How the Laws of Physics Lie
Cartwright (Nancy)
Source: Cartwright - How the Laws of Physics Lie
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Introduction (Extracted)

  1. Philosophers distinguish phenomenological from theoretical laws. Phenomenological laws are about appearances; theoretical ones are about the reality behind the appearances. The distinction is rooted in epistemology. Phenomenological laws are about things which we can at least in principle observe directly, whereas theoretical laws can be known only by indirect inference. Normally for philosophers 'phenomenological' and `theoretical' mark the distinction between the observable and the unobservable.
  2. Physicists also use the terms ‘theoretical' and 'phenomenological'. But their usage makes a different distinction. Physicists contrast ‘phenomenological' with ‘fundamental'. For example, Pergamon Press's Encyclopaedic Dictionary of Physics says, ‘A phenomenological theory relates observed phenomena by postulating certain equations but does not enquire too deeply into their fundamental significance.'
  3. The dictionary mentions observed phenomena. But do not be misled. These phenomenological equations are not about direct observables that contrast with the theoretical entities of the philosopher.
    [ … snip … ]
  4. The divide between theoretical and phenomenological commonly separates realists from anti-realists. I argue in these essays for a kind of anti-realism, and typically it is an anti-realism that accepts the phenomenological and rejects the theoretical. But it is not theory versus observation that I reject. Rather it is the theoretical as opposed to the phenomenological. In modern physics, and I think in other exact sciences as well, phenomenological laws are meant to describe, and they often succeed reasonably well. But fundamental equations are meant to explain, and paradoxically enough the cost of explanatory power is descriptive adequacy. Really powerful explanatory laws of the sort found in theoretical physics do not state the truth.
  5. I begin from the assumption that we have an immense number of very highly confirmed phenomenological laws. Spectra-physics Incorporated continuously runs a quarter of a million dollars' worth of lasers to death to test their performance characteristics. Nothing could be better confirmation than that. But how do the fundamental laws of quantum mechanics1, which are supposed to explain the detailed behaviour of lasers, get their confirmation? Only indirectly, by their ability to give true accounts of lasers, or of benzene rings, or of electron diffraction patterns. I will argue that the accounts they give are generally not true, patently not true by the same practical standards that admit an indefinite number of commonplace phenomenological laws. We have detailed expertise for testing the claim of physics about what happens in concrete situations. When we look to the real implications of our fundamental laws, they do not meet these ordinary standards. Realists are inclined to believe that if theoretical laws are false and inaccurate, then phenomenological laws are more so. I urge just the reverse. When it comes to the test, fundamental laws are far worse off than the phenomenological laws they are supposed to explain.
  6. The essays collected in this volume may be grouped around three different but interrelated arguments for this paradoxical conclusion.
    1. The manifest explanatory power of fundamental laws does not argue for their truth.
    2. In fact the way they are used in explanation argues for their falsehood. We explain by ceteris paribus laws, by composition of causes, and by approximations that improve on what the fundamental laws dictate. In all of these cases the fundamental laws patently do not get the facts right.
    3. The appearance of truth comes from a bad model of explanation, a model that ties laws directly to reality. As an alternative to the conventional picture I propose a simulacrum account of explanation. The route from theory to reality is from theory to model, and then from model to phenomenological law. The phenomenological laws are indeed true of the objects in reality — or might be; but the fundamental laws are true only of objects in the model.

  1. I will argue that the falsehood of fundamental laws is a consequence of their great explanatory power. This is the exact opposite of what is assumed by a well-known and widely discussed argument form—inference to the best explanation. The basic idea of this argument is: if a hypothesis explains a sufficiently wide variety of phenomena well enough, we can infer that the hypothesis is true. Advocates of this argument form may disagree about what counts as well enough, or how much variety is necessary. But they all think that explanatory power, far from being at odds with truth, leads us to it. My first line of argument in these essays denies that explanation is a guide to truth.
  2. Numerous traditional philosophical positions bar inferences to best explanations. Scepticism, idealism, and positivism are examples. But the most powerful argument I know is found in "Duhem (Pierre) - The Aim and Structure of Physical Theory", reformulated in a particularly pointed way by Bas van Fraassen in his recent book "Van Fraassen (Bas) - The Scientific Image". Van Fraassen asks, what has explanatory power to do with truth? He offers more a challenge than an argument: show exactly what about the explanatory relationship tends to guarantee that if x explains y and y is true, then x should be true as well. This challenge has an answer in the case of causal explanation, but only in the case of causal explanation. That is my thesis in ‘When Explanation Leads to Inference'. Suppose we describe the concrete causal process by which a phenomenon is brought about. That kind of explanation succeeds only if the process described actually occurs. To the extent that we find the causal explanation acceptable, we must believe in the causes described.
    [ … snip … ]

  1. Debate between realists and non-realists has been going on for a long time. Does the outcome have any practical consequence? I think it does. The last essay in this volume provides one example. I have argued that many abstract concepts in physics play merely an organizing role and do not seem to represent genuine properties. Unitarity has the earmarks of being just such a concept in quantum mechanics2.
  2. Unitarity is a property of operators. Those operators that are unitary represent motions that are indeterministic. Unitarity plays no causal role in the theory; nothing else about its use argues for interpreting it as a real property either. Yet there is a tendency to think of it not only as a mathematical characteristic of operators, but also as a genuine property of the situations represented by the operators. This, I claim, is the source of the notorious measurement problem in quantum mechanics3. Unitarity marks no real property in quantum theory4, and if we do not suppose that it must do so we have no interesting philosophical problem about measurement.
  3. Essay 9 is concerned exclusively with the measurement problem, and not with the other conceptual difficulty in quantum mechanics5 that philosophers commonly discuss, the Einstein-Podolsky-Rosen paradox. These two problems tend to sit at opposite ends of a balance: philosophical treatments that offer hope for solving one usually fare badly with the other. This is certainly the case with the programme I propose. If it should work, it would at best eliminate the measurement problem, which I believe to be a pseudo-problem. But it would have nothing to say regarding the very perplexing facts about locality brought out by the EPR paradox.

  1. The picture of science that I present in these essays lacks the purity of positivism. It is a jumble of unobservable entities, t1$usnl processes, and phenomenological laws. But it shares one deep positivist conviction: there is no better reality besides the reality we have to hand. In the second sentence of this introduction I characterized the distinction between phenomenological and theoretical laws: phenomenological laws are about appearances; theoretical ones about the reality behind the appearances. That is the distinction I reject.
  2. Richard Feynmann talks about explaining in physics as fitting phenomena into ‘the patterns of nature'. But where are the patterns? Things happen in nature. Often they happen in regular ways when the circumstances are similar; the same kinds of causal processes recur; there are analogies between what happens in some situations and what happens in others. As Duhem suggests, what happens may even be organized into natural kinds6 in a way that makes prediction easy for us (see the last section of ‘When Explanation Leads to Inference'). But there is only what happens, and what we say about it. Nature tends to a wild profusion, which our thinking does not wholly confine.
  3. The metaphysical picture that underlies these essays is an Aristotelean belief in the richness and variety of the concrete and particular. Things are made to look the same only when we fail to examine them too closely. Pierre Duhem distinguished two kinds of thinkers: the deep but narrow minds of the French, and the broad but shallow minds of the English. The French mind sees things in an elegant, unified way. It takes Newton's three laws of motion and turns them into the beautiful, abstract mathematics of Lagrangian mechanics. The English mind, says Duhem, is an exact contrast. It engineers bits of gears, and pulleys, and keeps the strings from tangling up. It holds a thousand different details all at once, without imposing much abstract order or organization. The difference between the realist and me is almost theological. The realist thinks that the creator of the universe worked like a French mathematician. But I think that God has the untidy mind of the English.

    The last essay on quantum mechanics7 shows how anti-realism can be put to work. The first essay defends causes. The principal arguments for theoretical entities and against theoretical laws are in the middle essays. Although the essays argue in favour of theoretical entities and against theoretical laws, the main emphasis is on the latter theme. This book is a complement, I think, to the fine discussions of representation, experimentation, and creation of phenomena in "Hacking (Ian) - Representing and Intervening - Introductory Topics in the Philosophy of Natural Science". Hacking provides a wealth of examples which show how new entities are admitted to physics. Essay 6 here has some detailed examples and many equations that may not be of interest to the reader with pure philosophic concerns; but the general point of the examples can be gleaned by reading the introductory sections. Although Essay 9 is about quantum mechanics8, it is not technical and readers without expert knowledge will be able to follow the argument.

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