• Frankly
    17
    Why should one be shocked by QM? Why you don't understand it if you claim to understand it? Why your innocence is lost when the quantum apple has been bitten?
  • Landoma1
    38
    Why can't reality be non-local? Two features of a spatial extended system could be non-causally connected can't they? Why isn't this compatible with realism?
  • Jackson
    1.8k
    Why can't reality be non-local?Landoma1

    I agree.
  • 180 Proof
    9.3k
    :fire: Thanks for your clarifications!
  • noAxioms
    1k
    If you don't know what relativity of simultaneity (RoS) is, then you don't have the tools to assess the validity of my criticism of the wording used in the article.
    — noAxioms
    To do with reference frames and the relativity of time of measurement, I guess.
    Wayfarer
    It does, but you seem to be on thin ground to be agreeing with a pop site written for the lay public instead of say grad students. Argument from authority doesn’t help. These PhDs write differently for different audiences.

    Per RoS, there is no unambiguous meaning to ‘instantly’ at a distance. Relative to a local measurement event, there are different times at the distant location, each simultaneous with the measurement event, but relative to different frames. That’s RoS in a nutshell.

    If one asserts objective time and space (there’s only one time on say Mars that is actually simultaneous with a given moment on Earth), it is a rejection of Einstein’s theory which posits only that all frames are equally valid and speed of light is c in any inertial frame. Neither of those is true if one posits an absolute frame, which necessarily implies light speed being something other than c in any other frame.

    That’s all besides the point of this entanglement topic. The point I’m really trying to get at is the implied assumption of Bohmian mechanics in the article. Only in Bohmian mechanics are the asserted statements true, and indeed, in that interpretation, locality is (and must be) violated. For the PhD to never explicitly call this out is bad form. There are other interpretations, including many well known that hold to the principle of locality.

    I can only get information from popular science, like Quanta Magazine and PBS Space Time, but the writers in those media are qualified in physics, in fact both have PhD's in the subject. Nowhere have you referred to any sources, so I'm inclined to believe them over you.
    Such articles are not accepted as evidence at a site like physicsforums.com . A college level textbook is, but most college courses teach quantum mechanics theory and barely touch on the interpretations, which is not theory.

    Choose between what principles?
    Principle of locality and principle of counterfactual definiteness, the latter being summarized in wiki thus:
    In quantum mechanics, counterfactual definiteness (CFD) is the ability to speak "meaningfully" of the definiteness of the results of measurements that have not been performed (i.e., the ability to assume the existence of objects, and properties of objects, even when they have not been measured).

    The articles you quote all speak meaningfully of unmeasured things, and rightfully drive that to demonstration of contradiction of locality.

    The Copenhagen interpretation are philosophical speculations about what it means.
    Agree, but the other interpretations are specific speculations about what it means. I’m saying there’s not one speculation that is the official Copenhagen speculation. With the other interpretations, one can point to one paper that defines the initial (and sometimes revised) view.

    It is my understanding that the Copenhagen Interpretation is not a "philosophical speculation." It represents a refusal to speculate. Metaphysics pared down to a minimum.Clarky
    This sounds close to the mark.
    The video you provided talked about the violation of realism versus the violation of locality. According to the narrator, if realism is violated, but locality isn't, there is no superluminal causality or communication. Or is it the other way around. Please don't ask me to explain, — Clarky
    I didn’t watch any videos, but that sounds right: CFD vs locality. Yes, if locality isn’t violated, there isn’t superluminal causality. That’s what locality means.
    With CFD, there’s not only superluminal causation, there’s reverse causation, with effect demonstrated years before the cause.

    It is meaningless to assign reality to the Universe in the absence of observation.
    — Neils Bohr
    This is a rejection of CFD, but if CFD is accepted (as your articles do), then that’s a different speculation. CFD can’t be proved, but neither can it be falsified.

    Here, it is explained, "object permanence" is being questioned. It is typical of the 'copenhagen interpretation'. — Wayfarer
    Copenhagen indeed does not typically list CFD as a premise (on wiki say), but I went hunting for an article you might like, and they all say different things, and the vast majority of the articles I found made meaningful statements about unmeasured things.

    Quantum entanglement—physics at its strangest—has moved out of this world and into space. In a study that shows China's growing mastery of both the quantum world and space science, a team of physicists reports that it sent eerily intertwined quantum particles from a satellite to ground stations separated by 1200 kilometers, smashing the previous world record.
    They put a beam splitter in space. Is that so remarkable? There is no maximum distance to entanglement, so ‘smashing’ some kind of distance record seems news worthy only to the lay public. I’ve seem similar claims of smashing the speed record, which, per RoS, is utterly meaningless.

    So, you're disputing that this is evidence of 'spooky action at a distance'?
    Yes, for the reasons I posted, not one of which has been refuted by somebody who understands the basics.

    I don’t deny the correlation at a distance. I deny that this is necessarily any kind of ‘action’, which would constitute a falsification of, among other things, all of relativity theory. There are several interpretations that ‘speculate’ local physics that account for the correlation. None of them presume CFD (yet again, with a single loophole exception, which is superdeterminsim)

    Why can't reality be non-local?Landoma1
    It can be. Nobody has proven locality. It just hasn’t been falsified.
  • Wayfarer
    16.3k
    Such articles are not accepted as evidence at a site like physicsforums.com .noAxioms

    That's because physics forum gives short shrift to anything the classify as philosophy. I've posted there a bit.

    I don’t deny the correlation at a distance.noAxioms

    Thanks for clearing that up. That's what I had thought you were doing. But I still don't think you've come to terms with Einstein's objection, and the subsequent experiments that falsify it.

    //ps// and there's no correlation until a measurement is made. That is another important point. It's not as if the correlation pre-exists the measurement - that is precisely what the Bell inequality disproves.//

    Here's the wiki article on counterfactual definiteness https://en.wikipedia.org/wiki/Counterfactual_definiteness
  • noAxioms
    1k
    That's because physics forum gives short shrift to anything the classify as philosophy. I've posted there a bit.Wayfarer
    They have a whole subforum for quantum interpretations, and yes, it's all philosophy in there. But they have standards for what constitutes an authoritative source, so say Everett's paper on Relative State Formulation is an authoritative source, but the wiki page on MWI is not. The latter is much easier to understand, and actually gets it reasonably correct.
  • Metaphysician Undercover
    10.2k
    Here, it is explained, "object permanence" is being questioned. It is typical of the 'copenhagen interpretation'.Wayfarer

    In mysticism, the principle is that every object must be recreated at each moment of passing time. This is the moment of the present. The principles employed by modern physics make the moment of the present observer dependent. This renders the moment of recreation of the object as vague.

    But I am going to say that I think to all intents, (a) simultaneous and instantaneous mean the same in this context,Wayfarer

    Simultaneous means at the same time, and as noAxioms explained, in relativity theory whether or not two events are simultaneous may be dependent on the frame of reference. This implies that whether one event is prior to another, or posterior to the other, is also frame dependent.

    Instantaneous is more of a mathematical concept derived from calculus I believe. I think it represents an infinitesimal period of time. So for instance, if one event causes another, the one is prior to the other, and there must be an infinitesimal amount of time which separates the two. The concept is useful for applying mathematics to acceleration. Acceleration has never been adequately understood by human beings.
  • jgill
    2.3k
    Acceleration has never been adequately understood by human beings.Metaphysician Undercover

    From past posts I assume you refer to instantaneous acceleration.
  • Wayfarer
    16.3k
    They (physics forum) have a whole subforum for quantum interpretationsnoAxioms

    Indeed they do. The current top thread is on interpretations of non-locality. Hey, I could spot the error in the first sentence of the second paragraph straight away, so I must understand something.

    I've participated in a few discussions on Physics Forum and even started a thread, but one of the later discussions I posted - I can't remember exactly the substance, but I think it was about the reality of number - was locked immediately on the grounds of being too philosophical (the mod said nobody there had expertise on questions of that kind).

    Simultaneous means at the same time, and as noAxioms explained, in relativity theory whether or not two events are simultaneous may be dependent on the frame of reference.Metaphysician Undercover

    According to some interpretations of quantum mechanics, the effect of one measurement occurs instantly. Other interpretations which don't recognize wavefunction collapse dispute that there is any "effect" at all. However, all interpretations agree that entanglement produces correlation between the measurements and that the mutual information between the entangled particles can be exploited.

    But logically, as the superposition refers to all of the elements in an entangled system, then to measure the one is to measure the other.
  • Metaphysician Undercover
    10.2k
    From past posts I assume you refer to instantaneous acceleration.jgill

    Acceleration in general, is not well understood. If an object is at rest, and later it is in motion, then there must be a time when acceleration is infinite, when it goes from zero motion to having some motion. This
    problem, of accurately representing acceleration, is tied together with the problem of representing how a force acts on an object, such as when one object hits another. I believe the acceptable way of representing this (application of force), is through the means of fields, so that the kinetic energy of the one object is represented as potential energy in relation to the other object. There is always a discrepancy between the two which is written off as entropy.

    But logically, as the superposition refers to all of the elements in an entangled system, then to measure the one is to measure the other.Wayfarer

    The issue is with those who "dispute that there is any 'effect' at all". Of course measurement has an affect, because that is how measurement in quantum systems is done, by eliciting an effect. If there is an effect in the measuring device then by Newton's third law there is also an effect on the thing measured. That thing being measure is the system. I believe the mode of measurement is to measure a part of the system, then through logic and extrapolation, extend this to the entirety of the system.

    The problem of entanglement is an extension of the simple measurement problem; physicists have no accurate way to measure any part of a quantum system. A "particle" does not have independent existence, it is always a part of something. Be wary of the use of "system" as well. A system is always artificial, or else it is how something natural is represented as "a system". If it is artificial, there is losses of energy to the system, accounted for with entropy. And representing something natural as "a system", is to neglect aspects of the reality of the thing, accidentals in Aristotelian terms.
  • Andrew M
    1.4k
    Both of those links are really helpful. Thanks.Clarky

    :up:

    Here's some more from Peres that argues for the locality point-of-view.

    Bell’s theorem (1964) asserts that it is impossible to mimic quantum theory by introducing a set of objective local “hidden” variables. It follows that any classical imitation of quantum mechanics is necessarily nonlocal. However Bell’s theorem does not imply the existence of any nonlocality in quantum theory itself. In particular relativistic quantum field theory is manifestly local. The simple and obvious fact is that information has to be carried by material objects, quantized or not. Therefore quantum measurements do not allow any information to be transmitted faster than the characteristic velocity that appears in the Green’s functions of the particles emitted in the experiment. In a Lorentz invariant theory, this limit is the velocity of light.

    In summary, relativistic causality cannot be violated by quantum measurements. The only physical assumption that is needed to prove this assertion is that Lorentz transformations of the spacetime coordinates are implemented in quantum theory by unitary transformations of the various operators. This is the same as saying that the Lorentz group is a valid symmetry of the physical system (Weinberg, 1995).
    Quantum Information and Relativity Theory - Asher Peres, Daniel R. Terno, 2003
  • T Clark
    9.4k


    Thanks again. I downloaded the paper, although it may be a bit over my head.
  • Wayfarer
    16.3k
    The world is not locally realistic.Andrew M

    What does 'locally realistic' mean? It doesn't make a lot of sense as plain English.

    Incidentally, I've been reading an article on QBism. As far as I understand it, it makes sense to me.

    Schrödinger thought that the Greeks had a kind of hold over us — they saw that the only way to make progress in thinking about the world was to talk about it without the “knowing subject” in it. QBism goes against that strain by saying that quantum mechanics is not about how the world is without us; instead it’s precisely about us in the world. The subject matter of the theory is not the world or us but us-within-the-world, the interface between the two. — Chris Fuchs

    That really nails it for me, because, if you think about it, it actually lines up with Kant.
  • Andrew M
    1.4k
    Thanks again.Clarky

    :up:

    What does 'locally realistic' mean? It doesn't make a lot of sense as plain English.Wayfarer

    Below is the broader quote that that phrase was taken from, describing Bell's Theorem. Both locality and realism are technical terms. Don't equate the latter with philosophical or scientific realism. In the sense used here, realism is the assumption that a superposition has a well-defined value independent of measurement (also termed counterfactual definiteness). So, for example, that a particle described by a superposition as being "here + there" really is just here or there independent of measurement, we just don't know which it is.

    There are two assumptions made in the proof of (2.225) which are questionable:

    (1) The assumption that the physical properties PQ, PR, PS, PT have definite values Q, R, S, T which exist independent of observation. This is sometimes known as the assumption of realism.
    (2) The assumption that Alice performing her measurement does not influence the result of Bob’s measurement. This is sometimes known as the assumption of locality.

    These two assumptions together are known as the assumptions of local realism. They are certainly intuitively plausible assumptions about how the world works, and they fit our everyday experience. Yet the Bell inequalities show that at least one of these assumptions is not correct.

    What can we learn from Bell’s inequality? For physicists, the most important lesson is that their deeply held commonsense intuitions about how the world works are wrong. The world is not locally realistic. Most physicists take the point of view that it is the assumption of realism which needs to be dropped from our worldview in quantum mechanics, although others have argued that the assumption of locality should be dropped instead. Regardless, Bell’s inequality together with substantial experimental evidence now points to the conclusion that either or both of locality and realism must be dropped from our view of the world if we are to develop a good intuitive understanding of quantum mechanics.
    — Quantum Computation and Quantum Information - Nielsen and Chuang
  • Andrew M
    1.4k
    Incidentally, I've been reading an article on QBism. As far as I understand it, it makes sense to me.

    Schrödinger thought that the Greeks had a kind of hold over us — they saw that the only way to make progress in thinking about the world was to talk about it without the “knowing subject” in it. QBism goes against that strain by saying that quantum mechanics is not about how the world is without us; instead it’s precisely about us in the world. The subject matter of the theory is not the world or us but us-within-the-world, the interface between the two.
    — Chris Fuchs

    That really nails it for me, because, if you think about it, it actually lines up with Kant.
    Wayfarer

    :up: As Fuchs implies with "us-within-the-world", there's no view from nowhere.

    But logically, as the superposition refers to all of the elements in an entangled system, then to measure the one is to measure the other.Wayfarer

    Just to be precise here, measurement involves an interaction between a measurer and what is being measured. That Alice measures her entangled particle doesn't imply that a measurement has been made or ever will be made on Bob's entangled particle. Instead, if both Alice and Bob do measure their particles and later meet up to compare notes, then they will find that their measurements are correlated per the predictions of quantum theory. That is, Alice needs to not just perform her local experiment, she also needs to locally interact with Bob and his measurement.
  • T Clark
    9.4k
    For physicists, the most important lesson is that their deeply held commonsense intuitions about how the world works are wrong. — Quantum Computation and Quantum Information - Nielsen and Chuang

    Then again, physicists and the rest of us can count on both realism and locality in the world where we live our lives. I'm not saying the results of quantum mechanics aren't important, but they are scale-dependent. Here at human scale, we can live our lives as we always have.
  • Andrew M
    1.4k
    Then again, physicists and the rest of us can count on both realism and locality in the world where we live our lives. I'm not saying the results of quantum mechanics aren't important, but they are scale-dependent. Here at human scale, we can live our lives as we always have.Clarky

    Yes, for macroscopic systems at low velocities in weak gravitational fields, QM and relativity approximate classical Newtonian mechanics (as an emergent classical limit).
  • Wayfarer
    16.3k
    That Alice measures her entangled particle doesn't imply that a measurement has been made or ever will be made on Bob's entangled particle.Andrew M

    I was referring to this thread on physics forum. I felt I had spotted an error that the first response set straight but this is obviously not the place to discuss Physics Forum threads. I only went there because @noAxioms mentioned there was a sub-forum on interpretations, and that was the first thread I looked at.

    "Quantum Computation and Quantum Information - Nielsen and Chuang"]For physicists, the most important lesson is that their deeply held commonsense intuitions about how the world works are wrong.

    Add 'and naturalists' :wink:


    Here at human scale, we can live our lives as we always have.Clarky

    People do say that often when encountering the paradoxical quality of quantum mechanics. But don't forget that the subject concerns what has always been thought of as the 'fundamental constituents of reality'.
  • Landoma1
    38
    Position and momenta can be in superposition like spin. If position of one electron is measured then the global becomes local but the spin is still globally, non-locally, attached to the other.
  • universeness
    2.3k


    I may be demonstrating my limited physics knowledge here but does the theory that 'dark energy,' (which I take to infer an energy type that is undetectable using any current known scientific technology) is the cause of the accelerating expansion rate, not contradict the evidence that the total energy of the spatial vacuum is zero?
  • Wayfarer
    16.3k
    That’s a question fir physics forum (although I’ve looked it up there before and the answer was ‘no’ for reasons I couldn’t follow).
  • Landoma1
    38
    Yes. A lamda is added to the energy-mass-momentum tensor. The DE is an energy that doesn't dilute if space grows. If you put giant springs between all galaxies you could stop expansion.
  • universeness
    2.3k

    :up: Yeah I've read some of it as well and I felt the familiar whoosh as the explanations went above my head. I was hoping you or @noAxioms could improve my grasp of it a little.
  • Landoma1
    38
    An isolated piece of vacuum contains huge power. If you put two particles in it they get pushed away with huge force.
  • universeness
    2.3k
    The DE is an energy that doesn't dilute if space grows. If you put giant springs between all galaxies you could stop expansion.Landoma1

    Yes but surely the 'force' of dark energy must overcome the 'negative' pull of gravitation to create an accelerating expansion. So does the dark energy effectively add to the positive 'push' of the 5% matter content of the universe? So that the totality of energy from the vacuum > 0.
    There is also the issue of dark matter? Does that proposed 95% of all 'matter' not also not add to the positive push and gravitational pull of the vacuum? One clump of dark matter will be gravitationally attracted to another clump, yes? I think I will take @Wayfarer's advice and post this as a question on quora. I will direct it at some of the physicists there.
  • Landoma1
    38


    DE isn't worn by particles. Its a property of space that pushes matter away from each other. There are no force exchange particles involved. There is a question on quora: "Is it possible to use DE to do work?" A similar one (the same, I guess) on PSE.

    Look here
  • Wayfarer
    16.3k
    I’m no authority on physics but I’m interested in the philosophical implications.
  • Landoma1
    38


    Maybe physics is philosophy. Or at least a part of it. Like metaphysics is a part too.
  • universeness
    2.3k
    I’m no authority on physics but I’m interested in the philosophical implicationsWayfarer

    Me neither, to my shagrin! I am interested in all the implications of science and of philosophy to a lesser degree due, to its dalliances with the esoteric and the metaphysical/supernatural but I am still interested in those aspects as I have to know and be able to explain and provide evidence for why I disagree with their significance/existence.
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