Lee Smolin’s Realism

by Mark English

Lee Smolin is a respected physicist who has always had strong philosophical interests and convictions. He recently articulated his realist views in a public lecture. What follows are my notes on his lecture mixed in with a few comments and observations.

Smolin is strongly opposed to postmodernists who reject the notion of objective truth and who see reality as a social or historical construct. He draws parallels between the anti-realism of postmodernists and the anti-realism of the generation of physicists who, from the late 1920s, embraced and promoted quantum mechanics (QM) and the so-called Copenhagen interpretation.

Because the measurement process is built into QM, Smolin claims (as Einstein did) that QM is an incomplete theory and so, in a real sense, wrong. It is not just that a particular interpretation of the theory is wrong. The basic structure of the theory itself is flawed because it has at its heart two laws which are in tension with one another.

This, then, is the key problem with QM as Smolin sees it. It is often called the “measurement problem”, and it relates specifically to the notion of wave-particle duality and the two laws or rules that QM provides to describe how things change over time. Rule 1 or Law 1 says, in effect, that (except during a measurement) the wave evolves smoothly and deterministically (somewhat like a wave on water). This allows the system to simultaneously explore alternative histories which lead to different outcomes all of which are represented by the smooth flow of the wave. Rule 1 applies when you are not making a measurement. Rule 2 applies only when you make a measurement and it tells you, when you make a measurement of position, say, that the probability that you will find a particle in a particular position is correlated with the height of the wave at that position.

Smolin argues that the 2nd rule means that QM is not a realist theory. If we (or other observers) were not around, only Rule 1 would apply.

One of the main developers of the theory, Erwin Schrödinger, was uncomfortable with the theory and its implications. He crystallized his doubts in the form of the famous live/dead cat-in-the-box thought experiment (which is explained by Smolin in his talk (starting at 39.54)).

Niels Bohr, in contrast to Schrödinger, embraced the paradoxical nature of QM, partly because it fitted in with ideas which he had developed previously. The notion of wave-particle duality predated QM by many years and marked the beginning of the quantum revolution, and Bohr’s notion (or philosophy) of complementarity was inspired by these ideas and by the observed behavior of elementary particles. Sometimes such particles seem to behave as if they are waves, sometimes as if they are particles and, crucially, how they are observed to behave depends on the details of how we go about observing them.

Smolin takes an unequivocally negative view of Bohr’s metaphysical views as well as of the views of Bohr’s protégé, Werner Heisenberg. Here he is on the former:

Now, of course, Bohr had a lot to say about things being complementary and in tension all the time and you always have to have two or more incompatible viewpoints at the same time to understand anything, and that especially goes […] for knowledge and truth and beauty. And he got off on the Kabbalah, of course. Anyway [long pause] … it doesn’t cut it with me.

Smolin’s claims are more than just an expression of a particular metaphysical disposition, however. It is generally accepted that QM doesn’t “make sense.”

“I think I can safely say,” Richard Feynman ventured, “that nobody understands quantum mechanics.” And according to a long line of physicists, from Einstein and Schrödinger through to contemporary figures such as Smolin and Roger Penrose, the reason QM doesn’t make sense is because it is incomplete. Or, to put it in a stronger way, because it is wrong.

How do we know that it is incomplete? Well, apart from the problems mentioned above, there is the small matter of gravity. QM in its current form can’t deal satisfactorily with gravity.

But Smolin is convinced that its weirdness and incompatibility with realism also count against it. QM is not consistent with realism because the properties it uses to describe atoms depend on us to prepare and measure them.

“A complete theory,” insists Smolin, “should describe what is happening in each individual process, independent of our knowledge or beliefs or interventions or interactions with the system.” He is interested in understanding “how nature is in our absence.” After all, we were not around for most of the history of the universe.

Smolin defines realism as the view that nature exists independently of our knowledge and beliefs about it; and that the properties of systems in nature can be characterized and understood independently of our existence and manipulation. Our measuring, etc. “should not play a role in what the atoms and elementary particles are doing.” What he means, I think, is that our interventions should not play an essential or crucial role in the descriptions and explanations that our theories provide.

“A theory can be called realist,” Smolin explains, “if it speaks in terms of properties whose values do not require us to interact with the system. We call such properties ‘beables’.”

By contrast, a theory whose properties depend on us interacting with a system is called operational. Such properties are called “observables.”

Observables are defined as a response to our intervention. Beables, by contrast, are not defined as a response to our intervention. They are just there, it seems.

But how do we get to know the values of these properties unless we interact with the system? Also, there is the framework question. Properties and values arguably only exist within the context of a particular perspective or theory. In order for properties and values to be properties and values, we need to conceptualize them as such. I will ignore this broader question, however, and focus on what Smolin means by interaction.

Even ordinary observations (like seeing or hearing or recording something electronically) involve us or our measuring devices interacting in some way with the system we/they are observing/recording. Smolin appears not to be concerned with such interactions here because, although the nature of the observer’s perceptual apparatus and/or the nature and settings of the equipment being employed determine or pick out what is and what is not being observed or recorded, the results are otherwise quite independent. The type of datum is determined by the nature of the observer or the observing or recording process, but not the data themselves.

In the case of experiments with elementary particles, however, the situation is subtly – and sometimes dramatically – different. Interactions are such that they determine, or play an active role in determining, the values in question.

Arguably, ordinary cases of measurement and observation do not pose problems for the commonsense realist. But if our observations alter in a material way whatever it is which is being observed – as appears to be the case in the quantum realm – problems arise.

Operationalism was first defined by the physicist Percy Bridgman (1882–1961). The book in which he elaborated his views, The Logic of Modern Physics, was published in 1927, the same year QM was put into definitive form. Bridgman’s philosophical approach has much in common with the instrumentalism which characterized the views of the majority of thinkers (physicists, logicians, philosophers) associated with logical positivism. Bridgman was in fact personally involved in the activities of the Vienna Circle.

It was the physicist John Bell who introduced the concept of beables. According to Bell – and according to Smolin – it should be possible to say what is rather than merely what is observed. This is all very well but – quite apart from philosophical arguments questioning the notion of a noumenal world – experimental results continue to come out against the realists. Experiments with entangled particles, for example, seem to exclude the possibility of any form of local realism. Some form of non-local realism is still very possible however.

Smolin is at his weakest when he talks history. The story he tells about the generation of physicists who grew up during the Great War is hard to swallow. It seems that they were predisposed to anti-realism by virtue of the unusual circumstances of their early lives. They had witnessed at an impressionable age the destruction of the social optimism of the 19th century, and so were skeptical of rationality and optimism and progress. They had lost older brothers and cousins and fathers and uncles and had “nobody above them …” No wonder they didn’t believe that elementary particles etc. have properties which are independent of our interactions with them!

You would think that the fact that Niels Bohr, the father of the Copenhagen interpretation, was not a part of this generation would sink Smolin’s generational explanation from the outset. As would even a cursory knowledge of the history of 19th century thought which is shot through with various forms of idealism, anti-realism and radical empiricism. The phenomenalist philosophy of science of Ernst Mach (1838–1916) is a case in point. At the end of the 19th century, Mach articulated ideas which were later picked up by the thinkers Smolin is criticizing.

Smolin explicitly recognizes that Bohr’s main ideas were formed well before the development of quantum mechanics and that he was influenced by 19th century thinkers, including by Kierkegaard, whom Smolin clearly does not hold in high esteem.

Smolin quotes some of Bohr’s early claims:

“Nothing exists until it is measured.”

“When we measure something we are forcing an undetermined, undefined world to assume an experimental value. We are not measuring the world, we are creating it.”

“Everything we call real is made of things that cannot be regarded as real.”

Heisenberg followed the same general approach:

“The atoms or elementary particles themselves are not real: they form a world of potentialities or possibilities rather than one of things or facts.”

“What we observe is not nature itself but nature exposed to our method of questioning.”

Bohr said: “We must be clear that when it comes to atoms, language can be used only as in poetry. The poet […] is not nearly so concerned [with] describing facts as [with] creating images and establishing mental connections.” What he meant, presumably, is that the normal referential function of natural language cannot be used in relation to the quantum world, and anything we say about that world (using natural language) will necessarily be a creative construct shot through with metaphor and paradox.

Maybe so. Or maybe not. It is not something we can know a priori. It all depends on how our models develop and on the results of experiments. So far, it must be said, QM remains intact and Bohr’s view still looks plausible.

41 Comments »

  1. Mark, interesting piece. I agree that it’s implausible Heisenberg, Bohr etc. were predisposed to anti-realism by the experiences of their early lives; the Great War etc.

    I don’t know about Bohr, but I think Heisenberg’s metaphysical position has a simpler explanation. If I remember correctly, he discovered QM when he decided to focus on those properties of a system that are observable (I’m simplifying a bit here).

    I imagine that must have impressed him enormously. In “Physics and Philosophy” he mentions that it’s futile to ask what “really” happens between observations. It’s a view that’s more compatible with the Copenhagen interpretation than with other, more realistic interpretations of QM.

    One could argue that focusing on observable properties is a metaphysical position in itself. But it should be noted that one doesn’t have to take this position to discover QM. The metaphysical position of Schrödinger, that other discoverer of QM, is much less clear, and I wonder if he had a recognizable metaphysical position at all (other than that nature is comprehensible and describable in mathematical terms).

    In general, I don’t like this division of physicists in Bad Guys – Bohr, Heisenberg – and Good Guys that seems to be made by Smolin.

    To be honest, I don’t know who these Good Guys are supposed to be. Yes, there’s Penrose etc., but a huge number of very able physicists did incredibly good work without being bothered by the incompleteness of QM. Some may say it was merely “shut up an calculate”, but on the other hand, shut up an calculate gave us extremely impressive results. Feynman freely admitted he didn’t understand QM but that didn’t stop him to do immensely valuable work.

    The incompleteness of QM has the fascinating distinction to be the deepest, most important problem in physics, while being at the same time astonishingly irrelevant.

    Of course, there’s gravity and general relativity. QM is not compatible with GR – or should we say GR is not compatible with QM? This incompatibility is fascinating, because QM and GR both are very successful. But is it caused by the incompleteness of QM? If there is a convincing physical argument in that direction, I haven’t seen it.

    Interesting is also what you write about beables and observables. Unfortunately you conclude with “I will ignore this broader question”. What’s your opinion on this distinction between beables and observables? Superficially, it seems fine but when I start to think about it, I rapidly draw a blank.

    Like

    • couvent2104

      Thanks.

      “… a huge number of very able physicists did incredibly good work without being bothered by the incompleteness of QM. Some may say it was merely “shut up an calculate”, but on the other hand, shut up and calculate gave us extremely impressive results.”

      Nobody is denying this. Smolin greatly respects the work of these people. It is the metaphysical view which he finds fault with.

      “The incompleteness of QM has the fascinating distinction to be the deepest, most important problem in physics, while being at the same time astonishingly irrelevant.”

      I think its relevance is twofold: to *future* advances in physics and to the implications it has for how we conceptualize the world in general terms (i.e. metaphysical implications). A crucial point is that some frameworks are better than others in terms of their capacity to deal with the complexities of the world in which we find ourselves. And the fact that our two most fundamental physical theories are not coordinated with one another is unsatisfactory. How this plays out could potentially affect the way we see our world in profound ways.

      “Interesting is also what you write about beables and observables. Unfortunately you conclude with “I will ignore this broader question”. What’s your opinion on this distinction between beables and observables? Superficially, it seems fine but when I start to think about it, I rapidly draw a blank.”

      I know what you mean. I have some sympathy for operationalism/ instrumentalism as an approach to scientific inquiry, but in the end I see such inquiry as an extension of ordinary, curiosity-driven behavior. For me there is no clear dividing line between the two, and science is not just about prediction.

      In the back of my mind are philosophical arguments about realism and idealism etc.. As I suggested above, scientific advances can impinge on these arguments, favoring some and undermining others. But even the favored approaches will need to be revised in the light of the findings which gave them renewed relevance or credibility.

      Liked by 1 person

  2. I am reminded here of an old Zen koan:

    From: The Gateless Gate, by Ekai, called Mu-mon, tr. Nyogen Senzaki and Paul Reps [1934]:
    29. Not the Wind, Not the Flag

    “Two monks were arguing about a flag. One said: “The flag is moving.”
    “The other said: “The wind is moving.”
    “The sixth patriarch happened to be passing by. He told them: “Not the wind, not the flag; mind is moving.”

    “Mumon’s comment: The sixth patriarch said: “The wind is not moving, the flag is not moving. Mind is moving.” What did he mean? If you understand this intimately, you will see the two monks there trying to buy iron and gaining gold. The sixth patriarch could not bear to see those two dull heads, so he made such a bargain.

    “Wind, flag, mind moves,
    ” The same understanding.
    “When the mouth opens
    “All are wrong.

    There are several readings one could give this, including a mystical one; but it should be remembered that koans were intended as thought problems to think on as one was struggling with the effort to empty one’s thinking in the process of meditation. At any rate, certainly a literal reading has the Sixth Patriarch, Huineng, reminding the monks that the question is irresolvable because it arises from an over-active mind; as Mumon remarks, “When the mouth opens/ All are wrong.”

    But of course, if we’re not monks or students of zen, entering a meditative state, we can develop a ‘scientific’ response to the debate; quite evidently, if the flag rests at inertia, only some force, such as that provided by wind, would seem to be needed to make it move.

    But here’s a problem: if I am looking at the flag from inside, through a window, the wind is invisible. Nonetheless, I can use the moving flag as not only demonstration that some such force exists, but as measurement of the force: say, ‘the force has the momentum of seven waves of the flag to-and-fro per minute.’ Now suddenly we’re opening the door to Smolin’s problem here. Bohr: “Nothing exists until it is measured.” Without the flag, where is the wind?

    All right, but I can stick my hand out the window. The movement of the hairs on my hand vouchsafe the reality of the wind. However, although we don’t generally perceive it as such, we are still engaged in measurement; we can tell the difference between a simple breeze and a hard wind. We can compare the sensation of the wind on our hands just standing at the window of a house, to that with our hand out the window of an automobile traveling 60 kilometers an hour. (I’m using ‘kilometer’ because the metric is held to be more precise than the milage system we use in America – but more precise to what purpose? or rather to whose? All measuring systems are inventions, all need human input.

    That’s the real crux of the matter, isn’t it? I wrote “The movement of the hairs on my hand vouchsafe the reality of the wind.” But what would be this thing called wind if there wasn’t some entity capable of perceiving it? What is a ‘force’ that isn’t witnessed?

    I don’t think recognition of such issues inevitably leads down some relativistic/ post-modern rabbit hole. My own view is that we can entertain differing epistemologies for differing purposes, as we employ differing methodologies for differing research inquiries, or even differing ontologies (eg., suggested in distinguishing the Manifest and Scientific Images). Reality may be one, but we approach it for differing purposes, and hence through differing perspectives.

    I echo what some of the commenters on the youtube posting complain, that one problem Smolin has here is that he takes great pains to announce a problem, but doesn’t even suggest an avenue by which solutions might be discovered. Ultimately, his talk seems to boil down to, ‘Quantum mechanics is Anti-realist in its assumptions, and therefore wrong.’ I would need to hear some greater defense of realism before I entertain that charge.

    Liked by 4 people

    • ejwinner

      “… All measuring systems are inventions, all need human input… That’s the real crux of the matter, isn’t it?”

      Well, I tried to draw a distinction between ordinary measurement and quantum measurement (as it is usually understood), suggesting that the latter poses more problems for realism than the former.

      ” “The movement of the hairs on my hand vouchsafe the reality of the wind.” But what would be this thing called wind if there wasn’t some entity capable of perceiving it? What is a ‘force’ that isn’t witnessed?”… I don’t think recognition of such issues inevitably leads down some relativistic/ post-modern rabbit hole.”

      And yet you seem to be taking us down *some* kind of rabbit hole here. Your comment relates directly, however, to what Bohr said, and coincides (in a general way) with how many others react to QM and/or deploy the theory or aspects of it in the context of philosophical or more general debate, basically as supporting an idealist or anti-realist view.

      “My own view is that we can entertain differing epistemologies for differing purposes, as we employ differing methodologies for differing research inquiries, or even differing ontologies (eg., suggested in distinguishing the Manifest and Scientific Images). Reality may be one, but we approach it for differing purposes, and hence through differing perspectives.”

      You talk of differing epistemologies and ontologies for differing purposes and differing perspectives. You also say that “reality may be one.” There is a tension here, and room for disagreement about the relative value or worth of different kinds of knowledge (or purported knowledge). There is also scope for disagreement concerning the role scientific knowledge plays (or should play) in general human understanding.

      “I echo what some of the commenters on the youtube posting complain, that one problem Smolin has here is that he takes great pains to announce a problem, but doesn’t even suggest an avenue by which solutions might be discovered. Ultimately, his talk seems to boil down to, ‘Quantum mechanics is Anti-realist in its assumptions, and therefore wrong.’ I would need to hear some greater defense of realism before I entertain that charge.”

      Despite my criticisms of his use of history, and my openness to the idea that he may be altogether on the wrong track (he admits his view is a minority one), I take a much more sympathetic view of what Smolin is doing here. He is a serious scientist grappling with one of the greatest — and deepest — scientific puzzles of the last 100 years. This is enough to engage my interest.

      A key point here is that Smolin’s realist intuitions are motivating him, just as Einstein’s realist intuitions motivated him, as a scientist. This is one of the things which makes this general controversy so interesting to me. It can be conceived of in terms of a kind of test for realism (bearing in mind that any realism which survives these tests would be unlike past forms (most obviously because it would have to deal with quantum nonlocality)).

      Thanks for your comment which, as is often the case, has prompted me to say a little more than I had originally set out to say.

      Liked by 2 people

      • On Einstein’s intuitions, there’s an amusing anecdote mentioned in “Uncertainty – The Life and Science of Werner Heisenberg” by David Cassidy. It’s based on Heisenberg’s much later recollection of a meeting with Einstein in April 1926.

        “But you don’t seriously believe,” Einstein objected, “that none but observable magnitudes must go into a physical theory? ”Heisenberg attempted to raise Einstein’s formulation of the special theory of relativity in his defense. Einstein had excluded such notions as absolute space and time because they could not be observed, and he had used an operational definition of the simultaneity of two events.
        Muttering that a “good trick should not be tried twice,” Heisenberg’s recollected Einstein called such empirical reasoning nonsense. “In reality the very opposite happens,” he declared. “It is the theory that decides what we can observe.” (p. 239 in my edition)

        Like

  3. I like your discussion of his lecture and your historical counterpoints are sharp, but I don’t feel the force of your last sentence. I don’t think Smolin wants QM to fall apart – he wants a more complete and consistent version to emerge. It’s also hard to say why we should take serious issue with Bohr’s view. There’s a tendency to speak as if QM and the Copenhagen interpretation (CI) walk hand in hand, and that the CI and Bohr walk hand in hand as well, but I don’t think either is the case. We’re confident in the success of QM predictively, but that doesn’t necessarily support CI, which itself has drifted away from Bohr’s interpretation under the influence of Heisenberg, von Neumann, and others. (The Stanford article on CI really plays up the complexities here.) Again, yes, QM is successful in its predictions, and the outcomes of experiments (e.g. on Bell’s Inequalities) have confirmed some of its weirder assumptions, but none of that has resulted in a satisfactory, broad-consensus reading of the so-called measurement problem, which is what bothers Smolin.

    Maybe there’s a collapse – does the measurement cause it (CI) or does it happen spontaneously? The latter appears more realistic, but the former is either non-realistic or realistic for a world we might not even be able to coherently describe. Maybe there’s no collapse – is that because the superposition is literally real (many-worlds) or because no collapse ever needed to happen since the superposition wasn’t literally real and hidden variables set the outcomes? Both are realistic, but they also have bullets to bite: the former muddying distinction between possibility and actuality for one, while the latter still needs to accept non-locality. There are a lot of balls to juggle, in other words. Lots of bullets to bite. I think Smolin’s underlying concerns are fair. If you have conflicting principles within a theory, you’ll have to resolve it or convince people that it isn’t a really a conflict. The CI, in its various iterations, hasn’t managed to do either. Similarly, if your interpretation veers into the philosophical terrain of subjectivism or operationalism, expect to face their usual pitfalls and for everyone to end up in the same aporias.

    Like

    • Zac

      Thanks for that. I agree with most of what you say. My goals here were very limited.

      “I like your discussion of his lecture and your historical counterpoints are sharp, but I don’t feel the force of your last sentence. I don’t think Smolin wants QM to fall apart – he wants a more complete and consistent version to emerge.”

      I realize that QM will not “fall apart”, but it would be a big deal if it were revised and fitted into a broader theory. And, by the way, when I talked about “Bohr’s view” in that final sentence, I was thinking specifically of what he said about atoms and poetic language in the preceding quote.

      “It’s also hard to say why we should take serious issue with Bohr’s view.”

      Smolin certainly talked about Bohr a lot, and presented his general philosophy as having played a significant role both in shaping and in garnering support for a particular research direction. His little counterfactual story about what might have happened if Louis de Broglie’s ideas had set the research direction instead of Bohr’s is fanciful and exaggerated but I think he is trying to make a serious point.

      “There’s a tendency to speak as if QM and the Copenhagen interpretation (CI) walk hand in hand, and that the CI and Bohr walk hand in hand as well, but I don’t think either is the case. We’re confident in the success of QM predictively, but that doesn’t necessarily support CI, which itself has drifted away from Bohr’s interpretation under the influence of Heisenberg, von Neumann, and others.”

      Yes, but Bohr and his interpretation were historically important.

      “Again, yes, QM is successful in its predictions, and the outcomes of experiments (e.g. on Bell’s Inequalities) have confirmed some of its weirder assumptions, but none of that has resulted in a satisfactory, broad-consensus reading of the so-called measurement problem, which is what bothers Smolin.”

      Right. And I think the confusion and disagreement indicates that there is a genuine problem (or set of problems) here which calls for some kind of resolution.

      “There are a lot of balls to juggle… Lots of bullets to bite. I think Smolin’s underlying concerns are fair. If you have conflicting principles within a theory, you’ll have to resolve it or convince people that it isn’t a really a conflict. The CI, in its various iterations, hasn’t managed to do either. Similarly, if your interpretation veers into the philosophical terrain of subjectivism or operationalism, expect to face their usual pitfalls and for everyone to end up in the same aporias.”

      Well said.

      Like

  4. Mark,
    this is another thoughtful and stimulating piece.

    Some time ago I was sitting in casualty, waiting for treatment for yet another injury. A young black woman and her three year old son came in behind me. Bored with waiting, he discovered the automatic door and experimented, moving back and forth, watching the door open and close in response. His mother quickly apologised, but I interrupted, saying what is happening is quite marvellous. Why? she asked, puzzled. Well, I said, he is learning cause and effect, that the world can be predictable, testable, orderly and rational, that it can be known and understood, through reason and testing.

    Most of us in the West have implicitly, until fairly recently, subscribed to this belief, but this young black township woman found this very novel. She inhabits a different world, like many in Africa. To understand her viewpoint you should read that marvellous Nigerian author, Ben Okri. Having spent my working life in Africa, Europe and East Asia I was well aware that these three regions had very different basic metaphysical viewpoints.

    To explain this I must introduce the concept of the circle of understanding. We all inhabit a circle of understanding, larger for some, smaller for others. Within the circle of understanding, events are explainable, rational, testable and predictable. Outside the circle of understanding lies the unknown, about which we can only speculate. Between the two is a deep, grey zone of uncertainty. In this grey zone of uncertainty things are chaotic, unpredictable and defy understanding. It is the way that we deal with the boundary to the circle of understanding that defines our basic metaphysical world view. Three broad strategies are available, depending on whether we believe:

    1) the world is driven by a unitary, orderly, rational agent;
    2) the world is driven by multiple capricious agents;
    3) the world is characterised by the ineffable, unknowable, irreconcilable and contradictory.

    1) the world is driven by a unitary, orderly, rational agent(the West).
    The agent can be called the Laws of Nature or it can be called God, depending on your ideological predilection. Or it can be both, as I believe, that the Laws of Nature are the properties of God. But it doesn’t matter, since the outcomes are the same. We still believe the world is rational, orderly, testable and explainable, ultimately derivable from its origin. Given this belief-set it makes sense to explore the grey zone at the boundary to our circle of understanding, progressively pushing it back, since in principle this can be done. The result has been an extraordinary explosion of scientific knowledge in the West, as we vigorously expand the circle of understanding.

    2) the world is driven by multiple capricious agents (Africa and others)
    This is a world that defies understanding in our sense of the word. Instead they create narratives that describe the past behaviour of the capricious agents. But past behaviour is a weak predictor of future behaviour, consequently the boundaries of the circle of understanding can hardly be expanded outwards.

    3) the world is characterised by the ineffable, unknowable, irreconcilable and contradictory (Asia)
    In this worldview great effort is expended in trying to reconcile and coming to terms with the irreconcilable, unknowable and contradictory where we are asked to believe that contradiction make sense. This is a philosophy of stasis since the emphasis is on coming to terms with the ineffable. This inhibits the drive to expand the circle of understanding and it has paralysed Asia, giving the West a huge lead in science. It is a singularly unproductive worldview.

    But given that the Western belief in a unitary, orderly, rational agent is the only productive one, what happens in the grey zone? In this zone multiple explanations compete, driven by the egos of their authors. These explanations are incomplete or incompatible. Slowly however, these problems of incompatibility or incompleteness are resolved, resulting in settled science, expanding the circle of knowledge and exposing new grey zones with more problems of their own. Underlying all of this is a bone deep belief, that no matter how difficult the problems, they will eventually yield to rational enquiry. And so science progresses, in fits and starts.

    However you can be sure there will always be a grey zone at the border of the circle of understanding and this grey zone will always be muddied by competing explanations and competing egos. That is simply the nature of incomplete and provisional science. And this is what explains the quantum conundrum. This is science that is still in the grey zone on the border of our circle of understanding. Science progresses in fits and starts, or, as the mechanical engineer would have it, it is an example slip-stick friction. It is at the sticking point that the grey zone seems deeper and impenetrable. This is where we are today, at the sticking point, but there will inevitably be a startling breakthrough and science will slip forward to a new understanding.

    All of this is predicated on a belief that the world is ultimately understandable and explainable. You might question this but then I would ask what are your grounds for questioning this assumption? I would point out that it is this very assumption that has given rise to such remarkable progress. This assumption has motivated us to explore the grey zone, expanding our circle of understanding and it is an assumption that works in practice. It is not a philosophy paralysed in stasis or anchored in primitive narratives. We believe that the grey zone can be and should be explored, and that it will yield to rational enquiry so that rational explanations are found, because, deep down, the world is rational, orderly and explainable. This belief has never failed us.

    labnut

    Like

    • Labnut/Peter

      What you say is very germane to the issues I raised. I certainly agree with you that the assumption that the world works according to rational (and so potentially understandable) principles has underpinned scientific progress. Like you (and Smolin) I think it will continue to do so — in spite of the intellectual trends to which Smolin alludes.

      Liked by 1 person

  5. Ontology vs Epistemology. If you insist on denoting the wave function as the wave function OF the electron, or photon, or cat, or whatever, describing their presently evolving states, you end in paradox. If you denote the wave function as the wave function OF the OBSERVER, describing the OBSERVER’S possible futures in relation to the electron, or photon, or cat, or whatever, the paradox disappears. Before the observation, the observer calculates, in its own ignorance of what the future will be, a continuous, smooth evolution of possibilities of what the future MIGHT be. Upon the happening of the measurement, the observer has an experience, the actuality is observed, its ignorance is dispersed, and all alternatives are revealed as impossible. The wave function is always the wave function OF of the observer. Taking it to be so allows it to be both epistemological in relation to the observer, and ontological in relation to the observer. No other interpretation allows that superposition to occur.

    Liked by 1 person

    • indeterminate student

      Smolin sees the fact that QM gives the observer a central role as an indication that the theory is unsatisfactory or deficient. For him it is not just a question of getting rid of paradoxes. He wants a realist theory.

      Your approach (obviously) is not a realist one and you seem happy to embrace a physics which is ultimately about *us* (observers and their knowledge) rather than about the world which produced us.

      Personally, I resist this approach but remain open to the possibility that sentience is somehow fundamental to reality. And it *could* be that the paradoxes of QM constitute the first signs that the old realist approaches to scientific inquiry are reaching their limits.

      Liked by 1 person

  6. In my earlier comment I dealt with the question:
    1) Is the world, in principle, fully knowable?
    In this comment I raise the question:
    2) Are we capable of fully knowing the world?

    My youngest sister has an IQ of 67. As a result she cannot function in a modern society and so lives in a home for the mentally handicapped. This has been such a source of enduring pain for our family, but not for her. Mercifully she is largely unaware of her condition and is accepting of life as she finds it, leading a moderately happy life in the care home. You might say that she suffers from anosgnosia, also known as the Dunning-Kruger effect. See this NY Times article(Something’s wrong but you’ll never know what it is).

    Now what if we, as a species, suffer from anosgnosia? In other words, are we too stupid to know that we are stupid? If that were true, then, as we expand the borders of our circle of knowledge we will inevitably reach a point limited by our capacity for understanding. In other words we would have reached our anosognosic limit. But, as anosognosics, we could not know that, because we could not know there are concepts beyond our capacity for understanding. They would be invisible to us, just as the arguments of Plato and Aristotle will forever be invisible to my sister.

    Is there an anosognosic boundary that limits the growth of our understanding? Is it even possible to know there is an anosognosic boundary? Or will we forever butt our heads in frustration against this boundary? Because if that were the case, then knowledge at this boundary will be of an impenetrable, confusing, fragmented and incoherent sort. Is that where we are today?

    I don’t believe this and yet I can’t discount this possibility. The thought experiment of Mary’s Room explores a related idea, where Mary is wholly unaware of the experience of colour until she leaves the room. Is it possible for us to know that our cognitive apparatus is capable of understanding all essential features of our universe?

    Certainly this is a basic assumption that underlies our practice of science. It is an assumption that is derived from Jewish-Christian thought where it is believed that we are made in the image of God, where ‘image’ refers to attributes of our mind, and not our bodies.

    For now all we can say is that this has been a good working assumption, that we have a capable cognitive apparatus, one that has sustained intellectual enquiry with remarkable results.

    labnut

    Like

    • Are we capable of fully knowing the world?

      What does it even mean, to talk of “fully knowing the world”?

      As best I can tell, the world is infinitely complex. And we are but finite creatures. So our abilities are seriously limited.

      I often hear claims that the world is intelligible. But I see no evidence for that. We have evidence only that the intelligible aspects of the world are intelligible. But that says nothing at all.

      You illustrate the issue with the sad situation of your sister. I have been illustrating it in other ways. Marie Curie and her co-workers taught us about radioactivity. Before her discovery, nobody knew that we were missing such knowledge. This suggests, as your own example suggests, that what we do not know may be effectively invisible to us. And we can see something similar with many examples of historical scientific discoveries.

      Liked by 1 person

    • labnut/Peter

      I recall a previous discussion of these topics in which you were involved. I agree that there are limitations to what we can reasonably aspire to know or understand but, given that we have full command of one or more natural languages and varying degrees of familiarity with mathematics and similar intellectual constructions, one could readily imagine a far more advanced intelligence than ours who *did* understand the universe sitting down with us and explaining the cosmos in terms we could understand. The thing is — unlike the case of your sister — there are lots of very specific questions we would want answered. In other words, we have the capacity to know and understand much more than we do and, if there were someone with immensely greater intellectual resources than ourselves, we could learn from them.

      Limitations would still apply in this hypothetical situation. We may not have the necessary raw intelligence (individual or collective). The languages we are capable of learning may not have the required level of complexity or sophistication to encompass the full detail of a “final theory”.

      And, a forteriori, assuming that such a (super-complex) theory *is* required to explain the universe — it may not be, of course — and assuming that our descendants are not significantly more intelligent than we are, we would have zero chance of developing such a theory ourselves.

      Liked by 2 people

  7. A more general comment. I have not closely followed Smolin, but I have found his remarks interesting.

    I have always considered myself a realist. But some philosophers are telling me that I am an anti-realist.

    For me, realism means that there is a world — a reality — that is independent of us. And scientists are studying that reality.

    Philosophers seem to have made realism into a theory about truth. And that’s why they see me as anti-realist. Truth is a property of descriptions of the world. But, unavoidably, descriptions are human constructs. And the truth conditions for descriptions unavoidably depend on how we have constructed our ways of describing. The idea that reality is socially constructed, seems to me to be a consequence of that move to make realism about truth.

    Like

    • Neil

      “I have always considered myself a realist. But some philosophers are telling me that I am an anti-realist… For me, realism means that there is a world — a reality — that is independent of us. And scientists are studying that reality.”

      I am with you so far (with the proviso that we, as physical and social beings, constitute part of that reality).

      “Philosophers seem to have made realism into a theory about truth. And that’s why they see me as anti-realist. Truth is a property of descriptions of the world. But, unavoidably, descriptions are human constructs. And the truth conditions for descriptions unavoidably depend on how we have constructed our ways of describing. The idea that reality is socially constructed, seems to me to be a consequence of that move to make realism about truth.”

      This is not a bad way of expressing the problem. I tend to see it more explicitly in terms of language. (You implicitly refer to language, of course, when you talk about the “human constructs” which are our descriptions.) Partly because psychology split from philosophy, there has been a pronounced emphasis on language within philosophical circles over the last century or so. This has led to new insights but also to some distortions. For example, there has been a tendency to see *all* thought in linguistic terms. This, I think, is a mistake and (in conjunction with other factors) it leads directly to some of the problems to which you (and Smolin) are alluding.

      Liked by 1 person

  8. labnut wrote, “Certainly this is a basic assumption that underlies our practice of science. It is an assumption that is derived from Jewish-Christian thought where it is believed that we are made in the image of God, where ‘image’ refers to attributes of our mind, and not our bodies.”

    So, would you say that science is based upon a fundamentally untrue assumption? Or do you think that this assumption is not untrue? Please, I am not asking about the usefulness or success etc. of this assumption. My question is only about truth or untruth.

    Like

  9. Hi ontologicalrealist,
    let me preface my reply by saying that my statement was intended to be a brief historical reference that attempted to account for the origin of a successful style of thought. It was not intended to be anything else and especially not advocacy. I was merely waving[!] my hand at an idea that needs a far fuller treatment(in another forum).

    But yes, I believe it is a true assumption, that God does exist and that we are an integral part of God’s central purpose. Atheists will of course believe the opposite, that there is no God and that this assumption is no more than a useful spandrel of a primitive, ancient, outdated belief system.

    Vive la différence, or as Mao Zedong said, “Let a hundred flowers bloom; let a hundred schools of thought contend”. But Mao ended up suppressing all other schools of thought in a determined attempt to extinguish them. Sadly the spirit of Mao is still wandering through modern Western thought.

    Like

  10. I said “Sadly the spirit of Mao is still wandering through modern Western thought.“. I should have added that he abandoned the realm of Chinese thought in horror at its opportunistic recidivism and instead took up residence in Western thought where he found a far more receptive audience.

    Like

  11. ontologicalrealist,
    My question is only about truth or untruth.

    It is so interesting that you said this. Broadly speaking, we could say there are two kinds of truth, pragmatic truth and absolute truth.

    Pragmatic truth is a provisional truth seen in a social context where we say “as far as we know” or “to the best of our knowledge”, or “in the present circumstances”. This is the view that prevailed in the ancient world. After all, there could be no absolute truth in a world governed by capricious agents, nor for that matter, in a world that lacks any agent, a world that is characterised by the ineffable, unknowable, irreconcilable and contradictory.

    But that changed with the adoption of Jewish-Christian thought in the West, with its belief in a unitary, orderly, rational governing agent . This belief system introduced the idea of absolute truth to the theological realm. This belief naturally extended into the material realm because the belief in a unitary, orderly, rational governing agent lent itself to the idea that there was an absolute truth that underlay everything.

    This had two consequences, one good and one bad. The good consequence was that it enabled the growth of science, since the pursuit of science requires at its very foundation the belief that there are absolute truths to be found. After all it is pointless to research the behaviour of multiple capricious agents and equally pointless to research a system that lacks any kind of agent to give a predictable order to the world.

    The bad consequence was that truth acquired an overtly moral tone. Untruth became a falsehood and if you possessed the truth you had a moral duty to suppress falsehood. This resulted in the well known abuses by the Church several centuries ago. Happily the Church reformed itself. And for a while the desire to punish untruth lay fallow in the ground of our society. During this time science grew apace, revealing that the world was indeed governed by absolute truths. Science was so successful that it changed our culture, with the belief in material truths being extended into cultural matters.

    Now it is a good thing to suppress scientific untruths because known, absolute truths do not permit any alternatives. Science cannot permit false science, since that destroys science. But this habit of mind has slowly, over time, infected our culture to the point where cultural beliefs have acquired the patina of absolute truths. And this same desire to punish untruths has now been extended into cultural matters.

    Here it has found fertile ground because society has any number of the petty, mean minded, looking for levers to exert power. Hence the widespread silencing, shaming and de-platforming movement. The same tendency exists in science but is held in check by the restraints of empiricism. No such checks exist outside science and so the flourishing movement to punish, squelch and extinguish ‘dissenting’ views seems to know no bounds. The spirit of Mao Zedong lives on in its new home.

    Like

  12. And yet though I fully agree with causal realism yet there is a quasi Humean doubt. What were things like before humans existed and created the concept of cause and effect. I think of a cosmos (order) in which all things were moving forward in a unified way as almost a solid unit. In Process and Reality Whitehead proposed the idea that no contemporary events are causally connected. In Vedanta you have the theory of asatkaryavada</i. or the non-difference of cause and effect. It is the potential which resides in natural kinds that moves things along. Milk will give you yoghurt, plus starter etc; sand will not. Only when you have the concept of time and its mathematization into instants can the before and after of things become visible. Though useful this brings on the Paradox of Zeno.

    Like

  13. And yet though I fully agree with causal realism yet there is a quasi Humean doubt. What were things like before humans existed and created the concept of cause and effect. I think of a cosmos (order) in which all things were moving forward in a unified way as almost a solid unit. In Process and Reality Whitehead proposed the idea that no contemporary events are causally connected. In Vedanta you have the theory of asatkaryavada</i. or the non-difference of cause and effect. It is the potential which resides in natural kinds that moves things along. Milk will give you yoghurt, plus starter etc; sand will not. Only when you have the concept of time and its mathematization into instants can the before and after of things become visible. Though useful this brings on the Paradox of Zeno.

    Like

  14. (correction of italics)
    And yet though I fully agree with causal realism yet there is a quasi Humean doubt. What were things like before humans existed and created the concept of cause and effect. I think of a cosmos (order) in which all things were moving forward in a unified way as almost a solid unit. In Process and Reality Whitehead proposed the idea that no contemporary events are causally connected. In Vedanta you have the theory of asatkaryavada or the non-difference of cause and effect. It is the potential which resides in natural kinds that moves things along. Milk will give you yoghurt, plus starter etc; sand will not. Only when you have the concept of time and its mathematization into instants can the before and after of things become visible. Though useful this brings on the Paradox of Zeno.

    Like

    • ombhurbhuva

      It is very difficult to know how we should think in general terms about the world before sentient beings appeared. No one was there to observe it then. But we observe galaxies etc. as they were millions or even billions of years ago (depending on their distance from us). And the cosmic microwave background gives clues about the nature of the very early universe.

      Both time and cause/effect are concepts which need clarification, of course.

      One thing that is relevant to the paradoxes you allude to is that physicists now seem to have shown pretty conclusively that neither space nor time is infinitely divisible.

      Like

  15. Peter DO Smith,

    Aristotle’s definition of truth:

    To say of that which is, that it is and to say of that which is not that it is not, is true

    and to say of that which is, that it is not and to say of that which is not that it is, is untrue.

    Rorty and Chomsky etc. said something like: The statement, “Snow is white.” is true if and only if snow is white.

    Like

  16. Peter,

    You wrote,” “Certainly this is a basic assumption that underlies our practice of science. It is an assumption that is derived from Jewish-Christian thought where it is believed that we are made in the image of God, where ‘image’ refers to attributes of our mind, and not our bodies.”

    Do you also think that neanderthals and proto-humans were made in the image of God?

    Like

  17. ontologicalrealist,

    Do you also think that neanderthals and proto-humans were made in the image of God?

    Don’t know. One needs to be careful with one’s language. The word ‘image’ contains a host of misleading associations. But even given that qualification I can only say – don’t know. The Bible is not a science manual and should never be read in that light.

    But if God exists he either created the laws of nature or the laws of nature are some of the properties of God. I hold the second view. In either case God(if he exists) intended that the laws of nature are the means by which the Universe was created, is sustained and is operated. I like to joke with some of my friends in the science community that if they want to know how God does things one should study science. In which case science is a branch of theology. I always enjoy their startled reaction as they digest this idea. The word ‘discombobulated’ nicely encapsulates their reaction. But we digress and I fear this digression will arouse Mao’s spirit. The result is always unpleasant.

    labnut

    Like

  18. Neil,

    What does it even mean, to talk of “fully knowing the world”?
    As best I can tell, the world is infinitely complex. And we are but finite creatures. So our abilities are seriously limited.

    For your sense of the word we would need to have Laplace’s demon at hand – https://en.wikipedia.org/wiki/Laplace's_demon

    We may regard the present state of the universe as the effect of its past and the cause of its future. An intellect which at a certain moment would know all forces that set nature in motion, and all positions of all items of which nature is composed, if this intellect were also vast enough to submit these data to analysis, it would embrace in a single formula the movements of the greatest bodies of the universe and those of the tiniest atom; for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes.
    — Pierre Simon Laplace, A Philosophical Essay on Probabilities[3]

    We however talk about ‘knowing’ in a more restricted sense, that of good enough for our purpose. If I toss a tennis ball to you, you instinctively reach out and catch it. Your mind has quickly calculated the trajectory and speed of the ball, allowing you to anticipate its arrival time and position. That is knowledge good enough for your purpose.

    A fuller knowledge would require measurement of mass, spin, surface roughness, air temperature and density, wind speed and direction, wind eddy currents, and local gravitational forces. The simple formulas of motion no longer suffice and a fuller formula for motion would become very complex but it might be necessary for some purposes.

    But even this is an intermediate knowledge, good enough for some very specific purposes. And so it goes on, with increasing levels of complexity. But even so, it is in principle knowable, given sufficiently accurate observation and sufficiently powerful computing facilities.

    Like

  19. Neil,
    This suggests, as your own example suggests, that what we do not know may be effectively invisible to us.

    Well, not quite, and my metaphor of the circle of knowledge was intended to illustrate this. The boundary between the known and the unknown is not a sharply defined and impermeable line. There is a large, grey zone of partial knowledge between the two. It is the existence of this grey zone of partial knowledge that arouses our curiosity and motivates the scientific endeavour. Outside the grey zone lies the unknown which is only open to metaphysical speculation and because we can speculate, we do, giving philosophers employment. 🙂

    But what is within the grey zone of partial, uncertain knowledge is open to scientific investigation. And as it succumbs to scientific investigation we expand the circle of knowledge, pushing it outwards, bringing some of the unknown into the grey zone, making it available to scientific investigation.

    This model has worked so far. But what we don’t know is if there are natural limits to this process. The limits may be cognitive, practical or inherent in nature. We have already encountered one inherent limit, that of the multiverse. Good mathematical reasoning suggest the multiverse exists but seemingly it is forever beyond verification because information cannot be transmitted through the Big Bang. Discovering the origin of the Laws of Nature seems also to be a similar limit. The origin of life and the nature of consciousness might also be other such limits, but that remains an open question.

    The big question I am asking is if there are cognitive limits in our mind that limit this process of expanding the circle of knowledge. I don’t think so but for the time being my thinking on the subject is quite muddied. Some unkind people suggest my thinking is always muddied. I am open to that possibility. 🙂

    Like

  20. Non-locality is not an issue in quantum mechanics, but in quantum field theory. They are not the same. Smolin of course knows this, but must have made a judgment call, and omitted this complication. Bohr and Einstein were also not entirely aware of it, since the distinction between the two fields was only made clear in the 1950’ies by Richard Feynman and other physicists of that generation. Nevertheless, it’s a distinction that matters.

    Quantum Mechanics is expressed in the Schrödinger wave function, and although other formalisms exist, including Heisenberg’s matrix mechanics, several attempts at a phase space formalism, and the currently emerging field of quantum reconstruction – basically, a formal logical approach, they all have one thing in common: they do not contain an operational definition of spacetime, or of location. It is therefore not even possible to say what spacetime locality is. Quantum reconstruction does have a notion of computational locality, and it appears that QM is computationally local. But this is not a subject currently within my purview.

    Quantum field theory (QFT) is a unification of QM and Special Relativity. Consequently it does give operational meaning to the concept of spacetime locality; and the theory is, it appears, irreducibly spacetime non-local.
    A system is local if it is in principle possible to put it in a box, no matter how big, such that all relevant phenomena are inside the box, and none are outside.
    By way of example: if consciousness is a property of humans, and if a human understood in physical terms is an organism, then consciousness is spacetime local, since the human can fit inside a box, such as an office or a living room, even if consciousness cannot be localized to any particular part of the human, such that it is, therefore, not computationally local.

    Since spacetime non-locality is a property of QFT, and since the operational meaning of that concept derives from special relativity, it might be sensible to inquire whether that particular issue might not stem from the latter also.
    We know from Planck’s E = hν that energy and scale (∼1/ν) are inversely correlated; the smaller the scale, the higher the energy required to probe it. At the LHC we* are currently probing the scale around 10^-17 cm. Yet at some point, around 10^-34 cm – aka the Planck Scale – we would have to pour so much energy into such a tiny region that the whole thing collapses into a black hole; and if we pour even more energy in, we’ll just make an even bigger black hole. So, there is simply no operational meaning to distances or durations (∼10^-44 seconds) shorter than the Planck scale. And in that case, when there is no operationally meaningful measure, it is good practice to regard the entity in question – scalar spacetime – as non-fundamental, and we will say, depending on temperament, the time of day, or whatever, that it is an emergent property, or that it is a low-energy approximation.
    It should come as no surprise, then, that weird and baffling things might happen when we push the envelope of this approximation, and spacetime non-locality seems to be most appropriately regarded as one of those.

    *We here is the all-inclusive, we, humans. I am not personally engaged in any of this in a professional capacity, but as a citizen scientist and philosopher of physics.

    I am in this mostly following theoretical physicist Nima Arkani-Hamed, many of whose lectures, public and technical, are available on Youtube, like this one, which should be broadly accessible:

    Like

    • Jesper Valgreen

      Thanks for that, and the link to the lecture by Nima Arkani-Hamed. He said some very interesting things, but he didn’t want to speculate too much, obviously.

      Significant points came out in question time. The main one was that he had been deliberately *not* talking about the thing which apparently motivated and provided a superstructure for the ideas he *was* talking about. Wouldn’t it have been nice to know from the outset what this was? (Dark energy.)

      Secondly, his refusal to publicly engage with the question about the foundations of QM and the measurement problem was disappointing. He said something like, come and talk to me later about it. But this is something which I (and I suspect many others) wanted to see more directly addressed.

      I was also intrigued by the reaction of the woman questioner. The words of her response to his response to her question were not audible (edited out?). Strange.

      I will follow up on Arkani-Hamed. Thanks again for the tip.

      Like

      • I did not mean to imply that the woman questioner I referred to asked the question about the measurement problem. She was asking about something else (GR-related).

        Like

  21. Mark:
    I went a bit metaphysical there on you for a bit but I do think that the sceptically vulnerable physical can get confused with it.. In good light and not having ingested psychotropic substances and facing the right way I can say with assurance – ‘there is an tree in the yard’. As a brain in a vat and as a subject trapped in a computer simulation I could say the same thing with the same assurance and be wrong. What would ‘wrong’ mean in this case? Is it not parasitic on the true ‘wrong’, the one that is open to correction? All observations are subject to determined scepticism and we can only stay calm and carry on.

    However metaphysical realism is different. It relies on their being an ontological substratum which unites Subject and Object. This is the approach of Platonic, Aristotelian and Vedantic philosophy. It is coherent with the project of critical realism in the physical sense. We accept the truth of our observations as a default assumption. We could be wrong though, but this ‘wrong’ is a true ‘wrong’ i.e. one connected to the metaphysical reality of the unity of the substratum.

    My point is that realism which tries to establish itself solely in the domain of observation is not on the ‘wrong’ track if you will forgive a paradox.

    Like

    • ombhurbhuva

      “All observations are subject to determined scepticism and we can only stay calm and carry on.”

      But how seriously should we take this thought-experiment-driven “doubt” (Descartes’ evil demon, brain in vat, etc.)? First of all, I would say that most of us are not seeking any sort of *absolute certainty*.

      We know (in the sense that we can be confident in the belief) that the brain in the vat idea, for example, is just a fanciful fiction designed to explore philosophical space, like Descartes’ demon. Some people do believe in the computer simulation idea, but this is a question which can be addressed scientifically.

      Some scientific findings (the holographic principle, for example) strongly suggest that the world is structured in counterintuitive ways.

      Of course, the differing meanings and uses of the word ‘realism’ confuse the picture. But Smolin is fairly clear in what he wants: he wants to say that certain kinds of claims about the world can be seen to be objectively true; that the sorts of things and/or processes studied by physicists are not dependent on us for their existence or for the way they are or operate. We discover and describe to the best of our ability what is actually going on.

      You could see this as a philosophy of scientific practice, and it doesn’t seem to be a bad one to me. Paradoxes, however, indicate that something is going wrong. And the paradoxes of QM or quantum field theory need to be resolved if fundamental physics is going to progress in the way that science has progressed in the past.

      It is possible that we will need to embrace a logic that allows paradoxes. If the physics requires dialetheism or whatever, okay. But I certainly haven’t given up on standard logic yet.

      “My point is that realism which tries to establish itself solely in the domain of observation is not on the ‘wrong’ track if you will forgive a paradox.”

      I think I see your point. But maybe some forms of realism don’t need to be grounded (philosophically at any rate). You can just take the-world-with-us-in-it as a given, can’t you? Especially if you leave open the question (as physicists do) of what all this is made of and how it is structured.

      Like

  22. New here by way of Leiter’s blog, and as an ex-physicist, I’m a bit surprised to see the repeated assertion that QM and gravity are “incompatible”. Not surprised that Smolin would assert that, as he is a highly visible and vocal anti-string theory guy. But for those taking a broader view of the field, there’s no shortage of publicity for a now 20+ year old and widely accepted framework demonstrating the equivalence of a class of quantum field theories with a class of gravitational theories (the so-called AdS/CFT duality). In these models, one finds that a theory of strongly interacting quantum fields (CFT) of a type whose weakly interacting counterpart has been very well understood since the early 1970s (and which differs mainly insofar as one dials up the interaction strength and increases the number of fields involved) is identical to general relativity up to energies far above those we have probed with accelerators, in a sort of cosmological box (AdS).

    There are lots of places to read in detail about this fascinating discovery (e.g., Polchinski earlier and Hubeny later have written non-technical reviews that can be found on arxiv.org). Certainly puzzles remain. E.g., the black hole information loss problem, now thought to be solved in the abstract sense that the duality shows it to be a non-issue, but the details remain poorly understood. The larger point though is that the claim of incompatibility between QM and gravity can no longer by maintained.

    Liked by 1 person

    • OC

      “I’m a bit surprised to see the repeated assertion that QM and gravity are “incompatible”. Not surprised that Smolin would assert that, as he is a highly visible and vocal anti-string theory guy.”

      I did not claim that QM and gravity are incompatible. I am aware that attempts are being made to extend or modify the theory to encompass gravity.

      One commenter said that QM and GR are incompatible and in my reply I referred to the two theories as “not being coordinated with one another.” Is there a problem with this?

      And with regard to Smolin, his main concern in the lecture is with the incompatibility (as he sees it) of QM with *realism*.

      Like

      • I guess I shouldn’t have used scare quotes there, as they’re easily mistaken for, uh, quote quotes.The para I was reacting to reads “How do we know that [QM] is incomplete? Well, apart from the problems mentioned above, there is the small matter of gravity. QM in its current form can’t deal satisfactorily with gravity.”

        An incompatibility (or dis-“coordination”) of QM and gravity would be a real problem, and bothered physicists seriously for a long time, particularly after Hawking’s discovery of his eponymous radiation that seemed to have troubling implications for the foundational assumptions of QM (unitarity of evolution of pure states). If true, it would mean that an eventual unified explanation covering the large & the small, or, say, inflationary cosmology, would entail some fundamental modification of one or the other. (“Fundamental” is not a very helpful word here. I’m struggling to find the right one. I think here of Scott Aaronson’s characterization of QM as an “operating system” for the rest of physics. It grounds everything else.)

        What AdS/CFT (also commonly called gauge/gravity) duality shows instead is that there is a well defined strongly interacting quantum mechanical field theory, not too different from the familiar QCD model of quarks and nucleons, that is equivalent at low energies to GR with a specified background geometry. So the puzzles of Hawking radiation now have a plausible program for their resolution, with some existing examples of success. For example: the Strominger & Vafa (1996) matching of entropy calculations for black holes based on string theory, an immediate precursor of the Maldacena (1997) analysis of the duality. If that’s not “coordination”, I don’t know what is.

        It’s true that AdS/CFT does not leave both gravity and QM unmodified. It’s GR that gives way. GR is embedded in the larger framework of string theory, modifying its features at ultra-high energies. But long before AdS/CFT there was already a widespread belief in the field that GR would have to be modified at high energy to incorporate QM (e.g., references to “quantum foam” in Misner, Thorne & Wheeler’s idiosyncratic textbook). So this is just a working implementation of that belief within the QM operating system. I think it should count for *something* towards acceptance of QM as it stands (leaving interpretation aside) that this unification can be made to work.

        A quote from Polchinski & Horowitz (2006): “The AdS/CFT system is entirely embedded in the framework of quantum mechanics. On the gauge theory side we have an explicit Hamiltonian, and states which we can think of as gauge invariant functionals of the fields. Thus the gravitational theory on the other side is quantum mechanical as well.”

        Like

        • “… So the puzzles of Hawking radiation now have a plausible program for their resolution, with some existing examples of success… It’s true that AdS/CFT does not leave both gravity and QM unmodified. It’s GR that gives way…”

          As you indicate, this is an ongoing research program. Puzzles persist and the details (as you put it in your first comment) “remain poorly understood.” But I concede your point that significant progress has been made.

          Thanks for engaging.

          Like

  23. Philosopher turned physicist turned philosopher Mario Bunge’s volume 7, part 1 of the _Treatise on Basic Philosophy_ has a table to decode Einstein and Bohr’s debate. He suggests that there was some confusion between realism and (for lack of a better phrase) sharpness. Also, he shows (earlier) that one can axiomatize standard QM and get nothing about “measurements” – so there is no problem. (I understand this is spelled out much later in the “decoherence” program – the interactions that people worry about are not “us” but just interactions. Smolin knows this, so I am a bit confused.)

    Like

    • Keith Douglas

      I am familiar with the decoherence program but there is a lot of controversy about it, and (as I understand it) no general agreement that it leads to a solution of the measurement problem.

      Like