Submitted by ADefiniteDescription t3_xyumwc in philosophy
DBeumont t1_irkek2m wrote
Reply to comment by sticklebat in Quantum philosophy: 4 ways physics will challenge your reality by ADefiniteDescription
It is still only a behavior of the quantum particles. The point is that it has nothing to do with all the metaphysical stuff ascribed to it.
sticklebat t1_irktrbx wrote
I’m not sure what you mean by that. What is “it”?
DBeumont t1_irkz6n7 wrote
"It" being quantum physics.
sticklebat t1_irl0aca wrote
Then that doesn’t make any sense… Macroscopic phenomena are explained and underpinned by quantum mechanics. Whatever metaphysics surrounds quantum mechanics also necessarily applies to macroscopic phenomena. That it’s not usually noticeable is another matter.
DBeumont t1_irl0x7u wrote
No. A person, a rock, a chunk of dirt, etc. do not hold superpositions, do not entangle states, or any other quantum phenomenon. Quantum physics only describes the behavior of atomic and sub-atomic particles at an atomic and sub-atomic scale.
>Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles.[2]: 1.1 It is the foundation of all quantum physics including quantum chemistry, quantum field theory, quantum technology, and quantum information science.
sticklebat t1_irl3do1 wrote
Please point to the part of that article that you think supports your claim. Yes, it provides a description of the physical properties of nature at the scale of atoms and subatomic particles, and those things make up macroscopic systems. You can recover all of Newtonian mechanics from quantum mechanics.
The properties of a rock are determined by the properties of the things that makes up the rock, and how they interact with each other, and all of those are quantum mechanical. Macroscopic systems can absolutely demonstrate quantum mechanical behavior. I even gave you an explicit example already. A macroscopic system would be represented in quantum mechanics by a very high dimensional density matrix, but a density matrix nonetheless, no different in principle from the density matrix representing a pair of entangled electrons.
Smooth_Notice8504 t1_irms24e wrote
I think the misunderstanding on DBeumont's part here is that he's taking the idea of decoherence in macroscopic objects to mean that they aren't governed fundamentally by QM when it just means we don't tend to see that kind of behaviour on our scale.
There have been experiments done with high numbers of coherent particles showing that it is a matter of maintaining the conditions to allow for coherence rather then some inherent exclusivity in macroscopic objects or that they are somehow exempt from the predictions of the theory, as you say, you can derive classical physics from QM.
TMax01 t1_irmqptv wrote
>You can recover all of Newtonian mechanics from quantum mechanics.
I think it is fair to say this is true in principle, but in real terms you are overstating the case, and expressing a profession of faith rather than fact. In general I definitely support your side of the argument, but at this point you seem to be missing the nature of the counter-argument in order to "be right". We know that classic physics relates to, for instance, the collapse of superpositions and entanglement through decoherence into classically deterministic states, yes, but not really how or why. That's just putting words to mathematically described aspects of quantum systems. It doesn't really mean we actually can derive classic physics from QM, explicitly, just that we assume it must be possible theoretically. Your profession of faith in physical realism is scientifically appropriate, but philosophically it is akin to a declaration of omniscience.
sticklebat t1_irn0p1k wrote
> I think it is fair to say this is true in principle, but in real terms you are overstating the case
No, not really. What do you think condensed matter physics is, if not the application of quantum mechanics to macroscopic systems? What I said is both true in principle and proven in reality, even if it’s often too difficult to do.
> We know that classic physics relates to, for instance, the collapse of superpositions and entanglement through decoherence into classically deterministic states, yes, but not really how or why.
That’s fine. Scientific models aren’t concerned with how or why. It’s pretty easy to prove that the mathematical model that we call quantum mechanics reduces to classical mechanics in the appropriate limits of energy and scale based solely on the fundamental principles of quantum mechanics. In fact, mathematically the only distinction between the two arises entirely from the fact that in classical mechanics [x,p] = 0 and in quantum mechanics [x,p] = ihbar.
You’re right that we don’t fully understand the mechanisms by which macroscopic systems lose coherence. But that doesn’t mean we don’t know that, regardless of those details, quantum mechanical behavior necessarily reduces to classical mechanics in appropriate macroscopic limits. We also know that macroscopic systems are represented in our models of quantum mechanics by the same sorts of density matrices as everything else is. Of course, this is all predicated on the assumption that quantum mechanics is an accurate model, which there’s some small chance it isn’t, but this conversation is meaningless outside of that assumption.
> It doesn't really mean we actually can derive classic physics from QM, explicitly, just that we assume it must be possible theoretically.
No, you’re wrong. We cannot derive the stress tensor for a chair when I’m sat on it using quantum mechanics (which we could do using classical mechanics) because it’s simply much too complex a feat. But the neat thing about physics and math is that we can often prove things to be true in general more easily that we can actually do something for a specific, complicated case, but that first proof nonetheless implies that a determined and resourceful enough entity could do the latter, too. This is one such case, where mathematical proofs of the correspondence principle between quantum mechanics and classical mechanics exist. See, for example, the Ehrenfest Theorem. A different alternative is to take the limit as the ratio of hbar to a relevant scale factor (multiple choices could be made here) approaches zero, and then quantum mechanics and classical mechanics become mathematically identical models.
> Your profession of faith in physical realism is scientifically appropriate, but philosophically it is akin to a declaration of omniscience.
My comment has nothing to do with physical realism. My comment is entirely based purely on the mathematical properties of quantum and classical mechanics.
TMax01 t1_irnihwe wrote
>What do you think condensed matter physics is, if not the application of quantum mechanics to macroscopic systems?
The term "systems" seems a bit of over-reach, in line with your original premise. It may be common for people to assume that quantum mechanics is intrinsically limited to sub-atomic systems, but that isn't important. What is important, for the purposes of this discussion, is that condensed matter physics is a specific sub-domain of physics, rather than all of physics itself, which exemplifies the fact that QM doesn't literally explain how or why classic physics ("Newtonian physics" was the iconic representative) arises from the principles of QM. In theory we "know" it must, but as it has not yet been convincingly demonstrated in general cases, insisting that conjecture is fact is problematic. At least as far as philosophy goes, which is not restricted to even presuming that classic physics accurately describes "the macroscopic world".
>Scientific models aren’t concerned with how or why.
I would dispute half of that. Scientific models are entirely about how, and necessarily unconcerned with why. But the nature of language (capable of absurdity as functional, which logic and mathematical systems are not) makes the distinction itself less certain than scientists and scientificists are capable of addressing.
>In fact, mathematically the only distinction between the two arises entirely from the fact that in classical mechanics [x,p] = 0 and in quantum mechanics [x,p] = ihbar.
I would say that the notation arises from the distinction rather than the other way around. But the direction of the teleology itself is a philosophical matter, not a scientific consideration, because as I said, science is all about how, not about why.
>You’re right that we don’t fully understand the mechanisms by which macroscopic systems lose coherence
Bingo.
>But that doesn’t mean we don’t know that, regardless of those details, quantum mechanical behavior necessarily reduces to classical mechanics in appropriate macroscopic limits
Actually, it genuinely does mean exactly that. While it is not a possibility that science needs to deal with at the moment (though I might wonder why 0 is not the same as ihbar) it is one that must be considered philosophically, lest we assume that science is omniscient by definition.
But of course, and I may be mistaken about this and please enlighten me about your reasoning if I am, I presume you meant classic physics reduce to QM, rather than the other way around, which is what you actually typed. I think the idea that quantum behavior necessarily reduces to Newtonian mechanics is absurd, isn't it?
>We cannot derive the stress tensor for a chair when I’m sat on it using quantum mechanics (which we could do using classical mechanics) because it’s simply much too complex a feat.
I don't mean to sound flippant, but that is an awfully convenient excuse. Which is to say that since you cannot demonstrate that you can perform such a feat, it remains conjecture rather than knowledge, faith rather than fact, a valid supposition but not a foregone conclusion, that it actually can be done.
> But the neat thing about physics and math is that we can often prove things to be true in general more easily that we can actually do something for a specific, complicated case,
And the unfortunate reality about logic (physics and math) is that we can often make presumptuous assumptions without demonstrating their validity in practical cases. "Often", after all, does not mean 'always', and whether the instant case is such an example requires empirical demonstration or else it is simply not convincing, all the more so because of the specifically confounding results that differentiates QM from classic physics.
>This is one such case, where mathematical proofs of the correspondence principle between quantum mechanics and classical mechanics exist.
As I've said all along, your conjecture is true in principle and theoretically. And also as I pointed out, it remains an act of faith to suppose that means it is true in reality.
>My comment has nothing to do with physical realism
Then it, quite arguably, has nothing to do with the discussion, in a way very analogous (or perhaps entirely identical) to whether QM "has nothing to do with" actual reality, but only mathematically models particular systems in scientific laboratories. I don't fault or question your principles, and I realize that discoveries founded on quantum mechanics have provided real results in terms of useful engineering results. But I still insist you are overstating the case of their applicability, since functional utility in restricted examples does not actually prove general accuracy in all instances, even with further theoretical bases to support the belief that QM fully explains why Newtonian physics arises from quantum interactions.
Thanks for your time. Hope it helps.
sticklebat t1_iroq2uv wrote
Your entire post uses ignorance of physics as a bludgeon.
> The term "systems" seems a bit of over-reach, in line with your original premise.
No, it is precisely the right word. Which you’d know if you knew enough about physics to have this conversation.
> What is important, for the purposes of this discussion, is that condensed matter physics is a specific sub-domain of physics, rather than all of physics itself,
None of this makes sense. Condensed matter physics is an application of quantum mechanics used to model properties of macroscopic systems. I used it as an example of how macroscopic things absolutely do demonstrate quantum mechanical properties, and gave examples of macroscopic phenomena that we can only explain in terms of quantum mechanics. I never said that it is “all of physics,” but that’s a nice strawman.
> which exemplifies the fact that QM doesn't literally explain how or why classic physics ("Newtonian physics" was the iconic representative) arises from the principles of QM. In theory we "know" it must, but as it has not yet been convincingly demonstrated in general cases, insisting that conjecture is fact is problematic.
I even gave you a link to a general proof of the correspondence principle and described an approach for an alternative proof, and it’s telling that you didn’t even respond to that at all, and instead built a strawman to argue against instead. Neither of those are conjecture, they are proofs. Your ignorance of them doesn’t mean they don’t exist. You should stop arguing about things you don’t know. You may be the best philosopher in the universe, but you can’t do philosophy about topics you don’t understand, let alone those that you aren’t even aware of.
> I would dispute half of that. Scientific models are entirely about how, and necessarily unconcerned with why.
Semantics. Science is about constructing models that reflect reality insofar as we can measure it. A scientific model is good if it is consistent with existing data and accurately predicts the results of future experiments. For example, quantum mechanics doesn’t address how things happen, only what will happen. GR does the same, although in both cases we use words that ascribe some sense of “how,” but it’s more to help us talk about and understand the math, than intrinsic to the model. For example, we often say that mass curves spacetime, and that’s what gravity is, but it’s possible to reframe GR in terms that have nothing to do with spacetime curvature. e.g. it can equivalently be thought of as arising from torsion instead of curvature, or even as a field on a standard spacetime background; all of these are probably mathematically equivalent and no experiment can ever, even in principle, distinguish between them. This nearly identical to the issue of interpretations in QM, it just gets less attention for a variety of reasons.
> I would say that the notation arises from the distinction rather than the other way around.
I’m not talking about notation, I’m talking about the meaning behind the notation (which I suspect you probably don’t know). Either way, you’re missing the point. The point is that in circumstances when hbar is small compared to the relevant scale factors of a system, quantum mechanics turns into classical mechanics. In that sense, classical mechanics is embedded in quantum mechanics.
> But of course, and I may be mistaken about this and please enlighten me about your reasoning if I am, I presume you meant classic physics reduce to QM, rather than the other way around, which is what you actually typed. I think the idea that quantum behavior necessarily reduces to Newtonian mechanics is absurd, isn't it?
No, I meant what I said. In the macroscopic limit, quantum mechanics reduces to classical mechanics. Just like GR reduces to classical mechanics in the limit of low masses and small scales. This is an important aspect of the development of scientific models, it is what the word “reduce” means in this context. It means that quantum mechanics is a more encompassing model, and by taking the appropriate limit you can reduce it to recover classical mechanics.
> I don't mean to sound flippant, but that is an awfully convenient excuse. Which is to say that since you cannot demonstrate that you can perform such a feat, it remains conjecture rather than knowledge, faith rather than fact, a valid supposition but not a foregone conclusion, that it actually can be done.
It’s not an excuse. In a Newtonian world, Newtonian mechanics could be used to deterministically predict the precise time evolution of a gaseous system given accurate and precise initial conditions, regardless of the number of gas particles. It is wildly impractical to do that for anything above a small number of particles, but that doesn’t make it conjecture. And again, I’ve already proved your second sentence wrong. You just chose not to even acknowledge it.
> "Often", after all, does not mean 'always', and whether the instant case is such an example requires empirical demonstration or else it is simply not convincing, all the more so because of the specifically confounding results that differentiates QM from classic physics.
Again, I literally gave you the proof. You’re not even just using ignorance as a weapon here, you’re using willful ignorance. QM has been unambiguously and explicitly proven to reduce to classical mechanics in the macroscopic limit. Hard stop.
> And also as I pointed out, it remains an act of faith to suppose that means it is true in reality.
And again, it’s been proven true in reality. The model of QM reduces to the model CM in the macroscopic limit. You can argue all you want against that, but you’d be wrong. The only place “faith” shows up is in the assumption that QM accurately models reality, but I’m not arguing whether it’s correct or not (and also that is always the case for every scientific model that ever has and ever will be constructed, making it a pedantic argument in the first place). The fact that QM reduces to CM is mathematical fact, regardless of the applicability of either model to the real world.
> Then it, quite arguably, has nothing to do with the discussion, in a way very analogous (or perhaps entirely identical) to whether QM "has nothing to do with" actual reality, but only mathematically models particular systems in scientific laboratories.
No, the other person made false claims about the limits of applicability of quantum mechanical systems. They weren’t arguing that we can’t know whether QM is actually, truly correct. They were clearly under the wrong impression that QM, even if true, doesn’t apply at macroscopic scales. That is what I argued against. You are merely creating strawmen.
> But I still insist you are overstating the case of their applicability, since functional utility in restricted examples does not actually prove general accuracy in all instances, even with further theoretical bases to support the belief that QM fully explains why Newtonian physics arises from quantum interactions.
Except I’ve given explicit examples of ways that QM empirically is relevant in macroscopic systems. But as usual, you simply don’t engage with the parts of my arguments that you don’t know how to address and pretend they never happened.
TMax01 t1_irouiml wrote
>Your entire post uses ignorance of physics as a bludgeon.
Nah. It is an effort to explain to people who understand physics but little else why other peope, who don't understand physics, understand more than they do.
>No, it is precisely the right word. Which you’d know if you knew enough about physics to have this conversation.
You're mistaking what is conventional within physics for what is meaningful in real life. "System" is the wrong word for a single substance, even one so profoundly important to physicists as Bose-Einstein condensates.
>Condensed matter physics is an application of quantum mechanics used to model properties of macroscopic systems.
It is used to model one very specific and particular (pun intended) kind of quantum system, which is really important because that specific "condensed matter" is a macroscopic substance, unlike most quantum systems, which are sub-atomic, so small that even using the contrast macro/microscopic is actually weird.
>I used it as an example of how macroscopic things absolutely do demonstrate quantum mechanical properties,
Nobody disputes that deterministic objects "demonstrate quantum mechanical properties"; as far as I know, they do so simply by existing. The issue being address here is how, and whether that is known with enough detail and accuracy in a wide enough variety of instances to be considered important outside of the singular domain of physics. Most directly observable ("macroscopic") systems don't demonstrate quantum mechanical properties over and above classical mechanical properties. So the use of one example of a "macroscopic thing" demonstrating quantum properties (which, as far as I know, aren't observable as distinct from conventional properties in BEC without special equipment and in highly restricted circumstances) really doesn't have the weight you think it would, in this discussion.
> I never said that it is “all of physics,” but that’s a nice strawman.
Not a strawman, just an example of what it would take to justify saying that QM effects "the macro world" of everyday objects.
>Semantics
AKA language. AKA discussion. AKA the real world.
>I’m not talking about notation,
Semantics.
>The point is that in circumstances when hbar is small compared to the relevant scale factors of a system, quantum mechanics turns into classical mechanics.
A very important issue, in theory. Why is it that you have trouble excepting that proving something in principle to other scientists isn't the same as having an effect on the rest of the world?
>Except I’ve given explicit examples of ways that QM empirically is relevant in macroscopic systems
"Relevant". What a pleasantly useful dragging of the goalposts halfway down the field that is.
I never disputed that QM is relevant in those examples. But despite that, the relevance of those examples is less than you are insisting. At least to the person who made the comment, which we both disagreed with. I just did a better job of it, and I thought I'd be helpful and explain what it is you were doing wrong in that regard.
>But as usual, you simply don’t engage with the parts of my arguments that you don’t know how to address and pretend they never happened.
You have it backwards. The parts I don't engage are either trivial or accurate. The sections of your comments I directly address are mostly just the more illustrative mistakes in your reasoning.
sticklebat t1_irpaayk wrote
> Nah. It is an effort to explain to people who understand physics but little else why other peope, who don't understand physics, understand more than they do.
Except you can’t do that effectively if you don’t understand physics in the first place.
> You're mistaking what is conventional within physics for what is meaningful in real life. "System" is the wrong word for a single substance, even one so profoundly important to physicists as Bose-Einstein condensates.
What? No. A system is any portion of the universe chosen to be analyzed. Anything outside the system is considered an environment, and it is ignored except for its effects on the system. System is a perfectly valid word to mean what I intended to mean, and it absolutely can refer to a “single substance.” What even does that mean? If I want to know why a metal is lustrous I can’t treat it as a single thing. Its luster arises from quantum mechanical effects arising from its atomic scale structure and properties.
> It is used to model one very specific and particular (pun intended) kind of quantum system, which is really important because that specific "condensed matter" is a macroscopic substance, unlike most quantum systems, which are sub-atomic, so small that even using the contrast macro/microscopic is actually weird.
Condensed matter doesn’t apply only to one specific kind of system. It applies to a huge range of systems. It is in fact so broad that it’s the single largest sub field within physics, and has significant overlap with other disciplines. Things as mundane as metallic surfaces, salt crystals and as exotic as superconductivity, BECs, and liquid helium fall under the umbrella of condensed matter, as do most phase transitions.
And again, you’re missing the point. I gave it as an example. I also gave other examples, too. Over the years, quantum coherence has been observed in bigger and bigger systems, from large particles all the way to the 40 kg mirrors used in the LIGO experiment, each of which was placed near its quantum mechanical ground state.
> Nobody disputes that deterministic objects "demonstrate quantum mechanical properties"
Are you really that dense? Nobody except for the person I was talking to before you jumped into the conversation. I literally made my arguments to a person disputing what you’re saying no one disputes. It seems like you’re just being contrarian at this point.
> So the use of one example of a "macroscopic thing" demonstrating quantum properties (which, as far as I know, aren't observable as distinct from conventional properties in BEC without special equipment and in highly restricted circumstances) really doesn't have the weight you think it would, in this discussion.
That might be the case if it’s what I did. But it’s not. And you’d know that if you weren’t basing your responses to me based on brief skims of relevant Wikipedia articles about condensed matter, for example. Once again you’re outing yourself here. You not only don’t understand the physics, you don’t even know what entire fields within physics refer to. There’s a reason why I said “condensed matter” and not “BECs.” That’s like confusing “Newtonian mechanics” for “the mechanics governing how balls roll.”
> Not a strawman, just an example of what it would take to justify saying that QM effects "the macro world" of everyday objects.
No, very much a strawman. We haven’t proved that Newtonian mechanics works for every conceivable macroscopic system, either. Nor can we do ever prove such a thing: science relies on induction, and while we can’t prove the validity of inductive logic in science, if that’s the point you’re making then it applies to every iota of scientific understanding ever, not just to QM.
> AKA language. AKA discussion. AKA the real world.
And here you’re using language to deliberately misrepresenting my meaning. My point was, whether it’s about “how” or not is a matter of semantics, it just depends on what we each meant by “how,” which can be interpreted different ways. But it’s telling that instead of engaging with my lengthy argument after that word, you’ve latched onto this one word to make a pithy point with little bearing on the argument at hand, instead.
> A very important issue, in theory. Why is it that you have trouble excepting that proving something in principle to other scientists isn't the same as having an effect on the rest of the world?
How many times must we complete this circle? I show you that it’s been proven in principle, and you say “okay but prove that it has an effect on the world.” So I give you countless examples of ways that it has an effect on the world. And then you ignore all but one and say “but prove that it’s always true.” Do you truly think you’re being reasonable here?
> "Relevant". What a pleasantly useful dragging of the goalposts halfway down the field that is.
Please explain how that word shifted any goalposts.
> I never disputed that QM is relevant in those examples.
So wtf are you on about? The other person did and they’re who I was talking to. You jumped into a conversation between two people to have your own side argument with the wind?
> I just did a better job of it, and I thought I'd be helpful and explain what it is you were doing wrong in that regard.
Of course you think you’ve done a better job. You also think you’re more qualified to talk about quantum mechanics than Bohr and Einstein were, and that your personal philosophy makes you immune to falling for misconceptions. You have a very high opinion of yourself; of that much I’m sure we can agree.
> You have it backwards. The parts I don't engage are either trivial or accurate. The sections of your comments I directly address are mostly just the more illustrative mistak
No, you consistently ignore important points that derail your entire argument. If they’re accurate, you’d have gone away already. If you view them as trivial, then you clearly don’t understand them.
TL;DR Stick to arguing about things you understand. You don’t understand quantum mechanics.
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