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thought experiment

Definition of thought experiment

Examples of thought experiment in a sentence.

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1854, in the meaning defined above

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“Thought experiment.” Merriam-Webster.com Dictionary , Merriam-Webster, https://www.merriam-webster.com/dictionary/thought%20experiment. Accessed 30 Aug. 2024.

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9 Philosophical Thought Experiments You Should Know About

Thought experiments are imaginative devices that can help us better understand philosophy. They are a useful tool in education and entertainment and can be a great way to apply complex concepts to practical situations. Since philosophy looks at questions about life, you can make a thought experiment for nearly any philosophical idea. Learn about some of the most popular ones commonly used in philosophical discussions.

The Trolly Problem

The trolly problem is an ethical thought experiment. It first appeared in philosopher Philippa Foot's 1967 paper, "Abortion and the Doctrine of Double Effect." To start off the thought experiment, imagine you have control of a railway switch. There is an out-of-control trolley headed your way. Up ahead, the tracks of the railway branch into two different paths. On the first track, there is a group of five people; on the other track, there is one person. If you stand, watch, and do nothing, the trolley will head down the first track and kill five people. However, your control allows you to switch the path of the trolley. This way, it heads down track two and kills one person instead of five. The dilemma in this situation is whether or not to flip the switch. A utilitarian answer would be to flip the switch and kill one instead of five.

Selective Surgery

Imagine you are a doctor in the future, and an ill patient comes into your practice. The patient's symptoms lead you to the diagnosis that their heart is failing. Without treatment, the patient is going to die. In your office, the patient passes out. Fortunately, the patient can be saved with surgery that will give them a synthetic heart. The patient can live what you consider to be a good life after this surgery. However, as you are preparing the patient for surgery, a small card falls out of their pocket. The card says for religious reasons; the patient does not want any synthetic organs. Now you must make a decision. If you do not install the heart, the patient will die. However, if you install the heart, the patient will survive at the cost of you violating their wish to have no synthetic organs.

At the heart of this thought experiment is a choice between honoring someone's individual rights and honoring an outside moral code . This is a relevant topic today in bioethics. Philosophers who advocate strongly for personal rights would argue that doing the transplant is wrong. While philosopher John Locke wasn't exposed to this thought experiment, he is someone who expressed the importance of individual rights and consent. According to Locke, individual consent is a fundamental part of creating a political society. In his view, doing the transplant on an unconsenting individual would be wrong.

The Bad Father

A thought experiment that tests loyalty against ethical principles is the bad father. In the thought experiment, there is a son who holds honesty as the highest value. However, his father is not an honest man. One day, his son catches him stealing from a local farmer. In this situation, the son must make a choice. He could turn his father in for breaking the law and stealing. Or the son might feel an ethical obligation to keep silent about his father's crime. While you might find this question silly, ask yourself the implications this scenario has on a larger scale. Would it be better for children to stay loyal and protect their parents or better for them to alert the authorities when their parents stray from the law?

This thought experiment is a variation of the thought experiments proposed by the ancient Greek philosopher Plato. He wrote a dialogue called Euthyphro, where Euthyphro takes his father, Socrates, to court. Euthypro argues taking his father to court is the right thing to do and the pious thing to do. However, Socrates disagrees with Euthypro about his impiety charges and gets into a debate with Euthypro about philosophical questions of universal justice, goodness, and piety. At the core of the philosophical thought experiment is the question of what happens when there is a conflict between our personal lives and the impersonal tenets we believe justice demands. The thought experiment brings old philosophical questions about justice to life.

Prisoners Dilemma

The prisoner's dilemma is a game that was created as a model of human cooperation. The experiment shows how people choose to cooperate or how they don't. The mathematician Albert Tucker is credited with formalizing the thought experiment. Today, a wide array of disciplines use the thought experiment, including philosophy, psychology, economics, and political theory.

For the experiment, imagine a cop arrests both Chris and Cindy for robbing a bank. They are in separate cells where they cannot communicate. Both want to be free and care more about their personal freedom than the freedom of their accomplice. A clever prosecutor will use their desire for freedom to his or her advantage. The prosecutor will tell each person separately that if they confess and their accomplice remains silent, they will drop all charges against them and their testimony to ensure their accomplice does serious time. If they both confess, the prosecutor will ensure they both get early parole. If they both remain silent, they will have to settle for sentences on firearms possession charges. The dilemma for the prisoners is that if they both confess, the outcome is worse than it would have been if they had both remained silent.

The prisoner's dilemma compares individual and group rationality. It shows there can be conflict between individual and collective interests. Conclusions drawn from the Prisoner's Dilemma have been used in modern-day philosophical discussions about arms races and the use of limited natural resources.

The Chinese Room

A thought experiment about artificial intelligence is the Chinese room, designed by philosopher John Searle. He asks us to imagine a situation where someone who only knows the English language is sitting alone in a room. They have instructions for changing rows of Chinese letters. Anyone outside the room would think the person inside the room understood Chinese since they would see them sorting through Chinese characters. However, this is not the case. The person inside the room just understands the instructions. Searle made this thought experiment to show that artificial intelligence cannot have a human-like mind. His thought experiment stresses that while there is understanding, there is not comprehension. 

The Experience Machine

A thought experiment that will make you question the value behind experience, is Robert Nozick's Experience Machine. The experiment is from his book Anarchy State and Utopia . Imagine that there is a machine that will give you any experience you desire. You could enter the machine and have an experience that you were eating the world's best cookie or that you were an astronaut. While you are in the experience machine, you are floating in a tank with electrodes attached to your brain. The question here is if you should plug into this machine to preprogram your life experiences. While in the tank, you wouldn't know that you were in the tank, making the experience even more real. The thought experiment brings questions about the meaning of life. What is the purpose of life if we are plugging into a machine? Will plugging into a machine satisfy all of our desires?

The Ship of Theseus

The Ship of Theseus is a thought experiment that questions whether an object that has all of its components replaced or rearranged is in fact the original object. This paradox was recorded by Plutarch, Theseus, who asks if a ship that was fully restored and replaced completely, down to every single wooden part, was the same ship. Later, other philosophers expanded on this idea. Thomas Hobbes asked if the original planks of the first ship were entirely replaced and then the original planks were used to build another ship, if the second ship would be the original ship. The thought experiment asks questions about what the essence of an object is. The Greek philosopher Heraclitus attempted to solve this paradox. To do this, Heraclitus thought of a river that has water replenishing it. According to Heraclitus, this is the same river. However, Plutarch disagreed and claimed the nature of a river to scatter and then come together means you never step into the same river twice.

Original Position

Ever thought the system was unfair? The original position is a thought experiment centering around achieving a better form of justice. Developed by John Rawls, the thought experiment asks us to imagine that we are in a situation where we do not know our actual life. This way, we are behind what Rawls calls a veil of ignorance. This veil prevents us from knowing the political or economic system that we live under and the laws that are in place.  From this position, we are then asked, with a group of other people behind the veil of ignorance, to look at a list of classic forms of justice. We must draw conclusions from different social and political philosophies. Then, we have to choose a system of justice that we believe would be best for everyone under this veil. This thought experiment calls us to question our beliefs about justice. It forces us to confront the flaws of our political and economic systems.

The Beetle in the Box

The Beetle in The Box thought experiment is also known as the Private Language Argument. Philosopher Ludwig Wittgenstein developed the thought experiment to challenge the way we look at introspection and how it informs the language we use. The thought experiment starts by imagining a group of individuals, each holding a box. The boxes contain what each individual calls their beetle. Nobody can see into anyone else's box. Everyone describes their beetle to each other. However, each person only sees and knows their own beetle. According to Wittgenstein, the descriptions are unimportant. This is because, over time, the individuals would understand the word beetle as the thing in a person's box. While the thought experiment might sound silly, it makes the comparison that human minds are like a beetle. We can never know what is in another individual's mind.

Why Use Thought Experiments?

Thought experiments help us explore philosophical concepts in a more practical way. For example, the trolly problem forces us to confront how we would apply our ethics in a situation. The point of thought experiments isn't to arrive at a specific answer. Instead, thought experiments force us to reason through our ideas and give us insight into solving complex questions. When you come up with an answer to a thought experiment, why you arrived at your answer is just as important as the answer itself.

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7 thought experiments that will make you question everything

• Thought experiments provide a platform to examine abstract concepts in a playful and imaginative manner. 
• The best thought experiments challenge our beliefs and offer fresh perspectives on how the world operates by presenting hypothetical situations. 
• These hypothetical situations are often constructed in extremes so we can see how certain ideas might play out — all without suffering any real-world repercussions.

Thought experiments are among the most important tools in the intellectual toolbox. Widely used in many disciplines, thought experiments allow for complex situations to be explored, questions to be raised, and complex ideas to be placed in an understandable context. Here are seven thought experiments in philosophy you might not have heard of, complete with explanations of what they mean and what questions they raise.

Written by Donald Davidson in 1987, this thought experiment raises questions about identity.

Suppose a man is out for a walk one day when a bolt of lightning disintegrates him. Simultaneously, a bolt of lightning strikes a marsh and causes a bunch of molecules to spontaneously rearrange into the same pattern that constituted that man a few moments ago. This “Swampman” has an exact copy of the brain, memories, patterns of behavior as he did. It goes about its day, works, interacts with the man’s friends and is otherwise indistinguishable from him.

Question: Is the Swampman the same person as the disintegrated fellow?

Davidson said no. He argues that while they are physically identical and nobody would ever notice the difference, they don’t share a casual history and can’t be the same. For example, while the Swampman would remember the friends of the disintegrated man, it never saw them before. Another person saw them and the Swampman just has his memories.

There are objections to the idea that the two characters in the story are different. Some argue that the identical minds of Swampman and the original person mean that they are the same person. Others, like philosopher Daniel Dennett, argue that the entire experiment is too far removed from reality to be meaningful.

This raises problems for teleportation as seen on Star Trek and for those who want to download their brains into a computer. Both cases rely on one version of you being created and one disappearing, but is the second version of you still you ?

Thompson’s violinist

This one was written by Judith Thomson in her 1971 essay A Defense of Abortion . She writes: “You wake up in the morning and find yourself back to back in bed with an unconscious violinist. A famous unconscious violinist. He has been found to have a fatal kidney ailment, and the Society of Music Lovers has canvassed all the available medical records and found that you alone have the right blood type to help. They have therefore kidnapped you, and last night the violinist’s circulatory system was plugged into yours, so that your kidneys can be used to extract poisons from his blood as well as your own. If he is unplugged from you now, he will die; but in nine months he will have recovered from his ailment, and can safely be unplugged from you”

Question: Are you obligated to keep the musician alive, or do you cut him loose and let him die because you want to?

Thompson, who has several excellent thought experiments to her name, says no. Not because the violinist isn’t a person with rights, but rather because he has no right to your body and the life-preserving functions that it provides. Thompson then expands her reasoning to argue that a fetus also lacks the rights to another person’s body and can be evicted at any time.

Her argument is subtle, however. She doesn’t say you have a right to kill him, only to stop him from using your body to stay alive. His resultant death is viewed as a separate, yet related, event that you have no obligation to prevent.

The Veil of Ignorance

This experiment was devised by John Rawls in 1971 to explore notions of justice in his book A Theory of Justice.

Suppose that you and a group of people had to decide on the principles that would establish a new society. However, none of you know anything about who you will be in that society. Elements such as your race, income level, sex, gender, religion, and personal preferences are all unknown to you. After you decide on those principles, you will then be turned out into the society you established.

Question: How would that society turn out? What does that mean for our society now?

Rawls argues that in this situation we can’t know what our self-interest is so we cannot pursue it. Without that guidepost, he suggests that we would all try to create a fair society with equal rights and economic security for the poor both out of moral considerations and as a means to secure the best possible worst-case scenario for us when we step outside that veil. Others disagree, arguing that we would seek only to maximize our freedom or assure perfect equality

This raises questions for the current state of our society, as it suggests we allow self-interest to get in the way of progressing towards a just society. Rawls’ ideas about the just society are fascinating and can be delved into here .

The Experience Machine

Robert Nozick came up with this thought experiment, which appears in his book Anarchy, State, and Utopia.

Imagine that super neuroscientists have created a machine that can simulate pleasurable experiences for the rest of your life. The simulation is ultra-realistic and indistinguishable from reality. There are no adverse side effects, and specific pleasurable experiences can even be programmed into the simulation. Regarding pleasure experienced, the machine offers more than is possible in several lifetimes.

Question: Do we have any reason to not go in?

Nozick argues that if we have any reason to not get in then hedonistic utilitarianism, the idea that pleasure is the only good and that we ought to maximize it, is false. Many people value having real experiences or being a person who does things rather than dreams about doing them. No matter what the reason, if you don’t go in you can’t claim pleasure is the only good, and Nozick thinks most people won’t go in.

There are counter-arguments, however. Some hedonists argue that people really would go into the machine or that we have a status quo bias that leads us to treat the reality we are currently in as more important than other, better ones. In either case, the experiment does present us with a problem for those who argue we only want pleasure.

Mary’s Room

In 1982, philosopher Frank Jackson proposed this thought experiment that raises questions about the nature of knowledge.

Mary lives in a black and white room, reads black and white books, and uses screens that only display images in black and white to learn everything that has ever been discovered about color vision in physics and biology. One day, her computer screen breaks and displays the color red. For the first time, she sees color.

Question: Does she learn anything new?

If she does, then it shows that qualia, individual occurrences of subjective elements of experience, exist; as she had access to all possible information other than experience before she saw the color but still learned something new.

This has implications for what knowledge and mental states are. Because if she learns something new then mental states, like seeing color, can’t be described entirely by physical facts. There would have to be more to it, something subjective and dependent on experience.

If she doesn’t learn anything new, then we would have to apply the idea that knowing physical facts is identical to experiencing something everywhere. For example, we would have to say that knowing all about echolocation is similar to knowing what it is like to use it.

This experiment is unique of the ones on this list as the author later changed their mind and argued that Mary seeing red doesn’t count as evidence that qualia exist. However, the problems posed by the experiment remain widely debated.

Buridan’s Ass

Variations on this experiment date back to antiquity, this formulation was named after the philosopher Jean Buridan, whose views on determinism it ridicules.

Imagine a donkey placed precisely between two identical bales of hay. The donkey has no free will, and always acts in the most rational manner. However, as both bales are equidistant from the donkey and offer the same nourishment, neither choice is better than the other.

Question: How can it choose? Does it choose at all, or does it stand still until it starves?

If choices are made based on which action is the more rational one or on other environmental factors, the ass will starve to death trying to decide on which to eat- as both options are equally rational and indistinguishable from one another. If the ass does make a choice, then the facts of the matter couldn’t be all that determined the outcome, so some element of random chance or free will may have been involved.

It poses a problem for deterministic theories as it does seem absurd to suppose that the ass would stand still forever. Determinists remain split on the problem that the ass poses. Spinoza famously dismissed it while others accept that the donkey would starve to death. Others argue that there is always some element of a choice that differentiates it from another one.

The life you can save

This experiment was written by famed utilitarian thinker Peter Singer in 2009.

Imagine that you are walking down the street and notice a child drowning in a lake. You can swim and are close enough to save her if you act immediately. However, doing so ruins your expensive shoes. Do you still have an obligation to save the child?

Singer says yes, you have a responsibility to save the life of a dying child and price is no object. If you agree with him, it leads to his question.

Question: If you are obligated to save the life of a child in need, is there a fundamental difference between saving a child in front of you and one on the other side of the world?

In The Life You Can Save, Singer argues that there is no moral difference between a child drowning in front of you and one starving in some far off land. The cost of the ruined shoes in the experiment is analogous to the cost of a donation, and if the value of the shoes is irrelevant than the price of charity is too. If you would save the nearby child, he reasons, you have to save the distant one too . He put his money where his mouth is, and started a program to help people donate to charities that do the most good .

There are counter-arguments of course. Most of them rely on the idea that a drowning child is in a different sort of situation than a child who is starving and that they require different solutions which impose different obligations.

Thought Experiments

Thought experiments are devices of the imagination used to investigate the nature of things. We need only list a few of the well-known thought experiments to be reminded of their enormous influence and importance in the sciences: Newton's bucket, Maxwell's demon, Einstein's elevator, Heisenberg's gamma-ray microscope, Schrödinger's cat. The same can be said for their importance in philosophy. Much of ethics, philosophy of language, and philosophy of mind is based firmly on the results of thought experiments. Again, a short list makes this evident: Thompson's violinist, Searle's Chinese room, Putnam's twin earth, Parfit's people who split like an amoeba. The 17th century saw some of its most brilliant practitioners in Galileo, Descartes, Newton, and Leibniz. And in our own time, the creation of quantum mechanics and relativity are almost unthinkable without the crucial role played by thought experiments. Contemporary philosophy, even more than the sciences, would be severely impoverished without them.

1. Examples of Thought Experiments

2. objections to thought experiments, 3. types of thought experiments, 4. some recent views on thought experiments, bibliography, other internet resources, related entries.

Among scientists, Galileo and Einstein were, arguably, the most impressive thought experimenters, but they were by no means the first. Thought experiments existed throughout the middle ages, and can be found in antiquity, too. One of the most beautiful early examples (in Lucretius, De Rerum Natura ) attempts to show that space is infinite: If there is a purported boundary to the universe, we can toss a spear at it. If the spear flies through, it isn't a boundary after all; if the spear bounces back, then there must be something beyond the supposed edge of space, a cosmic wall that stopped the spear, a wall that is itself in space. Either way, there is no edge of the universe; space is infinite.

This example nicely illustrates many of the common features of thought experiments: We visualize some situation; we carry out an operation; we see what happens. It also illustrates their fallibility. In this case we've learned how to conceptualize space so that it is both finite and unbounded. Consider a circle, which is a one dimensional space: As we move around, there is no edge, but it is nevertheless finite. The universe might be a many-dimensional version.

Often a real experiment that is the analogue of a thought experiment is impossible for physical, technological, or financial reasons; but this needn't be a defining condition of thought experiments. The main point is that we seem able to get a grip on nature just by thinking, and therein lies the great interest for philosophy. How is it possible to learn apparently new things about nature without new empirical data?

Ernst Mach did a great deal to popularize the idea of a Gedankenexperiment . He also popularized the term, but he was not the first to use it. That honour seems to go to Georg Lichtenberg, writing about a century earlier (Schildknecht 1990). Mach developed an interesting empiricist view in his classic, The Science of Mechanics . We possess, he says, a great store of "instinctive knowledge" picked up from experience. Some of this is from actual experience and some we have inherited through the evolutionary process, thanks to the experience of our ancestors. This knowledge needn't be articulated at all, but comes to the fore when we encounter certain situations. One of his favourite examples is due to Simon Stevin. When a chain is draped over a double frictionless plane, as in Fig. 2a, how will it move? Add some links as in Fig. 2b. Now it is obvious. The initial setup must have been in static equilibrium. Otherwise, we would have a perpetual motion machine; and according to our experience-based "instinctive knowledge", says Mach, this is impossible.

Figure 2(a) and 2(b) “How will it move?”

Judith Thompson provided one of the most striking and effective thought experiments in the moral realm. Her example is aimed at a popular anti-abortion argument that goes something like this: The fetus is an innocent person with a right to life. Abortion results in the death of a fetus. Therefore, abortion is morally wrong. In her thought experiment we are asked to imagine a famous violinist falling into a coma. The society of music lovers determines from medical records that you and you alone can save the violinist's life by being hooked up to him for nine months. The music lovers break into your home while you are asleep and hook the unconscious (and unknowing, hence innocent) violinist to you. You may want to unhook him, but you are then faced with this argument put forward by the music lovers: The violinist is an innocent person with a right to life. Unhooking him will result in his death. Therefore, unhooking him is morally wrong.

However, the argument does not seem convincing in this case. You would be very generous to remain attached and in bed for nine months, but you are not morally obliged to do so. The parallel with the abortion case is evident. The thought experiment is effective in distinguishing two concepts that had previously been run together: “right to life” and “right to what is needed to sustain life.” The fetus and the violinist may each have the former, but it is not evident that either has the latter. The upshot is that even if the fetus has a right to life (which Thompson does not believe but allows for the sake of the argument), it may still be morally permissible to abort. Theorizing about thought experiments usually turns on the details or the patterns of specific cases. Familiarity with a wide range of examples is crucial for commentators. Most discussions of thought experiments include several illustrations (e.g., Brown 1991, Horowitz and Massey 1991, and Sorenson 1992). There are also two recent books devoted mainly to the presentation of brief, non-technical examples, Cohen 2005 and Tittle 2005. Some special examples with very nice animations can be found at John Norton's website (see below).

Of course, particular thought experiments have been contested. But for the most part, thought experimenting in the sciences has been cheerfully accepted. The great historian of physics, Pierre Duhem, is almost alone in his condemnation. A thought experiment is no substitute for a real experiment, he claimed, and should be forbidden in science. However, in view of the important role of actual thought experiments in the history of physics — from Galileo's falling bodies, to Newton's bucket, to Einstein's elevator — it is unlikely that anyone will feel or should feel much sympathy for Duhem's strictures.

Philosophers are more critical. They worry, with some justice, about how reliable our intuitions really are. Can we trust them in bizarre situations? Kathleen Wilkes, for instance, was very distrustful of Parfit's people splitting like an amoeba. She declared that we simply don't know what to say when thinking about this sort of thing. She declared that a thought experiment should not violate what we take to be the laws of nature. This would rule out Parfit's examples. But such a proposal seems much too strong. We learn a great deal about the world and our theories when we wonder, for instance, what would have happened after the big bang, if the law of gravity had been an inverse cube law instead of an inverse square. Would stars have failed to form? Reasoning about such a scenario is perfectly coherent and very instructive, even though it violates a law of nature.

There are other objections, too. Jonathan Dancy thinks thought experiments in ethics are circular. Daniel Dennett thinks they use folk concepts, so they are inevitably conservative. These objections can likely be met, but they illustrate an ongoing debate.

There are many ways of classifying thought experiments: science vs philosophy, or normative (moral or epistemic) vs factual, and so on. I will outline a taxonomy here based on how they function as evidence. The main division is constructive vs destructive, that is, a thought experiment might be used positively to establish a theory or it might be used negatively to undermine a theory. Each of these is subject to further divisions.

Thought experiments are used negatively in a number of different ways. The simplest of these is to draw out a contradiction in a theory, thereby refuting it. A second way is to show that the theory in question is in conflict with other beliefs that we hold. Schrödinger's cat, for instance, does not show that quantum theory (as interpreted by Bohr) is internally inconsistent. Rather it shows that it is conflict with some very powerful common sense beliefs we have about macro-sized objects such as cats. The bizarreness of superpositions in the atomic world is worrisome enough, says Schrödinger, but when it implies that same bizarreness at an everyday level, it is intolerable.

There is a third type that, in effect, undermines a central assuption or premiss of a thought experiment. Thompson showed that "right to life" and "right to what is needed to sustain life" had been run together. When distinguished, the argument against abortion is undermined. A fourth type of negative thought experiment is quite a bit more complex. I will call these counter thought experiments. Mach produced one against Newton and Dennett produced another against Jackson. Newton offered a pair of thought experiments as evidence for absolute space. One was the bucket with water climbing the wall, the other was a pair of spheres joined by a cord that maintained its tension in otherwise empty space. The explanation for these phenomena, said Newton, is absolute space: the bucket and the joined spheres are rotating with respect to space itself. In response, Mach said that, contra Newton, the two spheres would move toward one another thanks to the tension in the cord, and if we rotated a very thick, massive ring around a stationary bucket, we would see the water climb the bucket wall. Mach's counter thought experiment undermines our confidence in Newton's. Absolute space explained the phenomena in Newton's thought experiments, but now we're not so sure of the phenomena itself (at least, this is Mach's intent).

Figure 3. Stages in the bucket experiment Figure 4. Two spheres held by a cord in otherwise empty space

Frank Jackson created a much discussed thought experiment that aimed to show that physicalism is false. This is the doctrine that all facts are physical facts. In the thought experiment, Mary is a brilliant scientist who, from birth, is confined to a laboratory with only black and white experiences. She learns all the physical facts about perception there. One day, she leaves the laboratory and experiences colours for the first time; she learns what it's like to experience red. Clearly, says Jackson, she learns something new. Since she already knew all the physical facts, she must have learned something non-physical when she experienced colour. Thus, physicalism must be wrong.

Dennett replied to this thought experiment with one of his own. It begins like Jackson's, but when Mary leaves the lab, she says “Ah, colour perception is just as I thought it would be.” Like Mach, Dennett denies the phenomenon of the original thought experiment. And like Mach, his counter thought experiment is effective in undermining Jackson's in so far as it seems similarly plausible.

To be effective, counter thought experiments needn't be very plausible at all. In a court of law, the jury will convict provided guilt is established "beyond a reasonable doubt." A common defence strategy is to provide an alternative account of the evidence that has just enough plausibility to put the prosecution's case into some measure of doubt. That is sufficient to undermine it. A good counter thought experiment need only do that much to be effective.

Thought experiments can also be constructive. There are many ways a thought experiment could provide positive support for a theory. One of these is to provide a kind of illustration that makes a theory's claims clear and evident. In such cases thought experiments serve as a kind of heuristic aid. A result may already be well established, but the thought experiment can lead to a very satisfying sense of understanding. Newton provided a wonderful example showing how the moon is kept in its orbit in the just same way as an object falls to the earth. He illustrated this by means of a cannon shooting a cannon ball further and further. In the limit, the earth curves away as fast as the ball falls, with the eventual result being that the cannon ball will return to the spot where it was fired, and, if not impeded, will go around again and again. This is what the moon is doing. We could arrive at the same conclusion through calculation. But Newton's thought experiment provides that illusive understanding. It's a wonderful example of the “aha effect.”

Figure 5. “The shot heard around the world”

Einstein's elevator showed that light will bend in a gravitational field; Maxwell's demon showed that entropy could be decreased; Thompson's violinist showed that abortion could be morally permissible even when the fetus has a right to life; Newton's bucket showed that space is a thing in its own right; Parfit's splitting persons showed that survival is a more important notion than identity when considering personhood. I say they “showed” such and such, but, “purport to show” might be better, since some of these thought experiments are quite contentious. The thing they have in common is that they aim to establish something positive. Unlike destructive thought experiments, they are not trying to demolish an existing theory, though they may do that in passing.

Thomas Kuhn's "A Function for Thought Experiments" employs many of the concepts (but not the terminology) of his well-known Structure of Scientific Revolutions . On his view a well-conceived thought experiment can bring on a crisis or at least create an anomaly in the reigning theory and so contribute to paradigm change. Thought experiments can teach us something new about the world, even though we have no new empirical data, by helping us to re-conceptualize the world in a better way. Tamar Gendler has recently developed this view in a number of important respects.

Recent years have seen a sudden growth of interest in thought experiments. The views of Brown (1991) and Norton (1991, 1996) represent the extremes of platonic rationalism and classic empiricism, respectively. Norton claims that any thought experiment is really a (possibly disguised) argument; it starts with premisses grounded in experience and follows deductive or inductive rules of inference in arriving at its conclusion. The picturesque features of any thought experiment which give it an experimental flavour might be psychologically helpful, but are strictly redundant. Thus, says Norton, we never go beyond the empirical premisses in a way to which any empiricist would object. (For criticisms see Bishop 1999; Brown 1991, 2004a, 2004b; Haggqvist 1996; Gendler 1998, 2004; Nersessian 1993; and Sorenson 1992; and for a defense see Norton 1991, 1996, 2004a, and 2004b.)

By contrast, Brown holds that in a few special cases we do go well beyond the old data to acquire a priori knowledge of nature. (See also Koyré 1968.) Galileo showed that all bodies fall at the same speed with a brilliant thought experiment that started by destroying the then reigning Aristotelian account. The latter holds that heavy bodies fall faster than light ones ( H > L ). But consider (Fig. 6), in which a heavy cannon ball ( H ) and light musket ball ( L ) are attached together to form a compound object ( H + L ); the latter must fall faster than the cannon ball alone. Yet the compound object must also fall slower, since the light part will act as a drag on the heavy part. Now we have a contradiction. ( H + L > H and H > H + L ) That's the end of Aristotle's theory. But there is a bonus, since the right account is now obvious: they all fall at the same speed ( H = L = H + L ).

Figure 6. Galileo: “I don't even have to look”

This could be said to be a priori (though still fallible) knowledge of nature, since there are no new data involved, nor is the conclusion derived from old data, nor is it some sort of logical truth. This account of thought experiments can be further developed by linking the a priori epistemology to recent accounts of laws of nature that hold that laws are relations among objectively existing abstract entities. It is thus a rather Platonistic view, not unlike Platonistic accounts of mathematics such as that urged by Gödel. (For details see Brown 1991.)

The two views just sketched might occupy the opposite ends of a spectrum of positions on thought experiments, at least within the philosophy of science. Some of the promising alternative views include those of Sorensen (somewhat in the spirit of Mach) who holds that thought experiments are a "limiting case" of ordinary experiments; they can achieve their aim, he says, without being executed. (Sorensen's book is also valuable for its extensive discussion of thought experiments in a wide range of fields.) Other promising views include those of Gooding (who stresses the similar procedural nature of thought experiments and real experiments), Miscevic and Nersessian (each of whom tie thought experiments to "mental models"), and several of the accounts in Horowitz and Massey 1991. Besides these, a sample of recent excellent discussions includes: Arthur 1999; Gendler 1998, 2000, 2002a, 2004; Haggqvist 1996; Humphreys 1994; McAllister 1996, 2004; and many others. German readers will find the very recent book by Kühne (2005) a very thorough history as well as an interesting discussion of contemporary topics. The literature on thought experiments in the sciences continues to grow rapidly.

Outside of the philosophy of science, philosophers continue to debate the merits of particular thought experiments such as Searle's, Thompson's, Jackson's, and so on. At a more general level there is debate over the usefulness of highly contrived examples. Just how reliable are our intuitions in these cases anyway? The subject of intuition has itself been the topic of recent debate. A small but significant group of philosophers uphold their use while others downplay their reliability and significance. (See DePaul and Ramsey 1998 for a sample of articles on this topic.) The relationship between conceivability and possibility is another topic that has been aired recently and has much to do with thought experiments. (See Gendler and Hawthorne 2002.) The relation between thought experiments and literary fiction is starting to be explored. (See Swirski 2007.)

Thanks are due to Tamar Gendler, from whom I borrowed heavily in constructing the bibliography below. Much more can be found in the bibliographies in Sorenson 1992, Gendler 2000, and Kühne 2005.

• Arthur, R., 1999, "On Thought Experiments as A Priori Science," International Studies in the Philosophy of Science , 13/3: 215-229
• Bishop, M., 1998, "An Epistemological Role for thought Experiments", in N. Shanks (ed.), Idealization IX: Idealization in Contemporary Physics , Amsterdam: Rodopoi, pp. 19-33
• Bishop, M., 1999, "Why Thought Experiments are Not Arguments", Philosophy of Science , 66 : 534-41
• Bokulich, A., 2001, "Rethinking Thought Experiments", Perspectives on Science , 9/3: 285-307
• Brendel, Elke, 2004, "Intuition Pumps and the Proper Use of Thought Experiments", Dialectica , 58/1: 88-108
• Brown, James Robert, 1991, Laboratory of the Mind: Thought Experiments in the Natural Sciences , London: Routledge
• Brown, James Robert, 1993, "Why Empiricism Won't Work." Proceedings of the Philosophy of Science Association , 2: 271-279
• Brown, J.R., 2004a, "Why Thought Experiments Transcend Experience," in C. Hitchcock (ed.), Contemporary Debates in the Philosophy of Science , Malden, MA: Blackwell, pp. 23-43
• Brown, James Robert, 2004b, "Peeking into Plato's Heaven." Philosophy of Science , vol. 71, 1126-1138
• Bunzl, Martin, 1996, "The Logic of Thought Experiments." Synthese , 106/2 (Fall): 227-240
• Buzzoni, Marco, 2004, Esperimento Ed Esperimento Mentale , Milano: FrankoAngeli
• Cargile, James, 1987, "Definitions and Counterexamples." Philosophy , 62: 179-193
• Cohen, M., 2005, Wittgenstein's Beetle and Other Classic Thought Experiments , Oxford: Blackwell
• Cohnitz, Daniel, 2006, Gedankenexperimente in der Philosophie , Paderborn: Verlag GmbH
• Cooper, Rachel, 2005, Metaphilosophy 36:3, 328
• Dancy, Jonathan, 1985, "The Role of Imaginary Cases in Ethics." Pacific Philosophical Quarterly , 66 (January-April): 141-153
• Dennett, D., 1991, Consciousness Explained , New York: Little Brown
• Dennett, D., 2005, Sweet Dreams , Cambridge, MA: MIT Press
• DePaul, M. And W. Ramsey (eds.), 2002, Rethinking Intuition: The Psychology of Intuition & Its Role in Philosophical Inquiry , New York: Rowan and Littlefield
• Duhem, P., 1954, Aim and Structure of Physical Theory , Princeton: Princeton University Press
• Gendler, Tamar Szabo, 1998, "Galileo and the Indispensability of Scientific Thought Experiment." The British Journal for the Philosophy of Science , 49/3 (Sept): 397-424
• Gendler, Tamar Szabo, 2000, Thought Experiment: On the Powers and Limits of Imaginary Cases. NY: Garland Press (now Routledge).
• Gendler, Tamar Szabo, 2002a, "Personal Identity and Thought-Experiments." Philosophical Quarterly , 52/206: 34-54.
• Gendler, Tamar Szabo., 2002b, "Thought Experiment." Encyclopedia of Cognitive Science . NY/London: Nature/Routledge.
• Gendler, Tamar Szabo, 2004, "Thought Experiments Rethought — and Reperceived." Philosophy of Science , 71: 1152-1164.
• Gendler, Tamar Szabo, 2005, "Thought Experiments in Science." Encyclopedia of Philosophy . New York: MacMillan
• Gendler, Tamar Szabo and John Hawthorne, eds., 2002, Conceivability and Possibility. NY/Oxford: Clarendon/Oxford University Press.
• Genz, H., 1999, Gedankenexperimente , Weinheim: Wiley-VCH (in German)
• Gooding, D., 1993, "What is Experimental About Thought Experiments?" in D. Hull, M. Forbes, and K. Okruhlik (eds.) PSA 1992 , vol. 2, East Lansing, MI: Philosophy of Science Association, pp. 280-290
• Gooding, David C., 1992, "The Cognitive Turn, or, Why Do Thought Experiments Work?" In Giere ed., Cognitive Models of Science . Minneapolis: University of Minnesota Press, 1992, 45-76
• Gooding, David C., 1994, "Imaginary Science." British Journal for the Philosophy of Science , 45/4 (December): 1029-1045
• Hacking, I., 1993, "Do Thought Experiments have a Life of Their Own?" in D. Hull, M. Forbes, and K. Okruhlik (eds.) PSA 1992 , vol. 2, East Lansing, MI: Philosophy of Science Association, pp. 302-308
• Haggqvist, S., 1996, Thought Experiments in Philosophy , Stockholm: Almqvist & Wiksell International
• Horowitz, T. and G. Massey (eds.), 1991, Thought Experiments in Science and Philosophy , Savage, MD: Rowman and Littlefield
• Humphries, P., 1994, "Seven Theses on Thought Experiments", in J. Earman et al ., (eds) Philosophical Problems of the Internal and External World , Pittsburgh: University of Pittsburgh Press, pp. 205-227
• Ierodiakonou, K., 2005, "Ancient Thought Experiments: A First Approach", Ancient Philosophy , 25: 125-140
• Irvine, A., 1991, "Thought Experiments in Scientific Reasoning," in Horowitz and Massey 1991, pp. 149-166
• Jackson, F., 1982, "Epiphenomenal Qualia", Philosophical Quarterly , 32: 27-36
• Jackson, M. W., 1992, "The Gedankenexperiment Method of Ethics." The Journal of Value Inquiry , 26: 525-535
• Janis, Allen I., 1991, "Can Thought Experiments Fail?" In Horowitz and Massey 1991, pp. 113-118
• King, Peter, 1991, "Mediaeval Thought-Experiments: The Metamethodology of Mediaeval Science." In Horowitz and Massey 1991, pp. 43-64
• Klassen, S., 2006, "The Science Thought Experiment: How Might it be Used Profitably in the Classroom?", Interchange 37/1: 77-96.
• Koyré, Alexandre, 1968, Metaphysics and Measurement . London: Chapman and Hall.
• Kuhn, T., 1964, "A Function for Thought Experiments", reprinted in T. Kuhn, The Essential Tension , Chicago: University of Chicago Press, 1977, pp. 240-265
• Kühne, U., 2005, Die Methode des Gedankenexperiments , Frankfurt: Suhrkamp
• Kujundzic, Nebojsa, 1992, "How Does the Laboratory of the Mind Work?" Dialogue , 32/3 (Summer): 573-578
• Kujundzic, Nebojsa, 1995, "Thought Experiments: Architecture and Economy of Thought ." The Journal of the British Society for Phenomenology , 26/1 (January): 86-93.
• Laymon, Ronald, 1991, "Thought Experiments of Stevin, Mach and Gouy: Thought Experiments as Ideal Limits and as Semantic Domains." In Horowitz and Massey 1991, pp. 167-192.
• Lennox, James G., 1991, "Darwinian Thought Experiments: A Function for Just-So Stories." In Horowitz and Massey 1991, pp. 223-245
• Lichtenberg, Georg Christoph, 1983, Schriften und Briefe : Sudelbücher, Fragmente, Fabeln, Verse (Erster Band). Ed. Franz H. Mautner. Frankfurt: Insel Verlag
• Mach, E., 1960, The Science of Mechanics , trans. by J. McCormack, sixth edition, LaSalle Illinois: Open Court
• Mach, E., 1976, "On Thought Experiments", in Knowledge and Error , trans. by J. McCormack), Dordrecht: Reidel, pp. 134-147
• Massey, Gerald, 1991, "Backdoor Analyticity." In Horowitz and Massey 1991, pp. 285-296
• McAllister, James, 1996, "The Evidential Significance of Thought Experiments in Science", Studies in History and Philosophy of Science , 27/2: 233-250
• McAllister, James, 2004, "Thought Experiments and the Belief in Phenomena" Proceedings of the 2002 Biennial Meeting of the Philosophy of Science Association, Philosophy of Science , 71: 1164-1175
• McAllister, James, 2005, "The Virtual Laboratory: Thought Experiments in Seventeenth-Century Mechanics", in Helmar Schramm, Ludger Schwarte, and Jan Lazardzig, eds., Collection, Laboratory, Theater: Scenes of Knowledge in the 17th Century . New York: Walter de Gruyter; pp. 35-56
• Miscevic , N., 1992, "Mental Models and Thought Experiments", International Studies in the Philosophy of Science , 6/3: 215-226
• Miscevic, Nenad, 1997, "Categorial and Essentialist Intuitions: A Naturalist Perspective." Acta Analytica 12/19: 21-39
• Nersessian, Nancy, 1992, "How Do Scientists Think? Capturing the Dynamics of Conceptual Change in Science." In R. Giere (ed), Cognitive Models of Science . Minneapolis: University of Minnesota Press, pp. 3-44
• Nersessian, N., 1993, "In the Theoretician's Laboratory: Thought Experimenting as Mental Modeling" in D. Hull, M. Forbes, and K. Okruhlik (eds.) PSA 1992 , vol. 2, East Lansing, MI: Philosophy of Science Association, pp. 291-301
• Norton, J., 1991, "Thought Experiments in Einstein's Work", in Horowitz and Massey 1991, pp. 129-148
• Norton, J., 1996, "Are Thought Experiments Just What You Always Thought?" Canadian Journal of Philosophy , 26: 333-366
• Norton, J., 2004a, "On Thought Experiments: Is There More to the Argument?" Proceedings of the 2002 Biennial Meeting of the Philosophy of Science Association, Philosophy of Science , 71: 1139-1151. [ Preprint available online ].
• Norton, J., 2004b, "Why Thought Experiments Do Not Transcend Empiricism", in Christopher Hitchcock (ed.) Contemporary Debates in the Philosophy of Science. Oxford: Blackwell, pp. 44-66. [ Preprint available online ].
• Parfit, Derek, 1984/1987, Reasons and Persons . Oxford: Clarendon Press
• Rescher, N., 2005, What If?: Thought Experimentation in Philosophy , New Brunswick, NJ: Transaction Publishers
• Schildknecht, Christiane, 1990, Philosophische Masken: Literarische Formen der Philosophie bei Platon, Descartes, Wolff und Lichtenberg. Stuttgart: Metzler
• Sorensen, R., 1992a, Thought Experiments , Oxford: Oxford University Press
• Sorensen, Roy, 1992b, "Thought Experiments and the Epistemology of Laws." Canadian Journal of Philosophy , 22/1 (March): 15-44
• Stinner, A., 1990, Philosophy, Thought Experiments, and Large Context Problems in the Secondary Physics Course. International Journal of Science Education , 12/3: 244-157
• Swirski, Peter, 2007, Of Literature and Knowledge: Explorations in Narrative Thought Experiments, Evolution and Game Theory . London & New York: Routledge
• Thompson, Judith Jarvis, 1971, "A Defense of Abortion." Philosophy and Public Affairs , 1/1 (Fall): 47-66
• Tittle, P., 2005, What If…Collected Thought Experiments in Philosophy , New York: Pearson Longman
• Urbaniec, Jacek, 1988, "In Search of a Philosophical Experiment." Metaphilosophy , 19 (July-August): 294-306
• Wilkes, Kathleen V., 1988, Real People: Personal Identity without Thought Experiments . Oxford: Clarendon Press
• Witt-Hansen, Johannes, 1976, "H.C. Orsted, Immanuel Kant, and the Thought Experiment." Danish Yearbook of Philosophy , 13: 48-65
• Yablo, Stephen, 1993, "Is Conceivability a Guide to Possibility?" Philosophy and Phenomenological Research , 53/1 (March): 1-42
• Goodies , a collection of intriguing questions in the philosophy of science, some about thought experiments, by John Norton (U. Pittsburgh).

[Please contact the author with additional suggestions.]

Descartes, René | -->intuition --> | Leibniz, Gottfried Wilhelm | Mach, Ernst | Platonism: in metaphysics | rationalism vs. empiricism | -->science, philosophy of -->

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Thought experiments have been a source of creative and philosophical thinking since the days of ancient philosophers. From the Socratic method to Descartes' wax analogy, thought experiments have been used to explore the boundaries of our understanding and push the limits of our imagination. This article explores the use of thought experiments in both creative and philosophical thinking, offering insights into how they can be used to expand our horizons and challenge our preconceived notions. Thought experiments are a powerful tool for making connections between different disciplines and exploring the complexity of human thought. By using them to examine our assumptions and beliefs, we can gain valuable insights into ourselves and the world around us.

Thought experiments can also provide us with the opportunity to break free from our traditional methods of reasoning and engage in imaginative exploration. Through this process, we can uncover new perspectives, develop innovative ideas, and explore new possibilities. This article will provide an overview of thought experiments, exploring their history, principles, and uses. We will discuss how thought experiments can help us to think more creatively and analyze philosophical problems. We will also explore how thought experiments can be used to generate new ideas and challenge existing assumptions.

This experiment explored whether or not a computer could possess genuine understanding or intelligence. The experiment consisted of a person sitting in a room with no knowledge of Chinese language or culture. The person was presented with slips of paper containing Chinese symbols, and instructed to put together responses based on a set of rules they had been given. The question posed by the experiment was whether or not this person truly understood the Chinese symbols, or if they were merely following instructions.

The Chinese Room experiment has been widely discussed in philosophical circles since it was first proposed. It has been used to explore questions about artificial intelligence, the limits of computers, and the nature of understanding. Thought experiments can also be used to explore creative ideas. Artists often use them as a way of sparking new ideas and exploring creative solutions to problems. One example is the “Ladder of Inference” thought experiment proposed by Chris Argyris in 1974. This experiment explores how we make assumptions about the world based on our experiences.

How Can I Get Started With Thought Experiments?

What are the benefits of thought experiments.

They provide an opportunity to explore different ideas and concepts in a safe environment without any negative consequences. They also allow us to gain greater insight into our own thinking processes and develop better strategies for dealing with difficult situations. Additionally, they can help us develop new ways of looking at the world and become more creative thinkers. Thought experiments offer an invaluable opportunity to explore the boundaries of our knowledge, creativity, and philosophical thinking. By engaging in thought experiments, we can gain a better understanding of how our thoughts shape our lives and the world around us.

By taking the time to reflect on our experiences, think outside the box, and explore different scenarios, we can become more creative and develop new perspectives. Thought experiments are a powerful tool for expanding our horizons and pushing the boundaries of our thinking.

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Top 10 Most Famous Thought Experiments

Thought experiments are mental concepts or hypotheses, often resembling riddles, which are used by philosophers and scientists as simple ways of illuminating what are usually very dense ideas. Most often, they’re used in more abstract fields like philosophy and theoretical physics, where physical experiments aren’t possible. They serve as some hearty food for thought, but given their complex subject matter, it’s not unusual for even the thought experiment itself to be nearly incomprehensible. With this in mind, here are ten of the most famous thought experiments , along with explanations of the philosophical, scientific, and ethical ideas they work to explain:

10. The Trolley Problem

One of the most well known thought experiments in the field of ethics is the “Trolley Problem,” which goes something like this: a madman has tied five innocent people to a trolley track. An out of control trolley car is careening toward them, and is moments away from running them over. Luckily, you can pull a lever and divert the trolley to another track. The only problem is that the madman has also tied a single person to that track. Considering the circumstances, should you pull the lever?

What it Means:

The trolley problem was first proposed by the philosopher Philippa Foot as a means of critiquing the major theories in ethical philosophy, in particular utilitarianism, the system which proposes that the most moral decision is always the one that provides “the greatest good for the greatest number.” From a utilitarian point of view, the obvious choice is to pull the lever, saving five and only killing one. But critics of this theory would state that in pulling the lever you become complicit in what is clearly an immoral act—you are now partially responsible for the death of the lone person on the other track. Others, meanwhile, argue that your mere presence in the situation demands that you act, and that to do nothing would be equally immoral. In short, there is no wholly moral action, and this is the point. Many philosophers have used the trolley problem as an example of the ways that real world situations often force individuals to compromise their own moral codes, and that there are times when there is no totally moral course of action.

9. The Cow in the Field

One of the major thought experiments in epistemology (the field of philosophy that deals with knowledge) is what is known as “The Cow in the Field.” It concerns a farmer who is worried his prize cow has wandered off. When the milkman comes to the farm, he tells the farmer not to worry, because he’s seen that the cow is in a nearby field. Though he’s nearly sure the man is right, the farmer takes a look for himself, sees the familiar black and white shape of his cow, and is satisfied that he knows the cow is there. Later on, the milkman drops by the field to double-check. The cow is indeed there, but it’s hidden in a grove of trees. There is also a large sheet of black and white paper caught in a tree, and it is obvious that the farmer mistook it for his cow. The question, then: even though the cow was in the field, was the farmer correct when he said he knew it was there?

The Cow in the Field was first used by Edmund Gettier as a criticism of the popular definition of knowledge as “justified true belief”—that is, that something becomes knowledge when a person believes it; it is factually true; and they have a verifiable justification for their belief. In the experiment, the farmer’s belief that the cow was there was justified by the testimony of the milkman and his own verification of a black and white object sitting in the field. It also happened to be true, as the milkman later confirmed. But despite all this, the farmer did not truly know the cow was there, because his reasoning for believing it turned out to be based on false premises. Gettier used this experiment, along with a few other examples, as proof of his argument that the definition of knowledge as justified true belief needed to be amended.

8. The Ticking Time Bomb

If you’ve paid any attention to political discourse over the past few years—or ever seen an action movie, for that matter—then you are no doubt familiar with the “ticking time bomb” thought experiment. It asks you to imagine that a bomb or other weapon of mass destruction is hidden in your city, and the timer on it will soon strike zero. You have in your custody a man with knowledge of where the device is planted. Do you resort to torture in order to get him to give up the information?

Like the trolley problem, the ticking time bomb scenario is an ethical problem that forces one to choose between two morally questionable acts. It is most often employed as a counter argument to those who say the use of torture is inexcusable under any circumstances. It’s also used as an example of the way laws—like those the U.S. has against torturing prisoners—will always be set aside given extreme circumstances. Thanks to its fictionalized use in television shows like 24 , along with its constant position in political debates , the ticking time bomb scenario has become one of the most frequently repeated thought experiments. An even more extreme take on the problem was presented in a British news article earlier this year. That version proposes that the terrorist in question won’t respond to torture, and asks if one would be willing to resort to torturing the man’s wife and children as a means of extracting the information from him.

7. Einstein’s Light Beam

It’s a little known fact that Albert Einstein’s famous work on special relativity was spurred by a thought experiment he conducted when he was only 16 years old. In his book Autobiographical Notes , Einstein recalls how he once daydreamed about chasing a beam of light as it traveled through space. He reasoned that if he were able to move next to it at the speed of light, he should be able to observe the light frozen in space as “an electromagnetic field at rest though spatially oscillating.” For Einstein , this thought experiment proved that for his imaginary observer “everything would have to happen according to the same laws as for an observer who, relative to the Earth, was at rest.”

In truth, no one really knows for sure. Scientists have long debated how this deceivingly simple thought experiment helped Einstein make the massive theoretical leap required to arrive at special relativity theory. At the time, the ideas in the experiment contradicted the now-debunked belief in the “aether,” an invisible field through which light was believed to travel. It would be years before he could prove he was right, but this thought experiment was somehow the “germ,” as he called it, for Einstein’s theory of special relativity, one of the ideas that first established him as a towering figure in theoretical physics.

6. The Ship of Theseus

One of the oldest of all thought experiments is the paradox known as the Ship of Theseus, which originated in the writings of Plutarch. It describes a ship that remained seaworthy for hundreds of years thanks to constant repairs and replacement parts. As soon as one plank became old and rotted, it would be replaced, and so on until every working part of the ship was no longer original to it. The question is whether this end product is still the same Ship of Theseus, or something completely new and different. If it’s not, at what point did it stop being the same ship? The Philosopher Thomas Hobbes would later take the problem even further: if one were to take all the old parts removed from the Ship of Theseus and build a new ship from them, then which of the two vessels is the real Ship of Theseus?

For philosophers, the story of the Ship of Theseus is used as a means of exploring the nature of identity, specifically the question of whether objects are more than just the sum of their parts. A more modern example would be a band that had evolved over the years to the point that few or no original members remained in the lineup. This notion is also applicable to everything from businesses, which might retain the same name despite mergers and changes in leadership, to the human body, which is constantly regenerating and rebuilding itself. At its heart, the experiment forces one to question the commonly held idea that identity is solely contained in physical objects and phenomena .

5. Galileo’s Gravity Experiment

One of the earliest thought experiments originated with the physicist and astronomer Galileo . In order to refute Aristotle’s claim that the speed of a falling object is dictated by its mass, Galileo devised a simple mental example: According to Aristotelian logic, if a light object and a heavy object were tied together and dropped off a tower, then the heavier object would fall faster, and the rope between the two would become taut. This would allow the lighter object to create drag and slow the heavy one down. But Galileo reasoned that once this occurs, the weight of the two objects together should be heavier than the weight of either one by itself, therefore making the system as a whole fall faster. That this is a contradiction proved that Aristotle’s hypothesis was wrong.

One of the most famous stories about Galileo is that he once dropped two metal balls off the Leaning Tower of Pisa to prove that heavier objects do not fall faster than lighter ones. In actuality, this story is probably just a legend; instead, it was this elegant thought experiment that helped prove a very important theory about gravity: no matter their mass, all objects fall at the same rate of speed.

4. Monkeys and Typewriters

Another thought experiment that gets a lot of play in popular culture is what is known as the “infinite monkey theorem.” Also known as the “monkeys and typewriters” experiment, the theorem states that if an infinite number of monkeys were allowed to randomly hit keys on an infinite number of typewriters for an infinite amount of time, then at some point they would “almost surely” produce the complete works of Shakespeare. The monkeys and typewriters idea was popularized in the early 20 th century by the French mathematician Emile Borel, but its basic idea—that infinite agents and infinite time will randomly produce anything and everything—dates back to Aristotle.

Simply put, the “ monkeys and typewriters” theorem is one of the best ways to illustrate the nature of infinity. The human mind has a difficult time imagining a universe with no end or time that will never cease, and the infinite monkeys help to illustrate the sheer breadth of possibilities these concepts create. The idea that a monkey could write Hamlet by accident seems counterintuitive, but in fact it is mathematically provable when one considers the probabilities. The theorem itself is impossible to recreate in the real world, but that hasn’t stopped some from trying: In 2003, science students at a zoo in the U.K. “tested” the infinite monkey theorem when they put a computer and a keyboard in a primate enclosure. Unfortunately, the monkeys never got around to composing any sonnets. According to researchers, all they managed to produce was five pages consisting almost entirely of the letter “s.”

3. The Chinese Room

The Chinese Room is a famous thought experiment first proposed in the early 1980s by John Searle, a prominent American philosopher. The experiment asks you to imagine that an English speaking man has been placed in a room that is entirely sealed, save for a small mail slot in the chamber door. He has with him a hard copy in English of a computer program that translates the Chinese language. He also has plenty of spare scratch paper, pencils, and file cabinets. Pieces of paper containing Chinese characters are then slipped through the slot in the door. According to Searle, the man should be able to use his book to translate them and then send back his own response in Chinese. Although he doesn’t speak a word of the language, Searle argues that through this process the man in the room could convince anyone on the outside that he was a fluent speaker of Chinese.

Searle conceived the Chinese Room thought experiment in order to refute the argument that computers and other artificial intelligences could actually think and understand. The man in the room does not speak Chinese; he can’t think in the language . But because he has certain tools at his disposal, he would be able convince even a native speaker that he was fluent in it. According to Searle, computers do the same thing. They don’t ever truly understand the information they’re given, but they can run a program, access information, and give a clear impression of human intelligence.

2. Schrodinger’s Cat

Schrödinger’s Cat is a paradox relating to quantum mechanics that was first proposed by the physicist Erwin Schrödinger. It concerns a cat that is sealed inside a box for one hour along with a radioactive element and a vial of deadly poison. There is a 50/50 chance that the radioactive element will decay over the course of the hour. If it does, then a hammer connected to a Geiger counter will trigger, break the vial, release the poison, and kill the cat. Since there is an equal chance that this will or will not happen, Schrödinger argued that before the box is opened the cat is simultaneously both alive and dead.

In short, the point of the experiment is that because there is no one around to witness what had occurred, the cat existed in all of its possible states (in this case either alive or dead) simultaneously. This notion is similar to the old “if a tree falls in the woods and there’s no one there to hear it, does it make a sound?” riddle. Schrödinger originally conceived of his theoretical cat in response to an article that discussed the nature of quantum superpositions, a theory that defines all the possible states in which an object can exist. Schrödinger’s Cat also helped to illustrate just how weird the rules of quantum mechanics really were. The thought experiment is notorious for its complexity, which has encouraged a wide variety of interpretations. One of the most bizarre is the “many worlds” hypothesis, which states that the cat is both alive and dead, and that both cats exist in different universes that will never overlap with one another.

1. Brain in a Vat

There has been no more influential thought experiment than the so-called “brain in a vat” hypothesis, which has permeated everything from cognitive science and philosophy to popular culture. The experiment asks you to imagine a mad scientist has taken your brain from your body and placed it in a vat of some kind of life sustaining fluid. Electrodes have been connected to your brain, and these are connected to a computer that generates images and sensations. Since all your information about the world is filtered through the brain, this computer would have the ability to simulate your everyday experience. If this were indeed possible, how could you ever truly prove that the world around you was real, and not just a simulation generated by a computer?

If you’re thinking this all sounds a bit like The Matrix , you’re right. That film, along with several other sci-fi stories and movies, was heavily influenced by the brain in a vat thought experiment. At its heart, the exercise asks you to question the nature of experience, and to consider what it really means to be human. The idea for the experiment, which was popularized by Hilary Putnam, dates all the way back to the 17 th century philosopher Rene Descartes. In his Meditations on the First Philosophy, Descartes questioned whether he could ever truly prove that all his sensations were really his own, and not just an illusion caused by an “evil daemon.” Descartes accounted for this problem with his classic maxim “cogito ergo sum” (“I think therefore I am”). Unfortunately, the brain in a vat experiment complicates this argument, too, since a brain connected to electrodes could still think. The brain in a vat experiment has been widely discussed among philosophers, and many objections have been raised over its premise, but there is still no good rebuttal to its central question: how do you ever truly know what is real ?

68 Comments

I remember the Chinese room! I Think there was a riddle after that. I saw a similar riddle too that I wanted to share here if that was okay: 3 Gods Riddle

If you liked the one about Schrodinger’s Cat, checkout Quantum Suicide: https://thoughtexperiments.net/quantum-suicide/

Long ago (&FA) Star Trek has an episode, “The Squire of Gothos” https://en.wikipedia.org/wiki/The_Squire_of_Gothos Who’s Toys are we?

I have an axe which once belonged to Abraham Lincoln. Since then, it’s had six new heads and six new handles.

Trolley Problem Five innocent lives versus one innocent life seems like an easy decision to make when looking at it from a distance; everyone thinks that saving five people is better than saving one person and to an extent I agree. But the actual person pulling the lever knows nothing about each person, yes they are all innocent but how can that stranger pull a lever and put a value on a life during such a short and stressful situation. That one person could have done more with his life than the five people did together. Or the one person could have been getting his life back together and the five people could have been valued members of their community, involved in everything with a family and a full job. When looking at someone else’s life from the outside no one really knows what they live with and go through in their daily life. It is very hard to judge a person and put a value on their life when they are strangers. As the background information tells us that in a utopian world saving five lives is better than saving one. I think most people would agree with this. After they are saved they could go on and better their lives or change something that they have wanted to. Also in most people’s heads five of almost anything is more valuable than one. Although most people have morals and I’m sure one of them for everyone is a person should not kill another person, being put in that situation a stranger is forced to decide between five people and one person. If they don’t act they become a bystander and they will know that with them doing nothing they watched five people die and one person walk away instead of the other way around. With not knowing anything about anyone I think the stranger should pull the lever, as horrible as it is to put a value on a life saving five people sounds better than saving one.

That’s a great list; the brain in the vat experiment is particularly interesting but I’d love to try out a virtual reality. I’ve heard people saying that the The Matrix ripped off the idea but The Matrix is actually based on Simulacra and Simulacrum, a book that deals with hyperreality, written by Jean Baudrillard.

So which is it? You make two directly opposing statements:

“The probability of each keystroke is completely independant of everyother keystroke. ”

“the probability of getting tails twice in a row when fliping a coin is .25, right? But if you flip the coin and get tails once, the probability rises to .50, because the first variable has become a certainty (1.0).”

Both statements cannot be true, and indeed are not true. The first is correct, the second is the “Gambler’s Fallacy”. Prior coin tosses have zero influence on future coin tosses, just like prior keystrokes have zero influence on future keystrokes.

Keystrokes and coins are no different from each other. Each act of flipping a coin is completely independent of every other act of flipping a coin. The odds do not change just because a particular outcome already happened, or did not happen.

English can’t be your first language and/or you must have failed your one statistics course. The two statements do not counter each other at all. I’ll explain the second statement like I would to my 5 year old niece. The probability of a heads or tails is 1/2 or .5. You with me? One result of two possible outcomes. The probability of getting tails twice in a row is 1/4 or .25. One result of 4 possible outcomes (HH, HT, TH, TT). After flipping the coin once and getting a tails it limits the outcome from the first set to either TH or TT so there is now a 50% chance of flipping TT. You have a little information but no true understanding of anything and all your comments make me weep for the education system.

Maybe there is only 1 original thinker amongst us… the rest are just creations of their mind.

How can #2 be called a Paradox? Its often described as a paradox. But I don’t think its really thought of one at all by physicists. The apparent paradoxical part is the cat is both alive & dead, but what about single atoms & quantum states? They are in superposition & ill defined just like the cat. How can it even be described a paradox if the measurement problem is still unresolved? And than adding decoherence? The experiment only deals with the copenhagen interpretation & argues that it is absurd especially when scaled up to macro scale.

well ive just seen this for the first time in science and ive got to say its very interesting. the theories created arguments between me and friends =) lol any will defo be back to look in more depth

Because the state of the atom determines if the cat is alive or dead and because quantum physics proposes that the atom is in the state in which the cat is both alive and dead, it means that quantum physics do not translate into the real world. That’s why people are trying to find a Universal Theory (such as the proposed String Theory) because quantum mechanics and gravity (i.e. small math, large math) do not agree with each other, yet they are both correct in their calculations.

Well, I could explain it to you (it’s actually not hard to understand at all), but I seem to have used up all my “time to waste” (as you call it) on showing why Number 4 is not correct for any conceivable universe… 🙂 Sorry!

( But here’s a hint: The Schrodinger’s cat paradox is based on observation, just as the entire universe is based on observation. And it has nothing at all to do with anyone observing the cat. The experiment, as laid out here, is not stated correctly as a demonstration of quantum mechanics: If it were, the cat actually would be both alive and dead at the same time, in exactly the same manner as particles on the quantum scale being in multiple indeterminate states at once, until observed. )

I really don’t get Schrodinger’s Cat….. can someone dumb it down further to the level of a 10 year old for me? haha… i’ve tried reading up on quantum mechanics, but somehow my brain refuses to absorb any of it. what exactly is Schrodinger arguing against and what’s his point when actually applied in quantum mechanics?

“because there is no one around to witness what had occurred, the cat existed in all of its possible states”. this particular line doesn’t make sense to me. it’s just dead OR alive so how can anyone say that the cat existed in all of its possible states just because no one knows what happened to it? is this based on an external observer’s viewpoint?

It can. It really depends on how you want to interpret it. There’s a few ways. The one you’re thinking of is one of them.

http://en.wikipedia.org/wiki/Schr%C3%B6dinger's_cat#Interpretations_of_the_experiment

The answer given for #4 is, of course, not correct: The monkeys never can type the entire works of Shakespeare, nor any other similar volume of text, in any realistic amount of time. The reason is simple: each time a monkey starts getting a string of text right, it is far more probable that he will get next keystroke wrong than right, thus invalidating the entire string. The longer the string gets, the more improbable it becomes that the next letter will be correct. For short sequences (just a few letters) the monkey might get it right by shear chance, but for anything longer than a half dozen words, it just won’t happen. Not even in the entire age of the universe.

Think of it this way: Assume that the monkey has a keyboard that can produce 26 uppercase letters, 26 lowercase letters, and a half a dozen punctuation marks (space, full stop, comma, quotes, exclamation mark, and question mark.) That makes 60 characters. The monkey starts typing at random, and produces a “W”, which happens to be the first letter of the first line in Macbeth: (“When shall we three meet again”). Let’s say “the force is with him”, and on the next few keystrokes he hits an “h” an “e” an “n” and a space. Great! Now he has entire first word right! The problem is, on every single “next keystroke”, there are 59 ways the monkey can be wrong, and only one way he can be right. If he does not hit an “s” then everything he has typed so far is useless, the entire text must be scrapped, and he has to start again.

He is 59 times more likely to hit the WRONG key than the RIGHT one, at random. He only has a 1 in 60 chance that the next letter will be correct.

But this isn’t just a matter of adding up the letters and multiplying by 60: this is an exponential problem. The chances that he will get two letters in a row correct are one in 60×60, which is also written 60^2, which works out to 3600. So he’d need to type 3600 random keystrokes to be stand a good chance of producing the first two letters (“Wh”)

The chances of getting three letters right are 1 in 60^3 (60x60x60), which is one in 216,000. For 4 letters is one in 12,960,000. To get “When” right, he’d need to type about 13 million keystrokes! Maybe you are starting to get the picture…

Mathematically, the chances that he’ll get “n” letters correct are 60^n (“60 to the power n”, which is the mathematical way of saying “there are 60 ways of getting each of “n” letters.).

The entire first line of Macbeth (“When shall we three meet again?”) has 31 characters, so the chances of the monkey getting it right are 60^31, which is roughly one in 1,326,443,500,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000. Wow!

Let’s say this monkey types really fast, never sleeps, eats or takes vacations, and can tap out 10 characters per second. So roughly every 3 seconds he will produce a line of text that we can compare against that first line from Macbeth. How long will it take the monkey to produce that line? One sample every 3 seconds is 20 samples per minute, which is 1200 per hour, 28,800 per day, and 10,519,200 per year. Ten million samples per year! Not bad…. At that rate, it will only take the monkey a bit more than a year to type the single word “When” correctly, and about 126,097,376,067,039,332,591,704,312,114,990,000,000,000,000,000 years to get the entire first line of Macbeth correct! Well, it turns out that, so far, the entire universe has only aged about 15,000,000,000 years (give or take a billion), so that poor hard-working monkey is going to need a bit more time…

So we add more monkeys! Let’s be generous and put not just ONE monkey to work, but a BILLION monkeys to work. Cool! Between them, it will only take them about 1,260,973,760,670,393,325,917,043,121,149,900,000,000 years! That’s MUCH better, isn’t it?

Hmm, so it seems a billion monkeys working for the entire age of the universe isn’t enough. So let’s get REAL generous, and say that there will be one billion monkeys on each of one billion planets in each of one billion galaxies… how does that work out?

Turns out, we are now down to just 1,260,973,760,670,393,325,917 years! Or roughly 840,649,173,780 TIMES the age of the universe.

In other words, a billion billion billion monkeys, typing for the entire age of the universe, (ever since the Big Bang and right up to now), multiplied eight hundred and forty billion times over, stand a roughly even chance of producing ONLY THE FIRST LINE OF MACBETH correctly!!!! Just 31 characters.

Maybe now you get to see why this is such an incredibly improbable feat! And that’s just for a very simple phrase: “When shall we three meet again?”.

But Shakespeare wrote quite a bit more than just 31 characters. There are roughly 130,000 characters in “Macbeth”, so instead of the problem being just 60^31 it is actually 60^130,000 for just that one play (Macbeth). But Shakespeare wrote a total of 38 plays, 154 sonnets, two rather long poems, and several shorter poems. ….

Sorry, but that ain’t gonna happen. Not even if you could miniaturize the monkeys, and speed them up a thousand times. In fact, not even if you could get every single atom in the entire known universe typing out text at the rate of millions of characters per second! Even then, you STILL could not get the job done in any realistic amount of time. Not even in an incredibly unrealistic amount of time!

(And all of this is without even considering who is going to CHECK what the monkeys typed, compare it against the works of Shakespeare, and see if they got it right or not…)

That’s the difference between theory and reality. Yeah, with an “infinite” amount of time and an “infinite” number of monkeys you could do it, in theory, but NOT with any realistic scenario of time, monkeys, typewriters or text.

So the claim the correct answer is that all those monkeys and all those typewriters don’t stand even the vaguest chance of producing even the tiniest fraction of the works of Shakespeare. #4 is wrong.

Thank you for one of the most compete replies I have seen on Toptenz.net. Great comment.

wow… u obviously have a lot of time to waste.

the beauty of the concept of “infinity” is that compared to infinity 1,326,443,500,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 raised to itself is almost just like a speck of dust in this… errr…. dusty universe…. in short, unimaginable. who knows, with all those monkeys one may have been bitten by a radioactive clone of shakespeare that has given that said monkey the super power to not only remember all his works verbatim but also type it using a typewriter (heck, if i can think it then it’s probably one of the infinite possibilities, right?)……… “Realistic” has been thrown out of the window when the term “infinite” was used. u don’t need crazy mathematical skills to get the point of this thought experiment, u just need your imagination! =D

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don’t mind me…. i’m just bored.

For waaaaaaaaaayyy too many of these comments, people are not grasping a) the point of a thought experiment in the first place (it’s not literal) and b) the idea or concept behind the experiment! Infinity is a concept, a never ending number. The authors for instance never claimed that we should actually rely on monkeys to type Shakespeare. In the scenario of an infinite number of monkeys with an infinite number of typewriters, every keystroke that goes on has an infinite number of chances at being the correct keystroke, so some of the monkeys get it right one letter at a time. The odds of the next keystroke being correct as well are incredibly slim, but that is where the element of infinite time factors in. Given enough time, these monkeys WILL type every possible combination of characters imaginable, and within those possible combinations will be every written work known to man. The thought experiment never claimed that this would happen in “a reasonable amount of time.” Maybe the give away was the “infinite amount of time” factor. Regardless, please don’t waste your time attempting to poke meaningless holes in a THEOREM by which you are simply spreading your own ignorance of a concept rather than learning for yourself.

When people have to resort to insults and straw-man arguments in their vain attempt to defend an indefensible position, all that it shows is that they don’t actually have any basis for their superfluous wafflings and splutterings at all! 🙂

The point, of course, is that infinite time changes nothing: with every single keystroke, it becomes statistically more and more UNLIKELY that the monkeys can ever type the entire works of Shakespeare! I did, of course, point this out in the very first paragraph of my original post:

“The reason is simple: each time a monkey starts getting a string of text right, it is far more probable that he will get next keystroke wrong than right, thus invalidating the entire string. The longer the string gets, the more improbable it becomes that the next letter will be correct.”

Got that last part? “The longer the string gets, the more improbable it becomes that the next letter will be correct.” In other words, as time goes on toward infinity, then chance of getting it WRONG increase, not the chances of getting it RIGHT.

In other words (for those who seem to have a problem understanding basic high-school statistics, and simple logic), each time that a monkey types a letter, the chances that he will get the next letter WRONG increase EXPONENTIALLY, while the chances he will get it RIGHT only increase LINEARLY. It doesn’t take very long before the probability of getting it wrong approached infinity… And each time a monkey strikes yet another key, the probability that he will fail at the task get even closer to 1, while his chances at succeeding get closer to zero.

On the very first keystroke his chances his chances of getting that one right are very high, but on the second keystroke, the changes drop dramatically. By the twentieth keystroke, his chances are so close to zero as to be not worth mentioning, and as time progresses, his chances get every closer to zero, and not only that, they ACCELERATE towards zero.

The belief to the contrary is, of course, closely related to the gambler’s fallacy: The gambler believes that a string of unbroken losses means that his chances of winning on the next bet are improving, when in fact they are not. The inverses case for the monkeys is similar (although infinitely more negative) : A string of unbroken “wins” (hitting the correct letter) does not increase the chances of success, and in fact increases the chances of FAILURE.

And no, the fact of extending the experiment for an infinite amount of time does NOT make it more probable that the monkeys will eventually succeed: In reality, it makes it infinitely more likely that they will continue to fail, eternally. Inability to see this rather obvious implication is a clear indication of your basic misunderstanding of statistics and the concept of infinity. Despite what intuition tells you, actual reality is somewhat different. No, that’s not a personal insult: it is simply a statement of fact.

So, if you can’t grasp the simple basics of statistical analysis, then maybe you shouldn’t post unfounded opinions on the internet: That way, you could avoid embarrassing yourself further.

The mere fact that you attempted to embarrass ME into not refuting your childish position is a glaringly obvious indicator of your fear of being refuted. Which, I believe, I have accomplished rather successfully anyway. (And which, of course, is your cue to spew forth yet another unfounded, infantile response of meaningless drivel.)

The objective does become more improbable however the probability never becomes zero (impossible). Therefore given infiniate time,a period without end,it will eventually occur.

Don’t forget the infinite monkeys, infinite typewriters, and infinite time. I think you’re trapped into seeing a finite amount of monkeys. If that were the case, then the chances would be decreasing as such. But the probability of recreating such Shakespearean works given infinite monkeys, and infinite time…with the use of infinite keyboards surely must be 1. The probability of each monkey getting it is so small that it would approach zero, but the probability of one of them getting it eventually would approach 1.

Except that there is also an infinite number of possibilities that do not contain the works of Shakespeare. Thus making it possible that even with infinity and an infinite number of monkeys, they may never type the complete works of Shakespeare.

The probability of each keystroke is completely independant of everyother keystroke. The overall probability of the monkeys writing all of billy shakes’ works is inconcievably low before said monkey begins, but becomes exponentially greater each time he selects the correct key. For example, the probability of getting tails twice in a row when fliping a coin is .25, right? But if you flip the coin and get tails once, the probability rises to .50, because the first variable has become a certainty (1.0). And beside that, assuming assumingall the mokeys are working at once, one failure wastes little time or energy, because there are infinite other monkeys typing away, at least a few of them are already killing off there third or fourth character by now. Remember, nobody ever said the circumstances were possible, but given such generous circumstances it is almost certain that the works will come out in a few years.

“In other words (for those who seem to have a problem understanding basic high-school statistics, and simple logic), each time that a monkey types a letter, the chances that he will get the next letter WRONG increase EXPONENTIALLY, while the chances he will get it RIGHT only increase LINEARLY. It doesn’t take very long before the probability of getting it wrong approached infinity… And each time a monkey strikes yet another key, the probability that he will fail at the task get even closer to 1, while his chances at succeeding get closer to zero.”

Those two statistics don’t exist at the same time. They can easily even be considered the same statistic based purely on respect to temporal perspective. Each additional character required causes the initial probability of failure to approach infinity. Each additional character gotten correct, from that point on, literally decreases the amount of required characters for that instance, causing the probability of success to approach 100%. Each incorrect character merely resets the counter. The statistic you keep bringing up is more akin to a starting line and can’t change once monkeys are started typing.

What’s more damning, however, is that that “exponentially increasing” statistic is rooted in the single finite variable in the entire experiment: the length of The Complete Works of Shakespeare.

Because the length of The Complete Works of Shakespeare is finite, it will always be infinitely less than infinity. This is the crux that your argument neglects.

No matter how infinitesimally small the probability of a monkey producing The Complete Works of Shakespeare is, with infinite monkeys and infinite typewriters, you’re directly comparing a finite number to infinity.

You don’t even need infinite time. All possible occurrences are happening simultaneously with the monkeys alone and the time it takes to produce The Complete Works of Shakespeare is literally the shortest time possible for a monkey to type it. There will be an infinite amount of failures and an infinite amount of successes because everything that could ever happen will happen at once an infinite amount of times. All your calculations are ultimately meaningless because infinity breaks math. Once it’s introduced, there’s really only two numbers: infinity and not-infinity. This is why calculus is so convoluted; it bends over backwards to avoid this.

I think Chileman2020 has not in the least grasp of the word infinty. When we are talking of infinte universe, anything having probability of more than zero will recur not 1, 2 but infinite times.so even if probality of monkeys typing the series is 1X10^-100000…… it will happen infinite times.There will also be infinite harry potter collections , infinite oxford dictionaries as well as infinite times aaaaa…./bbbbb…./cccc…. etc.

There are an infinite number of numbers on the decimal line between 1 and 2, but none of them are other whole numbers. Just because you have an infinite series does NOT mean you can count on everything being contained within that series. There are still probabilities in infinite series, especially since we cannot directly observe and quantify the things within that series. That is why it can be said that in an infinite series things may be more or less likely to occur. For example, in this mind experiment it is far more likely that infinite monkeys will poop, play, mate, and fight each other than they are to make intentional keystrokes. The point of the thought experiment is to say that a RANDOM element has the ability to produce non-random things (such as all of Shakespeare). The problem is, random elements cannot be quantified.

If you put a truly random element in a scenario (monkeys are actually pretty predictable) there is NO possible world (a way of saying that no matter how you couch the mind experiment it won’t work) where you can say for certain that the truly random element will produce anything. You cannot even say that the random element will produce nothing (since it is random). Every “set” is possible to the random element but NO set can be proven actual even in an infinite space, with infinite elements, infinite time, and infinite materials. And don’t try to argue that by proving that no set can be proven I’ve proved that the set “no set can be proven” is proved. That is a logical absurdity and to argue it is to cut your own legs off.

I’m not sure my mind is working properly after those last couple of sentences I just read.

That is proof your mind is working properly. 😉

the movie inception deals with number 1 and 2! go see it

Why am I myself, rather than someone else?

This is a very basic question about life, but it may also strike someone as nonsensical. What would it mean for someone else to be me? Or, what would it mean for me to be someone else?

These questions, which are not easily addressed empirically, can be dealt with by way of thought experiments.

First, I can imagine someone else being me if a duplicate were to be made of my body, with all my features, memories, habits, etc., and then if I were to be replaced by it. This was essentially the plot of the science fiction movie The Invasion of the Body Snatchers (1956, 1978), although the duplicates in those cases were not precise copies of the replaced individuals — they were actually alien beings that were duplicates to all external appearances, but not internally. However, it is not hard to imagine true duplicates being made, especially with the kind of technology imagined for the transporter machines in the Star Trek television series. The 6th Day, a recent Arnold Schwarzenegger movie (2000), was about just such complete duplicates. Nature itself produces duplicates, but only in the very first stages of life: Identical twins are genetically the same, but their experiences and memories begin to diverge as soon as the individuals start to develop separately — something already happening in the womb. A true duplicate of an adult would require a mapping of every atom in the body, which can now more or less be done with Nuclear Magnetic Resonance Imaging (NMR or MRI) technology, and then a duplicate set of such atoms being assembled in precisely the same way, something rather further from present technology. This would not be a “clone,” as presently understood, since a clone is only genetically identical. A clone would not have the same memories as the original individual, and it would be no more and no less like the original than an identical twin would be.

Could I be replaced with such a complete duplicate — every atom, not just genetically identical — it would think that it was me. But clearly it would not be me, especially if I were not destroyed in the replacement and continued to exist off somewhere else. We can imagine that such complete identity might produce a being that would simply see itself as existing in two places at once, but this would require some kind of communication; and that would require the existence of some kind of extrasensory or paranormal connection between the two bodies, which is not now part of established science. Without such paranormal communication, the identical individuals would each think of themselves as the original individual, although only one of them would be right; and they would immediately begin to diverge as individuals because of differing experiences.

So what would be the difference between the two individuals? Well, they would exist in different spatial locations, and they would consist of different, albeit identical, atoms — and it is a postulate of quantum mechanics that all particles of the same kind are absolutely identical. I know what it would mean for me not to be that other individual, since it would not be part of my consciousness. However, what if I were to be instantaneously destroyed and replaced with that individual, so that there was, to all appearances, a spatial continuity between us, and a material continuity since, as noted, identical material particles really are identical (there is, according to quantum mechanics, absolutely nothing about them that would enable us to tell them apart). If that individual would still not be me, then there would have to be something else about me that makes me myself apart from physical content, memories, and spatial continuity. In other words, I can perform the thought experiment that would remove “me” from my body, leaving behind an individual that looked, thought, and felt like me, but was not. It would simply not have my consciousness, but another one, which could then ask over again why it is itself and not someone else.

This same kind of thought experiment can be run the other way around: What would it mean for me to be someone else? I can easily imagine suddenly waking up and having another body. Franz Kafka wrote a famous story (“The Metamorphosis,” 1915) in which someone wakes up and has turned into a cockroach. I can also imagine suddenly losing my memory and not remembering who I am. This actually happens to people occasionally. It is also possible to imagine, as in the science fiction movie Total Recall (1990), that the memories of a different person have been put into me, and I wake up, not just not remembering who I am, but actually thinking that I am someone else. Combining these would produce a very dramatic effect: I might wake up both with a very different body and thinking and believing that I am a very different person. If this left me with at least the same brain, however, we would have no difficulty imagining how this could still be “me” in some accountable sense — it would still be my brain regardless of how the body around it might change or what kind of memories might be scrambled or reprogrammed in it. Interestingly, however, our own brain is usually something that we never experience; so were body and memories to be changed, it would be difficult to verify our personal continuity short of neurosurgery. From an internal point of view, and an external one for most practical purposes, everything would be different.

Now if I imagine body, memories, and brain to be replaced, then it would be easy to say that the result could not possibly then be me. However, it is still possible to imagine that the resulting individual could be me, and this act of imagination has actually occurred in multiple world religions for centuries: it would still be me if it were the same immaterial soul. Thus, if I were to believe in reincarnation, I would actually think that I have been innumerable different persons in the past, all with different bodies, memories, and brains. As Krishna says to Arjuna in the Bhagavad Gita: “I have been born many times, Arjuna, and many times has thou been born. But I remember my past lives, and thou has forgotten thine” [4:5, Juan Mascaró translation, Penguin Classics]. Krishna, implies, of course that memories of past lives are retained by the soul. This is not necessary to the thought experiment. It is possible to imagine a soul that does not carry memories but still carries an identical consciousness that would distinguish Arjuna from another individual physically and mentally identical. Since Arjuna (and most of us) does not seem to remember any past lives, this is what is given in experience anyway.

What the thought experiments demonstrate is a truth of metaphysics that the same attributes can belong to different individuals, or in other terms that an individual as an individual cannot be exhaustively defined by abstract predicates. Thus, bodily features, memories, personality, etc. cannot uniquely determine an individual; so I cannot identify myself as an individual by any such qualities. This metaphysical principle has only been disputed by philosophers like Leibniz, who postulate the identity of indiscernibles, that individuals that cannot be told apart are actually the same individual. But such a postulate only works for Leibniz because he denies the existence of space, which can serve to distinguish otherwise identical individuals.

The spatial separation of otherwise identical individuals also can be interpreted to mean that the individuals consist of different quantities of matter. To philosophers as diverse as Aristotle, Descartes, Spinoza, and Schopenhauer, different space and different matter are ontologically identical conditions: Space itself, in effect, is matter. This may now be restated in terms of quantum mechanics: If identical subatomic particles are postulated as absolutely identical by quantum mechanics, then spatial separation, again, is the only thing that individuates identical particles as materially different.

In the thought experiments on my personal identity, spatial or material difference might seem to do the job. An identical copy of me would be spatially and materially different, and if I were replaced by an identical copy, however quickly, it is still possible to imagine that it is materially different, even if instantaneously placed in the same space. However, such a transference would result in no externally ascertainable difference whatsoever, which sounds somewhat paradoxical if were are to say that the “matter” is different. In these terms “matter” must actually be defined in such a way that it is not materially or empirically distinguishable from other matter. Another postulate of quantum mechanics is that if two things cannot be in principle distinguished, then they are the same thing. The only thing that can distinguish identical particles is their spatial location. Thus, if we say that two individuals consist of identical particles and cannot be spatially distinguished (because they are temporally contiguous in the same space), quantum mechanics would then judge that they are the same individual. That there would be a temporal difference doesn’t help, since there is no empirical criterion by which it could be determined whether the “matter” has been switched from one moment in time to another or not. The only way in which we could then say that an identical individual could replace me instantaneously in the same space and still not be me is to require that there be a form of “matter” that is not accessible to physical science. A form of “matter” not accessible to physical science, however, would not be “matter” in any familiar or common sense meaning. An immaterial substance standing in the place of what we would ordinarily call “matter,” however, would more easily be called the “soul.”

If quantum mechanics loses track of matter by only using space to individuate identical particles, the thought experiment of me becoming a different individual contrariwise loses track of space and is only able to use matter for individuation. Thus, I can imagine instantaneously acquiring a different body, different memories, and also finding myself in a different place. If that is nevertheless still me, with my consciousness, it would have to be because the “matter,” or the substantial substrate of my self, was moved to that new location, even if nothing else moved by way of the contents and characteristics of my physical and mental identity. Since such “matter” would then be inaccessible to physical science, it would be reasonable to call such a substantial substrate “immaterial”; and an immaterial substance would reasonably be the “soul.”

It may help to recall what it would mean to say that I could find myself with a different body, a different mind, and in a different location and still be me. It would mean that the conscious existence that I experience now, the conscious existence that seems to disappear in sleep, and which I imagine, or suspect, or fear may simply become nothing in death, can still be imagined as the same conscious existence even if what appears in it is a different body, a different mind, and different place. Thus, I have not become nothing and can still be me, even if I seem to be someone else, cannot remember my old self, and have appeared in a different place. This conception of conscious existence as perfectly divorced from, and so possibly perfectly empty of, content first occurs in the Upanishads, especially the great Brhadâranyaka and Mândûkya Upanishads. Advaita Vedânta then concludes it is only the Self (Âtman) that has substantial, independent existence, while physical objects only exist as illusory appearances in consciousness.

Although “matter” in the senses examined, whether physical or immaterial, is a metaphysical conception that is not accessible to physical science, the device of thought experiments to examine these issues is a perfectly legitimate procedure, not only for philosophy, but even for physical science itself: Einstein’s entire theory of Relativity was based on his own thought experiments. Thus, the basic question here, “Why am I myself, rather than someone else?” is no more dismissible than Einstein’s question about what a light wave would look like if we were moving at the velocity of light with it. The paradox, however, of ending up with a definition of “matter” that abstracts from it all identifiable qualities was not lost on Buddhism, which rejected the idea of a substantial substrate to anything. Like Hume, Buddhism adopted a kind of empiricism where the very conception of substance, whether material or immaterial, did not qualify. However, that produced its own paradoxes, since Buddhism, like Hume, could not then account for the duration in time of objects or persons. Much of Buddhism accepted the doctrine of “momentariness,” that individual objects do not abide for more than a moment, but this is considerably more paradoxical and counter-intuitive that the duration of a substantial substrate. What the Buddhist paradoxes show us is that the substrate, however intangible, is not an unnecessary hypothesis — without it, as a synthetic ground a priori (as Kant would put it), the duration of individuals cannot be accounted for.

Instead, I must appeal to the doctrine of The Origin of Value in a Transcendent Function. Both kinds of “matter” are conceptions of “Negative Transcendence,” the emptiness of existence over and above the phenomenal content of consciousness. Negative Transcendence has internal and external poles. External transcendence then corresponds to physical substance, which in terms of quantum mechanics, as we have seen, is functionally identical to space itself. Internal transcendence is then the substrate for the sense of personal identity that has been examined here in the “thought experiments on the soul.” The question left open in The Origin of Value in a Transcendent Function was in what way internal and external transcendence corresponded to each other.

Now it appears that internal and external transcendence must in an important sense be independent of each other, since external transcendence, as space, cannot account for personal identity from an internal point of view, and internal transcendence, as the “matter” of personal identity, varies independently of space and what can be accessed by physical science. Thus, for there to be personal identity, there must be more than just space and external transcendence. Such a conclusion, however, does not produce a Cartesian Dualism of material and immaterial substances existing in the same logical space, for internal and external transcendence are kept ontologically apart. They are only united through “Positive Transcendence.” Negative Transcendence, in other words, cannot be added as a transcendent object to the order of phenomenal objects. Transcendent objects are subject to the Kantian Antinomies. Rather than being added as a transcendent object to phenomenal reality, internal transcendence casts a “shadow” of Positive Transcendence on phenomenal objects: the numinosity of the self or soul in religious conceptions, or even just the “supernatural dread” associated with dead bodies or cemeteries.

The question, “Why am I myself, rather than someone else?” then, cannot be answered just with natural objects. It can only be answered with transcendence. But transcendence appears in the phenomenal world as the numinous quality of natural objects. This may be called the “soul.” The soul, as an independent, transcendent object, however, cannot be said to be established by this argument. The fact that Buddhism rejects such an object is an important clue that it is subject to the undecidability of a Kantian Antinomy. There is no doubt, on the other hand, of the numinosity of persons in Buddhism, especially as they become Bodhisattvas and Buddhas, and of the reality of karma and reincarnation, despite the denial that reincarnation is the transmigration of a substantial self. Buddhist doctrine thus expresses the paradox of Negative Transcendence as an existence which nevertheless cannot be placed as an object in conceivable (i.e. phenomenal) reality. Later this would be conceived as the “Buddha nature” of individuals, an idea that, not surprisingly, set off controversy about whether this involved a “substantialist heresy” or not. It is, indeed, a fine line, although easily drawn with the theories of Negative and Positive Transcendence.

As noted, it is a postulate of quantum mechanics that subatomic particles in the same quantum states are absolutely identical in characteristics. Although many have believed that Einstein vindicated Leibniz’s view of space, as relative, over Newton’s, this feature of quantum mechanics decisively contradicts Leibniz, for whom space does not exist and objects that are indistinguishable from each other are identical to the same thing. But indistinguishable electrons are not identical to the same thing. They are distinguished from each other by their locations in space (although their possible locations may be summed in the wave function). Leibniz, of course, could respond that what makes the electrons different is their history, and their relationship to other objects. However, while Leibniz believed that his “monads” contained their history, and a representation of their relationships, within themselves, this is not the case for electrons. Indeed, quantum mechanics rules out any such things as “hidden variables.” With an electron, what you see is what you get. And since Leibniz’s monads don’t actually interact with each other, the only terms of their history and their relationship with other objects are their motions and relationships in space. If space does not then exist, monads actually have no history and no relationships.

If we allow that identical objects, however, are distinguished by their locations in space, location in space will not work to account for identity. That is because, as an object moves, it comes to be at a different location. So if different locations serve to distinguish different objects, why does not a object become a different object by moving and coming to be in a different location? This poses a grave difficulty for the theories of matter in Descartes and Spinoza, where matter is all but indistinguishable from space itself. But space does not move around, while matter must move around, to maintain its identity. On the other hand, it is not clear that fundamental particles in quantum mechanics possess any “matter” in the traditional, substantial sense. Energy turns into electrons and positrons. Electrons and positrons collide and turn back into energy. What we see is a collections of attributes, or quantum numbers — mass, charge, spin, etc. — that looks like nothing so much as the “aggregates” (skandhas) of non-substantial existence in Buddhism.

Unfortunately, the denial of substance in Buddhism is intended to effect a denial of identity. If the problem is accounting for the identity of an object or sub-atomic particle from moment to moment, Buddhist metaphysics is specifically designed not to do this. The result is an effective thought experiment in what is required for identity: The “aggregates” are not enough. If an electron has an enduring existence, something has the mass, charge, spin, etc. that characterize it. And if the electron, as electron, ceases to exist, neither Parmenides nor Democritus would be surprised to learn that it does not simply become nothing. Mass/energy is conserved, and there are particles that carry them away. Matter will not be a Cartesian fixed quantity of “stuff” that no transformation can alter, but it will represent a durable continuity of identity, which carries the quantum attributes and can merge with other objects or itself divide into new objects.

This, indeed, is more an Aristotelian than a Cartesian view of matter. Perhaps the only difference is that Aristotelian matter only accounts for different individuals of the same kind. Something unique of its kind (sui generis) doesn’t need matter and can exist as pure form (like God or the celestial intelligences). In the argument here, however, material substance does not merely account for different things of the same kind, or for different individuals that are otherwise identical in every way, but also for the identity of anything with itself from moment to moment — and Aristotle’s substance (ousia), after all, was in the form, not the matter. A Buddhist analysis of Aristotle’s God would be that it has no self, no identity, and duration. Probably not what Aristotle wanted to say, but then he is vulnerable to the critique, since for “substance” he can only offer attributes, i.e. the form.

While Aristotle thought of form as substance, it might be noted that a curious thing happened to the terminology in the translation from Greek to Latin. Ousia is from the participle of the verb “to be” in Greek. Thus, it looks rather like essentia, “essence,” in Latin, which is from the infinitive of the verb “to be” (esse). Substantia, “substance,” itself, is entirely different, meaning to “stand under.” There is a word that means “stand under” in Greek, and that is hypokeimenon. Aristotle does not use that synonymously with ousia. He applies it, as it happens, to matter. Perhaps it would be better to translate ousia as “essence,” in which case we could take substance, the underlying thing, as always being what Aristotle associated with matter. His reluctance, however, is understandable, since he thought of matter as mere power or potential, which would disappear in God. By the time we get to St. Thomas, of course, that idea of a powerless God was unappealing.

If our concern then becomes personal identity, will the identity of material substance account for that? As I have argued, no. In physical terms alone, we know that there is a turnover of matter in our bodies. I believe that after 20 years or so, all the matter in our bodies is supposed to be different. A defendant in a legal case once even tried to argue that he was literally not the same person who had committed the crime, some twenty years plus in the past. His argument was not allowed as, indeed, we trace personal identity across that transformation. With the material objects, this can indeed produce some paradoxical results. The Stoics noticed that in their day the ship kept at Athens, which was supposed to have born Theseus to Crete, had finally been repaired so much that every single plank and other part of it was no longer original. Was it the “same” ship? In a way yes, and in a way no. With material objects, the less the original material, the less it is the original thing. There is no such ambiguity with people. And we can ask them.

Similarly, we can use the thought experiments detailed above. We can think of ourselves persisting even through transformations in body, memories, and everything else. We can even, as it happens, think of ourselves persisting through absences of consciousness. Indeed, we do that every day, as we awake from sleep. This would be challenging for Descartes, for whom the soul was essentially thinking, or for Advaita Vedanta, where the self (âtman) is essentially conscious. But it is not really a problem — consciousness is not essential to identity when the identity of consciousness from moment to moment must itself be accounted for. If personal identity requires a substantial substrate different from material existence, our word for it would be “soul.” This would be a different and more fundamental meaning for it than what soul was for the Greeks, the life force, or for Descartes, consciousness (Searle’s “mental substances”).

The remaining problem would be the epistemological one of why we believe there are substances at all. Not only Buddhism, but Berkeley and then, especially, Hume point out that since substances are behind or beneath everything we experience, we are not directly acquainted with them as such. So what is our evidence that there are such things? The Kantian argument of the “possibility of experience” is then that “substance” is a category, like causality, which is an a priori expectation about experience, not something deduced, derived, or proven from it. Our expectation that the existence of objects is durable, separable, and identical is the principle of “substance” by which we organize and understand experience. While Hume himself said that all reasonings about matters of fact are based on the relation of cause and effect, it is obvious enough that many such reasonings are also based on the persistence, independence, and identity of substance.

What Kant would ask, of course, is what we can know about a substantial soul outside the limits of a possible experience. The soul, after all, is not a natural or phenomenal object, and it is difficult or impossible to imagine how it can exist, as a substance, in the phenomenal world. Kant’s answer then is that the limits of possible experience represent the limits of our knowledge of objects, so that we do not know how it is that substantial souls can exist. An immortal soul, which would be immune to the slings and arrows of man and nature, is in that regard an unconditioned reality, the sort of thing that does not appear in phenomenal existence, either for Kant or Buddhism. Yet even Buddhism does not deny that there are unconditioned realities — most importantly Nirvana. Thus Buddhism, which is ultimately neither materialistic nor naturalistic, actually has more in common with Kant than it does with Hume or, for that matter, John Searle. The soul as a numinous reality, is fully present in the numinosity of the Buddhist Arhat, Bodhisattva, and Buddha. This is no comfort for the materialist, the skeptic, or the nihilist.

No. 5: "In actuality, this story is probably just a legend; instead, it was this elegant thought experiment that helped prove a very important theory about gravity: no matter their mass, all objects fall at the same rate of speed." True, but only in a VACUUM!

that’s what i heard too! were they on the same page about the setting (vacuum or not)? i’m a bit too lazy to research about it right now…. aristotle is probably not talking about a vacuum if he’s considering drag.

what’s wrong with aristotle’s logic? wouldn’t galileo’s reasoning be a bit off if he tied a small parachute-like contraption to a small rock and threw it off a small building?

i didn’t really pay too much attention in my physics classes so a little enlightenment would be appreciated. =)

Mass has no effect on drag. Air resistance is caused by two things, the number of particles hitting the object, and their velocity relative to the object. This has nothing to do with the objects mass, and so it doesn’t matter whether Aristotle was imagining drag or not, it still has nothing to do with mass.

To give an example, if you drop two bricks, but one is denser than than the other, they will still fall at the same rate. They have the same drag, because they are the same shape and size, but their mass is different.

This is crazy. No one is crazy enough to hook up a brain to a computer. That is cruel and unusual. It is also impossible.

I will give you proof why I am right. If this supposed 'mad scientist' created an artificial world for you, then they would never let you find out about the 'brain in a vat'. They wouldn't want you to figure out what's going on.

Also, think about what you love in life. I'm not talking about material things. I'm talking about the stars in the sky, or when flowers are blooming in spring. You can't imagine them being artificial.

Think about yourself. You KNOW you are real. I am real. We are all real.

Most importantly, God created the world for us, not a mad scientist. Read the book of Genesis in the Bible to find out how the world was created.

Please don't let yourself be brainwashed by this 'brain in a vat' nonsense. You are too smart for that.

Don't let yourself be brainwashed by the Bible. Most of the stuff in the Bible is ten times more far-fetched than this stuff. And if you are going to take the book of Genesis seriously, then you have to take it ALL seriously, which is just ridiculous considering the Bible contradicts itself every other page.

Well, all sensory experience takes place in the brain. I'm afraid that you just don't know that you aren't a brain in a vat and that your Bible is just a byproduct of the evil scientists attempts to coerce into believing your reality is real.

I KNOW I am real. I DO NOT know that you are real, nor do you KNOW that I am real. However, because the claim that I exist is not so extraordinary, it takes very little faith to take this statement as truth.

You need to re-read the Cartesian method of doubt if you don't believe it makes logical sense, because I ASSURE you it does. Descartes was an extremely intelligent man and if you haven't read any of his work, it's pretty disrespectful to discard it as "nonsense."

I actually took my time to read the bible before I discarded it as nonsense.

Your "proof" also doesn't make any sense. If you are a brain in a vat…why would the scientist care whether you knew of the possibility of you being a brain in a vat? To you, this simulated reality is 100% convincing and as "real" as the "real" universe.

"I will give you proof why I am right. If this supposed ‘mad scientist’ created an artificial world for you, then they would never let you find out about the ‘brain in a vat’. They wouldn’t want you to figure out what’s going on."

I'm still waiting for your proof. How about you read Carl Sagan to find out how the world was created. I mean, you put your faith in a document written by man as it is. Why not put your faith in a document written by a smart one? As 'aquiredthoughts' says, the bible contradicts itself every other page. It's obviously a load of rubbish.

"Also, think about what you love in life. I’m not talking about material things. I’m talking about the stars in the sky, or when flowers are blooming in spring. You can’t imagine them being artificial."

First off, our brains process all those things, including our emotional reactions to them.

"Most importantly, God created the world for us, not a mad scientist. Read the book of Genesis in the Bible to find out how the world was created."

Second, what you're arguing is that no "mad scientist is controlling us," but that God created everything that we see, hear, touch, experience, etc… Therefore, I could argue that God is the mad scientist. Essentially, God and this "mad scientist" are creating human beings in a certain way, giving them free will and the capacity to gain knowledge. The only difference is believing in God is much more socially accepted, and a person gets a reward at the end of their lifespan if they are a good person. The scientist, however, is given a negative and "cruel" connotation.

If you believe that this theory is "impossible," then what makes God so much more likely? Granted, I am not saying I believe in either option necessarily; however, I do believe that blind faith is not nearly as reliable as science or facts.

"Also, think about what you love in life. Iâ??m not talking about material things. Iâ??m talking about the stars in the sky, or when flowers are blooming in spring. You canâ??t imagine them being artificial."

This is all theoretical. Nobody is going to fly side by side a beam of light either. It’s simply brain food.

That’s one of the most illogical comments I’ve ever had the displeasure of reading.

Firstly, you make the assumption that ‘no one is crazy enough to hook up a brain to a computer’. Says who, exactly?

Secondly, you state that ‘they would never let you find out about the ‘brain in a vat”. Once again, how on earth do you know? That’s just a wild guess!

Thirdly, your thoughts are real, for they are being thought. But the stars? Saying you ‘know they are real’ has no rational reasoning behind it. Have you ever been sat down, and thought someone was standing behind you when they weren’t? Or carried on talking to a friend who had stopped a few yards back to do up their shoelaces? In these scenarios, you ‘know’ there is someone next to you – your senses deceive you. Why couldn’t the same occur in every single aspect of life?

As for ‘knowing’ that God exists, I am yet to hear a reason for doing so that does not, somewhere along the line, include a logical fallacy. Please, give me one?

Oh and finally, ‘don’t let yourself be brainwashed….you are too smart for that’. Are you actually a complete moron? It’s a thought experiment. It is actually suggesting that this is the case, only showing you that you don’t actually know if it is or not! Are you, by chance,desperately worried for the infinite number of innocent monkeys, forced into an eternity of typewriting?

These are crazy! Haven't heard but one of them!

"Descartes accounted for this problem with his classic maxim “cogito ergo sum” (“I think therefore I am”)."

You misunderstand Descartes' meaning. He posed that because you couldn't be sure that you are just a brain in a vat, this implicitly states that your mind must exist, because only that which exists can be deceived. "I think therefore I am" is therefore the ONLY statement you can make with 100% certainty. He was not "accounting for [a] problem"

Should read: "He posed that because you couldn’t be sure that you aren't just a brain in a vat"

In fact, he accounts for the demon problem by appealing to God’s existence and that He could never be a deceiver or allow us to be deceived in such a way. The person who wrote this shouldn’t just guess what Descartes said based on what he’s famous for saying, that’s sloppy stuff.

Also, wasn’t Gettier’s thought experiment called the “Sheep-Shaped Rock”? This could just be another philosopher’s version of the experiment however…

#10 – Sure, you're responsible for the death of 1 person, but you are also responsible for saving the lives of five others. And I guess it depends on who the people are. If that person on the other track was your BFF, then you would not pull the lever.

Or, if the lever acts as a dimmer and not just an on-off switch, you can switch it to the halfway position which would cause the train to derail and kill nobody.

#9 – If the farmer openly stated that he knew the cow was in the field, then yes, he technically knew where his cow was – in the field. He just didn't know where in the field.

#8 – Call the bomb squad, evacuate everyone, and throw the terrorist right next to the bomb.

#6 – Evolution is the answer to all your problems.

#5 – I'm pretty sure this one has to do with covalent bonds between atoms. If there exist no covalent bonds between the rope atoms and feather atoms, or the rope atoms and hammer atoms; then the entire hammer+feather+rope cannot be regarded as one system, it must be regarded as three.

#2 – Keyword: quantum mechanics , not real-life stuff. In real life, you can only say "you just don't know", because a partially-dead cat would be like a zombie.

#1 – Kind of like "we don't know if the universe is going backwards in time [shrinking,] not expanding" because if the universe and everything within it was indeed going backwards, our minds would be thinking backwards. Two negatives cancel out, so we'd perceive time as going forwards.

You changed the variables on some of them and then your other answers didn’t really make a whole lot of sense.

#10 the derailing train would kill the driver or whoever was in the train (not like whoever was in charge was even driving the train anyway though…)

You are totally missing the point of most of those you have commented on.

For #10, you are complicating an essentially simple moral question, and I really hope the bit about the lever acting as a dimmer was a joke.

For #8, I hope that too is meant to be a joke.

#6, what are you on about?

#5, utterly missing the point again, it’s not a matter of definition. Or, if you are actually suggesting that by fusing covalently they would suddenly fall faster, you don’t actually understand the theory of gravity…..

If some of those were actually a joke, sorry for missing it, but if not, then dear God read something on just one of these, because that was depressing to read.

If the person on the other track is a House of Representatives Rightwing Teanut, pull the lever, Quick! Pull it even if there’s no one on the other track ;’)

Failed Logic, Mooney.

Number 8 (The Ticking Time Bomb) – look up the movie Unthinkable – http://www.imdb.com/title/tt0914863/

Number 8 (The Ticking Time Bomb) poses the moral question – Is it right to torture one person in order to get information to save many more? BLOODY RIGHT IT IS! I have heard the PC brigade bleat on about Guantanamo Bay and human rights abuses going on there. So what? If it provides any information that stops another atrocity then it is right. "But some of these people may be innocent" some of you might say. My parents told me if i played with matches I might get burnt! Every one of these "innocent people" I have read about have been questionable to say the least. One of these poor, innocent chaps, released to Britain, had used a false name and passport to leave the country before being captured. Whilst I am on my soapbox, and as a British person, why are these detainees always referred to as British citizens (where i live anyway), when in fact they have been born elsewhere (usually in the middle east somewhere).

Torture the one to save the many! TOO RIGHT! If the person being tortured was a direct threat to the wooly hatted, vegetarian, petrol hating, hippy who is ranting about human rights then the hippy wouldn't be a shouting so loudly.

I wonder if you would still hold this view if the person being tortured was your mother, father siblings, children or spouse/girlfriend or even YOU?

Kleanthis01 you make the argument that our outlook is changed if our loved ones are the ones in question,but this argument works both ways. What if it was your family/friends/significant other who was trapped in said city?

Haha you sound like the byproduct of a brainwashed fascist authority paradigm… Meaning, you’re completely controlled by fear and willing to dispense of inalienable human rights for safety. This is the greatest illusionary sham ever created. Every communist and totalitarian system stems from the disposition that it knows what’s in your best interest. So long as you let fear control you, your life’s efforts will remain futile.

Except the CIA and State Dept Created both Iran and Al Quada in their current form. Maybe their leaders should be sent to Guantanamo.

I like the Brain In A Vat. Sure, The Matrix ripped off this idea, but it's still a good one. How do we know we're not just some evil entity's toy, a brain in a vat?

The only thing you can be sure of is that we exist. Yes, life may be just an impression, a lucid dream. But in order for you to be deceited, you have to exist. So life will always be true, even if it is a lie.

But you could have only just started existing your memories lies and time is infinetly divisible so your life could be infinetly small

but an infinitely small life, since time is infinitely divisible, is also infinitely large. As long as life exists as a duration, not just a single moment in time, than between its beginning and end there are an infinite number of moments

“since time is infinitely divisible,” Except, of course, that time is NOT infinitely divisible. It occurs in discrete units, just like all other fundamental phenomena of the universe. and the smallest possible measure is one Planck Time (Google it). One Planck Time is 0.000000000000000000000000000000000000000000054 seconds. Anything shorter than that is meaningless, in physics. So there are a finite number of moments between the “beginning” and the “end” of any event, including life. Your days are numbered, and so are your Planck Times. 🙂

You can’t hold that life is illusory then try to use scientific knowledge gained through that illusion. For all you know, Planck’s time unit is a complete fabrication. The only types of thought that hold weight in an illusory world are thoughts which do not depend upon that world for evidence (such as formal logic or abstract thought). Since Planck’s time unit is based upon the travel of light in a vacuum it is therefore dependent upon evidence in this possibly illusory world. Thus, it is inadmissible as evidence to disprove that time is infinitely divisible.

The “brain in a vat” is easily debunked, some of the more interesting brain teasers should have been ranked higher, as they have far more moral, scientific, or philosophical conundrums than the “brain in a vat” theory. Let’s say my brain is a simulation, furthermore, let us say that it has been since birth… take 10 children, ask them to identify a shape in a particular cloud, chances are you will receive 10 different variations in a single cloud. Now let’s go back to just me and assume I am the only one affected by the “vat,” that a particular simulation would already determine that I would think of this idea… the “program” could never account for the answers I would get from 10 random children seeing 10 very different shapes. Yes we age and it can become increasingly easy for us to believe that the world may already be run by “Skynet,” but as long as we have the abilithy to find art and random beauty in nature, I find it very hard to believe that a simulation could ever “predict” how we would perceive a natural phenomenon as witnessed not only by our own “computer generated psyche,” but how the same phenomenon would be witnessed completely different by the same “vat” mentality. Witness the world you live in through the eyes of a child and rest assured, there is no mechanical program that could ever judge how we perceive our world through the eyes of a child.

I think you are not taking into account that the same way the evil scientist is making trees appear for you to interact with he could very easily make ten kids and whatever the results of that experiment to be. Thus not proving anything but that you are now further convinced the matrix is real in your vat.

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What is a Thought Experiment, Anyhow?

Our philosophical science correspondent massimo pigliucci asks..

Philosophers are often accused of engaging in armchair speculation, as far removed from reality as possible, inside the proverbial ivory tower. The quintessential example of this practice is the thought experiment, which many scientists sneer at precisely because it doesn’t require one to get one’s hands dirty. And yet scientists have often engaged in thought experiments, some of which have marked major advances in our understanding of the world.

Just consider the famous example of Galileo’s thought experiment demonstrating (rather counterintuitively) that two objects of different weight must fall at the same speed. (Contrary to popular belief, Galileo never actually climbed the leaning tower of Pisa to do this experiment – he didn’t need to.) Galileo knew Aristotle would have predicted that a heavy body (H) would fall faster than a lighter one (L). But, the Italian scientist reckoned, suppose we connect the two bodies by a string, thereby making the compound object H+L. Following Aristotelian physics, one would predict that H+L should fall faster than H by itself because of the compound weight: therefore H+L > H. However, it’s also possible to use the same logic to claim that the compound body should fall at a slower pace than H because of the drag created by L, so that H+L < H. But this yields a contradiction, which means – by reductio ad absurdum – that really H = L = H+L. Neil Armstrong, the first human to set foot on the moon, dramatically showed the whole world that Galileo was right when he let go of a hammer and a feather in the absence of atmospheric friction while standing on our satellite, and, sure enough, they hit the Moon’s surface at the same time. Such is the predictive power of thought experiments!

Then again, some thought experiments can lead to misleading conclusions – as in the case of Lucretius’ ‘demonstration’ that space must be infinite. In the De Rerum Natura he reasoned that one might walk up to the boundary of the universe and throw a spear (there were no weapons of mass destruction in Roman times). If the spear flies through the alleged boundary, then it is no boundary at all, and we conclude that the universe is infinite. But what if the spear bounces back? Then there is a boundary; but by definition if there is a boundary then there must be something beyond it – which again leads to the conclusion that the universe is infinite. The problem with this is that today’s mathematics and physics show us how a universe can be both finite and unbounded (it’s like a toroid, ie a donut).

These and other thought experiments are discussed in an elegant paper by James Robert Brown, who goes on to ask what sort of beast, exactly, is a thought experiment? Brown contrasts two theories, his own – according to which thought experiments are a perception of a kind of Platonic reality – and that of John Norton, who thinks that thought experiments are actually a form of argument. I will not take sides, partly because I’m not sure that the two views are actually incompatible with each other; but it is instructive to examine both views in an attempt to wrap our minds around what exactly our minds are doing in these cases.

Let’s start with Brown’s position, which he claims to derive from two starting points: a Platonic view of mathematics, and a realist view of the laws of nature. Platonism in mathematics is the idea that certain entities – like numbers, and relations among numbers – are ‘out there’ independently of human minds. Numbers in some sense ‘exist’ regardless of the presence or ability of a mind to conceive them. Accordingly, mathematicians are akin to scientists: they do not invent things, they discover them. Similarly, following Brown, natural laws like say the law of gravity described by Galileo and later formalized by Newton are ‘real’ in the sense that they exist, again, independently of human observers. (If all this talk of human-independent phenomena has you wondering about the sound of a tree falling when there is nobody there to hear it, stop right now:the analogy is only superficial.)

What does all of this have to do with thought experiments? According to Brown, thought experiments are genuine examples of how the human mind can ‘perceive’ laws of nature by simply thinking about reality. This was the goal of rationalist (as opposed to empiricist) philosophers since Plato: to discover things about the world by sheer intellectual power, independently of empirical evidence, which was seen as unreliable.

In contrast, Norton has a very different take on the whole matter. For him, thought experiments are a form of argument, starting from empirically derived premises and reaching conclusions by deductive logic. In essence, Norton thinks of experiments such as Galileo’s as ‘if-then’ forms of reasoning, which yield valid results when the premises are empirically justified and the reasoning is logically correct.

There is something very appealing about both Brown’s and Norton’s notions. On the one hand, with Brown there is a sense in which thought experiments are formalizations of an intuitive grasp of an objective reality. Yet this reality – if it exists – is surely of the Platonic, abstract type, not of the more mundane “this table is real” kind. On the other hand, it is hard to resist Norton’s construction of thought experiments as arguments based on a proper mix of induction (the empirical premises) and deduction.

Whatever thought experiments really are, they have been instrumental in the progress of both philosophy and science, and they constitute a powerful tool for understanding the world. True, sometimes they don’t work, but the same can be said for physical experiments. In both cases it’s all in the soundness of the premises and the rigor with which the conclusions are derived.

© Dr Massimo Pigliucci 2006

Massimo Pigliucci has a PhD in evolutionary biology and one in philosophy. He is a professor at SUNY-Stony Brook on Long Island, New York. His ramblings can be found at www.rationallyspeaking.org .

Further reading: • Brown, J.R. 2004. ‘Peeking into Plato’s heaven.’ Philosophy of Science 71.

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Einstein’s Relativity Explained in 4 Simple Steps

The revolutionary physicist used his imagination rather than fancy math to come up with his most famous and elegant equation.

Albert Einstein’s theory of relativity is famous for predicting some really weird but true phenomena, like astronauts aging slower than people on Earth and solid objects changing their shapes at high speeds.

But the thing is, if you pick up a copy of Einstein’s original paper on relativity from 1905, it’s a straightforward read. His text is plain and clear, and his equations are mostly just algebra—nothing that would bother a typical high-schooler.

That’s because fancy math was never the point for Einstein. He liked to think visually, coming up with experiments in his mind’s eye and working them around in his head until he could see the ideas and physical principles with crystalline clarity. (Read “ 10 Things You (Probably) Didn’t Know About Einstein. ”)

To bring his process to life, National Geographic created an interactive version of one of Einstein’s most famous thought experiments : a parable about lightning strikes as seen from a moving train that shows how two observers can understand space and time in very different ways.

Here’s how Einstein got started on his thought experiments when he was just 16, and how it eventually led him to the most revolutionary equation in modern physics.

1895: Running Beside a Light Beam

By this point, Einstein’s ill-disguised contempt for his native Germany’s rigid, authoritarian educational methods had already gotten him kicked out of the equivalent of high school, so he moved to Zurich in hopes of attending the Swiss Federal Institute of Technology (ETH). (Also see “ Why the FBI Kept a 1,400-Page File on Einstein .”)

First, though, Einstein decided to put in a year of preparation at a school in the nearby town of Aarau—a place that stressed avant garde methods like independent thought and visualization of concepts. In that happy environment, he soon he found himself wondering what it would be like to run alongside a light beam.

Einstein had already learned in physics class what a light beam was: a set of oscillating electric and magnetic fields rippling along at 186,000 miles a second, the measured speed of light. If he were to run alongside it at just that speed, Einstein reasoned, he ought to be able to look over and see a set of oscillating electric and magnetic fields hanging right next to him, seemingly stationary in space.

Yet that was impossible. For starters, such stationary fields would violate Maxwell’s equations, the mathematical laws that codified everything physicists at the time knew about electricity, magnetism, and light. The laws were (and are) quite strict: Any ripples in the fields have to move at the speed of light and cannot stand still—no exceptions.

Worse, stationary fields wouldn’t jibe with the principle of relativity, a notion that physicists had embraced since the time of Galileo and Newton in the 17th century. Basically, relativity said that the laws of physics couldn’t depend on how fast you were moving; all you could measure was the velocity of one object relative to another.

But when Einstein applied this principle to his thought experiment, it produced a contradiction: Relativity dictated that anything he could see while running beside a light beam, including the stationary fields, should also be something Earthbound physicists could create in the lab. But nothing like that had ever been observed.

This problem would bug Einstein for another 10 years, all the way through his university work at ETH and his move to the Swiss capital city of Bern, where he became an examiner in the Swiss patent office. That’s where he resolved to crack the paradox once and for all.

1904: Measuring Light From a Moving Train

It wasn’t easy. Einstein tried every solution he could think of, and nothing worked. Almost out of desperation, he began to consider a notion that was simple but radical. Maybe Maxwell’s equations worked for everybody, he thought, but the speed of light was always constant.

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When you saw a light beam zip past, in other words, it wouldn’t matter whether its source was moving toward you, away from you, or off to the side, nor would it matter how fast the source was going. You would always measure that beam’s velocity to be 186,000 miles a second. Among other things, that meant Einstein would never see the stationary, oscillating fields, because he could never catch the light beam.

This was the only way Einstein could see to reconcile Maxwell’s equations with the principle of relativity. At first, though, this solution seemed to have its own fatal flaw. Einstein later explained the problem with another thought experiment: Imagine firing a light beam along a railroad embankment just as a train roars by in the same direction at, say, 2,000 miles a second.

Someone standing on the embankment would measure the light beam’s speed to be the standard number, 186,000 miles a second. But someone on the train would see it moving past at only 184,000 miles a second. If the speed of light was not constant, Maxwell’s equations would somehow have to look different inside the railway carriage, Einstein concluded, and the principle of relativity would be violated.

This apparent contradiction left Einstein spinning his wheels for almost a year. But then, on a beautiful morning in May 1905, he was walking to work with his best friend Michele Besso, an engineer he had known since their student days in Zurich. The two men were talking with about Einstein’s dilemma, as they often did. And suddenly, Einstein saw the solution. He worked on it overnight, and when they met the next morning, Einstein told Besso, “Thank you. I’ve completely solved the problem.”

May 1905: Lightning Strikes a Moving Train

Einstein’s revelation was that observers in relative motion experience time differently: it’s perfectly possible for two events to happen simultaneously from the perspective of one observer, yet happen at different times from the perspective of the other. And both observers would be right.

Einstein later illustrated this point with another thought experiment. Imagine that you once again have an observer standing on a railway embankment as a train goes roaring by. But this time, each end of the train is struck by a bolt of lightning just as the train’s midpoint is passing. Because the lightning strikes are the same distance from the observer, their light reaches his eye at the same instant. So he correctly says that they happened simultaneously.

Meanwhile, another observer on the train is sitting at its exact midpoint. From her perspective, the light from the two strikes also has to travel equal distances, and she will likewise measure the speed of light to be the same in either direction. But because the train is moving, the light coming from the lightning in the rear has to travel farther to catch up, so it reaches her a few instants later than the light coming from the front. Since the light pulses arrived at different times, she can only conclude the strikes were not simultaneous—that the one in front actually happened first.

In short, Einstein realized, simultaneity is what’s relative. Once you accept that, all the strange effects we now associate with relativity are a matter of simple algebra.

Einstein dashed off his ideas in a fever pitch and sent his paper in for publication just a few weeks later. He gave it a title—“ On the Electrodynamics of Moving Bodies ”—that spoke to his struggle to reconcile Maxwell’s equations with the principle of relativity. And he concluded it with a thank you to Besso (“I am indebted to him for several valuable suggestions”) that guaranteed his friend a touch of immortality.

September 1905: Mass and Energy

That first paper wasn’t the end of it, though. Einstein kept obsessing on relativity all through the summer of 1905, and in September he sent in a second paper as a kind of afterthought.

It was based on yet another thought experiment. Imagine an object that’s sitting at rest, he said. And now imagine that it spontaneously emits two identical pulses of light in opposite directions. The object will stay put, but because each pulse carries off a certain amount of energy, the object’s energy content will decrease.

Now, said Einstein, what would this process look like to a moving observer? From her perspective, the object would just keep moving in a straight line while the two pulses flew off. But even though the two pulses’ speed would still be the same—the speed of light—their energies would be different: The pulse moving forward along the direction of motion would now have a higher energy than the one moving backward.

With a little more algebra, Einstein showed that for all this to be consistent, the object not only had to lose energy when the light pulses departed, it had to lose a bit of mass, as well. Or, to put it another way, mass and energy are interchangeable.

Einstein wrote down an equation that relates the two. Using today’s notation, which abbreviates the speed of light using the letter c , he produced easily the most famous equation ever written: E = mc 2 .

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The Power of Thought Experiments

What thought experiments can teach us about ourselves..

Posted June 8, 2022 | Reviewed by Lybi Ma

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Part I of II

Thought experiments are a way to craft free experiences in our mind, designed to answer a question or validate a hypothesis we have about human nature without imposing any demands on us for physical resources, time, or risk-taking .

The greatest scientist of modern time, Einstein, arrived at many of his breakthroughs via thought experiments. At the age of 16, he asked himself, “What if you could ride alongside a beam of light? What would that be like?” It seemed to him that you would perceive a light wave to be stationary since you were traveling at the same speed. He kept deepening his understanding of this concept for the next 10 years until it led to his famous theory of relativity. What’s remarkable is that the experimental proof of some of the propositions of his theory required the building of a particle accelerator that was several miles long and cost billions of dollars. But the actual breakthrough came from a thought experiment in Einstein’s mind. It didn’t even require a pen and napkin.

Just like Einstein used thought experiments to make discoveries about nature, we can use thought experiments to make discoveries about human nature–and about our true nature. Start by formulating a hypothesis, a conjecture about your true nature or human nature that you wish to prove. Design a mental experience, a situation in which you place yourself where this conjecture will be tested. Note the thoughts, feelings, and behaviors that flow freely from the core of your being as you visualize yourself in this situation. Then ask yourself, what understanding does this visualization give me about what values and behaviors are most authentic to me?

Discovering Your True Self

Many people strongly identify with their personality . If you see yourself as an introvert , for instance, you may believe it is natural for you to be reserved in group meetings and get-togethers, not wanting to attract attention to yourself. But what if your true self was something beyond your personality?

Imagine a moment where you are walking in a bustling city with your 10-year-old son or nephew. He breaks free from your grasp and turns to run across the street. There’s traffic all around.

Will you in that moment say to yourself, “I can’t raise my voice! I am an introvert. I don’t feel comfortable shouting in public and attracting all kinds of attention.” Or will you shout at the top of your voice? “Jamie! Stop!” Would you feel more true in that moment by acting like the introvert you see yourself to be, or by acting just the opposite?

A simple thought experiment ends up revealing a powerful truth: We feel more true to ourselves when our behavior is motivated by what we deeply care about, even if this behavior is the opposite of our personality. When it comes to being authentic, purpose triumphs over personality.

In years past, when I met people who were highly successful executives in a certain industry, or highly successful academics, I would do a thought experiment, “What if this is the career path I pursued, and this is where I ended up. Would I feel deeply fulfilled?” Most of the time, the answer I received from within was, “No.” While I admired them and looked up at them, and while others might seek to emulate them, this thought experiment showed me that their path was not going to be my path; my true self was seeking something else, even if I did not know what it was at that time.

The people I was most drawn to visualizing as my end-state were typically either creative people–movie directors, authors–or spiritual truth-seekers. A thought experiment of visualizing who I would need to be in the future for me to feel fulfilled helped me not get entrapped in career paths that weren’t true to me.

Developing Empathy

In studying Mother Teresa’s life, I initially found myself deeply inspired by her commitment to serving the poorest among the poor. But I also learned that she had consorted at times with people of disrepute, such as a banker convicted of a crime and a dictator. I wondered why she was not more discriminating in whom she engaged with for her cause. Then I constructed a thought experiment.

I visualized that I was traveling in a remote country with a loved one. Our car meets with an accident, and my loved one is seriously injured. Her life is in danger as she bleeds by the side of the road. There is no help in sight. One car passes by on the road, and despite our entreaties, it does not stop. Nor do the next 10. The twelfth car I try to wave down stops to help us. I am overwhelmed with relief. Then I suddenly notice that the driver of the vehicle is a corrupt dictator I have long been critical of. What would I do in that moment?

Would I ask him to leave, because I have judged him to be a bad person? Or would I jump at his offer to help, thank him for doing so, and focus on getting my loved one to the nearest hospital? I realized that this was probably what Mother Teresa had experienced. Her loved ones were the street people that most of the world had abandoned like those 11 cars that I had imagined passing my dying loved one. Whoever offered help, she received it with gratitude and without judgment. Her business was not to investigate their lives or support their agenda; it was to attract love, care, and support for the people on the sidewalks that most of us had chosen to pass by. This thought experiment taught me the importance of cultivating empathy. We cannot judge someone’s character based on a behavior we see without first trying to see the world through their eyes. We need to understand their motivations and context before critiquing their behavior, and thought experiments can help us do so.

Hill, P. L., Cheung, F., Kubel, A., & Burrow, A. L. Life engagement is associated with higher GDP among societies. (2019). Journal of Research in Personality, 78, 210-214.

Hitendra Wadhwa, Ph.D. , is Professor of Practice at Columbia Business School, the Founder of the Mentora Institute, and the author of Inner Mastery, Outer Impact.

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Thought Experiment: How Einstein Solved Difficult Problems

Thought experiments are a classic tool used by many great thinkers. They enable us to explore impossible situations and predict their implications and outcomes. Mastering thought experiments can help you confront difficult questions and anticipate (and prevent) problems .

The purpose of a thought experiment is to encourage speculation, logical thinking and to change paradigms. Thought experiments push us outside our comfort zone by forcing us to confront questions we cannot answer with ease. They demonstrate gaps in our knowledge and help us recognize the limits of what can be known.

“All truly wise thoughts have been thought already thousands of times; but to make them truly ours, we must think them over again honestly, until they take root in our personal experience.” Johann Wolfgang von Goethe

Famous thought experiments

Thought experiments have a rich and complex history, stretching back to the ancient Greeks and Romans.

An early example of a thought experiment is Zeno’s narrative of Achilles and the tortoise, dating to around 430 BC. Zeno’s thought experiments aimed to deduce first principles through the elimination of untrue concepts.

In one instance, the Greek philosopher used it to ‘prove’ motion is an illusion. Known as the dichotomy paradox, it involves Achilles racing a tortoise. Out of generosity, Achilles gives the tortoise a 100m head start. Once Achilles begins running, he soon catches up on the head start. However, by that point, the tortoise has moved another 10m. By the time he catches up again, the tortoise will have moved further. Zeno claimed Achilles could never win the race as the distance between the pair would constantly increase.

Descartes conducted a thought experiment, doubting the existence of everything he could until there was nothing left he could doubt.  Descartes could doubt everything except for the fact that he could doubt. His process left us with the philosophical thought experiment of ‘a brain in a vat’.

In the 17th century, Galileo used thought experiments to affirm his theories. One example is his thought experiment involving two balls (one heavy, one light) which are dropped from the Leaning Tower of Pisa. Prior philosophers had theorized the heavy ball would land first. Galileo claimed this was untrue, as mass does not influence acceleration.

According to Galileo’s early biography (written in 1654), he dropped two objects from the Leaning Tower of Pisa to disprove the gravitational mass relation hypothesis. Both landed at the same time, ushering in a new understanding of gravity. It is unknown if Galileo performed the experiment itself, so it is regarded as a thought experiment, not a physical one.

In 1814, Pierre Laplace explored determinism through ‘Laplace’s demon.’ This is a theoretical ‘demon’ which has an acute awareness of the location and movement of every single particle in existence. Would Laplace’s demon know the future? If the answer is yes, the universe must be linear and deterministic. If no, the universe is nonlinear and free will exists.

In 1897, the German term ‘Gedankenexperiment’ passed into English and a cohesive picture of how thought experiments are used worldwide began to form.

Albert Einstein used thought experiments for some of his most important discoveries. The most famous of his thought experiments was on a beam of light, which was made into a brilliant children’s book . What would happen if you could catch up to a beam of light as it moved he asked himself? The answers led him down a different path toward time, which led to the special theory of relativity.

Natural tendencies

In On Thought Experiments , 19th-century Philosopher and physicist Ernst Mach writes that curiosity is an inherent human quality. Babies test the world around them and learn the principle of cause and effect. With time, our exploration of the world becomes more and more in depth. We reach a point where we can no longer experiment through our hands alone. At that point, we move into the realm of thought experiments.

Thought experiments are a structured manifestation of our natural curiosity about the world.

Mach writes:

Our own ideas are more easily and readily at our disposal than physical facts. We experiment with thought, so as to say, at little expense. It shouldn’t surprise us that, oftentime, the thought experiment precedes the physical experiment and prepares the way for it… A thought experiment is also a necessary precondition for a physical experiment. Every inventor and every experimenter must have in his mind the detailed order before he actualizes it.

Mach compares thought experiments to the plans and images we form in our minds before commencing an endeavor. We all do this — rehearsing a conversation before having it, planning a piece of work before starting it, figuring out every detail of a meal before cooking it. Mach views this as an integral part of our ability to engage in complex tasks and to innovate creatively.

According to Mach, the results of some thought experiments can be so certain that it is unnecessary to physically perform it. Regardless of the accuracy of the result, the desired purpose has been achieved.

“It can be seen that the basic method of the thought experiment is just like that of a physical experiment, namely, the method of variation. By varying the circumstances (continuously, if possible) the range of validity of an idea (expectation) related to these circumstances is increased.” Ernst Mach

Thought experiments in philosophy

Thoughts experiments have been an integral part of philosophy since ancient times. This is in part due to philosophical hypotheses often being subjective and impossible to prove through empirical evidence.

Philosophers use thought experiments to convey theories in an accessible manner. With the aim of illustrating a particular concept (such as free will or mortality), philosophers explore imagined scenarios. The goal is not to uncover a ‘correct’ answer, but to spark new ideas.

An early example of a philosophical thought experiment is Plato’s Allegory of the Cave , which centers around a dialogue between Socrates and Glaucon (Plato’s brother.)

A group of people are born and live within a dark cave. Having spent their entire lives seeing nothing but shadows on the wall, they lack a conception of the world outside. Knowing nothing different, they do not even wish to leave the cave. At some point, they are led outside and see a world consisting of much more than shadows.

Plato used this thought experiment to illustrate the incomplete view of reality most of us have. Only by learning philosophy, Plato claimed, can we see more than shadows.

Upon leaving the cave, the people realize the outside world is far more interesting and fulfilling. If a solitary person left, they would want others to do the same. However, if they return to the cave, their old life will seem unsatisfactory. This discomfort would become misplaced, leading them to resent the outside world. Plato used this to convey his (almost compulsively) deep appreciation for the power of educating ourselves. To take up the mantle of your own education and begin seeking to understand the world is the first step on the way out of the cave.

Moving from caves to insects, here’s a thought experiment from 20th-century philosopher Ludwig Wittgenstein.

Imagine a world where each person has a beetle in a box. In this world, the only time anyone can see a beetle is when they look in their own box. As a consequence, the conception of a beetle each individual has is based on their own. It could be that everyone has something different, or that the boxes are empty, or even that the contents are amorphous.

Wittgenstein uses the ‘Beetle in a Box’ thought experiment to convey his work on the subjective nature of pain. We can each only know what pain is to us, and we cannot feel another person’s agony. If people in the hypothetical world were to have a discussion on the topic of beetles, each would only be able to share their individual perspective. The conversation would have little purpose because each person can only convey what they see as a beetle. In the same way, it is useless for us to describe our pain using analogies (‘it feels like a red hot poker is stabbing me in the back’) or scales (‘the pain is 7/10.’)

Thought experiments in science

Although empirical evidence is usually necessary for science, thought experiments may be used to develop a hypothesis or to prepare for experimentation. Some hypotheses cannot be tested (e.g, string theory) – at least, not given our current capabilities.Theoretical scientists may turn to thought experiments to develop a provisional answer, often informed by Occam’s razor .

In a paper entitled Thought Experimentation of Presocratic Philosophy , Nicholas Rescher writes:

In natural science, thought experiments are common. Think, for example, of Einstein’s pondering the question of what the world would look like if one were to travel along a ray of light. Think too of physicists’ assumption of a frictionlessly rolling body or the economists’ assumption of a perfectly efficient market in the interests of establishing the laws of descent or the principles of exchange, respectively.

In a paper entitled Thought Experiments in Scientific Reasoning , Andrew D. Irvine explains that thought experiments are a key part of science. They are in the same realm as physical experiments. Thought experiments require all assumptions to be supported by empirical evidence. The context must be believable, and it must provide useful answers to complex questions. A thought experiment must have the potential to be falsified .

Irvine writes:

Just as a physical experiment often has repercussions for its background theory in terms of confirmation, falsification or the like, so too will a thought experiment. Of course, the parallel is not exact; thought experiments…no do not include actual interventions within the physical environment.

In Do All Rational Folks Think As We Do? Barbara D. Massey writes:

Often critique of thought experiments demands the fleshing out or concretizing of descriptions so that what would happen in a given situation becomes less a matter of guesswork or pontification. In thought experiments we tend to elaborate descriptions with the latest scientific models in mind…The thought experiment seems to be a close relative of the scientist’s laboratory experiment with the vital difference that observations may be made from perspectives which are in reality impossible, for example, from the perspective of moving at the speed of light…The thought experiment seems to discover facts about how things work within the laboratory of the mind.

“We live not only in a world of thoughts, but also in a world of things. Words without experience are meaningless.” Vladimir Nabokov

Biologists use thought experiments, often of the counterfactual variety. In particular, evolutionary biologists question why organisms exist as they do today. For example, why are sheep not green? As surreal as the question is, it is a valid one. A green sheep would be better camouflaged from predators. Another thought experiment involves asking: why don’t organisms (aside from certain bacteria) have wheels? Again, the question is surreal but is still a serious one. We know from our vehicles that wheels are more efficient for moving at speed than legs, so why do they not naturally exist beyond the microscopic level?

Psychology and Ethics — The Trolley Problem

Picture the scene. You are a lone passerby in a street where a tram is running along a track. The driver has lost control of it. If the tram continues along its current path, the five passengers will die in the ensuing crash. You notice a switch which would allow the tram to move to a different track, where a man is standing. The collision would kill him but would save the five passengers. Do you press the switch?

The Trolley Problem was first suggested by philosopher Phillipa Foot, and further considered extensively by philosopher Judith Jarvis Thompson. Psychologists and ethicists have also discussed the trolley problem at length, often using it in research. It raises many questions, such as:

• Is a casual observer required to intervene?
• Is there a measurable value to human life? I.e. is one life less valuable than five?
• How would the situation differ if the observer were required to actively push a man onto the tracks rather than pressing the switch?
• What if the man being pushed were a ‘villain’? Or a loved one of the observer? How would this change the ethical implications?
• Can an observer make this choice without the consent of the people involved?

Research has shown most people are far more willing to press a switch than to push someone onto the tracks. This changes if the man is a ‘villain’- people are then far more willing to push him. Likewise, they are reluctant if the person being pushed is a loved one.

The trolley problem is theoretical, but it does have real world implications. As we move towards autonomous vehicles, there may be real life instances of similar situations. Vehicles may be required to make utilitarian choices – such as swerving into a ditch and killing the driver to avoid a group of children.

The Infinite Monkey Theorem and Mathematics

“Ford!” he said, “there’s an infinite number of monkeys outside who want to talk to us about this script for Hamlet they’ve worked out.” Douglas Adams, The Hitchhiker’s Guide to the Galaxy

In Fooled By Randomness , Nassim Taleb writes:

If one puts an infinite number of monkeys in front of (strongly built) typewriters, and lets them clap away, there is a certainty that one of them will come out with an exact version of the ‘Iliad.’ Upon examination, this may be less interesting a concept than it appears at first: Such probability is ridiculously low. But let us carry the reasoning one step beyond. Now that we have found that hero among monkeys, would any reader invest his life’s savings on a bet that the monkey would write the ‘Odyssey’ next?

The infinite monkey theorem is intended to illustrate the idea that any issue can be solved through enough random input, in the manner a drunk person arriving home will eventually manage to fit their key in the lock even if they do it without much finesse. It also represents the nature of probability and the idea that any scenario is workable, given enough time and resources.

To learn more about thought experiments, and other mental models, check out our book series, The Great Mental Models .

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What is a thought experiment in behavioral science, what is a thought experiment.

A thought experiment is a hypothetical scenario used to understand the nature of things or to explore the potential consequences of a principle or theory. Thought experiments have been used since ancient times and play an essential role in philosophical, scientific, and ethical investigations. They allow for the testing of hypotheses, theories, or philosophical stances in a controlled and imaginary environment, free from real-world limitations or potential risks. Thought experiments often involve envisioning complex or simplified versions of reality to draw out unexpected implications or to challenge established perspectives.

Examples of Thought Experiments

Schrödinger’s cat.

Perhaps one of the most well-known thought experiments is Schrödinger’s Cat, proposed by physicist Erwin Schrödinger in 1935. The experiment involves a cat placed in a sealed box with a radioactive substance that might trigger the release of a lethal poison. According to quantum theory, the cat would be in a superposition state, both alive and dead, until observed. This paradoxical scenario challenges our understanding of quantum mechanics and the nature of reality itself.

The Trolley Problem

The Trolley Problem is a classic thought experiment in ethics and moral philosophy. In this experiment, a trolley is heading towards five people tied to the tracks. You have the power to divert the trolley onto a different track, where only one person is tied. The question is whether it’s morally acceptable to actively intervene, thereby killing one person to save five. This thought experiment provokes discussion on consequentialism, deontology, and the ethics of decision-making in life-or-death situations.

Galileo’s Leaning Tower of Pisa

Galileo’s thought experiment involved imagining dropping two spheres of different masses from the Leaning Tower of Pisa. According to Aristotelian physics, the heavier object should fall faster. However, Galileo concluded that they would hit the ground simultaneously, contradicting the prevailing theory of the time. While it’s disputed whether Galileo conducted the physical experiment, the thought experiment was pivotal in developing the laws of motion.

Significance of Thought Experiments

Thought experiments are significant tools in various fields, from physics to philosophy, ethics, and even in law and economics. They stimulate critical thinking, unveil hidden implications of theories, challenge established views, and can lead to new discoveries or philosophical insights. Thought experiments can simplify complex real-world problems and provide a controlled cognitive environment to explore them. They also allow for the exploration of hypothetical or counterfactual scenarios that might not be practically or ethically feasible to physically carry out.

Controversies and Criticisms of Thought Experiments

Despite their widespread use, thought experiments are not without criticism. Some argue that they are mere rhetorical devices, persuading rather than proving. Critics question their reliability, noting that different people might derive different, sometimes contradictory, conclusions from the same thought experiment. Some also contend that thought experiments lack empirical controls and can be prone to biases, making them unreliable compared to physical experiments. However, many acknowledge that, despite their limitations, thought experiments can provide valuable insights and stimulate innovative thinking.

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In This Article Expand or collapse the "in this article" section Thought Experiments

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Thought Experiments by James Robert Brown , Michael T. Stuart LAST REVIEWED: 29 July 2020 LAST MODIFIED: 29 July 2020 DOI: 10.1093/obo/9780195396577-0143

Thought experiments are performed in the imagination. We set up some situation, we observe what happens, then we try to draw appropriate conclusions. In this way, thought experiments resemble real experiments, except that they are experiments in the mind. The terms “thought experiment,” “imaginary experiment,” and “Gedankenexperiment” are used interchangeably. There is no consensus on a definition, but there is widespread agreement on which are standard examples. It is also widely agreed that they play a central role in a number of fields, especially physics and philosophy. There are several important questions about thought experiments that naturally arise, including what kinds of thought experiments there are, what roles they play, and how, if at all, they work. This last question has been the focus of much of the literature: How can we learn something new about the world just by thinking? Answers range from “We don’t really learn anything new” to “We have some sort of a priori insight into how nature works.” In between there are a great variety of rival alternative accounts. There is still no consensus; debate is wide open on almost every question pertaining to thought experiments.

There has always been some interest in the nature of thought experiments, but it is only in recent years that it has become a popular topic of philosophical interest. Arcangeli 2017 and Stuart, et al. 2018 provide recent overviews of the issues. Brown and Fehige 2019 offers a periodically updated survey of thought experiments and the literature on it. Otherwise, the early works from the current period may be the best place to start, since they provide lots of examples and have tended to set the agenda for subsequent discussion. Horowitz and Massey 1991 is one of the first works stimulating the current interest in thought experiments. Brown 2011 (originally published in 1991) is an early work with many examples. For German readers, Cohnitz 2006 and Kühne 2005 both offer extensive coverage of many topics. Häggqvist 1996 is a critical survey, with an emphasis on modal considerations. Rescher 2005 and Sorensen 1992 both cover a variety of issues and provide many examples.

Arcangeli, Margherita. “Thought Experiments in Model-Based Reasoning.” In Springer Handbook of Model-Based Science . Edited by Lorenzo Magnani and Tommaso Bertolotti, 463–495. Dordrecht, The Netherlands: Springer, 2017.

DOI: 10.1007/978-3-319-30526-4_21

An overview of the recent literature on thought experiments, with a focus on model-based reasoning.

Brown, James Robert. Laboratory of the Mind: Thought Experiments in the Natural Sciences . 2d ed. New York: Routledge, 2011.

DOI: 10.4324/9780203847794

An early work with several standard examples and a taxonomy classifying the different forms that thought experiments take. The author argues for a rationalistic, or Platonistic account of thought experiments, claiming that in some (but not all) we gain a priori access to the abstract realm of laws of nature. Originally published in 1991.

Brown, James Robert, and Yiftach Fehige. “Thought Experiments.” In The Stanford Encyclopedia of Philosophy . Edited by Edward N. Zalta. Stanford, CA: Stanford University, 2019.

A survey of the major issues with a comprehensive bibliography, periodically updated.

Cohnitz, Daniel. Gendankenexperimente in der Philosophie . Paderborn, Germany: Mentis, 2006.

Presents an argument for the usefulness of thought experiments in philosophy. Extensive discussion of different theories of modality to defend thought experiments in philosophy for different purposes, much like conceptual analysis.

Gendler, Tamar S. Thought Experiment: On the Powers and Limits of Imaginary Cases . Abingdon, UK, and New York: Routledge, 2000.

A revised version of Gendler’s PhD thesis, which discusses the role of imagination in thought experiments that use “exceptional cases” to generate new knowledge. Focuses on three case studies: Galileo’s falling bodies, Theseus’s Ship, and Parfit’s fission thought experiment concerning personal identity. Provides four separate and useful bibliographies.

Häggqvist, Sören. Thought Experiments in Philosophy . Stockholm: Almqvist & Wiksell, 1996.

A critical discussion of the early rival accounts of thought experiments. Especially concerned with the relation between thought experiments and modal notions (necessity and possibility).

Horowitz, T., and G. Massey, eds. Thought Experiments in Science and Philosophy . Proceedings of a conference held at the Center for Philosophy at the University of Pittsburgh, 18–20 April 1986. Savage, MD: Rowman & Littlefield, 1991.

Stems from a conference at the University of Pittsburgh in 1986 and contains several excellent and influential articles on a wide range of topics. It is currently out of print, but fortunately, a PDF of the whole book is available online .

Kühne, Ulrich. Die Methode des Gedankenexperiments . Frankfurt: Suhrkamp, 2005.

Comprehensive study of the history of inquiry into thought experiments from Kant to the Brown-Norton debate. Noteworthy are the chapters on Ørsted and Einstein. Argues that Ørsted’s notion of thought experiment is hopelessly confusing and that Einstein, contrary to widespread belief, did not approve of the method of thought experiments.

Rescher, Nicholas. What If? Thought Experimentation in Philosophy . New Brunswick, NJ: Transaction, 2005.

A general and less specialized discussion of thought experiments, includes several historically famous examples. Explores the distinctions between thought experiments and real experiments.

Sorensen, Roy. Thought Experiments . Oxford: Oxford University Press, 1992.

Very wide-ranging. Covers a great many topics in both philosophy and the sciences, and provides a great many examples and deep insights on many issues. One of the author’s central claims is that thought experiments are experiments that merely have not been performed. Develops a theory of the epistemic power of thought experiments in terms of Darwinian evolution.

Stuart, Michael T., Yiftach Fehige, and James R. Brown. “Thought Experiments: State of the Art.” In The Routledge Companion to Thought Experiments . Edited by Michael T. Stuart, Yiftach Fehige, and James R. Brown, 1–28. Abingdon, UK, and New York: Routledge, 2018.

Provides an overview of the literature with examples, and a brief history of the philosophy of thought experiments.

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Thought experiments – like Schrödinger’s cat and the trolley problem – are a way for inquirers to focus the power of the imagination. What makes a thought experiment different from fantasies and daydreams is that they aim to produce new knowledge, wisdom, understanding, illumination, or something like that. They typically also have a narrative structure, with a beginning, middle, and end. Usually there are several phases in a thought experiment: one in which we set up some imaginary scenario, another in which we “see” what happens in that scenario, and, finally, one in which we draw some conclusions. At this level of description, thought experiments are like laboratory experiments, except they are carried out in the imagination.

This entry will consider what thought experiments are, who performs them, how they have been investigated, what they aim to do, how they work, and how they connect to the possible.

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Similar notions (under different names) were in circulation before Ørsted. For example, we find some of these in the work of Georg Christoph Lichtenberg, Novalis, and Immanuel Kant (see Schildknecht 1990 ; Daiber 2001 ; Fehige and Stuart 2014 ).

Did all of these people really conduct thought experiments? As James McAllister ( 2018 ) argues, the term “thought experiment” includes the modern Western concept of scientific experiment, which arguably did not exist before Galileo. When it is legitimate to attribute a thought experiment to a historical figure? This is an open question.

Gendler’s definition takes elements from John D. Norton's earlier definition (see Norton 1991 , 129).

According to Plutarch, Theseus returned to Athens on a ship. This famous ship became a tourist attraction, and had its planks replaced, one by one, as they decayed. The question is, if all the parts are replaced with new ones, is this still Theseus’s ship? If not, at what point does it cease to be the same ship? This thought experiment has developed over time, and there are now many more elaborate versions.

Something like this distinction was first made by Hans Radder ( 1996 ) when discussing laboratory experiments. It was then applied to thought experiments by Sören Häggqvist ( 1996 ) and Tim De Mey ( 2003 ).

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Stuart, M.T. (2022). Thought Experiments. In: Glăveanu, V.P. (eds) The Palgrave Encyclopedia of the Possible. Palgrave Macmillan, Cham. https://doi.org/10.1007/978-3-030-90913-0_59

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