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Truth and Science
From: Cambridge University Press
| By:
Nancy Cartwright |
EDITOR'S INTRODUCTION |
Science is regarded by many as dealing with unbiased, verifiable truth, and is therefore often thought to surpass all other disciplines. But is scientific knowledge really superior to other forms of knowledge? As part of a broader search for the boundaries of science, philosopher Nancy Cartwright poses some of the more difficult questions surrounding truth, objectivity and realism. |
 owadays the social constructivists provide us with powerful arguments against taking the laws of physics as mirrors of nature. Scientists, after all, operate in a social group like any other; and what they do and what they say are affected by personal motives, professional rivalries, political pressures, and the like. They have no special lenses that allow them to see through to the structure of nature. Nor have they a special connection or a special ear that reveals to them directly the language in which the Book of Nature is written. The concepts and structures that they use to describe the world must be derived from the ideas and concepts that they find around them. We can improve these concepts, refine the structure, turn them upside down, inside out; we can even make a rather dramatic break. But always the source must be the books of human authors and not the original Book of Nature. What we end up with through this process is bound to be a thoroughly human and social construction, not a replica of the very laws that God wrote. |
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| Nobel Prize winner Trygve Haavelmo. | |
What then of the startling successes of science in remaking the world around us? Don't these successes argue that the laws on which the enterprise is based must be true? Social constructivists are quick to point out that the successes are rather severely restricted to just the domain I mentioned  the world as we have made it, not the world as we have found it. With a few notable exceptions, such as the planetary systems, our most beautiful and exact applications of the laws of physics are all within the entirely artificial and precisely constrained environment of the modern laboratory. That in a sense is a commonplace. Consider one of the founders of econometrics, Trygve Haavelmo, who won the Nobel prize in 1989 for his work in originating this field. Haavelmo remarks that physicists are very clever. They confine their predictions to the outcomes of their experiments. They do not try to predict the course of a rock in the mountains and trace the development of the avalanche. It is only the crazy econometrician who tries to do that, he says. |
Constructing environments
Even when the physicists do come to grips with the larger world they do not behave like the econometrician, argue the social constructivists. They do not take laws they have established in the laboratory and try to apply them outside. Rather, they take the whole laboratory outside, in miniature. They construct small constrained environments totally under their control. They then wrap them in very thick coats so that nothing can disturb the order within; and it is these closed capsules that science inserts, one inside another, into the world at large to bring about the remarkable effects we are all so impressed by. The flashlight battery is a good example. |
Another illustration is provided by the measurement of the magnetic field gradients for neuromagnetism in order to look for evidence of strokes. The authors of a paper on the SQUIDS (Superconducting Quantum Interference Devices) employed in such measurements explain: |
One measures minute magnetic signals ... emanating from the electrical currents in neurons in the brain. These signals must be measured in the presence of both man-made and natural magnetic field noise that can be [far higher]. An elegant way of rejecting the ambient interference in favor of the locally generated signal is by means of a gradiometer ... To reduce magnetic field fluctuations even further, it is becoming common practice to place the instruments and patient in a shielded room consisting of multiple layers of mu-metal and aluminium.
(J. Clarke and R. Koch, "The Impact of High Temperature Superconductivity on SQUID Magnetometers," Science 242 (1988), pp. 217-223.) |
The conclusion I am inclined to draw from this is that, for the most part, the laws of physics are true only of what we make. The social constructivists tend to be scornful of the "true" part. There is almost always the suggestion lurking in their writings that it is no surprise that the laws work for the very situations they have been designed to work for. The scientists in turn tend to shrug their shoulders in exasperation: "You try for a while and you'll find out. It is a major achievement to get anything to work, and it is just as hard to get a good model to describe it when it does." |
Newton and nature
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| Isaac Newton (1642-1727). We do not need to assume that he discovered a fundamental structure that governs all of nature. | |
The observation that laws of physics are general claims, like the morals of fables, and that the concepts they employ are abstract and symbolic can provide a middle ground in the dispute. Newton's law, for instance, can be true of exactly those systems that it treats successfully; for we have seen how we can take it to be true of any situation that can be simulated by one of the models where the force puts on a concrete dress. That does not mean that we have to assume that Newton has discovered a fundamental structure that governs all of nature. That is part of the point of seeing force as an abstract concept, like work, and not a more concrete one, like extension. We may ask of any object, "What is its extension?" and expect there to be an answer. But not work. My children's teachers used to say to me "Play is a child's work." Were they right? I am inclined to think this is one of those situations where they were neither right or wrong. The normal activities of middle-class pre-schoolers are not an arena to which we can lead back the abstract concept of work and its relations, like labour, value and leisure. The concepts do not apply here. |
Similarly with force. You may assume that for every object this book, a ship in the Atlantic Ocean, or the rocks sliding over each other in the avalanche there is an answer to the question, "What is the force on this object?" But you need not. Whether you do will depend on how widely you think our models apply. I have argued that the laws are true in the models, perhaps literally and precisely true, just as morals are true in their corresponding fables. But how much of the world are fables true of? I am inclined to think that even where the scientific models fit, they do not fit very exactly. This question bears on how true the theory is of the world. But it is a different question from the one at stake here. Choose any level of fit. Can we be assured that for every new situation, a model of our theory will fit at that level, whether it be a model we already have, or a new one we are willing to admit into our theory in a principled way? This is a question that bears not on the truth of the laws, but rather on their universality. |
What about force? You may agree with the great British physicist Kelvin that the Newtonian models of finite numbers of point masses, rigid rods, and springs, in general of inextendable, unbendable, stiff things can never simulate very much of the soft, continuous, elastic, and friction-full world around us. But that does not stop you from admitting that a crowbar is rigid, and, being rigid, is rightly described by Newton's laws; or that the solar system is composed of a small number of compact masses, and, being so composed, it too is subject to Newton's laws. It is a different question to ask, "Do Newton's laws govern all of matter?" from "Are Newton's laws true?" Once we recognise the concept of force as an abstract concept, we can take different views about how much of the world can be simulated by the models that give a concrete context to the concept. Perhaps Newton's models do simulate primarily what we make with a few fortuitous naturally occurring systems like the planets to boot. Nevertheless, they may be as unproblematically true as the unexceptionable and depressing claim that the weaker are prey to the stronger. |
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