How the Laws of Physics Lie by Nancy Cartwright

Author:Nancy Cartwright [Cartwright, Nancy]
Language: eng
Format: epub, pdf
ISBN: 0198247044

7 See Hilary Putnam, 'The "Corroboration" of Theories', Philosophical Papers, Vol. 1 (Cambridge: Cambridge University Press, 1975) for a nice discussion of this.

end p.110

the planet Neptune, and to keep our satellites in space. Idealizations are no threat to the progress of science.

But what solace is this to the realist? How do idealizations save the truth of the fundamental laws? The idea seems to be this. To call a model an idealization is to suggest that the model is a simplification of what occurs in reality, usually a simplification which omits some relevant features, such as the extended mass of the planets or, in the example of the circuit model, the resistance in the bypass capacitor. Sometimes the omitted factors make only an insignificant contribution to the effect under study. But that does not seem to be essential to idealizations, especially to the idealizations that in the end are applied by engineers to study real things. In calling something an idealization it seems not so important that the contributions from omitted factors be small, but that they be ones for which we know how to correct. If the idealization is to be of use, when the time comes to apply it to a real system we had better know how to add back the contributions of the factors that have been left out. In that case the use of idealizations does not seem to counter realism: either the omitted factors do not matter much, or in principle we know how to treat them.

In the sense I just described, the circuit model is patently an idealization. We begin with equation (6.3), which is inadequate; we know the account can be improved—Nordby and I show how. But the improvements come at the wrong place for the defender of fundamental laws. They come from the ground up, so-to-speak, and not from the top down. We do not modify the treatment by deriving from our theoretical principles a new starting equation to replace (6.3). It is clear that we could not do so, since only part of the fault is diagnosed. What we do instead is to add a phenomenological correction factor, a factor that helps produce a correct description, but that is not dictated by fundamental law.

But could we not 'in principle' make the corrections right at the start, and write down a more accurate equation from the beginning? That is just the assumption I challenge. Even if we could, why do we think that by going further and further backwards, trying to get an equation that will be right when all the significant factors are included, we will eventually

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