Local QM? MWI, RQM, QFT, LQM, + ?

[wm]

I'm interested in studying LOCAL theories within QM. I have the impression that the following theories claim to be such:

MWI (Everett)
RQM (Rovelli's Relational QM?)
QFT (Originated by ?)
LQM (There's a book titled ''Local QM'' as I recall.)
+

Questions:

1. Are there any other LOCAL quantum theories?

2. Does the definition of locality vary within the above schools?

3. Given some unanimity on the meaning of locality, I guess each of the above differs in the conceptualisation of ''reality''. Where might I find a summary of such differences? OR: Might those differences be developed here?

Thanks, wm

 

[Demystifier]

For a very very brief summary take a look here:
https://www.physicsforums.com/showthread.php?t=146601

 

[vanesch]

QFT (Originated by ?)

QFT is not an interpretation of quantum theory, it is the application of quantum theory to a specific classical model (classical fields). As such, all interpretational issues remain with QFT in the same way as they remain with other applications of quantum theory.

However, QFT people are often less concerned with this, because they usually only calculate S-matrix elements, which are transition probabilities from t = - infinity to +infinity, and they have already so many other technicalities to worry about that interpretational issues really only come in at low priority.

 

[Schrodinger's Dog]

Ah MWI, the new string theory. If I didn't think string theory was bad enough, with all it's extra dimensions no one could percieve, and strings no one could likely ever detect; someone comes along and suggests their are infinite realities we can't percieve too? Is anyone doing science these days or has physics turned into philosophy

MWI is likely to remain unfalsifiable forever, as is string theory. I personally think as it says on the link it's metaphysics repackaged as science, but hey prove me wrong.

IF MWI theory is right I'll eat my hat, and I have one too so you can hold me to it. It's a woolen one.

Looking at all those you mentioned I'd go for QM and will probably learn about QFT at some stage anyway; I'd probably look into that too. If I had time I'd glance over the RQM, and if I was bored I'd look at LQM. If i wanted to read about MWI I'd probably go with A.C.Clarke or Asimov?

 

[Anonym]

Vanesch:” QFT is not an interpretation of quantum theory, it is the application of quantum theory to a specific classical model (classical fields). As such, all interpretational issues remain with QFT in the same way as they remain with other applications of quantum theory.”

Allday:” One "law" that you can keep in mind is that quantum objects travel as waves and interact as particles”.

It is follow deterministically from your discussion with me in the Particle-Wave duality and Hamilton-Jacobi equation session that

There is no legitimation for M.Born statistical interpretation any more and it may be removed from the formalism of the Quantum Theory. Quantum Theory is the local field theory of the massive waves. No interpretation required.

 

[Demystifier]

QFT is not an interpretation of quantum theory, it is the application of quantum theory to a specific classical model (classical fields). As such, all interpretational issues remain with QFT in the same way as they remain with other applications of quantum theory.

That is true. However, a kind of locality is very manifest in QFT, much more than in QM of particles, which is why QFT is often mentioned in the context of "locality". Nevertheles, this kind of locality has almost nothing to do with locality inherent to some specific interpretations of QM.

 

[vanesch]

Ah MWI, the new string theory.

Has nothing to do with it. MWI is just a rigorous application of the basic postulate of quantum theory applied to everything: the superposition principle. You have to *violate* that postulate in order NOT to obtain MWI. You have to say that there are things in the universe which do NOT obey the principles of quantum theory.

Now, this can very well be the case ! I'm not saying that MWI is a correct description of nature. I'm usually just claiming that MWI is the most natural interpretation of a funny theory which we call quantum theory, and which starts with a totally crazy postulate: the superposition principle.

The superposition principle says: if A is a possible state of nature, and B is a possible state of nature, then u A + v B is also.
Well, if "me seeing the red bulb going on" (A) is a possible state of nature, and "me seeing a green bulb going on" (B) is another possible state of nature, then according to that superposition principle, any superposition of this is also a state of nature. Crazy ? Sure ! But that's a basic postulate of quantum theory. Doesn't apply to humans ? Why not ? Maybe it doesn't apply to humans. Could very well be. Because it is in contradiction to OBSERVATION ?

At first sight, you would think so ! But when you work out what would be observed *if this postulate applied also to humans and everything else*, well, to your surprise you'd find that there is no observable consequence of this statement which is in blunt contradiction with what is actually observed.

In other words, imagine for a moment the toy universe which is that "crazy world of MWI". What would its inhabitants observe ? Answer: they would observe exactly a universe as if "standard quantum theory" were valid. They wouldn't "observe their twins (that is, the other states in superposition)" most of the time (except in EPR experiments!).

So, MWI is *not* in any observational contradiction with what is observed. You do NOT see your "doubles" in other branches (if you would, then you could do things differently depending on these observations, and this would then mean that the evolution equation would be non-linear and non-unitary), thanks to the strict unitarity of time evolution.

So this indicates that there is *no observational indication* to assume that the basic postulates of quantum theory do NOT apply to macroscopic systems. Maybe they don't, but in absence of any evidence, there is no reason to assume this. Usually we assume that a physical law is valid until cases are found where it is clearly in contradiction with observation. Well, the superposition principle for macroscopic objects is NOT in contradiction with observation.

Moreover, there are almost incomprehensible things going on in quantum theory, UNLESS you look upon them from an MWI viewpoint: locality is preserved in EPR business, there is no dichotomy between two different evolution laws (unitary and projection), things such as delayed quantum erasers find natural explanations in an MWI setting... everything looks formally much smoother in an MWI setting than in a projection scenario. This shouldn't surprise us, because in an MWI setting, the dynamical laws are not violated, and the kinematical descriptions remain the same.

The only problem with MWI - which makes it unacceptable for many - is that it has a strange ontology: there COME OUT of the theory that there seem to exist "parallel worlds". This is not - as is sometimes assumed - PUT IN BY HAND. This comes out of it, and is actually very evidently seen, from the basic postulates: the superposition principle, and the postulate of unitary time evolution. It's the fault of these crazy postulates that we end up with such a crazy view ! If it weren't for their experimental success, we'd never consider such a crazy idea in the first place.

MWI is likely to remain unfalsifiable forever, as is string theory. I personally think as it says on the link it's metaphysics repackaged as science, but hey prove me wrong.

I think that the MWI debate is a bit like the debate of whether the spacetime manifold "exists" or whether "the EM field exists".
I think that if you work with a theory, such as GR, which cries out that the spacetime manifold exist, then it is easier to work with when you keep that in mind. In the same way, when you work with electromagnetism, it is easier to assume that there exists such a thing as the EM field. In the same way, when working with quantum theory, things come out much easier, conceptually, when you assume that the state vector of the entire system exists.

Again, it is a metaphysical discussion of whether "the spacetime manifold exists for real" or whether "the EM field exists". You can do GR and say that this is just a mathematical trick that helps you calculate the effects of gravity, but that the whole BS of bending spacetime is forever unfalsifiable. You can say the same about the existence of an EM field. And you can say the same about MWI.

If i wanted to read about MWI I'd probably go with A.C.Clarke or Asimov?

I think you can start with some very good articles by Vaidman on the arxiv.

 

[Schrodinger's Dog]

Has nothing to do with it. MWI is just a rigorous application of the basic postulate of quantum theory applied to everything: the superposition principle. You have to *violate* that postulate in order NOT to obtain MWI. You have to say that there are things in the universe which do NOT obey the principles of quantum theory.

Now, this can very well be the case ! I'm not saying that MWI is a correct description of nature. I'm usually just claiming that MWI is the most natural interpretation of a funny theory which we call quantum theory, and which starts with a totally crazy postulate: the superposition principle.

The superposition principle says: if A is a possible state of nature, and B is a possible state of nature, then u A + v B is also.
Well, if "me seeing the red bulb going on" (A) is a possible state of nature, and "me seeing a green bulb going on" (B) is another possible state of nature, then according to that superposition principle, any superposition of this is also a state of nature. Crazy ? Sure ! But that's a basic postulate of quantum theory. Doesn't apply to humans ? Why not ? Maybe it doesn't apply to humans. Could very well be. Because it is in contradiction to OBSERVATION ?

At first sight, you would think so ! But when you work out what would be observed *if this postulate applied also to humans and everything else*, well, to your surprise you'd find that there is no observable consequence of this statement which is in blunt contradiction with what is actually observed.

In other words, imagine for a moment the toy universe which is that "crazy world of MWI". What would its inhabitants observe ? Answer: they would observe exactly a universe as if "standard quantum theory" were valid. They wouldn't "observe their twins (that is, the other states in superposition)" most of the time (except in EPR experiments!).

So, MWI is *not* in any observational contradiction with what is observed. You do NOT see your "doubles" in other branches (if you would, then you could do things differently depending on these observations, and this would then mean that the evolution equation would be non-linear and non-unitary), thanks to the strict unitarity of time evolution.

So this indicates that there is *no observational indication* to assume that the basic postulates of quantum theory do NOT apply to macroscopic systems. Maybe they don't, but in absence of any evidence, there is no reason to assume this. Usually we assume that a physical law is valid until cases are found where it is clearly in contradiction with observation. Well, the superposition principle for macroscopic objects is NOT in contradiction with observation.

Moreover, there are almost incomprehensible things going on in quantum theory, UNLESS you look upon them from an MWI viewpoint: locality is preserved in EPR business, there is no dichotomy between two different evolution laws (unitary and projection), things such as delayed quantum erasers find natural explanations in an MWI setting... everything looks formally much smoother in an MWI setting than in a projection scenario. This shouldn't surprise us, because in an MWI setting, the dynamical laws are not violated, and the kinematical descriptions remain the same.

The only problem with MWI - which makes it unacceptable for many - is that it has a strange ontology: there COME OUT of the theory that there seem to exist "parallel worlds". This is not - as is sometimes assumed - PUT IN BY HAND. This comes out of it, and is actually very evidently seen, from the basic postulates: the superposition principle, and the postulate of unitary time evolution. It's the fault of these crazy postulates that we end up with such a crazy view ! If it weren't for their experimental success, we'd never consider such a crazy idea in the first place.



I think that the MWI debate is a bit like the debate of whether the spacetime manifold "exists" or whether "the EM field exists".
I think that if you work with a theory, such as GR, which cries out that the spacetime manifold exist, then it is easier to work with when you keep that in mind. In the same way, when you work with electromagnetism, it is easier to assume that there exists such a thing as the EM field. In the same way, when working with quantum theory, things come out much easier, conceptually, when you assume that the state vector of the entire system exists.

Again, it is a metaphysical discussion of whether "the spacetime manifold exists for real" or whether "the EM field exists". You can do GR and say that this is just a mathematical trick that helps you calculate the effects of gravity, but that the whole BS of bending spacetime is forever unfalsifiable. You can say the same about the existence of an EM field. And you can say the same about MWI.




I think you can start with some very good articles by Vaidman on the arxiv.

Thanks Vanesch that's a very neat summation of the idea.

I still can't help thinking though that MWI is making an assumption based on assumption. Using Occam's razor I would say it's too complex and invoking properties that it need not, my personal view is that we're not quite their yet, we haven't quite got how it works, so therefore anything based on the extension of what we know at the moment is subject to being based on faulty suppositions to begin with.

Not that I think QM is wrong, I haven't seen anything that would suggest that, just that when you read a discussion about what a wave function describes, you tend to get the impression that it's pretty much a matter of mathematical interpritation, and obviously that's because we cannot observe directly a superposition.

Sometimes when I'm floating around discussions, I often have to ask myself, how do you make that out? I could as easilly say x alot, it's all a little to grey to start making hypothesis based in incomplete theory, in other words let's get the foundation right first before we start invoking strings and many worlds. I have a bit of an issue with Hawking radiation as well, but that's a whole 'nother topic.

I guess it's just a matter of what your interested in and what you think will pan out though. I don't see any problem with this hypothesis, but if like string theory it's ultimately going to prove philosophical I'd rather see top scientists discussing something a little more this world interpritation.

There is no reason to assume God exists, their is no reason to assume he doesn't scientifically either. But logic and proof are very different beasts.

 

[JesseM]

Ah MWI, the new string theory.

MWI is hardly "new", it's been around since 1957. You may be confusing it with the landscape proposal that grew out of string theory, which postulates a huge number of different universes with different values of various physical constants.

 

[Schrodinger's Dog]

MWI is hardly "new", it's been around since 1957. You may be confusing it with the landscape proposal that grew out of string theory, which postulates a huge number of different universes with different values of various physical constants.

Well I was comparing it to the faddy nature of string theory it's kind of like the latest fashion in the physics world.

 

[masudr]

...that's because we cannot observe directly a superposition.

That's not strictly true. The Stony Brook and Delft groups observed a superposition of current flowing both ways (in a SQUID) by detecting the energy gap between the two states. The energy measurement did not disturb the superposition as the respective observables commute.

 

[vanesch]

I still can't help thinking though that MWI is making an assumption based on assumption. Using Occam's razor I would say it's too complex and invoking properties that it need not, my personal view is that we're not quite their yet, we haven't quite got how it works, so therefore anything based on the extension of what we know at the moment is subject to being based on faulty suppositions to begin with.

We will ALWAYS be in that case, as long as we (and our descendants, or another species which thinks about physics) will be around. We will always have a finite knowledge, and we will always have to "extrapolate" if we are going to pose grand visions of the meaning of life, the universe and everything. So "waiting until we finally find out" is Waiting for Godot.

My point is simply this: *IF* we insist on having a world picture, then it seems more reasonable to do this by extrapolating currently well-established theories than to postulate half-baked and not-yet-completely-worked-out dreams of theories of what "ought" to be (this sounds like string theory ). So, totally aware of the extrapolation and its hypothetical character, I think it is more conservative to stick to the principles of established theories than to invent properties of principles of unestablished theories, and it is based upon that attitude that I think that an MWI view is more natural with quantum theory than a Copenhagen based view. But I'm well aware of the extrapolation this contains. I would even say (with Penrose), that there is probably a serious problem, which is gravity. But, or unitary quantum theory can cope with gravity (in which case the serious problem disappears), or unitary quantum theory will undergo a modification in order to deal with gravity, in which case we will not need an interpretation of unitary quantum theory anymore (and maybe we can do away with MWI, depending on how the new, and unknown, theory will be put together). However, given that at this moment, the only thing we have, is unitary quantum theory, we extrapolate to its universal applicability, and then you end up with MWI in one way or another.

In this light, MWI is rather favored by Occam's rasor. Because what is "cut away" is all the extra hypotheses needed for the NON-applicability of unitary quantum theory (somehow the EXTRA rules that say that the superposition principle is NOT applicable to humans or so).
There are two ways to consider Occam: one can try to simplify the RULES of the game (that is, cut away all extra rules which don't bring in anything), or one can cut in the acceptable solutions: that is, by adding rules, we can limit the kind of solutions we like to see. Usually, with Occam's razor, one means the first kind of simplification: one likes to limit the number of RULES, and wants to apply them as universally as possible. If this leads to a more involved set of solutions, then so be it. In this light, applying the superposition principle universally is a simpler view (preferred by Occam) than specifying extra rules of when it applies, and when not, and what to do when not (projection).

Now, I can accept very well that people "shut up and calculate", because strictly speaking, that's what science is about: building models which make predictions and falsify them. It is when people start to talk about the weirdness of quantum theory (and more specifically about its confrontation with logic, or its lack of sensibility or the like) that I like to bring up an MWI view. In those "paradoxial" situations, like EPR-Bell, or delayed quantum erasers and so on, this view really helps "understanding" the quantum-mechanical machinery (in the same way as imagining that a spacetime manifold is curved helps you understand general relativity), and avoids all these "impossibilities" which are displayed. But if you are happy with saying "hey, that's what comes out of the calculation, and that's also what we find experimentally", then that's also fine. It is when one starts saying "uh, this must be wrong, this doesn't make any sense, although we calculate it, and we measure it all the same", that it helps to consider exactly what we assumed as a starting point and how these very same assumptions are also the key to the "understanding" of the "paradox".

Not that I think QM is wrong, I haven't seen anything that would suggest that, just that when you read a discussion about what a wave function describes, you tend to get the impression that it's pretty much a matter of mathematical interpritation, and obviously that's because we cannot observe directly a superposition.

Well, it is part of the superposition principle that we can't observe it directly ! However, we can observe its consequences indirectly (each time this happens, we talk about a "quantum effect" or something of the kind).

Sometimes when I'm floating around discussions, I often have to ask myself, how do you make that out? I could as easilly say x alot, it's all a little to grey to start making hypothesis based in incomplete theory, in other words let's get the foundation right first before we start invoking strings and many worlds.

We will never be sure that we have the foundations "right", and we will always have an "incomplete theory". There may be moments when we will be deluded in thinking that we have it all right. Happily right now that's not the case: we KNOW we don't know everything. The day we think we do, we are deluding ourselves.

Again, MWI is just a conceptual tool to help you understand quantum theory, as we have it right now, in the same way as the spacetime manifold is a tool to understand general relativity, or Euclidean space is a tool to understand our visual impressions.

There is no reason to assume God exists, their is no reason to assume he doesn't scientifically either. But logic and proof are very different beasts.

True, but there's a difference. It is a common misunderstanding of MWI that one has *introduced* the idea of "several worlds". As I tried to point out: this is a *consequence* of applying a basic postulate strictly and universally. If we used a theory in which there was a fundamental postulate that introduced a deity for the behavior of electrons in an atom, then wouldn't it be natural to assume that that deity also existed for us ?
THIS is what is done in MWI: we APPLY an *already existing postulate* of the theory universally, beyond where it is "really needed". We don't introduce a totally new concept (such as a deity). It also indicates the weakness of an MWI view: it might be that the postulate is *not* universally true, and then of course, the view based upon it doesn't make any sense. But that day, we will also know WHAT is then applicable. Up to today, we haven't gotten any indication of a limitation to the applicability of the superposition principle (but gravity might be a spoiler - we simply don't know). As such, we can only GUESS at what might eventually replace it, IF it even needs replacement. So all non-MWI views are in fact based upon a *guess* of new physics - usually to bring it in agreement with intuitively more acceptable macroviews.
And WHEN we do so, we run into a lot of paradoxes. So why do this ? Clearly, the day that we DO KNOW whether or not the superposition principle has limitations of its applicability, and we DO KNOW what replaces it eventually, we will also know what are the solutions to eventual "paradoxes". So we shouldn't worry about that. But right now we don't. So let us not worry about paradoxes that might not even be there, and which aren't there when we extrapolate our current theory's principles.

 

[Schrodinger's Dog]

Of Course though Vanesch, this is precisely the sort of discussion I could say: but I could just as easilly say X. In other words all the other myriad of theories are equally as viable, and since yours has no proof except in some logical theory, it's philosophy, essentially your saying that because a is more logically consistant, it must be more viable, I don't personally see it that way, I find it mind numbingly overcomplicating the deal but then I guess it's a matter of interpritation?

There is no real reason to believe it stands on it's own as viable and until there is, isn't it is as guilty of speculation as string theory, more consistant? Is this hypothetically more consistent, or really more consistent?

Since also it is unlikely to ever get proof then what is the point of speculating about the existence of the Invisible Pink Unicorn? How does this advance science?

I think at heart that is my biggest question to resolve before I accept that faries exist at the bottom of my garden if you see what I mean. Shut up and calculate. Or at the very least show me the money

The only difference between many worlds and string theory is the philosophy is worded differently, both are as guilty of putting the cart before the horse.

Speculation is good, healthy even, but be sure to make sure you bear in mind that is all it is atm, and if that's all it's likely to be, I don't personally see why I should indulge in speculation for the sake of speculation.

Wake up with a hypothesis disprove it over breakfast, then you're ready to work.

Anon.

 

[vanesch]

In other words all the other myriad of theories are equally as viable, and since yours has no proof except in some logical theory, it's philosophy, essentially your saying that because a is more logically consistant, it must be more viable, I don't personally see it that way, I find it mind numbingly overcomplicating the deal but then I guess it's a matter of interpritation?

It is of course partly philosophical, but then every consideration of the foundations of a theory is partly philosophical. So I don't see the qualifier "it is philosophical" as a counter argument !

What we know of quantum theory, is that no matter what will come next, if anything, it can't be good old classical physics, in the good old way we used to do it, unless quantum theory makes entirely wrong predictions in some aspects. There is still a crowd of people hoping for exactly that: empirical falsification of quantum theory, not in an entirely eccentric part of the universe, but in a lab, using rather daily stuff. However, it hasn't happened yet, and as such, I still stick to quantum predictions as quantum theory makes them. Any empirical falsification of quantum theory would of course shine a totally new light on the issue. But we aren't there for the moment.

As such, Bell's argument shows us that any underlying mechanism, if any, will not be both relativistically invariant AND kind of to be dealt with the way we used to do classical physics. Some are prepared to sacrifice relativity in its inner bearings. That's what the Bohmians do. Who knows.
But the principle of relativity has shown to be very powerful, and giving it up for no apparent reason then leaves us with more explanations to give than by keeping it. So I want to keep relativity too. I'm quite conservative. I want to keep those theories that worked well.

So I have to have quantum theory AND relativity. And this is entirely possible. I only have to apply *strictly* the principles of quantum theory, and *strictly* the principles of relativity, and I find that there's no problem. So allow me to point this out to anyone who comes to the conclusion that there are very "impossible" things going on.

There is no real reason to believe it stands on it's own as viable and until there is isn't, it is as guilty of speculation as string theory, more consistant? Is this hypothetically more consistent, or really more consistent?

What do you mean "no real reason to believe it stands on its own" ? All axioms are laid down ; they are simply the same axioms as those of special relativity and of quantum theory, with the "extra requirement" that they are universally valid - in other words, that they apply to everything. What *follows* from doing that, is that quantum theory as we know it, applies, and that relativity, as we know it, applies. It is not a "dream of a theory" of which the postulates still have to be written down (as is string theory), but of which we are already listing all the properties we hope we will derive once we find the right set of postulates. The postulates are known, and they are those of quantum theory!

Since also it is unlikely to ever get proof then what is the point of speculating about the existence of the Invisible pink unicorn? How does this advance science?

The invisible pink unicorn is not the result of verified postulates. As such, there's no reason to *INTRODUCE* it. But the superposition postulate has been at the basis of a lot of useful quantum theory. So instead of talking about a *totally new and useless* concept such as an invisible pink unicorn, it is like talking about the "back side of the Andromeda galaxy". It is very unlikely we ever get proof that there's light emitted from the backside (from our PoV) of the Andromeda galaxy into outer space. Now, do you have a reason to assume it "is there" or not ? Or is it more reasonable to *introduce* a new postulate which tells you that far away galaxies don't emit light away from Earth ? And then find out that "paradoxes abound" because now it seems that there is an inbalance in the total energy output of those galaxies. And then start talking about "spooky actions" on remote galaxies, which change the physics in some yet-to-be-explained ways which can then explain why the radiant flux of remote galaxies is different from nearby stars ?

So we have first a theory which tells us that stars and so on emit light in all directions. Now, for far-away galaxies, the only thing that matters for most observations, is that part of the light which comes our way. It wouldn't make a difference if we said that in those cases, the light emitted is ONLY in our direction. Except for certain observations (such as a kind of radiation balance), where we then get into trouble. We then start speculating about new physics that might happen to those remote galaxies, for which the light is only emitted in our direction, and get their radiation imbalance all wrong because of that.

Because this is exactly what happens in quantum theory. We have the superposition postulate, which gives good results on microscopic scale. We also know that we could apply it on macroscale, and that this would, most of the time, not make any observational difference (decoherence). However, we decide that somehow, it doesn't apply on the macroscale. And then we have problems in those cases where it WOULD have made a difference. But we refuse to go back to the idea that we could apply it to macroscale.

That said, I have nothing against "shut up and calculate", but I find it a bit "inspirationless".

 

[Schrodinger's Dog]

It is of course partly philosophical, but then every consideration of the foundations of a theory is partly philosophical. So I don't see the qualifier "it is philosophical" as a counter argument !

Partly or totally? is their any experimental evidence of MWI, I'd be keen to hear if their is?

What we know of quantum theory, is that no matter what will come next, if anything, it can't be good old classical physics, in the good old way we used to do it, unless quantum theory makes entirely wrong predictions in some aspects. There is still a crowd of people hoping for exactly that: empirical falsification of quantum theory, not in an entirely eccentric part of the universe, but in a lab, using rather daily stuff. However, it hasn't happened yet, and as such, I still stick to quantum predictions as quantum theory makes them. Any empirical falsification of quantum theory would of course shine a totally new light on the issue. But we aren't there for the moment.

No because classical physics does not describe the quantum this is self evident.

As such, Bell's argument shows us that any underlying mechanism, if any, will not be both relativistically invariant AND kind of to be dealt with the way we used to do classical physics. Some are prepared to sacrifice relativity in its inner bearings. That's what the Bohmians do. Who knows.
But the principle of relativity has shown to be very powerful, and giving it up for no apparent reason then leaves us with more explanations to give than by keeping it. So I want to keep relativity too. I'm quite conservative. I want to keep those theories that worked well.

Agreed, ditching the baby with the bathwater is not a viable way of proceeding.

So I have to have quantum theory AND relativity. And this is entirely possible. I only have to apply *strictly* the principles of quantum theory, and *strictly* the principles of relativity, and I find that there's no problem. So allow me to point this out to anyone who comes to the conclusion that there are very "impossible" things going on.

Well it's a bit of a stretch to say that coming to a conclusion should from the basis of a theory no? Equally those who think their are possible things going on can come to any number of conclusions of the possible and that's what I mean by I could as easilly say X.

What do you mean "no real reason to believe it stands on its own" ? All axioms are laid down ; they are simply the same axioms as those of special relativity and of quantum theory, with the "extra requirement" that they are universally valid - in other words, that they apply to everything. What *follows* from doing that, is that quantum theory as we know it, applies, and that relativity, as we know it, applies. It is not a "dream of a theory" of which the postulates still have to be written down (as is string theory), but of which we are already listing all the properties we hope we will derive once we find the right set of postulates. The postulates are known, and they are those of quantum theory!

No they aren't until you prove they are they are hypothetical, and so is everything the MWI says until it can show us something tangible in either experimentation or at least in inference, I can quite easilly conclude myself that the reason we cannot see what we are measurinbg is because we don't have the right sort of tools, and if we could it would be obvious how the Dirac equation works so beautifully, it is because it describes perfectly x. Whatever x is. But in mathematical form.

The invisible pink unicorn is not the result of verified postulates. As such, there's no reason to *INTRODUCE* it. But the superposition postulate has been at the basis of a lot of useful quantum theory. So instead of talking about a *totally new and useless* concept such as an invisible pink unicorn, it is like talking about the "back side of the Andromeda galaxy". It is very unlikely we ever get proof that there's light emitted from the backside (from our PoV) of the Andromeda galaxy into outer space. Now, do you have a reason to assume it "is there" or not ? Or is it more reasonable to *introduce* a new postulate which tells you that far away galaxies don't emit light away from Earth ? And then find out that "paradoxes abound" because now it seems that there is an inbalance in the total energy output of those galaxies. And then start talking about "spooky actions" on remote galaxies, which change the physics in some yet-to-be-explained ways which can then explain why the radiant flux of remote galaxies is different from nearby stars ?

I think you can assert as many postualtes as you like and in fact if you gave me a couple of years I could come up with something very simmillar to MWI, call it many existence theory, meaning that every event takes place but only one is realized. So that reality itself is a quantum superposition? How is this less valid than your hypothesis? In fact it's simmilar? BUt I don't say there are infinite realities only infinite possibilities? Explain how this hypothesis is worse than yours or better? I hereby anounce the formalisation of a new theory: single world interpritation. SWI or Schrodingers World Interpritation Maths paper to follow, where I show how this all works beautifully with a series of thought experiments and a few tweaks of the math.

So we have first a theory which tells us that stars and so on emit light in all directions. Now, for far-away galaxies, the only thing that matters for most observations, is that part of the light which comes our way. It wouldn't make a difference if we said that in those cases, the light emitted is ONLY in our direction. Except for certain observations (such as a kind of radiation balance), where we then get into trouble. We then start speculating about new physics that might happen to those remote galaxies, for which the light is only emitted in our direction, and get their radiation imbalance all wrong because of that.

Indeed a lot of observation relies on the idea that our area of the universe is consistently how the universe works everywhere and although I can't prove that is true, it's probably the best way to proceed with theory for now.

Because this is exactly what happens in quantum theory. We have the superposition postulate, which gives good results on microscopic scale. We also know that we could apply it on macroscale, and that this would, most of the time, not make any observational difference (decoherence). However, we decide that somehow, it doesn't apply on the macroscale. And then we have problems in those cases where it WOULD have made a difference. But we refuse to go back to the idea that we could apply it to macroscale.

That said, I have nothing against "shut up and calculate", but I find it a bit "inspirationless".

But what happens at the quantum scale is not what happens at the classical scale, this is a fundamental of QM? Why therefore do we assume that? What reason is there to make this assumption other than a philosophical one?

Shut up and speculate then

 

[vanesch]

Partly or totally? is their any experimental evidence of MWI, I'd be keen to hear if their is?

What I personally consider as experimental evidence for MWI, are EPR-Bell situations. They are an "observable way" of putting macroscopic observers in superpositions of "observer states", and have them interfere.

It is about the closest you could get to "showing MWI true". But it is not really an experimental *proof* of it ; it only shows that quantum-mechanical superpositions happen at scales which could easily be considered "macroscopic" (namely, several kilometers). Once we are there, and we have to consider quantum-mechanical superpositions for:
- systems on the scale of kilometers
- systems with 10^20 particles (like the currents in superconductors)
then why would we consider that this principle does NOT apply to "macroscopic things" ? Especially when IF we do, we can keep both relativity and the EPR kind of results ?

No they aren't until you prove they are they are hypothetical, and so is everything the MWI says until it can show us something tangible in either experimentation or at least in inference

As I said: is the "resolution" of the Bell-EPR paradox not good enough ?
It is about the only situation in which one can "demonstrate" the actuality of macroscopic superposition: take an entangled microsystem, get the parts far apart, and entangle them *in arbitrary ways* (= choice of angle) with two macrosystems (Alice and Bob). Then have Alice and Bob interfere. Remember that quantum interference is the difference between a superposition and a mixture. Now, if our Alice and Bob were in a kind of mixture, they wouldn't show the "singlet interference correlation pattern". So they were clearly in a quantum superposition.

I think you can assert as many postualtes as you like and in fact if you gave me a couple of years I could come up with something very simmillar to MWI, call it many existence theory, meaning that every event takes place but only one is realized.

You should refine your definitions of "take place" and "is realized". Depending on how you do so, you end probably up with or a kind of collapse theory, or with just another flavor of MWI.
In the first case, you run into Bell's theorem.

So that reality itself is a quantum superposition? How is this less valid than your hypothesis? In fact it's simmilar? BUt I don't say there are infinite realities only infinite possibilities? Explain how this hypothesis is worse than yours or better? I hereby anounce the formalisation of a new theory: single world interpritation.

You can play semantics only so far. At a certain moment, you have to tell me, whether yes or no, when Bob does a measurement, there *is* only a unique outcome, or whether the two outcomes somehow happen both.
In the first case, you unavoidably run into Bell's theorem. From the moment you consider the second, you are in an MWI kind of frame.

Many people have tried what you propose, you know. That's now about 80 years that this issue is with us.

But what happens at the quantum scale is not what happens at the classical scale, this is a fundamental of QM?

No, this is just a vision on QM (the Copenhagen school) which somehow is called the standard view, and it leads to all these interpretational problems. One should still show me what exactly is meant with "quantum scale" if it can encompass 10^20 particles, and and be of the size of several kilometers.

Now, don't get me wrong, I don't want people to adhere to MWI as if it were a kind of dogmatic religion ! I'm only saying that, given that MWI respects the basic postulates of QM rigorously, and given that it gives quite a natural explanation for otherwise quite strange or even incomprehensible situations, it is IMO the natural view on the formalism of quantum theory - in as far as one is in the need of a view at all (hence also my respect for those who "shut up and calculate").

You could use your arguments just as well against the idea that gravity is the bending of spacetime. You could call all those tensor equations just a mathematical tool, but gravity is, well, gravity, the thing that attracts stuff in an Euclidean space, and seems to also affect clocks, and those curvature things in spacetime is just a totally speculative view on things, taking the mathematics too seriously. This can very well be. Nevertheless, imagining that gravity actually IS the bending of spacetime makes the understanding of general relativity much more natural. "paradoxes" in relativity become naturally explained when you accept that spacetime is bend - even if you want to keep in your mind that this is just a trick to remember those pesky tensor equations, but that of course no-one in his healthy mind would take seriously the idea that there is something as a "bent spacetime", whatever that might mean.
I take MWI versus quantum theory on the same level as imagining a bent spacetime is versus general relativity. Whether this has anything to do with "what is really out there" or not. In both cases.

 

[Tomsk]

Here's a paper I read on RQM a while ago, I really like it, and I think trying to derive the QM formalism from a bunch of postulates sounds like a very good idea, as we would probably get a better understanding of QM.

http://fr.arxiv.org/PS_cache/quant-ph/pdf/9609/9609002.pdf

It's not too complicated or long, I could understand most of it and I'm only a 2nd year undergrad. Didn't understand any of the stuff on information though.

Here's a paper on RQM-EPR

http://fr.arxiv.org/PS_cache/quant-ph/pdf/0604/0604064.pdf

It would be interesting to see what you all think. You probably all know a lot more about QM than me. :)

 

[Schrodinger's Dog]

What I personally consider as experimental evidence for MWI, are EPR-Bell situations. They are an "observable way" of putting macroscopic observers in superpositions of "observer states", and have them interfere.

It is about the closest you could get to "showing MWI true". But it is not really an experimental *proof* of it ; it only shows that quantum-mechanical superpositions happen at scales which could easily be considered "macroscopic" (namely, several kilometers). Once we are there, and we have to consider quantum-mechanical superpositions for:
- systems on the scale of kilometers
- systems with 10^20 particles (like the currents in superconductors)
then why would we consider that this principle does NOT apply to "macroscopic things" ? Especially when IF we do, we can keep both relativity and the EPR kind of results ?




As I said: is the "resolution" of the Bell-EPR paradox not good enough ?
It is about the only situation in which one can "demonstrate" the actuality of macroscopic superposition: take an entangled microsystem, get the parts far apart, and entangle them *in arbitrary ways* (= choice of angle) with two macrosystems (Alice and Bob). Then have Alice and Bob interfere. Remember that quantum interference is the difference between a superposition and a mixture. Now, if our Alice and Bob were in a kind of mixture, they wouldn't show the "singlet interference correlation pattern". So they were clearly in a quantum superposition.




You should refine your definitions of "take place" and "is realized". Depending on how you do so, you end probably up with or a kind of collapse theory, or with just another flavor of MWI.
In the first case, you run into Bell's theorem.




You can play semantics only so far. At a certain moment, you have to tell me, whether yes or no, when Bob does a measurement, there *is* only a unique outcome, or whether the two outcomes somehow happen both.
In the first case, you unavoidably run into Bell's theorem. From the moment you consider the second, you are in an MWI kind of frame.

Many people have tried what you propose, you know. That's now about 80 years that this issue is with us.




No, this is just a vision on QM (the Copenhagen school) which somehow is called the standard view, and it leads to all these interpretational problems. One should still show me what exactly is meant with "quantum scale" if it can encompass 10^20 particles, and and be of the size of several kilometers.

Now, don't get me wrong, I don't want people to adhere to MWI as if it were a kind of dogmatic religion ! I'm only saying that, given that MWI respects the basic postulates of QM rigorously, and given that it gives quite a natural explanation for otherwise quite strange or even incomprehensible situations, it is IMO the natural view on the formalism of quantum theory - in as far as one is in the need of a view at all (hence also my respect for those who "shut up and calculate").

You could use your arguments just as well against the idea that gravity is the bending of spacetime. You could call all those tensor equations just a mathematical tool, but gravity is, well, gravity, the thing that attracts stuff in an Euclidean space, and seems to also affect clocks, and those curvature things in spacetime is just a totally speculative view on things, taking the mathematics too seriously. This can very well be. Nevertheless, imagining that gravity actually IS the bending of spacetime makes the understanding of general relativity much more natural. "paradoxes" in relativity become naturally explained when you accept that spacetime is bend - even if you want to keep in your mind that this is just a trick to remember those pesky tensor equations, but that of course no-one in his healthy mind would take seriously the idea that there is something as a "bent spacetime", whatever that might mean.
I take MWI versus quantum theory on the same level as imagining a bent spacetime is versus general relativity. Whether this has anything to do with "what is really out there" or not. In both cases.

To be honest we're both guilty of semantics here, your saying that an incomplete understanding of a leads to b,and I'm saying that an incomplete understanding of a might lead to b, but I think it doesn't because of occams razor? Who's right? I'm sticking with my SWI, I can explain all you can with MWI just by sticking to the three dimensions we know and time, I prefer the idea of infinite possibilities not dimensions, and until someone shows me something other than the bell theorem, I won't be leaping to any tangental conclusions, have you ever thought that an entangled particle may be in some sort of state we haven't accounted for? And that there may be no locality or non locality as such it's just an account of unobserved variables.? Probably. I'm more inclined to believe this than that it leads naturally to MWI.

At the end of the day though provided you acknowledge it's speculation and don't take it seriously in the same way you would a theory, I don't have any problem with it. It's the faddiness that worries me, too many people with little or no understanding reading about it and then you get serious PhD students trying to find the fairies at the bottom of the garden, to rehash an old analogy. I personally jost don't think the answer is that bizzare, but of course that is just my own flavour of speculation.

 

[vanesch]

http://fr.arxiv.org/PS_cache/quant-ph/pdf/9609/9609002.pdf

It's not too complicated or long, I could understand most of it and I'm only a 2nd year undergrad. Didn't understand any of the stuff on information though.

Here's a paper on RQM-EPR

http://fr.arxiv.org/PS_cache/quant-ph/pdf/0604/0604064.pdf

It would be interesting to see what you all think. You probably all know a lot more about QM than me. :)

Do a search here on Rovelli or relational quantum mechanics: there have been long discussions about that. I'm pretty convinced that RQM is some other wording of an MWI, but then some people don't agree with that.

 

[vanesch]

To be honest we're both guilty of semantics here, your saying that an incomplete understanding of a leads to b

I'm not claiming any "incomplete understanding", on the contrary. I'm just saying that, with the postulates we have, we can build an entirely coherent picture which doesn't lead to contradictory situations as some claim. That's rather the opposite than "claiming incomplete understanding", no ?
However, I place the caveat, that our understanding *in general* of nature will always be incomplete, and as such, that the picture can change, when we learn more. It can also be correct if no such change is required. THAT is the point: it CAN also be correct. Many other views cannot claim that. They NEED vague, new, ununderstood postulates which must somehow fix the obvious problems. THAT's where I apply Occam's razor.

I don't see why one should introduce the idea of vague, unspecified, ununderstood postulates which are needed to solve problems which don't even appear in the first place when you don't modify anything.

I'm sticking with my SWI, I can explain all you can with MWI just by sticking to the three dimensions we know and time, I prefer the idea of infinite possibilities not dimensions, and until someone shows me something other than the bell theorem, I won't be leaping to any tangental conclusions, have you ever thought that an entangled particle may be in some sort of state we haven't accounted for? And that there may be no locality or non locality as such it's just an account of unobserved variables.? Probably.

What else do you think Bell's theorem does, than exactly inquire that possibility, and find out that it doesn't exist ?

At the end of the day though provided you acknowledge it's speculation and don't take it seriously in the same way you would a theory, I don't have any problem with it.

I take it exactly as seriously as the theory from which it follows: namely quantum theory, in its unitary form. That's why I don't take it 100% seriously, and leave open the possibility that quantum theory is in fact wrong or limited in its application. THIS is the kind of "incompleteness" I refer to: the possiblity that we discover one day an empirical falsification of unitary quantum theory. That day will probably also be the end of MWI.

I personally jost don't think the answer is that bizzare, but of course that is just my own flavour of speculation.

Right.

This is in fact the single and only objection to quantum theory and its natural consequence, which is MWI: 'I really don't think the answer is that bizarre'.
Which is rather strange, because this "bizarreness" is a basic postulate of quantum theory!

I'll admit that I ALSO find this very bizarre. That's why I leave open the possibility that this postulate (the superposition principle) may one day turn out to be wrong. But unfortunately, this day hasn't come yet, and may never come, and as such, I have no choice but to accept that, to the best of our knowledge today, this bizarreness is real.

Now, many people also think that "one day one will find a reasonable explanation for all that" ; but that's nothing else but introducing our "vague, undetermined and ununderstood hopeful postulate that will solve it all". Until this is EXPLICITLY DONE (and many tried, only Bohm succeeded somehow), I don't think it is a fair application of Occam's razor to accept this unspecified postulate, and to reject the systematic application of known postulates, ONLY to satisfy the subjective desire for less bizarreness.

 

[Schrodinger's Dog]

I'm not claiming any "incomplete understanding", on the contrary. I'm just saying that, with the postulates we have, we can build an entirely coherent picture which doesn't lead to contradictory situations as some claim. That's rather the opposite than "claiming incomplete understanding", no ?
However, I place the caveat, that our understanding *in general* of nature will always be incomplete, and as such, that the picture can change, when we learn more. It can also be correct if no such change is required. THAT is the point: it CAN also be correct. Many other views cannot claim that. They NEED vague, new, ununderstood postulates which must somehow fix the obvious problems. THAT's where I apply Occam's razor.

I don't see why one should introduce the idea of vague, unspecified, ununderstood postulates which are needed to solve problems which don't even appear in the first place when you don't modify anything.



What else do you think Bell's theorem does, than exactly inquire that possibility, and find out that it doesn't exist ?



I take it exactly as seriously as the theory from which it follows: namely quantum theory, in its unitary form. That's why I don't take it 100% seriously, and leave open the possibility that quantum theory is in fact wrong or limited in its application. THIS is the kind of "incompleteness" I refer to: the possiblity that we discover one day an empirical falsification of unitary quantum theory. That day will probably also be the end of MWI.



Right.

This is in fact the single and only objection to quantum theory and its natural consequence, which is MWI: 'I really don't think the answer is that bizarre'.
Which is rather strange, because this "bizarreness" is a basic postulate of quantum theory!

I'll admit that I ALSO find this very bizarre. That's why I leave open the possibility that this postulate (the superposition principle) may one day turn out to be wrong. But unfortunately, this day hasn't come yet, and may never come, and as such, I have no choice but to accept that, to the best of our knowledge today, this bizarreness is real.

Now, many people also think that "one day one will find a reasonable explanation for all that" ; but that's nothing else but introducing our "vague, undetermined and ununderstood hopeful postulate that will solve it all". Until this is EXPLICITLY DONE (and many tried, only Bohm succeeded somehow), I don't think it is a fair application of Occam's razor to accept this unspecified postulate, and to reject the systematic application of known postulates, ONLY to satisfy the subjective desire for less bizarreness.

You misunderstand that's precisely what I'm saying there is nothing funny going on, we're just making some pretty wacky assumptions about something we cannot properly see, underlying it is something better. That's exactly what I mean, and why I think that ultimately MWI will be useless. Sorry if I gave any other impression, probably the way I wrote it, as I said though I'm for modifying the current theory or for rehashing it, glancing at RQM it seems this is what other scientists are doing too, although I can't read all of it as I am supposed to be working and my tea break isn't an hour long, I will show it to one of my colleagues as well, probably understand it better than I.

 

[Schrodinger's Dog]

That's pretty funny I had a spare quarter of an hour so I read the Relational EPR, I said precisely this 6 months ago to a colleague, that the two particles had a relationship that was "non local", and that this meant that something is missing he said he agreed at the time. I think they may be onto something here, all that can be determined is that the EPR experiment is working on an incomplete set of determinate characteristics, in other words watch this space?

I've always been a great believer in take no1's word for it.

 

[Anonym]

Tomsk:” Here's a paper I read on RQM a while ago, I really like it, and I think trying to derive the QM formalism from a bunch of postulates sounds like a very good idea, as we would probably get a better understanding of QM.

http://fr.arxiv.org/PS_cache/quant-p...09/9609002.pdf

It's not too complicated or long, I could understand most of it and I'm only a 2nd year undergrad.”

It seems that you are very talented 2nd year undergrad. Notice that even M.Bulgakov don’t go that far (see below).

Vanesch:” Do a search here on Rovelli or relational quantum mechanics: there have been long discussions about that. I'm pretty convinced that RQM is some other wording of an MWI, but then some people don't agree with that.”

Unfortunately, I was not able to penetrate quant-ph/9609002 abstract. I always enjoy your explanations, especially since they present linear superpositions of explanations and “explanations” without collapse inspite that you are the macroscopic object. I have several questions connected with quant-ph/9609002 (“some other wording of an MWI”):

1.what does it mean “observer-independent time”? Is it related to the fact that the paper written at April 11,2006 but dated at arXiv 24Feb 1997?

2. The writer in section E.Information (p.9) wrote “Correlation is “information” in the sense of information theory [Shannon 1949, “The mathematical theory of communication]. Is it also so in MWI that people know only to write but do not know to read?

3. You use to talk about the postulates of QM. If QM is part of physics, then they should be also the postulates of physics, otherwise QM is outside of physics. If QM is physical theory, then how your potulates are applied to A.Einstein GR for example?

Sorry that I use the classical logic, but I consider myself the macroscopic object.(Now I go to enjoy the presentation of our president that will try to explain to us why he allowed to himself actions similar to the other president).

Dany.

 

[vanesch]

You misunderstand that's precisely what I'm saying there is nothing funny going on, we're just making some pretty wacky assumptions about something we cannot properly see, underlying it is something better. That's exactly what I mean, and why I think that ultimately MWI will be useless.

You cannot know. Maybe, maybe not. MWI will be useless when unitary quantum theory will not be true. Nobody did come up with something that replaces it yet, however. So there's no way to know whether it will stay or not. As long as we don't KNOW that it needs a replacement, I don't ASSUME that it will, because in any case I wouldn't know with what.

However, you make an assumption which is far from justified. What tells you that whatever will replace quantum theory, will not be far wackier than what we have right now ? What makes you think that *a more sensible* (read, something more closely to our intuitive desires) theory will come along, and not a far more strange view, compared to which the strangeness of MWI pales completely ?

Sorry if I gave any other impression, probably the way I wrote it, as I said though I'm for modifying the current theory or for rehashing it, glancing at RQM it seems this is what other scientists are doing too

RQM claims that there are SEVERAL DISTINCT OBJECTIVE REALITIES. Namely for each community of observers which agree onto something, what they agree upon is (their) objective reality.

So Bob (and collaborators) agree upon their objective worldview that they have a result, and that Alice DOESN'T HAVE A RESULT. While at the same time, Alice (and collaborators) agree upon their objective worldview that they have a result, while Bob didn't have any. (not that they are ignorant about which result, they claim that Bob didn't have a result)

Finally, when they come together, they agree upon their objective worldview that both finally had results all along.

Now, in my opinion, this is just a semantic exercise on MWI. Replace "didn't have a result" with "is in a superposition", and replace "their objective reality" with "their branch" and both are in agreement.

What I object to in the semantics of RQM, is the the idea of an observer-dependent objective reality.

The word "objective" is misused in this semantics. However, I entirely agree with the formal aspects of RQM.

 

[vanesch]

3. You use to talk about the postulates of QM. If QM is part of physics, then they should be also the postulates of physics, otherwise QM is outside of physics. If QM is physical theory, then how your potulates are applied to A.Einstein GR for example?

Well, there is no satisfactory formulation of gravitational interaction in a unitary quantum formalism yet, as far as I know, so all this MWI business only applies to a world in which there is no gravity of course.
There is no need to consider "an MWI view on quantum theory" in gravitational settings, because there is no quantum theory of gravitation. So there is no need to have a view on a non-existing theory.

I could ask the same in the opposite way: if one considers the "block universe" ontology which gives a natural view on GR, how do these postulates apply to atomic physics ? The answer would be the same: given that there is no satisfactory formulation of atomic physics in a geometrical 4-dim manifold formalism yet, there's no need to have a "block universe" view on it to help you understand it.

Things go both ways. In the case that one finds one day a geometrical formulation of atomic physics (some claim they do, but they only have some dreams), then the 4-dim geometrical view will overtake atomic physics. In the case that one finds one day a unitary formulation of gravity, then the MWI view will overtake the 4-dim geometrical view. And if something totally new is needed, then a totally new view will have to be developed. My bet would be, in this last case, that we will crank up the weirdness even a few orders of magnitude, at least if the history of physics has been any guide. Things never became "more intuitive". They always became "more weird".

 

[Schrodinger's Dog]

You cannot know. Maybe, maybe not. MWI will be useless when unitary quantum theory will not be true. Nobody did come up with something that replaces it yet, however. So there's no way to know whether it will stay or not. As long as we don't KNOW that it needs a replacement, I don't ASSUME that it will, because in any case I wouldn't know with what.

However, you make an assumption which is far from justified. What tells you that whatever will replace quantum theory, will not be far wackier than what we have right now ? What makes you think that *a more sensible* (read, something more closely to our intuitive desires) theory will come along, and not a far more strange view, compared to which the strangeness of MWI pales completely ?

Well of course but aren't you as guilty of making the same assumption, that because what we see now is so wierd, the underlying principle or intepritation must be even wierder, and that of course you base on the fundementals we know now as being correct. Since we're both speculating though, it's an excercise in what we believe not what we know, so there's no problem here.

RQM claims that there are SEVERAL DISTINCT OBJECTIVE REALITIES. Namely for each community of observers which agree onto something, what they agree upon is (their) objective reality.

So Bob (and collaborators) agree upon their objective worldview that they have a result, and that Alice DOESN'T HAVE A RESULT. While at the same time, Alice (and collaborators) agree upon their objective worldview that they have a result, while Bob didn't have any. (not that they are ignorant about which result, they claim that Bob didn't have a result)

Finally, when they come together, they agree upon their objective worldview that both finally had results all along.

Now, in my opinion, this is just a semantic exercise on MWI. Replace "didn't have a result" with "is in a superposition", and replace "their objective reality" with "their branch" and both are in agreement.

What I object to in the semantics of RQM, is the the idea of an observer-dependent objective reality.

The word "objective" is misused in this semantics. However, I entirely agree with the formal aspects of RQM.

I like the aspect of the viewer or indeed "object" being able to see a different possibility, and the EPR interpritation sits better with me, that we just don't know exactly what is going on. It's a nice theory that doesn't destroy the others, but merely asks the questions about their tennants from it's perspective.

Well, there is no satisfactory formulation of gravitational interaction in a unitary quantum formalism yet, as far as I know, so all this MWI business only applies to a world in which there is no gravity of course.
There is no need to consider "an MWI view on quantum theory" in gravitational settings, because there is no quantum theory of gravitation. So there is no need to have a view on a non-existing theory.

I could ask the same in the opposite way: if one considers the "block universe" ontology which gives a natural view on GR, how do these postulates apply to atomic physics ? The answer would be the same: given that there is no satisfactory formulation of atomic physics in a geometrical 4-dim manifold formalism yet, there's no need to have a "block universe" view on it to help you understand it.

Things go both ways. In the case that one finds one day a geometrical formulation of atomic physics (some claim they do, but they only have some dreams), then the 4-dim geometrical view will overtake atomic physics. In the case that one finds one day a unitary formulation of gravity, then the MWI view will overtake the 4-dim geometrical view. And if something totally new is needed, then a totally new view will have to be developed. My bet would be, in this last case, that we will crank up the weirdness even a few orders of magnitude, at least if the history of physics has been any guide. Things never became "more intuitive". They always became "more weird".

So it doesn't answer the unanswerable questions about unification of QM with GR and SR? Not very usefull really then is it? Except from a speculative basis.

And again your assuming that wierdness is an aspect of QM, not a result of misinterpritation.

 

[masudr]

Schrodinger's Dog:

it's simpler than that. All vanesch is saying is that if you assume the unitary evolution from quantum mechanics to be true (along with the other postulates), then logically MWI must follow, and that he finds it a compelling description.

Now, of course we can debate whether or not the unitary evolution is assumption is valid or not. Experimental evidence so far has not been able to dispute it. If it does at some point, I'm fairly sure vanesch will not bother with MWI anymore. All he is saying is that if the assumption is valid, then he's most comfortable with MWI, and he's pointing out his reasoning.

Either:

(i) you disagree with the unitary evolution postulate as describing the dynamics of the quantum state (along with all the other postulates required to make sense of and even define what a quantum state is), in which case you guys are discussing different things; or

(ii) you are saying that you prefer some other non-MWI interpretation over MWI, in which case some of your points are invalid (e.g. "that because what we see now is so wierd, the underlying principle or intepritation must be even wierder"), since here you are questioning the validity of the QM postulates.

 

[Anonym]

Well, there is no satisfactory formulation of gravitational interaction in a unitary quantum formalism yet, as far as I know, so all this MWI business only applies to a world in which there is no gravity of course.There is no need to consider "an MWI view on quantum theory" in gravitational settings, because there is no quantum theory of gravitation. So there is no need to have a view on a non-existing theory.

Dear Vanesch,

according to rules of PF, you are not required to answer, however, you know that I enjoy to discuss with you different but related problems. But I require integrity.I ask a simple question:you use to talk about the postulates of QM. If QM is part of physics, then they should be also the postulates of physics, otherwise QM is outside of physics. If QM is physical theory, then how your potulates are applied to A.Einstein GR for example?

A.Einstein GR unambiguously mean firmly established and experimentally confirmed classical theory of gravitation. If your answer “so all this MWI business only applies to a world in which there is no gravity of course” (classical gravitation included) then you are talking about business that have nothing to do with physics. If your “postulates” do not apply to classical GR there are two options: 1) classical GR is not a physics (wrong); 2) your “postulates” are not a physical postulates. Neither QG nor Statistical Physics knowledge required to answer my question. It is just demonstration why the collapse of the wave packet is necessary.
As we already discussed, the delta x*delta p >0 is only the particular example of the UR’s. There are many of these, everyone express the essential feature of Quantum World. The collapse is the universally valid phenomenon when the transition to the Classical World take place. The projection operators, connected with the knowledge, process of the acquisition of knowledge and the communication of knowledge included.

Dany.

 

[Schrodinger's Dog]

Schrodinger's Dog:

it's simpler than that. All vanesch is saying is that if you assume the unitary evolution from quantum mechanics to be true (along with the other postulates), then logically MWI must follow, and that he finds it a compelling description.

Of course.

Now, of course we can debate whether or not the unitary evolution is assumption is valid or not. Experimental evidence so far has not been able to dispute it. If it does at some point, I'm fairly sure vanesch will not bother with MWI anymore. All he is saying is that if the assumption is valid, then he's most comfortable with MWI, and he's pointing out his reasoning.

Either:

(i) you disagree with the unitary evolution postulate as describing the dynamics of the quantum state (along with all the other postulates required to make sense of and even define what a quantum state is), in which case you guys are discussing different things; or

No just the conclusions made, I find some difficulty with, they seem to be assuming all sorts of natural progressions that I don't agree with, and I don't personally find the EPR as hugely convincing for the same reasons, although let me make it clear I don't disagree with it, just the assumptions made. Too much assumption.

(ii) you are saying that you prefer some other non-MWI interpretation over MWI, in which case some of your points are invalid (e.g. "that because what we see now is so wierd, the underlying principle or intepritation must be even wierder"), since here you are questioning the validity of the QM postulates.

Of course, but based on the reasons I give. I find it a little dead endish. I think it's interesting to state why you think certain interpritations are better no? It's an amiable chat. I think we'd do better to refine the original theory before we make grandiose claims, that is all. But as stated I have no problem with such claims. My disagreement with string theory was for simillar although not the same reasons.

EDIT: I'm not meaning to claim he's wrong, only that I prefer other theories, and I hope there's no offense taken, I've learned a great deal about MWI, I'm hoping Vanesch got something out of explaining his reasoning, I now see that my initial statement was a bit rash. And got exposed to QRM which I like because of it's questioning of the basics, not a bad deal. Of course my knowledge is not in the same league as Vanesches, but it's not a bad thing to prod someone for information, particularly someone who knows as much as Vanesch, and who is well respected here.

 

[vanesch]

Schrodinger's Dog:

it's simpler than that. All vanesch is saying is that if you assume the unitary evolution from quantum mechanics to be true (along with the other postulates), then logically MWI must follow, and that he finds it a compelling description.

Now, of course we can debate whether or not the unitary evolution is assumption is valid or not. Experimental evidence so far has not been able to dispute it. If it does at some point, I'm fairly sure vanesch will not bother with MWI anymore. All he is saying is that if the assumption is valid, then he's most comfortable with MWI, and he's pointing out his reasoning.

Either:

(i) you disagree with the unitary evolution postulate as describing the dynamics of the quantum state (along with all the other postulates required to make sense of and even define what a quantum state is), in which case you guys are discussing different things; or

(ii) you are saying that you prefer some other non-MWI interpretation over MWI, in which case some of your points are invalid (e.g. "that because what we see now is so wierd, the underlying principle or intepritation must be even wierder"), since here you are questioning the validity of the QM postulates.

Thanks. That's indeed EXACTLY what I wanted to say. But I didn't, you did

 

[vanesch]

I ask a simple question:you use to talk about the postulates of QM. If QM is part of physics, then they should be also the postulates of physics, otherwise QM is outside of physics. If QM is physical theory, then how your potulates are applied to A.Einstein GR for example?

I don't know if you noticed it, but we have, as of today, only an incomplete description of physics. So we don't HAVE the postulates of all of physics. We don't even know if they exist, but let us assume they do for a moment. That means that we assume that there exists (in a Platonic sense) a set of axioms, postulates if you wish, which are the ultimate and fundamental laws of nature. One thing is sure: we don't have that complete set yet. We might even have none of it (probably). So that already invalidates your objection, because we are NOT talking about this hypothetical set, we are well aware that we don't have that set (and it might even be that it doesn't exist, and even if we have it, we will never be able to find out). So, "the postulates of physics" (if understood in that sense), is a thing of which we know at least one thing: that is that we don't have it. (and I claim that any fool who thinks he has them is deluding himself) Hence I'm surely not talking about that.

However, we have theoretical descriptions of *parts* of physics, and they are based upon some set of postulates. The union of them, however, doesn't make any sense (which is how we know that we don't have the "ultimate set"). Certain subsets of postulates apply, and set up theories which can explain certain aspects of physics. However, it might very well be that CERTAIN postulates we have today, ARE part of that "ultimate set of physics". Only, we don't know which ones, if any.

So, how far can we go, today ? We seem to have 3 kinds of postulates:
1) "special" relativity (spacetime manifold as geometrical structure)
2) quantum theory (the superposition principle + unitarity)
3) gravity (The Einstein equation)

I put "special" relativity between quotes, because I don't mean the usual kind of SR, with Minkowski space, but an extension of it, which is a pseudo Riemannian manifold, but who is GIVEN.

It seems that we can combine 1 and 2, with some extra assumptions and we get out QFT (which does have mathematical problems, but this is probably more related to the "point particle" idea than to a more fundamental issue ; proof is that elementary versions of string theory get around it). However, we have difficulties including 3).

It also seems that we can combine 1 and 3, and out comes GR. That is, making the pseudo-riemanian manifold DYNAMICAL. However, we then get serious problems with 2. We don't know how to handle "superpositions of geometries and their unitary evolution" (yet?).

Now, all of our observational data are related to situations where OR 3 doesn't play a DYNAMICAL role, or 2 doesn't play a dynamical role.

Mind you, in 1+2 we CAN have "gravity" but only in a kinematical way: that is, we can work in a curved (but non-dynamical) spacetime (1), and we can even do quantum mechanics in such a case (like neutron interferrometry, or the work of my colleague about bound states of neutrons in a gravitational potential). Most of the time we don't even need that, and can work in flat minkowski space to do 2. All of elementary particle, solid state etc... physics happens in this case.

Each time we are looking at *dynamical* effects of gravity, we don't need to consider 2. It is extremely difficult to consider situations in which we both need essentially 2 and 3 together.

A.Einstein GR unambiguously mean firmly established and experimentally confirmed classical theory of gravitation.

ONLY in those cases where it is clear that the superposition principle wouldn't have any influence !

It has NOT been tested in cases where the superposition principle might matter. I'm thinking of attempts, such as the proposed Felix experiment by Penrose, where one tries to establish the gravitational influence of a superposition of localized masses.

If your answer “so all this MWI business only applies to a world in which there is no gravity of course” (classical gravitation included) then you are talking about business that have nothing to do with physics. If your “postulates” do not apply to classical GR there are two options: 1) classical GR is not a physics (wrong); 2) your “postulates” are not a physical postulates.

For sure classical GR is "wrong" as it doesn't incorporate anything like the superposition principle, which has a far better empirical history than GR itself. So in any case *something* will have to be changed to it, even to describe the helium atom. Classical GR, with just tensor fields defined over it, cannot give rise to all predictions of quantum theory (of which many, many have been tested empirically), and in casu Bell's theorem (unless you adhere to superdeterminism or you still think that there are serious empirical loopholes). I start from the idea that the quantum-mechanical predictions are correct, unless they are explicitly demonstrated to be erroneous. As I said, I'm quite conservative.

The collapse is the universally valid phenomenon when the transition to the Classical World take place. The projection operators, connected with the knowledge, process of the acquisition of knowledge and the communication of knowledge included.

You understand that this is a "deus ex machina" which poses a problem if there is no clear definition of what exactly IS the "classical world" (in other words, how do we define what is a system to which a quantum description doesn't apply ?), and this transition ALSO introduces the problem of breaking of Lorentz-invariance in the quantum-mechanical description.

It is exactly THESE potential difficulties which are tackled with MWI: that the full quantum-mechanical treatment gives rise, each time we could consider a "transition to a classical world", to the emergence of a state which can be put in a 1-1 relationship with AN ENSEMBLE of classical, non-interacting worlds. As such, this "transition" simply emerges from the underlying unitary dynamics, instead of having to be introduced "by hand". We have then a precise physical description of what exactly happens "during the transition", and moreover, we can respect the Lorentz invariance.
But of course, this view doesn't solve the FORMAL problems of uniting 1,2 and 3. Only, at least it:
1) allows for a coherent view between 1 and 2
2) doesn't need a dichotomy in nature, about an ill-defined separation between "classical world" and "quantum world", when sometimes the "quantum world" applies to systems with 10^20 degrees of freedom (superconduction), and sometimes it applies to systems which extend over several kilometers (optical Bell tests).

 

[Schrodinger's Dog]

Thanks. That's indeed EXACTLY what I wanted to say. But I didn't, you did

Then say it If I'm being direct with you, I can hardly complain if your direct in return.

I don't see why there is any issue with what I said though? I simply don't agree with you, and I don't think MWI is as viable as some of the other theories, that's it. Maybe I'm missing some fundamental understanding that makes all worlds exist or maybe I'm just "string theory" once bitten twice shy, ie assume nothing. This is all I meant to convey and I certainly hope there's no offence. In essence it seems to me string theory and MWI share the same faults, assumption based on assumption. Is it true, let's just say I seriously personally doubt it, but that is most sincerely IMHO.

And from those I talk with on a regular basis about such things I get the impression many people are leary of this "new" theory.

An esteemed colleague of mine, finds it hard to keep a straight face reading Vanesches replies, he has a PhD in gamma ray astronomy, so I'm not exactly unusual, I showed him what you were saying about 5 mins ago, and he just could not believe the philosophy here. It's very contraversial, hopefully it'll remain so; it certainly keeps the field interesting.

I'd say though if you don't want to discuss the inconsistencies of your philosophy then don't. I can live with that. The only problem I have I think though to state my view is that Vanesch said that he takes MWI almost as seriously as CI, this to me is just crazy but each to his own. Everyone is welcome to his own opinion.

Your theory is crazy but not crazy enough to be true

Niels Bohr.

Whatever floats your boat

 

[vanesch]

The only problem I have I think though to state my view is that Vanesch said that he takes MWI almost as seriously as CI, this to me is just crazy but each to his own.

Uh, no ! I don't take CI seriously at all !

I can live with 3 views on QM:
- Bohmian mechanics (too bad we have to drop relativity)
- Shut up and calculate (too bad we don't know what we are doing)
- MWI (too bad many people can't get over their subjective intuition)

CI is full of inconsistencies, jumping back and fro of different interpretations for the same concept, as a function of the objections made to it. The closest to CI is "shut up and calculate", but this is not really CI.

CI jumps essentially back and fro about what exactly is the meaning of the quantum state, and changes, during the argumentation, regularly between two incompatible views: 1) the 'quantum state' of a system is just a record of the information an observer has of a system / 2) it is a physical state of the system.

Indeed, in the former 1), destructive quantum interference wouldn't really be possible. It is not because you KNOW or don't KNOW something about a system, that some events can or cannot happen. Or better, it is not because you DO NOT KNOW something about a system, that some events CANNOT happen. (the other way around is possible). So when talking about destructive interference phenomena, the CI proponent maintains that the state vector describes a genuine *physical state*.

However, when confronted with the measurement problem, and collapse, which would, if the quantum state were indeed a physical state, violate relativity in its inner workings, then the CI proponent tells you that the quantum state is just a "summary of what we know about the system" and that we mustn't be surprised that when we learn something about the system, that this changes our "state of knowledge of the system".

The other inconsistency in CI is the quantum/classical transition, and the dichotomy between what constitutes an "observer" and what constitutes "a system". An observer observing another observer illustrates the problem, and was already pointed out by Wigner. Finally, given that "classical" systems are just conglomerates of quantum systems, and that quantum effects have been demonstrated as well for systems consisting of many many subsystems, as for quantum systems which have a large size, means that it is NOT the physical extension in space or time of the system, nor the number of constituents, which can determine when the quantum description is not correct anymore. The only exception that could be made, is by going to vitalist primitive theories, where "living matter" is ruled by different rules than "dead matter" (and organic chemistry is different from anorganic chemistry). This is exactly the kind of statement that the CI makes.
In other words, the question that CI cannot answer, is: "what is the physical process going on during an observation ?", because there is, according to the CI doctrine, no physical language in which this process can be described. The classical electron in the detector suddenly gets ejected, when the quantum electron of the system "is measured" at a certain position. One electron is a classical one, because it is part of a "position measurement apparatus", while the other electron is a quantum electron, because it is "part of the system".

The shut-up-and-calculate approach (which, I repeat, is NOT the CI view!) is more agnostic: it just posits that we find, using the quantum mechanical formalism, correlations between "experiment preparations" and "observations" and remains entirely agnostic about what might happen in between - even whether something actually happens at all.

 

[Schrodinger's Dog]

Uh, no ! I don't take CI seriously at all !

I can live with 3 views on QM:
- Bohmian mechanics (too bad we have to drop relativity)
- Shut up and calculate (too bad we don't know what we are doing)
- MWI (too bad many people can't get over their subjective intuition)

CI is full of inconsistencies, jumping back and fro of different interpretations for the same concept, as a function of the objections made to it. The closest to CI is "shut up and calculate", but this is not really CI.

CI jumps essentially back and fro about what exactly is the meaning of the quantum state, and changes, during the argumentation, regularly between two incompatible views: 1) the 'quantum state' of a system is just a record of the information an observer has of a system / 2) it is a physical state of the system.

Indeed, in the former 1), destructive quantum interference wouldn't really be possible. It is not because you KNOW or don't KNOW something about a system, that some events can or cannot happen. Or better, it is not because you DO NOT KNOW something about a system, that some events CANNOT happen. (the other way around is possible). So when talking about destructive interference phenomena, the CI proponent maintains that the state vector describes a genuine *physical state*.

However, when confronted with the measurement problem, and collapse, which would, if the quantum state were indeed a physical state, violate relativity in its inner workings, then the CI proponent tells you that the quantum state is just a "summary of what we know about the system" and that we mustn't be surprised that when we learn something about the system, that this changes our "state of knowledge of the system".

The other inconsistency in CI is the quantum/classical transition, and the dichotomy between what constitutes an "observer" and what constitutes "a system". An observer observing another observer illustrates the problem, and was already pointed out by Wigner. Finally, given that "classical" systems are just conglomerates of quantum systems, and that quantum effects have been demonstrated as well for systems consisting of many many subsystems, as for quantum systems which have a large size, means that it is NOT the physical extension in space or time of the system, nor the number of constituents, which can determine when the quantum description is not correct anymore. The only exception that could be made, is by going to vitalist primitive theories, where "living matter" is ruled by different rules than "dead matter" (and organic chemistry is different from anorganic chemistry). This is exactly the kind of statement that the CI makes.
In other words, the question that CI cannot answer, is: "what is the physical process going on during an observation ?", because there is, according to the CI doctrine, no physical language in which this process can be described. The classical electron in the detector suddenly gets ejected, when the quantum electron of the system "is measured" at a certain position. One electron is a classical one, because it is part of a "position measurement apparatus", while the other electron is a quantum electron, because it is "part of the system".

The shut-up-and-calculate approach (which, I repeat, is NOT the CI view!) is more agnostic: it just posits that we find, using the quantum mechanical formalism, correlations between "experiment preparations" and "observations" and remains entirely agnostic about what might happen in between - even whether something actually happens at all.

no one would argue that their aren't flaws in CI, but is MWI not guilty of making flawed interpritation on flawed interpritation itself?

Anyway I find their are too many logical fallacies in the argument for MWI, I can think of six or seven off the top of my head but the worst of which I think is:-

http://en.wikipedia.org/wiki/Proof_by_example and a little bit of

with a soupcon of http://en.wikipedia.org/wiki/Validity

and a small measure of
http://en.wikipedia.org/wiki/Spurious_relationship

To name a few that spring to mind. I know Vanesch isn't claiming his ideas are true, but I would prefer a theory to be logically consistent at least, as it is philosophy for the time being, I think this is not too much to ask no? :tongue2:

I share your worries about CI by the way, definitely something missing.

EDIT: I missed this one, http://en.wikipedia.org/wiki/Modus_ponens

 

[setAI]

no one would argue that their aren't flaws in CI, but is MWI not guilty of making flawed interpritation on flawed interpritation itself?

no- because the MWI strictly speaking- is not an interpretation- but rather it accepts unitary QM as-it-is- which is the point- and the basis for much of it's appeal- there are no logical fallacies with the MWI- only aesthetic ones