Back when I was in high school, I became interested in philosophy, and to tell the truth it was also by starting with some popular books on quantum mechanics, just as Feynman said: if you think you understand quantum mechanics, then you don’t understand it. The astonishment that quantum mechanics brought me has stayed with me ever since. But then again, though I may be overstepping or even being presumptuous, I still feel that I have some understanding of quantum phenomena; especially after several years of studying philosophy, I have gained quite a few insights. From the standpoint of some of the philosophical ideas I have accepted, quantum phenomena are not all that incomprehensible after all—on the contrary, they ought to be just that way.
The most典型典 example of quantum phenomena is undoubtedly the double-slit experiment and its variants, such as delayed-choice experiments. There are also things like Schrödinger’s cat. Although these phenomena are indeed extremely marvelous, some explanations seem to have a tendency toward contrived mystification. For example, a common way of putting it is to emphasize the intervention of intelligent beings as observers (some people especially stress this point). In the double-slit experiment (or delayed-choice experiment), people say that the observer’s choice changes the state of a photon as it passes through the double slit (or semitransparent mirror), so it seems that human subjective will can alter events millions of light-years away or tens of thousands of years in the past. But in fact there is no need for such mystification. To explain the delayed-choice experiment, one need neither introduce parameters such as the subjective will of an intelligent observer, nor bring in new ontological principles like holism or complementarity; one only needs to drive out “God” more firmly.
By “God,” we know, is meant the being who supplied classical physics with the notion of absolute space-time; relativity shattered this absolute space-time. In fact, quantum mechanics also needs to break this absolute space-time in order to be understood. And the more fundamental form of this “absolute space-time” is embodied in a kind of “God’s-eye view,” that is, a perspective standing outside the world, not participating in it, and looking on coolly from the sidelines. This “God’s-eye view” is extremely common in Western classical philosophy as well as in modern Anglo-American philosophy. For example, when it comes to some historical event, it seems that beyond the accounts given by various different real perspectives, there is also an independent “truth”; likewise, in discussions of ethical and moral issues, the “God’s-eye view” also crops up frequently.
And in quantum phenomena, what should be done is not to introduce a mysterious observer, but rather to drive out the mysterious God’s-eye view. For example, when we describe a photon, we cannot say: if a bright spot appears on screen A, then this photon came along path a. For the fact that a bright spot appeared on screen A is something observed by the experimenter, whereas saying that this photon traveled along path a is not an observed phenomenon, but a theoretical reconstruction, because according to our understanding (which in fact treats the photon like an ordinary small ball), we can only imagine it passing along path a to reach screen A. In short, the statement “the photon passed through path a” is merely the result of imagination, not a fact. Even what is called the “photon” itself is a construct of imagination. Saying that it is a construct of imagination does not mean that it is illusory or dependent on human will; quite the contrary, here the behavior of the photon does not depend on the experimenter’s will. By “construct” I mean that its state and properties are a theoretical device we set up on the basis of the phenomena we can observe ourselves. If the concept of an entity or property cannot provide anything related to our observations, then setting up this concept is meaningless (Occam’s razor). When we remove the screen in the delayed-choice experiment, we can observe whether the photon arrives at A or at B, and in that case it is still somewhat meaningful to say that the photon went through a or through b (though not very meaningful, really). But when we do not remove the screen—that is, when we cannot observe whether the photon arrived at A or at B—then the description “the photon either passed through a or passed through b” is meaningless. (I explained all this earlier using intuitionism.)
Removing the God’s-eye view means that we can only honestly describe what happens in our own language, on the basis of our own observations. Talking about events that no one can realistically observe in any way, and that are stated from some abstract God’s-eye view, is illegitimate. In addition, another thing that needs to be broken is the “principle of sufficient reason,” though this is not a rejection of “causality.” By causality, I mean the mutual connections between things; no event occurs in isolation. For example, a blow from Zhang San is the cause of Li Si’s death. To say that causality universally exists means that when Zhang San strikes down with his club, it will certainly produce some result, or that if Li Si is beaten to death there must certainly be some cause. But the causality we usually talk about is not the principle of sufficient reason: Zhang San’s blow may lead to Li Si’s death, but it may also lead to Li Si’s injury, or to the club breaking, and so on; Li Si’s death may have been caused by Zhang San’s blow, or it may have been caused by poison, or by a sudden heart attack, and so on. Causes and effects possess an inexhaustible richness, whereas the so-called principle of sufficient reason—that every event has its sufficient reason, that is, a cause which necessarily brings about that event rather than some other event—is a highly abstracted concept. What we in reality seek when we seek causality is not some necessary and sufficient condition at all, but merely a close connection.
Quantum mechanics can still preserve causal relations, but it no longer supports the principle of sufficient reason. For example, there is a 50 percent chance of a bright spot appearing on screen A and a 50 percent chance of one appearing on screen B, and we cannot find a necessary and sufficient condition that would guarantee a bright spot on screen A rather than on screen B. But the appearance of a bright spot on screen A or screen B is not completely without cause; once we affirm a causal concept that does not require a sufficient reason, we can understand the delayed-choice experiment. That is to say, the reason a bright spot appears on screen A (or on screen B) is that the experimenter did not insert the interference screen. And if the interference screen is inserted, the result is that bright spots appear one by one on the interference screen, while no bright spots appear on screens A and B. In these causal relations, there is no inversion in which the effect comes before the cause: after removing the God’s-eye view, the only events we can actually talk about are these three: 1. emitting photons one by one — 2. inserting or removing the interference screen — 3. bright spots appearing. We can ask: why did the bright spots appear this way? The answer: because photons were emitted and the screen was inserted, and so on. This is to provide a reason that is not a sufficient reason. Only when we additionally insert some “events” that did not actually occur but are imagined from the God’s-eye view does the so-called “delayed-choice experiment” produce the paradox of causal inversion.
March 26, 2010
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- benjaminbai
2010-03-29 13:12:09 Anonymous 124.205.77.77
Or we can imagine the existence of the principle of sufficient reason, but we must avoid thinking that one reason, or a group of reasons, might ultimately constitute an absolute sufficient reason; instead, we should always leave some blank space in the causes, because when we infer backward from the result, there are always factors we cannot imagine, or factors beyond the range of our calculations, affecting the result. And even if we arrive at some reason, that reason itself should also be placed in a position open to questioning, because it cannot provide its own legitimacy. The problem with positivism is not that it fails to see the limitations of positivism itself, but that the very concept of the positive already implies a background that cannot be explained by positivist methods; what is called “God” here is one of them.
——A thought, though I don’t know whether I have misunderstood it - Gu Ču
2010-03-29 21:37:13
In debates about quantum mechanics, broadly speaking, one side holds that uncertainty is due to the limited capacity of experiments and measurements and is insufficient to reveal the full cause, with additional hidden causes at work; this line of thought develops into hidden-variable interpretations, which are relatively marginal. The orthodox interpretation of quantum mechanics denies those “undiscovered causes” and instead emphasizes that uncertainty is an inherent property of nature rather than the result of limits in experimental precision. Of course, the philosophical issues here are very complex and hard to sort out clearly. For example, so-called “positivism” actually leans more toward the orthodox interpretation of quantum mechanics, because true positivists are anti-realists, whereas realism is more likely to receive support from idealism, and so on.
Translated from the Chinese original with AI assistance. The original text is authoritative.
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