in the world must be susceptible to being understood in terms of a single, unitary and simple constituent, which he calls apeiron, the indistinct; that the animals and plants evolve and adapt to changes in the environment, and that man must have evolved from other animals. Thus, gradually, was founded the basis of a grammar for understanding the world which is substantially still our own today.

The Singular Universe and the Reality of Time

The future instead is uncertainty, desire, anxiety, open space, destiny, perhaps.

The secret of time lies in this slippage that we feel on our pulse, viscerally, in the enigma of memory, in anxiety about the future. This is what it means to think about time.

This is the only basic law of physics that distinguishes the past from the future.

Thoughts, for instance, unfold from the past to the future, not vice versa—and, in fact, thinking produces heat in our heads. . .

We inhabit time as fish live in water. Our being is being in time. Its solemn music nurtures us, opens the world to us, troubles us, frightens and lulls us. The universe unfolds into the future, dragged by time, and exists according to the order of time.

As vivid as it may appear to us, our experience of the passage of time does not need to reflect a fundamental aspect of reality.

If more gently than Orpheus who moved even the trees you were to pluck the zither the life-blood would not return to the vain shadow . . . Harsh fate, but its burden becomes lighter to bear, since everything that attempts to turn back is impossible. (I, 24)

For now, I will end with the mind-boggling fact that entropy, as Boltzmann fully understood, is nothing other than the number of microscopic states that our blurred vision of the world fails to distinguish.

Proper time” depends not only on where you are and your degree of proximity to masses; it depends also on the speed at which you move.