Where we stand-Baez talk at Luminy

[f-h]

Careful, Hamiltons and Lagranges Mechanics are simpler then Newtons and enable us to understand things like Noethers Theorems.

In this sense I am sure that there are tremendous simplifications to be found in QFT. Our current mathematical and conceptual framework is not well suited to doing QFT.

Beyond that it seems (please correct me if I'm wrong) that your interprete our collective failure to get a good grip on all the revolutions of 20th century as an indication that these are spurious, temporary and shouldn't be taken to serious, that instead we need to disregard them and go "back to the basics".
You are convinced that a theory of Quantum Gravity is impossible in the conventional sense (care to elaborate?), the efforts of reconciling QM and GR are wrong headed because one or both of these are fatally flawed, which is expressed in our failure to unify them.

I think that from a historical viewpoint this conclusion is not warranted. At no point in the history of science was there a unified theory of all that was known at the time.

From a personal PoV I do not think that you can deduce physical insights from the fact that we are collectively to stupid to figure out a certain problem. As Bell said: What is proved by impossibility theorems is a lack of imagination.

Also what are you thinking about for QM? t'Hooft style discrete dispersive deterministic mechanics? Or the Bell experiment loopholes where you postulate complicated ocrrelations between macroscopic entities to explain simple microscopic correlations? (Conspiracy Theory Interpretations of QM: The Lord is subtle AND malicious).

 

[Mike2]

You clearly do not understand the meaning of physics, the
MOST reliable laws of nature simply do not exist. That is just marketing pep talk for the public: the holy grail is much sexier than honest labor. I am looking for a *consistent* view and that is in some sense much more than what the holy grail chasers can legitimatly claim.

What I may not understand is the campus politics that prevent us from even considering the goal of a complete theory.

But when you say a "consistent" theory, I assume you mean with every possible measurement that may be predicted from said theory. If that is the case, then I don't know that we disagree. For I suppose we may one day need a theory that does explain everything, spacetime, matter, energy, QM, GR, QG, and the number of dimensions in the universe. We may need to explain where spacetime itself came from. This might be required, for example, as boundary conditions that give us this vacuum from the landscape. And if a theory should give us how spacetime emerged from nothing (perhaps a singularity), then that would sound to me to be a theory from logic itself. For then you have some entity coming from nothing like a true proposition coming from a false proposition. All things derive from one point. How more logical can things get?

 

[Careful]

**Careful, Hamiltons and Lagranges Mechanics are simpler then Newtons and enable us to understand things like Noethers Theorems.**

Sure, I did not contradict that, I just said that it does not cover the full range of Newtonian physics and that it came from a NEW nontrivial view upon physics (minimization of energy instead of forces acting on...)

**
In this sense I am sure that there are tremendous simplifications to be found in QFT. Our current mathematical and conceptual framework is not well suited to doing QFT. **

But you will require a new physical idea for that.

**
Beyond that it seems (please correct me if I'm wrong) that your interprete our collective failure to get a good grip on all the revolutions of 20th century as an indication that these are spurious, temporary and shouldn't be taken to serious, that instead we need to disregard them and go "back to the basics". **

Well, I do not say you have to disregard them: you have to draw the right lessons from the wrong theories. They all contain useful information about nature, I am just afraid (actually convinced) that we have misinterpreted some crucial experiments in the sense that perfectly simple and rational explanations within classical physics were possible. Of course the Schrodinger wave contains some useful information : it was designed exactly to cover such experiments which should reveal particle wave duality.

** You are convinced that a theory of Quantum Gravity is impossible in the conventional sense (care to elaborate?), the efforts of reconciling QM and GR are wrong headed because one or both of these are fatally flawed, which is expressed in our failure to unify them **

They are probably both wrong headed : GR in the minimal coupling principle and QM in the radical, unnecessary departure from local realism with as a consequence the need for a collapse of the wavefunction. Here you have one reason why QM and GR won't get married in a background independent way : it is logically impossible to define LOCAL observables in quantum gravity without introducing a preferred vacuum metric (or background frame) unless you have a mechanism which kills off superposition or put in by hand classical boundaries to a piece of ``observable space time foam´´.


**I think that from a historical viewpoint this conclusion is not warranted. At no point in the history of science was there a unified theory of all that was known at the time.**

Nah, sure there was: this was the great feeling at the end of the 19'th century. People thought they knew it all until they found out that an electron radiates, oeeps

**
From a personal PoV I do not think that you can deduce physical insights from the fact that we are collectively to stupid to figure out a certain problem. As Bell said: What is proved by impossibility theorems is a lack of imagination. **

Well Bell was speaking clearly about his own NO GO theorems then : I appreciate your idea that local realism is not for a waste yet. In my opinion, people had a lack of imagination when they saw black body radiation for the first time and thought about the Young double slit experiment in the beginning of the 20'th century. Let me tell you : if your QM professor would tell you that for all these experiments there exists a perfectly rational explanation, no student would accept QM anymore.

**Also what are you thinking about for QM? t'Hooft style discrete dispersive deterministic mechanics? **

Something like that yes, but I do not start from the weird deterministic quantum systems he uses (neither do I need information loss), moreover he has no clear answer yet how to avoid the measurement problem as far as I know. But I do admire the spirit of his curiosity and honesty.

**Or the Bell experiment loopholes where you postulate complicated ocrrelations between macroscopic entities to explain simple microscopic correlations? (Conspiracy Theory Interpretations of QM: The Lord is subtle AND malicious).**

There are also other possibilities which are by far not as malicious as people want you to believe (most of them are actually pretty simple toy models), but I would certainly like to avoid constructions involving backwards causation, yes. *IF* you come up with a theory which predicts non trivial correlations beyond the lightcone (in either when you break special relativity) you better do it in a natural and clear cut way (that is actually what 't Hooft is doing).

 

[Careful]

The point Mike is that perhaps you do not need to do all of these things you mention, partially because some of them don't ``melt´´ together and partially because some of the insights coming from each of these theories are obsolete and incorrect. I stress that we do not need to see these theories as immutable : you have to come up with some insight which captures the essence of all of them. (a) QM tells you that particles and waves interact on the microscale (b) GR gives you the strong equivalence principle and so on. For example : (b) does *not* logically imply that the ``metric field´´ has to be the dynamical variable for gravitation, neither does it tell you that the minimal coupling principle needs to be valid (ie. light could travel at speed > c in curved spacetime).

Again, take a deep look at geometric unification attempts for GR and EM and you might better understand my point of view.

Cheers,

Careful

 

[CarlB]

I've been following the fascinating discussion with great interest and entertainment. I find myself agreeing with careful on the need for extreme variation in approaches to the foundations of physics. Uh, I guess I should mention that I was recently awared "Crank of the Day" at http://www.crank.net .

Carl

 

[f-h]

Now we're talking, there are specific assumptions within the overall conceptional framework that seem unjustified/amendable. Trying to find a *physically* motivated replacement for them is certainly a very good idea. Trying to replace them just for the heck of it, certainly isn't.

I happen to think that LQG has a lot of potential in relation to matter coupling (and I don't mean Sundance et al). And John Baez has an intriguing paper out that suggests, citing TQFT, that maybe we will only get a good grasp of (at least some of) the strangeness of QM if we view it from the PoV of QG.

But this is a world from claiming that GR/QM are fundamentally "wrong headed". In fact this approach must take each theories core claims extremely serious to possible cure some of the defects of the other theory.

BTW your claim why we can't marry GR and QM is wrong, see Rovelli/Dittrich partial/complete observables.
The Dirac Observables are of course highly "nonlocal" (whatever that may mean in this context) but there are classes of them which have a clear local interpretation neithertheless.

 

[Careful]

BTW your claim why we can't marry GR and QM is wrong, see Rovelli/Dittrich partial/complete observables.
The Dirac Observables are of course highly "nonlocal" (whatever that may mean in this context) but there are classes of them which have a clear local interpretation neithertheless.

Entirely false. These observables are all *classical* and the constructions involved are based upon old ideas of Karel Kuchar (and involve good old fashioned gauge fixing ), hardly worthwhile calling something new. Classically, the problem is still tractable of course (albeit very messy and technically complicated), it is just that it becomes impossible *quantum mechanically*. It is clear you did not understand my comments and did not fully comprehend these papers either.

You might for a change think about what I say. The issue of matter coupling in LQG is very disputable : where are the usual anomalies which reflect *physics* ? - actually ``anything goes´´ is a disadvantage in that respect - there has been quite some discussion about that involving Jacques Distler et al.

 

[f-h]

Of course the ideas are not new, they are a reaction to Kuchars ideas but they are exactly critical of his views. They say that gauge fixing is not needed (or if you want to insist on calling it gauge fixing, it is also needed in non relativistic QM). The correct physical motivation is in the "What is observable in GR" paper. They are the correct conceptual interpretation of the actual calculations done in GR.

If you interprete them as nothing but a fancy way to do gauge fixing I guess they don't make much sense quantum mechanically, but that's not Rovellis point.
Of course Dittrichs papers are classical, but there are people working on the Quantum Mechanics of this ideas, and it turns out it's not completely untractable. Far from it.

Even if it was technically untractable Dittrichs work proves that classically there are Dirac Observables with good local interpretations, so why shouldn't there be Dirac Observables like that in QM? If you have objections that are specific to QM I'd love to hear them.

 

[f-h]

Of course in a background independent theory the adjective "local" becomes highly ambigious anyways. Local with respect to what? If you have a second field interacting with the first you can talk about observables of the first local relative to the second. That's the strongest statement that is well defined, and it's the notion of loaclity essentially captured in Rovellis approach.

 

[Careful]

**Of course the ideas are not new, they are a reaction to Kuchars ideas but they are exactly critical of his views. They say that gauge fixing is not needed (or if you want to insist on calling it gauge fixing, it is also needed in non relativistic QM). The correct physical motivation is in the "What is observable in GR" paper. They are the correct conceptual interpretation of the actual calculations done in GR. **

I know of Rovelli's points of view as well on relativity as on QM. The latter - that is his relational QM - I firmly disagree with (just a sequence of words), his GR view on the other hand is ``from the old school´´, solid and beautiful. Please, do you want to drop the word CORRECT - something physicist use too often when they don't fully understand what they are talking about.

**
If you interprete them as nothing but a fancy way to do gauge fixing I guess they don't make much sense quantum mechanically, but that's not Rovellis point. **

But they ARE nothing but gauge fixing (I don't remember all the details but that was certainly a very shared feeling at the time).

**
Of course Dittrichs papers are classical, but there are people working on the Quantum Mechanics of this ideas, and it turns out it's not completely untractable. Far from it. **

Of course, in principle you can try to quantize these observables (Hamiltonian constraint or master constraint - did not hear about that for a while ?? you cannot speak about an observable before solving these issues), the point is that *quantum mechanically* they have no *local* meaning whatsoever.

**Even if it was technically untractable Dittrichs work proves that classically there are Dirac Observables with good local interpretations, so why shouldn't there be Dirac Observables like that in QM? **

But that was already known for about at least 40 years (!), relativists had plenty of candate observables in their pocket. It is just that these work only LOCALLY on the classical level (for example when you try to find a dynamical arrow of time). This is a problem which they face too, but do not adress so far - exactly this issue killed off the work of Kuchar and company. What Dittrich and Rovelli did was rewriting it in the ADM Hamiltonian framework. Concretely, you can say in this framework : I can label star X by metric invariants (a,b,c,d) and this coordinate labelling will be unique in the neighborhood of X and probably provides you with an arrow of time and some other physical coordinates. However, star Y can have the same labels, then you need to add a new one and so on and so on. In the end you might end up with 25 labels to characterize all stars in the universe. This indeed gives you *classically* information about *localized* curvature hence *perhaps* matter (you know Einsteins theory violates the Mach principle).

**
If you have objections that are specific to QM I'd love to hear them. **

I told you that already: in LQG or any background independent approach you treat the *entire* universe as a quantummechanical black box. Anyone who has learned about the dirty word entanglement knows that you cannot split it up into subsystems (decoherence is something you have to show, not to assume), so what can you do ? Aha, the only thing which is left is to promote the above coordinates to operators and evalute them on all (unknown ) physical states. So *all* information you have quantum mechanically acces to is just this, nothing else. Now, if your universe would be one ``riggmapped´´ spin network (no superposition) each of whose subnetworks are eigenvectors of your preferred observables, there would not be any problem since this is actually analogous to the classical situation: you can map events to mathematical points here. But what if your universe is a superposition of ``riggmapped´´ spin networks ? How do you define then the action of a *localized* observable without knowing how the nodes in the different spin networks are relatively ``positioned´´? Topological information like knotting of spinnetworks in not enough here : *localization* is a metrical issue ! You cannot do it without an artificial labelling which is tantamount to choosing a background frame. Another possibility would be to restrict to global observables and calculate expectiation values of them and then try in good faith - with an infinite number of ambiguities - to fit a Lorentzian manifold to the data. The latter procedure certainly makes you wonder about the ambiguities in perturbative quantum gravity (these are actually not that bad) and is perpendicular to the way WE make measurements in the universe. The last possibility I see is to put classical boundaries which is a somewhat more liberal version of the labelling procedure.

Cheers,

Careful

 

[Careful]

Of course in a background independent theory the adjective "local" becomes highly ambigious anyways. Local with respect to what? If you have a second field interacting with the first you can talk about observables of the first local relative to the second. That's the strongest statement that is well defined, and it's the notion of loaclity essentially captured in Rovellis approach.

HUH ?? In classical GR, the METRIC gives me a notion of locality (the Alexandrov sets), nothing more is needed for that.

 

[f-h]

I see what you are saying but you seem to be confusing a lot of different things. I recommend taking a step back and looking at this problem with all the different notions of (non)locality flying around again.
States in QM are nonlocal in some sense, but there are of course local observables on nonlocal states.
The existence of nonlocal states says nothing about the existence of local observables.

Also yes that's what I said, I can localize something else relative to the metric field, but the metric field is localized with respect to what? The question doesn't make sense. (at least in the naive sense of "local"). That is Kuchars objection to the possibility of constructing locally interpretable Observables in a gaugeinvariant theory/fully constrained theory (which you reinvoke quantum mechanically when you talk about "rigging" but which is not really related to superposition/entanglement).
One can study this problem and the formalism to overcome it in any toy model, no Master constraint program needed.

A more detailed response later.

 

[Careful]

**I see what you are saying but you seem to be confusing a lot of different things. I recommend taking a step back and looking at this problem with all the different notions of (non)locality flying around again.
States in QM are nonlocal in some sense, but there are of course local observables on nonlocal states. **

No, I am not confusing different things: you are. You speak from experience in *background dependent* QFT in which anyone knows that what you say is correct. Actually, it is easy to see where the virtues of that theory (local observables on entangled states) are destroyed in a ``background independent´´ approach whatever that may mean.

**
The existence of nonlocal states says nothing about the existence of local observables. **

Again, that is only true in a background dependent approach since you have an *a priori* notion of locality there.

**Also yes that's what I said, I can localize something else relative to the metric field, but the metric field is localized with respect to what? **

But it is the metric field which gives locality simply by measuring distances

**That is Kuchars objection to the possibility of constructing locally interpretable Observables in a gaugeinvariant theory/fully constrained theory (which you reinvoke quantum mechanically when you talk about "rigging" but which is not really related to superposition/entanglement).**


Well, my objections are MINE, I can only conclude that Karel is a clever chap. No smartusz, I just added rigging for constructing diff invariant states, otherwhise you might have complained that I work with ``unphysical´´ objects which I still do since my master/hamiltonian constraint is not solved.

**
One can study this problem and the formalism to overcome it in any toy model, no Master constraint program needed. **

Rubbish, all these toy models probably have the wrong classical limit.

 

[masudr]

This is a very interesting discussion which I have been following for a while now. It also seems that others have been too, with an average of 163 views a day.

 

[arivero]

**Careful, Hamiltons and Lagranges Mechanics are simpler then Newtons and enable us to understand things like Noethers Theorems.**

Sure, I did not contradict that, I just said that it does not cover the full range of Newtonian physics and that it came from a NEW nontrivial view upon physics (minimization of energy instead of forces acting on...)

Can I contradict it, then? Newtons conception of time and movement is a lot simpler than phase space and symplectic areas.

 

[Careful]

Can I contradict it, then? Newtons conception of time and movement is a lot simpler than phase space and symplectic areas.

Hehe, it is all yours for the taken

 

[Hurkyl]

Please, do you want to drop the word CORRECT - something physicist use too often when they don't fully understand what they are talking about.

Turnabout is fair play -- do you want to stop using words like "wrong", "rational", and "magic"?

 

[Careful]

Turnabout is fair play -- do you want to stop using words like "wrong", "rational", and "magic"?

Wrong I can replace by extremely unlikely sometimes yes, master Hurkyl Magic is justified, unless you believe Harry Potter is actually around. Rational hmmm better replace it by classical rationality.

 

[marcus]

...I told you that already: in LQG or any background independent approach you treat the *entire* universe as a quantummechanical black box...

don't understand. there are QG approaches which have a boundary. there is an observer outside. what is studied is inside the boundary and is not the *entire*

Are you saying that these are invalid, or that they are not "background independent" (in your definition of background independence)?

 

[Careful]

don't understand. there are QG approaches which have a boundary. there is an observer outside. what is studied is inside the boundary and is not the *entire*

Are you saying that these are invalid, or that they are not "background independent" (in your definition of background independence)?

Well, you have to make a distinction between types of boundaries. If you have a timelike tube with as boundary two closed spatial hypersurfaces, then basically you are computing transition amplitudes between closed universes, that is fine but has no bearing upon the issue of local observables.

On the other hand, when you take a spatio temporal four dimensional cube, force classical boundary conditions and ``quantize´´ only the internal degrees of freedom, then of course you are doing a major cheat. Not only can you not make any local statements yet about what is happening inside the box, but worse: you have entirely ignored the problems of (a) entanglement versus environmental decoherence (b) how to define local observables.

Stricly speaking doing such act is illegal within pure quantum gravity, you might want to read what James Hartle has written about the quantum mechanics of closed systems. That some people do it is more a sign that they have run out of ideas than anything else. Since, if you allow for such travesty, then simply divide a classical universe UNIV into tiny boxes A, subdivide these further into boxes B. Imprint boundary conditions on A induced by UNIV and do quantization with fixed boundary conditions within A selecting wavelengths larger than B. The Feynman series will be finite and no need for an infinite number of counterterms. End of story: if this is all you mean by quantum gravity then we could have solved it 30 years ago by putting in physical regulators on the perturbation series (something which appears to be superior to LQG for now).

Another person who realizes this problematic very well is Roger Penrose who actually explicitly introduces a Newtonian time and a set of dynamically preferred Newton Schrodinger states.

 

[jarek]

Really, but quantum statistics is not even a well defined business yet.

Careful

Nah, Careful, please...Mackey put it in a very well defined form. If you don't accept other forms of statistics apart from the classical one (who was talking about thinking out of the box ), then sure entanglement is magic, local realism is lost (at least on paper) and we desperately need a genius who will restore it (at least on paper)

Cheers,
jarek

 

[Careful]

Nah, Careful, please...Mackey put it in a very well defined form. If you don't accept other forms of statistics apart from the classical one (who was talking about thinking out of the box ), then sure entanglement is magic, local realism is lost (at least on paper) and we desperately need a genius who will restore it (at least on paper)

Cheers,
jarek

Haha, I guess what Mackey did was to extend upon the work of Von Neumann and Shannon about quantum entropy no? The entire difficulty is of course to tell what your quantal degrees of freedom are : in the framework of dynamical geometry (such as quantum gravity), you do not even know where to choose them (although there are some proposals by 't Hooft). Moreover, as I seem to remember, Bernard d'Espagnat has written some rather severe comments upon the conceptual difficulties quantum statistics faces in light of the measurement problem (I do not remember that well anymore) - my comment was intented in that direction not on the technical aspect of the matter (in cases where the degrees of freedom can be easily identified).

Concerning your silly entanglement; IF such thing were observed (one day ) the easiest possibility is to allow for classical signals traveling > c, there is no law in nature which forbids that. The point is that for the undisputed QM experiments I have checked (double slit, black body, etc) I don't need QM at all

Cheers,

Careful

 

[marcus]

Well, you have to make a distinction between types of boundaries. [A] If you have a timelike tube with as boundary two closed spatial hypersurfaces,

On the other hand, when you take a spatio temporal four dimensional cube, force classical boundary conditions...

I am not talking about A or B. the boundary does not consist of two spatial hypersurfaces, nor does it consist of a four dimensional cube.

I am imagining a boundary with no beginning or end. I think of it as a tube (your word) but it has no space-like initial/final pieces.

AFAIK I am not imagining something that is a major cheat or illegal.

"course you are doing a major cheat. Not only can you not make any local statements yet about what is happening inside the box,..."

As a rule the observer can never say what is happening inside the box, he has only observations at the boundary. this is not illegal or a cheat, it is normal, or so I think.

maybe there are other ways of handling the observer problem---I understand it is a connundrum for all quantum mechanics I believe (not just some specialized subject like LQG or some other QG) and doubtless lots of people have written about it.

I am impressed by how negative your views are, careful. You seem to always be arguing that nobody's approach can ever be successful. You already know at the outset that various works in progress, like LQG, are doomed to failure. I find it curious.

 

[Careful]

**I am not talking about A or B. the boundary does not consist of two spatial hypersurfaces, nor does it consist of a four dimensional cube.

I am imagining a boundary with no beginning or end. I think of it as a tube (your word) but it has no space-like initial/final pieces. **

What is the damn difference? You still have to put asymptotic boundary conditions on future and past timelike infinity. Do you think that changing the classical boundaries are offering you a way out of my argument ??!

**
AFAIK I am not imagining something that is a major cheat or illegal.

"course you are doing a major cheat. Not only can you not make any local statements yet about what is happening inside the box,..." **

I am sorry to tell you that you did not understand the difficulties of quantum gravity then. BTW what you say is even complete heresy in QFT where you can still calculate expectation values of local observables in the box.


** As a rule the observer can never say what is happening inside the box, he has only observations at the boundary. this is not illegal or a cheat, it is normal, or so I think. **

See my previous comments.

**maybe there are other ways of handling the observer problem---I understand it is a connundrum for all quantum mechanics I believe (not just some specialized subject like LQG or some other QG) and doubtless lots of people have written about it.**

The problem of the observer becomes much more difficult in QG than in ordinary QM (any student of QG learns that).

**
I am impressed by how negative your views are, careful. You seem to always be arguing that nobody's approach can ever be successful. You already know at the outset that various works in progress, like LQG, are doomed to failure. I find it curious. **

What I find curious is that:
(a) nobody offers rational counterarguments to my reasonable no-go statement : I mean an LQG protege could friendly give me a reasonable physical mechanism why I should believe the contrary.
(b) actually, many prominent LQG'ers have left the field for similar reasons
(c) many good scientists outside the field think likewise (amongst others roger penrose)

Moreover, I find my comments far from negative, they clearly indicate where the stumblestones are : recognizing those and looking for plausible cures are necessary conditions for succes. These problems are with us from the real beginning Marcus and very little if no progress has been made on these issues by any of the traditional approaches. There has been written a lot of crap about it undoubtedly. Moreover, I have given a LOGICAL reason why defining local observables within a *background independent* quantum universe is IMPOSSIBLE; it seems to me that people like you have tremendous problems with logic.

Cheers,

Careful

 

[jarek]

Haha, I guess all Mackey did was to extend upon the work of Von Neumann and Shannon about quantum entropy no?

Concerning your silly entanglement; IF such thing were observed (one day ) the easiest possibility is to allow for classical signals traveling > c, there is no law in nature which forbids that. The point is that for the undisputed QM experiments I have checked (double slit, black body, etc) I don't need QM at all

Careful

No, I'm talking about orthomodular lattices more than about silly entropies You will call it kinematics and say that it should be dynamically determined etc and I will agree. But if you need quantum statistics per se, understood here rather abstracly like you can speak of classical probability theory - here you are!

Silly entanglement, I like the name , has no connection whatsoever to superluminal signalling and you perfectly know that. C'mon, you know why Einstein called it spooky action at a distance and how he proposed to resolve it

Cheers,
jarek

 

[marcus]

What I am mainly challenging is what you said in post #70

... in LQG or any background independent approach you treat the *entire* universe as a quantummechanical black box...

what I said was

don't understand. there are QG approaches which have a boundary. there is an observer outside. what is studied is inside the boundary and is not the *entire*

Are you saying that these are invalid, or that they are not "background independent" (in your definition of background independence)?

I still don't understand. Why do you think that " LQG or any background independent approach" necessarily treats the *entire* universe as one black box?

 

[Careful]

**No, I'm talking about orthomodular lattices more than about silly entropies You will call it kinematics and say that it should be dynamically determined etc and I will agree. But if you need a quantum statistics, understood here rather abstracly, like you can speak of classical probability theory - here you are! **

Ah, indeed that is just kinematics I remember a joke about those following Piron et al : that they have forgotten there is something like the Schrodinger equation in QM

** Silly entanglement, I like the name , has no connection whatsoever to superluminal signalling and you perfectly know that. C'mon, you know why Einstein called it spooky action at a distance and how he proposed to resolve it **

Who says that I was talking about superluminal signalling (which we only know to be forbidden in free theories ), I was talking about waves which can go faster than c and transmit information between the particles. That is *not* forbidden, it does not necessarily lead to superluminal signalling. Although as I said, I don't care for the moment about this too much, first concentrate on double slit, atomic physics and so on. I feel that a natural solution for this (which I am working out now) will clarify the issue of EPR too.

na zdrowie

Careful

 

[marcus]

Moreover, I have given a LOGICAL reason why defining local observables within a *background independent* quantum universe is IMPOSSIBLE

first, please tell me what you mean by *background independent*

what I usually mean is that the theory does not explicitly assume a background metric on the manifold

but in discussions background independence is often used comparatively. one theory is MORE background independent than another (no theory is perfectly background independent, that might not even be meaningful)

what do you mean, exactly, by background independent?

 

[jarek]

Who says that I was talking about superluminal signalling (which we only know to be forbidden in free theories ), I was talking about waves which can go faster than c and transmit information between the particles. That is *not* forbidden, it does not necessarily lead to superluminal signalling.

Careful

Erm, by superluminal signalling I mean transmitting information faster than c. And this you cannot do with entangled pairs. You can invent whatever waves you like (Gisin and co once even put experimental bounds on their velocities) which propagate between entangled pairs, but information (meaning something you can access) carry they will not

Although as I said, I don't care for the moment about this too much, first concentrate on double slit, atomic physics and so on. I feel that a natural solution for this (which I am working out now) will clarify the issue of EPR too.

I'm waiting especially for double slit :!)

na zdrowie

Ah, that's something you say when you drink vodka (provided you can still speak )


jarek

 

[Careful]

What I am mainly challenging is what you said in post #70
what I said was
I still don't understand. Why do you think that " LQG or any background independent approach" necessarily treats the *entire* universe as one black box?

And I referred you to papers of James Hartle on closed quantum systems. Actually, there are people working in the foundations of quantum mechanics, trying to extend it in order to allow for ``classical components´´- the followers of Piron et al which I made a joke about to Jarek - so this is all kinematics for now. But your question is fairly basic quantum mechanics, which amounts to : where can we put the observer? In order to know that you have to be able to *dynamically* identify your classical components (Schroedinger cat problem, here she is again ) : you cannot just put it in by hand. Hence you notice immediatly a logical loophole : in order to identify dynamically classical localized subsystems you need local observables


As a further example: anyone believing QG agrees that it was the dominant mechanism at the origin of the universe - unfortunatly you cannot put the observer in there in the way you see it.

If you want to know more about this, you can consult the road to reality of R. Penrose (not that I support everything he says there) - he explains it (in many pages) in a fairly entertaining way.

Cheers,

Careful