Y２网上的那个哈佛大学教授讲课大堂实况录像大家估计都看过了。里面举出的阻止车祸难题是来自于下文中英国Virtue Eethics伦理哲学家Philippa Foot的著名＂电车难题＂。

不过，她的难题仅仅位列１０大 Thought Experiments 中的第１０。位列第一的是电影《黑客帝国》里面引用的用来阻截笛卡尔“我思故我在”哲学论断的＂大脑与模拟环境＂。

 

 

 

 

　　思想实验是一种精神上的观念或假想，通常和谜语相似，是哲学家和科学家用以了解什么是大众思想的一种简单方法。他们的运用在如哲学和理论物理(理论物理无需做实验)等抽象领域是最为广泛的。他们像是为思想准备的一份大餐，最终给出复杂的答案。即使思想实验本身也会有无法理解的时候，这并不奇怪。下面是10个著名的思想实验，还有他们所要表达的哲学、科学和伦理意义。

　　10.电车难题

　　它是伦理学领域最为知名的思想实验之一，内容大致是：一个疯子把五个无辜的人绑在电车轨道上，一辆失控的电车朝他们驶来，且马上就要辗过他们。幸运的是，你可以拉一个拉杆，让电车开到另一条轨道上。但是还有一个问题，那个疯子在那另一条轨道上也绑了一个人。想想这个情况，你应该拉拉杆吗?

　　意义:

　　电车难题最早由哲学家Philippa Foot提出，是用来批判伦理哲学主要理论的，特别是对功利主义的批判。功利主义认为，大部分道德决策都是根据“为最多的人提供最大的利益”的原则做出的。从一个功利主义者的观点来看，明显应去拉拉杆，只杀死一个人来拯救五个人。但是功利主义的批判者反驳说，一旦拉了拉杆，你就变得不道德——你要为另一条轨道上那一个人的死负担部分的责任。然而，其他人认为，这种状况下要求你要有所作为，什么都不做也是不道德。总之，不存在完全的道德行为，这也就是重点所在。许多哲学家都用电车难题作为例子来表现现实生活中经常强迫一个人违背自己道德准则的状况，并且有的时候根本没有完全道德的做法。

　　9.空地上的奶牛

　　认知领域中一个重要的思想实验就是“空地上的奶牛”。实验是这样的，一个农民担心自己获奖的奶牛走丢了。一个送奶工来到农场后，他让农民不要担心，因为他看到那头奶牛就在附近。虽然农民很愿意相信送奶工，但他还是自己去看了下，他看到了熟悉的黑白相间条纹，为自己的奶牛在那里感到很满意。过了一会，送奶工到那里再次进行了确认。那头奶牛确实在那里，但它躲在了树林里，而且有一大张黑白相间的纸缠绕在了一棵树上，显然，农民把这张纸错当成自己的奶牛了。问题于是来了，就算奶牛一直在那里，但农民说自己知道那头奶牛在那里时是否正确?

　　意义:

　　空地上的奶牛最初被EdmundGettier用来批判主流对知识定义的 JTB(justifiedtruebelief)理论，即当人们相信一件事时，它就成为了知识;这件事事实上是真的，且可以被充分验证。实验中，农民之所以相信奶牛在那里，是送奶工证词和他自己所见黑白相间物所共同构成的结果。而之后送奶工的确认，这件事也碰巧是真实的。尽管如此，农民并非真正知道奶牛在那里，因为他认为奶牛在那里的结论是建立在错误的前提上的。Gettier利用这个实验和其他一些例子，说明了将知识定义为JTB的理论需要修正。

　　8.定时炸弹

　　如果你关注近几年的政治时事，或看过动作电影，那么你对“定时炸弹”实验肯定很熟悉。它要求你想象有一个炸弹或其他大规模杀伤性武器藏在你的城市中，并且倒计时马上将归零。城市里有一个知情者，他知道炸弹的埋藏点。你会使用酷刑来让他吐出情报吗?

　　意义:

　　与电车难题类似，定时炸弹实验也是强迫一个人从两个不道德行为中选择其一的伦理问题。它一般用来反驳那些说在任何情况下都不能使用酷刑的言论。它也被用作在极端形势下法律可以被放在第二位的情况，如美国严禁虐囚的法律。归功于《24小时》之类的电视节目，还有一些政治辩论，定时炸弹已成为最常被提起的思想实验之一。今年早些时候，一份英国报纸提出了更为极端的看法。这份报纸说，如果这个恐怖分子对酷刑毫无反应，那么当局者是否愿意拷打他的妻子和儿女来逼他吐出情报。

　　7.爱因斯坦的光线

　　很少有人知道爱因斯坦著名的狭义相对论是受到他16 岁时一个思想实验的启发。在他的著作《自述注记》中，爱因斯坦回忆道他当时幻想在宇宙中追逐一道光线。他说如果他能够以光速在光线旁边运动，那么他应该能够看到光线在空间内呈现为“不断振荡但停滞着的电磁场”。对于爱因斯坦，这个思想实验证明了对于他作为一个富有想象力的观察者，”在有相同定律和一个相对于地球静止观察者的情况下，任何事都有可能发生。”

　　意义:

　　事实上，没人真正知道这意味着什么。科学家一直都在争论一个如此简单的思想实验是如何帮助爱因斯坦完成到狭义相对论这个巨大飞跃的。在当时，这个实验中的想法与现在已被抛弃的“以太”理论相违背。“以太”理论即存在一个隐性的空间供光线穿越。他经过了好多年才证明了自己是正确，但从某种程度上这个实验对于狭义相对论是“有害的”，他自己这么说，后者第一次让他站上了理论物理学的顶点。

　　6.忒修斯之船

　　史上最为古老的思想实验之一便是被称为忒修斯之船的悖论。这个实验最早出自普鲁塔克的记载。它描述了一艘可以在海上航行几百年的船，这归功于不断的维修和部件的替换。只要一块木板腐烂了，它就会被替换掉，以此类推，直到所有的部件都不再是最初的那些。问题是，最终产生的这艘船还是原来的忒修斯之船，还是一艘完全不同的新船?如果不是原来的船了，那么从什么时候开始它不再是原来的船了?哲学家ThomasHobbes后来对此进行了更深刻的探讨：如果有人用忒修斯之船上取下来的老部件来重新建造一艘新的船，那么两艘船中哪艘才是真正的忒修斯之船?

　　意义:

　　对于哲学家来说，忒修斯之船被用来研究身份的本质，特别是讨论一个物体是否仅仅就是其部件之和。一个更现代的例子是假设有一个乐队，到某一阶段乐队成员中不再有任何一个原始成员。这个问题还可以应用于其他如商业等领域。商业领域中，在不断并购和更换股东后仍然保留企业原来的名字;对于人体，人体不断地进行着新陈代谢和自我修复。这个实验的核心思想在于强迫人们去反问身份是否仅仅局限在实际物体和现象中这一普遍知识。

　　5.伽利略的重力实验

　　史上最早的思想实验之一，由物理和天文学家伽利略进行实验。为了反驳亚里士多德的自由落体速度取决于物体质量的理论，伽利略设计了一个简单的思想实验：根据亚里士多德的逻辑，如果一个较轻的物体和一个较重的物体绑在一起后从塔上扔下去，那么教重的物体会下落的比较快，且两个物体间的绳子会被拉紧。这时较轻的物体会对较重的物体产生一个拽力，使得重物的下落速度变慢。但是，伽利略认为两个物体绑在一起后的重量应比其中任意一个物体都大，那么一起下落的速度应该是最快的。于是他用这个矛盾证明了亚里士多德理论是错误的。

　　意义:

　　关于伽利略有一个著名的故事：有一次他从比萨斜塔扔下两个铁球，想要证明较重的物体并不较轻的物体下落速度快。现实中这个故事可能只是作为一种传奇，但这个思想实验证明了一个关于重力很重要的理论：无论物体的质量，所有物体自由落体的速率都是一样的。

　　4.猴子和打字机

　　另一个在流行文化中获得广泛关注的思想实验是“无限猴子定理”，也叫做“猴子和打字机”实验。该定理认为，如果有无数多的猴子在无限久的时间里，在无数多的打字机上随机打字，那么在某个时间点，它们“几乎必然”会打出莎士比亚的全部著作。猴子和打字机的设想在20世纪早期由法国数学家EmileBorel推广，但其基本思想，即无数多的人员和无数多的时间能产生任何/所有东西的理论，可以追溯至亚里士多德。

　　意义:

　　简单来说，“猴子和打字机”定理是用来描述无限本质最好的方法之一。人的大脑很难想象无限的空间和无限的时间，无限猴子定理可以帮助理解这些概念。猴子碰巧能写出《哈姆雷特》，听上去是天方夜谭，但当一个人考虑到所有的可能性后，这个说法在数学上是可以被证明的。这个定理本身在现实生活中不可重现，但这并没有阻止一些人的尝试：2003年，英国修读科学的学生在一家英国动物园“试验”了无限猴子定理，他们把一台电脑和一个键盘放进了灵长类园区。可惜的是，猴子们没有打出任何十四行诗。根据研究，它们只打出了5页几乎完全是字母“s”的纸。

　　3.中文房间

　　“中文房间”最早由美国杰出哲学家 JohnSearle于20世纪80年代初提出。这个实验要求你想象一位只会说英语的人身处一个几乎完全密闭的房间中，房间门上有一个小窗口。他有一台具有英汉翻译功能的电脑，房间里还有足够的纸、铅笔和文件柜。随后写着中文的纸片通过小窗口将被送入房间中。根据Searle的理论，房间中的人可以翻译这些文字并用中文写上他的回复。虽然他完全不会中文，但Searle认为通过这个过程，房间里的人可以让任何房间外的人以为他会说流利的中文。

　　意义:

　　Searle 创造了“中文房间”思想实验来反驳电脑和其他人工智能都能够真正思考的观点。房间里的人不会说中文;他无法用中文思考。但就因为他拥有某些工具，他甚至可以让以中文为母语的人以为他能说流利的中文。Searle还说，电脑就是这样工作的。它们无法真正理解他们所给出的信息，但它们可以运行一个程序、处理信息、然后给出一个具有人工智能的印象。

　　2.薛定谔的猫

　　薛定锷的猫最早由物理学家薛定锷提出，是量子力学领域中的一个悖论。内容是：一只猫被封闭在一个盒子里一个小时，和它一起的还有一些放射性元素和一瓶毒气。在一小时内，放射性元素的衰变几率为50%。如果发生了衰变，那么会触发一个连接在盖革计数器上的锤子，打碎瓶子，释放毒气，杀死猫。因为这件事是否发生的概率相等，薛定锷认为在盒子被打开前，盒子中的猫可以同时被认为是既死又活的。

　　意义:

　　简而言之，这个实验的核心思想是因为事件发生时不存在观察者，盒子里的猫可能同时存在所有的状态(实验中既死又活)。这个观念同一个古老的谜题相似，谜题内容为，如果一棵树倒在了树木中，且没有人听到声音，那么它有没有发出声响?薛定锷最早是在回复一篇讨论量子态叠加本质的文章时提出这个实验的。薛定锷的猫同时也说明了量子力学的理论是多么奇怪。这个思想实验因其复杂性而臭名昭著，同时也产生了各种各样的解释。其中最古怪的是“多重世界”假说，这个假说表示有一只既死又活的猫，那么两只猫是存在于不同的宇宙间，且永远不会有交集。

　　1.缸中的大脑

　　没有比所谓“缸中的大脑”更有影响力的思想实验了，这个思想实验涵盖了从认知学到哲学到流行文化等各个领域。这个实验要求你想象有一个疯狂科学家把你的大脑从你体内取出，放在一个装有维持生命液体的缸中。大脑是连着电极，电极还连到一台能产生图像和感官信号的电脑上。因为你获取的所有关于世界的信息都是经由大脑过滤，这台电脑就有能力模拟你日常的体验。如果这确实可能的话，你要如何来证明你周围的世界是真实的，而不是由一台电脑所产生的模拟环境?

　　意义:

　　如果你觉得这一切听起来很像《黑客帝国》，你说对了。这部电影以及其他一些科幻小说和电影，都受到了这个实验很大的影响。这个实验的核心思想是让人们质疑经历的本质，并思考作为一个人的真正意义是什么。这个实验的原型可以追溯至笛卡尔，由希拉里·普特南推广。在笛卡尔的《第一哲学沉思录》一书中，笛卡尔提出了是否证明能他所有的感官体验都是他自己的，而不是由某个“邪恶魔鬼”所产生的幻想。笛卡尔用他的经典名言“我思故我在”回答了这个问题。不幸的是，“缸中的大脑”将问题复杂化了，因为连着电极的大脑仍然可以思考。这个实验被哲学家广泛讨论，也有许多针对实验前提的反驳，但仍没有人能有力的回应其核心问题：你到底怎么才能知道什么是真实?

 

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Top 10 Most Famous Thought Experiments

with videos

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?

What it Means:

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?

What it Means:

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.”

What it Means:

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?

What it Means:

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.

What it Means:

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.

What it Means:

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.

What it Means:

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.

What it Means:

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.