More on this book
Community
Kindle Notes & Highlights
Is this surprising? Perhaps it is. But this is how the world works. Time passes more slowly in some places, more rapidly in others.
Things fall downward because, down there, time is slowed by the Earth.5
Rebellion is perhaps among the deepest roots of science: the refusal to accept the present order of things.
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. None of the others do so.
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.
Clausius’s entropy, indicated by the letter S, is a measurable and calculable quantity15 that increases or remains the same but never decreases,
ΔS ≥ 0
“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. It’s a strange enough fact in itself, but its consequences are extraordinary. Hold on tight, because we are about to take off. “NOW” MEANS NOTHING
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.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. If I were to ask, “Are these two stones at the same height?” in interplanetary space, the correct answer would be: “It’s a question that doesn’t make sense, because there isn’t a single notion of ‘same height’ throughout the universe.” If I ask whether two events—one on Earth and the other on Proxima b—are happening “at the same
...more
It is only in the fourteenth century in Europe that people’s lives start to be regulated by mechanical clocks. Cities and villages build their churches, erect bell towers next to them, and place a clock on the bell tower to mark the rhythm of collective activities. The era of clock-regulated time begins.
In 1883, a compromise is reached with the idea of dividing the world into time zones, thereby standardizing time only within each zone.
Aristotle was the first to discuss in depth and with acuity the meaning of “space,” or “place,” and to arrive at a precise definition: the place of a thing is what surrounds that thing.
But—here is the key point—there is also a “gravitational” field: it is the origin of the force of gravity, but it is also the texture that forms Newton’s space and time, the fabric on which the rest of the world is drawn. Clocks are mechanisms that measure its extension. The meters used for measuring length are portions of matter that measure another aspect of its extension.
More than a drawing on a canvas, the world is like a superimposition of canvases, of strata, where the gravitational field is only one among others. Just like the others, it is neither absolute nor uniform, nor is it fixed: it flexes, stretches, and jostles with the others, pushing and pulling against them. Equations describe the reciprocal influences that all the fields have on each other, and spacetime is one of these fields.*
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.
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.
I’ll repeat this point, because it is a key one: a macroscopic state (which ignores the details) chooses a particular variable that has some of the characteristics of time. In other words, a time becomes determined simply as an effect of blurring.
Proust could not be more explicit on this matter, writing in the first book: “Reality is formed only by memory.”118 And memory, in its turn, is a collection of traces, an indirect product of the disordering of the world, of that small equation written earlier, ΔS ≥ 0, the one that tells us the state of the world was in a “particular” configuration in the past and therefore has left (and leaves) traces. “Particular,” that is, perhaps only in relation to rare subsystems—ourselves included. We are stories, contained within the twenty complicated centimeters behind our eyes, lines drawn by traces
...more
This table has dimensions: the one that we call space, and the one along which entropy grows, called time. In our everyday life we move at low speeds in relation to the speed of light and so we do not perceive the discrepancies between the different proper times of different clocks, and the differences in speed at which time passes at different distances from a mass are too small for us to distinguish.
Fearing the transition, being afraid of death, is like being afraid of reality itself; like being afraid of the sun. Whatever for?
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.
