The Order of Time

by Carlo Rovelli

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

Time has lost its first aspect or layer: its unity. It has a different rhythm in every different place and passes here differently from there.

The difference between past and future, between cause and effect, between memory and hope, between regret and intention . . . in the elementary laws that describe the mechanisms of the world, there is no such difference.

The crucial point here is the difference from what happens with falling bodies: a ball may fall, but it can also come back up, by rebounding, for instance. Heat cannot. This is the only basic law of physics that distinguishes the past from the future.

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.

The growth of entropy is nothing other than the ubiquitous and familiar natural increase of disorder. This is what Boltzmann understood. The difference between past and future does not lie in the elementary laws of motion; it does not reside in the deep grammar of nature. It is the natural disordering that leads to gradually less particular, less special situations.

The notion of “particularity” is born only at the moment we begin to see the universe in a blurred and approximate way.

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.

Time passes more slowly for the one who keeps moving.

“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.

The light takes time to reach you, let’s say a few nanoseconds—a tiny fraction of a second—therefore, you are not quite seeing what she is doing now but what she was doing a few nanoseconds ago. If she is in New York and you phone her from Liverpool, her voice takes a few milliseconds to reach you, so the most you can claim to know is what your sister was up to a few milliseconds ago.

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

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

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

In the nineteenth century, the telegraph arrives, trains become commonplace and fast, and the problem arises of properly synchronizing clocks between one city and another. It is awkward to organize train timetables if each station marks time differently. It is in the United States that the first attempt is made to standardize time.

only a few years passed between the moment at which we agreed to synchronize clocks and the moment at which Einstein realized that it was impossible to do so exactly.

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.

Time is the measure of change:42 if nothing changes, there is no time.

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.

For Newton, between two things there may also be “empty space.” For Aristotle, it is absurd to speak of “empty” space, because space is only the spatial order of things.

both these ways of thinking about space

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. 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.

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.

But it isn’t absence that causes sorrow. It is affection and love. Without affection, without love, such absences would cause us no pain.

From the most minute events to the more complex ones, it is this dance of ever-increasing entropy, nourished by the initial low entropy of the universe, that is the real dance of Shiva, the destroyer.

Our present swarms with traces of our past. We are histories of ourselves, narratives.

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.

When we cannot formulate a problem with precision, it is often not because the problem is profound: it’s because the problem is false.

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

I love life, but life is also struggle, suffering, pain. I think of death as akin to a well-earned rest. The sister of sleep, Bach calls it, in his marvelous cantata BWV 56.

But what drives us is not reflecting on life: it is life itself.

The hypertrophy of our frontal lobes is considerable, and has taken us to the moon, allowed us to discover black holes, and to recognize that we are cousins of ladybugs. But it is still not enough to allow us to explain ourselves clearly to ourselves.

We are 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.

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,

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.