It is also worthless to reason as follows: “It is true that you are sitting in eternity because you are sitting in time; likewise—for the same reason—it will be true that you are not sitting in eternity; therefore both states, ‘you are sitting’ and ‘you are not sitting,’ occur simultaneously in the same instant.”

Robert Kilwardby, De tempore

Using the Lorentz transformation, we can express the special principle of relativity in the following way: the laws of nature are invariant under the Lorentz transformation (that is, the form of physical laws does not change when we pass to a new inertial frame, if we do so by means of the Lorentz transformation).

Albert Einstein, Special Theory of Relativity

The necessity and praise of opposites. Measure as the place where contradictions meet. Sun and darkness.

Albert Camus, Notebooks, Notebook VIII

This forest has been called by many names. Its nature has been understood in many ways. Sometimes it was treated as the very core, almost the definition of existence; at other times its very existence was denied. At one moment it was claimed to be an absolute foundation; at another, that its roots reach something far deeper and more important. People argued over whether the paths that run through it are straight and go only one way, or whether they are curved, perhaps even circular—or whether, in the end, all paths are merely an illusion. They tried to determine whether this forest grows or remains unchanged; they tried to mark its boundaries and imagine what it looks like from the outside, and whether the notions of “boundary” or “outside” make any sense at all. They measured it in countless ways, across and upward; they counted the trees and the rings in the trunks and the thickness of bark and the density of foliage, and so on. Some insisted the forest exists independently of these operations; others, on the contrary, that it appears only in the very act of measuring and calculating. And nothing certain was ever established.

And I, too, will establish nothing certain, nor will I contribute anything new to that dispute. But I can say something—I must even—if I am to go further. I can / must give an account of my impressions and invoke whatever, in some way, explains those impressions to me. This forest is time.

Impressions and beliefs
First of all, I have the impression that the notion of “now” is not pointless, and that all “nows” are elements of a set organized according to some principle or set of principles. These principles are not clear, though at first glance they may seem so. It is hard not to fall into strong convictions about certain matters—for instance, that their organization is directional, and that the direction or directions are governed by some kind of dynamics that forms some kind of hierarchy; that forces are at work here, grounded in the possibility of similarity, difference, and change. That repetitions occur, but modifications are unavoidable. So that there are analogies between different “nows”—some “nows” are linked with one another; it seems that many of these links—though maybe not all, and in a way far from obvious—display some form of causality. And perhaps above all: that some “nows” bear traces of other “nows,” some clearer, others blurred, but still legible—and able to awaken strong desires: to preserve something from one “now,” and to retrieve something from another.

But I also have an irresistible impression that no “now” is entirely real. If one can distinguish reality (that is, what exists) from the world (that is, what appears), then “now” is probably part of the world rather than reality. It is not a fiction, but rather a handy tool—perhaps adequate as an access to something real—allowing one to orient oneself toward that something, while only seemingly being a defining feature of it. It seems to me that “now” is a concept, or perhaps a complex (a tangle of habitual tendencies) that lets one grasp something real and illusorily stabilize it. It is a nucleus of condensation that allows something real, yet unformed and un-directed, to condense and take on an apparently concrete shape, like a cloud. The dynamics–directionality mentioned earlier, binding different “nows” to one another, is for time what a temperature gradient is for a cloud: the condition of formation and the determinant of structure. And this cloud is not so much in the world as it is the world itself—on some real sky; and I do not so much look at the cloud as I am made of it.

And I also have the impression that it is not without reason that “now” is so often tied to “here.” I trust those who see an inseparable connection between the notions of time and space. I trust that explaining time by motion—whether by treating time as a measure of motion, or by claiming that time itself is motion—has a deep sense. I even trust those who claim that time is, in some way, an act—an active doing. And further still, I trust as well (though with some distance) those who see a link between time, action, and attention—the possibility and the modes of perception, though not necessarily consciousness (about which, in general, we scarcely know what to do—it is a suspicious and slippery matter). That perception is in some way a condition and a point of departure, and that its basis is in some way time. Though I would be very cautious in attempting to indicate who would be the subject of that perception and what its object. Perhaps it is I who, in time, perceive the world. Or perhaps the world perceives itself; time is the echo of that, and I am a splinter.

At the same time, I trust those—though not unconditionally—who do not want too easily to renounce precise measurements and calculations, and who seek the deepest answers in what these reveal. I believe in rigor and accept the reservations about the impossibility of explaining anything by free thought alone. But I also believe that whatever can be thought exists—though not necessarily in the world, it necessarily exists in reality. And that thought, whose lining is by definition meaning, hits its target better or worse. And even if it misses, it nevertheless misses a target. So, for instance, the notion of simultaneity—even if, in the light of calculation, it has lost its sense, and turned out not to be part of the world but an illusion within that world—is nonetheless, like “now,” not entirely pointless. It points to something. And even more, it points to something in the shock one can experience upon learning—upon seeing incontrovertibly, in a coherent calculation—that simultaneity in the world is pure illusion.

I also trust those who grasp time in terms of conflict—an ineradicable tension between some contradictions that generates motion. I believe that the world, and perhaps reality as well, is layered; that each layer has its own characteristic tensions; and that time is motion—between the poles of tension and through these layers—spiral, moving consistently in a certain direction through some hierarchy of layers; and that this motion and this hierarchy in some way constitute what and how the world is, and what and how I am.

Finally, I trust those—though with the greatest number of reservations and the broadest scope of doubts—who argue for an ethical dimension of time. I understand that there is no talk of being without talk of time; that the most essential question about any being is the question of meaning; and that any answer to that question—positive, negative, closed, or open—necessarily orients itself somehow toward values, and in particular toward the notion of the good. And the good has much to do with “now,” and also with “here,” with all the reservations and doubts mentioned earlier about their nature, their reality, their mode of being in the world, and so forth. And with one further, the most important reservation: the good is not written here with a capital letter. It is not meant to suggest some all-embracing blissful order. It is not like a lion—fearless, self-constituting king and lawgiver—but rather like a guinea pig: a small, fragile, slightly shapeless and wary rodent always ready to dart into shadow and freeze motionless. Not like a self-sustaining, inextinguishable glow of a star, the source of life, but rather like a wobbly flame of a candle, which, left to itself, will soon go out—blown out, or having burned through its fleeting essence. It is perhaps like the sound of a foghorn, often barely audible in the wind, and when heard it gives strength and comfort; it seems to promise rescue and calm; it testifies to someone’s care and foresight; it calls forth, like a figure one can almost make out in the dark and recognize, like a mother who does not call the child to shelter it in her arms and soothe it, but warns it of something terrible that must be avoided.

People once spoke of three faces of time: Kronos—linear, objective, absolute time that can be measured; Kairos—momentary time that makes events possible; and Aion—eternal time, unchanging and immeasurable. If reality were a dark, boundless sea, then the world would be a wave on its surface; I would be a little boat with a sail; Kronos the wind; Kairos an island; and Aion the horizon.

Some of the maps I have looked into
Aristotle, Physics
Julian Barbour, The New Theory of Time
Albert Einstein, Relativity and Other Essays
Richard Feynman, Lectures on Physics
Fr. Pavel Florensky, The Meaning of Idealism
Julius Fraser, Of Time, Passion and Knowledge
Martin Heidegger, Being and Time
Douglas R. Hofstadter, Gödel, Escher, Bach
Henryk Paprocki, Time
Lee Smolin, Time Reborn
Alfred N. Whitehead, Process and Reality; Science and the Modern World