Layman's Question on Quantum Mechanics

[vanesch]

But this really is irrelevant to the issue that I brought up originally. Even when we know all the interactions, we presently cannot use it can CM physicist, nor can we make use of it to predict other yet-undiscovered emergent behavior. My training as an experimentalist is rearing its ugly head again. I'm asking "yeah, so? What can I do with it?"
Currently, nothing.
Zz.

Sure, I'm not disputing that. It's what I call "practical holism". And indeed many phenomena are difficult/impossible to practically calculate ab initio.

But you seem to make no distinction between "the answer exists (the "there exists" symbol in logic)" and "I know how I can find the answer". I'm claiming that "there exists" an answer for any measurable quantity related or not to an emerging property, and that there are only two possibilities: it agrees (the microscopic laws predict the property) or it doesn't agree (clash between the laws and the observation).
Of course if I cannot KNOW the answer, I cannot find out in which case I am, but it is not because I don't KNOW the answer that it doesn't exist (Fermat's last theorem was true, even before the proof was discovered).
And this means that there CANNOT be a peaceful coexistance between microscopic laws and macroscopic laws predicting emergent properties UNLESS the macroscopic properties are all in agreement (in the above sense) with the microscopic laws, which is all which the reductionist view requires.

 

[vanesch]

Is it simply because we cannot do all the complexities? Or is it because there is a built-in shortcoming in the model that simply neglect some "long-range, collective order" that will only emerge once one crosses over some scale? These are questions no one can answer. But because of that, it is also wrong to assume that a "Theory of Everything" is everything! Elementary particle physicist may get multiple orgasms when they find it, but CM physicists will simply ask "Is that all there is?" We can't use it, and it isn't useful.

I agree with you of the sole spiritual value of this and total lack of practical use, except for the multiple orgasm: see, it WAS useful to some :rofl:

But I could formulate the reductionist-holist debate in another way, which is probably more meaningful.

Suppose that I have some microscopic laws, and that I CAN derive SOME macroscopic properties WITH mathematical certainty from these microscopic laws (such as conservation of momentum! But there might be others) ab initio, without making extra assumptions and approximations. COULD IT HAPPEN that there are specific "macroscopic" laws that contradict these ab initio predictions, while nevertheless the microscopic laws are supposed to be "correct" ? THIS is, to me, the essence of the holistic viewpoint, and, in my not so humble opinion, self-contradictory. If the answer to the above question is "no" then that, to me, is the essence of the reductionist viewpoint.

But that's a far cry from the indeed arrogant claim that if we know the fundamental microlaws, we know "all of physics". I will not hide that this was my initial motivation to go into particle physics, but one ends growing up :grumpy:

 

[selfAdjoint]

Patrick, given your test of holism, how would you rank broken symmetries, as found in the standard model for example. The usual account of these is that the ab initio physics predicts - e.g. - zero mass quarks, but "interactions" produce mass. Is this emergent in your view? Is it an example of emergent physics contradicting micro physics?

 

[ZapperZ]

Sure, I'm not disputing that. It's what I call "practical holism". And indeed many phenomena are difficult/impossible to practically calculate ab initio.
But you seem to make no distinction between "the answer exists (the "there exists" symbol in logic)" and "I know how I can find the answer". I'm claiming that "there exists" an answer for any measurable quantity related or not to an emerging property, and that there are only two possibilities: it agrees (the microscopic laws predict the property) or it doesn't agree (clash between the laws and the observation).
Of course if I cannot KNOW the answer, I cannot find out in which case I am, but it is not because I don't KNOW the answer that it doesn't exist (Fermat's last theorem was true, even before the proof was discovered).
And this means that there CANNOT be a peaceful coexistance between microscopic laws and macroscopic laws predicting emergent properties UNLESS the macroscopic properties are all in agreement (in the above sense) with the microscopic laws, which is all which the reductionist view requires.

You will note that my objection to reductionst approach isn't just based on the argument that we have not found an example or an answer. It is also based on indications, such as the examples in Laughlin book, of why there are many observations in which even Weinberg cannot come up with even hand-waving arguments to explain how such phenomena can emerge out of an elementary description. These are not slam-dunk proofs, but rather compelling evidence.

Take a lot of identical balls. Now shoot them through a hole. At the hole, you have a detector that measures the number of balls going through the hole at any given instant. Now make the hole smaller... and smaller... and smaller. At some point, only ONE ball at a time can pass through the hole. This is the SMALLEST number (other than none) that will pass through, carrying the entity equivalent to ONE ball.

This is NOT what happens in fractional charges/QHE. I can get an equivalent to 1/5 of a ball! The SMALLEST entity under such emergent phenomenon is SMALLER than the smallest entity at the microscopic scale. This is what I point out as compelling evidence on why elementary interactions have even conceptual problems (forget about mathematical formalism) of accounting for this.

I'm not using this to discuss the phenomenon. I'm using this to show you that I'm not simply using the "there are no answers" and the sole argument.

Zz.

 

[quantumcarl]

I'm just a layman, and a casual student of QM. ZapperZ is a working physicist -- I think he's currently at Argonne National Laboratory. Neils Bohr was one of the original developers of quantum theory.
I don't think there's anything necessarily wrong with speculating about the possible makeup and behavior of an underlying reality in terms of imagery from our ordinary experience. But that's not how QM was developed or what QM means, afaik.
If QM is about experimental setups and results (which it is), and not a description of an underlying quantum reality (which, afaik, it isn't), then the existence of nonlocal propagations in nature, or the idea that the existence of some object or event in nature depends on our consciousness of it, isn't entailed by QM.
QM books often weave metaphysical (using classical analogs/imagery) language with the physical, instrumentalist/mathematical language in a way that makes it sort of unclear that, say, the word 'particle' as it's used in QM has only a mathematical (and instrumental) existence and meaning. Phrases like, "the probability that the particle will be found ...", used in contexts involving detector clicks or dots on a screen tend to obscure the fact that it's the detector clicks or dots on a screen, and their probability of occurance wrt specified experimental setups, that are being talked about mathematically and not some underlying quantum world of particles and waves.
It's not that anybody is denying the possibility, or existence, of an underlying quantum world. But how are you going to talk about it unambiguously? This was one of the main problems that the developers (including Niels Bohr, who you've asked about) of quantum theory were faced with. Whatever it might be, it's not amenable to our direct sensory perception and can only be approximately tracked by instruments. So, QM is about what can be unambiguously stated wrt the various experimental results that have historically defied classical explanation -- that is, QM is all about the experimental results not their possible underlying causes. It's a purely correlational theory, not a causal one.
Of course the underlying quantum world, whatever it might be, is presumed to be a bit more sensitive to observational probing than the moon is.
However, the existence of quantum phenomena in the physical forms of experimental preparations and results, and the math which describes these, (which are the only physical forms in which quantum phenomena can be unambiguously said to exist) doesn't depend on our consciousness of them any more than the existence of the moon depends on our consciousness of it.
The physical fact that the experimental preparations and the math have the specific forms that they do has of course something to do with the conscious decisions that went into their construction. But those conscious decisions were preceded by sensory apprehensions of the physical world which didn't just pop into existence because we wanted or willed them to be there. The physical facts are what they are -- and to the extent that all people with normal (and sober) sensory capabilities see the same physical facts, then they're considered to be objective (not just subjective, ie., not just in your or my imaginings) and part of our physical world.
The working assumption in all of the physical sciences is that the world of our objective sensory experience exists whether you or I or anybody is paying attention to it.
And there's nothing in either quantum theory or quantum experiments which contradicts this view ... at least as far as I'm aware.
In order to really understand what Bohr and ZapperZ and others are saying it's necessary to put down the QM popularizations and actually start learning the theory -- and then a fascinating (not just the physical/experimental phenomena themselves, but also the ingenious ways that physicists have devised to produce them) world of discovery will be revealed to you.

I tend to agree with you here. Your explanation is akin to the differences between the two schools of "emotionalism" and "detached objectivism". An example would be where we see two observers viewing the painting of the Mona Lisa by Da Vinci. One viewer only sees the emotional content, the smile, the reticent attitudes and garments the subject in the painting is shown to exhibit and the other viewer sees the techniques and the materials the painter used to depict an "emergent phenomenon" that apparently no longer exists with the exception of the painted record.

The terminologies of physics and quantum physics can be confusing and mis-leading for the general public. For instance the words "photon" and "graviton" simply describe a quantum measurement of an area of a wave... as far as I can decifer. Yet many, many people take these words as factual descriptions of existing and tangable particles. They see gravity as a kind of collection of little undecernable "gravitons" spewing off a mass and exherting an attractive force. Similarily with the idea of photons, people actually think they can feel little particles called "photons" hitting them when a light wave reaches their location.

This ambiguity that's been set up by the terminology of physics, which is really exclusively meant to clarify various theories of physicists alone, can tend to bleed over into terms and conditions of molecular physics where again, we cannot easily discern molecules in our daily lives yet we are told that all matter is comprised of these quanta. What is also confusing is that some of us are told that the ideas of molecules and atoms are also simply convenient ways of describing waves and energy packettes.

So, perhaps what I am asking about nature (after Bohr) is this:.. at what point do we "emerge" from the micro-microscopic, non-solid condition that quantum physics proports to be able to (physically) measure and what are the catylists or the conditions that make it possible to distiguish between the two seemingly contradictory states?

I realize that to imagine awareness to be fundamental to the condition of solid matter is pushing anthropomorphism to its outer limits. But, it is also hard to prove that there is any other fundamental basis for waves of energy to be perceived as solid matter.

 

[quantumcarl]

I can do better. Look in my journal entry under "Theory of Everything?". There's a series of appers by Laughlin (and citing Anderson) on this subject. You'll realize how ironic it is for you to indicate TO ME what an emergent phenomenon is.
Zz.

Quite to the contrary, you asked me the question with regard to whether or not the quantum hall effect is an example of an emerging phenomenon. It is more ironic that you would ask me, a lay person to quantum physics and physics in general, the question. I simply had to google the proposition and hope it was an approximate to what you were asking. I didn't do the math and I didn't do the quantum trough or hall effect experiments.

Is it true that when light colides with light (at this point carrying only relative mass or rest mass, I forget which) that particles like sigmas and others are formed, constituting something we are able to observe and classify as matter?

 

[ZapperZ]

Quite to the contrary, you asked me the question with regard to whether or not the quantum hall effect is an example of an emerging phenomenon. It is more ironic that you would ask me, a lay person to quantum physics and physics in general, the question. I simply had to google the proposition and hope it was an approximate to what you were asking. I didn't do the math and I didn't do the quantum trough or hall effect experiments.

No, look again. I asked you if you actually understood what "emergent phenomena" were when you "cut-and-paste" something that Anderson did. I questioned your understanding of the things you're using to either illustrate your point, or to use as an argument point. Instead, when I asked you this, you were trying to point to me what emergent behavior is. This is what I find ironic.

Is it true that when light colides with light (at this point carrying only relative mass or rest mass, I forget which) that particles like sigmas and others are formed, constituting something we are able to observe and classify as matter?

Light doesn't need to collide with light to produce matter (we have no photon colliders at the moment.). Pair production does this very often and it is the source of many positrons. But why is this even relevant here?

Zz.

 

[quantumcarl]

No, look again. I asked you if you actually understood what "emergent phenomena" were when you "cut-and-paste" something that Anderson did. I questioned your understanding of the things you're using to either illustrate your point, or to use as an argument point. Instead, when I asked you this, you were trying to point to me what emergent behavior is. This is what I find ironic.

OK I see what your angle was with the question... and now I have a .000301 percent better understanding of the concept of emergent property... and that's probably an over-estimate. Still, I appreciate the motivation to study an idea I have never actually heard of...

Light doesn't need to collide with light to produce matter (we have no photon colliders at the moment.). Pair production does this very often and it is the source of many positrons. But why is this even relevant here?
Zz.

In my reply to Sherlock I explained that I don't understand what the threshold, the catylist or the condition is where waves of energy become observed and classified as matter. This is in keeping with my original question concerning matter and its fundamental origin. I explained that, as far as I know, photons and gravitons are convenient units of measurement used in quantifying a light wave/frequency or a field of gravity and that these units are not particles or considered to have a real mass and stuff like that.

Then I mentioned the contradictory notion that matter is also considered to be a result of waves and frequencies of energy and that terminology like "atoms" and "molecules" could also be considered units of measurement being used to describe densities of energy... (I'm sure you have a better description of this). This is when I remembered reading in PF Physics Section that collisions of photons, at the early stages of the universe produced something like sigmas, hadrons(?) and other (things i don't have a name for suchas quarks or top quarks or something(??)).


With your experience in these "matters" would you say that photon units of a light wave are also an emergent phenomena and so would not be considered fundamental to the existence of matter? Or would simply tell me to... "do the math boy?!"

 

[Sherlock]

So, perhaps what I am asking about nature (after Bohr) is this:.. at what point do we "emerge" from the micro-microscopic, non-solid condition that quantum physics proports to be able to (physically) measure and what are the catylists or the conditions that make it possible to distiguish between the two seemingly contradictory states?

The point of Bohr's spiel was that instead of speculating about another level (or other levels) of physical reality (instead of building metaphysical constructions to account for quantum phenomena), the quantum theory, in order to have a clear meaning (an unambiguous formulation) and thereby to progress, had to concern itself only with what happens at the instrumental level -- that is, as far as the science of physics can be concerned, there isn't any other level. (Sure, there might be some sort of imagery attached to this or that mathematical model, but it would be a mistake to take that literally as some sort of reference to the composition or behavior of an underlying reality. Quantum theory isn't an ontology of an underlying quantum world.)

The concern is then to what experimental phenomena does quantum theory solely apply, to what experimental phenomena can a semi-classical formulation be applied, and to what experimental phenomena can a purely classical formulation be applied.

I realize that to imagine awareness to be fundamental to the condition of solid matter is pushing anthropomorphism to its outer limits. But, it is also hard to prove that there is any other fundamental basis for waves of energy to be perceived as solid matter.

I think of human awareness or consciousness as the physical body monitoring (detecting, sensing) stuff impinging on it from outside, and also monitoring stuff that's happening inside it. Eventually, stimuli of sufficient magnitude become electro-chemical changes in the brain -- at which point we are aware or consicous of something or other, or, more usually, many things at once. We as well as other organisms are, then, just more or less complex, mobile detecting and adapting devices, which, through many generations of adaptation and alteration are, additionally, able to reproduce within species using only our self-contained biological components (and perhaps some wine and mellow music).

Waxing metaphysical, whoops, we're just a particular bounded complex (a manifestation of several different scales) of wave interactions.

A particular consciousness, then, arises out of a particular material configuration -- not the other way around. This general conception of consciousness avoids the usual anthropomorphizing.

At this point, I think you should present your consciousness-matter considerations to the metaphysics or philosophy forums (if you haven't already) in order to work out any semantic inconsistencies that might be present or that might arise -- because QM, per se, doesn't address this sort of thing -- and anyway there are people frequenting those forums who have thought a lot about the meaning of consciousness, etc.

I'll no doubt join in the discussion there at some point, as I love to speculate about such matters.

As for your latest questions (I just noticed your last post), maybe one of the mentors can answer some of them in a way that satisfies you, but to really understand what physics has to say it's necessary to learn it in steps. I could outline a program of self-study for you, but you're probably better off getting it from one of the mentors.

 

[vanesch]

Patrick, given your test of holism, how would you rank broken symmetries, as found in the standard model for example. The usual account of these is that the ab initio physics predicts - e.g. - zero mass quarks, but "interactions" produce mass. Is this emergent in your view? Is it an example of emergent physics contradicting micro physics?

I tried to point out that "emergent phenomena" (meaning, special behaviour seen in large collection of constituents which does not directly seem to occur in small collections of said constituents) are not, by themselves, any indication of "holism" (the way I understand it, namely the negation of reductionism, and reductionism in my book means: there is a UNIQUE set of laws of nature (a mathematical structure, say) which describe ALL of nature). For sure there are emergent phenomena. But you know that you can have emergent phenomena too in computer simulations (from Conway's game of life to many other funny things people have thought up). And these computer simulations are OF COURSE reductionist: the program describes the individual interactions of the constituents. So the program (which is the computer equivalent of the "physical laws on microscale") IS capable of generating "emergent behaviour" such as little conglomerates which walk across the screen and so on.
I would even think that the very name of "emergent" phenomena meant exactly this: they EMERGE from the playing together of the microscopic components following their microscopic laws.

The school example is the Ising model: http://en.wikipedia.org/wiki/Ising_model

which shows a phase transition emerging from the microscopic interaction between vertices.

What I thought was at stake here, was that there are several (according to ZZ, a majority) of physicists which think that the laws of nature on microscopic scale ARE NOT RESPONSIBLE for certain macroscopic phenomena (which are hence not *emerging* from the microlaws but "appear out of the blue"). So you have the validity of the microlaws for the constituents, but nevertheless, a large set of constituents shows behaviour which is NOT emerging from the workings of these microlaws.

As I tried to point out, this view, on a purely conceptual side, looks to me self-contradictory. Because any measurable quantity that shows us the appearance of the new phenomenon has - in principle - a predicted value based on the microlaws. If that predicted value INDICATES US the "new phenomenon" (so there is agreement), then after all, the new phenomenon WAS emerging from the microlaws, and it was NOT a new phenomenon. And if the predicted value does not indicate us the "new phenomenon" then there is a CONTRADICTION between the microlaws and the macroscopic behaviour observed, which FALSIFIES the microlaws.
My silly example was: if the microlaws say that the atoms of the apple all go to the left, this can not be in coexistance with a macrolaw saying that the apple as a whole goes to the right.
The only way of reconciling both would be if the microlaws DID NOT MAKE ANY DEFINITE PREDICTION of the measurable quantity ; but this cannot happen, because the microlaws already define the behaviour of the constituents entirely.

 

[quantumcarl]

The point of Bohr's spiel was that instead of speculating about another level (or other levels) of physical reality (instead of building metaphysical constructions to account for quantum phenomena), the quantum theory, in order to have a clear meaning (an unambiguous formulation) and thereby to progress, had to concern itself only with what happens at the instrumental level -- that is, as far as the science of physics can be concerned, there isn't any other level. (Sure, there might be some sort of imagery attached to this or that mathematical model, but it would be a mistake to take that literally as some sort of reference to the composition or behavior of an underlying reality. Quantum theory isn't an ontology of an underlying quantum world.)
The concern is then to what experimental phenomena does quantum theory solely apply, to what experimental phenomena can a semi-classical formulation be applied, and to what experimental phenomena can a purely classical formulation be applied.
I think of human awareness or consciousness as the physical body monitoring (detecting, sensing) stuff impinging on it from outside, and also monitoring stuff that's happening inside it. Eventually, stimuli of sufficient magnitude become electro-chemical changes in the brain -- at which point we are aware or consicous of something or other, or, more usually, many things at once. We as well as other organisms are, then, just more or less complex, mobile detecting and adapting devices, which, through many generations of adaptation and alteration are, additionally, able to reproduce within species using only our self-contained biological components (and perhaps some wine and mellow music).
Waxing metaphysical, whoops, we're just a particular bounded complex (a manifestation of several different scales) of wave interactions.
A particular consciousness, then, arises out of a particular material configuration -- not the other way around. This general conception of consciousness avoids the usual anthropomorphizing.
At this point, I think you should present your consciousness-matter considerations to the metaphysics or philosophy forums (if you haven't already) in order to work out any semantic inconsistencies that might be present or that might arise -- because QM, per se, doesn't address this sort of thing -- and anyway there are people frequenting those forums who have thought a lot about the meaning of consciousness, etc.
I'll no doubt join in the discussion there at some point, as I love to speculate about such matters.
As for your latest questions (I just noticed your last post), maybe one of the mentors can answer some of them in a way that satisfies you, but to really understand what physics has to say it's necessary to learn it in steps. I could outline a program of self-study for you, but you're probably better off getting it from one of the mentors.

I see your point. My question was raised in the "hand-waving, tree-hugging" philosophy section through my initial ascertation that awareness (the neurophysicist's term for the more ambiguous term of "conscousness") is fundamental to the bio-specific experience of (solid) matter. This is not a question of metaphysics but one of biological perception and adaption with regard to survival and a biological unit's ability to function in an environment it perceives itself to be a part of.

Our environment also includes our thoughts and our beliefs (which may or may not be truths regardless of how collectively they are experienced) and these beliefs are formed in what is termed a classical environment by people who are "emergent phenomena". Doesn't this constitute a kind of bias on the part of the observer with regard to the results of quantum measurements, etc...?

 

[vanesch]

This is NOT what happens in fractional charges/QHE. I can get an equivalent to 1/5 of a ball! The SMALLEST entity under such emergent phenomenon is SMALLER than the smallest entity at the microscopic scale. This is what I point out as compelling evidence on why elementary interactions have even conceptual problems (forget about mathematical formalism) of accounting for this.
I'm not using this to discuss the phenomenon. I'm using this to show you that I'm not simply using the "there are no answers" and the sole argument.
Zz.

I looked up a bit on the fractional quantum hall effect:
http://www.pha.jhu.edu/~qiuym/qhe/qhe.html

as far as I can make up anything from the explanation (by Laughlin) of the FQHE:
http://www.pha.jhu.edu/~qiuym/qhe/node5.html#SECTION00050000000000000000

I would say that this is entirely a reductionist approach, no ? He's putting together wavefunctions for electrons in such a way that the FQHE is explained.

Of course I'm not a condensed matter physicist, and probably many subtleties escape me totally here. But I don't see the shocking contradiction between the reductionist view (for instance, claiming that electrons have to be described by a wavefunction in hilbert space), and the FQHE. I guess that if Weinberg has problems with it, I'm no party !

 

[ZapperZ]

I looked up a bit on the fractional quantum hall effect:
http://www.pha.jhu.edu/~qiuym/qhe/qhe.html
as far as I can make up anything from the explanation (by Laughlin) of the FQHE:
http://www.pha.jhu.edu/~qiuym/qhe/node5.html#SECTION00050000000000000000
I would say that this is entirely a reductionist approach, no ? He's putting together wavefunctions for electrons in such a way that the FQHE is explained.
Of course I'm not a condensed matter physicist, and probably many subtleties escape me totally here. But I don't see the shocking contradiction between the reductionist view (for instance, claiming that electrons have to be described by a wavefunction in hilbert space), and the FQHE. I guess that if Weinberg has problems with it, I'm no party !

No, the ground state wavefunction is not the wavefunction of a "free" charge carrier. It's the ground state of a "quasiparticle". So this already is a wavefunction of a many-body system.

Zz.

 

[vanesch]

No, the ground state wavefunction is not the wavefunction of a "free" charge carrier. It's the ground state of a "quasiparticle". So this already is a wavefunction of a many-body system.
Zz.

Ok, but we know how these effective quasi-particles appear as "helpful bookkeeping devices" of the stationary states of a many-particle system with periodic potentials, so this is not impossible to obtain "ab initio" (again: in principle, though it may be intractable in practice).

As such, constructing wavefunctions of quasiparticles is nothing else but exploring the zoo of ab initio solutions of the many-body problem, in a smart way (by first making superpositions that correspond to "quasiparticles" - call them stationary states of the hamiltonian, or good approximations of it), and then again making superpositions of these quasiparticle states. So, as such, using wavefunctions of quasiparticles does not clash, in my eyes, with any reductionist view.

Of course, the precise modelling of the interaction terms (that is, the matrix elements of the neglected parts of the hamiltonian that we are now putting in in the "quasiparticle states") is probably more guesswork than ab initio deduction, and it requires a great deal of physical intuition, guesswork, good luck, insight and whatever to DO what people like Laughlin did, but I fail to see the shock with the principle of reductionism. That's - I admit this freely - probably more due to my naivity than my ability to outsmart Weinberg . It might very well be that there are subtle reasons that would seriously make you expect that this kind of wavefunction should NOT be obtained ab initio and that I fail to see the difficulty because I fail to know about these reasons.
But if it is only based upon the usually NAIVE explanation of quasiparticles acting like normally charged particles, behaving classically (as is usually explained the hall effect in a first course), and that in this naive picture, we now have to use fractionally charged "bullets" to find agreement with the FQHE, then this argument doesn't have much weight in my eyes. The picture, in all likelihood, is simply wrong for this case.

So, in my great naivity, I fail to see how one can conclude that the FQHE is not - in principle - obtainable from the exact solution to the quantum mechanical problem of the many-electron system, though I concede, and I repeated this often, that this may be practically totally unfeasable and that it is indeed MUCH SMARTER to do what condensed matter physicists are doing and to model phenomenologically.

 

[ZapperZ]

Ok, but we know how these effective quasi-particles appear as "helpful bookkeeping devices" of the stationary states of a many-particle system with periodic potentials, so this is not impossible to obtain "ab initio" (again: in principle, though it may be intractable in practice).

I'm not sure what you mean by "ab initio" here. It certainly doesn't HAVE to mean "start from elementary interactions". The ab initio starting point in condensed matter physics has always been the many-body hamiltonian.

The confusion comes in when condensed matter uses the phrase such as "single-particle" excitation. This does NOT mean it is starting with elementary particle and adding the interactions one at a time. A single particle spectral function ALREADY comes in with a baggage load of many-body interactions absorbed within the self-energy term inside the many-body Green's function. This is what allows us to treat this as if it is a one-body problem.

Now, while you can "turn off" the many-body interactions and regain the "bare particle", the problem is not tractable if you instead decides to change the problem from a many one-body problem (which is what Landau did) to a single, many-body problem. You can't solve this. So by doing what appears to be only a one-body problem, you are already commited to an emergent entity - the quasiparticle that arises out of the many-body interactions.

This is why I said that the starting point is the many-body ground state. The "electrons" that you measure in a conductor is already a many-body normalized quasiparticle, not the bare electrons. And if Anderson and Laughlin are correct, ALL of our elementary particles are emergent particles arising out of some field excitations, including the quarks.

Zz.

 

[quantumcarl]

Out of respect of the learned people who have contributed to this thread and to help me clarify my question I'd like to thank you all for entertaining it and me and my ineptitude with the study of the nature of quantum physics, mechanics and physics in general.

Since there has been such an open attitude toward disclosing everyone's level of understanding of physics I'll include my own background with the topic. As a medical illustrator for many years with a well established cancer treatment centre I was fortunate enough to be exposed to varied amounts of knowledge about every discipline that goes into the treatment of cancer. My favorite group to spend well over 4620 coffee breaks and lunch breaks with was the medical physicists.

One man in particular became a sort of mentor for me who originally immigrated from China, became a dishwasher and supported himself through university and became a PhD medical physicist. That is the extent of my informal training in physics... with the exception of this incredible forum, the Physics Forum.

Before I completely blow this thread out of quantum physics into philosophy or get my knuckles wrapped by a mentor I'll just say that I have completely enjoyed the responses I've received to my question.
I realize now that physicists really can't progress in their studies if they are continually questioned or in doubt about niggling little philosophical questions concerning the nature of their work. It would be like stopping Wayne Gretsky every five minutes during a hockey game and asking him if he really exists! Totally inappropriate.. and absurd!

I am actually satisfied with the "speil' from Bohr that suggests "physics is not about what nature is but more about what physicists can say (with regard to their observations) about nature. Thank you very much Dr. Bohr and everyone else here that has done and is doing the math!

 

[vanesch]

I'm not sure what you mean by "ab initio" here. It certainly doesn't HAVE to mean "start from elementary interactions". The ab initio starting point in condensed matter physics has always been the many-body hamiltonian.

Well, start with "real" electrons (in the framework of non-relativistic quantum mechanics, sufficient for most of condensed matter physics), and real nucleae. Consider the crystal structure as a given (if you want to discuss this, go to the Born-Oppenheimer approximation of the many body problem which allow you to treat the electron system and the nucleae system - in most cases - separately) and consider hence the many-electron system in a periodic potential. Then realize that stationary solutions for the many-body system without interactions can be classified using a Fock space approach, and call the bookkeeping state countings "quasi particles". We have now a "free quantum field theory" of quasiparticles. Next, add in the interactions of the individual real particles, but modeled as interactions of quasi-particles. It is usually here where we totally leave the ab-initio approach and start guessing reasonable effective interactions of quasi particles ; but in order to be right, these should be the matrix elements of the up hereto neglected interaction hamiltonian in the real many-body problem, but between the Fock basis states, and not between the real-single-particle states. It is only to be hoped that the guessed-at effective interaction term corresponds to this matrix element, but in the case it is, we are still "in parallel" with an approximation to an ab initio calculation.
The point I'm trying to make is that if I were some god-mathematician with a brain a billion times the size of the visible universe, I WOULD be able to do all these calculations ab initio. Because some of us are lesser mortals we have to ressort to intuition and guesswork.

The confusion comes in when condensed matter uses the phrase such as "single-particle" excitation. This does NOT mean it is starting with elementary particle and adding the interactions one at a time. A single particle spectral function ALREADY comes in with a baggage load of many-body interactions absorbed within the self-energy term inside the many-body Green's function. This is what allows us to treat this as if it is a one-body problem.

I understand that, but I'm claiming that the idea behind it is still ab initio, but not from calculations, but from intuition and guesswork, because of the limited size of our brains. It does not mean that the ab initio approach is going to FAIL. It is simply untractable by us, lesser mortals. And maybe the smarter we get, the more cases we will find where we CAN, within some approximation, do the true ab initio calculation.

Now, while you can "turn off" the many-body interactions and regain the "bare particle", the problem is not tractable if you instead decides to change the problem from a many one-body problem (which is what Landau did) to a single, many-body problem. You can't solve this. So by doing what appears to be only a one-body problem, you are already commited to an emergent entity - the quasiparticle that arises out of the many-body interactions.
This is why I said that the starting point is the many-body ground state. The "electrons" that you measure in a conductor is already a many-body normalized quasiparticle, not the bare electrons. And if Anderson and Laughlin are correct, ALL of our elementary particles are emergent particles arising out of some field excitations, including the quarks.
Zz.

I understand that, but I don't find that an argument against reductionism. The quasi particles EMERGE from the underlying microphysics - or at least, we conceptually think of it that way (and in some toy models, we can even do it explicitly). I'm not arguing against "emergent properties" at all. I'm arguing against the idea that we can have microphysical laws which are "correct" and apply to the microphysics, and that we have INDEPENDENT and co-existing macrophysical laws, which have nothing to do, even in principle, with these microphysical laws. I'm claiming that as a matter of principle, these microphysical laws make a definite statement concerning the macrolaws ; and if they are in agreement, all the better, and if they are in contradiction, the microlaws are simply FALSIFIED. But I don't buy that they can INDEPENDENTLY exist next to each other.

However, I totally agree that the above statement is only one of principle (available to said god-mathematician with said brain) and that we have to realize our mortal limitations, and as such, that the said approach is a total waste of time in a great many number of cases, and that you indeed BETTER do as if you are discovering (almost) independent laws: you'll get faster to a useful theory.

So you can tell me: well, if you know that it is the only practical method, what the hell are you blathering about ? I think that there IS a fundamental difference. We get smarter as time goes on. We learn new mathematical techniques, and we get smarter machines. We get more and more experience with how these many-body systems behave. This means that there is some hope that we can do more and more ab-initio-like calculations, or at least derive general properties of the kinds of solutions we can hope to obtain ab initio. And in the reductionist approach, these derivations and properties make sense ; while in the true holistic approach, this is a total waste of time.

As I said, I think that reductionism together with the hypothesis of the existence of an objective world are the two founding principles of physics. I'm not willing to give them up so easily.

 

[Schrodinger's Dog]

Fascinating stuff

Really walking a fine line between explaining your method and philosophy, here I'll step over that line.

all good stuff. But accepting that there is an objective reality and accepting there is no objective reality only a subjective one are different sides of the same coin . Neither has any proof and neither is more credible than the other? This maybe a philosophical point, but it does at least raise one important issue? What if what we see is not objectively real? What if we are merely seeing it that way because that is how we evolved to see it, evolutionaly speaking the reality of photons properties are less beneficial to survival than seeing them the way we do now? Yeah I know you can dismiss such questions as specualtion and philosophy.

But if I had a machine that did 1000 experiments which all got the same results. And you did the experiment and got 1000 slightly different results. You'd check the machine and see that those results where caused by an error brcause of reason A. But what if the machine is right and your perception is wrong? We cannot simply dismiss the idea that what we see experimentally is the absolute truth any more than we can dismiss that it is all delusion. With that in mind, we have to be really careful about what we say is true from our perspective, getting 1 million peope to corroborate results is sciences way of mitigating the subjectivity but barring meeting an alien that tells us QM is all tosh because of Reason B or that QM is all right because of reason A, we will never truly know what objectivity is. With this in mind all we can do is experiment and hope that everything exists that we say does and that QM isn't just some bizarre fantasy, because the alternative doesn't bear thinking about

Yep total philosophy I agree, but I still think it's a point... Like I said before if we're wrong then we'll never know it 'till someone teaches us how to percieve reality properly

I must say though that this thread is one of the best I've read in my short time on here. You'd be hard pressed to come up with a better suming up of scientific ideals and methodology; bravo gentlemen

I think I agree with Vanech and ZZ, I'm just hoping I'm not wrong

 

[ZapperZ]

Well, start with "real" electrons (in the framework of non-relativistic quantum mechanics, sufficient for most of condensed matter physics), and real nucleae. Consider the crystal structure as a given (if you want to discuss this, go to the Born-Oppenheimer approximation of the many body problem which allow you to treat the electron system and the nucleae system - in most cases - separately) and consider hence the many-electron system in a periodic potential. Then realize that stationary solutions for the many-body system without interactions can be classified using a Fock space approach, and call the bookkeeping state countings "quasi particles". We have now a "free quantum field theory" of quasiparticles.

But these aren't "quasiparticles". They ARE particles. Their non-interactions make them to be "ideal gasses", and statistically, we can deal with that.

Next, add in the interactions of the individual real particles, but modeled as interactions of quasi-particles. It is usually here where we totally leave the ab-initio approach and start guessing reasonable effective interactions of quasi particles ; but in order to be right, these should be the matrix elements of the up hereto neglected interaction hamiltonian in the real many-body problem, but between the Fock basis states, and not between the real-single-particle states. It is only to be hoped that the guessed-at effective interaction term corresponds to this matrix element, but in the case it is, we are still "in parallel" with an approximation to an ab initio calculation.

Actually, this is not true all the time. In Landau's Fermi Liquid theory, it is ONLY in the weak coupling limit (i.e. the interaction is weak enough that you can use mean field approximation) that will produce a 1-to-1 correspondence to the "bare", many one-body scenario. Crank up the coupling, and you lose everything! It is why strongly-correlated systems are such a fundamental and hot topic in condensed matter physics. We LOSE quasiparticles here! We have no well-defined entity to call a "quasiparticles" (see the normal state of an underdoped high-Tc superconductor). So no, there's nothing "parallel" here. At some point, your well-defined entity goes away.

And not only that, if you do this in 1-dimension, even the smallest correlation can produce a fractionalization of the spin and charge degree of freedom - they go their own separate ways with their own dispersion. There's nothing to match anything with the "non-interacting" case here - bluntly put, a "quasiparticle" is no longer "a good quantum number".

The point I'm trying to make is that if I were some god-mathematician with a brain a billion times the size of the visible universe, I WOULD be able to do all these calculations ab initio. Because some of us are lesser mortals we have to ressort to intuition and guesswork.

But as I've said, if this is OBVIOUS, we won't be having this discussion. It is NOT obvious, at least not to me, and certainly not to Anderson and Laughlin. You could be looking all you want at the individual dots on a piece of paper, but you will never been able to deduce from the local arrangement of those dots that it forms a picture. The long-range pattern is just not there for you to see it. It is why such interactions at that microscopic scale tells us nothing about the larger ensemble. Only when you step back and consider the whole thing as a clumb do you see the emergent behavior.

Zz.

 

[Rade]

The true holistic (anti-reductionist) approach is that EVEN IF YOU WERE TO USE THE EXACT MICROSCOPIC LAWS OF NATURE without any approximation, you would not be able to derive certain macroscopically observed phenomena. I think that that claim is self-contradictory...

This is not a correct understanding of holism, at least as understood by the science of cybernetics. If the state conditions of two black boxes (A,B) are given, and each is studied in isolation until its "canonical representation" is established and if they are then coupled in a known pattern by known linkages, then it must follow logically that the behavior of the whole [A-B] is determinate, and can be predicted. Thus such a "holistic" system will show no emergent properties since there is a 1:1 canonical transformation (U) linking A --> B. Likewise, there must be a 1:1 inverse of U (V) which may be also U^-1 for B --> A (= unitary transformation of a QM system).
Now the concept of "reducibility" and its relationship to "holism" in general system theory is such that a holistic system [(A)-(B) from above example] has immediate effects on each other as thus shown [ (A) <-----> (B) ] or perhaps one way only [ (A) -----> (B). The "reductionist" representation is only obtained when the two parts are functionally independent, thus [ (A) (B) ].
Now, in cases where the "parts" are at a range of size greatly different than the "whole", then the fundamental properties of the whole can be very different indeed from the parts, and what is "true" at one end (the reduced state) may not be true at the other (the holistic state). For example, consider the concept "taste" as relates to the atoms carbon (C), hydrogen (H), oxygen (O). If we treat these as black boxes each has a fundamental taste property (= no taste). However, when we couple to form a large molecule H-C-O (a sugar) we find a new property of taste has "emerged" (= sweet) that could not be predicted from the parts via any formalism of QM.
And I take it that this is what ZapperZ is articulating when he states:
[ZapperZ: "QM has many features that merge into the classical properties, especially at high quantum number, high temperatures, or large interactions (decoherence). But this doesn't mean that using QM description for classical, macroscopic system is any more valid than using classical physics for QM systems. There are a bunch of things we still don't quite know at the mesoscopic scale where these two extremes clash their heads. All we know right now is that one should not simply adopt QM's "world view" on classical systems. It will produce absurd conclusions."]

 

[quantumcarl]

You could be looking all you want at the individual dots on a piece of paper, but you will never been able to deduce from the local arrangement of those dots that it forms a picture. The long-range pattern is just not there for you to see it. It is why such interactions at that microscopic scale tells us nothing about the larger ensemble. Only when you step back and consider the whole thing as a clumb (clump) do you see the emergent behavior.
Zz.

Sorry to bother you again. This sounds like a fundamental requirement to observing matter. You have to exist at a similar scale to the scale of other emergent phenomena... or "step{ped} back" to see the emergent behaviours of energy.

It is boggling for me to figure out how physicists do the opposite and reduce their observations to the scale of energy fields or EM energy.

Do the Quantum Physicists consider themselves as one of the instruments in an experiement? Or as one of the conditions?

By the way, "how salty is spring tension (Zapper z)?!" :rofl: (ref:"How big is a photon..." thread, PF)

 

[ZapperZ]

Sorry to bother you again. This sounds like a fundamental requirement to observing matter. You have to exist at a similar scale to the scale of other emergent phenomena... or "step{ped} back" to see the emergent behaviours of energy.

Please note that when I said "observe", it has NOTHING to do with "I have to exist" requirement. This makes the rest of your point in that post moot.

You are more than welcome to start a new thread in the Philosophy section to discuss what is obvously the main thing you are so interested in. I just don't have the patience to deal with such issues.

Zz.

 

[vanesch]

This is not a correct understanding of holism, at least as understood by the science of cybernetics. If the state conditions of two black boxes (A,B) are given, and each is studied in isolation until its "canonical representation" is established and if they are then coupled in a known pattern by known linkages, then it must follow logically that the behavior of the whole [A-B] is determinate, and can be predicted. Thus such a "holistic" system will show no emergent properties since there is a 1:1 canonical transformation (U) linking A --> B. Likewise, there must be a 1:1 inverse of U (V) which may be also U^-1 for B --> A (= unitary transformation of a QM system).

Ah, that's a much more restricted definition of "reductionism" which makes even no sense in the frame of QM, in that the QM state space of the system [A-B] is BIGGER than the state space of [A] and the statespace of (entangled states).

I understood "reductionism" as: all macroscopic behaviour is *in principle* determined by the laws (in casu QM) gouverning the microsystems (and holism as the negation of reductionism). This means that the laws governing the microsystem have mathematically fixed (even if you don't know how to *derive* it in practice) the emergent properties.

Now the concept of "reducibility" and its relationship to "holism" in general system theory is such that a holistic system [(A)-(B) from above example] has immediate effects on each other as thus shown [ (A) <-----> (B) ] or perhaps one way only [ (A) -----> (B). The "reductionist" representation is only obtained when the two parts are functionally independent, thus [ (A) (B) ].

Well, in physics, that's simply called: 'interacting systems'. Of course we allow the constituents to interact...

Now, in cases where the "parts" are at a range of size greatly different than the "whole", then the fundamental properties of the whole can be very different indeed from the parts, and what is "true" at one end (the reduced state) may not be true at the other (the holistic state). For example, consider the concept "taste" as relates to the atoms carbon (C), hydrogen (H), oxygen (O). If we treat these as black boxes each has a fundamental taste property (= no taste). However, when we couple to form a large molecule H-C-O (a sugar) we find a new property of taste has "emerged" (= sweet) that could not be predicted from the parts via any formalism of QM.

That's because "taste" is not a well-defined measurement observable (it's in fact a qualium). As I tried to point out, one needs to describe an *experiment* that measures a "holistic" quantity. The microscopic description of the experiment, in the reductionist version, should then also give the correct outcome for the experimental measurement. That's what I tried to do with the description of the measurement of the index of refraction of water, that evaporates. The phase-transition introduces a change in refractive index, and that gives rise to a change in the configuration of the EM field, something that "makes microscopic sense". So considering the entire physical microdescription of all the particles and fields involved, if reductionism holds (meaning: if the microdescription determines mathematically the macroproperties) then this microdescription determines also this change in the configuration of the EM field.

And I take it that this is what ZapperZ is articulating when he states:
[ZapperZ: "QM has many features that merge into the classical properties, especially at high quantum number, high temperatures, or large interactions (decoherence). But this doesn't mean that using QM description for classical, macroscopic system is any more valid than using classical physics for QM systems. There are a bunch of things we still don't quite know at the mesoscopic scale where these two extremes clash their heads. All we know right now is that one should not simply adopt QM's "world view" on classical systems. It will produce absurd conclusions."]

I agree with ZapperZ statement as such, but we both interpret this differently. I see this as a statement that QM might need a modification, while he can - apparently - accept this situation happily and doesn't see any contradiction in it.
In a reductionist view, there can only be ONE theory of the universe. Now, it could be that classical and QM theories we have now are only approximations, in certain limits, of this one theory.
Nevertheless, I think there IS a view of QM as a world view which does NOT produce absurd (although weird, agreed) results as such, and that is a "many world" view. So it is not the argument of the absurdness which is for me sufficient to conclude that QM does not work at macroscopic scales. The more difficult aspect is its relationship to GR. This, to me, is the only compelling reason to think there might be something wrong with QM - apart of course from an eventual clear experimental deviation of its predictions.

 

[quantumcarl]

Please note that when I said "observe", it has NOTHING to do with "I have to exist" requirement. This makes the rest of your point in that post moot.
You are more than welcome to start a new thread in the Philosophy section to discuss what is obvously the main thing you are so interested in. I just don't have the patience to deal with such issues.
Zz.

Right on. I'll consider your recommendation and if I follow it I can only hope to see a contribution there from the objectivistic quarter of the equation.

All the best in your endeavors.

 

[ZapperZ]

Right on. I'll consider your recommendation and if I follow it I can only hope to see a contribution there from the objectivistic quarter of the equation.
All the best in your endeavors.

Sorry. I avoid physics discussion in the philosophy forum like a plague.

Zz.

 

[Sherlock]

I understood "reductionism" as: all macroscopic behaviour is *in principle* determined by the laws (in casu QM) gouverning the microsystems (and holism as the negation of reductionism). This means that the laws governing the microsystem have mathematically fixed (even if you don't know how to *derive* it in practice) the emergent properties.

The sort of reductionism that eg. the standard (particle theory) model represents is an ontological analysis into smaller and smaller constituent parts. Whether the rules defining the experimental production of the particles are actually abstractions of general rules governing the behavior of phenomena on any and all scales is questionable, and apparently, wrt meso and macro scale observations, not the case. This sort of reductionism seems to be at odds with a holistic approach.

Then there is the sort of reductionism that refers solely to the abstraction of the truly general principles governing the behavior of phenomena on any and all scales. This is an epistemological rather than an ontological reductionism, and it seems to me to be a holistic approach, in any sense that I can now think of using the term, holistic.

In a reductionist view, there can only be ONE theory of the universe. Now, it could be that classical and QM theories we have now are only approximations, in certain limits, of this one theory.

It seems reasonable to assume that the currently standard theories will undergo modifications with advances in technology. It also seems at least somewhat reasonable to me to assume that the sort of reductionist approach underlying the currently standard particle model is just the wrong approach if the goal is to get at the truly general principles which apply to any and all scales of behavior.

I think there IS a view of QM as a world view which does NOT produce absurd (although weird, agreed) results as such, and that is a "many world" view.

The adoption of the Many Worlds Interpretation of QM requires taking at least some parts of the QM algorithm and mathematical models employed as more or less accurate representations of what is happening in real 3D space independent of observation. But I think it's reasonable to view this (the MWI prerequisite that the QM formalism is, in some/any sense, a description of the physical reality between emitters and detectors) as a perversion of the meaning and application of QM.

Or am I just wrong about what I'm supposing to be prerequisite to the MWI view?

There is a view of QM which doesn't produce absurd continuations. It just requires accepting that the theory is not intended as, and doesn't function as, a description of an underlying quantum world.

 

[selfAdjoint]

The sort of reductionism that eg. the standard (particle theory) model represents is an ontological analysis into smaller and smaller constituent parts.

This is the way it's presented in popularizations, but the quarks and gluons are actually quanta of the gauge field, which is a large scale phenomenon. The size of the experimental spaces at the colliders, at which the SM is applied are actually quite large on a human scale. Rather than "smaller" perhaps "prior" would be a better word.

Whether the rules defining the experimental production of the particles are actually abstractions of general rules governing the behavior of phenomena on any and all scales is questionable, and apparently, wrt meso and macro scale observations, not the case.

I don't know what you mean by this. Ab initio calculation of, say, chemical reactions is difficult because of computational complexity, but much progress has been made and there is no bar in principle to deriving all chemistry, biology, and indeed the whole experienced world, from particle physics.

This sort of reductionism seems to be at odds with a holistic approach.

Well, weak emergence (as gas pressure emerges from the conservation of particle momentum) is envisioned. But holism as it is usally presented simply seems to be almost content-free to me. What does it predict?

 

[Sherlock]

This is the way it's presented in popularizations, but the quarks and gluons are actually quanta of the gauge field, which is a large scale phenomenon. The size of the experimental spaces at the colliders, at which the SM is applied are actually quite large on a human scale. Rather than "smaller" perhaps "prior" would be a better word.

The experimental spaces are large because of the energies and instrumental complexity required to produce the particles. But the particles that are experimentally produced (or theoretically hypothesized) are neither large nor complex wrt the human scale.

I'm only barely at the level of semi-sophisticated popularizations of the standard particle model. Maybe my characterization of the enterprise as "an ontological analysis into smaller and smaller constituent parts" was wrong -- or at least a possibly misleading way to describe it. Maybe it's meaningless to rank the particles that high energy physics has been able to produce (or which it has hypothesized) on a scale of 'size'. But if it isn't, then the upper limit on the size of quarks and gluons (100 attometers ?) is certainly smaller than the particles which confine them. However, I was thinking (most heuristically, for which I might apologize if it weren't for this feeling that if the fundamental laws of nature apply to all scales of behavior, then there is evidence of them at the level of our ordinary sensory perception ) more along the lines of scales of complexity (a hierarchy of 'media' ?) rather than size, per se.

I'm not sure what you mean in suggesting that, eg. quarks, are 'prior' (some sort of temporal hierarchy?). According to what parameter scale might the particles of the standard theory be ranked?

Recent experimental data and the size of the quark in the constituent quark model
http://www.edpsciences.org/articles/epjc/pdf/2002/11/100520277.pdf

Quarks, diquarks, and pentaquarks
http://physicsweb.org/articles/world/17/6/7/1

Ab initio calculation of, say, chemical reactions is difficult because of computational complexity, but much progress has been made and there is no bar in principle to deriving all chemistry, biology, and indeed the whole experienced world, from particle physics.

It isn't known if there's "no bar in principle to deriving ... the whole experienced world from particle physics". It is known that it can't be done from the current standard model. The current standard model isn't fundamental in the sense that fundamental refers to behavioral laws which apply to any and all scales of interaction. While the standard model is certainly an abstraction, it apparently isn't an abstraction of what's truly fundamental wrt nature.


The Theory of Everything
http://www.pnas.org/cgi/content/full/97/1/28

... holism as it is usally presented simply seems to be almost content-free to me. What does it predict?

Holism, like reductionism, is an approach to (ostensibly eventually) understanding what's fundamental wrt the behavior of anything and everything in our universe. Since modern physics has taken an analytical reductionist approach rather than a holistic reductionist approach, then the latter hasn't produced much theoretical content.

The weak and strong forces, electromagnetism, and gravity (and who knows what else the analytical reductionist approach might tack on) --- maybe these aren't truly fundamental. Even with it's success in quantitatively accounting for many phenomena, considering the problems facing the standard model, it seems at least worth considering that maybe it's just the wrong way to go about getting at what's fundamental wrt all phenomena.

What's fundamental must be operating (evident) at the level of our sensory perception and wrt more or less everyday phenomena, not just wrt quantum experimental phenomena -- so there's no reason why we shouldn't, eventually, be able to express the fundamental principles of our universe in familiar terms. Maybe it just hasn't been looked at carefully enough, or sorted out according to the right paradigm. Of course, the standard model (or any model for that matter) isn't wrong wrt what it's able to predict. It just isn't telling us what's fundamental in the sense of universal physical principles.

Anyway, my main reason for entering the holism-reductionism discussion in the first place was to get vanesch to expound in more detail on his reasons for becoming an MWI er (or ist). But thanks for your comments, selfAdjoint, and I welcome any criticism of my comments.

 

[vanesch]

There is a view of QM which doesn't produce absurd continuations. It just requires accepting that the theory is not intended as, and doesn't function as, a description of an underlying quantum world.

Yes, I know, the "shut up and calculate" view. I call that a non-view . It is maybe the most accurate interpretation of QM :rofl: . But it leaves you with a problem: how do you identify the mathematical objects you're manipulating with things in the lab ? Which you need to do in order to give some sense to the numbers you're calculating in the first place. This means no matter, that you DO implicitly identify certain objects in the lab with certain mathematical structures. Now why can you do that for those things that suit you, and why do you obstinately refuse to do so with the rest of the mathematical formalism - just because it bothers your intuition ?

However, I'm much less hostile to this view than you might think. It is a bit like the Mendelian theory of genetics before the recognition of DNA: the theory worked, used certain concepts but didn't really correspond to a representation of reality. Once DNA and several cellular mechanisms were discovered, Mendelian genetics could be EXPLAINED on the basis of these biological mechanisms.

Maybe QM does the same, and is some statistical mechanism that has no correct representation of reality in it, but nevertheless arrives at correct predictions. The analogy can be continued: one should then look for an underlying representation of reality that explains the success of the formalism. But there are serious sea monsters in that ocean!
My point of view is that one should row with the tools one has, and in as much that the formalism of QM DOES allow for a representation of reality, take the opportunity to use it (were it only to devellop an intuition for the formalism!) - even if you want to keep in mind that it MIGHT not be the correct representation of reality. And then, it might be, too.

 

[ZapperZ]

Yes, I know, the "shut up and calculate" view. I call that a non-view . It is maybe the most accurate interpretation of QM :rofl: . But it leaves you with a problem: how do you identify the mathematical objects you're manipulating with things in the lab ?

You don't! You adopt a "working" view to deal with the formalism which you know isn't necessary kosher but works. By the time you actually make a measurement, these are then classical concepts. You measure energy, position, momentum, etc. So there's no problem with interpretation of what you observe in the lab.


Zz.

 

[vanesch]

You don't! You adopt a "working" view to deal with the formalism which you know isn't necessary kosher but works.

You mean, let's take a modest attitude, we haven't gotten *a clue* how nature "really" works, but we've noticed that in certain domains, certain formalisms give good results, and that's all we can say ?

 

[ZapperZ]

You mean, let's take a modest attitude, we haven't gotten *a clue* how nature "really" works, but we've noticed that in certain domains, certain formalisms give good results, and that's all we can say ?

On the contrary, we DO have a clue, and in fact, more than a clue. The clue here is that our classical concepts are having loads of weird properties when applied to where they shouldn't be applied. But this doesn't mean we're clueless, or else we will have no useful information.

Zz.

 

[selfAdjoint]

On the contrary, we DO have a clue, and in fact, more than a clue. The clue here is that our classical concepts are having loads of weird properties when applied to where they shouldn't be applied. But this doesn't mean we're clueless, or else we will have no useful information.
Zz.

It has always seemed to mr that science progresses mostly by showing things that aren't true, rather than things that are. The Earth isn't flat; it isn't at the center of the solar system,..., and nature isn't classical!

 

[vanesch]

Anyway, my main reason for entering the holism-reductionism discussion in the first place was to get vanesch to expound in more detail on his reasons for becoming an MWI er (or ist). But thanks for your comments, selfAdjoint, and I welcome any criticism of my comments.

I've done that already a few times, but probably the time to find back the original posts is just as long as typing it here again.

My reason for taking on the MWI viewpoint is this:
1) QM is seen as a "universal" theory (is supposed to describe what happens in the universe). This can be correct or wrong, but it is what QM claims. The axioms of QM do not include a domain of applicability.
2) QM contains precise rules of how composite systems, build up from smaller systems, are supposed to work (namely: the tensor product of hilbert spaces). There is no postulated limit to this, and as such, I can construct, if I want, the hilbert space of all particles in my body, and in the lab's instruments, and ...
3) The superposition principle is a basic postulate of QM
4) The unitary time evolution is a basic postulate in QM (it's time derivative is the hamiltonian).
5) All relevant physical interactions (except gravity, acknowledged) are known how to be represented by this unitary time evolution.

As such, there is, from the postulates,
1) a natural description of the measurement apparatus, including the body of the observer, as a vector in hilbert space (follows from the build-up as tensor products of hilbert spaces of the constitutents)
2) the unitarity of the time evolution operator acting upon this state

and from these two points, invariably, the body state of the observer ends up entangled with the different possible outcomes of measurements WITHOUT CHOOSING ONE of them (as is said in the projection postulate). As such, it almost naturally follows that, if we are going to require that we only observe ONE outcome (and not all of them in parallel, as do our bodies), we can only be aware of one of these terms, with a certain probability. Once we accept that we only observe ONE of our body states, a classical awareness can emerge.

This is the essence of MWI. There are variations on the theme. It follows from taking the postulates of QM seriously ; there's no escaping from this view if you accept the axioms of QM and apply them universally. The objection can be that we are using the quantum formalism way outside of where it was somehow *intended* to work, but in absence of a theory that tells us WHY this formalism doesn't work the way it does (in other words, an underlying theory explaining QM), this is what the current formalism of QM says, by itself. And although very weird, it is not self-contradictory (and, as I often tried to show here, gives even a natural frame to view certain "bizarre" results, such as EPR situations, quantum erasers, and other such things). The real problem doesn't reside in the weirdness, the real problem resides with gravity. I think that given this difficulty, all bets are still open.

Nevertheless, I still advocate the MWI view for practical reasons (can sound bizarre): it helps elucidate EPR paradoxes and other weird quantum phenomena. It is a great TOOL for understanding the QM formalism.

 

[ZapperZ]

It has always seemed to mr that science progresses mostly by showing things that aren't true, rather than things that are. The Earth isn't flat; it isn't at the center of the solar system,..., and nature isn't classical!

But is there a difference between showing something is "true" and showing something is "valid"? Newton's laws are valid to be used to construct a building. Even if more fundamental description of the universe is found, Newton's laws will STILL be valid to build a house.

At some point, the extreme Popper's view of science is no longer useful.

Zz.