Interpretations of Quantum Mechanics

[alexepascual]

Which interpretation of QM do you like?

 

[fleem]

Non-local hidden variables, but not Bohm/pilot waves. Bohm & de Broglie assumed the rules we've devised simply to describe the average, large-scale behavior of many countless little machines (particle-particle interactions), namely classical mechanics like space, time, continuums, etc., must also be the founding axioms of understanding the behavior of a single such machine. That assumption is not logical.

 

[Count Iblis]

The MWI, because it is a minimal interpretation. Tegmark in his most recent article has argued that the "many worlds" are actually a consequence of symmetry. Thgis is implemted by unitary time evolution, but even if you get rid of unitary time evolution, you don't necessarily get rid of the many worlds.


E.g., we have some system in some symmetrical but unstable state, like a pencil balanced perfectly on its tip at zero temperature. Then QM predicts that the pencil will fall to the ground. According to CI, the rotational symmetery around the z-axis must somehow be broken. But that's impossible if the laws of physics are exactly symmetrical and the initial state respects this symmetry, no matter how you modify the unitary time evolution law.

 

[humanino]

Rovelli's relational QM by far.

 

[humanino]

But that's impossible if the laws of physics are exactly symmetrical and the initial state respects this symmetry, no matter how you modify the unitary time evolution law.

That's called "spontaneous symmetry breaking" and I do not see why this should be impossible. It is used in the standard model of particle physics for instance.

 

[Count Iblis]

That's called "spontaneous symmetry breaking" and I do not see why this should be impossible. It is used in the standard model of particle physics for instance.

What is impossible is for any proposed physical mechanism for the "collapse" to respect the symmetry. In the CI this whole issue is sidestepped and in the MWI you have a global superposition which is symmetric. Of course, this does not stop anyone from doing physics in the usual way...

 

[RUTA]

I prefer Relational Blockworld, but I'm very biased

 

[Adrian59]

The MWI, because it is a minimal interpretation.

I have one problem with MWI, though I accept I may be looking at it too literally. The original MWI was devised to explain the double slit experiment conundrum. So the one photon goes through each slit but in different worlds. Not to upset causality or the conservation of mass or energy, each world only sees one photon – no problem. However now each photon is in a parallel world (universe), why does interference happen?

 

[Fra]

I do not confess cleanly to any of the major interpretations. There are fragments of reasoning in Rovelli's RQM paper that I think is outstanding, but others are not.

I guess I have my own intrinsic relational subjective information interpretation, without multiverses and most of all without the bird view realism that rovelli has.

Take RQM and add more undecidability and replace his realist symmetries with emergent frog-view symmetries and I am close.

/Fredrik

 

[humanino]

I just collapsed to preferring Fra's interpretation. Can I change my relational interpretation of my own self ?

 

[Fredrik]

QM is just an algorithm that tells us how to compute probabilities of possible results of experiments. It doesn't need an interpretation, and I doubt that it's even possible to find one that's both well-defined and logically consistent. I think the attempts to find a correct interpretation are fundamentally misguided. They are all trying to tell us what QM really describes, but a theory doesn't have to describe anything. All it has to do in order to be falsifiable is to make predictions about probailities of possible results of experiments.

 

[Fra]

QM is just an algorithm that tells us how to compute probabilities of possible results of experiments. It doesn't need an interpretation, and I doubt that it's even possible to find one that's both well-defined and logically consistent. I think the attempts to find a correct interpretation are fundamentally misguided. They are all trying to tell us what QM really describes, but a theory doesn't have to describe anything. All it has to do in order to be falsifiable is to make predictions about probailities of possible results of experiments.

If we are talking about interpretations only that have no ambition to improve or solve new problems that I can almost agree. But my "interpretation" actually implies that the formalism of quantum mechanics is only a special case and not the formalism we need for a intrinsic relational measurement theory. I do not only view the standar model as an effective theory, it's worse that that, I view the standard framework or QM and QFT as en effective framework! And my personal view is that the problems implicit in the open question in physics can not be solved or even properly posed within the current framework of proper QM etc.

And if you want to improve something, just knowing that it apparently works isn't enough I think. You need to ask different question to drive a car than to build a car, or to improve an existing car.

/Fredrik

 

[Fra]

But that's impossible if the laws of physics are exactly symmetrical and the initial state respects this symmetry, no matter how you modify the unitary time evolution law.

If you see no reason to treat physical law different than any other measurement, then inference of physical law from interaction experiences, are subject to the same physical constraints as is any physical measurement/interaction.

In my view, there is no such thing as an exact certain inference of perfect symmetry. Therefore the symmetry arguments commonly used, are not really strict. They represent special cases.

I share Lee Smolin critique of the notion of timeless law, and by consequence also the notion of timeless universal symmetry. This doesnt' mean symmetry arguments are useless, it just means that we might need a new undertand of what a symmetry is, and it's general origin. A system can act as if the symmetry is exact, but this doesn't mean the symmetry will stay exact forever, and neither is there a contradiction.

I think a lot of contradiction comes because an expectation that the universe as a whole is more decidable and predictable than it really is. Probabilistic determinism isn't enough. The notion of probability is even a key suspect as the physical basis of statistics is one of the things that isn't properly abstracted in current formalisms.

Rovelli's also avoids the "physical meaning of probability" s in his RQM papper. If he didn't, a good reasoning could I think have been even better.

/Fredrik

 

[ajw1]

... but a theory doesn't have to describe anything. All it has to do in order to be falsifiable is to make predictions about probailities of possible results of experiments.

I have seen these kinds of arguments before, but for me this is a really strange attitude towards physics:
- you can make a fitting simulation model for any problem without knowing any law of physics.
- it would mean that physicist only needs to start thinking when an experiment contradicts their current models.

Furthermore it seems this view on physics is mostly used in relation to QM and its interpretaions.

 

[sokrates]

QM is just an algorithm that tells us how to compute probabilities of possible results of experiments. It doesn't need an interpretation, and I doubt that it's even possible to find one that's both well-defined and logically consistent. I think the attempts to find a correct interpretation are fundamentally misguided. They are all trying to tell us what QM really describes, but a theory doesn't have to describe anything. All it has to do in order to be falsifiable is to make predictions about probailities of possible results of experiments.

Don't youthink this is a little too humble? How do you reach the conclusion that it's "just an algorithm"?

You are confusing the scientific method with intrinsic facts about nature. These are two independent things. Quantum Physics is at a level low enough to answer those very fundamental questions. It is definitely not "just an algorithm". We don't even know how it works yet...

 

[Count Iblis]

Yes, I think it is fair to say that if you think QM is "just an algorithm" you must also be similarly open minded about the very existence of particles like electrons, quarks etc. We can't directly detect them. All that we can directly observe are the states of macroscopic measurement devices.

So, if I play the Devil's advocate, I could claim that Nature is described by a fundamental theory that one can turn into an effective theory yielding statistical predictions using a path integral formalism involving integrating over fictitious field configuarations.

The formalism is then the same as the Standard Model, except for the fact that only the sources and sinks of particles are real, not the particles themselves. So, when you compute amplitudes for process using Feynman diagrams, the external lines always start end end at detectors/sources. The amplitude is associated to the state of the detectors, not to particle states.

 

[fleem]

These debates are always really debates about reductionism, Occam's razor, that sort of thing, and why Occam's razor is true. Epicycles worked pretty well and there were those that said, "Therefore we understand the movement of planets pretty well". But embracing epicycles certainly slowed progress. Here's why Occam's razor is true: The simpler the explanation, the more things it will describe. Thus we replaced epicycles with gravity and were able to predict both planetary motion and apples falling from trees with one theory. Right now QM, QFT, QED, all seem a little contrived, especially considering they really don't predict individual experiments (only statistically). So someone using the phrase "interpretation of QM" typically means, "Why is it only statistical?" and "Why does it look like classical laws like conservation of energy are disobeyed while a system is closed (not interacting with the rest of the universe) until it once again interacts with us?".

 

[Fredrik]

I have seen these kinds of arguments before, but for me this is a really strange attitude towards physics:
- you can make a fitting simulation model for any problem without knowing any law of physics.
- it would mean that physicist only needs to start thinking when an experiment contradicts their current models.

Those "fitting simultion models" would be pretty bad theories because of their limited predictive power. We would always be trying to find better theories, e.g. by unifying several different theories into a new one, like we did with electricity and magnetism.

Furthermore it seems this view on physics is mostly used in relation to QM and its interpretaions.

This is because before QM we could always claim that our theories at the very least are descriptions of "fictional" universes that are similar to our own. It's not clear that such a claim about QM even makes sense. I still haven't seen a well-defined and logically consistent many-worlds formulation of QM. (A "Copenhagenish" formulation of QM looks very much like it can't be interpreted as a description of the universe, since you can't include yourself in the physical system that you're trying to describe).

Don't youthink this is a little too humble? How do you reach the conclusion that it's "just an algorithm"?

I can't prove it conclusively, but arguments such as the one from section 9.3 in Ballentine's book look pretty strong to me. (I think that's the right section number, but it's from memory). Ballentine's view on these matters appears to be the same as mine, but he says it in a different way. His way is to say that a wavefunction isn't a representation of the properties of a physical system, but a representation of the properties of en ensemble of identically prepared systems.

You are confusing the scientific method with intrinsic facts about nature.

Uhm, no. What would it even mean to do that?

I don't doubt that there are "intrinsic facts about nature", but the only knowable facts in science are statements about how accurate a theory's predictions are.

These are two independent things. Quantum Physics is at a level low enough to answer those very fundamental questions. It is definitely not "just an algorithm".

Sounds like you think that's a fact. If you're sure about that, then you should be able to justify it.

Yes, I think it is fair to say that if you think QM is "just an algorithm" you must also be similarly open minded about the very existence of particles like electrons, quarks etc. We can't directly detect them. All that we can directly observe are the states of macroscopic measurement devices.

Yes. I think the right approach to these matters is to re-interpret questions like "do electrons exist?" to something like "does the theory that defines what an electron is make accurate predictions?".

The other day I answered the question "is gravity a force?" by saying that it's a force in Newton's theory and not a force in Einstein's theory. It just isn't possible to say that gravity "is a force" or "isn't a force" in some absolute, theory-independent, way. I think of electrons the same way.

So, if I play the Devil's advocate, I could claim that Nature is described by a fundamental theory that one can turn into an effective theory yielding statistical predictions using a path integral formalism involving integrating over fictitious field configuarations.

The formalism is then the same as the Standard Model, except for the fact that only the sources and sinks of particles are real, not the particles themselves. So, when you compute amplitudes for process using Feynman diagrams, the external lines always start end end at detectors/sources. The amplitude is associated to the state of the detectors, not to particle states.

I wouldn't have any problem with that, so I guess I'm the

 

[Dmitry67]

Interesting that nobody voted for Copenhagen :) Looks like it is finally declared dead :)

 

[humanino]

The problem with this kind of thread is that it systematically ends up in an endless gathering of poorly informed opinions, such as

We don't even know how it works yet...

You do not know how it works maybe, however since (1932) Von Neumann wrote a book where he clearly explained why it is unnecessary to let go mathematical rigor (as Dirac did), as a matter of fact we have a pretty robust definition of every single step in the quantum algorithm. The book is elementary and pretty much requires no prior knowledge. There is nothing left unproven, to such an extent that the couple of flawed demonstration have been corrected by other authors.

If you do not realize that there is no mathematical difficulty with QM, you may very well have misunderstood what drags people towards various interpretations. So for the (N+1)th time, where N is an arbitrarily large number, when we say "shut up and calculate" we do not mean there is nothing to understand or interpret. We mean that there is nothing convincing enough to unite the community available on the market.

when you compute amplitudes for process using Feynman diagrams, the external lines always start end end at detectors/sources. The amplitude is associated to the state of the detectors, not to particle states.

I do not know what "playing the devil advocate" has anything to do with the above statement. Any interpretation in disagreement with the above statement could not be falsified !

 

[RUTA]

Yes, I think it is fair to say that if you think QM is "just an algorithm" you must also be similarly open minded about the very existence of particles like electrons, quarks etc. We can't directly detect them. All that we can directly observe are the states of macroscopic measurement devices.

So, if I play the Devil's advocate, I could claim that Nature is described by a fundamental theory that one can turn into an effective theory yielding statistical predictions using a path integral formalism involving integrating over fictitious field configuarations.

The formalism is then the same as the Standard Model, except for the fact that only the sources and sinks of particles are real, not the particles themselves. So, when you compute amplitudes for process using Feynman diagrams, the external lines always start end end at detectors/sources. The amplitude is associated to the state of the detectors, not to particle states.

Are you calling me the Devil?

But seriously, do you have a citation for this interpretation -- proponents, opponents, discussion, etc?

 

[sokrates]

I can't prove it conclusively, but arguments such as the one from section 9.3 in Ballentine's book look pretty strong to me. (I think that's the right section number, but it's from memory). Ballentine's view on these matters appears to be the same as mine, but he says it in a different way. His way is to say that a wavefunction isn't a representation of the properties of a physical system, but a representation of the properties of en ensemble of identically prepared systems.

Ballentine is emphasizing the statistical nature of the wavefunction, he's not making general epistemological arguments about what a theory could tell us, and what it means. I don't think anyone would object to the argument that
" a wavefunction isn't a representation of the properties of a physical system, but a representation of the properties of en ensemble of identically prepared systems."

Honestly, I find this irrelevant to your previous remark on Quantum Mechanics being "just an algorithm". Ballentine isn't implying that. Or is he?

Uhm, no. What would it even mean to do that?

I don't doubt that there are "intrinsic facts about nature", but the only knowable facts in science are statements about how accurate a theory's predictions are.

The process of developing a theory and the measure of its success are well-defined by the scientific method. But overrating it, and blindly sticking to its "formulated" restrictions, I think, is unimaginative and rather boring. The facts are out there, and we know that in some examples (as Count Iblis aptly pointed out) different "formulations" could explain the same facts - and WE get to decide which "algorithm" is better than the other and so forth. So this is like choosing a basis to explain an experiment. It is irrelevant.

My take is that quantum mechanics is much more than just an algorithm and chances are that the theory is trying to lead us the underlying facts by creating hard problems (measurement, interpretation issues, and so on). Maybe when we understand it better some day, we'll understand these issues in retrospect.

Sounds like you think that's a fact. If you're sure about that, then you should be able to justify it.

I can't prove it conclusively either. But in science, you know, the burden of proof is on the person asserting the positive claim, not on the skeptics to refute it.

 

[sokrates]

You do not know how it works maybe, however since (1932) Von Neumann wrote a book where he clearly explained why it is unnecessary to let go mathematical rigor (as Dirac did), as a matter of fact we have a pretty robust definition of every single step in the quantum algorithm. There is nothing left unproven, to such an extent that the couple of flawed demonstration have been corrected by other authors.
[...] So for the (N+1)th time, where N is an arbitrarily large number, when we say "shut up and calculate" we do not mean there is nothing to understand or interpret. We mean that there is nothing convincing enough to unite the community available on the market.

When I said, "we don't even know how it works", I was referring to the existing problems of QM, i.e, non-locality, measurement problem, how different ways of thinking about it could possibly lead to different conclusions and so forth. As Feynman put it: We don't know the machinery was what I was implying.

I very well know how the "algorithm" works, and you don't know me, so please control yourself and refrain from pointless personal attacks. Believe me it pollutes the forum more than the interpretation debates. I think I told you this a number of times in a number of other threads, but you constantly stalk my posts and seize every opportunity to launch an assault :) Please don't hijack this one too, with your personal issues with me. You could PM me all day for personal comments. I don't mind.

You happily claim that "there's nothing left unproven" in Quantum Mechanics, so could you enlighten us on how the measurement problem is solved mathematically? Because to your dismay, it still is an unresolved problem.

There are lots of things "on the market"(whatever you mean by that) that are evolving to make us understand QM better, they are just not in 'textbooks' yet. Some people are working on this, and this is an active field.

 

[humanino]

When I said, "we don't even know how it works", I was referring to the existing problems of QM, i.e, non-locality, measurement problem, how different ways of thinking about it could possibly lead to different conclusions and so forth. As Feynman put it: We don't know the machinery was what I was implying.

I'm sorry I can not read your mind when you are trying to repeat what you read Feynman said 50 years ago.

I mention the measurement problem to you in another thread when you were complaining about angular momentum.

 

[freelance4lyf]

I vote for Copenhagen! Then again I haven't actually taken QM yet, only intro to modern phys. I recently read Atomic Physics and Human Knowledge by Bohr (a collection of essays and lectures) and he has some very interesting points about the Copenhagen Interpretation. Again, I'm barely a 3rd year undergrad but this is an interesting debate.

 

[Fredrik]

Ballentine is emphasizing the statistical nature of the wavefunction, he's not making general epistemological arguments about what a theory could tell us, and what it means. I don't think anyone would object to the argument that
" a wavefunction isn't a representation of the properties of a physical system, but a representation of the properties of en ensemble of identically prepared systems."

Honestly, I find this irrelevant to your previous remark on Quantum Mechanics being "just an algorithm". Ballentine isn't implying that. Or is he?

Actually yes. It doesn't make much sense to say that a theory "describes" something unless it contains a mathematical representation of the properties of the system it's supposed to be describing (or at least an approximate version of it). I would say that that's the minimum requirement that must be satisfied. What else can we mean by a "description" or a "model"?

But overrating it, and blindly sticking to its "formulated" restrictions, I think, is unimaginative and rather boring.

The scientific method is unimaginative and boring?! That's a pretty controversial claim in a science forum.

The facts are out there, and we know that in some examples (as Count Iblis aptly pointed out) different "formulations" could explain the same facts - and WE get to decide which "algorithm" is better than the other and so forth. So this is like choosing a basis to explain an experiment. It is irrelevant.

Huh. I said these things myself. Why are you repeating them to me?

But in science, you know, the burden of proof is on the person asserting the positive claim, not on the skeptics to refute it.

This is a joke, right? The only thing that everyone agrees about is that QM is an algorithm that tells us the probabilities of possible results of experiments. The disagreement is about whether it's more than that. You're claiming it is. I'm claiming it isn't. How on Earth did you come to the conclusion that the burden of proof is on me?

 

[Fredrik]

Interesting that nobody voted for Copenhagen :) Looks like it is finally declared dead :)

On the contrary. My view (which I described above) is a version of the Copenhagen interpretation. I have really just removed the (in my opinion absurd) claim that "wavefunction collapse" is exact, and clarified a few points.

Actually, I strongly doubt that Bohr and Heisenberg really meant that the collapse is exact, or that measuring devices are exactly classical. They were too smart for that. It seems much more likely to me that they meant that for practical purposes, it's OK to use the approximation that wavefunction collapse is exact, and that measuring devices are exactly classical. So I would say that the CI is alive and well, and that the only problem with it is that people today are defining it in a way that the originators would have hated.

By the way (this is unrelated to the content of this post), I don't see why people like the "relational interpretation" so much. I know that the basic idea, that systems don't have properties in an objective sense, but rather with respect to some other system, is pretty appealing. But to me this sounds a lot more like an ingredient of a many-worlds interpretation than like a standalone interpretation. Maybe it's possible to take Everett's MWI, which really only defines the "bird's view" properly, and complete it by adding something like the "relational interpretation" to define the "frog's view".

 

[humanino]

Actually, I strongly doubt that Bohr and Heisenberg really meant that the collapse is exact, or that measuring devices are exactly classical. They were too smart for that. It seems much more likely to me that they meant that for practical purposes, it's OK to use the approximation that wavefunction collapse is exact, and that measuring devices are exactly classical. So I would say that the CI is alive and well, and that the only problem with it is that people today are defining it in a way that the originators would have hated.

I must say it feels good to hear reasonable voices. So I wanted to thank you.

 

[sokrates]

Actually yes. It doesn't make much sense to say that a theory "describes" something unless it contains a mathematical representation of the properties of the system it's supposed to be describing (or at least an approximate version of it). I would say that that's the minimum requirement that must be satisfied. What else can we mean by a "description" or a "model"?

This doesn't mean that the theory cannot penetrate its own shell and lead to us new theories. In fact, this is what ALL scientific theories have been doing, evolving to better theories by methods of falsification. SO let me get back to the REAL issue we were discussing:

Whether QM is JUST AN ALGORITHM - or is it more than that is what I was objecting, you skillfully avoid this point but this is what we are debating. If it was just an algorithm, it would have no potential for a future theory that would replace it. It wouldn't be able to do predictions and so forth... To tell you the truth, it's the first time I am using Quantum and Algorithm in the same sentence.

I am sorry but Ballentine isn't even remotely implying what you are saying here.

The scientific method is unimaginative and boring?! That's a pretty controversial claim in a science forum.

Calm down. I didn't say that. Maybe you could try to understand what I wrote by reading my earlier post. I said you are overrating it by misrepresenting quantum theory as an "algorithm".

Huh. I said these things myself. Why are you repeating them to me?

No; you didn't. Try reading carefully. And what's the point of such a question?

This is a joke, right? The only thing that everyone agrees about is that QM is an algorithm that tells us the probabilities of possible results of experiments. The disagreement is about whether it's more than that. You're claiming it is. I'm claiming it isn't. How on Earth did you come to the conclusion that the burden of proof is on me?

Do you even know what the word "algorithm" means and implies? Does an algorithm make predictions?? You are obviously using the word out of its context and definition. Maybe you should look it up and clarify your claims around this new definition of QM.

 

[Fredrik]

If it was just an algorithm, it would have NO POTENTIAL for a future theory that will replace it.

Yes it would. This is just crazy talk.

I am sorry but Ballentine isn't even remotely implying what you are saying here.

Yes he does. But you seem to have misunderstood what I'm saying. I hope you have. I can't think of any other explanation for the bizarre claim of yours that I quoted first in this post.

No; you didn't. And what's the point of such a question?

Yes I did, but thank you for proving that it's pointless to continue this discussion. I won't waste any more time on you.

 

[Fredrik]

I must say it feels good to hear reasonable voices. So I wanted to thank you.

You're welcome.

 

[sokrates]

Yes I did, but thank you for proving that it's pointless to continue this discussion.

You are welcome :). I happily debunk any pointless claim using inaccurate terminology and weak reasoning. Any time...

 

[humanino]

Does an algorithm make predictions?

All physical laws are algorithms to cook predictions.

 

[RUTA]

By the way (this is unrelated to the content of this post), I don't see why people like the "relational interpretation" so much. I know that the basic idea, that systems don't have properties in an objective sense, but rather with respect to some other system, is pretty appealing. But to me this sounds a lot more like an ingredient of a many-worlds interpretation than like a standalone interpretation. Maybe it's possible to take Everett's MWI, which really only defines the "bird's view" properly, and complete it by adding something like the "relational interpretation" to define the "frog's view".

Speaking for myself, I use a relational approach because I'm going with non-separability rather than non-locality in dealing with quantum non-locality. Mine certainly has nothing to do with MWI, so I can't speak to your point there.

 

[Fra]

By the way (this is unrelated to the content of this post), I don't see why people like the "relational interpretation" so much. I know that the basic idea, that systems don't have properties in an objective sense, but rather with respect to some other system, is pretty appealing. But to me this sounds a lot more like an ingredient of a many-worlds interpretation than like a standalone interpretation. Maybe it's possible to take Everett's MWI, which really only defines the "bird's view" properly, and complete it by adding something like the "relational interpretation" to define the "frog's view".

IMO the notion of many worlds or multiverse is simply weird. IMO, there are many-views within one world. And the differing views implies interactions between the observers. That's my "relational view".

The idea that most people have that does "relational stuff", including rovelli, DOES take place at a non-physical bird view, where the frog views are "derived" from the birds view. But that entire construction is missing the point or an intrinsic measurement theory. There is no justification for the birds view.

The birds view is nothing but a more sophisiticated structural realist fantasy.

They way I think of relational views, replaces the birds view with evolving frog views. This is also closely related to Smolins ideas of evolving law.

The type of "modern realism" I don't like comes in different disguises. "Structural realism" is also a closely related term and it's closely related to the notion of timeless universal law. Universal objective symmetries are also modern realism in disguise.

The problem, from the point of view of instrinsic inquiry is that all these elements are added to the reasoing without beeing intrinsically inferred from observations.

I'll bite on this

All physical laws are algorithms to cook predictions.

But if we look at this in the proper context, an algoritm must have a "computer" and physical resources for implementation. This is a physical scientist, and for example a receipe that is too complex to fit the scientists brain is simply worthless. So, there are constrains on the algortitms - they must be encodable and computable relative to the observer in question. This is the essence of the intrinsic view I hold.

Edit: Now ponder, what happens as the complexity of the observer scales! That's what is totally ignored in current QM.

Alot of people (it seems to me at least) think of these algorithms as existing in some external reality, or "mathematical reality". Now again, that a kind of modern realism that is not helping me.

My point is that, if you see it this way, you also see that the algoritm we call "standard QM" has the wrong form! It is not cast in the right way to be a proper intrinsic algorithm (to use your words).

/Fredrik

 

[div78football]

Before i start, i nothing of physics other than what I've seen in sci-fi.

Is it believed that universes are created through the collision with other universes? and that this created universe assumingly expands to ultimately contract till it implodes on itself unless of course it itself collides with another universe.

Further does the rate of expansion effect the outcome of a collision...ie does a rapidy expanding universe in collision with a slowly extracting universe create something different from a slowly expanding universe with a slowly contarcting universe or any permintation of the two.

Also if there are multiverses does the outcome of a collision of many of them create something totally different.

Cheers

 

[Count Iblis]

Are you calling me the Devil?

But seriously, do you have a citation for this interpretation -- proponents, opponents, discussion, etc?

When 't Hooft first proposed the sort of deterministic models he is working on, he was thinking along these lines, see e.g. here:

http://arxiv.org/abs/gr-qc/9903084

But his models are completely deterministic and local, so what he is proposing amounts to a local deterministic hidden variable models and a necessary ingredient in these models has to be that they are superdeterministic (i.e. the observer has no freedom to choose how to set up his experiments; the fact that he/she is deterministic too cannot be ignored). In later papers 't Hooft has argued why superdeterminism is a natural feature of any deterministic model:

http://arxiv.org/abs/quant-ph/0701097

 

[Demystifier]

When 't Hooft first proposed the sort of deterministic models he is working on, he was thinking along these lines, see e.g. here:

http://arxiv.org/abs/gr-qc/9903084

But his models are completely deterministic and local, so what he is proposing amounts to a local deterministic hidden variable models and a necessary ingredient in these models has to be that they are superdeterministic (i.e. the observer has no freedom to choose how to set up his experiments; the fact that he/she is deterministic too cannot be ignored). In later papers 't Hooft has argued why superdeterminism is a natural feature of any deterministic model:

http://arxiv.org/abs/quant-ph/0701097

That is an interesting idea that superdeterminism could save locality. However, even though local superdeterminism can explain existing experiments, I think that local superdeterminism cannot reproduce ALL conceivable predictions of quantum mechanics. For example, the principles of quantum mechanics allow entangled states of systems that have NEVER been in local interaction, in which case there is no local mechanism that could provide instructions for non-free experimenters how to set up their experiments in order to get quantum-like correlations.

Anyway, Bohmian mechanics assumes that everything, including the human braines and arms, is described by deterministic equations of motion. Hence, it is not only deterministic, but also superdeterministic. Yet, it is a nonlocal theory.

 

[RUTA]

When 't Hooft first proposed the sort of deterministic models he is working on, he was thinking along these lines, see e.g. here:

http://arxiv.org/abs/gr-qc/9903084

But his models are completely deterministic and local, so what he is proposing amounts to a local deterministic hidden variable models and a necessary ingredient in these models has to be that they are superdeterministic (i.e. the observer has no freedom to choose how to set up his experiments; the fact that he/she is deterministic too cannot be ignored). In later papers 't Hooft has argued why superdeterminism is a natural feature of any deterministic model:

http://arxiv.org/abs/quant-ph/0701097

Thanks very much. I do find the claim that particles are not real but I don't find any mention of fields as mere computational devices in the path integral approach in these papers. Do I need to look at his earlier work to find this and the fact that only external lines are "real" in the computation of amplitudes?

I ask because I'm writing a paper wherein I use discrete path integrals over graphs as a model fundamental to quantum physics and the mathematical approach I'm using captures essentially these same claims, so I need to cite him if he's already made these claims in his approach. Thanks again.

 

[fleem]

If I develop a theory to describe the average behavior of a hive of bees (that is, a theory to describe how the swarm acts), and move on to study a single bee, I might see some similarities in the behavior of a single bee and the behavior of the swarm. But it would be illogical of me to insist that my swarm theory must be used as the founding theory in understanding the behavior of a single bee.

But that is exactly what we've done. "local" means a zero-length space-time interval, and "non-local" means a non-zero-length space-time interval. But "space-time" was learned and developed solely to describe the (classical) large scale, average behavior of many particles. By insisting particle-particle interactions occur in something called "space-time", we've found apparent paradoxes (entangled particles disobey the tenants of space-time). Yet even after seeing those paradoxes, we still insist space-time is the right foundation to understanding individual particle behavior! The fact that entangled particles clearly and blatantly disobey the tenants of space-time should make us realize we have no business insisting a theory learned solely from classical observation must unequivocally be the founding theory describing the behavior of individual particles. Yes, if we watch several particles interacting, we see things similar to the tenants of space-time, like the concepts of dimension (certain conserved quantities are orthogonal and can be transformed by processes similar to euclidean rotation), intervals, etc. But then several particles is a bit of a swarm, and thus a bit classical.

Entangled particles act like they are local because they are just as local as particles we classically consider local. That is, they are in the same situation as classically local particles--whatever that might be. The clincher seems to be that the particles are entangled only while there is no interaction with the rest of the universe. (Classically) local particles find it easier to behave that way because they need not remain closed as long, because they are so close. So its really a matter of closed and open, not local and non-local.

 

[alexepascual]

I have one problem with MWI, though I accept I may be looking at it too literally. The original MWI was devised to explain the double slit experiment conundrum. So the one photon goes through each slit but in different worlds. Not to upset causality or the conservation of mass or energy, each world only sees one photon – no problem. However now each photon is in a parallel world (universe), why does interference happen?

The answer to this might depend on what you choose to think of as a separate world. Usually those who adheer to the many-worlds interpretation would consider the worlds "splitting" only after wave function collapse. If we choose this definition, then when the photon goes through the slits, we could say that it has split into several copies of itself, each being "less than real" (we could call them ghost particles). But each of these copies is still within the same "world" and that's the reason you can see interference.
The other approach would be to consider each "copy" of the photon to be in a different world. But in that case we would have to consider these worlds as being part of "our world". So you could say that it is the superposition of these different worlds that make up your world. But as I said before, I don't think this is the standard way of thinking about it (which nevertheless does not mean that it has less merit or potential than the more standard MWI thinking. It seems that this is only a different use of words, but some times trivial things like the use of words can have some influence in our thinking process. So I wouldn't dismiss it as irrelevant.

 

[Adrian59]

Usually those who adheer to the many-worlds interpretation would consider the worlds "splitting" only after wave function collapse. If we choose this definition, then when the photon goes through the slits, we could say that it has split into several copies of itself, each being "less than real" (we could call them ghost particles). But each of these copies is still within the same "world" and that's the reason you can see interference.
The other approach would be to consider each "copy" of the photon to be in a different world. But in that case we would have to consider these worlds as being part of "our world". So you could say that it is the superposition of these different worlds that make up your world... It seems that this is only a different use of words, but some times trivial things like the use of words can have some influence in our thinking process.

Thanks for the reply alexepascual since I thought my comment had been lost in the general discussion, hence my delay in responding. However I still think that the MWI doesn't do what it set out do do since in your first suggestion one has to insert collapsing waves which obviously gets us back to the Copenhagen interpretation. Also, I can see no difference between ghost waves & probability waves which I thought the MWI was trying to avoid. The second suggestion is that the parallel worlds are not truly separate but different states that result in a superpostion but this also seems like back to square one & probability waves.

 

[Dmitry67]

No, modern MWI does not include any collapse at all.
'Splitting' is explained via Quantum Decoherence , so no additional postulates are needed.
http://en.wikipedia.org/wiki/Quantum_decoherence

This is a beauty of MWI - no mysterious collapse.

 

[Albert V]

I would argue for "shut up and calculate!"


Two recent papers show the relationship between mathematical undecidable propositions and randomness.

View attachment Brukner01.pdf

View attachment Zeilinger01.pdf

 

[Dmitry67]

There are many misconceptions about the undecidable statements in physics

For example, well known Conway Game of Life
Rules are simple and deterministic
And yet there are undecidable statements about the outcomes!

 

[Adrian59]

No, modern MWI does not include any collapse at all.
'Splitting' is explained via Quantum Decoherence , so no additional postulates are needed.
http://en.wikipedia.org/wiki/Quantum_decoherence

This is a beauty of MWI - no mysterious collapse.

Thanks for the reply. I would agree with your dislike of collapsing waves though I still need convincing that MWI is the best interpretation. I followed your link to wiki. The paragraph using phase space explained everything to me & the following maths only confirmed this since the first equation seemed to encapsulate the whole argument because the system ket was expanded in basis states of the environment <i |ψ>. Though on a more general point, I understood that decoherence can be considered an interpretation of QM in its own right so what MWI adds is questionable to me. Or put another way, I see it as a minimizing the adversities: does MWI give enough to the interpretation of QM in return for having to put up with infinite parallel worlds.

 

[RUTA]

Thanks for the reply. I would agree with your dislike of collapsing waves though I still need convincing that MWI is the best interpretation. I followed your link to wiki. The paragraph using phase space explained everything to me & the following maths only confirmed this since the first equation seemed to encapsulate the whole argument because the system ket was expanded in basis states of the environment <i |ψ>. Though on a more general point, I understood that decoherence can be considered an interpretation of QM in its own right so what MWI adds is questionable to me. Or put another way, I see it as a minimizing the adversities: does MWI give enough to the interpretation of QM in return for having to put up with infinite parallel worlds.

Adrian Kent gave an interesting talk at Perimeter last Sep, "Theory Confirmation in One World and its Failure in Many." In this talk he pointed out that, if MWI is true, one cannot be sure what the true probablility is for any given experiment because one doesn't know where they reside in the multiverse. Consider, for example, a simple binary outcome (call it + or -) with a "true" probability of 50% either way. If MWI is correct, there is a world (call it A) in which the experiment always comes out + and a world (call it B) in which the outcome is always -, with all other combinations realized between these extremes. Only those worlds "in the middle" would be able to deduce something close to the "true" probability, but they wouldn't "know" it. Consider two poor theorists in worlds A and B who deduce the correct theory of QM and predict the "true" 50% probability distribution. Their "correct" theories are refuted and they die in poverty and disgrace To what extent can we do science in a multiverse?

 

[Dmitry67]

RUTA, yes, exactly, it is a problem.
We discuss it here: https://www.physicsforums.com/showthread.php?t=329807
How does MWI resolve low probability multiverse events?

 

[Dmitry67]

Thanks for the reply. I would agree with your dislike of collapsing waves though I still need convincing that MWI is the best interpretation. I followed your link to wiki. The paragraph using phase space explained everything to me & the following maths only confirmed this since the first equation seemed to encapsulate the whole argument because the system ket was expanded in basis states of the environment <i |ψ>. Though on a more general point, I understood that decoherence can be considered an interpretation of QM in its own right so what MWI adds is questionable to me. Or put another way, I see it as a minimizing the adversities: does MWI give enough to the interpretation of QM in return for having to put up with infinite parallel worlds.

What is interesting is that Quantum Decoherence (QD) is mathematical fact and can not be denied, no matter if one likes or hates MWI. So Copenhagen Int. now have not one, but 2 different 'agents' for collapse: old CI collapse and New QD. Which makes CI a total mess. Well, it was quite a mess even before the discovery of QD.

Regarding your last statement, if sounds like you see the existence of another branches as something 'bad'. People tend to critisize MWI for having extra worlds using occams razor argument. But on the contrary, occams razor must be used to justify the elimination of some worlds based on the random or unknown rule!

Finally, there is still one problem with MWI: Born rule. Based on the discussions here I see that Born rule must be reformulated to be used in MWI, because there is no such thing in MWI as 'probability', because it is deterministic. But I can not answer the question what is a physical meaning of the what we used to call a probability in MWI. Or, using RUTA's example, why are we observing a world 'in the middle'

 

[kote]

I would argue for "shut up and calculate!"Two recent papers show the relationship between mathematical undecidable propositions and randomness.

View attachment 20068

View attachment 20069

I just looked at these papers... and I'm sorry, but they are just completely wrong. Analytic propositions can't be proven a posteriori. Experiments can't serve as mathematical proofs.

Or maybe I missed the point of the papers.