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The Order of Time Summary

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The Order of Time PDF Summary

As Philomena Cunk so eloquently put it once: “What is clocks?

Carlo Rovelli is here to explain that—and so much more.

So that you can finally see:

The Order of Time.

Who Should Read “The Order of Time”? And Why?

Do you think you know what time is? Chances are: you don’t. For a simple reason: nobody really does. Even physicists. 

This one, however—the exceptional Carlo Rovelli—is so great in communicating this lack of knowledge that you’ll feel so much richer by the end of this fairly short, but infinitely rich and poetic book.

Read The Order of Time if you’re curious about how time works, and, moreover, about how scientists think. 

About Carlo Rovelli

Carlo Rovelli is an Italian theoretical physicist, founder of loop quantum gravity theory, and one of Foreign Policy’s 100 most influential global thinkers.

A regular collaborator with several Italian newspapers, Rovelli is one of the great popularizers of science, dubbed “the new Stephen Hawking” by The Sunday Times, and “the poet of quantum physics” by Ireland’s greatest modern novelist, John Banville.

Rovelli’s beautiful Seven Brief Lessons on Physics has been translated into no less than 40 languages and has sold over a million copies worldwide; this one, The Order of Time, was chosen as one of TIME’s Ten Best Nonfiction Books of 2018.

Find out more at http://www.cpt.univ-mrs.fr/~rovelli/

“The Order of Time Summary”

“Reality is often very different from what it seems,” writes Carlo Rovelli in the “Introduction” to The Order of Time, aptly dubbed “Perhaps Time Is the Greatest Mystery.” 

“The Earth,” he goes on, “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.”

Analogously, even though time appears to be uniform, universal flowing, it is anything but: we don’t inhabit it as fish swimming in the water (the water being the time in this metaphor), and it doesn’t drag the universe into the future from the past.

“Time works quite differently from the way it seems to,” says Rovelli, and he wastes no time to completely and utterly blow our minds with what lies behind that sentence.

Let’s go over the highlights.


In the first—and perhaps most interesting—part (especially for novices) of The Order of Time, Carlo Rovelli summarizes what modern physics knows about time. 

“It is like holding a snowflake in your hands,” he poetically notes, “gradually, as you study it, it melts between your fingers and vanishes”: 

We conventionally think of time as something simple and fundamental that flows uniformly, independently from everything else, from the past to the future, measured by clocks and watches. In the course of time, the events of the universe succeed each other in an orderly way: pasts, presents, futures. The past is fixed, the future open… And yet all of this has turned out to be false. One after another, the characteristic features of time have proved to be approximations, mistakes determined by our perspective, just like the flatness of the Earth or the revolving of the sun. 

Hence the title of this part: as we discovered more and more about time, it slowly disintegrated to mean something pretty much counter-intuitive: a complex collection of structures and layers that is neither unified nor independent, and which has neither a direction nor definite value.

Loss of Unity

Let’s start with perhaps the most fundamental aspect of time: it, we believe, passes everywhere at the very same speed.

This is, however, completely wrong: even if you place a clock on the table and compare it, after a few years, with one sitting at the floor, the two will differ. True, the differences would be minuscule, but it is measurable and exists: the clock on the table would always tick faster. 

This, of course, suggests something even bigger.

Namely, what if you are a twin who separates from his brother/sister to live on the mountain, leaving your sibling on the seashore?

Believe it or not, time will move faster for you, and you’ll live longer than your sibling in absolute terms. It is a scientific fact: “time passes faster in the mountains than it does at sea level.”

And it is also one of the things Einstein discovered a century ago: gravity is just a side-effect of large bodies modifying the structure of space-time between them.

Because of this modification, Earth slows down the flow of time, but it does so at different rates: the plains are closer to it, so their time slows more than it does in the mountains.

“If things fall, it is due to this slowing down of time,” writes Rovelli. “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.”


Wait till you hear the rest!

Loss of Direction

Another fundamental time-related thing we experience as pretty much a given is its parts: past, present, and future. 

“Past and future are different from each other,” explains Rovelli. “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, and memories. The future instead is uncertainty, desire, anxiety, open space, destiny, perhaps. We can live toward it, and 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.”

Strangely enough, this too isn’t true: “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.”

Believe it or not, the only law that distinguishes the past from the future is the Second law of thermodynamics, which states that the total entropy of a system can never decrease over time.

In plainer words, if nothing else changes, heat cannot pass from a cold body to a hot one.

In essence, this means that time is fundamentally interrelated with heat: “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.”

Even when you’re thinking: thinking produces heat in your head, and that is the only reason why your thoughts move from the past to the future.

The End of the Present

Now that we’re done with the past and the future, let’s strip time of yet another of its intuitively graspable levels: the present.

Believe it or not, the word “now” means nothing beyond your approximate surroundings: in universal terms, now is a non-existent concept.

Think of it this way: when you’re watching the sunset, the Sun is already set—because it takes its light approximately 8 minutes and 19 seconds to reach our planet, that’s precisely how far back into the past of the sun you’re seeing at your apparent “now.”

Put more plainly, the “now” of the Sun and your “now” are two different moments of time: it’s almost as if you and it exist in two parallel worlds.

What if that actually happens?

What if your sister decides to leave this planet and start life on the planet Proxima B, located about four light years away from the Earth?

What would you see through the telescope at any given moment?

Well, your sister from 4 years ago!

And this is where it gets even stranger: if, during this time she manages to discover some spaceship flying at a speed faster than the speed of light, you might be, in theory, able to both see her on Proxima B, and right around the corner of your street!

“It simply makes no sense to ask which moment in the life of your sister on Proxima B corresponds to now,” writes Rovelli. “It is like asking which football team has won a basketball championship, how much money a swallow has earned, or how much a musical note weighs.”

“There is no special moment on Proxima b that corresponds to what constitutes the present here and now,” he concludes.

Cue: Twilight Zone theme music.

Loss of Independence

The reason why time works so counter-intuitively is rather simple: it is not independent; it is directly related to something we are able to understand a bit better, i.e., space.

Time and space—after Einstein referred to, almost always and correctly, as “the time-space continuum”—are two sides of the same coin and they, quite materially, form the fabric of the cosmos.

When an object of massive size (such as the Earth) warps the time-space continuum, the result is gravity and a specific “flow of time” at that specific place, depending, of course, on the size of the denture. Black holes, for example, bend the time-space continuum so much that, there, time stops completely.

Quanta of Time

We managed to understand more about this via something Einstein didn’t believe in that much: quantum physics.

It led us to three fundamental discoveries: granularity, indeterminacy, and the relational aspect of physical variables.

Granularity is the most characteristic feature of quantum mechanics. It means that a minimum scale exists for all phenomena, including time. The smallest unit of time is called Planck time and it amounts to 10-44 seconds: a hundred millionth of a trillionth of a trillionth of a trillionth of a second. At such a minute scale, the notion of time is no longer valid.

Indeterminacy means that “it is not possible to predict exactly, for instance, where an electron will appear tomorrow. Between one appearance and another, the electron has no precise position, as if it were dispersed in a cloud of probability.

In addition, an electron is concrete only in relation to the other physical objects it is interacting with. In other words, concreteness happens only in relation to a physical system.

“Time has loosened into a network of relations that no longer holds together as a coherent canvas,” concludes Rovelli. 

The actual picture on the canvas is this: “spacetimes (in the plural) fluctuating, superimposed one above the other, materializing at certain times with respect to particular objects.”


In the second part of The Order of Time, Rovelli describes what we are left with once we’ve stripped time off all of its layers: “an empty, windswept landscape almost devoid of all trace of temporality.” And yet, this is precisely our world.

So, let’s see how that world actually looks like.

The World Is Made of Events, Not Things

One of the strangest consequences of this line of thinking is this: nothing ever is, everything, ultimately and merely, just happens

Because if time doesn’t exist the way we believe it does, things don’t exist either: every single thing you see around you is merely just a more durable event.

At first sight, there’s a big difference between a stone and a kiss: the first is the prototypal thing, the letter an embodiment of an event. 

We will never ask ourselves where the kiss will be tomorrow, but we can ask ourselves where the stone will be in twelve days. On the other hand, it is a pretty sound question to ask someone when he/she have his/her first kiss.

However, as we found out above, time and space work together, And on closer inspection, we realize that even the most “thinglike” things such as stones are nothing but long events.

“The hardest stone,” writes Rovelli, “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.”

“Thinking of the world as a collection of events, of processes,” he goes on, “is the way that allows us to better grasp, comprehend, and describe it. It is the only way that is compatible with relativity. The world is not a collection of things, it is a collection of events.”

The Inadequacy of Grammar

Unfortunately, our grammar is inadequate to grasp this. 

It is strange to think, but that quote which introduces the popular Netflix German TV show called Dark by Einstein isn’t a metaphor, but a physical fact:

“People like us who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion.”

This sentence is taken from a letter by Einstein to the son and sister of Michele Besso sent near the end of his life. And it’s one which makes the distinction between presentism and eternalism.

In presentism, we know precisely what “now” means because we believe in an objective global present. Yet, as physics discovered, the present is relative to the observer, i.e., what is real for one is not actually real for someone else.

That’s where eternalism comes: the idea that flow and change are illusory and that the past, present, and future are all equally real and existent.

This is closer to the truth than you can imagine, but it is also not the truth. 

The truth is that there is no order of time, i.e., the temporal structure of the world is not that of presentism. But the changes mentioned in Einstein’s quote are not illusory, but real. The thing is they do not follow a global order.

Einstein’s letter was sent to console a grieving sister, and it is only because of the inadequacy of grammar and our metaphor-laden language that we confuse things.

It is also because of this that we are unable to understand—or even speak about—certain natural phenomena.


“The third part of the book,” writes Rovelli, “is the most difficult, but also the most vital and the one that most closely involves us. In a world without time, there must still be something that gives rise to the time that we are accustomed to, with its order, with its past that is different from the future, with its smooth flowing. Somehow, our time must emerge around us, at least for us and at our scale.”

This is the return journey, back toward the time lost in the first part of the book when pursuing the elementary grammar of the world. As in a crime novel, we are now going in search of a guilty party: the culprit who has created time. One by one, we discover the constituent parts of the time that is familiar to us—not, now, as elementary structures of reality, but rather as useful approximations for the clumsy and bungling mortal creatures we are: aspects of our perspective, and aspects, too, perhaps, that are decisive in determining what we are. 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.

So let’s see how and why we created time in a timeless universe.


Imagine a group of children deciding between themselves the two opposing sides in a football game by, say, tossing a coin.

Of course, after some time there are two teams on the field pitted against each other.

The thought-provoking question?

Where were the teams before the coin toss?

Nowhere. Simply put, they didn’t exist: they are the result of the coin toss. They are an “emergent phenomenon.”

Well, you should think of time as something like that: it is not an objective fact, it is not something that exists out there. It is something that emerges due to our particular perspective of the universe, granted by a set of circumstances and our subjective vision.

“The entire difference between past and future,” writes Carlo Rovelli, “may be attributed solely to the fact that the entropy of the world was low in the past.”

As we saw above, in time, entropy always increases; if it was the other way around, we would have lived in a world not that unlike a rewound movie: pieces of shattered glass would form a bottle and the smoke—cigarettes.

What Emerges from a Particularity

So, in other words, if there’s no entropy—i.e., if nothing changes—there is no time as well. And, in a way, it is entropy, not energy, that drives the world.

Think of it this way: if entropy always increases, then only where it is tightly packed in orderly pieces of matter, there could be such things as history and evolution.

Fortunately, we live inside a universe where this is the case: we don’t know precisely why (Rovelli has a theory), but, for some reason, we are in that place of the universe where the second law of thermodynamics works to our benefit.

How and why?

Well, it all starts with the sun, a rich source of low entropy which is usable because it is located very close to our planet.

The sun radiates a hot photon (light particles) toward Earth, and the Earth harks back by emitting ten colder photons which have less energy and, thus, balance things out.

A hot photon, however, has much less entropy than ten colder photons (as we said above, heat always moves to cold, not the other way around).

This way, the Earth can use the Sun’s energy to power its processes and make things move around. This, of course, results in low entropy transforming in high entropy, such as the ones occurring in your body which, ultimately, will lead to a state of lowest entropy called death.

“The existence of common causes in the past is nothing but a manifestation of low entropy in the past,” writes Rovelli. “In a state of thermal equilibrium, or in a purely mechanical system, there isn’t a direction to time identified by causality.”

The Scent of the Madeleine

“We are processes, events, composite and limited in space and time,” concludes Rovelli. 

“But if we are not an individual entity,” he goes on, “what is it that founds our identity and its unity? 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?”

Many different ingredients, he says, but three are of the utmost importance: point of view, organization by grouping and segmenting, and memory.

Point of view is self-explanatory: “The world is reflected in each one of us through a rich spectrum of correlations essential for our survival. Each of us is a complex process that reflects the world and elaborates the information we receive in a way that is strictly integrated.”

The second ingredient (organization) suggests this: we tend to group and segment things into entities so that we can better grasp them. That’s why we call a certain collection of rocks and fields “Mount Everest” and a certain collection of atoms that change “Jack” or “Jill.”

Finally, the third ingredient that comprises our identity is memory, perhaps the most essential one as far as time is concerned. Because it is memory that catalogizes things in our brains in a narrative manner, making strict distinctions between past and future events.

That is why people who have memory problems can’t organize the world in such a neat manner and confuse between the past and the present. That is why they no longer seem as unified beings—but as someone different from them.

Memory is a guarantee of identity.

Key Lessons from “The Order of Time”

1.      The Faster You Are, the Slower Time Moves
2.      The Past and the Future Exist Because of Heat
3.      Our Universe Is a Special Case—And That’s Why Time Looks the Way It Does

The Faster You Are, the Slower Time Moves 

It may seem like some sort of a glitch taken straight out of SF-novels, but, as Carlo Rovelli says, “this is how reality works.”

In other words, whether you like it or not, we know for a fact (and thanks to Einstein) that the faster you move, the slower time moves for you, resulting in a singular paradox.

Namely, a twin who travels at speed near the speed of light and goes to another planet, after returning, would be much younger than his brother.

Don’t believe us?

In 1971, two Americans (a physicist and an astronomer) did the experiment, sending four cesium atomic clocks in different directions around the planet to see if they would gain nanoseconds when compared to the clocks at the US Naval Observatory.

They did—precisely as much as Einstein predicted.

The Past and the Future Exist Because of Heat

Interestingly enough, even though it is highly intuitive that time is what separates the past from the future, the only law that suggests that there is some kind of a distinction between the past and the future is the law of entropy, the irreversible progress of heat.

Leave a hot cup of tea, and it will inevitably grow cold in time; it will never get hot again by itself.

The same is true with time: it travels only in one direction, but merely because we see some things as irretrievably changed when going forward.

And we can see this only in the irreversible progress of heat.

Mind-blowing and counter-intuitive, right?

Also: true.

Our Universe Is a Special Case—And That’s Why Time Looks the Way It Does

Fascinatingly enough, the only reason why we can differentiate between the past and the present—which, in a much more fundamental sense, don’t really exist—is because we live in a universe whose entropy is low in the past

And only because of this, “the second law of thermodynamics obtains; memories exist, traces are left—and there can be evolution, life, and thought.”

In other words, as strange as it sounds, we’ve won the lottery. And that’s not merely the only reason why time looks to us the way it does—but also (and consequently) the only reason why we exist the way we do and understand things the way we understand them.

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“The Order of Time Quotes”

We are for ourselves in large measure what we see and have seen of ourselves reflected back to us by our friends, our loves, and our enemies. Click To Tweet Fearing the transition, being afraid of death, is like being afraid of reality itself; like being afraid of the sun. Click To Tweet When we cannot formulate a problem with precision, it is often not because the problem is profound: it’s because the problem is false. Click To Tweet The best grammar for thinking about the world is that of change, not of permanence. Not of being, but of becoming. Click To Tweet The world is not like a platoon advancing at the pace of a single commander. It`s a network of events affecting each other. Click To Tweet

Our Critical Review

The Order of Time has been described as “a pocket-sized guide to unraveling the mysteries of time” and as “a deep—and remarkably readable—dive into the fundamental nature of time.” 

The strange thing is that neither of these descriptions is an exaggeration—on the contrary, they may be understatements.

“Mind-bending” (Michael Pollan) and “compact” (Nature), highly allusive and dizzyingly poetic (The Guardian), The Order of Time, in our humble opinion, is the best book on the subject you can find out there.

Please do: this book deserves to be read by anyone who is even vaguely interested in the mystery of time.

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