Questions About Quantum Theory: What's Wrong?

[Hans de Vries]

C.H. van der Wal et al., Science v.290, p.773 (2000).
Zz.

This one is online here:

http://qt.tn.tudelft.nl/publi/2001/wal_science2000.pdf

and related papers:

More from Delft


Regards, Hans

 

[seratend]

Seratend -- I'm a bit confused by Jack and Joe. What is it exactly that they are doing, what are they measuring? Apparently they are getting different answers when they should not, and I don't get it.

Reilly

Well, my purpose is to underline (simply) the eternal problem of the interpretation in physics (the connection between the results of the theory and the "real" world).

Jack and Joe are just measuring a voltage of the current source in my basic example. However, a current source may be modeled, as a voltage source with a huge resistance in series. Therefore the two voltmeters give surely a different voltage measure (i.e we apply the well know voltage division: R1/(R1+R2) to get the measured voltage).
Therefore, if Jack and Joe say (interpretation) that they both measure the voltage of the current source, they will get different results (interpretation inconsistency).

Seratend.

 

[vanesch]

The CI deals only with logical statements and no logical inconsistency is embedded in this formulation (only additionnal intepretations may lead to inconsystencies)
In your example, if Joe is true (the result of his measure is A for the associated observable), Jack has the collapsed updated wave function of Jack. And vice versa. That's all.

Why ? In CI, you can CALL a photodetector a measurement apparatus, and then you should think like Joe (and collapse your wavefunction), but you are also free to consider it to be a system under study, and then you can write out its hamiltonian and evolve unitarily. This is what Jack does. NO CHANGE IN THE SETUP IS ASSUMED.

So why do we have "an outcome" in the case of Joe, and do we have "a physical system in evolution" in the case of Jack ?

The fact that CI remains very vague on when to apply process 1 and when to apply process 2, and that in many cases you can do both, according to your own taste (just as you can choose to work in cylindrical or cartesian coordinates), and that THE OUTCOMES ARE INCOMPATIBLE, sounds to me like an internal inconsistency.

The fact that Joe does not measure really the observable he assumes is outside the scope of the problem. It is equivalent to say that jack is wrong when he claims he has the result measurement A of his supposed observable (either the result or the observable is wrong).
CI interpretation just states that when a measurement gives a result A (the result A is true), the wavefunction is collapsed into |A>. The collapse itself is not explained by the CI (as I "interpret" it, it is not very different from the "shut up and calculate").

Yes, but you now simply changed the semantics: what used to be "a measurement" and a "process" is now changed into "having a result" or "not having a result". But that doesn't do away with the difficulty.

As Zzapper asked me, show me the relevant experimental results that make the difference, that's silly of course, there aren't any in the foreseeable future because decoherence makes it hard to do so.
But the very fact that saying that a photodetector is a measurement apparatus or saying that a photodetector is a physical system under study, makes you obtain DIFFERENT states (the former one is a statistical mixture, the latter is a pure state), means that it is IN PRINCIPLE (though it will be hard in practice) possible to do a (second?) "measurement", in an incompatible basis, on the system, and obtain different results (statistical mixtures and pure states give different results in a basis where the density matrix is not diagonal).
The very fact that this is IN PRINCIPLE possible (having two different predictions of outcomes), and that we have two ways of talking about the situation (just by CALLING a photodetector either a measurement apparatus, or a physical system under study, both equally allowable in CI), means to me that the system is logically inconsistent, even though for the time being, this inconsistency will not become visible in an experiment and hence that we can still use the machinery FAPP without any worry.

cheers,
Patrick.

 

[ZapperZ]

Why ? In CI, you can CALL a photodetector a measurement apparatus, and then you should think like Joe (and collapse your wavefunction), but you are also free to consider it to be a system under study, and then you can write out its hamiltonian and evolve unitarily. This is what Jack does. NO CHANGE IN THE SETUP IS ASSUMED.

So why do we have "an outcome" in the case of Joe, and do we have "a physical system in evolution" in the case of Jack ?

The fact that CI remains very vague on when to apply process 1 and when to apply process 2, and that in many cases you can do both, according to your own taste (just as you can choose to work in cylindrical or cartesian coordinates), and that THE OUTCOMES ARE INCOMPATIBLE, sounds to me like an internal inconsistency.

I disagree. I still do not see how the two cases you mentioned are the identical situations and should produce the identical results even via QM.

Yes, but you now simply changed the semantics: what used to be "a measurement" and a "process" is now changed into "having a result" or "not having a result". But that doesn't do away with the difficulty.

As Zzapper asked me, show me the relevant experimental results that make the difference, that's silly of course, there aren't any in the foreseeable future because decoherence makes it hard to do so.

It's not that silly. As I have said before, and as Carver Mead has said in that PNAS paper, we can use superconductivity. It is the clearest manifestation of QM effects, especially coherence, with very strong "quantum protectorate" regime that is immune to many external interactions. So use this and tell me what kind of measurement do you expect to be "different" between the two cases you mentioned.

Zz.

 

[seratend]

Why ? In CI, you can CALL a photodetector a measurement apparatus, and then you should think like Joe (and collapse your wavefunction), but you are also free to consider it to be a system under study, and then you can write out its hamiltonian and evolve unitarily. This is what Jack does. NO CHANGE IN THE SETUP IS ASSUMED.
.

Yes, but you seem to assume that the results of Joe and Jack may be inconsistent that is not possible under CI. As you know, unitary evolution preserves the orthogonality of the vectors (same stuff used in e.g. MWI, MMI etc..). Therefore if the result of a given measurement is true, only a part of the vector, before measurement, should be assumed under the unitary evolution to make other logical assertions on further measurements (the other part "is wrong" simply because the result of the measurement is true: formal logic).

CI does not say what is the "interpretation" of a collapse, just that "abstract measurements" on a system follows this rule. Do not forget that CI formalism does not say how we can realize a "real" ideal measurement, just how to use logical statements (the result of a measure is true) with abstract measurements.
After, an external additional interpretation may say more than what CI says, but it outside the consistency scope of CI.

So why do we have "an outcome" in the case of Joe, and do we have "a physical system in evolution" in the case of Jack ?

No, in CI Joe and Jack just assert that a given outcome is true and not that a system evolves under unitary evolution or not. In other words, Joe and Jack only exist as the logical statement result of the measurements, while the system keeps its unitary evolution. It is always external assumptions that say more than that.
I just recall what CI says with my words: A system is on the collapsed state just after the abstract measurement result is true. That's all.

The fact that CI remains very vague on when to apply process 1 and when to apply process 2, and that in many cases you can do both, according to your own taste (just as you can choose to work in cylindrical or cartesian coordinates), and that THE OUTCOMES ARE INCOMPATIBLE, sounds to me like an internal inconsistency.

Because CI does not intend to describe more (it is not its purpose to describe how the abstract measurements are realized). This resembles somewhat to recurring problem in PF of the paths of quantum particles. QM and CI does not say that particles have a path, just that we can measure the presence of a particle at a given position (the measure result statement). We usually have a classical and a deterministic bias in our way of thinking (surely due to our education) and we must take care in not adding more features to a given formalism (source of inconsistencies) due to this bias.

Yes, but you now simply changed the semantics: what used to be "a measurement" and a "process" is now changed into "having a result" or "not having a result". But that doesn't do away with the difficulty.

That is the heart of the external interpretation you seem to add to the CI. CI does not say what is a measurement. Just that this abstract object allows one to make logical assertions on the system and therefore compute probabilities and system evolutions. [/QUOTE]

Once I say I have a measurement, I have a result (I have a true property: i.e. one of the values of the observable). CI does not say how to activate/deactivate a measurement (no signification in this formalism). There is no time in the collapse, just a causal statement (e.g. like y=f(x) i.e. if x and f are true, then y is true). Therefore “not having a result” only means having another result of the measurement.

You have to understand the “a real photodetector” is not a genuine CI measurement apparatus, just an approximation that gives an approximated result.
Therefore, you have the right to construct “a measurement apparatus” that does not follow the CI results. I gave one such example (the voltmeters).
CI interpretation does not say that a huge system with an infinite (or huge) number of particles is a measurement apparatus, just “a system is on the collapsed state just after the result of the measure is A (i.e. A is true)”.
However, decoherence studies how a huge system may give results analog to the abstract measurement apparatuses of CI.
Note that I am already biased when I say “measurement apparatus” as I think CI deals only with measurements, results and collapse, i.e. it is already a causal bias analysis: what causes the results of a measurement? Answer “the measurement apparatus”. I am already out of the scope of core of CI.

Seratend.

 

[ZapperZ]

I disagree. You are discounting emergent phenomena that are entirely possible given the complexity of the situation. That's a distinct possibility that almost everyone ignores. I could tell you precisely the equation of motion of a bunch of gas particles, but there's nothing in that equation that will predict a phase transition and where it will occur. Such observation should caution anyone who thinks all of what we know can be extrapolated without any discontinuities. What if there is such a discontinuity between QM and GR equivalent of such a phase transition? Aren't there already people working on such ideas?

Zz.

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

Note that I'm NOT endorsing this. I just want to point out that when you deal with something having this type of degree of certainty, a LOT of things are still up in the air.

Zz.

 

[vanesch]

Yes, but you seem to assume that the results of Joe and Jack may be inconsistent that is not possible under CI. As you know, unitary evolution preserves the orthogonality of the vectors (same stuff used in e.g. MWI, MMI etc..). Therefore if the result of a given measurement is true, only a part of the vector, before measurement, should be assumed under the unitary evolution to make other logical assertions on further measurements (the other part "is wrong" simply because the result of the measurement is true: formal logic).

This is correct of course ; but such a statement is closer to MWI or relative-state views (to which I adhere more) than CI, which I thought, claimed a genuine, irreversible collapse of the wavefunction.

But what you claim is very true: IF the result of a measurement is known to be A, THEN for all matters WE CAN PRETEND THAT the system is in the projected state corresponding to the result A as in CI. But that is, I would say, almost the definition of a relative-state interpretation, and NOT CI.
We have shifted now the concept of what is a measurement into the phrase "the result of a measurement is known to be".

But you could, in principle, do experiments where some "observer" (be it a human being or just a small "measuring device") first "learns about a result" (but it is a different result in each of the different branches!) and then "interferes with itself" where in the process of course he forgot about "the" result because all the different branches of the observer states which had different results come together again (our language is not well-adapted to these situations).
This is thinkable in the case of Jack, but it is NOT in the case of Joe, because in that case, if we consider Joe to do a "measurement" there is a definite result and a definite collapse, and no interference with the other branches is possible anymore.
Embryonic experiments of this kind are delayed-choice quantum erasure experiments ; but you can hardly talk of a photon as a measurement device. However, if we could do the same thing, but this time with little photocells and integrated computers and memory instead of with photons, we would already be a bit further on the path.
If we could make such "microscopic photocells with integrated computer", and they record the "which path" information, but afterwards we make them interfere as to find out the "which interference pattern" information, then at a certain point, the computer "knew" the which path information, but was itself in a superposition of "I know it is the left path" and "I know it is the right path". Then, by making the two branches interfere, it wouldn't know anymore "which path" but you could now extract the "which interference pattern" information.
So from the point of view of the computer, a "measurement" was made, but the wavefunction didn't "collapse" ; it is only that the measurement gave different results for the different branches of the state of the computer (in a typical relative-state interpretation!). By making these different branches interfere again, the notion of "result of measurement" lost its meaning.
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...

However, to come back to what you said: IF you say that the result of the measurement is A THEN WE CAN PRETEND that the state is the collapsed state corresponding to A, is a very true statement. According to what I understood of CI, it is absolutely not what CI pretends, but then I might have missed what CI actually says. To me, the above statement is the essential content of relative-state interpretations.


cheers,
Patrick.

 

[vanesch]

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

Note that I'm NOT endorsing this. I just want to point out that when you deal with something having this type of degree of certainty, a LOT of things are still up in the air.

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
However, I have to say that I find the article "highly speculative", in an "original thinker" trademark style. Indeed, whenever people say that "future historians of science will wonder how it came that MyDiscovery-TM which is so obvious, took so long to be seen" or something of the kind, I get suspicious

cheers,
Patrick.

 

[seratend]

However, to come back to what you said: IF you say that the result of the measurement is A THEN WE CAN PRETEND that the state is the collapsed state corresponding to A, is a very true statement. According to what I understood of CI, it is absolutely not what CI pretends, but then I might have missed what CI actually says. To me, the above statement is the essential content of relative-state interpretations.
cheers,
Patrick.

Well, in the Messiah QM introduction book 1959 (for the 1st or 2nd edition), I consider as a CI interpretation book, we just have the collapse postulate of the ideal measurement written closely to my previous post. I.e. you *should* view it as a simple mathematical statement ("disconnected" from the physical reality). There is no "we can pretend" (interpretation) in this postulate, just the state of the system in the collapsed state corresponding to A. The collapsed word in this context only means the projection of the state (i.e. |A>= P|psi> is true). It is how I interpret the CI formalism (therefore I may be wrong for the interpretation).
I know, there are many papers on the flavours of CI (I like to call the interpretation of the Copenhagen interpretation ;). However, if we remove the extra words in order to focus on the logical statements of CI we get the following words: ideal measurement, collapse, result, before and after (may be there are some others words ;). The main danger with these words is to attach a meaning that does not exist in the CI (what physicist like to do), i.e. interpreting these words outside the CI formalism (therefore adding extra signification).

Again in your example of "microscopic photocells with integrated computer", (if we assume that a photocell allows an ideal measurement) your measurement apparatuses are there (there is no notion of time - logical statement). CI does not say if you do not look at the result, the result does not exist (no meaning in CI) and that the wavefunction is not collapsed. Just that the result of a measurement "collapses" the wave function in that result state (i.e. we need a measurement). Therefore in your experiment you have a global measurement apparatus made of independent unit measurement apparatuses. Therefore, you need to know all the results of the microscopic photocells to know the new wavefunction "after" the measurement.

CI is a very minimalist set in QM theory and I think it may handle (subset) most of the other interpretations of QM (yours MWI or relative state views or your own mind selection). (I have had a long time to remove all the external incoherent meanings of CI that my professors taught me in my first QM courses a long time ago ;). Now I just take CI for what I think it is: just a consistent basic math tool that connects experimental results to the theory predictions. It is not sufficient (How to realize a real ideal measurement?), but it is a good basis.

For a small analysis on the possible connections between the different interpretations of QM (and to see, a little how CI lives in some of these interpretations), I recommend the text:
Do we really understand quantum mechanics?, F. Laloe, 2002, Quant-ph/0209123 (section 4: historical perspective and section 6: various interpretations). The author sometimes underlines the link between the different interpretations.

Seratend.

 

[seratend]

Well, my purpose is to underline (simply) the eternal problem of the interpretation in physics (the connection between the results of the theory and the "real" world).

Jack and Joe are just measuring a voltage of the current source in my basic example. However, a current source may be modeled, as a voltage source with a huge resistance in series. Therefore the two voltmeters give surely a different voltage measure (i.e we apply the well know voltage division: R1/(R1+R2) to get the measured voltage).
Therefore, if Jack and Joe say (interpretation) that they both measure the voltage of the current source, they will get different results (interpretation inconsistency).

Seratend.

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?)

Even if this example is not a real QM one, i think it underlines perfectly most of the problem in QM measurements.

Seratend.

 

[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 Schrodinger 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 Schrodinger'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:

Schrodinger'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.