Heisenberg on physics and philosophy

Physics and Philosophy
by Werner Heisenberg (1958)

Werner Heisenberg was one of the founders of quantum mechanics and an exponent of its Copenhagen interpretation.  In this collection of essays, he tries to place the quantum revolution in a wider philosophical context.  Mostly, it is a story of prior philosophies having been proven inadequate, although interestingly enough, Heisenberg explicitly connects aspects of quantum states to the Aristotelian concept of potency.  The Copenhagen interpretation of quantum mechanics, to which Heisenberg subscribes in this book, has been subject to two well-known criticisms.  First, we can only make sense of quantum mechanics as giving us probabilities for given observations by measuring devices assumed to be classical objects, and the existence of a non-quantum realm is an embarrassment if quantum theory is to be regarded as fundamental.  Second, it can appear to eschew ontology altogether, to be not an interpretation of quantum mechanics but a positivistic reduction of it.  To the first criticism, Heisenberg says that what distinguishes measuring devices is that they are not isolated, but interact with the outside world in countless messy ways, and these random environmental couplings somehow produce classical behavior.  Physicists are still pursuing this idea; I suspect there’s something to it but am not yet sold on it.

More interesting is the quasi-Kantian framework in which Heisenberg places the Copenhagen interpretation.  The math terminates on classical measuring devices primarily because classical physics describes core categories of the human mind that we need to make any sense of phenomena.  Heisenberg is slightly more optimistic than Kant; we can get past the phenomena structured around our concepts to gain some knowledge of realms where deterministic causality, Euclidean geometry, etc break down, but this knowledge will always be mediated by the classical realm; the latter can never be entirely swept aside because of the kind of beings we are.  We can learn that our classical ideas of space, time, matter, and causality break down–although a general lesson is that we can’t predict ahead of time where one of our concepts will break down–but we still need them.  In the subatomic realm, we have the wave picture and the particle picture, each of which works in some regime and breaks down in others, but both of which are at least genuine ontologies.  On the other hand, there is the full mathematical machinery of quantum mechanics, which never breaks down (so far as we know) but fails to provide an ontology.

This is something Heisenberg thinks we must learn to live with, but something which may actually be a blessing.  As he understands it, the ultimate consequence of his great work has been to overthrow 19th century materialism.  He sees alternate interpretations, such as that of Bohm, as desperate and mathematically unnatural attempts to rescue the old materialistic ontologies.  No longer should we place blind trust in mathematically precise expressions of materialistic concepts.  These have a range of validity, but it is limited and not to be categorically preferred to the natural intuitions of the human mind.  As he writes

Furthermore, one of the most important features of the development and the analysis of modern physics is the experience that the concepts of natural language, vaguely defined as they are, seem to be more stable in the expansion of knowledge than the precise terms of scientific language, derived as an idealization from only limited groups of phenomena.  This is in fact not surprising since the concepts of natural language are formed by the immediate connection with reality; they represent reality.

our attitude toward concepts like mind or the human soul or life or God will be different from that of the nineteenth century, because these concepts belong to the natural language and have therefore immediate connection with reality.  It is true that we will also realize that these concepts are not well defined in the scientific sense and that their application may lead to various contradictions, for the time being we may have to take the concepts, unanalyzed as they are; but still we know that they touch reality.  It may be useful in this connection to remember that even in the most precise part of science, in mathematics, we cannot avoid using concepts that involve contradictions.

The general trend of human thinking in the nineteenth century had been toward an increasing confidence in the scientific method and in precise rational terms, and had led to a general skepticism with regard to those concepts of natural language which do not fit into the closed frame of scientific thought–for instance, those of religion.  Modern physics has in many ways increased this skepticism; but it has at the same time turned it against the overestimation of precise scientific concepts, against a too-optimistic view on progress in general, and finally against skepticism itself.

My copy has a fascinating afterward called “Science and Religion” in which Heisenberg reminisces on two conversations he had on religion with other physicists.  It seems that Wolfgang Pauli and Niels Bohr also entertained hopes that the principle of complementarity would provide grounds for a rapprochement between religion and science, or at least an ease of tensions.  Perhaps science does not provide a complete picture of reality because such a picture does not exist (at least for minds like ours), and perhaps religions speak in myths and parables not because they are false but because there are truths that can be expressed in no other way.  Perhaps there are even resources here for wider rapprochements between rival religions and philosophies.

There is certainly some irony here.  Heisenberg, a Lutheran Christian, thought he had dealt the death blow to 19th century materialism, just as Rene Descartes thought he had dealt the death blow to 17th century materialism.  Needless to say, materialism is still going strong–stronger than ever–despite the brilliance of its opponents.  In the case of Bohr and Heisenberg, even the memory that they ever saw their work in terms other than those of scientistic triumphalism has been largely forgotten.

23 thoughts on “Heisenberg on physics and philosophy

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  3. “Needless to say, materialism is still going strong–stronger than ever–despite the brilliance of its opponents.”
    Is it, though?
    Neo-paganism, both in its prog, SJW and alt-rightist incarnations, is rising, and progs have long been enamoured of New Age and quasi-Eastern pseudospiritual inclinations; and they have their own liberal mainline Christian and Jewish denominations, etc. Then there’s promotion of the concept of extraterrestrials, UFOs, etc., often in posters with the unintentional truth uttered, ‘I want to believe’… So they do.
    I’m not so sure materialism is anywhere near as strong as it appears. Sure, there is an official commitment of sorts to it as the party line, with which all GoodThinkers(TM) use to take swings at Christianity, especially against creationism, heterosexual ‘privileging’, etc. But it seems to me that the commitment to materialism is only skin-deep, and that the religious instinct, which all have but many self-delude into thinking they lack, is wholly present, manifesting itself in a variety of different forms.

  4. Oh and Bonald, it is good to see you posting on here again. Thanks for this stimulating article. It is refreshing to be reminded that many of the truly great minds of the last century were far more receptive to the notion of a Grounding Being than so many of the self-regarding mental pygmies that nowadays succeed them.

  5. We need to ask, firstly, is the physical world real? Heisenberg described the quantum world, of which everything else in the physical world is constituted, as existing somewhere in between possibility and actuality, did he not? I seem to remember that Bohr himself went so far as to say that there is no quantum world.

    The second thing we need to ask is what the heck is this actual, active, corporeal world our senses are perceiving and which is apparently consequent upon state vector collapse of the (potential) physical one?

    Even our instrumental measurement of quantum phenomena is ultimately an act of sensory perception as we perceive the movement of a dial or other device.

    I’m not asserting that our perceptions are merely mental exercises, with no real connection to extra-conscious reality, but suggesting that we haven’t even begun to comprehend what that reality, or actuality, is, so blinded have we been by reductionist materialism and the achievements of physics. Aristotle, perhaps because there were so few trees in the way of the wood, seemed to have a closer insight to the truth than we moderns.

    • Aye. The subcreative phase of creation proceeds by creaturely measurements (or registrations or prehensions or apprehensions or perceptions or sensations) of other creatures (and of God). These register previous vector state collapses in their actual past – that, as actual, have resulted in classical objects – and then themselves result in novel classical objects: new concrete facts (which, in the case of mundane creatures, are generally corporeal (in this world; in (at least some of) the Heavens, the resulting creatures are merely spiritual). Some result in the factual, objective, observable character of instruments. Some result in the factual, objective, observable character of persons, such as physicists.

      Bit : It :: Formal Potentiality : Concrete Actuality.

      The Copenhagen interpretation of quantum [mechanics is subject to a criticism:] we can only make sense of quantum mechanics as giving us probabilities for given observations by measuring devices assumed to be classical objects, and the existence of a non-quantum realm is an embarrassment if quantum theory is to be regarded as fundamental.

      The embarrassment vanishes when we recall that at the moment of the act of vector state collapse measured, the measuring device that performs its act of measurement of that collapse does not itself yet exist actually – i.e., classically. Rather, at that point, only *the past* of that classical measuring device – its history of differentiable, ergo distinct states – yet actually exists. The state of the classical measuring device in which its measurement of the quantum state collapse occurs does not itself become actual, factual, i.e., classical, and thus observable to the scientist, until as a completed act of measurement it is itself in the actual past of some subsequent event – whether in its own career, or in that of some other (such as that of some scientist who measures the latest state of the classical measuring device, thereby collapsing the state vectors of the measuring device and rendering it classical, and factual, and causally influential (to him, if to no one else)).

      It has always mystified me that this has mystified quantum theorists. Until he opens the box, the scientist does not know whether Schrödinger’s cat is dead. But the particles of the box know. The poison molecules know. The molecules that used to form part of a living cat all know. Where’s the mystery? Only in us, who, having not yet opened the box, do not yet know.

      This is why the Copenhagen Interpretation is rightly interpreted as an epistemological theory, rather than an ontological theory. As Bohr carefully and repeatedly insisted, it is not about what is happening, but about how much we can know about what is happening. It is about the information that we now have about what is now happening, and that – as still happening, and therefore not yet definite, not yet completely specified or therefore specifiable (which is to say, knowable) – we cannot yet know about definitively, but rather at most only probabilistically.

      • Kristor, in those last two paragraphs, are you saying that when Bohr asserts that ‘there is no quantum world’ he means this in the sense of what we know or can know about it, rather than in the sense of what is really happening, but beyond our facility to know it?

        Are you also saying that, in a measurement, the quantum world is causing an effect upon the measuring device which changes the latter, thus producing a ‘new’ measuring device and that this is the moment of interface between the quantum and corporeal worlds, there being thus no ’embarrassment’ to speak of?

      • I always took Bohr to mean something stronger. The reason we can’t know about the quantum realm is that, as Heisenberg suggests, it is not actual, but rather only formal – which is to say, that it is a world of potentialities. We can know something about formal potentialities (as we know about any maths), but we can’t nail down which of them is certainly going to cook out of the potentialities into actuality. We can’t nail that down until after the cooking has taken place.

        This all sounds Platonic because it is. It sounds Aristotelian because it is. It sounds Whiteheadian because it is.

        We want to ask the same thing of the quantum world that we want to ask of the Platonic Realm of the Forms: where is it? We can’t but think of those worlds as actual, like our own. But, they are purely formal. To think of the forms as themselves actual is to fall into a category error. I think that’s what Bohr is getting at when he says that the quantum world does not exist. But, it’s been a long time since I read him.

        Wolfgang Smith says essentially the same thing when he asserts that the physical realm – the realm that applied mathematics (including QM) limns – does not actually exist, whereas the corporeal world does actually exist.

        Are you also saying that, in a measurement, the quantum world is causing an effect upon the measuring device which changes the latter, thus producing a ‘new’ measuring device and that this is the moment of interface between the quantum and corporeal worlds, there being thus no ’embarrassment’ to speak of?

        I’m saying something close to that. The key thing to remember is that the classical measuring device – or any other corporeal object – is not just sitting there waiting to be affected. It is itself a stew of iterated motions from potential to actual. Perdurant corporeal objects are not one thing, but rather a series of repeated events that all take almost entirely the same form – and if we take corporeal things as events, happenings, acts that are completed and thus completely definite, we can say that a perdurant corporeal object is a temporally distributed series of things that share the same set of important formal characteristics.

        The classical measuring device is itself cooking out of the quantum world at each moment. If this were not so, it could not change from one moment to the next, and would not therefore work as a measuring device. Each moment of the actual existence of the classical measuring device is the fruit of a slew of events at the Planck scale – of quanta of action.

        No measuring device can measure what has not finished happening yet. We can measure only what has happened; what is done, past, come to pass, definite. So, contemporaneities are invisible to each other. The classical measuring device at t cannot measure anything happening at t. It can measure only what has happened at t – n.

        So, there is an event E, that finishes collapsing and terminates on a definite form, thereby becoming virtual. Only then can subsequent events register the facticity of that termination of E, and take the measure of its definite formal characteristics. It is in that registration of E by its successors that E finishes entering the causal system of the world, and attains full actuality. Without that registration, E would play no role in the subsequent world.

        As Aristotle insisted, what does not do anything does not actually exist.

        Those subsequent measuring events will themselves then finish their own collapse and terminate upon their own definite form. Some of those subsequent measuring events will constitute a future state of the classical measuring device. Its outputs – its objective state – will then likewise be registered by yet later subsequent measuring events. Some of those subsequent measuring events will be in a physicist.

    • Hello mickvet,

      Unlike Kristor, I have no settled opinion on the proper interpretation of quantum mechanics. Neither of the objections I noted against the Copenhagen interpretation are original to me, but I do think they have some force. It tells us how to use the theory, but doesn’t amount to an ontology, and (more seriously on its own terms), more work is needed to demonstrate the emergence of classical physics.

      • Would you mind outlining your views on these objections, Bonald? I am stretching my tiny little mind to understand these ideas, but I am attracted to the resemblance between the Copenhagen Interpretation of QM and the thinking of Plato and in particular, Aristotle. I don’t wish to continue over-heating my cerebrum in this manner if the resemblance is most likely spurious.

      • Well, the worrisome thing is that, as the CE is usually described, measurements somehow interrupt the normal, continuous, deterministic evolution of the state vector by the Schroedinger equation. It’s not clear how the Born law for interpreting state vector magnitudes in terms of probabilities is supposed to come about. And since not just any interaction triggers a state vector collapse, the threshold for classical behavior needs to be clarified.

        Obviously, proponents of the Copenhagen interpretation and related interpretations propose some answers to these problems. One move is to interpret state vectors / wavefunctions subjectively, as having to do with our knowledge, which unlike “reality” often does change abruptly. This is unsatisfying to me. Things like the double slit experiment pretty much make it impossible to believe that the particle “really” always just goes through one slit and we don’t know which. The remarkable thing about this experiment is that the correct quantum mechanical result is incompatible with both particle and wave pictures alone. Anyway, as soon as you say that reality is actually in something other than the state vector with more information, you’re in the land of hidden variables theories, with all the problems those have.

        The most promising way out is probably the one alluded to by Heisenberg in this book:
        when your system interacts with the surrounding environment, it becomes coupled to a big, messy system with many degrees of freedom which are basically stochastic to us in our ignorance. Somehow, this is supposed to batter the quantum system into classical behavior. I’m certainly not an expert on this. The attempts to fill in details to this process that I’ve seen involve adding such variables to the evolution of a density matrix and seeing that the effect is for the density matrix to diagonalize–meaning basically that entanglement effects go away. This is certainly necessary for the emergence of classical behavior, but I’m not sure if it’s sufficient. That doesn’t mean I suspect it isn’t; just that I haven’t given the matter the needed thought. Anyway, one could ask whether the crucial feature of the environment is that it’s big and complicated or just that its state is not being tracked by one’s quantum calculation. If the latter, then one might wonder if a complicated system could be “quantum” on the large scale on which it is isolated, while connected subsystems behave “classically” considered individually.

        There probably is something profoundly true in the identification of wavefunctions with potency, but a full theory of nature is also going to need a principle of actuality, and in the Copenhagen interpretation that is stuffed in more at the level of procedure than of theory.

      • Unlike Kristor, I have no settled opinion on the proper interpretation of quantum mechanics.

        I wouldn’t say I have a settled opinion. It’s more like a working hypothesis that has not yet run into fatal problems, so far as I can see.

  6. Bonald, I can’t seem to directly reply to your response above, for which I thank you. Is Heisenberg, in your extract, considering the possibility that a measured object might still portray quantum properties (“quantum on the large scale”)? If so, how can he consider that a classical object retains its ensemble of possibilities post-state vector collapse (please forgive me if I’m reading him completely wrong, which is very likely)?

    • Heisenberg doesn’t say anything like that. It’s just me speculating. Quantum cosmology is a field that runs into conceptual problems of this sort. The universe itself is, of course, an isolated system.

  7. I’m sure this has been asked before, but I am still not sure how arguments against materialism, atomism and classical mechanics necessarily lead to the truth of Biblical revelation. They just attack the foundations of modern ideas about how the world works, but they don’t necessarily furnish any evidence for a specific form of religious belief.

    Sure, wholism and Heisenberg may be true, but that really says nothing about whether to believe in Christianity. What’s the connection?

    • Only that if materialism is false, there is no particular reason to disbelieve in the supernatural, or therefore in Revelation. I mean, if materialism is true, then religion as such is just hogwash, and there is no need to think about it. But if materialism is false, then there may be something to religion; and, since religion concerns itself with matters of the utmost importance, it becomes imperative to investigate it seriously, and honestly. It becomes, i.e., imperative to open oneself to the possibility that revelation is True.

      The falsity of materialism furnishes no warrant for peculiarly Christian belief. But it does open the door to that belief.


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