Thank you for visiting this site. This article gathers the world’s most famous thought experiments into a single list.
A thought experiment is a method of testing a concept or position by setting up an imaginary situation purely in the mind and reasoning out what would follow, without ever running a real experiment. From the philosophers of ancient Greece to scientists like Galileo and Einstein, many of the greatest minds have used thought experiments to open up entirely new insights.
This article presents a curated set of famous thought experiments from every field — philosophy of mind, epistemology, ethics, political philosophy, and physics. Each one links to a full standalone explanation, so follow any that catch your interest.
Thought Experiments vs. Paradoxes
Thought experiments are often confused with paradoxes, but the two are different.
A “paradox” is a problem in which a seemingly valid premise or chain of reasoning leads to a contradictory or counterintuitive conclusion. A “thought experiment,” by contrast, is a method of setting up an imaginary scenario in the mind and reasoning about what happens in order to test a concept or position.
For example, “Laplace’s Demon” is a thought experiment designed to illustrate determinism — the idea that an intellect knowing the state of every particle could predict the future perfectly. It produces no contradiction in itself, so strictly speaking it is a thought experiment rather than a paradox.
The boundary is blurry, however. Cases like “Schrodinger’s Cat” and “Maxwell’s Demon” are thought experiments that also carry an apparent contradiction (a paradox). In this article we treat as thought experiments those cases whose main point is testing a concept through reasoning about an imagined situation, rather than deriving a contradiction.
For paradoxes, we have a separate list — please see it as well.
Thought Experiments of Mind & Consciousness
These thought experiments tackle the hardest questions about our inner life: “What is the mind?” and “Where does consciousness come from?” In the age of AI, they are drawing fresh attention.
| Thought Experiment | In One Line |
|---|---|
| The Chinese Room | Does an AI that only manipulates symbols truly “understand”? |
| Philosophical Zombie | Could a copy of a human exist that lacks only consciousness? |
| Mary’s Room | Does a scientist who knows all the facts about color learn something on first seeing it? |
| What Is It Like to Be a Bat? | Can subjective experience be explained by objective science? |
| Inverted Qualia | The red I see may be the blue you see |
| The China Brain | A billion people acting as neurons. Does a mind appear? |
| The Turing Test | If a machine passes as human, is it thinking? |
| The Split Brain | Can two consciousnesses share one person? |
| The Extended Mind | Is your phone already part of your memory? |
| Molyneux’s Problem | Could you name by sight a shape you learned by touch? |
| The Beetle in a Box | Can contents nobody else can see mean anything? |
Thought Experiments of Knowledge & Reality
“Is the world I see real?” — these thought experiments about reality and perception have troubled philosophers since antiquity, and are famous as the inspiration behind the film The Matrix.
| Thought Experiment | In One Line |
|---|---|
| Brain in a Vat | How can a brain in a tank disprove the fake world it is shown? |
| Descartes’ Evil Demon | After doubting everything, what is left that cannot be doubted? |
| The Simulation Argument | Is our universe a simulation run by an advanced civilization? |
| The Gettier Problem | Is justified true belief really knowledge? |
| Plato’s Cave | Prisoners who take shadows on a wall for reality |
| The Five-Minute Hypothesis | The universe may be five minutes old, memories included |
| The Devil’s Proof | How far does “you cannot prove absence” excuse you? |
| If a Tree Falls With Nobody There, Does It Make a Sound? | With nobody to hear it, is there a sound? |
| Solipsism | Is my own mind the only thing certainly real? |
| Barn Facades | You saw the real thing, and it still is not knowledge |
| Quaddition | Have I really been adding all along? |
Thought Experiments of Personal Identity
“Is the me of yesterday the same as the me of today?” “Is a copy of me still me?” — these thought experiments probe the identity of the self.
| Thought Experiment | In One Line |
|---|---|
| The Teletransporter | Is a person disassembled and rebuilt the same as the original? |
| Parfit’s Fission | Split into two, which one is me? |
| The Prince and the Cobbler | Swap bodies, and am I still me? |
| A Drug That Erases Memory | Delete the painful memory, and is it still you? |
| Cryonics and the Self | Waking decades after being frozen, the same person? |
Thought Experiments of Ethics & Morality
These thought experiments make us ask “what is the right thing to do?” By setting up extreme situations, they expose the true shape of our moral intuitions.
| Thought Experiment | In One Line |
|---|---|
| The Trolley Problem | Is it permissible to sacrifice one to save five? |
| The Experience Machine | Would you choose to live plugged into a machine of happiness? |
| The Ring of Gyges | Would people stay just even if they could turn invisible? |
| The Violinist | How far does the duty to keep another person alive extend? |
| The Drowning Child | Why save the child in front and not the one far away? |
| The Survival Lottery | Kill one to save two. Why do we refuse? |
| The Utility Monster | Should everything go to whoever enjoys it most? |
| The Non-Identity Problem | Nobody was harmed, so why does it feel wrong? |
| The Happy Slave | If they are content, is that enough? |
| The Murderer at the Door | Is a lie that saves a friend still forbidden? |
| The Last Man | Is burning a forest wrong when nobody is left? |
| Duties to Future Generations | Can you owe anything to people who do not exist yet? |
| Frankfurt Cases | No alternative was possible. Are you still responsible? |
Thought Experiments of Religion & Metaphysics
Questions about God, existence and the shape of the world have been argued over for millennia without settling. These thought experiments are the tools that keep the argument sharp.
| Thought Experiment | In One Line |
|---|---|
| Pascal’s Wager | Should belief in God be settled by expected value? |
| Russell’s Teapot | Is being unfalsifiable a reason to believe? |
| The Problem of Evil | If God is good, why is there suffering? |
| The Library of Babel | Every book exists, and nothing can be found |
| The Invisible Gardener | A claim qualified until it says nothing at all |
| Eternal Recurrence | Live this same life again, endlessly |
Thought Experiments of Language & Meaning
What fixes the meaning of a word? These thought experiments show that the answer is not simply “whatever is in the speaker’s head.”
| Thought Experiment | In One Line |
|---|---|
| Twin Earth | Putnam said meanings are not in the head |
Thought Experiments of Political Philosophy
A thought experiment for asking “what does a just society look like?” If you didn’t know what position you would be born into, what rules would you choose?
| Thought Experiment | In One Line |
|---|---|
| The Veil of Ignorance | Not knowing your own situation, what society would you choose? |
Thought Experiments of Physics & Science
Physicists run experiments not only in the lab but also in their heads. Many of the great discoveries in the history of science — including Einstein’s relativity — were born from thought experiments.
| Thought Experiment | In One Line |
|---|---|
| Laplace’s Demon | If an intellect knew everything, is the future already fixed? |
| Einstein’s Elevator | Are gravity and acceleration really indistinguishable? |
| Boltzmann Brain | The universe may contain more “accidental brains” than people like you |
| Chasing a Beam of Light | Catch up with light and does it stand still? |
| Galileo’s Falling Bodies | Tie them together and 2,000 years of doctrine collapses |
| Newton’s Bucket | Rotation relative to what, exactly? |
| Quantum Suicide | If many-worlds is right, do I never die? |
Thought Experiments of AI & the Future of Humanity
What happens to us as technology advances. These thought experiments have grown suddenly concrete with the arrival of capable AI.
| Thought Experiment | In One Line |
|---|---|
| The Paperclip Maximiser | Why would an AI with no malice remake the world? |
| The Great Filter | Is the silence because a barrier lies ahead of us? |
| Mind Uploading | Do you transfer, or a copy that resembles you? |
| The Doomsday Argument | Is being here now evidence that humanity ends soon? |
Summary
This article presented a list of the world’s famous thought experiments.
The wonderful thing about thought experiments is that they require no expensive equipment and no dangerous experiments — you can reach the essence of the world using your mind alone. And many of them shake the very assumptions we take for granted: what consciousness is, what reality is, what rightness is.
Plato’s “Ring of Gyges,” proposed over 2,000 years ago, still probes the foundations of morality today. Einstein’s “elevator thought experiment” gave birth to general relativity, one of humanity’s greatest intellectual achievements. And the Chinese Room is debated more fiercely than ever now that AI is part of everyday life.
Each thought experiment has its own full explanation linked above, so do read any that interest you. The more you think, the more the world looks different.
There is also an index of “Strategic Thinking Frameworks” covering game theory, behavioral economics, and more. If you like thought experiments about decision-making such as the Trolley Problem, I think you will enjoy that series as well.
Thank you for reading. We hope to see you in the next article.
Also popular with readers
📚 Series: Famous Thought Experiments (1/60)