Update on Popper

Popper is often perceived as an eccentric kind of positivist who adopted a slightly different take on the demarcation of science with the criterion of falsification in place of verification. People like Habermas and the late Richard Rorty regarded Popper as a positivist for all practical purposes.

That view does not do justice to the full extent of  Popper’s program, starting with the first step which can be described as a full-blooded “conjectural turn”, to claim that even our best theories may be rendered problematic by new evidence, new criticisms and new theories. This anticipated the “hermeneutic turn” when appreciation of the theory-dependence and framework-dependence of observations and arguments became more widespread in the wake of Kuhn and the modern French theorists.

Consequently to understand Popper it is necessary to take on board the “conjectural turn” which dates from 1935 with the original German version of The Logic of  Scientific Discovery and some other moves as well. These include the “objectivist turn” to break with the obsession with the justification of beliefs and instead to focus on the strengths and weaknesses of  theories that are stated in a public, inter-subjective or “objective” form. Then there is Popper’s “social turn” to examine the function of institutions, traditions, conventions and “rules of the game” in science and society. this has been spelled out by Ian Jarvie. And finally the “metaphysical turn” to recognse the pervasive influence of  philosophical or metaphsical ideas which are the framework assumptions or presuppositions of  thought.

It will help to explain more about each of these “turns”, starting with the turn to conjectural objective knowledge. In traditional epistemology the central concern was (and remains) the justification of beliefs . In “Epistemology without a knowing subject” Popper wrote

This 1 has led students of epistemology into irrelevancies: while intending to study scientific knowledge, they studied in fact something which is of no relevance to scientific knowledge. For scientific knowledge simply is not knowledge in the sense of the ordinary usage of the words ‘I know’.  While knowledge in the senses of ‘I know’ belongs to what I call the ‘second world’, the world of subjects, scientific knowledge belongs to the third world, to the world of objective theories, objective problems and objective arguments…Thus my first thesis is that the traditional epistemology, of Locke, Berkeley, Hume, and even of Russell, is irrelevant, in a pretty strict sense of the word. It is a corollary of this thesis that a large part of contemporary epistemology is irrelevant also.” (Popper, 1972, p.108).

In the course of explaining Popper’s turn from “justificationism” to critical rationalism, Bartley pointed out that all attempts to justify beliefs end up in an infinite regress. The alternative to the quest for justified beliefs is to form tentative critical preferences for theories (or policies) on the basis of their capacity to solve their problems and stand up to various forms of criticism, including experimental and practical tests.

Moving on to the “social turn”. The discovery of the social factor in science is often attributed to Kuhn and the sociologists of knowledge, however Jarvie identified what he called the social turn in Popper’s earliest published work, and especially in the chapter on the sociology of  knowledge in The Open Society. In the way that Hayek wrote about the constitution of liberty, Jarvie found in The Logic of Scientific Discovery the framework for a “constitution for science”, that is, a set of conventions or rules to ensure that theories are exposed to criticism, especially empirical tests. Popper’s focus on the institutional framework of science is explicit in the chapter on the sociology of knowledge in The Open Society and its Enemies and in the final sections of The Poverty of Historicism on situational logic and the institutional theory of progress.

Finally, the little-noticed metaphysical turn, possibly the most striking difference between the later Popper and the original logical positivists, whose signature idea was to render all talk of metaphysics strictly meaningless. Popper briefly mentioned the theory of metaphysical research programs in the autobiography written for the Library of Living Philosophers (Popper 1974, and 1976) but it was several years before it appeared in more detail in the Metaphysical Epilogue to the third volume of The Postscript to the Logic of Scientific Discovery.

The three books of the “Postscript” are “Realism and the Aim of Science”  (Volume 1), “The Open Universe: An Argument for Indeterminism” (Volume 2) and “Quantum Theory and the Schism in Physics” (Volume 3). They contribute to Popper’s long campaign in support of realism, indeterminism and objectivism which in turn support human freedom, creativity and rationality.

“Realism” has two parts, the first pursues various forms of inductivism and the second attacks the subjective interpretation of the probability calculus. “The Open Universe” critiques both scientific and metaphysical determinism and traces the linkage between metaphysical determinism and subjective probability theory. This volume carries the defence of realism and objectivism into the heart of quantum theory to challenge the dominant assumptions of the Copenhagen interpretation. Bartley points out in the editor’s introduction that this is a profoundly cosmological work, where “the basic theme of Karl Popper’s philosophy – that something can come from nothing – obtains its basis in physics”.

The book contains a ‘Metaphysical Epilogue’ that is remarkable (in addition to being the basis of Lakatos’s theory of scientific research programmes) because it provides a key to understanding a set of themes that unify Popper’s whole system of thought (the keystone to his arch of thought it you like). This gives some clues as to the depth of his thinking and the reason why it has been so badly received in the profession at large.

Popper’s theory of MRPs flows from his theory that we should look at the history of a subject, and its current status, in terms of its problem situations.

In science, problem situations are the result, as a rule, of three factors. One is the discovery of an inconsistency within the ruling theory. A second is the discovery of an inconsistency between theory and experiment – the experimental falsification of the theory. The third, and perhaps the most important one, is the relation between the theory and what may be called the “metaphysical research programme.

By raising the problems of explanation which the theory is designed to solve, the metaphysical research programme makes it possible to judge the success of the theory as an explanation. On the other hand, the critical discussion of the theory and its results may lead to a change in the research programme (usually an unconscious change, as the programme is often held unconsciously, and taken for granted), or to its replacement by another programme. These programmes are only occasionally discussed as such: more often, they are implicit in the theories and in the attitudes and judgements of the scientists.

I call these research programmes “metaphysical” also because they result from general views of the structure of the world and, at the same time, from general views of the problem situation in physical cosmology. I call them “research programmes” because they incorporate, together with a view of what the most pressing problems are, a general idea of what a satisfactory solution of these problems would look like.

The theme of the book is the way that the Copenhagen interpretation of quantum physics has been influenced by unstated and uncriticised metaphysical assumptions, especially determinism, subjectivism and instrumentalism. Of course the Copenhagen people are scientific indeterminists but Popper argues that there is a metaphysical form of determinism that they have not eliminated from their thinking.

The book contains four chapters after a 1982 Preface and an Introduction. The Preface makes a case for a realistic and commonsense interpretation of quantum theory to overcome the crisis in physics which Popper attributes to two things, the intrusion of subjectivism and the “end of the road” idea that quantum theory has reached the complete and final truth. In the Introduction he argues for an interpretation of quantum physics without the observer and he sharply formulated thirteen thesis to challenge the Copenhagen interpretation of the observer as an integral part of the system.

In Chapter I, ‘Understanding quantum theory and its interpretations’ Popper updated his ideas from the formulations in “The Logic of Scientific Discovery”. He still maintained that the problem of interpreting quantum theory is bound up with the interpretation of probability theory, and he argued that the theory of propensities that he described in the first and second volumes of The Postscript should be applied to the interpretation of quantum theory, thus resolving the difficulties that arise in the Copenhagen interpretation.

Chapter II ‘The objectivity of qauntum theory’ returned to the issue of the observer in the system and confronted the doctrine that experiments have to be interpreted with the observer, and especially the consciousness of the observer, as one of the variables. The discussion includes the nature of quantum jumps and the existence or non-existence of particles.

Chapter III attempts a resolution of the paradoxes of quantum theory, using the propensity interpretation of probability, applied to (1) the indeterminacy relations, (2) the expirement of Einstein, Podolsky and Rosen, and (3) the two-slit experiment.

The long fourth chapter is the Metaphysical Epilogue. This covers a lot of ground, starting with a brief statement of the theory of metaphysical research programs (above). He then ran through a series of ten research programs. First the block universe of Parmenides, then Atomism and Geometrization, followed by Essentialism and Potentialism (from Aristotle), then Renaissance Physics (Copernicus, Bruno, Kepler, Galileo), The Clockwork Theory (Hobbes, Descartes), Dynamism (Newton), Fields of Force (Faraday, Maxwell), Unified Field Theory (Riemann, Einstein, Schrodinger) and finally The Statistical Interpretation of Quantum Theory. After a discussion of schism, programs and metaphysical dreams he went on to indeterminism and the reduction of the wave packet and a model of a universe of propensities to account for the leading featues of all the ten programs that he sketched previously. After touching on some open problems he concluded with some comments on the role of metaphysical systems and the possibility of a demarcation within metaphysics, between good and bad systems.

The proper aspiration of a metaphysician…is to gather all the true aspects of the world (and not merely its scientific aspects) into a unifying picture which may enlighten him and others, and which may one day become part of a still more comprehensive picture, a better picture, a truer picture.

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13 years ago


I’ve no idea why you think Popper’s criticism of the Copenhagen interpretation is anything like Popper’s work that you would want to remember. It seems to me that Popper did exactly Einstein did, and spend a whole lot of effort finding out that Quantum physics is here to stay until something really spectacular comes along. Now, as it happens, it seems reasonable to believe that at least Einstein was looking for solutions in places you might have found it, but Popper certainly wasn’t.

In addition, maybe I’m misreading history, but I also don’t think this has ever been generally accepted either:”The Preface makes a case for a realistic and commonsense interpretation of quantum theory to overcome the crisis in physics which Popper attributes to two things, the intrusion of subjectivism and the “end of the road” idea that quantum theory has reached the complete and final truth.:

There’s always been a tension between different streams of physics because they don’t predict an overlapping set of things (and Quantum theory especially, because some of the predictions are so odd). That’s why people have been trying to find a unified theory ever since Quantum theory came along. I don’t think there’s ever been a time when there has been a consensus that quantum theory is the complete and final truth.

This of course leads us to String Theory, which I know we’ve argued about before, and you can dislike it as much as you want. But think of it this way — at least the people thinking about it are trying to find a solution, rather than it just being criticism.

13 years ago


My argument isn’t about whether this particular aspect of Popper’s work was good or not — indeed I quite like a lot of Popper’s stuff on science — and I certainly agree that he was and still is influential in the way many people think about science in general. I’m just not sure why you are highlighting what hasn’t survived through time. It seems to me that in 100 years from now, people will still be thinking about the types of data that is it best to test models with, how models can be tested against each other, how parts of models can be evaluated, and so on. These are generally important issues and always will be. Alternatively, I doubt they’ll be talking about this one particular argument against Quantum Physics which turned out to be wrong — there are thousands of people that have come up with one or two really good experiments or arguments, but the only ones we celebrate are those that got it right. Thus it isn’t going to represent what is best about Popper.

13 years ago

I think that Conjectures and Refutations is really a classic (and will remain so into the future) for two reasons. First, it’s basically proposing a way that people should be doing science which is still relevant in many but not all areas for a reasonable part of the scientific process (I wish all of our students would read it before doing their PhDs!). I think that if you want to move on from abduction, which is how many naive scientists work, it’s really a super start. The second reason I like it, which I don’t think is as important, is that it led to later work that allowed people to question how to evaluate models and indeed what models are. At least in the social sciences, I don’t think many people think hard enough about these questions, and so you end up with a profileration of models tested in ways that are not necessarily of interest to the main question.

13 years ago


The problem with discussing Popper and Quantum Mechanics is that his experiment has actually been carried out and the results agree with quantum mechanics. They also agree with EPR and Popper.

However, there are two flaws:-

1. is that Poppers formulation of the problem is subtly wrong (as is EPR’s). It confuses a single particle state with a dual particle state. There’s a good discussion of this in the last two sections of the paper (it’s only 6 pages long in all and is a very accessible read).

2. arguing against the Copenhagen Interpretation (or any interpretation) is a bit pointless and sterile. It’s only an interpretation, it doesn’t change the formulation of the theory, and there is no known experiment that can choose between different interpretations. Most people either accept the Copenhagen Interpretation by default – because they don’t otherwise care and the interpretation doesn’t affect results – or they don’t worry about interpretation at all (the “shut up and calculate” approach). There’s a good discussion at the wiki where it is carefully pointed out that Popper’s premise that his experiment could disprove the Copenhagen interpretation is false. It can’t and it doesn’t

In short, Popper proposes that his experiment should show that the Copenhagen interpretation implies that the second particle should acquire more uncertainty in its momentum. Firstly, Quantum Mechanics doesn’t say that and secondly the Copenhagen Interpretation doesn’t change the formulation of QM so it can’t affect the results of the theory.

That Einstein, Bohr and Schoedinger discussed this with Popper doesn’t really surprise me. This is a foundational issue much discussed at the time, and BTW Bohr and Einstein were on different sides of the fence with Schroedinger somewhere in the middle. (Schoedingers didn’t actually fully accept the conclusions of quantum mechanics himself despite being a principal architect of it. His famous cat was actually a thought experiment he proposed as a means of saying “Are you sure you want to believe Bohr’s nonsense? This is the sort of absurd conclusion it leads to”). But I did notice that Bartley in his review complains that physicists never paid much attention to Popper at the time anyway.

Also his objection to “the observer” is wrong-headed. He – like most pop science books – assumes that the observer is conscious. That’s not true. Any observation, any measurement – even if only interaction with a single other particle – creates an observation and “an observer”. The observer of a photon can therefore be a single particle or atom that absorbs it. He seems to be attacking the strawman of pop-science rather than any actual viewpoint held by physicists.

Physicists have ignored Popper because his viewpoint is incorrect (but it gets discussed because it’s quite similar to EPR and comes close to involving entanglement which is a hot topic these days)

And Bartley’s description of Popper’s views on entropy is incoherent, I don’t understand it at all. If it’s an accurate representation of Popper’s thoughts I’d have to say that Popper was an example of a philosopher confusing himself with the inadequacies of natural language. Physics uses maths to avoid that sort of thing, and has successfully thrashed out this whole entropy/information thing in enormous detail over the last several decades.

Lastly, Poppers example of a stone dropping into a placid lake “independent of any entropy increase” is just bizzare. Of course there’s been an increase in entropy. (BTW – on the subject of irreversibility, the arrow of time has been getting a bit of a workout lately, there was a paper a few weeks ago pointing out that quantum physics shows that if there are processes that go backwards in time we would never experience them as they would not impinge on our universe. While this is an insightful result, it doesn’t appear to be particularly controversial.)

I don’t think Popper’s somewhat obsolete views have much to offer anymore on these subjects.

13 years ago

Thanks JM, does that mean that Einstein’s views don’t have much to offer anymore?

Of course Popper will be remembered, if at all, as a philosopher, and I think that the varous “turns” that he offered are robust and helpful and put him the short list of great philosophers of the 20th century in the way that Einstein is on the short list of scientists.

13 years ago

Time doesn’t come into it, science isn’t fashion. Einstein’s ideas are proven, Popper’s aren’t – and they were wrong in the first place.

He was initially greatly embarrassed back in the ’30’s when Einstein pointed out a bone-headed error in a paper he had submitted, and his “pond paradox” is completely dumb and absolutely wrong.

As a philosopher I’d agree with you. Except perhaps to note that many scientists don’t recognize their working methods in his ideas of falsification as the be-all and end-all.

Verification, explanatory power and coherence with existing knowledge and observation is much more important. As a recent example of that consider the Steady State theory (which held that the universe had no beginning) and the Big Bang (which says that it does).

Steady State was never actually falsified it just became redundant and was abandoned under a mountain of verifying evidence for the Big Bang and the utility and explanatory power of the Big Bang in explaining features of the current universe became overwhelming.

But the claims for him as some sort of latter day Leonardo with significant contributions in a wide number of fields are really too much. He made “contributions” yes, but they weren’t right let alone influential or significant. The fanboys overstate the case.


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