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James Gleick on How Our Cultural Fascination with Time Travel Illuminates Memory, the Nature of Time, and the Central Mystery of Human Consciousness

“Every moment alters what came before. We reach across layers of time for the memories of our memories.”

James Gleick on How Our Cultural Fascination with Time Travel Illuminates Memory, the Nature of Time, and the Central Mystery of Human Consciousness

“Both in thought and in feeling, even though time be real, to realise the unimportance of time is the gate of wisdom,” Bertrand Russell in 1931 as he made his beautiful case for “a largeness of contemplation” in contemplating the nature of time. “Shard by shard we are released from the tyranny of so-called time,” Patti Smith wrote nearly a century later in her magnificent meditation on time and transformation.

As a child in Bulgaria, never having heard of either Russell or Smith, one aspect of time perplexed me to the point of obsession: In my history textbooks, dates relating to significant events or historical figures of Slavic origin were listed in pairs — each had a “new style” date and an “old style” date, always thirteen days apart. So, for instance, Hristo Botev — the great revolutionary who led Bulgaria’s liberation from a five-century Ottoman slavery — was born on January 6 of 1848 according to the new style and on Christmas Day of 1847 according to the old style.

I would later learn that this was the product of the League of Nations, formed after WWI. Its Committee on Intellectual Cooperation, headed by Henri Bergson — the great French philosopher who famously opposed Einstein in a debate that changed our modern conception of time — was tasked with eradicating the Julian calendar that many countries, including Bulgaria and Russia, still used and replacing it with the Gregorian calendar as the new global standard.

This is my earliest memory of confronting the nature of time as both an abstraction humans could make with a committee and a concrete anchor of existence mooring our births, our deaths, and our entire sense of history. But most perplexing of all was the question of what happened to the people who lived through the transition — what happened to the thirteen very real days between the two fictions of the calendars. If reading history wasn’t time-travelish enough, reading about real people forced to time-travel in their real lives by an international decree was both utterly fascinating and utterly confusing. Did the person actually exist between their old-style date of birth and the new-style one — were they alive or not-yet-born? (Even today, the Wikipedia biographies of a Slavic persons from that era list both old-style and new-style dates of birth and death.) The person, of course, most definitely did exist between the day they were born and the day they died, whatever dates posterity — our living present, their unlived future — may impose on those days, now far in the past.

That thirteen-day lacuna between being and non-being was, apparently, the price of globalization. But it was also a suddenly shrill echo of an eternal question: If time bookends our existence, and if it is so easily perturbed by a calendarical convention, is it a mere abstraction?

Discus chronologicus, a German depiction of time from the early 1720s, from Cartographies of Time

Time is the two-headed Baskerville hound chasing us as we run for our lives — and from our lives — driven by the twain terrors of tedium and urgency. Toward what, we dare not think. Meanwhile, our information-input timelines are called “feeds.” We feast on time as time feasts on us. Time and information, if they are to be disentwined at all, dictate our lives. Is it any wonder, then, that we would rebel by trying to subjugate them in return, whether by formalizing them with our calendars or by fleeing from them with our time travel fantasies?

How those time travel fantasies originated, what technological and cultural developments fomented this distinctly modern impulse of the collective imagination, and how it illuminates our greatest anxieties is what science historian and writer extraordinaire James Gleick explores in Time Travel: A History (public library) — a grand thought experiment, using physics and philosophy as the active agents, and literature as the catalyst. Embedded in the book is a bibliography for the Babel of time — a most exquisitely annotated compendium of the body of time literature. What emerges is a inquiry, the most elegant since Borges, into why we think about time, why its directionality troubles us so, and what asking these questions at all reveals about the deepest mysteries of human consciousness and about what Gleick so beguilingly calls “the fast-expanding tapestry of interwoven ideas and facts that we call our culture.”

Gleick, who examined the origin of our modern anxiety about time with remarkable prescience nearly two decades ago, traces the invention of the notion of time travel to H.G. Wells’s 1895 masterpiece The Time Machine. Although Wells — like Gleick, like any reputable physicist — knew that time travel was a scientific impossibility, he created an aesthetic of thought which never previously existed and which has since shaped the modern consciousness. Gleick argues that the art this aesthetic produced — an entire canon of time travel literature and film — not only permeated popular culture but even influenced some of the greatest scientific minds of the past century, including Stephen Hawking, who once cleverly hosted a party for time travelers and when no one showed up considered the impossibility of time travel proven, and John Archibald Wheeler, who popularized the term “black hole” and coined “wormhole,” both key tropes of time travel literature.

Illustration by Matthew Houston for a graphic interpretation of Wells’s The Time Machine

Gleick considers how a scientific impossibility can become such fertile ground for the artistic imagination:

Why do we need time travel, when we already travel through space so far and fast? For history. For mystery. For nostalgia. For hope. To examine our potential and explore our memories. To counter regret for the life we lived, the only life, one dimension, beginning to end.

Wells’s Time Machine revealed a turning in the road, an alteration in the human relationship with time. New technologies and ideas reinforced one another: the electric telegraph, the steam railroad, the earth science of Lyell and the life science of Darwin, the rise of archeology out of antiquarianism, and the perfection of clocks. When the nineteenth century turned to the twentieth, scientists and philosophers were primed to understand time in a new way. And so were we all. Time travel bloomed in the culture, its loops and twists and paradoxes.

Wells imagined time travel in an era where so much of what we take for granted was either a disorienting novelty or yet to be invented — bicycles, elevators, and balloons were new, and even the earliest visions of anything resembling the internet were half a century away. Gleick considers the direction of Wells’s imagination:

The object of Wells’s interest, bordering on obsession, was the future — that shadowy, inaccessible place. “So with a kind of madness growing upon me, I flung myself into futurity,” says the Time Traveller. Most people, Wells wrote — “the predominant type, the type of the majority of living people” — never think about the future. Or, if they do, they regard it “as a sort of blank non-existence upon which the advancing present will presently write events.” … The more modern sort of person — “the creative, organizing, or masterful type” — sees the future as our very reason for being: “Things have been, says the legal mind, and so we are here. The creative mind says we are here because things have yet to be.”

Wells wrote his masterpiece shortly before the rise of relativity remodeled our notions of time. There was Einstein, of course. And Kurt Gödel. And Hermann Minkowski, Einstein’s teacher, whose model used four numbers (x, y, z, and t) to denote a “world point” — what we now call spacetime. Gleick writes of his legacy:

“Mere shadows,” Minkowski said. That was not mere poetry. He meant it almost literally. Our perceived reality is a projection, like the shadows projected by the fire in Plato’s cave. If the world — the absolute world — is a four-dimensional continuum, then all that we perceive at any instant is a slice of the whole. Our sense of time: an illusion. Nothing passes; nothing changes. The universe — the real universe, hidden from our blinkered sight — comprises the totality of these timeless, eternal world lines.

But if we were able to conceive of this timeless totality — to integrate it into our conscious experience — the fantasy of time travel wouldn’t scintillate us so. A centerpiece of our temporal dissonance is one particular phenomenon of consciousness, a very palpable human experience: memory. “Perhaps memory is the time traveler’s subject,” Gleick observes. With an eye to Virginia Woolf’s memorable mediation on memory in Orlando, that supreme masterwork of time travel, he writes:

What is memory, for a time traveler? A conundrum. We say that memory “takes us back.” Virginia Woolf called memory a seamstress “and a capricious one at that.” … “I can’t remember things before they happen,” says Alice, and the Queen retorts, “It’s a poor sort of memory that only works backwards.” Memory both is and is not our past. It is not recorded, as we sometimes imagine; it is made, and continually remade. If the time traveler meets herself, who remembers what, and when?

Illustration by Lisbeth Zwerger for a special edition of Alice in Wonderland

The question of memory, of course, is inseparable from the question of identity, for if we live in “permanent present tense,” we are incapable of stringing together the narrative out of which our sense of self arises. This continuity of selfhood, after all, is what makes you and your childhood self the “same” person despite a lifetime of physical and psychological change. Time travel presents some serious paradoxes for memory and therefore for the self. “A person’s identity,” Amin Maalouf wrote of the genes of the soul, “is like a pattern drawn on a tightly stretched parchment. Touch just one part of it, just one allegiance, and the whole person will react, the whole drum will sound.” If we could travel back to our own past and alter even a tiny speck of the pattern, we’d be changing the entire drum — our identity would have a wholly different sound. Gleick writes:

What is the self? A question for the twentieth century to ponder, from Freud to Hofstadter and Dennett with detours through Lacan, and time travel provides some of the more profound variations on the theme. We have split personalities and alter egos galore. We have learned to doubt whether we are our younger selves, whether we will be the same person when we next look. The literature of time travel … begins to offer a way into questions that might otherwise belong to philosophers. It looks at them viscerally and naïvely — as it were, nakedly.

And so we arrive, at page 99 and no sooner, at the problem of free will. Gleick writes:

Free will cannot be easily dismissed, because we experience it directly. We make choices. No philosopher has yet sat down in a restaurant and told the waiter, “Just bring me whatever the universe has preordained.” Then again, Einstein said that he could “will” himself to light his pipe without feeling particularly free. He liked to quote Schopenhauer… Man can do what he will, but he cannot will what he wills.

The free will problem was a sleeping giant and, without particularly meaning to, Einstein and Minkowski had prodded it awake. How literally were their followers to take the space-time continuum — the “block universe,” fixed for eternity, with our blinkered three-dimensional consciousnesses moving through it?

A century later, the question has hardly budged. And yet we live our lives with such urgency and pointedness of intent — perhaps precisely because we are unwilling to relinquish the illusion of free will. Gleick observes:

Everywhere we look, people are pressing elevator buttons, turning doorknobs, hailing taxicabs, lifting sustenance to their lips, and begging their lovers’ favor. We act as though the future is, if not in our control, not yet settled… We would suffer illusions of free will, because, by happenstance, we tend to know less about the future than about the past.

Happenstance? Memory, self, free will — this Venn diagram of consciousness is indeed encircled by the lines we draw, often artificially, between causality and chance. (“No one’s fated or doomed to love anyone… The accidents happen,” wrote Adrienne Rich.) Gleick writes:

All the paradoxes are time loops. They all force us to think about causality. Can an effect precede its cause? Of course not. Obviously. By definition.


But we’re not very good at understanding causes. The first person on record as trying to analyze cause and effect by power of ratiocination was Aristotle, who created layers of complexity that have caused confusion ever after. He distinguished four distinct types of causes, which can be named (making allowances for the impossibility of transmillennial translation) the efficient, the formal, the material, and the final. Some of these are hard for us to recognize as causes. The efficient cause of a sculpture is the sculptor, but the material cause is the marble. Both are needed before the sculpture can exist. The final cause is the purpose for which it is made — its beauty, let’s say… We do well to remember that nothing, when we look closely, has a single unambiguous incontrovertible cause.

Gleick reality-checks the logicians’ causal models of reality:

If X, then Y means one thing in logic. In the physical world, it means something trickier and always (we should know by now) subject to doubt. In logic, it is rigid. In physics, there is slippage. Chance has a part to play. Accidents can happen. Uncertainty is a principle. The world is more complex than any model.


The physical laws are a construct, a convenience. They are not coextensive with the universe.

One of Antoine de Saint-Exupéry’s original watercolors for The Little Prince

Mistaking the model for what Virginia Woolf called “the thing itself” seems to be a perennial problem of science, and one particularly integral to the perplexity of time:

William Faulkner said, “The aim of every artist is to arrest motion, which is life, by artificial means and hold it fixed.” Scientists do that, too, and sometimes they forget they are using artificial means.


You can say the equations of physics make no distinction between past and future, between forward and backward in time. But if you do, you are averting your gaze from the phenomena dearest to our hearts. You leave for another day or another department the puzzles of evolution, memory, consciousness, life itself. Elementary processes may be reversible; complex processes are not. In the world of things, time’s arrow is always flying.

Illustration from a vintage children’s adaptation of Micromégas, Voltaire’s trailblazing scifi homage to Newton

With an eye to Borges’s ideas about time, Gleick returns to the puzzlement of memory, equally not coextensive with the physics of time:

We create memories or our memories create themselves. Consulting a memory converts it into a memory of a memory. The memories of memories, the thoughts of thoughts, blend into one another until we cannot tease them apart. Memory is recursive and self-referential. Mirrors. Mazes.

The formation of memory as a function of consciousness invites the chief religious opposition to science — a theological avoidance of the free will problem, the intellectually fragile contradictions of which Gleick captures elegantly in discussing the ideas in Isaac Asimov’s novel The End of Eternity:

Time is a feature of creation, and the creator remains apart from it, transcendent over it. Does that mean that all our mortal time and history is, for God, a mere instant — complete and entire? For God outside of time, God in eternity, time does not pass; events do not occur step by step; cause and effect are meaningless. He is not one-thing-after-another, but all-at-once. His “now” encompasses all time. Creation is a tapestry, or an Einsteinian block universe. Either way, one might believe that God sees it entire. For Him, the story does not have a beginning, middle, and end.

But if you believe in an interventionist god, what does that leave for him to do? A changeless being is hard for us mortals to imagine. Does he act? Does he even think? Without sequential time, thought — a process — is hard to imagine. Consciousness requires time, it seems. It requires being in time. When we think, we seem to think consecutively, one thought leading to another, in timely fashion, forming memories all the while. A god outside of time would not have memories. Omniscience doesn’t require them.

But whatever pitfalls, paradoxes, and perplexities might bedevil our individual memory, they are rendered into even sharper relief in our collective memory — nowhere more so than in the curious human obsession with time capsules, the grandest of which is the Golden Record that sailed into space aboard the Voyager in 1977, a civilizational labor of love dreamt up and rendered real by Carl Sagan and Annie Druyan that was also the record of their own love story.

The Golden Record
The Golden Record

Gleick considers what this strange millennia-old practice, this “prosthetic memory,” reveals about human nature:

When people make time capsules, they disregard a vital fact of human history. Over the millennia — slowly at first and then with gathering speed — we have evolved a collective methodology for saving information about our lives and times and transmitting that information into the future. We call it, for short, culture.

First came songs, clay pots, drawings on cave walls. Then tablets and scrolls, paintings and books. Knots in alpaca threads, recording Incan calendar data and tax receipts. These are external memory, extensions of our biological selves. Mental prostheses. Then came repositories for the preservation of these items: libraries, monasteries, museums; also theater troupes and orchestras. They may consider their mission to be entertainment or spiritual practice or the celebration of beauty, but meanwhile they transmit our symbolic memory across the generations. We can recognize these institutions of culture as distributed storage and retrieval systems. The machinery is unreliable — disorganized and discontinuous, prone to failures and omissions. They use code. They require deciphering. Then again, whether made of stone, paper, or silicon, the technology of culture has a durability that the biological originals can only dream of. This is how we tell our descendants who we were. By contrast, the recent smattering of time capsules is an oddball sideshow.

Building on the ideas he examined in his indispensable biography of information, Gleick adds:

As for knowledge itself, that is our stock in trade. When the Library of Alexandria burned, it was one of a kind. Now there are hundreds of thousands, and they are crammed to overflowing. We have developed a species memory. We leave our marks everywhere.


When people fill time capsules they are trying to stop the clock — take stock, freeze the now, arrest the incessant head-over-heels stampede into the future. The past appears fixed, but memory, the fact of it, or the process, is always in motion. That applies to our prosthetic global memory as well as the biological version. When the Library of Congress promises to archive every tweet, does it create a Borgesian paradox in real time or a giant burial chamber in progress?

Because time has this unsilenceable undertone reminding us of our morality, we grasp onto it — onto this intangible abstraction — the way we grasp onto material possessions, commodities, and all the other tangibilia by which we sustain our illusions of permanence in a universe dominated by impermanence and constant flux. From this angle, Gleick revisits the tenet that all paradoxes are time-loops:

Once we conceive of time as a quantity, we can store it up, apparently. We save it, spend it, accumulate it, and bank it. We do all this quite obsessively nowadays, but the notion is at least four hundred years old. Francis Bacon, 1612: “To choose Time, is to save Time.” The corollary of saving time is wasting it.


We go back and forth between being time’s master and its victim. Time is ours to use, and then we are at its mercy. I wasted time, and now doth time waste me, says Richard II; For now hath time made me his numbering clock. If you say that an activity wastes time, implying a substance in finite supply, and then you say that it fills time, implying a sort of container, have you contradicted yourself? Are you confused? Are you committing a failure of logic? None of those. On the contrary, you are a clever creature, when it comes to time, and you can keep more than one idea in your head. Language is imperfect; poetry, perfectly imperfect. We can occupy the time and pass the time in the same breath. We can devour time or languish in its slow-chapp’d power.

Still, memory remains. The key to understanding time, Gleick suggests, lies in understanding memory — understanding the dialogue, often dissonant, between the experiencing self and the remembering self. He writes:

The universe does what it does. We perceive change, perceive motion, and try to make sense of the teeming, blooming confusion. The hard problem, in other words, is consciousness. We’re back where we started, with Wells’s Time Traveller, insisting that the only difference between time and space is that “our consciousness moves along it,” just before Einstein and Minkowski said the same. Physicists have developed a love-hate relationship with the problem of the self. On the one hand it’s none of their business — leave it to the (mere) psychologists. On the other hand, trying to extricate the observer — the measurer, the accumulator of information — from the cool description of nature has turned out to be impossible. Our consciousness is not some magical onlooker; it is a part of the universe it tries to contemplate.

The mind is what we experience most immediately and what does the experiencing. It is subject to the arrow of time. It creates memories as it goes. It models the world and continually compares these models with their predecessors. Whatever consciousness will turn out to be, it’s not a moving flashlight illuminating successive slices of the four-dimensional space-time continuum. It is a dynamical system, occurring in time, evolving in time, able to absorb bits of information from the past and process them, and able as well to create anticipation for the future.


What is time? Things change, and time is how we keep track.

This act of keeping track, which is largely a matter of telling the present from the past, is what Gleick considers the key question of consciousness and the pillar of our very sense of self:

How do we construct the self? Can there be memory without consciousness? Obviously not. Or obviously. It depends what you mean by memory. A rat learns to run a maze — does it remember the maze? If memory is the perpetuation of information, then the least conscious of organisms possess it. So do computers, whose memory we measure in bytes. So does a gravestone. But if memory is the action of recollection, the act of remembrance, then it implies an ability to hold in the mind two constructs, one representing the present and another representing the past, and to compare them, one against the other. How did we learn to distinguish memory from experience? When something misfires and we experience the present as if it were a memory, we call that déjà vu. Considering déjà vu — an illusion or pathology — we might marvel at the ordinary business of remembering.

This dizzying tour of science, philosophy, and their interaction with literature is leading me to wonder: When a machine hums, does it hear or notice the hum? Could it be that time is the hum of consciousness?


Perhaps time is so troublesome because it foists upon us our perennial fear of missing out. Time travel, Gleick argues, is such an alluring fantasy precisely because it bridges the infinite possibility of life with the realm of the probable — by traveling in time, we get to live the myriad unlived lives which we are doomed to never experience under the physical laws of this one and only life we’ve been allotted. He captures this with uncompromising precision:

If we have only the one universe — if the universe is all there is — then time murders possibility. It erases the lives we might have had.

Time travel, then, is a thought experiment performed in the petri dish of existence itself, catalyzing its most elemental and disquieting questions. In a reframing of the central idea of the Butterfly Effect — a term Gleick himself wrested from the esoteric lexicon of meteorology and embedded in the popular imagination in 1987 with his groundbreaking first book, Chaos, which created an aesthetic for the history of science much like Wells created an aesthetic for time travel literature — he considers the logical loops of changing any one element of history, which ripples across all of being:

We have to ask these questions, don’t we? Is the world we have the only world possible? Could everything have turned out differently? What if you could not only kill Hitler and see what happens, but you could go back again and again, making improvements, tweaking the timeline, like the weatherman Phil (Bill Murray) in one of the greatest of all time-travel movies, reliving Groundhog Day until finally he gets it right.

Is this the best of all possible worlds? If you had a time machine, would you kill Hitler?

And so we arrive at the answer to the central question:

Why do we need time travel? All the answers come down to one. To elude death.

Time is a killer. Everyone knows that. Time will bury us. I wasted time, and now doth time waste me. Time makes dust of all things. Time’s winged chariot isn’t taking us anywhere good.

How aptly named, the time beyond death: the Hereafter.


But even death is strewn with the temporal asymmetry of our anxieties, which Montaigne articulated brilliantly half a millennium ago as he contemplated death and the art of living: “To lament that we shall not be alive a hundred years hence, is the same folly as to be sorry we were not alive a hundred years ago.” And yet we do dread death with infinitely greater intensity than we dread, if that’s even the appropriate term, not having lived before our birth. If the arrow of time is one-directional, so is the arrow of time-anxiety. But Gleick subverts Montaigne and delivers a sublime summation of the paradoxical impulse at the heart of our time travel yearnings:

You lived; you will always have lived. Death does not erase your life. It is mere punctuation. If only time could be seen whole, then you could see the past remaining intact, instead of vanishing in the rearview mirror. There is your immortality. Frozen in amber.

For me the price of denying death in this way is denying life.

Barring denial, our only recourse is to surrender our memory, our consciousness, our very selves to the flow of time. To borrow Sarah Manguso’s piercing observation, “time punishes us by taking everything, but it also saves us — by taking everything.” Gleick writes:

When the future vanishes into the past so quickly, what remains is a kind of atemporality, a present tense in which temporal order feels as arbitrary as alphabetical order. We say that the present is real—yet it flows through our fingers like quicksilver.


It might be fair to say that all we perceive is change — that any sense of stasis is a constructed illusion. Every moment alters what came before. We reach across layers of time for the memories of our memories.

Complement Time Travel — the kind of book that lodges itself in the imagination, planting seeds of ideas, insights, and revelations bound to go on blossoming for the remainder of this lifetime — with Bertrand Russell on the nature of time and Virginia Woolf on its astonishing elasticity, then revisit Gleick on the story behind Newton’s famous “standing on the shoulders of giants” metaphor, the source of Richard Feynman’s genius, and the origin of Type A.


The Difficult Balance of Intimacy and Independence: Beloved Philosopher and Poet Kahlil Gibran on the Secret to a Loving and Lasting Relationship

“Love one another but make not a bond of love: let it rather be a moving sea between the shores of your souls.”

The Difficult Balance of Intimacy and Independence: Beloved Philosopher and Poet Kahlil Gibran on the Secret to a Loving and Lasting Relationship

“What’s the use of falling in love if you both remain inertly as-you-were?” Mary McCarthy asked her friend Hannah Arendt in their correspondence about love. The question resonates because it speaks to a central necessity of love — at its truest and most potent, love invariably does change us, deconditioning our painful pathologies and elevating us toward our highest human potential. It allows us, as Barack Obama so eloquently wrote in his reflections on what his mother taught him about love, “to break across our solitude, and then, if we’re lucky, [be] finally transformed into something firmer.”

But in the romantic ideal upon which our modern mythos of love is built, the solidity of that togetherness is taken to such an extreme as to render love fragile. When lovers are expected to fuse together so closely and completely, mutuality mutates into a paralyzing codependence — a calcified and rigid firmness that becomes brittle to the possibility of growth. In the most nourishing kind of love, the communion of togetherness coexists with an integrity of individuality, the two aspects always in dynamic and fluid dialogue. The philosopher Martin Heidegger captured this beautifully in his love letters to Hannah Arendt: “Why is love rich beyond all other possible human experiences and a sweet burden to those seized in its grasp? Because we become what we love and yet remain ourselves.”

This difficult balance of intimacy and independence is what the great Lebanese-American artist, poet, and philosopher Kahlil Gibran (January 6, 1883–April 10, 1931) explores with uncommon insight and poetic precision in a passage from his 1923 masterwork The Prophet (public library).

Illustration by Julie Paschkis from Pablo Neruda: Poet of the People by Monica Brown

By way of advice on the secret to a loving and lasting marriage, Gibran offers:

Let there be spaces in your togetherness,
And let the winds of the heavens dance between you.

Love one another but make not a bond of love:
Let it rather be a moving sea between the shores of your souls.
Fill each other’s cup but drink not from one cup.
Give one another of your bread but eat not from the same loaf.
Sing and dance together and be joyous, but let each one of you be alone,
Even as the strings of a lute are alone though they quiver with the same music.

Give your hearts, but not into each other’s keeping.
For only the hand of Life can contain your hearts.
And stand together, yet not too near together:
For the pillars of the temple stand apart,
And the oak tree and the cypress grow not in each other’s shadow.

Complement this particular portion of the wholly enchanting The Prophet with Virginia Woolf on what makes love last, philosopher Alain Badiou on how we fall and stay in love, Anna Dostoyevsky on the secret to a happy marriage, Mary Oliver on how differences bring couples closer together, and Joseph Campbell on the single most important factor in sustaining romantic relationships, then revisit Gibran on the seeming self vs. the authentic self and the absurdity of our self-righteousness.


The Secret Life of Trees: The Astonishing Science of What Trees Feel and How They Communicate

“A tree can be only as strong as the forest that surrounds it.”

The Secret Life of Trees: The Astonishing Science of What Trees Feel and How They Communicate

Trees dominate the world’s the oldest living organisms. Since the dawn of our species, they have been our silent companions, permeating our most enduring tales and never ceasing to inspire fantastical cosmogonies. Hermann Hesse called them “the most penetrating of preachers.” A forgotten seventeenth-century English gardener wrote of how they “speak to the mind, and tell us many things, and teach us many good lessons.”

But trees might be among our lushest metaphors and sensemaking frameworks for knowledge precisely because the richness of what they say is more than metaphorical — they speak a sophisticated silent language, communicating complex information via smell, taste, and electrical impulses. This fascinating secret world of signals is what German forester Peter Wohlleben explores in The Hidden Life of Trees: What They Feel, How They Communicate (public library).

Wohlleben chronicles what his own experience of managing a forest in the Eifel mountains in Germany has taught him about the astonishing language of trees and how trailblazing arboreal research from scientists around the world reveals “the role forests play in making our world the kind of place where we want to live.” As we’re only just beginning to understand nonhuman consciousnesses, what emerges from Wohlleben’s revelatory reframing of our oldest companions is an invitation to see anew what we have spent eons taking for granted and, in this act of seeing, to care more deeply about these remarkable beings that make life on this planet we call home not only infinitely more pleasurable, but possible at all.

Illustration by Arthur Rackham for a rare 1917 edition of the Brothers Grimm fairy tales

But Wohlleben’s own career began at the opposite end of the caring spectrum. As a forester tasked with optimizing the forest’s output for the lumber industry, he self-admittedly “knew about as much about the hidden life of trees as a butcher knows about the emotional life of animals.” He experienced the consequence of what happens whenever we turn something alive, be it a creature or a work of art, into a commodity — the commercial focus of his job warped how he looked at trees.

Then, about twenty years ago, everything changed when he began organizing survival training and log-cabin tours for tourists in his forest. As they marveled at the majestic trees, the enchanted curiosity of their gaze reawakened his own and his childhood love of nature was rekindled. Around the same time, scientists began conducting research in his forest. Soon, every day became colored with wonderment and the thrill of discovery — no longer able to see trees as a currency, he instead saw them as the priceless living wonders that they are. He recounts:

Life as a forester became exciting once again. Every day in the forest was a day of discovery. This led me to unusual ways of managing the forest. When you know that trees experience pain and have memories and that tree parents live together with their children, then you can no longer just chop them down and disrupt their lives with large machines.

The revelation came to him in flashes, the most eye-opening of which happened on one of his regular walks through a reserve of old beech tree in his forest. Passing by a patch of odd mossy stones he had seen many times before, he was suddenly seized with a new awareness of their strangeness. When he bent down to examine them, he made an astonishing discovery:

The stones were an unusual shape: they were gently curved with hollowed-out areas. Carefully, I lifted the moss on one of the stones. What I found underneath was tree bark. So, these were not stones, after all, but old wood. I was surprised at how hard the “stone” was, because it usually takes only a few years for beechwood lying on damp ground to decompose. But what surprised me most was that I couldn’t lift the wood. It was obviously attached to the ground in some way. I took out my pocketknife and carefully scraped away some of the bark until I got down to a greenish layer. Green? This color is found only in chlorophyll, which makes new leaves green; reserves of chlorophyll are also stored in the trunks of living trees. That could mean only one thing: this piece of wood was still alive! I suddenly noticed that the remaining “stones” formed a distinct pattern: they were arranged in a circle with a diameter of about 5 feet. What I had stumbled upon were the gnarled remains of an enormous ancient tree stump. All that was left were vestiges of the outermost edge. The interior had completely rotted into humus long ago — a clear indication that the tree must have been felled at least four or five hundred years earlier.

How can a tree cut down centuries ago could still be alive? Without leaves, a tree is unable to perform photosynthesis, which is how it converts sunlight into sugar for sustenance. The ancient tree was clearly receiving nutrients in some other way — for hundreds of years.

Beneath the mystery lay a fascinating frontier of scientific research, which would eventually reveal that this tree was not unique in its assisted living. Neighboring trees, scientists found, help each other through their root systems — either directly, by intertwining their roots, or indirectly, by growing fungal networks around the roots that serve as a sort of extended nervous system connecting separate trees. If this weren’t remarkable enough, these arboreal mutualities are even more complex — trees appear able to distinguish their own roots from those of other species and even of their own relatives.

Art by Judith Clay from Thea’s Tree

Wohlleben ponders this astonishing sociality of trees, abounding with wisdom about what makes strong human communities and societies:

Why are trees such social beings? Why do they share food with their own species and sometimes even go so far as to nourish their competitors? The reasons are the same as for human communities: there are advantages to working together. A tree is not a forest. On its own, a tree cannot establish a consistent local climate. It is at the mercy of wind and weather. But together, many trees create an ecosystem that moderates extremes of heat and cold, stores a great deal of water, and generates a great deal of humidity. And in this protected environment, trees can live to be very old. To get to this point, the community must remain intact no matter what. If every tree were looking out only for itself, then quite a few of them would never reach old age. Regular fatalities would result in many large gaps in the tree canopy, which would make it easier for storms to get inside the forest and uproot more trees. The heat of summer would reach the forest floor and dry it out. Every tree would suffer.

Every tree, therefore, is valuable to the community and worth keeping around for as long as possible. And that is why even sick individuals are supported and nourished until they recover. Next time, perhaps it will be the other way round, and the supporting tree might be the one in need of assistance.


A tree can be only as strong as the forest that surrounds it.

One can’t help but wonder whether trees are so much better equipped at this mutual care than we are because of the different time-scales on which our respective existences play out. Is some of our inability to see this bigger picture of shared sustenance in human communities a function of our biological short-sightedness? Are organisms who live on different time scales better able to act in accordance with this grander scheme of things in a universe that is deeply interconnected?

To be sure, even trees are discriminating in their kinship, which they extend in varying degrees. Wohlleben explains:

Every tree is a member of this community, but there are different levels of membership. For example, most stumps rot away into humus and disappear within a couple of hundred years (which is not very long for a tree). Only a few individuals are kept alive over the centuries… What’s the difference? Do tree societies have second-class citizens just like human societies? It seems they do, though the idea of “class” doesn’t quite fit. It is rather the degree of connection — or maybe even affection — that decides how helpful a tree’s colleagues will be.

These relationships, Wohlleben points out, are encoded in the forest canopy and visible to anyone who simply looks up:

The average tree grows its branches out until it encounters the branch tips of a neighboring tree of the same height. It doesn’t grow any wider because the air and better light in this space are already taken. However, it heavily reinforces the branches it has extended, so you get the impression that there’s quite a shoving match going on up there. But a pair of true friends is careful right from the outset not to grow overly thick branches in each other’s direction. The trees don’t want to take anything away from each other, and so they develop sturdy branches only at the outer edges of their crowns, that is to say, only in the direction of “non-friends.” Such partners are often so tightly connected at the roots that sometimes they even die together.

Art by Cécile Gambini from Strange Trees by Bernadette Pourquié

But trees don’t interact with one another in isolation from the rest of the ecosystem. The substance of their communication, in fact, is often about and even to other species. Wohlleben describes their particularly remarkable olfactory warning system:

Four decades ago, scientists noticed something on the African savannah. The giraffes there were feeding on umbrella thorn acacias, and the trees didn’t like this one bit. It took the acacias mere minutes to start pumping toxic substances into their leaves to rid themselves of the large herbivores. The giraffes got the message and moved on to other trees in the vicinity. But did they move on to trees close by? No, for the time being, they walked right by a few trees and resumed their meal only when they had moved about 100 yards away.

The reason for this behavior is astonishing. The acacia trees that were being eaten gave off a warning gas (specifically, ethylene) that signaled to neighboring trees of the same species that a crisis was at hand. Right away, all the forewarned trees also pumped toxins into their leaves to prepare themselves. The giraffes were wise to this game and therefore moved farther away to a part of the savannah where they could find trees that were oblivious to what was going on. Or else they moved upwind. For the scent messages are carried to nearby trees on the breeze, and if the animals walked upwind, they could find acacias close by that had no idea the giraffes were there.

Because trees operate on time scales dramatically more extended than our own, they operate far more slowly than we do — their electrical impulses crawl at the speed of a third of an inch per second. Wohlleben writes:

Beeches, spruce, and oaks all register pain as soon as some creature starts nibbling on them. When a caterpillar takes a hearty bite out of a leaf, the tissue around the site of the damage changes. In addition, the leaf tissue sends out electrical signals, just as human tissue does when it is hurt. However, the signal is not transmitted in milliseconds, as human signals are; instead, the plant signal travels at the slow speed of a third of an inch per minute. Accordingly, it takes an hour or so before defensive compounds reach the leaves to spoil the pest’s meal. Trees live their lives in the really slow lane, even when they are in danger. But this slow tempo doesn’t mean that a tree is not on top of what is happening in different parts of its structure. If the roots find themselves in trouble, this information is broadcast throughout the tree, which can trigger the leaves to release scent compounds. And not just any old scent compounds, but compounds that are specifically formulated for the task at hand.

The upside of this incapacity for speed is that there is no need for blanket alarmism — the recompense of trees’ inherent slowness is an extreme precision of signal. In addition to smell, they also use taste — each species produces a different kind of “saliva,” which can be infused with different pheromones targeted at warding off a specific predator.

Wohlleben illustrates the centrality of trees in Earth’s ecosystem with a story about Yellowstone National Park that demonstrates “how our appreciation for trees affects the way we interact with the world around us”:

It all starts with the wolves. Wolves disappeared from Yellowstone, the world’s first national park, in the 1920s. When they left, the entire ecosystem changed. Elk herds in the park increased their numbers and began to make quite a meal of the aspens, willows, and cottonwoods that lined the streams. Vegetation declined and animals that depended on the trees left. The wolves were absent for seventy years. When they returned, the elks’ languorous browsing days were over. As the wolf packs kept the herds on the move, browsing diminished, and the trees sprang back. The roots of cottonwoods and willows once again stabilized stream banks and slowed the flow of water. This, in turn, created space for animals such as beavers to return. These industrious builders could now find the materials they needed to construct their lodges and raise their families. The animals that depended on the riparian meadows came back, as well. The wolves turned out to be better stewards of the land than people, creating conditions that allowed the trees to grow and exert their influence on the landscape.

Art by William Grill from The Wolves of Currumpaw

This interconnectedness isn’t limited to regional ecosystems. Wohlleben cites the work of Japanese marine chemist Katsuhiko Matsunaga, who discovered that trees falling into a river can change the acidity of the water and thus stimulate the growth of plankton — the elemental and most significant building block of the entire food chain, on which our own sustenance depends.

In the remainder of The Hidden Life of Trees, Wohlleben goes on to explore such fascinating aspects of arboreal communication as how trees pass wisdom down to the next generation through their seeds, what makes them live so long, and how forests handle immigrants. Complement it with this wonderful illustrated atlas of the world’s strangest trees and an 800-year visual history of trees as symbolic diagrams.


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