A lone figure stands at the edge of the Universe and hurls a spear into the unknown, only to find the edge wasn’t an edge after all. A demon tells a chronically ill person that every moment of their life — every high, every hardship — will repeat forever, exactly as it is. A 16-year-old boy tries to travel alongside a beam of light, hoping to catch up, but no matter how fast he goes, it never slows. Someone is offered the chance to live in a simulated paradise, but there’s a catch: Once inside, they’ll forget it isn’t real. And a human falls in love with a consciousness that has no body, no boundaries, and no need for them.
All five scenarios are drawn from what is classically termed thought experiments. They range from Lucretius’ spear flung at the edge of the Universe — one of the earliest on record (1st century BCE) — to the vision of eternal recurrence that gripped the chronically ill Nietzsche. From Einstein’s boyhood attempt to chase a beam of light, to Robert Nozick’s 1974 Experience Machine. And even to a sci-fi film: Spike Jonze’s Her, a tale of futile, aching love between a man and a bodiless mind.
The essential practice of a thought experiment is deceptively simple: picture a situation in the imagination, let it run its course — or intervene in some way — then watch what happens and draw a conclusion. In that sense, it’s not so different from a lab experiment, where researchers set the stage and observe what unfolds. The aim of these often fantastical scenarios is just as serious: to test, stretch, or even shatter our intuitions about how the world works.
The key difference? Everything takes place in the mind’s inner chamber. In this mental laboratory, as Peg Tittle writes in her book What If?, experiments rely on hypothetical reasoning — or, more simply, asking “what if?” Not as idle play, but as a sharp instrument for exploring reality.
What makes thought experiments so irresistible isn’t simply that they take place entirely in the mind, free from the constraints of physics, ethics, money, or technology. It’s the strange thrill that “we seem able to get a grip on nature just by thinking.” That heady possibility has drawn philosophers and scientists for millennia.
The ancient Greeks had no word for it, but the Pre-Socratics pioneered thought experimentation as a sharp intellectual tool, practiced with flair and dedication. The goal was always the same: to defend one’s theory and dismantle the claims of an opponent. When Zeno of Elea dreamed up his odd race between swift Achilles and a plodding tortoise, he was standing guard over Parmenides’ vision of reality. That both Zeno’s paradox and Lucretius’ flying spear were eventually disproven reminds us how far — and how fallibly — the mind can run on imagination alone.
Imagining what isn’t
In science, thought experiments aren’t just side notes — they’re part of the main event. Philosopher Martin Cohen, in Wittgenstein’s Beetle and Other Thought-Experiments, argues that modern science rests on surprisingly humble foundations: a handful of imagined scenarios. Picture Galileo’s falling bodies, Newton’s spinning bucket, or the cannonball orbiting Earth. These mental sketches, Cohen insists, are “no more elementary, say, than Einstein’s Theory of Relativity.”
Without thought experiments, relativity and quantum mechanics might never have taken shape. Einstein’s elevator and train, Schrödinger’s cat, Heisenberg’s microscope—each reveals the philosophical edge behind the equations. Einstein, famously, had no lab. With no machines or mountains of data, he built theories out of imagination alone. For most scientists, thought experiments served to test or visualize. For Einstein, they created reality. Fiction became fact. His mental models predicted time dilation, gravitational lensing, and the speed of light. And beyond him, thought experiments ripple across biology, mathematics, and physics — igniting, as Thomas Kuhn observed, revolutions in how we see the world.
The term “thought experiment” didn’t enter philosophy until 1811, when Hans-Christian Ørsted used it to describe the mental testing of a theory by imagining a scenario. Still, the phrase barely stirred until the 1980s, making it, by philosophical standards, practically newborn.
Yet thought experiments have been part of philosophy from the start. Ethics, philosophy of mind, and language all lean heavily on them, perhaps even more than science does. Imagine philosophy without Plato’s cave, Wittgenstein’s beetle, Foot’s trolley problem, Putnam’s brain in a vat, or Searle’s Chinese room. And outside the Western canon, there are others — like Avicenna’s flying man — equally bold.
These aren’t incidental illustrations; they often define the argument itself. One textbook, Doing Philosophy, introduces students to the entire field not through dry exposition, but entirely through thought experiments — those iridescent, electric-bright candies that burst into view right when you’re about to drown in abstraction.
What can these mental exercises actually do for us, philosophically? They’re not mere clarifying examples designed to prove a point. Thought experiments ask unsettling questions, reveal contradictions, highlight sloppy reasoning, or make us rethink what we thought we knew. They can defend a theory or quietly pull it apart. Like real experiments, they stress-test ideas. They flip assumptions on their head, untangle old problems, or make us see problems we didn’t know were there. As Peg Tittle suggests, the best way in is to ask: What is this thought experiment trying to do?
But why imagine wild, impossible scenarios instead of offering elegant arguments? As Julian Baggini writes, “reason without imagination is sterile.” Thought experiments pull us from abstract logic into felt experience. Whether the scenario is possible doesn’t matter. What matters is what it reveals in the realm of ideas — how we think, judge, and reason. They stretch concepts to the edge: If an idea fails under extreme conditions, maybe it fails altogether.
Take Thomas Nagel. To challenge the view that not knowing life’s meaning makes it absurd, he imagined creatures who revealed to us that our purpose is to become food for other species, forcing us to ask whether any answer to that question would ever truly satisfy us. Sometimes it’s by conjuring what isn’t — what has never been and couldn’t be — that we begin to understand what is, or what ought to be.
Still, there may be untapped power in what thought experiments can do for us. As we’ve seen, they pull philosophy down from the clouds, away from abstract argument and into vivid scenarios, whether wildly sci-fi or eerily plausible. They require a sensory hook — something seen, felt, or heard. More than illustrate, they provoke. They ask us to respond. That, perhaps, is the heart of their deeper potential: transformation.
Some thought experiments, if truly wrestled with, can act like inner detonations. They not only refine how we think but also shake how we live. That may be why ethicists return to them: even the strangest ones often touch real moral dilemmas. They show that philosophy, at its best, shifts our grip on life itself.
Mind games, perspective flips, inner quakes
Philosophers have offered many ways to sort the wide and wondrous range of thought experiments, from the roles they play to how they reveal cracks in what we take as given. But there’s another, less conventional lens: one that focuses on their potential to stir, disrupt, or even redirect our inner lives. Through this view, a new map emerges. Let me introduce three distinct types of thought experiments: Clarifiers, Shifters, and Transformers.
Clarifiers are philosophy’s precision tools — deployed to test concepts, expose flaws, and sharpen definitions. They bring clarity, not upheaval, offering a clean, striking glimpse into an idea’s structure without demanding a shift in worldview.
Consider John Searle’s Chinese Room, built to spotlight the limits of AI. A man sits inside, matching Chinese characters using an English rulebook. He follows the rules so well that outsiders believe he understands Chinese, though he’s never learned a word. The image sticks. This is what AI might do: manipulate symbols flawlessly, with no grasp of meaning. Syntax humming along, semantics absent. The point lands. You see something you hadn’t before. The concept clicks into place. Not a revelation, but a real clarification.
Shifters are architects of new vantage points. These thought experiments unsettle habits of mind, stretch the imagination, and tilt the frame through which we view reality. They tweak perception, shift angles — but stop short of demanding a deep personal overhaul.
Consider Thomas Nagel’s bat. Picture yourself hanging in a cave, wrapped in wings, seeing nothing, sensing everything through bursts of sonar. You’re not pretending to be a bat — you’re trying to be the bat, from the inside. But something blocks you. Its world remains sealed. The bat’s experience resists translation. And that failure does something. It humbles. It reveals the limits of your empathy. You begin to suspect that even your own inner life is partially veiled — and that the gap between minds is wider than it seems.
Transformers are philosophy’s psychedelics. These rare thought experiments ask for more than analysis — they press us to confront existence, question identity, and reevaluate what we live for. They run us through edge scenarios that expose hidden tensions: the desire for eternal life, the pursuit of endless pleasure. They’re not riddles to solve, but invitations to step into. Better called life experiments, they leave us changed. Consider Albert Camus’ Sisyphus. He is condemned to push a heavy rock up a mountain, only to watch it roll back down forever. At first, he rails, despairs, pleads. Then comes stillness. He opens his eyes, touches the stone, and whispers: This is mine. You feel the weight of your own life differently. You stop fleeing. You choose. And in the very act of choosing, something unexpected appears — joy, uninvited, waiting right where you are.
A Transformer is always potentially life-altering, though not always treated that way. Some thought experiments were born with transformation in their bones — crafted by philosophers who lived their questions. For them, philosophy was no armchair affair. Thinking was a practice of being. But others came from analytic traditions, forged as crisp tools for testing logic or clarity. They weren’t meant to shake the soul. Still, in the right hands, they change shape. They become something else — depending on how we meet them.
The key lies in how we enter the scenario. Transformation begins when we stop treating the experiment as an object of analysis and begin living it from within. Zen kōans offer a kindred approach: non-Western thought experiments meant to derail ordinary thinking and open the gates of direct experience. You don’t study the person dangling from a branch by their teeth; you become that person. You inhabit their urgency. In the same way, to grasp Camus’ Sisyphus, you must feel the stone, the slope, the repetition. Not as metaphor. As lived truth. That’s when the experiment begins to work on you.
3 life experiments that won’t let go
Let’s briefly inhabit three interwoven Transformers. The first — Nietzsche’s 1881 Eternal Recurrence — is a life test by design, echoing Camus’ Sisyphus. The next two began as Clarifiers: Bernard Williams’s 1973 Makropulos Case and Nozick’s 1974 Experience Machine. We’ll retell them to make abstraction felt and lived.
Nietzsche’s Eternal Recurrence. “What if a demon crept up to you in your loneliest moment and whispered: this life—as you live it now—you will live again, and again, and again, in every detail, forever?” For Nietzsche, this wasn’t a mere provocation. It was, he claimed, “the most scientific of all hypotheses.” If the Universe contains finite energy, but time is boundless, then every combination of events must recur. No escape, no variation, no redemption. Not a Groundhog Day with do-overs — the exact same life, repeated eternally. Could you bear it? Could you embrace it? Nietzsche thought most would recoil. But the strong—the “overhuman” — would say yes. They would live in such a way that nothing needed to be undone.
Now step into the moment — not as an observer, but as the one hearing the demon’s whisper. This isn’t about believing in eternal recurrence. It’s a way of magnifying life, stretching it across eternity to confront your bond with it. Take a clear, unsentimental look at your life as it is. Face every resistance — your unease with past failures, your struggle with the present, your unspoken craving for an elsewhere: a softer future, an afterlife, a transcendent escape. For a moment, shut all exits. Refuse the promise of redemption beyond this life. Let yourself feel the weight of living it again. Choose a day — perhaps today — and ask: Could I live this exact day eternally? Was it mine, or did I move through it half-asleep? If each moment echoes forever, every choice becomes a lasting act of affirmation or refusal.
Return to the demon’s challenge not as punishment, but as orientation. This practice does not ask for ease; it asks for presence. It calls you to stop delaying your aliveness, and shape a life you could meet again, with eyes open. In that “yes,” the distance between you and your life begins to dissolve.
Williams’s Makropulos Case. Elina Makropulos has lived for over 300 years. Her father, a 16th-century court physician, gave her an experimental elixir of life when she was young. At first, she welcomed it. But over time, lovers vanished, friendships withered, and purpose drained away. By age 342, she feels nothing but numbness. “In the end,” she says, “it is the same — singing or silence.” Joy is a distant echo; nothing moves her. When offered the elixir again, she declines. In choosing death, her life recovers a kind of shape.
Bernard Williams turned this scenario — borrowed from Karel Čapek’s 1922 play The Makropulos Affair — into a powerful argument against the desirability of immortality. Without death, he argued, meaning collapses. Time loses its urgency. The very idea of “wasting time” disappears. And with it, the drive to live it well.
Now inhabit this life-experiment: Imagine yourself 342 years old, indestructible, untouched by time. You’ve outlived lovers, children, cities. You’ve known every kind of joy, exhausted every human experience. And still, the horizon offers more — endless days to create, travel, fall in love again. But something has withered. You drift. Projects go unfinished. Without urgency, nothing holds weight. Everything is postponable, and so nothing feels real. The truth begins to surface: More time was never the answer. Even infinity slips through your fingers.
And with that, the shape of life begins to return. You realize: What created meaning wasn’t time’s abundance, but its edge. Deadlines, endings, the pressure to choose — they made your days vivid. Mortality carves time into significance. Without it, there are no stakes, no story, no love that matters. Let this imaginary immortality guide you back into your finite life. What would change if you knew time was running out? Because it is. And that’s your chance — not to have more life, but to live the one you have like it means everything.
Nozick’s Experience Machine. Imagine a device that lets you live any life you choose — writing a masterpiece, falling in love, basking in applause. Neuropsychologists wire your brain so precisely that every sensation feels real. Meanwhile, your body floats in a tank, electrodes humming. You select your experiences two years at a time, and when the cycle ends, you’re briefly awakened to choose again, never knowing it’s all artificial. Life inside feels seamless, perfectly tailored to your desires. So why hesitate? Because something in us resists. Robert Nozick offered this thought experiment to expose that resistance. If happiness were all we wanted, we’d enter without a second thought. But we want to live in touch with what’s real—to act, to respond, to be someone in the world, not simply feel as though we are. What matters isn’t only how life feels from the inside, but that it’s ours, shaped in contact with reality.
Now picture yourself before the consent form, deciding whether to sign or shred. Two futures unfold: in one, the real world, with its sharp edges, improbable hopes, and the fragile ache of meaning; in the other, the Experience Machine, where success is guaranteed, every desire satisfied, every sensation tuned to delight. No pain, no failure, no loose ends. Just bliss. And once immersed, you won’t remember it’s designed. You’ll believe it’s real. Perhaps you’re tired. Perhaps the thought of no more disappointment tempts you. Perhaps you wonder: If I feel happy, what else matters?
But a question stirs — sharp, persistent: Would pleasure without truth feel hollow, even if I didn’t know it was false? You begin to crave friction. Consequences. A life not engineered, but lived. You want your joy to be earned, your suffering to be real. You feel the metallic chill of the machine’s promise — its sterility beneath the sweetness. To walk away is to begin. The life that greets you is flawed, unresolved, irreplaceable. You choose presence over perfection: not safety, but significance; not bliss, but contact.
Philosophy’s return to life
While stepping into the worlds of these three thought experiments — now better seen as life experiments — two things may have stood out. First, though crafted by rigorous philosophers, each could easily double as the premise for a science fiction film. This isn’t accidental. In recent decades, philosophers have increasingly embraced novels and films — The Matrix, Her, and many others — as rich philosophical terrains. Science fiction, in particular, has emerged as a kind of cinematic thought experiment, exploring alternate realities to press questions about consciousness, identity, and existence.
The three Transformer examples do just that: They lead us elsewhere only to bring us back with new eyes. As we descend from each scenario, we return more awake to the life we already inhabit, more willing to bear its sorrows, limits, and truth.
That second insight, this reentry, is their quiet revolution: Philosophy doesn’t need to remain abstract. Thought experiments can walk alongside us, animating our inner lives. They aren’t merely tools of reason — they are instruments of reflection. At their best, they revive philosophy’s oldest purpose: not thinking for its own sake, but thinking that informs how we live.
This article The thought experiments that test your life, not your logic is featured on Big Think.
The post “The thought experiments that test your life, not your logic” by Shai Tubali was published on 08/05/2025 by bigthink.com