• andrewk
    658
    The problem is that we can't measure the exact state of something made up of many particles, because that would involve an enormous number of measurements.Marchesk
    Even if we could make enough measurements simultaneously to know the exact state of a system, it would not dispel uncertainty.

    It is a common misconception that the 'state' of a system is a specification of the exact value of every observable of the system - location, momentum, spin, energy, etc. But the Heisenberg Uncertainty Principle - which is core QM, not interpretation - tells us that for any pair of dual observables - of which position and momentum are the most commonly cited - a state that has a narrow range of possibilities for one of the observables must have a very wide range of possibilities for the other. This has nothing to do with the practical ability to make measurements and is instead based on what 'state' means in QM. It is a purely theoretical, mathematical result. To reject that result we would have to radically alter, or even jettison, QM, not just choose another interpretation.

    However, I wonder whether what your physicist was actually referring to was the notion of Decoherence, which is a fairly intuitive (some might say 'pseudo-classical, but one has to be careful using vague terms like that) way of explaining what happens in a measurement of a quantum system. The reason I think he might be referring to that is the reference to the interaction between the state of the observed system and the state of the measuring apparatus, which is what Decoherence addresses.
  • Agustino
    5.2k
    For those who like the pilot wave theories:
  • Marchesk
    1.2k
    However, I wonder whether what your physicist was actually referring to was the notion of Decoherence, which is a fairly intuitive (some might say 'pseudo-classical, but one has to be careful using vague terms like that) way of explaining what happens in a measurement of a quantum system. The reason I think he might be referring to that is the reference to the interaction between the state of the observed system and the state of the measuring apparatus, which is what Decoherence addresses.andrewk

    I don't know, sounded to me like he was denying that the Uncertainty Principle was fundamental instead of a useful approximation based on epistemic limitations.
  • Metaphysician Undercover
    2k
    The De Broglie-Bohm addresses the delayed choice by an instanteous action at a distance by the quantum field.Rich

    Let's consider the implications "an instantaneous action at a distance". Clearly this would bring us outside the confines of space-time, as Wayfarer suggests we should look. So we can separate space from time, to see if this instantaneous action at a distance would represent a function of space, time, or both. Here are some speculations.

    Nothing can traverse vast space in no time, so if instantaneous action is a reality we have to shrink space, such that what appears to us as a vast space, becomes a small space, such that something can traverse the small space rapidly. We know that space itself is not fixed, static, because of the phenomenon which is called the expansion of space. So we can allow the possibility that space can change in time.

    Next we have the phenomenon of time itself. We live at the present, and we can know with a good degree of certainty that there is no material existence in the future. This is very difficult to grasp, but our capacity to create, and shape the world through free will choices demonstrates that it is impossible that material things can exist prior to the present. This means that the entire material world, must come into existence anew, at each moment of time. You will find this principle well outlined in some religions. We can speculate about a "big bang" of rapid spatial expansion at each moment of passing time, as the material universe comes into existence at each moment in time.

    Prior to the present, in the future, must exist all the "information" (for lack of a better word, though we should refer to Neo-Platonic Forms here) which determines exactly how the physical world will be at each passing moment. This world of Forms is a non-spatial world, being prior to the spatial, material existence which we experience at the present. Here I believe we have the possibility of instantaneous action at a distance.
  • Rich
    485
    One way of envisioning an Implicate Order, as Bohm refers to it, is a field of information where any new information affects all existing information that is stored as a holomovement that is in constant flux. Duration would be a manifestation of this holomovement that we experience as the underlying consciousness of this flux. Space emerges as a product of these movements.

    http://dbohm.com/david-bohm-holoflux-holomovement.html

    Can we set all conceptualize what such an undivided whole might feel like? I propose that a dream may provide some clues.
  • Rich
    485

    I'm astounded by the number of comments on this video. Who would have thought that Pilot Wave is as popular as Kim Kardashian.
  • andrewk
    658
    sounded to me like he was denying that the Uncertainty Principle was fundamental instead of a useful approximation based on epistemic limitations.Marchesk
    I expect he just expressed himself poorly - not an unusual occurrence for scientists trying to communicate to a non-scientific audience. The Uncertainty Relation is derived directly from the four postulates of quantum mechanics, with no additional assumptions*. It doesn't get more fundamental than that.

    By the way, of the list you gave of weird things about QM - 'indeterminism, ... pilot waves, ... non-locality, ... other worlds, ... weird collapse' only one - non-locality - is potentially implied by bare QM - ie by the postulates. The others are implied only by interpretations such as Copenhagen, Bohm or Many Worlds.

    As for non-locality, whether that is implied by bare QM depends on how we define locality. If we restrict it to observables - ie interpret it to say that one observation can only affect another observation in its future light cone, then bare QM does not contradict locality - even with Bell, Aspect etc. It's only if we define locality to mean that unobservables - in particular, quantum states - also cannot be affected outside of the future light cone, that bare QM, in conjunction with Bell and Aspect, implies non-locality.

    * See for example Chapter 9 of Shankar's 'Principles of Quantum Mechanics'.
  • tom
    1k
    When you say 'MWI is a testable prediction', what you mean is that the results are compatible with the many worlds explanation; the results appear to support the idea that there are many worlds. But you can never actually detect 'the other worlds' directly, except by way of inference. Is that the case?Wayfarer

    Just to cover the most important point first, so it can be ignored immediately: Copenhagen Interpretation does not even begin to explain reality, so should be ruled out as a scientific theory.

    The Copenhagen Interpretation claims that at some time after a measurement has taken place, a certain rule must be applied which assigns to all possible outcomes a probability, and that one of these outcomes will happen. This is a can of worms, which turns out to be a normative theory, not a scientific one!

    The Copenhagen Interpretation also suffers from a class of inconsistencies called the "Measurement Problem".

    Yet people prefer a non-explanatory, normative, and inconsistent theory to a scientific one!

    Anyway, certain, not yet feasible, tests under which Copenhagen and Everett make different predictions have been put forward. And, when the first quantum computer becomes operational, Copenhagen will be over.
  • Marchesk
    1.2k
    I expect he just expressed himself poorly - not an unusual occurrence for scientists trying to communicate to a non-scientific audience. The Uncertainty Relation is derived directly from the four postulates of quantum mechanics, with no additional assumptions*. It doesn't get more fundamental than that.andrewk

    I don't think that was the case. He repeated himself a lot, and was rather adamant. He doesn't except certain postulates as being anything more than useful modelling tools. Also, becuase the other speaker conceded that MWI would be unnecessary if the measuring apparatus is the culprit of the wave function probability distribution.

    Binney did state several times that the measuring device has a precise quantum state that is mostly classical, we just lack the means to measure it accurately.

    If you want, you can listen to Binney's portion of the talk. It's a bit long.

    https://youtu.be/NKPI_wurNlo?t=37m21s
  • Wayfarer
    3.1k
    You didn't address the point. Putting it another way - the evidence for 'other worlds' can only ever be indirect. So it's an example of 'abductive inference' i.e. reasoning from effect to cause so as to come to the most likely explanation. In that way, and only in that way, it is not dissimilar to design arguments for God.
  • Wayfarer
    3.1k
    Incidentally I don't think the 'Copenhagen Intepretation' ever was intended as a scientific theory. It's more a meta-scientific commentary.
  • Metaphysician Undercover
    2k
    The Uncertainty Relation is derived directly from the four postulates of quantum mechanics, with no additional assumptions*.andrewk

    I know that you gave a reference here, but is it possible to state these four postulates in English? I took a look at the reference, and it seems to be all written in secret code (mathematics and symbols). Myself, I am very skeptical of imaginary numbers. I think that they introduce an unknown element into mathematical equations, because it is unknown how imaginary numbers truly relate to real numbers, so that using a mixture of the two will produce uncertainty. There hasn't yet been produced a set of numbers which incorporates real and imaginary numbers into one order, which demonstrates how they are differentiated from each other. For example, "zero" produces that means by which positive and negative integers are related to each other within one set.

    I like the wording in section 9.4, "Applications of the Uncertainty Principle". You will find this: "Now the hand waving begins. We argue that...[two functions of the same order of magnitude are not strictly equal]... Once again we argue that...[the same inequality between two representations of the same magnitude] and get ... "
    Here is the footnote:
    "We are basically arguing that the mean of the functions (of X, Y, and Z) and the functions of the
    mean (<X >, < Y>, and <Z>) are of the same order of magnitude. They are in fact equal if there are no fluctuations around the mean and approximately equal if the fluctuations are small (recall the discussion toward the end of Chapter 6)."

    Incidentally, the only part of the chapter which seems to be well spelled out in English terms, is the part concerning the time-energy uncertainty. I've found this uncertainty relationship explained elsewhere, and it seems to be excluded from QM uncertainty by the way that the Hamiltonian operator is produced. As stated by Shankar "time t is not a dynamical variable but a parameter". I believe I read elsewhere that this was a choice made by Von Neumann. The time-energy uncertainty has to do with the indefiniteness of light frequencies, especially in very short periods of time. Resolution appears to involve allowing for violation of the law of conservation of energy.
  • Rich
    485
    Reading Bohr's seminal work on Complementary and the Uncertainly Principle:

    https://www.marxists.org/reference/subject/philosophy/works/dk/bohr.htm

    It once again occurs to me that the absolute, fundamental issue here, as it is with Relativity, is the notion that instrumentation will provide all the necessary knowledge that we need in order to understand the nature of the Universe. The limitations are clear and Bohr spells them out in this paper. Quite literally, and simply, you cannot find out everything you want to know about something that is in continuous flux by attempting to freeze it in an instant with an instrument. And if you allow it to change in its continuous flow then whatever you may know has vanished and is no longer true.

    Hence, if one wishes to understand the nature of the universe, it is necessary to give up the notion that instruments will ever provide a full description. QM and Relativity are attempting to provide solutions to instrument measurement problems and at their limits they cannot. Beyond that, other means must be used.

    Heraclitus and Bergson were correct, as was Bohm who realized that in order to pry deeper one must use intuition (the mind). If this is unsatisfactory, then one must learn live within the limits of instrumentation. It appears that Binney has not. As I indicted, it is impossible to measure the state of an undivided whole if one is part of that whole.
  • tom
    1k
    I'll restate it briefly. There wavefunction is not real. Rather, our uncertainty about the exact quantum state (which is classical in Binney's interpretation) is translated to the particle or particles in these experiments. If we could take into account the exact state of the measuring device, then the uncertainty of the particle's property in question would dissipate, and thus there would be no need for the wavefunction.Marchesk

    Hidden variable theories are ruled out. I have absolutely no idea why people still cling to them. Well actually I do - they wand quantum mechanics to be about reality, but are desperate to avoid the implications.

    I think I found the video you were referring to. Have only had time to watch a few minutes, so far I'm deeply alarmed.
  • tom
    1k
    Binney's view of the wavefunction is that it's a really useful and powerful tool, given our limited knowledge, but it has unreal properties, such as superposition. He thought the notion of a superposed cat to be absurd, like Schrodinger did. Basically, Binney thinks all the other interpretations of QM go wrong because they took the wave equation to be something more than a useful tool.Marchesk

    Now it seems as if he is defending Copenhagen.
  • tom
    1k
    You didn't address the point. Putting it another way - the evidence for 'other worlds' can only ever be indirect.Wayfarer

    So, you've got "direct" evidence for the Higgs boson or gravitational waves? How about direct evidence for particles turning into waves when no one is looking? Maybe you have direct evidence for any fundamental particle, and how it behaves Maybe you have direct evidence for the force of gravity?

    But of course you must have direct evidence of wavefunction collapse surely?

    Some prefer to have a good explanation, which is possible, to direct evidence, which is impossible. This really is philosophy of science 101.
  • tom
    1k
    I don't think that was the case. He repeated himself a lot, and was rather adamant. He doesn't except certain postulates as being anything more than useful modelling tools. Also, becuase the other speaker conceded that MWI would be unnecessary if the measuring apparatus is the culprit of the wave function probability distribution.Marchesk

    I'd ask him to explain the Elitzur-Vaidman bomb tester - a device that can identify whether a photon-detecting trigger attached to a bomb is operational, by NOT interacting with it.
  • tom
    1k
    It is a common misconception that the 'state' of a system is a specification of the exact value of every observable of the system - location, momentum, spin, energy, etc. But the Heisenberg Uncertainty Principle - which is core QM, not interpretation - tells us that for any pair of dual observables - of which position and momentum are the most commonly cited - a state that has a narrow range of possibilities for one of the observables must have a very wide range of possibilities for the other. This has nothing to do with the practical ability to make measurements and is instead based on what 'state' means in QM. It is a purely theoretical, mathematical result. To reject that result we would have to radically alter, or even jettison, QM, not just choose another interpretation.andrewk

    But that does not seem to be what Professor Binney is saying. He is claiming that the uncertainty principle is epistemic due to the large number of states available to the measuring apparatus. i.e. the uncertainty principle is entirely due to our ignorance of interactions between apparatus and the system being measured.
  • Wayfarer
    3.1k
    Maybe you have direct evidence for the force of gravity?tom

    Most assuredly, as do you.
  • andrewk
    658
    Yes, I have no idea what he is saying, let alone what he meant to say. I am suspicious of all prose presentations of QM. QM is mathematics and needs to be presented as such. As soon as a significant amount of prose enters the picture it becomes an interpretation. I know what the uncertainty principle is as a mathematical inequality, derived straightforwardly from the postulates. If someone wants to characterise it as more than that then they are doing interpretation, regardless of whether they realise that.

    I'm not going to criticise Prof Binney though because I haven't watched his video, just as I don't read designs for perpetual motion machines or proofs that one can trisect an angle. I don't need to because I know it either doesn't say what people think it does, or it is wrong.
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