The mystery of time

We are time. We are this space, this clearing opened by the traces of memory inside the connections between our neurons. We are memory. We are nostalgia. We are longing for a future that will not come.

Carlo Rovelli is a theoretical physicist who is among the founders of the loop quantum gravity theory — which uses discrete mathematics to examine space and time. The Order of Time (Penguin Books, 2019), unravels this mystery through science, philosophy, and art.

What is your exact definition of time?

There is no single definition of time. Expecting that a single definition could capture the complexity of what we call time is what creates the confusion about the concept: what we call time comprises several related but distinct phenomena. For instance, we call time the simple counting of events that happen one after the other. Day changes into night, night changes into day. Time is, therefore, the counting of the sequence of days. This is a very general definition of time. It is a good one, but it fails to capture the richness of our own experience of the “passing” of time.

The passing, or “flowing” of time, includes the fact that we can remember the past but not the future, that the past is fixed while the future is open, and so on. If by time we mean this flow, then we are using a different definition of time than the previous one: we are denoting a complex phenomenon, that also involves the way our brain works.

What are the most solid properties of time that we can say that everyone agrees on?

There is more disagreement than agreement on what are the most solid properties of time, because different people call different aspects of time “fundamental.” For some it is the counting; for others, the geometry of spacetime; for yet others, the flowing time of our experience. People focus on different aspects of temporality and call that the “solid” part.

Is time “real” or is it “necessary”?

Time is definitely not “necessary.” In the basic equations that I use in my work in theoretical physics, for instance, there is no “time” at all. This shows that it is not necessary. To ask if time is “real” is a trick question, because “real” can mean all sorts of things. Is your love “real”? Is it “real” that there is this law? Was Hamlet real? No. Was his pain real? Yes.

Is time a mystery? Or is its mysterious halo a consequence of time being a limited, partial way to humanize something that is too complex for humans to grasp?

Time is surrounded by mysteries. We do not know how time started, nor whether it started. We do not know the source of the difference between past and future. We do not have clear ideas about why we sense time flow, and so on. These are different mysteries, that refer to distinct concepts that we do not yet understand in physics, cosmology, the neurosciences, and so on. We have learned a lot about the nature of time, and we are learning more. But we are still far from having learned everything.

Time is subjective. How can you research and study a theory that is inherently subjective with a scientific, rigorous method?

We can study subjective phenomena because the subject is itself part of nature. By studying the subject we understand subjective aspects of phenomena. For instance, the fact that we see the world colored in combinations of three primary colors is subjective (other animals see no color, or two colors, or four colors). By studying the retinas of humans and other animals, we have discovered the reasons for this perception: humans have exactly three kinds of light receptors. In this way, we have understood a subjective fact by studying the subject.

In what scenarios does ordering time by “past, present, and future” make sense? When doesn’t it make sense?

It is meaningless to use “past, present, and future” in a sentence unless we consider that the sentence is pronounced (or written, or conceived) at some moment in time. The meaning of “now” or “the present” in the sentence depends on when the sentence is spoken. In a phrase considered abstractly, independently from when it is spoken, “now” does not mean anything. For instance “now is September 13th” may be true when I wrote it and false when you read it.

How did we understand time before the advent of quantum physics, and what happened afterward?

The understanding of time has changed repeatedly throughout history. Aristotle gave us a clear understanding of the general nature of time as counting. Newton changed this, by focusing on a specific time that makes mechanics simpler: he introduced what we call “Absolute” or “Newtonian Time,” measured by good clocks. The idea is that this time passes even if nothing happens, even if there is nothing to count. This was a strange and new idea at the time of Newton, but we have gotten used to it. Einstein proved that this Newtonian time is affected by gravity and the way an object moves. As we learn and discover more, our understanding of time changes, and there is always more to learn.

Why is time crucial in the seemingly paradoxical clash between Quantum Theory and the Theory of Relativity?

We have not yet figured out the quantum effects of time. Time is affected by gravity, and we have not yet understood the quantum properties of gravity. Therefore we don’t know the quantum effects on time. That is: on clocks. These quantum effects on clocks are very tiny, so they are irrelevant in our daily lives. They become important inside black holes, for instance, and in our universe’s early life. In those situations, the properties that we instinctively attribute to the passage of time are no longer relevant. Clocks jump back and forth, for instance.

Is time dependent on the idea of self, identity, and, ultimately, death?

Yes, because our sense of identity is based on memory, and memory is what gives us a sense of flowing time. In a sense, our identity is our story that we hold in our memory and with which we identify. So, we are alive flowing in time, like a fish in water.

What does “now” mean in astrophysics?

It means nothing. It makes no physical sense to ask what is happening “now” at a distant location because there is no “now” that is exactly defined in the universe. When astrophysicists say “now,” they only mean “now here.” For instance, they may say “now a gravitational wave is being detected.”

Does “now” have the same value, philosophically and conceptually speaking, as “zero” in mathematics?

I would not say so. “Zero” is a number which is well defined independently from when it is said, while the meaning of “now” changes depending on when it is spoken.

Is time reversible? Does time run only forward or can it run in different directions?

The logic that explains why time “runs forward” and not “backward” is tricky. The main reason we have the sense that time runs in one direction, and not the other, is that we remember the past (we cannot remember the future). The reason we remember the past and not the future has to do with statistics. So, strictly speaking, the difference between the past and the future is only a matter of statistics, namely randomness. Which means that, in a sense, time runs “mostly” toward the future…

What are the greyest and most interesting areas when it comes to the notion of time?

I would say it is to distinguish which parts of our rich experience of temporality depends on specific brain functions (brain works with memories, anticipation, and so on), which parts depends on statistics, which parts depend on the approximations due to the poverty of our senses, and which, finally, is irreducible and independent from all of that.

A brief history of time

When speaking about time, where do we begin? Time is familiar to everyone, yet hard to define and understand. Do we start from the beginning, from the Big Bang? Should we speak about pendulums or the spacetime continuum? How can we describe something so vast, so infinite as time?

Science, philosophy, and religion have different definitions of time, but the system used to measure it is relatively consistent. Nowadays, clocks all over the world are based on seconds, minutes, and hours. But this was not always the case. Ever since human beings have existed, we’ve measured time by observing nature: the change of seasons, the dance of heavenly bodies across the sky. As the sun travels, shadows change direction and length, so a simple sundial can measure a day. From Stonehenge to the ancient Chinese observatory in Shanxi, many Neolithic constructions were built to mark the midwinter solstice and celebrate the start of each new year.

Throughout history, different cultures have used various tools to measure time: oil lamps, candle clocks, water clocks, hourglasses and so on.

Finally, mechanical clocks replaced these archaic devices and have become extraordinarily precise timekeepers. The first clock escapement mechanism is said to have been invented in 1275. In 1656, Christiaan Huygens made the first pendulum clock, regulated by a mechanism with a natural period of oscillation. It was not until 1884 that a conference adopted Greenwich Mean Time as the international time standard. Today’s atomic clockswhich operate by measuring the vibrations of strontium atoms as their electrons leap among energy levels—are so accurate that it is said they won’t lose a single second over the next 15 billion years. Yet time isn’t as natural or as objective as it seems and our attempts to measure time only scratch the surface.

All humans experience time, yet we rarely ask: What is time? At first glance, it seems obvious: it is the ticking of the clock, the turning of the pages of a calendar. But these are incidental physical manifestations of its underlying concept: time is a mystery that never ceases to puzzle us. In the ancient world, mythology and other traditional narratives were used to try and make sense of the universe. In Greek mythology, Kronos was the personification of time. Ancient Greeks actually had two different words for time: chronos, for numeric or chronological time, and kairos, for a correct or opportune moment. Other mythologies had time-related gods, such as Heh, the Egyptian deification of eternity, Zurvan, the Zoroastrian god of infinite time, and Elli, the Norse god of old age.

Our sense of time has to do with how we relate to one another and understand our place in the universe. Our awareness of it is, therefore, one of the most important distinguishing features of humankind and one of the sensations that truly separate us from the other animals. Time has always been a product of the human imagination. Judeo-Christian societies learned to perceive historical time as linear and unidirectional because of a story that they told themselves about humankind’s fate. Incas and the Mayans created cosmologies from cyclical and continuous tales. In Indian philosophy, the universe went through repeated cycles of creation, destruction, and rebirth. This led to viewing time as a cycle, the so-called “wheel of time” or Kalachakra, in which there are repeating ages over the infinite life of the universe. The wheel of time concept is also present in Hinduism and Buddhism.

Many philosophers believe that time is continuous and that it has an intrinsic order (i.e., events progress from past to future). Ancient Indian and Greek philosophies were among the first to question time as a mysterious concept. One major point of contention was whether or not time is linear or cyclical, endless or finite. Early Greek philosophers believed that the universe was infinite. Plato’s student, Aristotle, believed in continuous time. He was also the first to frame a commonly-mentioned paradox about the existence of time, reframed by St. Augustine several centuries later: If time essentially consists of two different kinds of non-existence (the future or the “no longer,” and the past or the “not yet”) separated by a nothing (the instantaneous and vanishing present or “now”), how then can we talk of time as actually existing at all?

St. Augustine (4th – 5th century CE), an early-Christian theologian, probably thought more deeply about the nature of time than any philosopher since ancient Greece, but his reflections were inconclusive. He concluded that time was a “distention” of the mind which allowed us to simultaneously grasp the past in memory, the present by attention, and the future by expectation. Christian and Muslim philosophers tried their best to incorporate Aristotle into their theology during the early Middle Ages, but they struggled mightily with his belief in infinite time. It was considered finite, in a doctrine known as temporal finitism. Various versions of Christian creationism persist today, although they are not all as literal as the pontifications of medieval philosophers.

In the 14th century, the French mathematician Nicole Oresme, studied time, from a mathematical and scientific perspective. During the 17th and 18th centuries, the nature of time once again became a point of philosophical contention: Is it real? Or is its passage an illusion? On one hand, there was the realist viewpoint, championed by Sir Isaac Newton: absolute time exists independently of any perceiver and can only be understood mathematically. Time is, therefore, an entity in its own right, and we (and all the objects in the universe) are temporarily “occupying” it. On the other hand, Gottfried Leibniz firmly believed that time does not refer to an existing dimension. The anti-realist view of time claims that it is a convenient intellectual concept (like space and numbers) that enables us to sequence and compare events. For him, time (and space) are the product of how we understand the world. Another German philosopher, Immanuel Kant, in his influential 1781 book The Critique of Pure Reason, described space and time as a priori, notions that are necessary to allow us to comprehend sensory experiences, but not substances or entities.

In the late 19th century, E. Robert Kelley, introduced “specious present.” He saw the present as the most recent part of the past. This idea was developed by William James as he described the specious present as “the short part of which we are immediately and incessantly sensible.” In the same period, Edmund Husserl, founder of the influential phenomenology movement, began to consider time and our internal consciousness of it. He asserted that we cannot perceive the immediate present without some memory of the past and some expectation of the future for context. Henri Bergson revolutionized our understanding of memory: he formulated a view of time that was not a mental construct but possessed what he referred to as duration. He saw the fluid flow of time as composed of myriad temporal particles, which are pieced together by our consciousness. In his book, Being and Time, the phenomenologist and existentialist Martin Heidegger concluded that we do not exist within time, but in a very real way we are time, and the whole concept of time is inseparable from the human experience.

There is a long-standing relationship between science and philosophy, a friendly rivalry. The two disciplines are different, they have different aims, but their subject-matters often overlap. The study of time is one topic where a philosophical perspective is helpful, even to scientists. From Boltzmann to quantum theory, from Einstein to loop quantum gravity, our understanding of time has radically changed. The idea of an alternative universe and the many-worlds interpretation of quantum mechanics adds a whole new dimension to the discussion of the nature of time. In disconnected time streams, in a potentially infinite number of parallel universes, some could be linear and others circular; time could continuously branch and bifurcate, or different time streams could merge and fuse into one; the laws of causality and succession could break down or not apply. The concept of imaginary time is derived from quantum mechanics and was introduced by Stephen Hawking in his book A Brief History of Time as a way of avoiding the idea of a singularity at the beginning of the universe. Hawking proposed that space and imaginary time together are finite, but have no boundary—in a similar way as the two-dimensional surface of a sphere has no boundary.

St. Augustine famously encapsulated the experience of so many of us, when he observed: “What, then, is time? If no one ask of me, I know; if I wish to explain to him who asks, I know not..” Maybe we should just define time, according to the Oxford Dictionary: “the indefinite continued progress of existence and events in the past, present, and future.”

The timeline of the subconscious

It all begins with the dream of the revolution, the dream of another time. “The following dream of Maury’s has become celebrated—wrote Freud in his Interpretation of Dreams. He was ill in bed; his mother was sitting beside him. He dreamed of the Reign of Terror during the French Revolution and witnessed some terrible murder scenes. Finally, he was brought before the Tribunal. There he saw Robespierre, Marat, Fouquier-Tinville, and all the sad heroes of those terrible days. He answered their questions, and after all manner of incidents which he eventually forgot, he was sentenced to death. Accompanied by an enormous crowd, he was led to his execution. He climbed up on the scaffold; the executioner tied him to the plank, it tipped over, and the blade of the guillotine fell. He felt his head severed from his trunk, and he woke up with terrible anxiety, only to find that the headboard of the bed had fallen, and had actually struck his neck vertebrae just where the blade of the guillotine would have fallen.

What happened first: The dreamed event of the guillotine or that of the headboard in reality? Freud hypothesizes that there is another time other than the one to which consciousness is accustomed. A non-linear time, which does not run like the first one, with a now and a then, from the past to the future. An underground time, that writes its record without us knowing about it and that decides for us without us realizing it, marking the passages due to which suddenly we find ourselves elsewhere, different, changed, infinitely others. It is thanks to this dream that Freud achieved his revolution, quite different from the one that the French revolutionaries imagined they could reach by their reorganization of time, with their pagan calendar made up of Brumaire, Fructidor, and Ventôse.

The Freudian revolution, is based precisely on the subversion of the modern subject who hoped to make the revolution, who hoped to force change upon the world, on itself and on others by an act of free will. Freud’s discovery of the unconscious tells us that this is not the case: we are not free to change: not because there are external forces that prevent us from doing so, but because we ourselves prevent it from happening. We tend to maintain balance, not to change, to see continuity on our horizon: I will be what I am and what I have been. So we dream of changing the lives of others — while we tend to keep going on with the same life as ever.

Behind this debate, Freud discovers another scene. While we tend to preserve ourselves and dream of Utopian changes, something happens without our knowing about it. That’s how the change occurs: once it happens, we find we are already elsewhere, all of a sudden, without knowing why. Freud’s revolution, after all, consists of acknowledging that real change takes place blindly.

Maury’s dream revealed to Freud that, behind our naïve perception of linear time, there is another time that acts instead of us. We are divided, crossed by a wound that consigns us into the hands of a master — the unconscious, in fact — who decides for us without us realizing it. However, this master is removed, so he can work in disguise, and let himself be seen only on the sidelines, between the lines, in the recesses of that conscious plot that we assume to be our life. Therefore, it is not so much a matter of chasing time that flees, or recovering lost time, but rather of knowing our own inner division and understanding that the life and times we dream of are, in fact, already here. And this occurs provided we listen to what the unconscious can tell us between the lines, always in an indirect, obscure, enigmatic way. The Freudian way is not that of understanding oneself, but rather that of the traumatic encounter with our obliterated and removed origin, whereby each of us is precisely what we are, never being able to understand it fully.

There is another world in store for us. However, it is a matter of ceasing all waiting since, due to its structure, it always comes from behind us, suddenly, without any possible prediction. Here’s the point: the time of the unconscious cannot be predicted, it cannot be forecasted, planned, or organized.

Illustration by Elisa Setzinger

What matters most is, therefore, not set in our past, nor could it be set in a hypothetical future. On the other hand, returning to our French revolutionaries, what could they know, while they were engaged in the revolution, about the revolution they were to hand down to history?

That’s why we do a lot to remove the removal by continually attempting to master time: we chase a time that always eludes us, we never have enough, we always seek more of it. It is the insatiable logic of desire, which drives us to request more time or to complain about the time wasted. All of this to avoid facing our own time, for which we cannot hold anyone else responsible except ourselves. A responsibility that anguishes us, because it involves deep loneliness.

Time, in analytic experience, is not the chronological, abstract, indifferent time that moves our clocks, for which — as Bergson said — every minute is the same as all the others. But it is also not the time experienced by the intentional consciousness, the subjective one that in contrast makes a day of joy seem to fly away in an instant or half an hour of waiting for a late train give us the impression of never ending. Unconscious time has nothing to do with duration; it does not depend on the perception that the conscious subject has of it. It is, instead, characterized by the anonymous and impersonal, but always singular dimension of incursion and surprise.

A good example can be taken from the experience of music. The rhythm and time of a musical composition are marked by an objective order, set by a metronome which can be divided according to the duration of the individual notes: eighth notes, sixteenth notes, and quarter notes. Then there is the expressive duration: The accelerando, the tempo rubato, and the rallentando. But then there is yet another time, which is neither subjective nor objective, neither expressive nor metronomic. A time that depends on the harmonic structure, that points out where the process is going. This is the time that characterizes the real passages of writing music: when the music breaks the silence, with its attack, or when its harmonic tension unexpectedly falls into a new constellation. It’s time as an event. This concerns psychoanalysis: a time that satisfies us.

Let’s take another example, one which is also famous, from Lacan. On March 6, 1963, Lacan ended his lecture on the theme of anxiety by evoking an anecdote about an orgasm: “How often have you been told that a subject had one of his first orgasms when he had to hand-up in a great hurry the copy of a scholastic composition or drawing that he had to finish quickly?” In the instant in which the other person awaits our “work,” our task, drawing, essay, just then the lack of time has a dizzying effect on the subject: “The collection of the copies: at that precise moment he ejaculates at the high-point of anxiety.” An extreme paradox, obviously, but real. Just when there is no more time, the other person’s demand causes in the subject an effect of enjoyment that is confused with the strongest and most unbearable anxiety. It is this affective bottleneck that affects the use of time that becomes the object of the analysis: not the chronological time, in which the minutes available for the task are precisely set and equal for all, nor that of the subjective duration, in which the task can last more or less depending on the perception that each student has of their difficulty. It’s the time that tightens around the instant that no longer has any duration, no minutes or seconds, dizzyingly plunged towards nothingness, between my offer and the other’s demand, in the midst of what starts to quiver: There, the anxiety is channeled towards what we care most about. An instant that at the same time is empty and infinite, in which the subject reaches its own satisfaction, a time that develops along a bottleneck, on the contingency of an unpredictable event.

Sixty years after Freud’s discovery of the unconscious, Lacan offered another interpretation of time — an act that cost him the excommunication from the International Psychoanalytical Association. It was in the early ‘60s; the analytical practice Lacan refounded precisely to remain as faithful as possible to the originality of the Freudian discovery was accused of heresy. Louis Althusser, the famous Marxist philosopher, offered him shelter at the École Pratique des Hautes Études. And all of a sudden Lacan found himself before a new audience: not only fellow psychiatrists and psychoanalysts, but also young philosophers. The revolution had a second chance here: the Marxists were attending the heretic psychoanalyst’s lectures.

How did this encounter translate into the logic of the cure? Through the originality with which Lacan changed the traditional technique of the duration of the sessions. The only real instrument to meet reality is time. It is not the meaning, it is not what we say, but it is its interruption that produces a revelation, an encounter, a surprise.

Illustration by Elisa Seitzinger

For Freudians, standard sessions have a fixed duration. Whether the patient says something, shuts up, sleeps, cries or shouts, the inexorable analyst, like a dead man, offers him his ear for exactly 45 minutes, then sends the patient off. On the analyst’s side time is chronological, on the patient’s side it is that of his experience, which can make a session seem longer or shorter. However, there is no contact with real time. To provoke this encounter, Lacan brought a peculiar innovation into the technique, which can only be supported through a very precise ethical rigor: the session does not have a standard duration, the time under analysis is not the dead time of a watch, but the time that is full of desire. Whose desire? That’s the key question. The desire of the unconscious, which for Lacan is not the patient story nor the psychoanalyst’s analysis, but rather a “different” dimension that opens up precisely because, between you and me, the transference has produced a new desire. There is no time in analysis without desire.

The session no longer has a standard duration because each time could be the last one. So it is from the first session, in fact, that something has been produced and has ended up in the background: a secret that supports the transference of the cure. Until it’s taken care of. Something that can occur at any time. In fact, to be more precise, in every session you always have to deal with this enigmatic aspect that can revitalize the analytical work or end it. Therefore, the time under analysis is neither the dead time of the clock, nor the living time that imaginatively is that of the consciousness of the patient or of the analyst. It’s the time that is eroticized by the analytical transference. There is “an erotics of time” — as Jacques-Alain Miller calls it — that animates the cure, punctuating its outcomes, surprises, and subterfuges.

The duration of the session is therefore variable: neither the analyst nor the analysand can know it in advance: it will depend on what arises during the dialog. It tends to be short, however. Short because time must be given its weight, or stated another way, short because there is no time to waste. The analysand must feel that he or she is being tended to and that time is running out, only by doing so can he or she also focus the conversation on the aspect that is felt to be most important? It’s a matter of grasping it. Except that, due to its very structure the thing we are trying to grasp is always elusive.

And this prompts a new question. How do we signal to the subjects that the time they dream of, and constantly search for, is right there where it apparently escapes them? Exactly how can we tell a subject that the unconscious is never where you expect it to be, but always a bit further away, from where it looks at us with a grin? How can we tell that subject that after all, what matters most is precisely what manifests itself for an instant and at the same time immediately disappears? Lacan’s invention of cutting the session time must be interpreted this way. Like a Zen master — said Lacan as early as 1953 — the analyst must “interrupt the silence with anything — with a sarcastic remark, with a kick,” suddenly cutting the session and dismissing the patient. Without an interpretation, without attempting to complete the sense of the patient’s speech. On the contrary, to show him that the time he has dreamed of is the empty instant of satisfaction at the limits of meaning. In a moment we understand each other, and there is satisfaction, of which laughter is direct evidence, but not mutual understanding. The important thing is that it remains a mis-understanding, a difference, a nonsense, which is the basis of the exhilarating effect. So even when cutting the session, the analyst gives the patient a chance to seize from that instantaneous interruption the best possible way of dealing with the other. The unconscious has the rhythm of stumbling, falling, oversight. Better yet, surprise.

There is, therefore, a way that the analyst must master to properly cut the duration of the sessions. In this sense, the art of the analyst is closer to surgery than to interpretation. The cut is not an imposition, violent, and arrogant, it involves absolute responsibility and a good dose of courage. The art of analysis is, after all, knowing how to deal with time. To act at the right time, not earlier or later, but on the point of onset, where the sense opens up, leaving behind the nonsense. For the subject this dialectic, this intermittent aspect, and this rhythm represents the opportunity to regain contact with the elasticity of his life that the symptom, with his or her aspirations or nostalgia, had contracted into an eternal present.

What is longitude?

If Great Britain built what, in its heyday, was the largest empire in history and maintained the status of a major global superpower during the entire 19th century, that was because of its maritime forces and domination over the seas. In part, that was a natural consequence of being an island, but it was also the result of the groundbreaking innovation to calculate longitude with astonishing precision. The clockmaker John Harrison is the man to whom every captain, sailor, shipowner, and passenger should say, “thank you.” Harrison committed his life to find a solution to a seemingly unsolvable problem, resisting failure, moments of despair, and, most of all, the acrimony-flavored skepticism of the scientific community. Strangely enough, this incredible story was unknown until 1996 when Dava Sobel released her best-selling (and Best British Book of the year) Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time.

The problem of longitude

Travelers know that a destination is as important as a current position. A Cartesian axis point is defined by its X and Y coordinates; on a map this is given by the values of latitude (the point along an ideal North-South line), and longitude (the point along an East-West line). If determining the former never was a particularly troublesome task—since it could be inferred by the Sun’s altitude at noon— calculation of the latter was thought to be almost impossible. Yet, defining this second point was absolutely essential for cartography and ocean navigation. In the open water, with no reference point but the sun, moon, and stars (when they were visible), as food and water supplies were shrinking, fearing the rise of a sudden storm was a real nightmare without a clear direction of where to go.

The problem of longitude meant that the Age of Discovery’s great captains, from the 15th to 17th centuries from Ferdinand Magellan to Sir Francis Drake and Vasco de Gama, were almost improvisers, “and they all got where they were going by willy-nilly, by forces attributed to good luck and the grace of God,” Sobel writes. Unfortunately, Lady Luck quite often deserted her maritime worshippers. As the global economy relied increasingly on sea journeys, not knowing, or miscalculating longitude, became problematic. “As more and more sailing vessels set out to conquer or explore new territories, to wage war, or to ferry gold and commodities between foreign lands, the wealth of nations floated upon the oceans. And still no ship owned the means for establishing her whereabouts. In consequence, untold numbers of sailors died when their destination suddenly loomed out to sea and took them by surprise.”

Don’t rock the boat

Although these incidents were quite frequent, monarchs and admirals still weren’t happy about losing men, ships, and goods. One tragedy proved to be particularly shocking and unacceptable: In 1707, Sir Clowdisley Shovell, a British Royal Navy senior commander, accidentally led his fleet toward the Isles of Scilly, off the Cornish Coast, sinking four ships and killing about 2,000 sailors. The British Parliament then decided that enough was enough. Seven years later, the Longitude Act was passed. It established the Board of Longitude and offered a monetary reward to those who would invent a practical means to determine a ship’s longitude: The more accurate, the higher the prize, reaching £20,000 (€3.2 million today), if the error was not greater than half a degree. Such a sum was a strong incentive. John Harrison was among those who tried hard to solve the problem. But he swam against the tide, firmly believing that the solution didn’t lay in the realm of astronomy—a blasphemy to almost everyone’s ears.

Before Harrison’s invention, sailors used dead reckoning (from deduced reckoning), to determine their ship’s position. This consists of calculating a current position by advancing to the last determined bearing once the speed and time elapsed are known or estimated. Of course, this method was anything but accurate. Seamen have no reference point but the sky, and this is problematic. The moon is invisible for eight days a month, the sky could be cloudy, the night could be particularly dark. Yet, astronomy was thought to have all the answers. For instance, the Board of Longitude was led by the Astronomer Royal, a post created by King Charles II in 1675, at the same time as he founded the Royal Greenwich Observatory. But those answers were incomplete and lacked accuracy. Instead of looking up, Harrison looked down at his work table. He was not a scientist, but a carpenter who had fallen in love with pendulum clocks and at age 20 built his first model: a wooden case, hands, and gears.

A matter of time

Harrison believed that to establish their position, seamen didn’t need a telescope, but a timekeeper, telling them the time back home. He posited that at noon, when the sun reaches its highest point in the sky, sailors could use the time at their port of origin to calculate their position, since the hour difference could be converted to geographical distance. In fact, since the Earth takes 24 hours to make a full, 360-degree rotation, then in one hour it makes 1/24 of its spin, a 15-degree rotation. With that in mind, Harrison worked relentlessly on his special Harrison N°1, or H1, presented in 1727. It was not a clock, but a spring-loaded brass contraption weighing 34 kilos and running for 24 hours. The clock didn’t provide the solution everyone was hoping for, but it was an indication that the clockmaker was on the right path, as the Board of Longitude recognized. In 1737, Harrison delivered H2, an improved version of the previous model, which was still not good enough to be tested on the sea. He then spent another 19 years working on his next attempt, H3.

Another clockmaker, John Jefferys, helped Harrison start from scratch, and that was a turning point. They abandoned the idea of building a pendulum, and switched to a pocket clock, deliberately ignoring Harrison’s lifetime of learning and own common sense. It was widely known at the time that pendulum clocks were more reliable and precise than pocket clocks but, unfortunately, they were also not fit for ships crossing oceans. In Sobel’s words: “On the deck of a rolling ship, such clocks would slow down, or speed up, or stop running altogether. Normal changes in temperature encountered en route from a cold country of origin to a tropical trade zone thinned or thickened the clock’s lubricating oil and made its metal parts expand or contract with equally disastrous results. A rise and fall in barometric pressure, or the subtle variations in the earth’s gravity from one altitude, to another, could also cause a clock to gain or lose time.”

The pendulum maker swings round

Harrison commissioned Jeffery to create a pocket watch with design specifications. The result was an inspiration for H4, a legendary clock that (almost) won the Longitude Prize. It was the first high-precision marine chronometer. About it, its maker said: “I think I may make bold to say, that there is neither any other Mechanical nor Mathematical thing in the World that is more beautiful or curious in texture than this my watch or Time-keeper for the Longitude (…) I heartily thank Almighty God that I have lived so long, as in some measure to complete it.” The clock was packed with innovative components and had a few secrets: It didn’t self-start and had very fast ticking (five ticks per second). “It beat so fast, and the balance wheel rotated so far, with such high energy, that it could not be pushed off-balance, even by a raging sea. The watch that was so hard to start was also hard to stop, hard to perturb,” the Guardian wrote in a 2014 piece dedicated to Harrison’s life.

Harrison worked on H4 between 1755 and 1759, while he was putting the final touches on the previous model. The timekeeper was completed in 1761 and tested on a voyage from Portsmouth, England to Kingston, Jamaica on the HMS Deptford. The ship set sail on 18 November 1761 and reached its destination after an 81 day and five-hour navigation. When all due corrections were made (H4 was losing 24 seconds each nine days, or 24/9 seconds per day), the jury found that the clock was only five seconds slow, corresponding to a longitude error of less than a nautical mile. Despite its performance, the jury thought it was a fluke and requested a second trip. Harrison felt betrayed and demanded his prize. The matter eventually went to the Parliament, which offered the clockmaker a £5,000 prize for the design, which angered him even more.

Trying to turn back the tide

Harrison eventually went on a second trial trip. This time, H4 was tested on the HMS Tartar on a voyage to Bridgetown, Barbados. The clock passed the test with flying colors, but the result was again attributed to good luck and coincidences, instead of precise navigation. Another matter arose and another offensive solution was found: Harrison was offered £10,000 in advance, but, to receive the second half of the prize, he had to relinquish his original design. To make matters worse, astronomer Nevil Maskelyne was asked to accompany Harrison on the voyage, to contextually determine longitude through a new Method of Lunar Distances. Maskelyne was a de facto rival of Harrison. He was appointed Astronomer Royal, thus becoming a member of the Board of Longitude, and in his new position, he filed a negative report on the second trip, but that didn’t deter the clockmaker.

Harrison never gave up and kept working on a new clock, H5. Thanks to the support of King George III, the stubborn carpenter filed a petition to the Parliament which, in 1773, won him £8,750. But he never won the Longitude Prize and never got the recognition he deserved. At least, not officially. But his clocks have stood the test of time and have changed navigation (and Great Britain’s history) forever.

The infinite debate around the reality of hours

Philosophical theory has been dealing with the nature of time for at least 2,000 years. The debate started with the opposing theories of Parmenides and Heraclitus. The former depicts time as a changeable element that contrasts with the timelessness and changelessness of being, while the latter considers time a fundamental component for the description of the world. The dispute has reached our times while retaining this duality.

“Physics has come up with compelling answers on the concept of time, pointing out how time flows differently according to our relative motion as observers — notes Giuliano Torrengo, the founder of the Center for Philosophy of Time at the University of Milan and member of the International Association for Philosophy of Time (IAPT). Yet only philosophy, standing at the intersection of different disciplines, can perhaps explain the meanings of expressions such as “time passes” and “time flows.” The real turning point was English philosopher John McTaggart’s article The Unreality of Time, published as a journal article in Mind in 1908, where he introduced the notions of “A series” and “B series”: Two different descriptions of the temporal ordering relation among events. The A Series considers time as a dynamic element, in which the concepts of being present, past and future are constantly changing so that what is present in this given moment, will no longer be present in another moment. Instead, the B Series replaces the concepts of present, past, and future with the ideas of “earlier than” and “later than.” So, according to the B Series, getting to a party will always come before leaving a party, and this will always be true, today as in two hundred years.”

McTaggart’s arguments were received in two contrasting ways, and they further polarized the debate in subsequent years.

For A-theorists, the flow of time is a genuine phenomenon of reality, while for B-theorists the flow of time is a metaphor that at most describes something of our experience without reflecting reality in its essence. Furthermore, according to the A-theory, present, past and future are genuine properties, and therefore what is past, what is present, and what is future changes absolutely with the flow of time. Conversely, for B-theorists, present, past, and future are only indexical notions, that is, we can say what is present in relation to a certain time, but we will never be able to say that something is present tout court. According to the B-theory, the flow of the present is to be interpreted only as a fact of our mind. This does not mean, however, that time does not exist, but rather that time is only made up of temporal relations, not by the flow of time. For the B-theory, in essence, there is no substantive dynamic element that is part of reality.

On the other hand, there is a dynamic element that is certainly part of experience, but it is only an “illusory” element. The B-theory has this main problem: it doesn’t fully explain why — in the common experience of each of us — time seems to flow. Undoubtedly, common sense seems to suggest that A-theories are more correct, but it is also true that common sense also suggests many wrong ideas.

So why is the A-theory less convincing?

The weak point of the A Series is that they are not compatible with Einstein’s relativity, since they assume a function of absolute simultaneity. But the theory of relativity tells us that there can be no absolute simultaneity, or rather it tells us that, if it exists, we cannot establish it empirically. Until the ’80s of the last century, the idea that the B Series was the correct theory prevailed among philosophers. More recently, there has been a renaissance of the A Series. In the 1950s, Arthur Prior was one of the very few philosophers to defend the A-theory, even to the extreme point of extremism of denying the conclusions of the theory of relativity. Prior was then upholding his opinion alone, while now there is a very heated debate concerning the A Series. Although the B Series continues to have more supporters.

Is there a common ground between A- and B-theorists?

No, the theories make radically different assumptions about the nature of time. There are so-called “deflationist” positions, but they do not convince either of the camps. In the past, when A-theorists were a clear minority, the problem of making B theories fit with the common sense of each of us, who would lean towards A theories, was snubbed, and philosophers tended to delegate its resolution to psychology. Until in 2010 the American philosopher Laurie A. Paul, in an article entitled Temporal Experience, clearly and directly asked exactly how we can explain the experience, admitting that Theory B is correct. From then on the debate resumed and tried to understand what kind of cognitive tools can be used to explain the opposite appearance.

There is a subject that also fascinates non-experts, namely the possibility, contemplated by philosophy, that time travel can really occur.

The metaphysical possibility of time travel — that is, the hypothesis that the occurrence of time travel is consistent — has found unanimous consensus in the philosophical community, since the philosopher David Lewis wrote the famous article The “Paradoxes” of Time Travel. The point to take into consideration is that from a logical point of view time travel can be considered entirely plausible if and only if there are no temporal inconsistencies. For example, to go back with the time machine to the thirties, kill Hitler and prevent the Second World War. If the time machine made it possible to stop Hitler, then we would find ourselves in the inconsistent hypothesis that the world war happened and at the same time did not occur. But the possibility of time travel is not inconsistent in itself. We tend to think about inconsistency because, when we talk about time travel, we usually tell stories in which the past happens twice. Instead, the problem arises when we consider the physical implications of this reasoning. If, in principle, I were to admit the possibility of being able to cross a space-time tunnel that leads from one point of the universe to another, how feasible would this possibility be according to quantum physics?