The Basic Idea
Have you ever been sitting around a campfire, when your friend proposes an outlandish, open-ended question? Perhaps they ask you something simple, like what you would do with a billion dollars, or what animal you would want to be if you could shapeshift. Sometimes, however, you might accidentally create a profound hypothetical question, which doesn’t appear to have an easy answer. If so, you may have stumbled upon a thought experiment.
Thought experiments are defined as the mental process of using hypotheticals to logically reason out a solution to a difficult question. As the name suggests, thought experiments often try to simulate the experimental process through imagination alone. We use thought experiments when actually performing said experiment would be ethically, physically, or financially impossible. Typically, thought experiments end up being circular and rhetorical, as they are designed to emphasize a point, rather than fully answer a question. Thought experiments are used across disciplines, but most often used in the realms of philosophy or theoretical sciences.1
As a way of thinking, it is difficult to trace back to the first use of a thought experiment. Written evidence of thought experiments began to appear in Ancient Greece with the Pre-Socratic philosophers, who used it as a conceptual framework for solving mathematical equations. One of the earliest examples is Greek philosopher Zeno’s paradox titled Achilles and the Tortoise. Proposed in 430 B.C, this thought experiment discusses Greek hero Achilles and a tortoise, who are competing in a race to the finish line. Being both speedy and generous, Achilles gives the tortoise a 100m head start. Zeno claims that once Achilles runs 100m and makes up for the head start, the small distance the slow tortoise has moved will keep it in the lead. By the time Achilles catches up again to where our speedy reptilian friend was, the tortoise will have moved even further. According to Zeno, Achilles would never win the race because the distance between the two would never fully close. While this isn’t true in reality, Zeno’s argument for this result cannot logically be disproven.2
Thought experiments famously made their way into the natural sciences in the form of Galileo’s gravity experiment with the Leaning Tower of Pisa. While often claimed to be a real experiment, this idea was simply a hypothetical proposed by Galilelo to explain how gravity works on objects of different weights. The thought experiment unfolded like this: if you dropped a heavy ball and a light ball off the Leaning Tower of Pisa, which one do you think would land first? Most early philosophers would say the heavy ball, but Galileo disagreed. He claimed that both balls would hit the ground at the same time because the degree of acceleration is unrelated to mass.3
While dozens of famous thought experiments existed prior, Austrian physicist Ernst Mach was the first to formalize the phrase “thought experiment” in 1883.4 Thus, all proceeding philosophical mental experiments were referred to as such. Since then, thought experiments have been crucial in easily describing complex phenomena, from Schodinger’s cat to Maxwell’s demon.
Thought experiments are common tools at every level of education. As highly effective instruments of communicating complex ideas for a generalized audience, thought experiments have been useful in democratizing academia and broadening the minds of the masses. From Parfit’s teleporter to the trolly problem, thought experiments have come to define our understanding of morality, humanity, and reality itself.
In an insightful philosophical piece, Mach claimed that thought experiments were born out of the inherent human characteristic of never-ending curiosity. Beginning in infancy, we go through our lives continuously learning more about the world around us. We grow to understand the cause-and-effects that exist in our society by constructing real-life experiments which uncover a new layer for us to explore. Eventually, we reach a point where our curiosity exceeds our ability to test something in real life, and this is when we unleash our imaginations to tackle thought experiments. According to Mach, thought experiments, in a way, are one of the most human things we can do.5
Not every experiment is a good thought experiment. Like any form of experimentation, there can be serious flaws built into thought experiments that ignore important pieces of contextual information to assure a manufactured solution. Of course, this is intentional: thought experiments are useful because they strip context out of the equation. Unfortunately, that lack of context can make them completely useless in addressing issues in reality.
We see this inadequacy in the realm of ethics quite a bit. A popular thought experiment is Peter Singer’s drowning experiment. In essence, the thought experiment questions if you are ethically required to save a drowning child in a lake. Saving the child would require you to wade in, make your clothes wet, and be late for work. Of course, practically everybody says that they would go in to save the child. The sacrifices are relatively minimal when compared to saving a human life. Singer counters this claim, by stating that we don’t make small sacrifices every day to save others.6 For example, our daily lifestyles can significantly contribute to escalating climate change, which could cause millions of deaths in the near future. While giving up some of our daily luxuries to help against the climate change effort, we often don’t maintain these habits. If we are obligated to save the child, we should be obligated to save everybody else that we can through drastic lifestyle changes.
Arguably, thought experiments like this one are inherently interesting. They give our imaginative, problem-solving brains plenty of material to chew on. Unfortunately, this is not how we deal with issues of mass ethics in reality. Typically, we design policies that don’t require us to take on so much individual responsibility. To tackle climate change, we build better renewable technologies, impose carbon taxes on large polluters, and wield the power of global agreements to bring down emissions. However, while consuming less meat and choosing to drive your car less help in decreasing greenhouse gas emissions, its effects don’t compare to that of collective techniques. To stop people from drowning, we hire lifeguards, fund the coast guard, and build fences to stop people from falling into the water. Certainly, you should save the drowning child, but in our reality, the situation probably won’t escalate to that point. While Singer’s thought experiment might present an interesting ethical dilemma, his suggestion to use individualistic solutions to solve an entire society’s problems ignores the vital reality that we often don’t rely on the goodness of others to fix large problems.
Furthermore, the usefulness of certain applications of thought experiments is debatable.7 While nobody would disagree with the legitimacy of tools that can explain complex phenomena for a lay audience, the use of thought experiments as a scientific tool is more controversial. After all, as we saw with Zeno’s tortoise, a thought experiment can be logically sound while not scientifically so. While thought experiments have been correct about scientific phenomenons in the past, our rapidly improving modeling and measuring tools have largely eliminated the use of thought experiments as the main tool of scientific inquiry.
Ship of Theseus
The ship of Theseus is one of the more interesting early thought experiments. Discussed by Plato, Heraclitus, and Plutarch in 500–400 BC, the ship of Theseus thought experiment provides an interesting question about identity. In the thought experiment, the famous Greek hero Theseus’s old ship has been kept for several years. Time has taken its toll on the ship, and pieces are beginning to decay. To keep the ship in good condition, the owner replaces a few rotten planks. More time passed, and the oars began to decay. The owner replaces them too. The sail gets weathered, and it too gets replaced. Piece by piece, the owner eventually replaces every old, decaying piece with a completely new one. This leads to the tricky philosophical question: is it still the same boat? After all, if it was only a few planks that were replaced, it would be ludicrous to call it a brand new boat. If it is a different ship, at what point did it stop being the ship of Theseus? This simple, ancient puzzle has been debated for centuries. Are we more than the sum of our parts? After all, you probably feel like the same person, despite your cells having completely regenerated multiple times in your lifetime. Whatever the answer may be, the ship of Theseus provides us with an easy avenue to grapple with our own identity and the nature of reality itself.8
The Chinese Room
Can a computer be conscious? This is the question that philosopher John Searle tried to answer with his Chinese Room thought experiment. The thought experiment works as such: suppose that Searle was sitting in a room. Searle doesn’t speak Mandarin or understand anything about Chinese languages. The room has a door, a box of Chinese characters, and a book of English instructions. If a Mandarin speaker slid a sheet of paper with a question on it under the doorframe, Searle could look up in the book which combination of characters to respond with. He wouldn’t actually understand what he is saying back, as he is simply pattern matching. However, once he slides his response under the doorframe, the other person would be convinced that they are talking to somebody fluent in Mandarin. Searle used this idea to argue against the concept that artificial intelligence can intelligently understand the meaning of its tasks. Suppose a highly advanced, language processing artificial intelligence system was built. You could type in whatever question you had, and the computer would accurately reply. The program is so good at this that if you messaged with it, you would be convinced that it was just a person texting you back. Searle then poses a difficult question: does the computer actually understand what you are saying, or is it just simulating all the steps involved in writing it? Searle argues that this AI system is no different than our confused philosopher sliding Chinese characters under the door. While the answer is correct, the meaning is lost along the way.9
Related TDL Content
As one of the most innovative thinkers of the early twentieth century, Einstein was no stranger to the power of thought experiments. As a child, he dreamed up a thought experiment about chasing a beam of light, which led him to uproot the existing physics paradigm. He outlined his general relativity theory through thought experiments that contained accelerating elevators, blind beetles exploring curved surfaces, and a person falling off a roof.10 If you want to learn more about Einstein’s innovative ideas and his effective ways of communicating them, this TDL thinker profile is an excellent place to start.
Perhaps the most impactful thought experiment of all time is Plato’s allegory of the cave. Plato describes a group of prisoners chained in a cave with a fire behind them. The shadows from the fire entertain these prisoners. To the prisoners, these shadows are reality. When one prisoner escapes the cave and realizes that the shadows are an illusion, he tries to convince the other prisoners to leave their false reality. The other prisoners refuse, as they know nothing else. This puzzling allegory raises many questions about the nature of our reality and human behavior. Want to hear more about the cave, Plato, and reality itself? Go check out TDL’s thinker profile on Plato.
- Brown, J. R., & Fehige, Y. (2019, September 26). Thought experiments. Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/entries/thought-experiment/#HisThoExp.
- Palmer, B. (2014, March 5). Zeno’s paradox is a trick-but a very interesting trick. Slate Magazine.
- See 1.
- Mach, E., & Hiebert, E. N. (1976). On thought experiments. Knowledge and Error, 134–147. https://doi.org/10.1007/978-94-010-1428-1_11
- Peter Singer’s POND illustration. The Life You Can Save. (2021, April 12). https://www.thelifeyoucansave.org/child-in-the-pond/.
- See 1.
- Perry, P. (2019, January 30). This ancient thought exercise will have you questioning your identity. Big Think. https://bigthink.com/philip-perry/this-ancient-thought-exercise-will-have-you-questioning-your-identity.
- Cole, D. (2020, February 20). The Chinese Room Argument. Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/entries/chinese-room/.
- Thought experiment: How Einstein solved difficult problems. Farnam Street. (2020, April 3). https://fs.blog/2017/06/thought-experiment/.