无法证伪的理论就是耍流氓

mtjs 2011-03-03

展开全文

奥卡姆剃刀发表于2011-02-28 20:23:27

你相信世间万物都是由一只黄鼠狼控制吗？死理性派当然不会被这类说法蒙骗，因为他们知道人类认识能力的局限性，依靠有限经验得出的结论并不是永恒的真理，而那些“永远正确”的说法，事实上已经否定了人类在认识上进步的可能性。

永远正确 = 永远耍流氓

指导员做战前动员，称“只要冲锋足够快，就不会受伤”。你拼尽全力冲锋，可战后却浑身血淋淋地被抬了回来。你说指导员的话不对，指导员却说：“那是因为你冲得不够快，否则就不会受伤了，记着下次冲快点啊。”面对这么流氓的解释，你只能哑口无言。但你已经知道了他是个骗子，原因在于他根本就没有给出冲锋足够快的标准，无论你冲得有多快，只要你受伤了，他永远可以称原因是你不够快，他的说法“永远正确”。

李大娘相信黄大仙，她认为世上万事万物，包括你我的思想都是由一只超级黄鼠狼完全控制着，当然包括我这篇文章的写作。依托这只黄鼠狼，李大娘可以解释一切，下雨是它流鼻涕，打雷是它打喷嚏。你还别跟李大娘较劲，因为你永远都无法证明这个黄鼠狼是不存在的。指导员和李大娘的说法有一个共性，那就是说法本身根本就没有可以否定它的途径，用科学哲学的术语说，就是该说法本身不具有“可证伪性”。

理智的人当然不会被这类说法蒙骗，因为他们有一个理性的共识，那就是人类认识能力的局限性是永恒的，依靠有限经验得出的结论并不是永恒的真理，总是存在着在将来某一天被证伪的可能性。而那些“永远正确”无法证伪的说法，事实上已经否定了人类在此问题的认识上进步的可能性，这是反智的。

科学理论的必要条件：可证伪性

科学是人类最可靠的知识体系，科学理论与其它理论的区别在哪里呢？奥地利裔英国哲学家波普尔给出了一个判断标准——可证伪性，作为验证一个理论是不是科学理论的必要条件。例如自由落体定律，在忽略空气阻力的情况下，找两个质量差距很大的铁球从高处同时抛下，若落地时间差很多，且实验结论可靠，那就把这个定律推翻了。

越容易构建证伪实验，就说明该理论的可证伪性越强，证伪自由落地定律的实验如此容易做，但全世界这么多人这么多年楞是一个成功证伪的实验都没做出来，就反过来说明了该定律的可靠性。

科学理论是这个样子的，它建立在有限的观察基础上，具有客观、逻辑、实证、可重复检验等特性，虽然不保证永远正确，但它是人类可以依赖的最可靠的知识。在科学理论的适用范围内，新出现的情况总是不断地验证它的正确性，它本身具有可以在将来被证伪的途径，一旦被证伪了，该理论就被推翻了，或者改变其适用条件成为2.0版。

例如，在狭义相对论和量子力学出现后，把牛顿力学的适用范围局限在宏观低速上，它依然成立。有的人拿科学未必永远正确来批评科学，这其实是站在了全知全能的上帝角度上，去指责人类认识的局限性，这种思维是反智的。

谁是可证伪的，谁是不可证伪的？

可证伪学说中有个著名的例子，说的是当我们观察到的所有天鹅都是白色的时，可以得出“天鹅都是白色”的结论，并用其指导实践，这是个科学论断。这个论断的可靠性不取决被再次验证的次数，而取决于可证伪性，即只要找到一只黑天鹅，原论断就被推翻了。

“上帝造人理论”是无法被证伪的，因为就算科学提供了一个明确透彻的机制来说明人类的每一个进化步骤，这仍不能排除有个未知力量设计人的可能性。相反地，只要在岩层里发现了与恐龙同时代的人类化石，进化论就会立即破产。事实上，进化论所判定的人类出现之前的岩层，越来越多地被考古学家挖掘分析，却始终找不到一个有人类化石的可靠证据，这就反证了进化论的可靠性。

令人遗憾的是，中国古代思想中没有“可证伪”的概念，也不受形式逻辑的约束，例如“天人合一”，可它怎么个合法呢？谁都可以说几句，但没人能说清，而且根本没办法证明天人不合一，因为它根本不具备可证伪性。这种说法天马行空不着边际，貌似宇宙真理，实则大而无当，易经、阴阳五行，莫不如此。若只是闲聊扯淡，不具有可证伪性的说法也无伤大雅，但若是对人类实践有指导作用的理论，不具有可证伪性的理论就不值得相信了，无法证伪的理论就是耍流氓。

后记：

波普尔的可证伪学说属科学技术哲学中的内容，其本身并不是科学理论，它虽然得到了哲学界和科学界的广泛认可，但也不是完全无保留地被接受，批评的声音也一直没断过。这个链接有细节。另外，波普尔认为达尔文的自然选择理论基本不具备可证伪性（这里），在今日看来，这是个笑谈。可证伪理论和其它哲学理论一样，可以影响我们的思考，但不能用来直接指导科学。

去年去世的著名科普杂志Scientific American（《环球科学》）专栏作家

Martin Gardner:

A Skeptical Look at Karl Popper

The following essay was published in Skeptical Inquirer (2001).

by Martin Gardner

"Sir Karl Popper / Perpetrated a whopper / When he boasted to the world that he and he alone / Had toppled Rudolf Carnap from his Vienna Circle throne." —a clerihew by Armand T. Ringer

ir Karl Popper, who died in 1994, was widely regarded as England's greatest philosopher of science since Bertrand Russell. Indeed a philosopher of worldwide eminence. Today his followers among philosophers of science are a diminishing minority, convinced that Popper's vast reputation is enormously inflated. I agree. I believe that Popper's reputation was based mainly on this persistent but misguided efforts to restate common-sense views in a novel language that is rapidly becoming out of fashion. Consider Popper's best known claim: that science does not proceed by "induction"—that is, by finding confirming instances of a conjecture — but rather by falsifying bold, risky conjectures. Conformation, he argued, is slow and never certain. By contrast, a falsification can be sudden and definitive. Moreover, it lies at the heart of the scientific method.

A familiar example of falsification concerns the assertion that all crows are black. Every find of another black crow obviously confirms the theory, but there is always the possibility that a non-black crow will turn up. If this happens, the conjecture is instantly discredited. The more often a conjecture passes efforts to falsify it, Popper maintained, the greater becomes its "corroboration," although corroboration is also uncertain and can never be quantified by degree of probability. Popper's critics insist that "corroboration" is a form of induction, and Popper has simply sneaked induction in through a back door by giving it a new name. David Hume's famous question was "How can induction be justified?" It can't be, said Popper, because there is no such thing as induction!

There are many objections to this startling claim. One is that falsifications are much rarer in science than searches for confirming instances. Astronomers look for signs of water on Mars. They do not think they are making efforts to falsify the conjecture that Mars never had water.

Falsifications can be as fuzzy and elusive as confirmations. Einstein's first cosmological model was a universe as static and unchanging as Aristotle's. Unfortunately, the gravity of suns would make such a universe unstable. It would collapse. To prevent this, Einstein, out of thin air, proposed the bold conjecture that the universe, on its pre-atomic level, harbored a mysterious, undetected repulsive force he called the "cosmological constant." When it was discovered that the universe is expanding, Einstein considered his conjecture falsified. Indeed, he called it "the greatest blunder of my life." Today, his conjecture is back in favor as a way of explaining why the universe seems to be expanding faster than it should. Astronomers are not trying to falsify it; they are looking for confirmations.

Falsification may be based on faulty observation. A man who claims he saw a white crow could be mistaken or even lying. As long as observation of black crows continue, it can be taken in two ways; as confirmations of "all crows are black," or disconfirmations of "some crows are not black." Popper recognized — but dismissed as unimportant — that every falsification of a conjecture is simultaneously a confirmation of an opposite conjecture, and every conforming instance of a conjecture is a falsification of an opposite conjecture.

Consider the current hypothesis that there is a quantum field called the Higgs field, with its quantized particle. If a giant atom smasher some day, perhaps soon, detects a Higgs, it will confirm the conjecture that the field exist. At the same time it will falsify the opinion of some top physicists, Oxford's Roger Penrose for one, that there is no Higgs field.

To scientists and philosophers outside the Popperian fold, science operates mainly by induction (confirmation), and also and less often by disconfirmation (falsification). Its language is almost always one of induction. If Popper bet on a certain horse to win a race, and the horse won, you would not expect him to shout, "Great! My horse failed to lose!"

Sir Karl Popper (1902-1994)

Astronomers are now finding compelling evidence that smaller and smaller planets orbit distant suns. Surely this is inductive evidence that there may be Earth-sized planets out there. Why bother to say, as each new and smaller planet is discovered, that it tends to falsify the conjecture that there are no small planets beyond our solar system? Why scratch your left ear with your right hand? Astronomers are looking for small planets. They are not trying to refute a theory any more than physicists are trying to refute the conjecture that there is no Higgs field. Scientists seldom attempt to falsify. They are inductivists who seek positive conformations.

At the moment the widest of all speculations in physics is superstring theory. It conjectures that all basic particles are different vibrations of extremely tiny loops of great tensile strength. No superstring has yet been observed, but the theory has great explanatory power. Gravity, for example, is implied as the simplest vibration of a superstring. Like prediction, explanation is an important aspect of induction. Relativity, for instance, not only made rafts of successful predictions but explained data previously unexplained. The same is true of quantum mechanics. In both fields researchers used classical induction procedures. Few physicists say they are looking for ways to falsify superstring theory. They are instead looking for confirmations. Ernest Nagel, Columbia University's famous philosopher of science, in his Teleology Revisited and Other Essays in the Philosophy and History of Science (1979), summed it up this way: "[Popper's] conception of the role of falsification . . . is an oversimplification that is close to being a caricature of scientific procedures."

For Popper, what his chief rival Rudolf Carnap called a "degree of confirmation"—a logical relation between a conjecture and all relevant evidence—is a useless concept. Instead, as I said earlier, the more tests for falsification a theory passes, the more it gains in "corroboration." It's as if someone claimed that deduction doesn't exist, but of course statements can logically imply other statements. Let's invent a new term for deduction, such as "justified inference." It's not so much that Popper disagreed with Carnap and other inductivists as that he restated their views in a bizarre and cumbersome terminology.

To Popper's credit he was, like Russell, and almost all philosophers, scientists, and ordinary people, a thoroughgoing realist in the sense that he believed the universe, with all its intricate and beautiful mathematical structures, was "out there," independent of our feeble minds, In no way can the laws of science be likened to traffic regulations or fashions in dress that very with time and place. Popper would have been appalled as Russell by the crazy views of today's social constructivists and postmodernists, most of them French or American professors of literature who know almost nothing about science.

Scholars unacquainted with the history of philosophy often credit popper for being the first to point out that science, unlike math and logic, is never absolutely certain. It is always corrigible, subject to perpetual modification. This notion of what the American philosopher Charles Peirce called the "fallibilism" of science goes back to ancient Greek skeptics, and is taken for granted by almost all later thinkers.

In Quantum Theory and the Schism in Physics (1982) Popper defends at length his "propensity theory" of probability. A perfect die, when tossed, has the propensity to show each face with equal probability. Basic particles, when measured, have a propensity to acquire, with specific probabilities, such properties as position, momentum, spin and so on. Here again Popper is introducing a new term which says nothing different from what can be better said in conventional terminology.

In my opinion Popper's most impressive work, certainly his best known, was his two-volume The Open Societyand Its Enemies (1945). Its central theme, that open democratic societies are far superior to closed totalitarian regimes, especially Marxist ones, was hardly new, but Popper defends it with powerful arguments and awesome erudition. In later books he attacks what he calls "historicism," the belief that there are laws of historical change that enable one to predict humanity's future. The future is unpredictable, Popper argued, because we have free wills. Like William James, Popper was an indeterminist who saw history as a series of unforeseeable events. In later years he liked to distinguish between what he called three "worlds"—the external physical universe, the inner world of the mind, and the world of culture. Like Carnap and other members of the Vienna Circle, he had no use for God or an afterlife.

Karl Raimund Popper was born in Vienna in 1902 where he was also educated. His parents were Jewish, his father a wealthy attorney, his mother a pianist. For twenty years he was a professor of logic and scientific method at the London School of Economics. In 1965 he was knighted by the Crown.

I am convinced that Popper, a man of enormous egotism, was motivated by an intense jealousy of Carnap. It seems that every time Carnap expressed an opinion, Popper felt compelled to come forth with an opposing view, although it usually turned out to be the same as Carnap's but in different language. Carnap once said that the distance between him and Popper was not symmetrical. From Carnap to Popper it was small, but the other way around it appeared huge. Popper actually believed that the movement known as logical positivism, of which Carnap was leader, had expired because he, Popper, had single-handedly killed it!

I have not read Popper's first and only biography, Karl Popper: The Formative Years (1902-1945), by Malachi Haim Hacohen (2000). Judging by the reviews it is an admirable work. David Papineau, a British philosopher, reviewed it for The New York Times Book Review (November 12, 2000). Here are his harsh words about Popper's character and work:

By Hacohen's own account, Popper was a monster, a moral prig. He continually accused others of plagiarism, but rarely acknowledged his own intellectual debts. He expected others to make every sacrifice for him, but did little in return. In Hacohen's words, "He remained to the end a spoiled child who threw temper tantrums when he did not get his way." Hacohen is ready to excuse all this as the prerogative of genius. Those who think Popper a relatively minor figure are likely to take a different view.
When Popper wrote "Logik der Forschung," he was barely thirty. Despite its flawed center, it was full of good ideas, from perhaps the most brilliant of the bright young philosophers associated with the Vienna Circle. But where the others continued to learn, develop and in time exert a lasting influence on the philosophical tradition, Popper knew better. He refused to revise his falsificationism, and so condemned himself to a lifetime in the service of a bad idea.

Popper's great and tireless efforts to expunge the word induction from scientific and philosophical discourse has utterly failed. Except for a small but noisy group of British Popperians, induction is just too firmly embedded in the way philosophers of science and even ordinary people talk and think.

Confirming instances underlie our beliefs that the Sun will rise tomorrow, that dropped objects will fall, that water will freeze and boil, and a million other events. It is hard to think of another philosophical battle so decisively lost.

Readers interested in exploring Popper's eccentric views will find, in addition to his books and papers, most helpful the two-volume Philosophy of Karl Popper (1970), in the Library of Living Philosophers, edited by Paul Arthur Schilpp. The book contains essays by others, along with Popper's replies and an autobiography. For vigorous criticism of Popper, see David Stove's Popper and After: Four Modern Irrationalists (the other three are Imre Lakatos, Thomas Kuhn, and Paul Feyerabend), and Stove's chapter on Popper in his posthumousAgainst the Idols of the Age (1999) edited by Roger Kimball. See Also Carnap's reply to Popper in ThePhilosophy of Rudolf Carnap (1963), another volume in The Library of Living Philosophers. Of many books by Popperians, one of the best is Critical Rationalism (1994), a skillful defense of Popper by his top acolyte.