Worrall J.: ‘Structural Realism: The Best of Both Worlds?’

RECOVERING A WEAKER FORM OF REALISM – STRUCTURAL REALISM

1.0 INTRODUCTION

Scientific realism is a doctrine that the entities postulated by scientific theories are real entities in the world, with approximately the properties attributed to them by the best available scientific theories. The doctrine was widely accepted till the late nineteenth century primarily due to success of Newtonian mechanics. But with the developments in physical theories especially quantum physics and relativity, it became very difficult to hold on to the realist position. In the paper, author’s aim is to recover some sort of realism. He argues in favor of structural realism, a position held by Poincaré also. I myself tend to believe in realism. I aim to work in physics and I find it very difficult to accept that my work is not about the real world. I think it is appropriate to quote Plank here, “Why should anybody go to the trouble of gazing at the stars if he did not believe that the stars were really there? … .”(Plank, quoted in Gomatam, pp.5)

2.0 NO-MIRACLES ARGUMENT

This is the main argument for a realist. The argument says that it would be a miracle, if a theory made many correct empirical predictions without what that the theory says about the fundamental structure of the universe being correct or “essentially” correct. Since, miracles are not to be accepted, thus, it is plausible to conclude that presently accepted theories are “essentially” correct. The argument requires empirical predictions for which the theory has not been engineered. For example, the predictions about the bending of light rays when they pass near the sun, made by GTR.

Although the argument is forceful it runs into problems right away. Newton’s theory of gravitation had a wide range of predictive success – the return of Halley’s Comet, discovery of Neptune etc. So according to no-miracles argument, Newton’s theory shows the fundamental structure of the universe. But we know that Newton’s theory was rejected in favor of Einstein’s GTR. What is even more striking is that the two theories are logically inconsistent, that is, if GTR is true then Newton’s theory is false and vice versa. That is, Einstein’s theory is not a mere extension of Newton’s theory. This shows that the development of science is not cumulative. Thus, no-miracles argument is not sufficient to establish realism.

Here, the author points out that no present-day realist would claim that we have grounds for holding that presently accepted theories are true. Instead, a scaled downed version called modified realism is propounded. Modified realism says our present theories in mature science are approximately true.


3.0 PESSIMISTIC INDUCTION

This is the main argument against realism. The history of science is full of theories which at different times and for long periods had been empirically successful, and yet were shown to be false in the certain they made about the world. It is similarly full of theoretical terms featuring in successful theories which do not refer. Therefore, by a simple induction on scientific theories, our current successful theories are likely to be false, and many or most of the theoretical terms featuring in them will turn out to be non-referential. Therefore, the empirical success of a theory provides no warrant for the claim that the theory is approximately true. This argument is known as the Pessimistic Induction. It was first propounded by Poincaré.

If the above argument is accepted then undoubtedly realism is untenable. Here author shows two ways that can help to show that the picture of theory-change is wrong. First, the successful empirical content of the previously accepted theory is in general carried over to the new theory, but its basic theoretical claims are not. Thus, theories are best construed as making no claims beyond their empirical consequences. This position is called pragmatic anti-realism. The other alternative uses the fact that although scientific theories are not explanatorily cumulative but predicatively they are cumulative. Here, it is believed that the observation-transcendental parts of scientific theories are not just codification schemes, they are accepted descriptions of reality hidden behind the phenomena, and our present best theories are our presently best shots at truth. Yet, there is no reason to believe that those present theories are closer to truth than their rejected predecessors. This is known as conjectural realism given by Popper. As a realist, I find this position to be fairly acceptable. But scientists generally agree to the point that present theories are closer to the truth than previous ones. Another problem with this position is that conjectural realism makes no concessions to no miracles argument (the main argument for realism).


4.0 STRUCTURAL REALISM

So the aim now is to accommodate intuitions lying under no-miracles argument and historical facts about the theory change in science. Then the position will be more plausible than pragmatic anti-realism and conjectural realism. Structural Realism is such a position. To explain this position, I will give the example used by author. Fresnel’s theory of light was based on the assumption that light consists in periodic disturbances originating in a source and transmitted by an all-pervading mechanical medium (ether). Fresnel’s theory had predictive success like prediction of white spot at the center of the shadow of an opaque disc held in light. Thus, it will be accepted as a mature science. But after Maxwell’s theory, light became to be viewed as a periodic disturbance, not in an elastic medium, but in electromagnetic field. Yet there is continuity in the shift from Fresnel to Maxwell, but the continuity is of structure and not of content. Now, we can say that Fresnel completely misidentified the nature of light, but it is no miracle that this theory enjoyed predictive success, because his theory attributed the right structure to the light.


5.0 CONCLUSION

From the paper, I conclude that the doctrine of Structural Realism is able to accommodate the no-miracles argument and the pessimistic induction argument. This is important because both these arguments are very strong. Falsifying any of them is not easy. Thus, structural realism seems to me to be the most appropriate stand for a realist.


6.0 REFERENCES

1. Worrall J. (1989), ‘Structural Realism: The Best of Both Worlds?’, Dialectica, Vol. 43, pp.99-124.
2. Gomatam R. (2005), ‘Einstein’s Conception of Scientific Realism’, Unpublished manuscript.