Scientific Realism

Scientific Realism A Tale of Two Theories

25-11-2005 Essay 1 Wijsgerige Vorming Chimed Jansen [email protected]

Contents Introduction

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Realism and Idealism

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Scientific Realism .

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Atomic Theory a Quintessential Theory for scientific realism

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Superpositions in Quantum Mechanics

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Superposition Theory, a Challenge for Scientific Realism

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Conclusion .

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Bibliography

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Introduction Scientific Realism is the major philosophy of scientists in regard to the relation between scientific theory and reality. There are however, differences amongst scientific theories as to how well they fit the mold of scientific realism. Atomic theory has proven to be a powerful evangelical theory for scientific realism within the scientific world. It meets all the premises of scientific realism and is a fundamental theory in many fields of science. However moving to moving to the peripheral theory of superpositions in quantum mechanics, studied exclusively within physics, applying the theory to scientific realism becomes more problematic. Can scientific realism still maintain tenability in light of experimental evidence for the existence of a superposition state? To answer this question we need to explore what scientific realism entails and the extent to a conflict is existent in the theory of superposition states. This essay explores scientific realism as a philosophy and applies these two theories to the premises it sets out.

Realism and Idealism Classical realism is an ancient philosophy which regards the world as existing independently of our perception of it. Our perceptions are seen as being caused by our interaction with an external world. It is best understood through its opposing philosophy, that of idealism, in which the world is regarded as purely the result of experience without a separate existence. In this case our mind is the source of our experience and an external reality is no longer a necessity. These two philosophies formed the poles of much of epistemological thinking since they were first contemplated by Aristotle, credited with founding realism and Plato, credited with founding idealism. To illustrate the point, imagine a tree in a forest with no living creatures around except itself. Now imagine the tree falls. Does the fall create a sound? For the idealist the sound cannot be separated from the experience of the sound and therefore there is no sound. The idealists accept that all perceptions of the ‘external world’ are in fact creations of the mind and conclude that all experiential phenomenon are therefore dependent on a perceiver. A more extreme idealist viewpoint is that without a perceiver the tree ceases to exist at all. In this case the idealist accepts that without the perceiver the ‘treeness’ of the tree does not exist and therefore the tree as a whole does not exist. They may even claim that no tree is there at all, the only tree to exist, exists in the perceivers mind. These views are related to phenomanalism which can be viewed as a branch of idealism. Phenomenalism holds that “to be is, to be perceived” in the view of its founder George Berkley. 1 He proposed that the only reality that exists is experience itself, it should be noted however that he believed in God and believed that God was always a perceiver and therefore all things are continuously perceived and exist. Contrasting these views are ‘naïve’ realism, or common sense realism, which holds that there exists an external reality which is the source that causes our experiences. This reality is considered to continue existing without our experience of it. It is the reality as we experience it and live with it during mundane activities. Its shortcoming is its failure to consider the psychological aspects of experience; experience is seen as a direct 1

http://en.wikipedia.org/wiki/Epistemology

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perception of reality. Through the development of science and the scientific method the criteria for what is considered a perception of reality were expended such that naïve realism no longer formed an appropriate epistemology for scientists or their followers. With the advent of information about phenomenon beyond direct perception through techniques such as microscopy, radiology, spectroscopy, etc it became clear that realism would have to be adapted to suit the expanding possibilities of ‘perception’.

Scientific Realism The new scientific realism which resulted was not merely a development from naive realism, but also formed a reaction to alternative theories on science. Several prominent theories about the role of science had been developing since the scientific revolution. With the process of the ‘enlightenment’, a term which it self implies learning the truth, science became a powerful social force. Its strength was in discovering the ‘truth’ about nature and applying that knowledge to advance society, a process which was greatly aided by the evolving scientific method. During the 16th and 17th century realism was a growing philosophy amongst scientists, however religious beliefs were still powerful and questions on metaphysics, or those questions about unobservables, were left to be explained by religion. However during the eighteenth century science began to delve deep into areas previously covered by metaphysics, most prominent being the structure of matter. The acceptance of atomic theory by the public was a major advance for science over religion, however it brought questions about the epistemology of science. Theories of science were advanced to understand the credibility of science and the relationship between science and reality. Those theories on the credibility of science, empirical theories, concerned themselves with the observable and verifiable side of science and the correct scientific method. Theories on the relationship between science and reality attempted to correlate the discoveries made by science with an ultimate ‘metaphysical’ reality. Scientific realism assumes that the two can be correlated and will be (at least more closely correlated) at some later date. Instrumentalism is the main alternative theory to scientific realism. It holds that scientific theory is simply a tool to understand and predict phenomenon, without any claim about the truth of the theory being possible. In other alternative theories the source of perception is questioned, with idealists placing it in the mind, theists placing it in a God, and phenomenalists placing it in experience itself.

Atomic Theory a Quintessential Theory for scientific realism How do these theories relate to atomic theory? For scientific realists there are external existent units called atoms which correlate to some degree with present atomic theory and will correlate to a greater degree in the future after improvements to the theory are made. For instrumentalists the atomic theory is the most useful theory to explain and predict data relating to physics and chemistry; however no statement can be made as to the truth or falsity of the theory as it relates to reality, as reality is metaphysical. For the idealists, theists and phenomanists the atomic theory might relate to reality but the nature of reality is different from that proposed by scientific realists and the correlation of science with reality is implicit.

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Atomic theory is a highly defensible theory for scientific realists. A major proof of it’s correlation to reality is the many ways through which the constant of Avogadro can be calculated. Jean-Baptiste Perrin published the book Les Atomes in 1913 in which he reported thirteen ways to calculate the constant of Avogadro, three of which were discovered by him and involved Brownian motion. His own Brownian motion methods were perhaps the most convincing as they involved directly observing the motion of particles of different elements in water under an ultramicroscope. The brilliant determinations of the number of atoms by Mr Perrin have completed the triumph of atomicism. What makes it all the more convincing are the multiple correspondences between results obtained by totally different processes. (…) The atom of the chemist is now a reality... 2 Perrin himself was only slightly less convinced of the reality of molecules stating: Our wonder is aroused at the very remarkable agreement found between values derived from the consideration of such widely different phenomena. Seeing that not only is the same magnitude obtained by each method when the conditions under which it is applied are varied as much as possible, but that the numbers thus established also agree among themselves, without discrepancy, for all the methods employed, the real existence of the molecule is given a probability bordering on certainty. 3 From these quotes it’s clear that the proofs were accepted as conclusive by many at the time. With the status of atoms accepted, chemistry itself was taken from the status of an instrument to that of a reality. Of course not all people, or even all scientists, were convinced. Instrumentalism, or anti scientific materialism, and idealism continued to form opposing philosophies though they never regained their earlier credibility amongst scientists.

Superpositions in Quantum Mechanics I would like to take a specific part of the quantum theory accepted by most people in the scientific community and apply it to the scientific realist philosophy. Quantum mechanics has proved to be a useful theory which accurately predicts many phenomena; however, one of its implications is the existence of a superposition between possible states of a quantum particle. The states which can exist in a superposition are position, speed or direction and resulting states such as mass or energy. The state is only resolved by ‘observing’ the particle. That superpositions are restricted to smaller particles and not to the macroscopic world, is explained by the massive number of particles and therefore oscillations between states which yield a spontaneous restriction to a single state. However this explanation is neither proven nor convincing and it remains a puzzle to those in the field of quantum mechanics. Before going further it may be useful to clarify that a superposition is distinct from simply not knowing which state exists. In a

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Poincaré 1913 [1963]: 91 (Dudau 2002) Perrin, J.-B. (1913), Les Atomes, Paris: Alcan. 215-216 (Dudau 2002)

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superposition there is a probability that any of the possible states exist at any given moment. This state was described by Erwin Schrödinger, a central figure in the discovery quantum mechanics, in 1935 in his classic thought experiment involving a cat. In this experiment a cat is placed in a box with a radioactive element which has a 50% chance of decaying and releasing a particle which would break a seal and release poison and kill the cat. As long as the box is closed the cat in the box is sometimes alive and sometimes dead, or 50% alive and 50% dead depending on your interpretation, in either case the situation defies logic. In the year 2000 two experiments were performed on the level of electron sized particles which seem to confirm the existence of the superposition. The experiments, performed in Delft and Stony Brook, measured the direction a current flowed around a superconducting ring (see figure 1). In these experiments the Superconducting Quantum Interference Device, or SQUID, has a current passed through it. In a superposition both, right, or left directions around the ring have the Figure 2: The type of superconducting ring (SQUID) same energy leading to a double used in Delft and Stony Brook to test for a energy well (center image in figure superposition. (Chang 2000) 2). Once the current passes through the ring the direction it takes causes the energy well for that direction to deepen while shrinking the energy well for energy flow in the direction (see the left and right images of figure 2). There continues to be some overlap into the higher energy well due to the phenomenon of tunneling, through which even energetically barred states are inhabited at

Figure 1: Energy wells for current passing through a SQUID, the side images represent currents passing in one direction, the center current passing in neither or both directions. (Leggett 2000)

the quantum level. The experiment represents “the first one in which there has been reasonably foolproof evidence you do have a superposition of macroscopic quantum

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states,” says Anthony J. Leggett who first devised it. 4 With the concept established let us try to fit it to the theory of scientific realism and see how well it fits.

Superposition Theory, a Challenge for Scientific Realism First let us review the premises of scientific realism once more and evaluate how well each is met by the superposition theory. 5 Firstly the claims made about unobservables by the theory are true or false depending on the degree of correlation with reality. This is a semantic statement which defines the parameter for application of the theory, namely the theory must have the possibility to be either true or untrue. Secondly the unobservables described in the theory must exist objectively and mind independently. This statement is questionable in relation to the superposition theory. What quantum mechanics tells us is that, without the observer the superposition persists for quantum particles. This places the observer in a causal role in the process, making the observed no longer operate mind independently. This is a conundrum for scientific realists and represents a serious incompatibility. For many scientists this is enough to doubt the theory of quantum mechanics and the existence of superpositions in particular, a testament to the strength of the realist philosophy within science and the wish to believe reality is compatible with it. Thirdly, there is reason to believe some significant portion of what the theory says about unobservables. This is another major stumbling block for the theory as its implications are repugnant to our everyday logic, yet there is growing experimental evidence in favour of the existence of superpositions which cannot be ignored. The position taken by many scientists on this problem is that the theory yet correct and that in the future a theory will be formulated which explains the experimental results in a manor favourable to our understanding and compatible with the macroscopic world. In the words of Dr. Leggett, “I'm interested in the possibility that quantum mechanics, at some stage, may be wrong." 6 These doubts are echoed by Dr. Philip Pearle, "What you get in quantum mechanics is not what you see, Schrödinger felt this acutely. He himself felt something with quantum mechanics was wrong." 7 These statements call to mind the final premise of scientific realism, namely that scientific theory is improving and that it will one day approach the ideal reality which perfectly correlates with reality. It is this premise which allows realists to accept the superposition theory in spite of its incompatibility on the grounds that it will be replaced in the future by a better theory. In doing so however they are, at least in this case becoming de facto instrumentalists and utilizing the theory merely as an explanation for experimental results while not excepting its truth. Fitting the theory of superpositions into scientific realist philosophy thus represents a serious challenge for scientists wishing to hold both views.

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Here, There and Everywhere: A Quantum State of Mind, Kenneth Chang,The New york Times, 2000 The premises used here are those given at: http://en.wikipedia.org/wiki/Scientific_realism 6 Here, There and Everywhere: A Quantum State of Mind, Kenneth Chang,The New york Times, 2000 7 Here, There and Everywhere: A Quantum State of Mind, Kenneth Chang,The New york Times, 2000 5

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Conclusion In summing up it is clear that scientific realism is logical and conceptually sound theory to hold and highly suited to those within the scientific arena. Taking the instrumentalist view seems to take the heart out of the science, especially with the high regard paid to the pursuit of (true) knowledge in science. If we accept scientific realism we are committing ourselves to certain a group of premises. When we look at atomic theory these premise fit well and our confidence in the philosophy is deepened. In the case of superpositions, and perhaps others phenomenon not explored in this essay (parapsychology for example), results may conflict with the premises of the philosophy however. How do we deal with these problems? We can ignore or deny the phenomenon as many do, or accept that the present theory is insufficient and defer judgment. At which point does this approach clash with scientific realism? In my opinion it is a matter of context. If a theory is central and is tied to many others with significant practical applications, such as atomic theory, I would argue that such a relativist treatment of the truth is unacceptable. In the case of superpositions, or parapsychology for that matter, both of which I would consider outside of ‘everyday’ science or experience I can accept some leniency. I think these are cases where we have to accept that science still has a lot of work to do to bring our current theories closer to the ideal theory. After all how close a theory is to reality is a relative concept, so we need not let go of our belief in scientific realism just because of a few controversial theories.

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Bibliography Anonymous, Epistemology, http://en.wikipedia.org/wiki/Epistemology Anonymous, Idealism, http://en.wikipedia.org/wiki/Idealism Anonymous, Instrumentalism, http://en.wikipedia.org/wiki/Instrumentalism Anonymous, Realism, http://en.wikipedia.org/wiki/Realism Anonymous, Scientific Realism, http://en.wikipedia.org/wiki/Scientific_realism Boyd, Scientific Realism, 2002, Stanford Encyclopedia of Philosophy, http://plato.stanford.edu/entries/scientific-realism/ Chang, Here, There and Everywhere: A Quantum State of Mind, The New york Times, 2000, http://www.amherst.edu/~jrfriedman/NYTimes/071100sci-quantummechanics.html Dudau, The Realism/Antirealism, Debate in the Philosophy of Science, Dissertation Universität Konstanz, 2002, http://www.ub.unikonstanz.de/v13/volltexte/2003/1032//pdf/Scientific%20Realism.pdf Leggett, New life for Schrödinger's cat, PhysicsWeb, 2000, http://physicsweb.org/articles/world/13/8/3

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