Focus of Kuhn lecture: Kuhn views the development of scientific knowledge and scientific disciplines as analogous to biological evolution.

I. Sample talk delivered at a physics conference
II. The sociology of scientific communities
III. Biological evolution as an analog for the evolution of scientific knowledge and disciplines
IV. Kuhn's view of scientific progress and his influence

Freshman Studies Lecture on The Structure of Scientific Revolutions, by Thomas Kuhn.

Matthew R. Stoneking, 5 February 2001

I. Sample talk delivered at a physics conference

Title: Coherent oscillations observed in a toroidal pure electron plasma; diocotron mode or magnetron mode?

1. title slide: I am reporting today on work done in a toroidal pure electron plasma at Lawrence University in Appleton, Wisconsin.
2. This transparency lists the parameters for our system... major radius is 43 cm, minor radius is 4.5 cm, density is in the range ..., and the magnetic field is about 200 G. The density is therefore quite low compared to the Brillouin limit, but sufficiently dense that the Debye length is smaller than the minor radius. Collective effects are therefore expected to be important. Note also, the electrons are well-magnetized as evidenced by the range of Larmor radius values.
3. Briefly, we have measured the confinement time for this plasma. The collector signal, shown here, has a prominent feature around 90 - 100 microseconds.
4. Here is the raw data from the wall probe diagnostic. I point your attention toward the steady state phase on the left. The power spectrum for that signal shows a distinct feature at around 100 thousand REVOLUTIONS per second, with a couple of harmonics also evident. This is the oscillation we are concentrating our attention on...
5. Its frequency shows a dependence on magnetic field that is consistent with a diocotron mode. The 1/B dependence could, however also be consistent with a magnetron mode.
6. The oscillation frequency does show dependence on the applied horizontal electric field, a possible signature of the magnetron mode. However, our preliminary calculation of the drift orbits in this system, including the ExB drift due to both the vacuum field and the space charge generated field, and including a curvature drift associate with a mean electron energy of 200 eV... these calculations suggest the oscillation are more diocotron in nature. The apparent dependence of the oscillation frequency on the vacuum electric field probably arises due to changes in the electron density at different values of the horizontal electric field. ...

scientific jargon
Whew ... not too many people walked out on me. I expect that almost none of you understood what I have been talking about for the last few minutes. Just now, you were the recipients of information "formatted," so to speak, for a much different audience... an audience of plasma physicists. Next summer, I will attend a workshop where I will likely present what I have just delivered to you (or something very similar to it). I expect (and hope) that everyone in the room will understand everything I just said.

Well... they would probably stop me and ask questions about one particular graph I showed you (#3 above). That is because the graph does not display data from a "collecter," and does not represent a measurement of the "confinement time" for the plasma. Rather this graph should be labelled like this... This is a graph of the number times the word 'paradigm' (or variations like 'paradigmatic') appear on each page of Thomas Kuhn's The Structure of Scientific Revolution (third edition). I may have missed a few instances, but probably not man. Yes, 'paradigm' shows up 13 times on page 94 alone! Check for yourself. 'Paradigm' certainly must be connected to Thomas Kuhn's main points in a fundamental way. In fact, Kuhn coined a new use for this word in the very essay you are reading, which was published in 1962. Undoubtedlty you have heard people use the term in phrases like ... "such and such has been the dominant paradigm since 1980 ..." or maybe more commonly ... "the work of so and so caused a paradigm shift in the field of such and such." If you haven't noticed phrases like these, you will in the future, now that you have read (or are reading) the book that launched paradigm into the popular usage it now enjoys. In Madison, where I lived for quite a few years, a popular bumper sticker read ... "subvert the dominant paradigm." I doubt that Mr. Kuhn intended his pet word to become a tool for political revolutionaries... or wannabe revolutionaries at least. Most of the popular uses of the word go far beyond the intentions of Mr. Kuhn, but they are testimony to the influence his essay has had in our larger culture.

The point of my little scientific conference presentation was to begin to give you some background understanding of aspects of the practice of science; background understanding that Kuhn at least in some measure assumes you already possess. I know that few of you have completed reading the book. My intent with this lecture is 1) to provide some useful background on how scientific communities function and 2) to develop an analogy that Kuhn uses at the end of the essay ... an analogy you are ripe to receive having just finished reading The Beak of the Finch. Both of these objectives are intended to aid you in your struggle to subdue this work, after all you probably already have the feeling that this book was not written with Lawrence freshmen in mind. My guess is that you reacted to your first contact with this book like you did to my sample scientific presentation. This is an academic essay written for other academics... philosophers and historians of science primarily. I hope what follows is useful... the payoff is potentially substantial.

language barrier between the scientist and non-scientist
Let's begin with 'how scientists communicate.' Why was my earlier scientific presentation so opaque to you? And why would I be reasonable in supposing that my colleagues in the COMMUNITY of plasma physicists would find it transparent? The public at large often views scientists as speaking another language. At times that view takes on the form of wonder and admiration ... "I could never understand that stuff." Some segment of the public associates the fact that they cannot understand the scientists language with the superior intelligence of the scientist. While that's flattering, the real reason scientists understand each other is because they have been trained (some might say indoctrinated) to speak the language of their discipline. At other times, the 'language barrier' between scientists and non-scientists is a source of suspicion. "What are they trying to hide from us?" "They get money from the government (my hard-earned tax dollars) and they don't want us to know what they did with it."

Why do scientists speak in 'jargon'? Must there be a 'language barrier' between non-scientist and scientists? The specialized use of words (many of which are used generally with other, often related meanings) represents a shorthand for concepts, phenomena and practices that the scientists have incorporated into their view of their work (and perhaps of the world). The scientists who will hear my talk and I share a common set of views about plasma physics, views we share because we had very similar training, we read the same scientific journals, and attend the same scientific conferences. In Kuhn's terminology, we share a common 'paradigm' or 'set of paradigms' or as he calls them in the post-script to your edition of Structure, a common 'disciplinary matrix.' All the people in the audience of next summer's workshop will already be familiar with what I mean when I say 'diocotron mode' or 'confinement time' or 'power spectrum' or 'ExB drift'. I do not need to start from scratch and explain these ideas to them. I can start with those concepts, principles, techniques, etc. and build on them. You can imagine how much longer my talk would have to be if I had to teach them (as I would have to teach all of you if I wanted you to understand the results of my experiments) all the fundamental ideas on which my work is built. The scientific enterprise functions so efficiently because the participants in scientific dialogue share a common paradigm.

In the post-script to Structure, Kuhn enumerates more carefully the kinds of things he means when he used 'paradigm' in the 1962 essay... 'symbolic generalizations,' 'models,' 'values,' and 'exemplars.' For much of the book you can get away with a simpler understanding of 'paradigm' as a word representing all the things that a scientist can assume that his colleague will understand about their common work without explicitly explaining them ... all the major prior results in the field... all the important experimental techniques ... all the important theoretical ideas or concepts that guide their research.

So scientists should be excused for speaking in jargon ... at least when they are speaking amongst themselves. It is essential to the efficient operation of the scientific enterprise. On the other hand, too few scientists are able to communicate the essence of their work in language accessible to the general public. Fortunately there are some excellent exceptions to the general rule, exceptions such as Professor Brian Greene, the string theorist and author who recently delivered a convocation to this community. There are also some excellent writers without scientific training who learn some of the scientists language and translate it appropriately into a generally accessible language. Jonathan Weiner, the author of The Beak of the Finch, which you have just finished reading and who also spoke here a few weeks ago, is an example of such a person. I must say that I feel somewhat humbled by the public speaking examples that have been set recently on this stage and across the way in the chapel, following as I do the Dean of the Faculty Brian Rosenberg, Professor Brian Greene and Pulitzer prize-winning author Jonathan Weiner.

language barrier between scientists of difference disciplines
I was careful to identify the intended audience for my earlier presentation as an audience of plasma physicists. I did not say an audience of scientists. If I were to show up at a conference on protein chemistry or sedimentary geology or aquatic ecology or even a physics conference on string theory... my audience would be nearly as much in the dark as you were. And, likewise, if I were to stay and listen to some of the presentations at any of those conferences, I would not come away knowing any more than when I entered ... other than something about my ignorance of string theory. The language barrier that exists between the scientist and the non-scientist also exists between members of different scientific DISCIPLINES. There are as many scientific dialects as there are scientific disciplines or subdisciplines. This is a facet of the SOCIOLOGY OF SCIENCE that Kuhn alludes to, but in large part assumes his readers understand ... the organization and operation of scientific communities or disciplines. His main points in the essay follow in large part from his understanding of the daily functioning of scientific communities.

Take an excerpt from The Beak of the Finch that illustrates the language barrier between members of even closely allied discipline... in this case evolutionary biologists and molecular biologists. One of the Grants' former graduate students, Peter Boag, became a professor in Ontario Canada where he took up the techniques of molecular biology as a tool to analyze evolutionary data... Boag "went molecular" as the traditional evolutionary biologists would say. On page 215 of Beak, Peter Grant is quited as saying of molecular biology,

" 'It really is a foreign language, ' ... 'I suppose ours is too, but I do have the impression that theirs is harder.'" -Beak of the Finch, p. 215

In addition to providing an example of the language barrier that exists between disciplines (or in this case between subdisciplines of the discipline of biology), this quotation reveals another aspect of the sociology of scientific communities. I will discuss that aspect shortly.

Thomas Kuhn has this to say (on p. 21) about the language barrier that exists between scientists in different disciplines,

"Although it is customary, and is surely proper to deplore the widening gulf that separates the professional scientist from his colleagues in other fields, too little attention is paid to the essential relationship between that gulf and the mechanisms intrinsic to scientific advance." -SSR p. 21

He is referring to his contention that the specialized language of a scientific community is central to its efficient operation, not only because it is a powerful shorthand or abbreviation for an enormous amount of collectively agreed upon background material other member of one's own community... but also because it prevents the polluting influence of others who might distract the work of the community with too many questions about fundamental and alread resolved issues. Since the 'others' do not speak the language, they are effectively prevented from communicating with 'us' about our work.

II. The sociology of scientific communities

The specialized language of scientific disciplines is one aspect and maybe the most important aspect of the sociology of scientific communities, but there are several others I think you should understand as you read Kuhn.

professional societies, scientific conferences and workshops
Scientists can be "labeled" as members of a particular discipline or community in a number of interrelated ways. If you observe a large group of scientists speaking their special language, chances are you are in the middle of a scientific conference, where members of a scientific community gather to present and discuss their work face-toface. They also, as you might imagine engage in other social activities like eating and drinking and playing poker. Scientific conferences are usually organized by professional societies or associations. All the right people end of coming to a particular scientific conference because they are all members of the professional society that is sponsoring the conference. They are all on the society's mailing list and receive its newsletters, etc. Most physicists in this country belong to the American Physical Society (or APS). Most chemists belong to the American Chemical Society (or ACS). Many of these societies are subdivided into smaller units or divisions. So for example the APS has a Division of Nuclear Physics, a Division of Particle Physics, a Division of Plasma Physics, and others. Each of these divisions may organize their own specialized conferences attended by specialists working in for example, plasma physics. The subdivision of the discipline reaches even further down with topical workshops organized by members of a division who are working on a very specific problem or small set of problems. The workshop I will attend next summer is such a topical workshop.

scientific journals
Besides organizing conferences, another primary function of professional societies like the APS is to edit and publish scientific journals. Presentations at scientific conferences and publications in scientific journals are the two principal ways that scientists communicate their results to the rest of the community. And, just as there is a hierarchy of specialization within the membership of the society (nuclear physicists, particle physicists, plasma physicists, etc.) and in the organization of conferences, there is also a hierarchy of specialization within the set of journals read by members of the society. For example, the American Association for the Advancement of Science (AAAS), a society that includes all of the natural sciences, publishes a journal called Science. Science contains articles from a wide range of scientific disciplines, and is therefore rad by scientists from a wide range of disciplines. The American Physical Society publishes a journal titled Physical Review Letters, a journal that is widely read by physicists in many subspecialties. The APS also publishes a series of journals titled Physical Review A, Physical Review B, Physical Review C, Physical Review D, and, most creative of all, Physical Review E. Phys. Rev. A contains only articles on atomic, molecular and optical physics and is read almos exclusively by physicists working in the area of atomic, molecular and optical physics. Phys. Rev. B contains articles pertaining to condensed matter and materials physics and is read by researchers working in those areas. You get the point. For each level in the hierarchy of scientific disciplines there are professional societies that 1) organize conferences and 2) edit and publish journals or conference proceedings. They do other things like communicate scientific results to the public, advise governmental organizations on science policy, etc... but their primary function is to facilitate communication between their members. But the most frequent and most complete commuication occurs between members at the finest subdivision of the sciences... between scientists who are working on the very similar types of problems. I will very rarely read more than the title of a physics article in the area of particle physics or condensed matter physics. I will read abstracts of articles in most areas of plasma physics, but will read entire articles in only two or three narrowly defined research areas. There are just too many articles to assimilate if one let's his reading interest stray beyond what is immediately relavant to his own research.

the family tree of natural science

I have attempted to draw an oral sketch of the way scientists associate themselves with other scientists, how that association is facilitated by professional societies, and to how scientists communicate their work to each other. The image I would like you to hold in your mind is, like most hierarchical sketches, something like a tree. At the top we have all natural sciences, a representative society being the AAAS with its journal Science. One level down ar the major disciplines of the natural sciences.. with abbraviations given for a few representative societies and journals. I then break down the discipline of physics into some of its subdisciplines and the subdiscipline of plasma physics into some its primary research areas. You can imagine how the chart would be completed by breaking down each of the major disciplines into its subdisciplines and further into major areas of research. It is at the finest level of specializaton where the most complete communication occurs and where rapid progress is made because the members of the research area are so narrowly focused on an esoteric set of problems.

The image is very rough and can be misleading, for there are twigs of this tree that one could easily identify with two or more of its major branches. For example, on which branch of this tree should I place biochemistry or geophysics. These are more and more referred to as interdisciplinary fields. I will say more about them later. Despite the limitations of this way of viewing the way scientists are related through their professional associations and personal identifications, I think one can also view this chart as a crude representation of the historical origins of the various subdisciplines of chemistry, physics, etc. , as a family tree for scientific disciplines. In the late nineteenth century, there were few or no subfields of physics. Although physicists were working on a wide range of problems, many of which were the seeds for future subdisciplines, the community of physicists was both smaller and more unified. Over the course of the last century, the subdisciplines of atomic physics, nuclear physics, particle physics split off. So I think you can view this tree (again with some caution) as a depiction of the historical relations of these subfields to each other. Going further back into the nineteenth century the distinction between physicist and chemist was nonexistent.

distinguishing scientific from non-scientific academic communities
Much of what I have said about the sociology of science applies also to nonscientific disciplines ... to the community of scholars of romantic English poetry... to the community of economists ... to the community of scholars of American history ... etc. What is it that makes scientific communities different from other academic communities? This question bring us back to Thomas Kuhn. In Kuhn's view, what makes a community scientific is its almost universal acceptance of a single shared paradigm (or set of paradigms) ... an agreed upon world view (at least in so far as the subject of their communal professional interests go). In most social sciences (at least at the time Kuhn was writing) and especially in the creative arts and humanities, disciplines are characterized by competing schools of thought. The observation that nonscientific academic communities were characterized by severe disagreements over very fundamental issues that went to the heart of the communities subject of study, whereas scientific communities almost never engaged in this kind of debate, was critical to Kuhn's initial conception of a 'paradigm.' In the preface to Structure he writes,

" the Center for Advanced Studies in the Behavioral Sciences ... I was struck by the number and the extent of the overt disagreements between social scientists about the nature of legitimate scientific problems and methods ... Attempting to discover the source of [the] difference [between the natural and social sciences] led me to recognize the role in scientific research of what I have since called 'paradigms.' " -SSR, preface p.x

The existence of a universally accepted 'paradigm' within a given academic discipline is for Kuhn the criterion by which we should determine whether the discipline is scientific or not. Several key sentences from section II of Kuhn's essay illustrate the point:

"Men whose research is based on shared paradigms are committed to the same rules and standards for scientific practice. That commitment and the apparent consensus it produces are prerequisites for normal science... Acquisition of a paradigm and of the more esoteric type of research it permits is a sign of maturity in the development of any given scientific field." -SSR p. 11

"... and it remains an open question what parts of social science have yet acquired such paradigms at all." -SSR p. 15

"What is surprising, and perhaps also unique in its degree to the fields we call science, is that such initial divergences [competing schools] should ever largely disappear. For they do disappear to a very considerable extent and then apparently once and for all." -SSR p. 17

"Except with the advantage of hindsight, it is hard to find another criterion [other than the acquisition of a paradigm] that so clearly proclaims a field a science." -SSR p. 22
Scientific communities are unusually united in their view of their own discipline. They agree on what types of questions are worth asking and what constitutes an acceptable answer to a question. They even agree to a large extent on how to go about answering the questions. They share a common paradigm (or set of paradigms or disciplinary matrix). In disciplines of the social sciences, humanities and arts, there are frequently competing schools of thought ... adherents to competing paradigms. Exceptions to the rule that scientific communities are unified in the way described are scientific communities in crisis or dealing with anomalies ... communities ripe for revolution.

In light of Kuhn's view of science as inherently a social enterprise, you might want to think about how Kuhn would view Victor Frankenstein's status as scientist at various stages of Frankenstein's career. Can one be a scientist in Kuhn's view if you are working alone and not communicating your results to anyone else? I can imagine such a question would make a fine midterm exam question. Of course, now that I have tipped you off, and since your instructors are present as well... maybe you won't see that particular question... but it is still worth thinking about.

III. Biological evolution as an analog for the evolution of scientific knowledge and disciplines

How does my sketchy overview of the sociology of science help you to understand Thomas Kuhn's The Structure of Scientific Revolution? Let's look at the very last section of Structure... not the post-script, but Section XIII: Progress Through Revolutions, and read some of Kuhn's parting words from 1962. Probably none of you have yet read to the end of this book. I hope you are not offended by my giving away the ending, but after all you are not reading a Whodunnit, but rather an academic essay. On page 170, Kuhn writes,

"The developmental process [of scientific knowledge and disciplines] described in this essay has been a process of evolution [my emphasis] from [Kuhn's emphasis] primitive beginnings - a process whose successive stages are characterized by an increasingly detailed and refined understanding of nature." -SSR p. 170.

Kuhn asks us to view the development of scientific knowledge and disciplines as analogous to the development (i.e. evolution) of biological organisms. Darwin's evolution is to be a metaphor for how scientific disciplines emerge and adapt. Kuhn introduces this analogy in the very last section of the essay, in a section that he probably viewed as the most speculative and preliminary. It is also the section that contains the most serious implications for the philosophy of science and made this essay as influential and controversial as it has been for almost forty years. The reason for introducing the analogy is to reinforce his argument about what kind of scientific "progress" can occur over the course of a scientific revolution... do we step closer to ultimate Truth? I will return to this import issue briefly at the end of my lecture, but for the moment I would like to take Kuhn's evolution analogy and see how it plays out for the less controversial elements of his thesis. As Kuhn himself warns not two pages after he first introduces it that...

"The analogy that relates the evolution of organisms to the evolution of scientific ideas can easily be pushed too far." -SSR p. 172.

I will take my license to push this one a little further from Kuhn himself, who extended the evolution analogy in some of the ways I will lay out now. He did so in a lecture titled The Road Since Structure delivered in 1990.

scientific disciplines as species
If the scientific enterprise develops in a manner analogous to biological evolution, then what is it that corresponds to the concept of a species? After all the concept of species is central to biology and evolutionary theory purports to describe how species emerge and evolve. So let's step back and ask 'what are biological species?' A species a geographically and/or reproductively isolated population of organisms. A species maintains its identity due to its isolation. If members of a population frequently bred with members of another group ... the first population would soon lose its separate identity; it would be swallowed up or incorporated into the larger population with which it is mixing. My discussion of the sociology of scientific communities led to an image of a "family tree" for scientific disciplines. My intent was to prepare you for the suggestion that scientific disciplines (or communities) are the entities that correspond to species in the Darwinian analogy for scientific development.

How are scientific disciplines "isolated" in a manner analogous to the reproductive or geographic isolation of a biological species? In The Road Since Structure, Kuhn says,

"... the unit [i.e. species] is a community of intercommunicating specialists, a unit whose members share a lexicon [i.e. jargon] that provides the basis for both the conduct and the evaluation of their research and which simultaneously, by barring full communication with those outside the group, maintains their isolation from practitioners of other specialties." --Road Since Structure, p. 98

Members of a scientific discipline are isolated by their specialized language ... their jargon. They are isolated by the inability to easily communicate with members of other disciplines on matters that relate to their scientific work. Let me say it another way... a scientist can only engage in "intercourse" (in the sense of communication) easily with another member of his own discipline, just as an animal can only engage in "intercourse" (of the other kind) easily with another member of its own species.

interdisciplinary fields as hybrids
Of course it is not impossible for scientists from different disciplines to communicate and perhaps even accomplish something that neither of them could have done had they remained within their own communities. I am speaking of interdisciplinary research. In fact, it is a widely held opinion these days that the most interesting and promising avenues for scientific reserch lie at the boundaries between traditional disciplines ... in such areas as environmental science, materials science, biophysics, neuroscience, etc. the existence and success of interdisciplinary efforts within the world of scientific research does not make Kuhn's Darwinian metaphor less illuminating. Your reading of The Beak of the Finch surely informed you that biological species are not rigid entities. Not only do they evolve, but there are substantial variations with in a species, and they are not usually so rigidly isolated as we might think. Interbreeding between species regularly occurs as Peter and RoseMarie Grant observed on Daphne Major among the Galapogos finches. Usually the products of such hybrid matings are not likely to gain an advantage over members of the existing species. However such hybridization does occur and occasionally provides a fortuitous combination of traits that imparts an advantage to the products of that union. So the analogy we are developing can encompass the existence of interdisciplinary research. Interdisciplinary work represents hybridization. If the hybridization produces a successful offspring, a new discipline can be spawned. The field of biochemistry is such an example.

scientific revolutions as speciation events
Let's continue to extend the analogy. The title of Darwin's greatest work was Origin of Species. If the analogy holds, what, in the course of scientific development corresponds to the origin of species... or the origin of new scientific disciplines. What corresponds to "speciation?' I just mentioned one possible way new disciplines can arise ... through hybridization, or interdisciplinary "unions" between members of separate disciplines. But there is a more natural origin for new disciplines and that is the scientific revolution. In Kuhn's view a scientific revolution rearranges the concepts that form the foundation of the world view for members of the community experiencing it. After a revolutiuon, they view their discipline in an entirely different way. Kuhn suggests they are practicing a different discipline than they were before the revolution.

In addition, a revolution introduces new concepts, maybe even new elements of reality that are open to future investigation. For example, prior to about 1900 the atom was the fundamental consituent of matter. There were a fairly large number of atomic flavors, roughly 100, corresponding to the different chemical elements. Atoms of each element emitted and absorbed their own characteristic wavelengths of light. The atoms of different elements interacted with each other in different ways; they had different chemical properties. As a part of the revolution that brought quantum physics onto the scene in the early decades of the 20th century, the internal structure of the atom became a subject for investigation. The disciplines of nuclear physics and nuclear chemistry could not even have been imagined 25 years prior. The quantum revolution did indeed spawn new disciplines (and continues to do so). Scientific revolution are therefor represented by "speciation events" within the analogy.

scientific communities in crisis as extinction events
In recent decades the theory of evolution has been further "articulated" by members of the evolutionary biology community including people like the Grants, but traditionally work on evolution has come from the field of paleontology... 'fossil scholars'. As Jonathan Weiner points out in The Beak of the Finch, until the work of the Grants and their close colleagues, there was not much evidence of evolution in action. The earlier evidence was historical, provided in the form of subtle clues in the fossil record. One of the significant results obtained from the fossil record is that life on earth has sustained a fair number of mass extinctions over the course of its history. As Harvard paleontologist and prodigious author Stephen Jay Gould puts it in his book Wonderful Life,

"The history of life is not a continuum of development, but a record punctuated by brief, sometimes geologically instantaneous, episodes of mass extinction and subsequent diversification." --Wonderful Life p. 54

The most famous mass extinction was about 65 million years ago at the end of the Cretaceous Period when it is likely that a comet impact altered the earth's climate for a period long enough to whipe out many species including the dominant large animals of the day ... the dinosaurs. Notice however in the quotation from Professor Gould's book, that episodes of mass extinction are coupled to periods of subsequent diversification, i.e. speciation. I have already identified the scientific revolutions as a primary origin for new scientific disciplines. If the analogy holds, there is likely to be a corresponding extinction event prior to a major speciation event.

I think Tom Kuhn would not roll over too violently in his grave if I suggested that the period prior to a scientific revolution, the period of crisis that Kuhn describes in section VII of Structure is a time when the "environment" in which a scientific community is "living" begins to change. The old way of doing things does not work for the new problems that are emerging. Those who learn adopt a new (and successful paradigm) at the time of a revolution survive as members of a new discipline. Those who cannot adapt eventually die out. The world of science was struck by a 'comet' during the 17th century. The man most responsible for the impact was Isaac Newton. When the dust settled, the scientists who lived and worked under a paradigm going back to Aristotle, were extinct. There are no Aristotelian physicists around. They are the dinosaurs of the scientific world. They certainly ruled the earth a lot longer than their successors have so far. Your modern physicist bears a much stronger resemblance to his Newtonian ancestor than he does to the Aristotelian. The Newtonian physicist is perhaps the rodent who emerged from obscurity once the behemoths had died out. In another rendition of the metaphor, the Aristotelian is the Neandertal, a vaguely human creature, but from whom we are not directly descended, and the Newtonian physicist is represented by our true ancestor, Homo erectus.

normal science as microevolution / local adaptation

In Kuhn's view of scientific development, all of most scientists' lives are spent doing normal science. The normal scientific period is the period between revolutions, when there is nearly universal agreement within a scientific community about what kinds of problems are worth attacking and what techniques should be used to attack them. In this phase of the scientific enterprise, the paradigm (or disciplinary matrix) provides the big picture. It is important to realize that it does not immediately provide all the answers. There is substantial fine-tuning to be done to make the paradigm work in as many specific cases as it possibly can. There are also specific questions that the paradigm can in principle provide answers to, but that require substantial work to derive them from the paradigm.

The work I presented to you at the beginning of this lecture is surely, as Professor Peregrine suggested an example of normal science. I do not take offense that he did does not see the revolutionary aspects of my work, for in truth I do not think there are any. Answering the question of whether the observed oscillations are magnetron or diocotron in origin will not incite a revolution even among the very small community of nonneutral plasma physicists. In principle the answer to that type of question exists within the mathematical framework of nonneutral plasma physics theory. If I was smart enough, I could just do a calculation to get the answer. But in fact, the system is too complex to work out the answers to all such questions. Even though the fundamental physical principles are well-known and not expected to fail in this case, there are too many particles involved to calculate exactly what they will do. Approximations must be made and then justified on the basis of correct predictions for the outcome of real experimental measurements. This is classic normal science.

In the Darwinian analogy normal science corresponds to the kind of microevolution that RoseMarie and Peter Grant and their graduate students have been observing on Daphne Major. The Grants did not observe the origin of even one new species. Rather they saw existing species adapting to short term changes in their environment. The mechanism that drove this microevolution was the inherent variation that exists within any single species. If all members of a species were identical in all features, then the species would be extremely vulnerable to even minor changes in the environment. As it is, when the environment changes, there are usually members of the species who are better suited to survive under the new conditions. The offspring of those individuals tend to be more numerous and better able to compete for resources than the offspring of other members of the species. The analogy to periods of normal scientific activity are crude, but fit pretty well. During periods of normal science, members of a given discipline adapt the paradigm theory to fit observation in as many specific cases as possible. The outcome of that work is a better articulated paradigm... one that works better in a wider range phenomena. During periods of normal science, the paradigm evolves in a smooth way, in a way analogous to the minor adaptations of species to short term changes in the environment.

At this point let me offer a summary of the Darwinian analogy for Thomas Kuhn's view of scientific development:
Summary of the Darwinian analogy for scientific development:

scientific communities/disciplines <---> species
linguistic isolation <--> reproductive or geographic isolation
interdisdiscplinary fields <---> hybrids
scientific revolutions <---> speciation events
scientific communities in crisis <---> extinction events
emergence of a dominant paradigm <---> survival of the fittest
normal science <---> adaptation or microevolution

The close match that this analogy seems to provide leads me to wonder why Kuhn chose for the title of his essay... The Structure of Scientific Revolutions, when a more appropriate title would seem to be ... The Structure of Scientific (r)Evolution(s).

how the analogy is circular

It is important to keep Kuhn's warning in mind... that the analogy (probably any analogy) can easily be pushed too far. Maybe I have already done so. There is a curious way in which this metaphor is circular: Darwin's theory of evolution is a scientific paradigm of the kind Kuhn's framework seeks to explain. In Kuhn's view of scientific development, it is perhaps only a matter of time before Darwin's theory is replaced through a revolutionary event. Darwinian evolution then becomes an "extinct" scientific theory that presumably still functions as a good metaphor for continued scientific development.

Brian Greene used a similarly flawed analogy in his convocation address. He made use of he image of a stratched rubber sheet with a bowling ball placed on it gives a sense of how matter distorts space in its vicinity, according to Einstein's general relativity. But that distortion of space is gravity in the general relativistic description, and gravity is necessary to the metaphor... without it the bowling ball would not distort the rubber sheet.

Having paid heed to the warning, let us push on ...

IV. Kuhn's view of scientific progress and his influence
scientific development is contingent
Where does this analogy lead? Let's allow it to lead us back to Kuhn's original intention when he introduced the metaphor. Recall the quotation from section XIII:

"The developmental process [of scientific knowledge and disciplines] described in this essay has been a process of evolution [my emphasis] from [Kuhn's emphasis] primitive beginnings - a process whose successive stages are characterized by an increasingly detailed and refined understanding of nature." -SSR p. 170.

The next sentence on page 170 is ...

"...But nothing that has been or will be said makes it a process of evolution [my emphasis] toward anything." -SSR p.170.

This is why Kuhn introduces the analogy, because he sees scientific development as a process with profound historical/social influences. He knows that science is a human social enterprise and being so means it is subject to many of the same kinds of influences that affect the development of other human social enterprises. This is his most controversial point. Also from page 170:

"We may have to relinquish the notion, explicit or implicit, that changes of paradigm carry scientists and those who learn from them closer and closer to the truth." -SSR p.170

In Kuhn's description, the worldview that emerges from a period of crisis in a scientific community ... the result of a revolution ... is strongly influenced by factors other than whether the new paradigm is the truest one in any objective sense. Kuhn sees no reason to believe that the progress of science is one which brings humanity closer to an understanding of an objective Reality. His evidence for this view is built up throughout the essay and includes examples of influences such as aesthetics upon the choice of a new paradigm theory. I do not have time here to review his argument any more completely than I just did. It is, I think, the climax of his argument, and is built upon the foundation of the entire work. There is plenty of grist here for the millstone of your discussions in your individual sections.

I warn you though, if you and your classmates set off down the path of pursuing objective truth, it is a long and deep sojourn underground and no one has yet emerged on the other side. Many of us continue to believe that there is a promised land on the other side, a land of eternal truth. Meanwhile we wait for an enlightened philosopher, a Platonic Moses to lead us there.

Although I cannot summarize Kuhn's argument here, I will pursue how it relates to his introduction of the Darwinian metaphor. Kuhn introduces the Darwinian metaphor to illustrate his view that the process of scientific development is contingent upon non-scientific influences, influences that arise from the social context in which science is practiced.

"All the well-known pre-Darwinian evolutionary theories ... had taken evolution to be a goal-directed process. The 'idea' of man and of the contemporary flora and fauna was thought to have been present from the first creation of life, perhaps in the mind of God... [Darwin's work,] Origin of Species recognized no goal set either by God or nature. Instead, natural selection, operating in the given environment and with the actual organisms presently at hand, was responsible for the gradual but steady emergence of more elaborate, further articulated, and vastly more specialized organisms." -SSR p.171

In the book I quoted earlier, Wonderful Life, Stephen Jay Gould emphasizes the profound extent to which the detailed progress of biological evolution is historically contingent, that if we were to rewind the tape and start evolution over again from very nearly the same initial conditions, the likelihood that any creature remotely similar to homo sapiens would emerge is vanishingly small. The principle of contingency is one historians must run up against daily. Change one small detail of the past and what followed would have been entirely different. The title of Gould's book is at once a reference to the author's state of awe at the natural world and a reference to the famous film, starring Jimmy Stewart. In that film, the main character, George Bailey gets to see how things might have been different in his hometown of Bedford Falls had he never existed. Another, more recent, popular film, Back to the Future also explores the idea of historical contingency. Marty McFly goes back in time to witness events surrounding his parents courtship. Of course his presence in the past has the potential to influence his own existence in the future. It makes great entertainment, and I suppose is part of the fascination historians have with their field.

As a physicist I would say that the flow of history is extremely sensitive to initial conditions. Here then is the reason for the metaphor Kuhn introduces. He suggests that the particular scientific theories that emerge from a revolution are contingent upon many details of the scientific communities experiencing them. At least some of the significant influences are in no way connected to the goal of moving toward an objective truth. Using the Darwinian metaphor, Kuhn says,

"... the resolution of revolutions is the selection by conflict within the scientific community of the fittest way to pratice further science... And the entire process may have occurred, as we now suppose biological evolution did, without benefit of a set goal, a permanent fixed scientific truth ..." -SSR p. 172

Unlike the global communist revolution that Marx believed was inevitable, the outcome of scientific revolutions is in Kuhn's view far from predetermined.

This is controversial stuff. Especially if you are a scientist who has dedicated her professional life to the pursuit of objective truth. I think it is fair to say that most scientists in almost all disciplines are realists, that is they believe there is an objective reality out there and that their work makes contact with that reality somehow. That view of the cumulative achievements of science permeates much of our larger culture. Here is Jonathan Weiner, on page 286 of The Beak of the Finch,

"Science formalizes our special kind of collective memory, or species memory, in which each generation builds on what has been learned by those that came before, following in each other's footsteps, standing on each other's shoulders." -The Beak of the Finch, p. 286

And here is Brian Greene from his book, The Elegant Universe,

" proceeds along a zig-zag path toward what we hope will be ultimate truth, a path that began with humanity's earliest attempts to fathom the cosmos and whose end we cannot predict." -The Elegant Universe, p. 20

And here is Steven Weinberg, a Nobel-prize-winning physicist and sometime spokesman for the discipline of physics itself, from an article that appeared in the New York Review, an article in which he voices his opposition to Kuhn's view of scientific progress,

"...for me as a physicist the laws of nature are real in the same sense (whatever that is) as the rocks on the ground... I know that it is terribly hard to say precisely what we mean by 'real' and 'true.' That is why... I added in parantheses 'whatever that is.' I respect the efforts of philosophers to clarify these concepts..." -Steven Weinberg, The NY Review, Oct. 8, 1998.

Although he realizes he is out of his depth when entering the philosophical arena, Weinberg makes his personal views known, views that I daresay resonate with many scientists,

"Kuhn's view of scientific progress would leave us with a mystery: Why does anyone bother? If one scientific theory is only better than another in its ability to solve the problems that happen to be on our minds today, then why not save ourselves a lot trouble by putting these problems out of our minds? ... What drives us onward in the work of science is precisely the sense that there are truths out there to be discovered, truths that once discovered will form a permanent part of human knowledge." --Steven Weinberg, The NY Review, Oct. 9, 1998.

At the same time, some of these same scientists readily admit that there are non-scientific influences, particularly aesthetic ones, on the choice of scientific theories. In admitting so, they are providing ammunition to the Kuhnians. Here is Brian Greene again,

"It is certainly the case that some decisions made by theoretical physicists are founded upon an aesthetic sense -- a sense of which theories have an elegance and beauty of structure on a par with the world we experience. Of course, nothing ensures that this strategy leads to truth." --The Elegant Universe p.167

And here is Steven Weinberg again, from the same New York Review article,

"Any set of data can be fit by many different theories. In deciding among thsese theories we have to judge which ones have the kind of elegance and consistency that make them worth taking seriously." -Steven Weinberg, The NY Review Oct. 8, 1998.

So Kuhn's point is that the scientists present at the time when a new paradigm is being chosen do not necessarily have as their one and only guide ... some objective, ultimate truth. The paradigm that emerges is one with strong historical influences in the same way that the species that emerge as successful from a period of rapid speciation (perhaps following a mass extinction) have their origins in species that existed formerly. Nature does not have access to all possible biological design plans at the time of speciation. Nature had to work with what she had on hand. In the same way, a scientific community in a time of crisis does not have access to all possible theories from which to choose. Inevitably, as many of the old concepts will be preserved as is possible. Others will be modified as little as need be to solve the crisis problems. Does this get us closer to ultimate truth? If I believed in such things, I would have us hold a seance in which we could summon the spirit of Plato and ask his guidance in this matter. I don't know if any one else can help us here. Plato?? Are you out there?




Gould, Stephen Jay, Wonderful Life, Norton (1990).

Greene, Brian, The Elegant Universe, Vintage Books (2000).

Kuhn, Thomas S., The Structure of Scientific Revolutions, 3rd edition, University of Chicago Press (1962).

Kuhn, Thomas S. ed. by J. Haugeland and J. Conant,The Road Since Structure, Universty of Chicago Press (2000).

Weinberg, Steven, The Revolution That Didn't Happen, The New York Review (8 October 1998).

Weiner, Jonathan, The Beak of the Finch, Vintage Books (1994).