Questions About Quantum Theory: What's Wrong?

[ZapperZ]

If your point is that there is still a lot to discover and that we are far to know all about gravity and so on, that's of course granted

cheers,
Patrick.

But that IS my point. So all these claims that QM and GR simply do not meet and implies an "logical inconsistency", especially in the vacinity of a BLACK HOLE is as speculative as any! We all know QM works, and works so far in every cases that we encounter. Yet, based on some speculative situation, we then conclude that QM is logically inconsistent? HELLO?

What is logically inconsistent is being able to utter that with such conviction.

Zz.

 

[vanesch]

I must add some corrections to my simple low cost experiment (I have made some implicit assumptions ).
* If both joe and jack measures the voltage of the current source (we suppose that the precision of the voltmeters are the same and not the internal resistance), they sureley get both the same result.
* If they measure at different times (one measurement is true at a time), they surely get different results
What is the real voltage of the non perfect current source? (does this sentence alone have a meaning?)

Well, I disagree. First of all, there is a UNIQUE (time-dependent) voltage and a UNIQUE impedance (supposed not to be time-dependent) which specifies a non perfect current source ; that's Norton's theorem
What you are saying is that Jack and Joe are electrical engineers of different degrees of competence in circuit theory but after they have reviewed their courses they should arrive at identical results for identical questions.

This is NOT the case in CI: depending on whether you consider a physical process a "measurement" and depending on whether you claim that a "result is known" (to whom ? to what ?) or not, your state description is different (statistical mixture or pure state), in such a way that successive measurements (this time performed by YOU) could potentially give different outcomes.
In my example, does it make sense to say that "the which-path information" is *known* by the molecular computer ? In which case the molecular computer made a "measurement" ? Did it physically collapse the wavefunction then ? (in which case it will be impossible to have two different states of that computer interfere with each other) Or should we only say that the molecule got entangled with the which-path state (and no mention of "measurement" or "known result by a molecular computer") ? The latter viewpoint is taken by all MWI/relative state variants, while I thought that, as far as it has a meaning to say that "something is known by a computer", the first viewpoint is the CI viewpoint.

Or do you now say that the only things which can be "known" can be "known by me" in which case you come awfully close to my view on QM

See, you cannot escape a discussion on what constitutes a measurement (which has now been renamed into "the result is known") when talking about CI.

And, to repeat the mantra: this does, for the time being, not affect any practical application of QM, simply because we haven't yet succeeded in doing quantum interference experiments with things of which it becomes reasonable to say that they "know the results of measurements". There's still plenty of room between things "that can know results of measurements" and the complexity of quantummechanically relevant objects to place the Heisenberg cut somewhere comfortably in between.
Maybe such experiments are impossible in principle ; but that principal reason has not been found yet. Maybe gravity DOES play a role there. I think that the question is still widely open. However, I think it should one day be answered because, in my opinion, current CI QM clearly indicates a problem there: when "things that can know results of measurements" can also interfere or not, quantummechanically. It is in this gedanken domain that CI is, in my opinion, inconsistent (as Jack and Joe illustrate).

cheers,
Patrick.

 

[vanesch]

But that IS my point. So all these claims that QM and GR simply do not meet and implies an "logical inconsistency", especially in the vacinity of a BLACK HOLE is as speculative as any! We all know QM works, and works so far in every cases that we encounter. Yet, based on some speculative situation, we then conclude that QM is logically inconsistent? HELLO?

What is logically inconsistent is being able to utter that with such conviction.

I agree with what you write, but I think you confused two points that have been raised:

point 1) QM is incompatible with GR.

point 2) CI, by itself, can lead to inconsistencies when pushed in certain domains.

I think that everyone agrees on 1). That, I agree with you, is absolutely no proof that QM is somehow inconsistent. It only means that OR QM, OR GR, OR both will have to be changed somehow in order to fit into a physically consistent theory that describes both quantum effects and gravitational effects ; there is the illustration that domains where both competences (QM like and GR like) are needed, namely when dealing with black holes and the very early universe ; so that this clash between QM and GR is in some sense "real" and not a purely academic discussion. But, again, I agree with you that this is not a proof that something is wrong with QM.

The second point however, is purely on the QM side, WHEN VIEWED IN THE COPENHAGEN INTERPRETATION. I only wanted to illustrate that there, we can potentially encounter inconsistencies from the moment that it will be possible to do interference experiments which things that can be considered to "perform measurements". Then there are two equally valid reasoning schemes, which give you, at the end, different outcomes.
I don't think that this is an issue for quantum mechanics per se, but only for its Copenhagen interpretation. Relative state views do NOT suffer from that problem (but are "weirder").
FAPP (for all practical purposes) however, we're still far from even conceiving such experiments. So FAPP, Copenhagen is fine as of now.

Finally, it *might be* (we're in speculative mode) that points 1) and 2) have something to do with one another. It might be that something copenhagen-like is correct, and relative-state views are wrong, and that gravity is the thing that will objectively define what is a wave function collapse. At that moment, it becomes well-defined what is a measurement, and at that moment, the potential inconsistency in CI-QM disappears. But it would mean a modification of QM, and not only of its interpretational scheme.

Amen,
Patrick.

 

[ZapperZ]

I agree with what you write, but I think you confused two points that have been raised:

point 1) QM is incompatible with GR.

point 2) CI, by itself, can lead to inconsistencies when pushed in certain domains.

I think that everyone agrees on 1). That, I agree with you, is absolutely no proof that QM is somehow inconsistent. It only means that OR QM, OR GR, OR both will have to be changed somehow in order to fit into a physically consistent theory that describes both quantum effects and gravitational effects ; there is the illustration that domains where both competences (QM like and GR like) are needed, namely when dealing with black holes and the very early universe ; so that this clash between QM and GR is in some sense "real" and not a purely academic discussion. But, again, I agree with you that this is not a proof that something is wrong with QM.

The second point however, is purely on the QM side, WHEN VIEWED IN THE COPENHAGEN INTERPRETATION. I only wanted to illustrate that there, we can potentially encounter inconsistencies from the moment that it will be possible to do interference experiments which things that can be considered to "perform measurements". Then there are two equally valid reasoning schemes, which give you, at the end, different outcomes.
I don't think that this is an issue for quantum mechanics per se, but only for its Copenhagen interpretation. Relative state views do NOT suffer from that problem (but are "weirder").
FAPP (for all practical purposes) however, we're still far from even conceiving such experiments. So FAPP, Copenhagen is fine as of now.

Finally, it *might be* (we're in speculative mode) that points 1) and 2) have something to do with one another. It might be that something copenhagen-like is correct, and relative-state views are wrong, and that gravity is the thing that will objectively define what is a wave function collapse. At that moment, it becomes well-defined what is a measurement, and at that moment, the potential inconsistency in CI-QM disappears. But it would mean a modification of QM, and not only of its interpretational scheme.

Amen,
Patrick.

But there is another possibility that you missed, and that's is what I mentioned to accompany that link I gave - that QM and GR are NOT supposed to meet and agree with each other.

The whole idea that these things can be smoothly interpolated so that they meet outside the front door of a black hole is somehow blind (or simply ignoring) the phase transition issues. Things can meet a discontinuity here. We know that from thermodynamics. A quantum phase transition is even MORE subtle and "amusing". So I do not see these extension of our knowledge into an even more hypothetical and speculative situation as a black hole as a given or even valid.

Thus, it is entirely possible that QM and GR ARE both correct. It is just that our propensity of extending them to meet smoothly is wrong.

And as far as the next point, then maybe you should clearify that you are trying to show the logical inconsistency of CI and not QM. I still wish someone would design a thought expt. using superconductors to illustrate this. After all, Leggett, when he wanted to show how the Schrödinger Cat-type states can be illustrated with larger and larger number of particles involved, he went to this phenomenon FIRST.

Zz.

 

[Hans de Vries]

But it is difficult as of now to make such microscopic devices interfere in 2-slit experiments or the like. How many atoms do you need to make such a thing (probably a large bio-molecule) ? 10000 ? 100000 ?

Buckyballs DO interfere with 70 atoms...

Do they ?

Have you ever extensively checked and simulated these experiments like I did?

Talbot Lau interferometry of carbon-70 fullerenes

Or is this just blind trust? Experiments that take a shadow pattern of a
grid as prove for macroscopic matter interference work for any size objects.
Up to living or dead cats.

If the location of large bio-molecules is so undefined that most of them go
both ways through splits a thousand or more nanometers apart. How can
we have reliable DNA reproduction if they don't have a clue in which cell
they are?

Since these test are also supposed to have proved decoherence theory
is correct, must we now also believe the claims from this theory that:

1) Particles don't exist...
2) Quantum Jumps don't exist...
3) Time does not exist...

see http://www.decoherence.de/

This is the website of Joos, who is referred to by Arndt and Zeilinger in their
latest article here:

http://physicsweb.org/articles/world/18/3/5


Regards, Hans

 

[reilly]

Today the obit of one of my favorite poets, Robert Creeley, appeared in the New York Times. And, in his poem, "I Keep to Myself Such Measures..." he touches on some of the issues involved in QM, if not in science more generally. He writes:

I keep to myself such
measures as I care for,
daily the rocks
accumulate position.

There is nothing
but what thinking makes
it less tangible. The mind,
fast as it goes, loses

pace, puts in place of it
like rocks simple markers
for a way only to
hopefully come back to

where it cannot. All
forgets. My mind sinks.
I hold in both hands such weight
it is my only description.

I think Dirac would have liked this poem. Make of it what you will.

Regards,
Reilly Atkinson

 

[vanesch]

Thus, it is entirely possible that QM and GR ARE both correct. It is just that our propensity of extending them to meet smoothly is wrong.

I think I sort of vaguely see what you mean. Yuck ! That would be a terrible situation for a theorist! He needs two theories which are mathematically incompatible, but of which there is such a kind of "quantummechanical singularity protection mechanism" that these mathematical inconsistencies are never experimentally relevant, because the weird parts of GR are "frozen out" by some QM phase transition before they become weird, and the tiny contradictory gravitational effects on quantum systems are too small ever to be measured (like the gravitational effects of electrons in a superposition of position states which give you then "which way" information). I would call that situation the final failure of theoretical physics!

And as far as the next point, then maybe you should clearify that you are trying to show the logical inconsistency of CI and not QM.

Yes, yes, I was talking about Copenhagen, not about QM (the machinery).

cheers,
patrick.

 

[Stingray]

Just to prove that I'm not making this up as I go along, read this...

http://www.nature.com/news/2005/050328/full/050328-8.html

I know you said you're not endorsing this, but I'm rather disappointed that Nature News doesn't seem much better than say, the New York Times. They pick a "paper" that is just something presented at a conference, and isn't even Latex'd properly. More importantly, it shows a poor understanding of relativity, and makes no real arguments. It also seems to imply FTL signalling, which he apparently doesn't realize.

 

[ZapperZ]

I think I sort of vaguely see what you mean. Yuck ! That would be a terrible situation for a theorist! He needs two theories which are mathematically incompatible, but of which there is such a kind of "quantummechanical singularity protection mechanism" that these mathematical inconsistencies are never experimentally relevant, because the weird parts of GR are "frozen out" by some QM phase transition before they become weird, and the tiny contradictory gravitational effects on quantum systems are too small ever to be measured (like the gravitational effects of electrons in a superposition of position states which give you then "which way" information). I would call that situation the final failure of theoretical physics!

HOORAY!

:)

OK, so I was being naughty, but is this really THAT bad, and is this really that uncommon? Take note that most condensed matter physicists disagree with Weinberg's reductionist philosophy that one can simply extend what one knows at the individual particle level and simply adds complexity to get ALL of the phenomena of the world. So already there are two separate 'scales' of phenomena - the elementary particle/interaction scale, and the "emergent" phenomena scale of superconductivity, quantum hall effect, magnetism, and other collective behavior. So far, these two do not "merge" into each other. The ground state of superconductivity is not a description of an individual particle, but rather the ground state of a many-body system.

But wait. This has been going on for eons in physics. No one yet has claimed this incompatibility as being the "failure" of theoretical physics! All it means is that those who think that there is such a thing as the "theory of everything" are just having an unrealistic imagination.

Zz.

 

[ZapperZ]

I know you said you're not endorsing this, but I'm rather disappointed that Nature News doesn't seem much better than say, the New York Times. They pick a "paper" that is just something presented at a conference, and isn't even Latex'd properly. More importantly, it shows a poor understanding of relativity, and makes no real arguments. It also seems to imply FTL signalling, which he apparently doesn't realize.

Nature news picks up a lot of conference reports, not just papers and preprints (I wish they'd go easy on the preprints).

It is why I made the disclaimer that I do not endorse this paper, because I'm using it simply to point out that such ideas ARE being thrown around. And if we worry about "FTL" signalling, we'd have to worry with a lot of other forms of QM formulation such as Bohmian mechanics.

Zz.

 

[Stingray]

And if we worry about "FTL" signalling, we'd have to worry with a lot of other forms of QM formulation such as Bohmian mechanics.

No, I mean classically faster than light signalling, which violates causality. There is nothing in accepted physics which does this.

All it means is that those who think that there is such a thing as the "theory of everything" are just having an unrealistic imagination.

Are you saying that such a thing might not ever exist, even in principle?

 

[ZapperZ]

Are you saying that such a thing might not ever exist, even in principle?

Correct. Both Robert Laughlin and Phil Anderson have argued that the "TOE" of Weinberg and elementary particle physicists is the "TOE for Reductionsm". I have written an essay on this quite a while back in one of my Journal entry, including citations to the relevant papers.

Note that TOE is not equal to "unification" as in the GUT, even though many people think they are one of the same.

Zz.

 

[Stingray]

Correct. Both Robert Laughlin and Phil Anderson have argued that the "TOE" of Weinberg and elementary particle physicists is the "TOE for Reductionsm". I have written an essay on this quite a while back in one of my Journal entry, including citations to the relevant papers.

Hmm, ok. I don't think that TOE-type goals are in any way unique to Weinberg. Anyway, I don't agree with your conclusion, but I'll take a look at what you wrote.

Note that TOE is not equal to "unification" as in the GUT, even though many people think they are one of the same.

I know.

EDIT: I skimmed over a couple of the links in your journal entry. I find the main argument there to be extremely weak, although there are some interesting comments. This isn't really related to the current thread, though, so I'll leave it alone.

 

[vanesch]

Take note that most condensed matter physicists disagree with Weinberg's reductionist philosophy that one can simply extend what one knows at the individual particle level and simply adds complexity to get ALL of the phenomena of the world. So already there are two separate 'scales' of phenomena - the elementary particle/interaction scale, and the "emergent" phenomena scale of superconductivity, quantum hall effect, magnetism, and other collective behavior.

I find this a peculiar view, honestly. I thought that most condensed matter people thought that "emergent properties" are, well, emerging from the underlying "reductionist" dynamics, at least in principle. So that IF you have the correct description of the interactions of molecules, that you ARE able to derive ab initio all "emergent properties", phase transitions and so on. Naively I thought even that that was one of the goals of condensed matter physics :-)
But of course, in the mean time, and maybe for practical reasons, you can build more effectively 'effective models' which describe much better the behaviour of condensed matter, but the price to pay is some ad hoc introduction of entities (experimentally determined, or guessed at). But I thought that the view in condensed matter was that if only we were smart enough, then we could derive this from the "reductionist" elementary description. You seem to claim the opposite ? That "emergent properties" are for ever cut off from the physics of the underlying building blocks ?


cheers,
Patrick.

 

[ZapperZ]

I find this a peculiar view, honestly. I thought that most condensed matter people thought that "emergent properties" are, well, emerging from the underlying "reductionist" dynamics, at least in principle. So that IF you have the correct description of the interactions of molecules, that you ARE able to derive ab initio all "emergent properties", phase transitions and so on. Naively I thought even that that was one of the goals of condensed matter physics :-)
But of course, in the mean time, and maybe for practical reasons, you can build more effectively 'effective models' which describe much better the behaviour of condensed matter, but the price to pay is some ad hoc introduction of entities (experimentally determined, or guessed at). But I thought that the view in condensed matter was that if only we were smart enough, then we could derive this from the "reductionist" elementary description. You seem to claim the opposite ? That "emergent properties" are for ever cut off from the physics of the underlying building blocks ?


cheers,
Patrick.

Being a condensed matter physicist, this is what I have come to conclude. That "emergent" properties are, by definition, not derivable simply by looking at all the interaction at the individual particle scale. Again, I do not see, for example, how superconductivity can be derived out of that. Bob Laughlin even played a trick to his graduate level QM class students by giving this as a "homework" (read his Nobel Prize lecture). You can't derive it simply by adding complexity to the individual particle. Superconductivity will simply not emerge out of that. Still don't believe me? Look at the description for a gas molecule or water molecule. You'll never see, in such a description, no matter how in detail it is, where the phase transition is going to occur. The information isn't in there!

Here's another kicker. If I have a bunch of electrons, for example, and I make a very small constriction, and then I apply, starting from zero, a very, very small voltage across that constriction, one would expect that the increase in current across through that constriction would be in multiples of the number of electrons. Maybe it'll start with only one electron being able to get thru at a time, and 2 electrons, etc... But look at the fractional quantum hall effect and fractional charges effect. You'll see that in this case, the amount of charge getting thru via the step-like increase in current implies a multiple of e/3! This is a fraction of a single electron! How does the smallest entity of a conglomorate of objects become smaller than the individual object within that conglomerate?

Again, such effects are only present as an emergent, collective behavior. We can argue all we want, but the simple fact as it stands today, is that NONE of them are ever derived or explained with the a priori assumption that they can be explained via reductionism. In fact, there are many indicators that they can't (fractional QE).

Zz.

 

[Mike2]

Again, such effects are only present as an emergent, collective behavior. We can argue all we want, but the simple fact as it stands today, is that NONE of them are ever derived or explained with the a priori assumption that they can be explained via reductionism. In fact, there are many indicators that they can't (fractional QE).
Zz.

Could emergent properties arise from symmetries that become effective at larger scales. At smaller scales things are discrete and discrete symmetries are in effect. But with larger collections of objects the discreteness gives way to an average effect that seems continuous. Such symmetries would not be derivable from the properties of the particles alone because they are the result of how the particles are arranged with respect to one another.

Just a moment. I just had another thought. Could these new and/or continuous symmetries at larger scales be responsible for collapse of the wave function and the reduction of the state? If the discrete values at the quantum level are obtained from the discrete symmetries of that smaller scale, then could the new and/or continuous symmetries at larger scales be responsible for collapsing the superposition of quantum states to the choice of one of them?

 

[ZapperZ]

Could emergent properties arise from symmetries that become effective at larger scales. At smaller scales things are discrete and discrete symmetries are in effect. But with larger collections of objects the discreteness gives way to an average effect that seems continuous. Such symmetries would not be derivable from the properties of the particles alone because they are the result of how the particles are arranged with respect to one another.

Eh?

Zz.

 

[vanesch]

We can argue all we want, but the simple fact as it stands today, is that NONE of them are ever derived or explained with the a priori assumption that they can be explained via reductionism. In fact, there are many indicators that they can't (fractional QE).

I find that highly disturbing. Not that it hasn't been done as of today, that's very well possible, but that it can't be done in principle, because, as you say, "the information is not there". I would think that all the information IS in the elementary interactions. Only, it can be real hard to get it out of it. But with enough computing power, that should not be a problem.
It would mean that, say, no monte-carlo simulation of molecular interactions could ever give rise to a phase transition. I'm not into condensed matter, but I thought *that* was exactly what these people tried to do ! In the style of:
Here's the structure of methane molecule, what's the boiling point of methane at 1 atmosphere. I thought that that was the essence of the future of condensed matter physics: ab initio predictions of phase transitions !

If what you say is true, it is essentially the end of any scientific discipline! Indeed, at ANY moment, "emergent properties" can appear out of the blue, and all predictive power is gone. You think you know Newtonian gravity, and you think that you can calculate orbits for a solar system with 3 planets, 4 planets... 9 planets. You add a 10th planet, and hey, emergent property, everything changes ?? Ok, I'm pushing things a bit but you get what I try to say, no ?

cheers,
Patrick.

 

[Stingray]

That "emergent" properties are, by definition, not derivable simply by looking at all the interaction at the individual particle scale. Again, I do not see, for example, how superconductivity can be derived out of that. You can't derive it simply by adding complexity to the individual particle. Superconductivity will simply not emerge out of that.

You're making a lot of very definite statements with no real evidence (i.e. rigorous theorems). Just because it is hard to do something doesn't mean it is impossible, or even likely to be impossible.

Look at the description for a gas molecule or water molecule. You'll never see, in such a description, no matter how in detail it is, where the phase transition is going to occur. The information isn't in there

Again, appeals to ignorance are not a way to win an argument. Given that I don't know much about condensed matter theory, I'll give the only example I am familiar with - the Ising model. At first description, it looks trivial. There is no obvious reason that there should be a phase transition. But there is. Now the Ising model can be solved by hand, but it is not at all difficult to modify it so that you can't do that anymore. There are still phase transitions, and it is not a priori obvious that they should be there (I had a homework problem in a numerical modelling course to simulate such things and characterise the transitions). I see water as being the same thing, but obviously much more complicated.

Has it been rigorously proven that the "accepted Hamiltonian" for a collection of water molecules does not lead to a phase transition? I doubt it, but if so, the Hamiltonian is wrong. If you found a corrected Hamiltonian which gave the proper macroscopic behavior and fundamentally contradicted the "reductionist" viewpoint, then I think you could get yourself a Nobel prize or two.

How does the smallest entity of a conglomorate of objects become smaller than the individual object within that conglomerate?

Since when is quantum mechanics about a bunch of charged balls flying around? It's not. This should be especially obvious in many-particle systems, which are often unintuitive even in simple classical systems.

Anyway, it is of course possible that our current understanding of "particle physics" is not sufficient to reproduce condensed matter, but it still wouldn't make any sense to suppose that reductionism is not possible even in principle. There MUST be a continuity of description which makes sense at all (allowed) scales. What happens if you cut up a (low-Tc) superconductor into smaller and smaller pieces? I'm presuming that you'll agree that a single molecule is describable by "reductionist" QM. What about two or three or...? Is there a sudden jump where BCS theory takes over (or whatever our best description is)?

 

[Stingray]

I thought that that was the essence of the future of condensed matter physics: ab initio predictions of phase transitions !

This is also what I thought. But then my impression is that theory hasn't been very useful in condensed matter. The experimentalists discover everything interesting, and the theorists just clean up the mess. Is this right Zz? I've had that view of the field without ever really knowing anybody who works in it (and that view has kept me from wanting to learn more).

 

[Crosson]

I found a book this past week, it is called "Who is afraid of Schrödinger's cat?" and is intended to explain modern physics to laymen. Fortunately for this discussion, this book gave me a focused example of exactly what I think is wrong with Quantum Physics. Here is the first paragraph in the book:

Schrödinger's cat is the mascot of the new physics. Concieved to illustrate some of the apparently impossible conundrums associated with quantum reality, he has become a symbol of much that is "mind boggling" about 20th century physics...would think the cat is either alive or dead, but this is a quantum cat so things don't work that way. In the quantum world, all possibilities have a reality of there own, ensuring the cat is both alive and dead.

This is my problem, physicists embracing nonsense. This view is all to popular, certainly in the general public, and much more importantly in the physics community. To say that the cat is alive and dead because of QM is asinine, because QM is a theory of observations. It does not make claim's about the way things "are".

The attitude is "look, we can get people interested in physics by making it seem weird and exotic". But what these sell outs (like Briane Greene) end up saying is such nonsense that it turns me off entirely. Most of you are unlikely to identify with this extreme nonsense view, but I have sat through lectures with professors who have subscribed to the "spooky quantum world" flavor of physics.

 

[ZapperZ]

I find that highly disturbing. Not that it hasn't been done as of today, that's very well possible, but that it can't be done in principle, because, as you say, "the information is not there". I would think that all the information IS in the elementary interactions. Only, it can be real hard to get it out of it. But with enough computing power, that should not be a problem.
It would mean that, say, no monte-carlo simulation of molecular interactions could ever give rise to a phase transition. I'm not into condensed matter, but I thought *that* was exactly what these people tried to do ! In the style of:
Here's the structure of methane molecule, what's the boiling point of methane at 1 atmosphere. I thought that that was the essence of the future of condensed matter physics: ab initio predictions of phase transitions !

Again, I would refer you to Laughlin's Nobel Prize lecture and see how he explicitly indicates that no, you cannot, in principle, derive superconductivity out of an individual particle interaction. And this has nothing to do with having enough computing power, in which Weinberg has often used to rebutt this argument, where Anderson in turn has counter-replied. So such arguments are well-known and have been addressed.

Note that the ab initio predictions in condensed matter starts off right away with a many-body ground state, NOT individual particle interactions.

What I see here is similar to the state of the EPR experiment before Bell theorem. People are simply arguing things based on tastes without having any concrete experiment to test one preference or another. I freely admit that my stand is based in large part on preference, based on what I have understood and encountered in condensed matter, and that I am almost convinced that emergent phenomena cannot be derived from reductionism.

If what you say is true, it is essentially the end of any scientific discipline! Indeed, at ANY moment, "emergent properties" can appear out of the blue, and all predictive power is gone. You think you know Newtonian gravity, and you think that you can calculate orbits for a solar system with 3 planets, 4 planets... 9 planets. You add a 10th planet, and hey, emergent property, everything changes ?? Ok, I'm pushing things a bit but you get what I try to say, no ?

cheers,
Patrick.

No, because strangely enough, a book titled "The End of Physics" indicates that the GUT signify the end of physics because we then would have a TOE. The failure of reductionism on the other hand would indicate that no, it isn't the end of physics, because there will be MORE to discover that cannot be derived out of reductionism. It isn't the end of science, nor the scientific discipline. It just means we will never reach an end to finding new things. I do not see any problem with that at all.

Zz.

 

[ZapperZ]

You're making a lot of very definite statements with no real evidence (i.e. rigorous theorems). Just because it is hard to do something doesn't mean it is impossible, or even likely to be impossible.

Again, appeals to ignorance are not a way to win an argument. Given that I don't know much about condensed matter theory, I'll give the only example I am familiar with - the Ising model. At first description, it looks trivial. There is no obvious reason that there should be a phase transition. But there is. Now the Ising model can be solved by hand, but it is not at all difficult to modify it so that you can't do that anymore. There are still phase transitions, and it is not a priori obvious that they should be there (I had a homework problem in a numerical modelling course to simulate such things and characterise the transitions). I see water as being the same thing, but obviously much more complicated.

Having done several Ising-type computation and even got paid to do quantum monte carlo on a catalyst surface energy system for Du Pont, I can clearly tell you that an Ising model is an N-body problem, and not a many-body problem. The Heisenberg coupling between spins (be it nearest, next-nearest, next-next-nearest neighbors, etc), are often put in by hand, whereas in a condensed matter computation, why something is ferromagnetic, antiferromagnetic (the sign of the coupling strength) is an emergent value that you do not know a priori. So such a comparison is not the same.

Has it been rigorously proven that the "accepted Hamiltonian" for a collection of water molecules does not lead to a phase transition? I doubt it, but if so, the Hamiltonian is wrong. If you found a corrected Hamiltonian which gave the proper macroscopic behavior and fundamentally contradicted the "reductionist" viewpoint, then I think you could get yourself a Nobel prize or two.

Since when is quantum mechanics about a bunch of charged balls flying around? It's not. This should be especially obvious in many-particle systems, which are often unintuitive even in simple classical systems.

QM is not about a bunch of charged balls flying around? I don't get it. What does this have anything to do with fractional charge/quantum hall effect? Are you saying charges moving through a constriction is outside the realm of QM?

Anyway, it is of course possible that our current understanding of "particle physics" is not sufficient to reproduce condensed matter, but it still wouldn't make any sense to suppose that reductionism is not possible even in principle. There MUST be a continuity of description which makes sense at all (allowed) scales. What happens if you cut up a (low-Tc) superconductor into smaller and smaller pieces? I'm presuming that you'll agree that a single molecule is describable by "reductionist" QM. What about two or three or...? Is there a sudden jump where BCS theory takes over (or whatever our best description is)?

That's what an "emergent" phenomena essentially implies. And no, we still do not know what happens at the mesoscopic scale (which is the OTHER Laughlin paper that I cited that addressed this issue) between the reductionist description and many-body collective phenomena.

Look, even if I simply cannot convince anyone of this, the VERY least that should happen is that people ARE aware that there are many prominent physicists who simply do not agree that such reductionist approach is acceptable. I have seen way too many arguments on here in which GUT=TOE by default without any qualm. All I'm saying is hold your horses, because such thing is not entirely obvious nor automatic. There a very large group of practicing physicists (the division of Condensed matter/material science is the largest division under the APS) that simply do not share that view. This view cannot be simply dismissed.

Zz.

 

[Stingray]

Again, I would refer you to Laughlin's Nobel Prize lecture and see how he explicitly indicates that no, you cannot, in principle, derive superconductivity out of an individual particle interaction.

I've only read the first page of this where he talks about giving his students the "impossible" problem. His reference for the claim that superconductivity cannot be derived from microscopics is a paper by Anderson in 1972. I looked that up, and found no such statements. Instead, it was filled with claims that it is IMPRACTICAL to deduce the properties of macroscopic systems from microscopic laws. This is essentially given as a defense that condensed matter physics is a "worthwhile" endeavor. He even says "we must all start from reductionism, which I fully accept." I completely agree with Anderson's viewpoint, but it is very different from your's (and apparently Laughlin's). Am I just skimming things too quickly here?

I can clearly tell you that an Ising model is an N-body problem, and not a many-body problem. The Heisenberg coupling between spins (be it nearest, next-nearest, next-next-nearest neighbors, etc), are often put in by hand, whereas in a condensed matter computation, why something is ferromagnetic, antiferromagnetic (the sign of the coupling strength) is an emergent value that you do not know a priori. So such a comparison is not the same.

What is the difference between N-body and many body? Does the latter just mean N->infinity? The analytic solution uses an infinite number of "particles."

This is irrelevant to my point, though. I was not giving the Ising model as an example of concrete physics, but of mathematics. It shows that you can get a phase transition from something very simple that doesn't appear to have any interesting features.

QM is not about a bunch of charged balls flying around? I don't get it. What does this have anything to do with fractional charge/quantum hall effect? Are you saying charges moving through a constriction is outside the realm of QM?

No, of course QM should work here. You seemed to be implying that the FQHE makes no sense because you get fractional charges when electrons should be indivisible. I was replying that, while this effect is interesting and surprising, it doesn't say anything for reductionism. QM is a wave theory. Our intuition of electrons as being little balls flying around is not remotely rigorous. The particle picture itself isn't even fundamental in field theory. Quantum "particles" are remnants of perturbation theory if you don't recall.

On that note, you might be interested to know how field theorists and relativists define "emergent" phenomena: Something is "emergent" if nobody can figure out how to understand it perturbatively (but nonperturbative methods work). QCD is an example of this, I believe. Anyway, it is well-known to mathematicians that perturbation theory does not generally agree with the theory from which it was derived. This is true even in regimes where "physics math" would claim otherwise. So the existence of emergent phenomena in this sense is not surprising. I also think that this is the definition that your field should be using.

Look, even if I simply cannot convince anyone of this, the VERY least that should happen is that people ARE aware that there are many prominent physicists who simply do not agree that such reductionist approach is acceptable.

I was indeed unaware that any physicists held this view. It still seems logically impossible to me. I think that understanding things at the mesoscopic scale will make condensed matter people change their minds, but it's clear that our current argument isn't going anywhere .

 

[Davorak]

I would like to point out Stingray that a TOE may mean that you can simulate every and any phenomena with enough computing power. This does not immediately mean that it is possible to derive every and any phenomena. Even if it possible to derive every thing with a TOE that does not mean that all interesting phenomena would then therefore be immediately apparent.

 

[Stingray]

I would like to point out Stingray that a TOE may mean that you can simulate every and any phenomena with enough computing power. This does not immediately mean that it is possible to derive every and any phenomena.

Are you defining "derive" to mean something that can be done by hand, whereas "simulate" necessarily involves a computer? If so, I agree with your statement, but the method by which a conclusion is reached isn't important for verifying logical statements (math).

It might also be worth noting that an equation doesn't have to be solved for one to show that experimental results follow from a given theory. Take a pendulum for a trivial example. We can write down the differential equation for its motion, but make believe that we don't know how to solve it. Some experimentalist can come along and measure displacement versus time for various pendula. His data can then be substituted into the DE, and one can check whether left-hand side=right-hand side to within experimental error. For more complicated systems, this is much simpler than a traditional solution. It is also just as valid in showing whether an equation is correct (though not nearly as satisfying).

 

[Davorak]

I found a book this past week, it is called "Who is afraid of Schrödinger's cat?" and is intended to explain modern physics to laymen. Fortunately for this discussion, this book gave me a focused example of exactly what I think is wrong with Quantum Physics. Here is the first paragraph in the book:

Schrödinger's cat is the mascot of the new physics. Concieved to illustrate some of the apparently impossible conundrums associated with quantum reality, he has become a symbol of much that is "mind boggling" about 20th century physics...would think the cat is either alive or dead, but this is a quantum cat so things don't work that way. In the quantum world, all possibilities have a reality of there own, ensuring the cat is both alive and dead.

This is my problem, physicists embracing nonsense. This view is all to popular, certainly in the general public, and much more importantly in the physics community. To say that the cat is alive and dead because of QM is asinine, because QM is a theory of observations. It does not make claim's about the way things "are".

The attitude is "look, we can get people interested in physics by making it seem weird and exotic". But what these sell outs (like Briane Greene) end up saying is such nonsense that it turns me off entirely. Most of you are unlikely to identify with this extreme nonsense view, but I have sat through lectures with professors who have subscribed to the "spooky quantum world" flavor of physics.

What exactly is wrong with this view? Would it help if the Cat was not a flesh and blood cat but rather a quantum cat that can have the states dead or alive? Somewhat like an electron can have a spin up or down. This makes the argument seem much more plausible does it not?

Quantum tunneling allows for the possibility [for] me to walk through a brick wall, however if I tried to do [so] I would just get a lot of bruises. Why? Because I am an object made of a number of constituents each which has a very small chance of tunneling through the brick wall.

Appling Quantum rules like superposition and tunneling [on a macroscopic level] is not mumbo-jumbo it is just very impractically.

 

[Stingray]

Although, I'm not sure that I'd agree with all of Crosson's issues regarding Schrödinger's cat, I'm a little annoyed at it as well. It has become popular for general physics writers to make a lot of statements designed solely to sound as outrageous as possible. This is obviously done so that people think that physics is "cool," but I think it is a bit of a disservice to those who try to think deeply about what they've read. The books rarely make an attempt to convince the reader that physics is indeed rational.

I think I first noticed this when talking to a student in a freshman physics class I was TA'ing. He was an engineering major, but had read some popular books. Anyway, he told me that these books basically made him equate physicists with theologians. One of the main things he couldn't believe was the concept of virtual particles. I gave him an idea of what they really were, but I didn't blame him. "Brian Greene virtual particles" are indeed pretty crazy.

 

[Davorak]

Are you defining "derive" to mean something that can be done by hand, whereas "simulate" necessarily involves a computer? If so, I agree with your statement, but the method by which a conclusion is reached isn't important for verifying logical statements (math).

It might also be worth noting that an equation doesn't have to be solved for one to show that experimental results follow from a given theory. Take a pendulum for a trivial example. We can write down the differential equation for its motion, but make believe that we don't know how to solve it. Some experimentalist can come along and measure displacement versus time for various pendula. His data can then be substituted into the DE, and one can check whether left-hand side=right-hand side to within experimental error. For more complicated systems, this is much simpler than a traditional solution. It is also just as valid in showing whether an equation is correct (though not nearly as satisfying).

By derive I mean predict before doing the experiment what will happen. This experiment can happen in a computer or it can happen in the real world. The computer experiment is not necessarily accurate though since it is a numerical simulation.

Some what like you can not derive the motion of the chaotic pendulum. You preform numerical methods and get its motion with a certain accuracy.

The unpredictability of the chaotic pendulum increases with the time you let it run. The unpredictability of emergent phenomena increases with the number of interacting particles.

 

[Crosson]

What exactly is wrong with this view? Would it help if the Cat was not a flesh and blood cat but rather a quantum cat that can have the states dead or alive?

Somewhat like an electron can have a spin up or down. This makes the argument seem much more plausible does it not?

It wouldn't help this discussion, because I am talking about a cat and you are talking about an electron. Quantum Mechanics correctly describes only one of these things.

Quantum tunneling allows for the possibility me to walk through a brick wall, however if I tried to do I would just get a lot of bruises. Why? Because I am an object made of a number of constituents each which has a very small chance of tunneling through the brick wall.

Appling Quantum rules like superposition and tunneling is not mumbo-jumbo it is just very impractically.

It is mumbo jumbo, because there is no experimental evidence or mathematical proof that a macroscopic object could pass through a brick wall. Remember, we have no reason to believe in QM any further than experiments can confirm its predictions (because its postulates are ad hoc).

In the bolded sentence you assume that the whole shares the properties of the parts, a common error in these "explanations" of quantum mechanics. Perhaps the macroscopic object has zero probability of being on the other side of the wall even though each of its parts has a nonzero property of being there. Unknown composite {whole more than parts} effects could play a role.

Here is the big problem: Cats cannot be both alive and dead. This shows that the superposition of states does not apply to cats, whatsoever. The most rational conclusion is: "QM is useful for predicting some things, but is not meant to be a literal description of reality." In their enthusiasm for selling books and attracting students, these authors and professors assert that QM supercedes logic! (Nothing can have both the property of being, and not being, at the same time.)