What is the quantum/classical divide?

A talk given at the University of Buenos Aires in June 2017 on the difference between classical systems and quantum ones:


(Note: Some of the slides were missing text here and there due to a compatibility issue; the correct version is provided here: Baires 2017 slides)

25 thoughts on “What is the quantum/classical divide?

  1. Hi, Ruth. Happy Holidays! I’ve got a question that I think applies to the quantum/classical divide that might seem kind of dumb to you; it’s something that’s always bugged me, but I’ve never thought to ask about it. So, since a collapsed particle still almost always has a slight uncertainty in position, does this mean that collapse is just narrowing to an extremely narrow superposition? If so, what does this say about a collapsed particle’s actuality and ability to inhabit spacetime? As usual, I’m probably missing something here! :)

    1. There are no ‘collapsed particles;’ collapses correspond to the emission and absorption of a photon by particular atoms or molecules. I take the emission and absorption events as actualized spacetime events, but they are not pointlike; they are only localized to within the size of an atom or molecule. Actualization doesn’t require pointlike location.

  2. Thanks, Ruth! I pretty much came to the same conclusion you gave in your reply shortly after I asked the question. The terminology just occasionally trips me up, even when I already understand the basic idea. Everyone calls quanta particles, though only Bohmians think they actually are (and they sort of have to cheat!). I still find this to be an interesting question, though–what IS actual? Everything is fuzzier than our intuitions tell us. Emptiness doesn’t exist; true ‘solidity’ doesn’t exist. ‘The Present’ (the way that most people think of it) doesn’t exist, pretty much no matter what interpretation of space-time you use. Even with irreversible collapse, I’m thinking the quantum/classical divide isn’t sharp–more of a ‘fuzzy horizon’ between two complementary worlds–a bit like the boundary between meta-consciousness and lower-order consciousness. In fact, I sometimes think that that might be what the two worlds are: the meta-consciousness and subliminal of the universe.
    Merry Christmas! :)

  3. Photon transfers really are ‘actual’ in that they define a spacetime interval and (in the direct-action theory of TI) their mathematical description is different from ‘mere’ quantum possibility. It’s just that spacetime is not a continuum; it’s discrete and granular, where the ‘granules’ are the effective sizes of the quantum bound states (which is indeed ‘fuzzy’ in a spacetime sense).
    This recalls the ‘quantum foam’ idea of some ‘quantum gravity’ theories, but in my view it’s a more precise characterization of what the ‘foam’ is. Remember also that ‘actual’ is a special case of ‘real’: the quantum possibilities are physically real in my view. In fact, as I noted in my 2015 book: “The possibility clouds of electrons are the impenetrable scaffolding upon which all apparently solid matter [i.e. its related set of spacetime phenomena] is constructed.”

  4. Hi, Ruth. Happy New Year. I had one other question regarding the formation of spacetime intervals. I was reading a bit of your literature on the ‘Maudlin Challenge’ and thought that you seemed to say that an absorption event is not actualized until the receiving electron emits a new photon which is confirmed elsewhere. In other words, an electron absorbs a photon from another electron, then, as a result, emits a second photon, which is absorbed by a third electron, and the CW that ‘returns’ from that third electron actualizes not only the emission of the second photon, but the absorption of the first. This confused me, because I’d always had the impression that a photon OW/CW exchange between two electrons was all that was required to actualize a spacetime interval. Is that correct?

  5. The electron in the Maudlin experiment is liberated from a bound state by the absorption of the first photon and enters a new bound state by emission of the second photon. In contrast, in the usual absorption/emission situation, the electron just changes energy levels within the same bound system when it absorbs or emits the photon. An actualized emission or absorption of a photon involves direct transitions between bound states in order to satisfy energy conservation. The key to deciding when spacetime events are established is to see whether E conservation is satisfied. A free electron propagator is not a well-defined bound state, so that’s why I don’t assume E conservation is satisfied at that level and I assume we need the entire trajectory from liberation to final detection in order to actualize both the electron and its associated photons. I allow for the possibility that there could be no definite energy value for the liberated electron. The definite E value is established through capturing of the electron in a bound state of definite value at its final detection point.

  6. Thanks, Ruth. One or two other questions. This is right isn’t it? An electron within a bound state is still an OW, within the bound state, while the bound state is a quantum object that has to be summed over all possible locations. Then an absorption event–by one of the atom’s electrons, for instance–results in actualization. But even then, it’s still fuzzy, because the other components of the atom are still OW’s. Is that right?
    Second question (and this may have to do with what you were saying about energy conservation): do electron OW components act as emitters and absorbers? For instance, an electron in superposition emits (or absorbs) a photon OW from one component of its OW, but another part of the superposition might also emit (or absorb) a photon. But these can’t all be transactions, because ultimately there’s only one actualized transaction. Most of this might be virtual photon activity, with no answering CW–but, as usual, I’m still a little confused. If an electron is an OW (superposition) before it is detected, couldn’t each component of the electron OW emit a photon OW, setting up a number of incipient transactions? But then it seems that each one would result in an actualized outcome, so I’m guessing that’s not right. I guess I’m just still confused about what state an electron is in when it emits a photon OW–is it in superposition?
    Sorry about my obtuseness…but remember…I was an English major! ;)

    1. Hi Eric,
      (1) Yes the atom is always fuzzy as a bound system of OWs. The event is therefore not localized to a size smaller than the bound system that absorbed it. This is reminiscent of the idea of ‘spacetime foam’–if you look closely enough, you see that it’s not a continuum, nor are the events pointlike.
      (2). It’s really the atom as a whole that absorbs, not the bound electron. Also, an electron in a bound state in an atom is not in a superposition in the sense that it’s in an eigenstate of energy. Energy is fundamental in RTI, since the spacetime parameters (x,t) are only emergent as a result of transactions. Indeed t is not an observable at any level and x is not an observable at the relativistic level, even in standard QM.
      One can have weird superpositions involving a whole atom (such as in the Hardy experiment that I discuss in Chapter 5 of my CUP book, 2012.) In these cases, the atom has amplitudes for absorption corresponding to both components of the superposition. These turn into Born probabilities when it’s taken into account that the emitter has matching amplitudes for those components.

  7. Thanks, Ruth. That made everything clearer. One other question–if one considers the bound state as a whole to be fairly well localized (even if it is fuzzy), aren’t I right in assuming that its momentum uncertainty, according to the HUP, is even fuzzier? For instance, the momentum of an atom localized to a particular part of my brain is fuzzier than the momentum of an atom somewhere between here and the sun?
    I’m quite aware of my obtuseness on these technical issues and thank you for your patience. :) If you’ll recall, I was writing a humorous philosophy book–actually, a novel–which I finished back in 2016. Since then, I’ve been writing a companion book of philosophy (also humorous), which is almost finished. I think you’d find the ideas interesting, even though I’ve had to struggle over the technical issues, doing research, asking babe-in-the-woods questions as I’ve just done with you. I’m always catching mistakes I’ve made and then have to go back and correct them, but, after two years, I think the book’s nearly done. My ideas about the mind do not necessarily require RTI–though the two fit together quite well. As you know, I think the self requires some form of nonlocality (and probably, on a certain level, timelessness). Selfhood is a global phenomenon, even though our neurons have to communicate.
    Thanks again. :) Eric.

  8. I’m really sorry to be bombarding you with questions, but I thought of one more. I was always under the impression (I’m probably wrong) that according to the Feynman path integral, an electron takes every path in the universe to orbit its nucleus, but that all paths except for the relevant paths around the nucleus cancel. Does this sort of sum-over-histories apply only to photons and free electrons and not to bound electrons–or does it apply to bound electrons, too, in the Feynman method? Does it apply to unmeasured bound electrons in your method–or does it not apply (since a bound electron is in an eigenstate of energy)?

  9. Well, the ‘orbit’ around the nucleus is not a spacetime path, but in a sense you could say that it is indeed taking ‘all possible paths’ as it goes around since it takes no particular path. The dynamics is also influenced of course by the potential well it’s in, so this alters the relationship among the possible paths so that e.g., paths away from the nucleus always cancel each other out. So yes, this holds in general.

  10. Thanks, Ruth. I’ve always been bothered by ‘I think, therefore I am’ sorts of questions, even when I was a little kid, and I came across some of Daniel Dennett’s ideas in high school and found them seriously disturbing. I felt a little better, though, when I realized that the self can’t be an ‘illusion’, because it’s an illusion that a selfless thing could never produce. First I thought about the Hard Problem of Consciousness, and then I started to realize that the so-called ‘Binding Problem’ in the brain is just part of the Hard Problem. The Hard Problem is, ‘Why are we conscious?’ and the Binding Problem is, ‘How do we get a single self out of all these different neural structures (actually, out of all these trillions of particles)? It’s kind of a two-part problem, and there isn’t a classical answer. I think we need to assume first that consciousness goes all the way down to particles, and secondly, that, in a living thing (whatever living may be), there is a nonlocal association between all of that organism’s particles–so that a baseball doesn’t have a complex mind, but I do. Maybe a tree does, too–who knows where complex minds develop? But I don’t think a baseball does, and THAT’S the real quantum/classical boundary–classical physics describes inanimate objects. In any case, I think selfhood is similar enough to EPR that the self sinks any strictly local interpretation of QM (though there’s no need for de Broglie-Bohm!). However, then I thought some more and realized that, when we take consciousness down to the particle level, there’s a river of energy flowing through me all the time (to say nothing of neural changes in my brain). Why do I even seem to have the same self as time passes? This could actually reintroduce the Problem of Time into a growing universe, because if I am always becoming a different person, a different mind, my existence as an agent might be confined to a series of ‘snapshots’ rather than unfolding as a ‘rolling film’. I could exist as ‘snapshot’ after ‘snapshot’ and never know about the movie (never know about Time). So then I thought that at least part of the mind has to exist outside of Time. Actually, I think of my life as a series of rooms, with each room being a particular ‘present’ in which I can say that I have changed. Yet all the rooms are joined by a timeless corridor–and of course your ontology does very well at providing such a corridor!
    Thanks again–and sorry about this long-windedness! ;)

  11. Thanks Eric. I agree that the Self probably exists out of ‘time’ in the sense of spacetime. The time index is just that, a number that is assigned for coordination purposes of shared phenomena so that there can be some 3rd-person coordination that allows us to thing that at least we’re all living in the same reality. It’s just a feature of the map, not the territory. The binding issue again reflects that volition has to be a part of the picture of Selfhood. Doug Marman has suggested that the individual structures in the body (e.g. cells) choose to participate together as a single organism and that organism then has its own over-arching Self.

  12. I may think of the self somewhat differently. I think that we have a space-time self and an ‘outside’ self, and that the two act as a pair of mirrors–a sort of infinity-mirror. The outside self I see as a sort of non-actual Wheeler-Dewitt state incorporating all possibilities and all times into a single essence. This state then ‘reflects’ a particular part of itself into the actual world, and that becomes a moment of my life–and also a second mirror that bounces a ‘reflection’ back to the outside self, which bounces a ‘reply’ back into the actual world–the next moment. In each moment I have changed, but I am also the same, because each moment comes from the same underlying self. The outside self is more fundamental and ultimately drives everything, but the space-time self plays a role, bouncing replies back into the quantum world–and because the two selves aren’t really separate, the space-time self retains some of the nonlocal characteristics of the outside self. At times the space-time self may be made of different materials (as energy flows through me and I take in nutrients and shed waste), but the Wheeler-Dewitt-style representation of me includes every particle that even MIGHT ever belong to me, so that I am always the same, even as I change. I am the same if I become brain-damaged or have a stroke–the Outside Self doesn’t change at all. However, after the stroke, certain aspects of that outside self can no longer be ‘reflected’ into the actual world. And some aspects of the outside self usually can’t or don’t become part of my ego at ANY time. I don’t divine the future (by reading the ‘tea-leaves’ of the outside quantum state); I don’t become aware of faraway locations or learn Neanderthal swear-words (assuming that Neanderthals cursed). This is like most interpretations of QM (including yours). QM can be nonlocal, but classical information isn’t. I’m probably not going to gain nonlocal insights into the dinosaurs! ;)
    P.S.–I’m not saying that either the Wheeler Dewitt Equation or its usual interpretation is right–I’m just using it as an analogy!

  13. Yes, in using the capitalized ‘Self’ I mean the ‘Quantum Self’ if you will, but I don’t rule out a more local spacetime aspect to the self, as you describe. This would be the ‘tip of the iceberg’ aspect of the Self.

  14. I note, as always, your capitalization of Self, and I agree. There is something of Divinity in volition. Descartes might have said, ‘I think, therefore God is’. No doubt this is why so many atheists choose to ignore the mind-like characteristics of nature. Personally, I think that scientists who assert that science disproves spirituality are being just as unscientific as religious fundamentalists who want ‘religion’ to overthrow science.

  15. I saw your science and spirit post a year or two ago (and think I commented on it). It’s quite good! The interesting thing is that I think both sides of the ‘religion vs. science’ debate tend to get things wrong (by thinking there’s a controversy in the first place). Weirdly, religious fundamentalists and atheists seem to have the same definition of God: the so-called ‘God of the Gaps’. They assume that, in order for God to exist, the laws of nature need to break down and require some outside entity to fix them. I’ve come to think that this is silly. The laws should work (or else God would be incompetent), and proving that they DO work should NOT disprove the existence of God.
    Oh–speaking of spirituality; I thought of your William Byrd screenplay the other day (the one you sent me in 2016). I saw the film-trailer of that new Mary Queen of Scotts movie and thought to myself, ‘I wonder if Ruth and her sister finally sold part of their screenplay?’

  16. I heartily agree re the silly ‘science vs religion’ stuff. Re new movie: I wish! Not yet, but it’s good to see that movie producers are realizing there are still great stories to tell from this period. I did get a nibble from an agent/coach who offered to help us rewrite it to make it more ‘Hollywood-ready’, for a modest fee. I’m hoping to pursue that once I get done with QM book writing ( a possible 2nd edition of my 2012 CUP book is under consideration).

  17. Glad to hear you haven’t given up on your Byrd play.
    You know, one idea that I’ve had about the self–and I know this isn’t a perfect analogy, because there aren’t quantum fields for composite entities…but I sometimes think of the self as an ‘excitation’ in a ‘field’. I think this might be true in some sense. If so, then I am the excitation, and I would consider the Field to be God.
    Ultimately, I think I’m a Christian and favor the Western views of the self and God…but that doesn’t mean the Eastern and Western views are adversarial. Rather, like religion and science, the Eastern and Western views of Divinity and Selfhood may be two sides of a single coin. You can see this in the New Testament idea of the Holy Spirit–the divinity to be found in all people–which parallels Hinduism and Buddhism. Then there is Jesus’ saying, ‘I am the vine and you are the branches.’ A very Brahman/Atman view being expressed right there in the Bible!
    ‘I am the vine and you are the branches’, I think, could also be rephrased, ‘I am the field and you are the quantum’.

  18. I think this is a nice way to look at it. Long ago I read a book called Quantum Self by Danah Zohar (sp.?) and she may have made similar points (although I don’t recall her discussing concepts of God explicitly). I agree that Eastern & Western views on the Self and God are not incongruous as is often assumed. Coincidentally, I’m currently reading the series of books by Paul Selig and they seem very consonant with the ideas you express here.

  19. Hi, Ruth. I thought of something else on the self. I’ve sometimes thought that a quantum self might be a sort of timeless, non-spacetime ‘path integral’ for a person.
    In any case, I have another question about path integrals. I’ve sometimes seen a QED explanation of mirrors attributed to Feynman in which it is said that, as a consequence of taking all paths, a single photon is absorbed and reemitted by ALL the electrons in a mirror (as if the photon remains in superposition throughout its contact with the mirror). It’s then said that filing away part of the mirror (messing with destructive interference) proves that this is what’s going on. But I was thinking that this explanation can’t be right–not in your interpretation or in any interpretation with collapse. Maybe it’s meant that a photon is potentially absorbed by every electron (as in the case of OW components), but only actually absorbed by one? It seems to me that superposition couldn’t continue through the process of striking the mirror–not in your interpretation and not in Copenhagen, either.. Am I missing something?

    1. Here, Feynman is referring to the amplitude for reflection from various parts of the mirror on its way to some final absorption point (other than the mirror). This is not real absorption at the mirror (which would be an inelastic process involving confirmations); but rather an elastic process in which no confirmations are generated at the mirror. It’s a form of elastic scattering. Technically, the time-symmetric propagator (corresponding to virtual photons rather than ‘real’ photons) is what interacts with the mirror.
      Of course, the interesting thing about mirrors (reflective surfaces) is that they have a very low amplitude to generate confirmations. The underlying reason is that the mirror’s internal structure cannot absorb the photon’s energy in a way that would satisfy energy conservation. Instead, the transaction is between the emitter and some final absorber, with the mirror as an intermediary. In the conventional approach to QM, the notion of ‘absorption’ is ambiguous, and that is reflected in the language about a photon being ‘absorbed and re-emitted at the mirror’. But it’s an elastic process, and in the TI account, there is no confirmation, so there is no real ‘absorption’, just scattering. Another way to say it: there is only unitary evolution at the mirror and thus no transaction between the emitter and the mirror; the mirror is not an absorber. One needs non-unitarity corresponding to CW generation to yield real absorption in TI.

  20. Thanks–I thought it might be something like that. A lot of explanations, while correct, seem to blur the distinction between ‘virtual’ and ‘real’–force and energy–activity. I think that’s what confused me.
    Have a nice St. Patrick’s Day!

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