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Big Questions Philosophy of Science Handout 3 Dr H Beebee Scientific Realism Anti Realism Introduction Scientific theories claim or at least seem to claim that the universe is populated by a host of entities that we cannot observe in any obvious sense we have genes quarks curved space time the superego if you think psychoanalysis is a science etc etc Do we including scientists have any right to believe in such entities Scientific realists say yes such entities really do exist while anti realists say no There are three basic positions which one can adopt on this issue Realism We have very good reason to believe that the unobservable entities postulated by well confirmed theories exist Constructive empiricism We have no good reason to suppose that such entities exist The evidence which supports scientific theories supports only the claim that such theories are empirically adequate that what they say about observable entities is true We have no reason to suppose that what they say about unobservable entities is true Instrumentalism This is a thesis about the meaning of theoretical terms i e terms which appear to refer to unobservable entities Instrumentalists claim that such terms don t really refer to any such entities A theory employing theoretical terms is really only about the observable world what makes the theory true is the observable facts being the way the theory says they are Theoretical terms are introduced into a theory only to make it simpler or more elegant Their presence does not indicate any ontological commitment to unobservable entities referred to by the terms since the terms don t despite initial appearances refer to such entities For example suppose that Quantum Mechanics makes a claim about the quantum state of a particular photon None of the realist constructive empiricist or instrumentalist need deny that Quantum Mechanics is a hugely successful theory for predicting and explaining the outcomes of all sorts of experiments None of them think there s anything wrong with Quantum Mechanics Rather they disagree over a what the theory is really telling us about the world when it says that say the photon is in state S b whether we have any good reason to believe this and c what the purpose of a theory like Quantum Mechanics is Realism and constructive empiricism agree on a the theory is telling us exactly what it appears to be telling us namely that the photon really is in quantum state S But they disagree on b the realist thinks we have every reason to believe what the theory says about the quantum state whereas the constructive empiricist thinks we have no reason to believe it Does it follow that the constructive empiricist takes rather a dim view of Quantum Mechanics After all if the aim of science is truth and this is what the realist thinks and we have no reason whatever to suppose that what current science tells us about the unobservable is true it follows that we have no reason to suppose that Quantum Mechanics is doing what a scientific theory ought to be doing namely telling us the truth about the universe 1 But the constructive empiricist does not take such a dim view of Quantum Mechanics because she does not believe that the aim of science is truth Rather she thinks the aim of science is empirical adequacy what we want and need from scientific theories is not the whole truth but merely the truth about observable phenomena It doesn t matter very much what a theory says about the unobservable so long as it gets its predictions right So we shouldn t really be concerned that we ve got no reason to believe what Quantum Mechanics says about the photon s quantum state so long as the observable consequences of this claim are borne out Instrumentalism on the other hand disagrees with both realism and constructive empiricism over a According to instrumentalism what Quantum Mechanics is really saying when it says that the photon is in quantum state S is merely that if I were to make such and such a measurement I would get so and so observable results The terms photon and quantum state are not intended to refer to real features of the world rather they have a purely instrumental role The photon is in state S is just a more convenient and more elegant way of saying doing this experiment would get you these results Both forms of anti realism instrumentalism and constructive empiricism thus agree against the realist that the primary aim of science is to get to the truth about the observable world that is empirical adequacy Two arguments for scientific realism 1 The no miracles or Ultimate argument Many realists regard this argument as the strongest motivation for scientific realism It would be a miracle a coincidence on a near cosmic scale if a theory made as many correct empirical predictions as say the general theory of relativity or the photon theory of light without what that theory says about the fundamental structure of the universe being correct or essentially or basically correct But we shouldn t accept miracles not at any rate if there is a non miraculous alternative If what these theories say is going on behind the phenomena is indeed true or approximately true then it is no wonder that they get the phenomena right So it is plausible to conclude that presently accepted theories are indeed essentially correct Worrall p 101 Put simply It would be a miracle if the universe behaved by and large as it does as if there were quarks and fields and photons if in fact there were no such things But we shouldn t believe in miracles The best explanation of why scientific theories are so successful of why the universe behaves as if there were quarks and fields and photons is that there really are such entities Hence we ought to believe that realism is true An anti realist response The no miracles argument basically says that the only sensible explanation of the predictive success of scientific theories is that what those theories say about the unobservable entities which give rise to the predicted phenomena is true But Bas van Fraassen the inventor of constructive empiricism has another explanation science is a biological phenomenon an activity by one kind of organism which facilitates its interaction with the environment And this makes me think that a very different kind of scientific explanation is required 2 I can best make the point by contrasting two accounts of the mouse who runs from its enemy the cat St Augustine provided an intentional explanation the mouse


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