The Order of Time by Carlo Rovelli

I finished this book in October 2025. I recommend this book 10/10.

Why you should read this book:

This is a great book if you are looking for something other than business book or a novel. The Order of Time is a very well-written book about what science knows about time. The book explains complex areas, such as quantum gravity, in an easy-to-digest way.

Get your copy here.

🚀 The book in three sentences

1. A well-written science book explains complex topics well.

2. Our scientific math doesn't compute in a human's day-to-day.

3. Nature is moving in its time, regardless of whether you rush through it.

📝 My notes and thoughts

• P10. It is not just the clocks that slow down: lower down, all processes are slower. Two friends separate, with one of them living in the plains and the other going to live in the mountains. They meet up again years later: the one who has stayed down has lived less, aged less, the mechanism of his cuckoo clock has oscillated fewer times. He has had less time to do things, his plants have grown less, his thoughts have had less time to unfold. . . Lower down, there is simply less time than at altitude.

• P31. If the first twenty-six cards in a pack are all red and the next twenty-six are all black, we say that the configuration of the cards is "particular," that it is "ordered." This order is lost when the pack is shuffled. The initial ordered configuration is a configuration "of low entropy." But notice that it is particular of how we look at the color of the cards—red or black. It is particular because I am looking at the color. Another configuration will be particular if the first twenty-six cards consist of only hearts or spades. Or if they are all odd numbers, or the twenty-six most created cards in the pack, or exactly the same twenty-six of three days ago. . . Or if they share any other characteristic. If we think about it carefully, every configuration is particular, every configuration is singular, if we look at all of its details, since every configuration always has something about it that characterizes it in a unique way. Just as, to its mother, every child is particular and unique.

• P40. 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. Not only is there no single time for different places—there is not even a single time for any particular place. A duration can be associated only with the movement of something, with a given trajectory. "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.

• P61. In 1883, a compromise was 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.

• P77. Curved spacetime. "Curved" because it is distorted: distances are stretched and contracted, just like the elastic sheet when it is pulled. This is why the light cones were inclined in the diagrams. Time thus becomes part of a complicated geometry woven together with the geometry of space. This is the synthesis that Einstein found between Aristotle's conception of time and Newton's. With a tremendous beat of his wings, Einstein understands that Aristotle and Newton are both right. Newton is right in intuiting that something else exists in addition to the simple things that we see moving and changing. True and mathematical Newtonian time exists; it is a real entity; it is gravitational field, the elastic sheet, the curved space-time in the diagram. But Newton is wrong in assuming that this time is independent from things—and that it passes regularly, imperturbably, separately, from everything else. For his part, Aristotle is right to say that "when" and "where" are always located in relation to something. But this something can also be just the field, the spatiotemporal entity of Einstein. Because this is a dynamic and concrete entity, like all those in reference to which, as Aristotle rightly observed, we are capable of locating ourselves.

• P91. There is no single time: there is a different duration for every trajectory; and time passes at different rhythms according to place and according to speed. It is not directional: the difference between past and future does not exist in the elementary equations of the world; its orientation is merely a contingent aspect that appears when we look at things and neglect the details. In this blurred view, the past of the universe was in a curiously "particular" state. The notion of the "present" does not work: in the vast universe, there is nothing that we can reasonably 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, fluctuates, materializes only by interacting, and is not to be found beneath a minimum scale. . . So, after all this, what is left of time?

• P97. The entire evolution of science would suggest that the best grammar for thinking about the world is that of change, not permanence. Not of being, but becoming. We can think of the world as made up of things. Of substance. 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, most of stasis in the motionless time. Thinking of the world as a collection of events, of processes, is the way that allows us to better grasp, comprehend, and describe it. It is the only way that is compatible with reality. 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 stones.

• P110.  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 thousands 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."

• P189. We are stories, contained within the twenty complicated centimeters behind our eyes, lines drawn by traces left by the (re)mingling together of things in the world, and oriented toward predicting events in the future, toward the direction of increasing entropy, in a rather particular corner of this immense, chaotic universe. This space—memory—combined with our continuous process of anticipation, is the source of our sensing time as time, and ourselves as ourselves. Think about it: our introspection is easily capable of imagining itself without there being space or matter, but can it imagine itself not existing in time?

• P210. 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 devils, angels, 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.