Ballentine's Ensemble Interpretation Of QM

[Maui]

Name 1 moderator that agreed with you that those experiments falsify Bohmian mechanics.

You are taking my words out of the context. You still appear to not understand some very basic stuff like the factthat the BI is forced to mimic superpositions(act as if there were) and which, due to a multitude of experiments, are now widely accepted as real and are put to use(see link above on quantum computers). Quantum computing relies on quantum superposition and entanglement to work--qbits must exist in all states simultaneously before giving a particular result when observed. And in Bohmian mechanics there are no superpositions of states.

If you need an authority opinion how a quantum computer could be compatible with Bohmian mechanics(I don't see how it could), send a pm to the moderators. But it would have been better if you followed the 'picture' yourself instead of taking someone's word on faith.
The adaptation of Bohmian mechanics to superpositions requires the conspiracy to get bigger and funnier to explain qubits and quantum computing.

 

[Maui]

The real issue with BM is how "artificial" the pilot wave feels, and that's subjective.

It feels like a superposition of states. Oh wait, we are back to standard quantum mechanics.

 

[bohm2]

If you need an authority opinion how a quantum computer could be compatible with Bohmian mechanics(I don't see how it could), send a pm to the moderators.

This criticism was already addressed in a previous thread and some links provided:

Quantum computation from a de Broglie-Bohm perspective
http://xxx.lanl.gov/pdf/1205.2563v1.pdf

Quantum Computing in the de Broglie-Bohm Pilot-Wave Picture
http://xxx.lanl.gov/pdf/1012.4843v1.pdf

And also addressed on Physics Stack Exchange:

Generally, when you make a quantum calculation, you have to make some sort of measurement of the qubits at the end of the algorithm where the result you're looking for is a very probable (but not necessarily certain) result. In any interpretation that actually agrees with the basic results of quantum mechanics, these probabilities will still hold and the algorithm will still work.

If an interpretation is ruled out by the possibility quantum computing, then it's (probably) wrong because it contradicts quantum mechanics. To the best of my knowledge all of the interpretations you mentioned, while deterministic, still give results in agreement with quantum mechanics and can't be ruled out by the existence of a quantum computer.

Does quantum computing rely on particular interpretations of quantum mechanics?
http://physics.stackexchange.com/qu...rticular-interpretations-of-quantum-mechanics

Personally, I find the arguments presented by those who propose that quantum theory itself is emergent from a deeper, more exact theory on a sub-quantum level as the most reasonable view, but we're not there yet, so I guess we're kind of debating which is the best means to achieve that goal (if achievable). Maybe it doesn't matter as Ken G argues. Maybe it does. But interpretations/foundations may shed light or spawn other areas of research that may shed light as pointed out by people like Lucien Hardy, Spekkens, Leifer, etc.

there are a number of elements of dBB/BM/BI that seem to directly be contradicted by QM. An(other) example is the entanglement of photons AFTER they are already detected.

Those experimental results are further evidence against local theories not dBB.

 

[kye]

You misunderstand. The ensemble is state and observational apparatus.

The interpretation says nothing about the interpretation of the state independent of measurement context.

Thanks
Bill

Can others confirm if Ballentine believe this too??

Because if he does. This is not different from Copenhagen Interpretation. Ballentine just focus on the ensemble and even if A and B was literally in superposition in real time. He doesn't care because his reasoning being that you only detect one at a time, so may well call it Ensemble without saying anything about the interpretation of the state independent of measurement context.

Also can Ballentine's convincingly explained violations of Bell's Theorem too and the contextual somewhat non-local nature of it?

 

[bhobba]

Can others confirm if Ballentine believe this too??

Its in his book, and so fundamental its in the early pages as well.

However in his 1970 paper he explicitly stated it was an actual value prior to observation and was reliant on a not spelled out sub quantum process, or hidden variable theory.

And no its not that different to CI, a point I have been trying to make. But that is fairly well known these days eg:
http://en.wikipedia.org/wiki/Ensemble_interpretation
'The standard Copenhagen Interpretation (CI) is no different in this respect. A fundamental principal of QM is that only probabilistic statements may be made, whether for individual systems/particles, a simultaneous group of systems/particles, or a collection (ensemble) of systems/particles. An identification that the wave function applies to an individual system in standard CI QM, does not defeat the inherent probabilistic nature of any statement that can be made within standard QM. To verify the probabilities of quantum mechanical predictions, however interpreted, inherently requires the repetition of experiments, i.e. an ensemble of systems in the sense meant by the ensemble interpretation. QM cannot state that a single particle will definitely be in a certain position, with a certain momentum at a later time, irrespective of whether or not the wave function is taken to apply to that single particle. In this way, the standard CI also “fails” to completely describe “single” systems.'

Plus, and probably even more importantly, its exactly what a little thought would show.

In his book Ballentine goes deeply into Bells stuff.

His book has not attained the status as one of the finest, if the not finest, books to learn QM from without good reason. It is by a LONG, LONG way the best book I have read. You may not hold to the ensemble interpretation after reading it, but you will understand it, as well as a lot of QM's foundational issues - that's one of its strengths - it goes deeply into it. IMHO its the anti Griffiths book which is very cookbook like - not to run down Griffiths - it's good - but Ballentine is WAY ahead IMHO. Still its at graduate level (ie assumes a certain level of math maturity) and Griffith is at undergrad level. Griffith is a good prep for Ballentine though.

Thanks
Bill

 

[kye]

Electron spin acts in abstract space.. because two revolutions made one turn. It has no correlate to physical world. In the same way. I wonder if configuration space or Hilbert space in a single quantum system is like the electron spin... no physical correlate.. I guess this is one reason one turn to Ballentine's because the other choices are bohemians and many worlds, right?

Mass is always definite in a quantum system. There is no superposition of mass. So I guess the higgs field which couples to the lepton field conspire together to make themselves undetectable in position but not in mass. I guess this is a problem quantum gravity can solve.. noting that mass curves spacetime.. and we still don't know how mass and spacetime are coupled as we don't know the physics of the Planck size. So do you believe quantum gravity is related to the foundational problems in QM or unrelated (and what's arguments they are unrelated?)

 

[atyy]

Mass is always definite in a quantum system. There is no superposition of mass.

http://www.slac.stanford.edu/econf/C040802/papers/L004.PDF
"This superposition of mass eigenstates is called the neutrino of flavor."

So do you believe quantum gravity is related to the foundational problems in QM or unrelated (and what's arguments they are unrelated?)

They are not necessarily related, since string theory, which is a plausible theory of quantum gravity for some universe (not necessarily ours) uses standard QM.

 

[kye]

http://www.slac.stanford.edu/econf/C040802/papers/L004.PDF
"This superposition of mass eigenstates is called the neutrino of flavor."



They are not necessarily related, since string theory, which is a plausible theory of quantum gravity for some universe (not necessarily ours) uses standard QM.

In the future if the higgs boson is made to pass through double slit.. it would also interfere with itself? Remember the higgs boson is the only (and first) scalar particle discovered in nature... what is the mathematical arguments scalar particles also obey quantum mechanics or QM don't care about spins?

I wonder what Ballentine says about the higgs.

 

[Ken G]

It feels like a superposition of states. Oh wait, we are back to standard quantum mechanics.

Yes, of course, that's why it is called an interpretation of standard quantum mechanics.

 

[Cthugha]

Quantum computing relies on quantum superposition and entanglement to work--qbits must exist in all states simultaneously before giving a particular result when observed.

This is simply wrong. QC relies solely on the math, not on its interpretation. The math is interpreted as a "real" superposition in standard qm, but there is no need to do that for QC to work. All Bohmian mechanics does is dividing the physics into something considered a real particle and a guiding wave. Shifting the math part which leads to superposition in standard QM to the guiding wave does not change a single prediction - even without superposition.

If you need an authority opinion how a quantum computer could be compatible with Bohmian mechanics(I don't see how it could), send a pm to the moderators.

The literature on that is relatively scarce. Aaronson investigated hidden variables in general from a quantum computing perspective (http://pra.aps.org/abstract/PRA/v71/i3/e032325) and I think there is some PhD or MSc thesis from Valentinis group on quantum computing in the Bohmian picture. But I do not know that for sure. I am not really a fan of Bohmian mechanics.

But it would have been better if you followed the 'picture' yourself instead of taking someone's word on faith.

The scientific standard on what to accept is still set by peer review. So if you insist on claiming that Bohmian mechanics is ruled out by quantum computing, please provide some peer reviewed article backing your opinion. BM may seem arbitrary, but personal liking or disliking is fortunately not a factor in deciding what is acceptable in science. Personally, for example, I think that imposing any kind of interpretation on quantum computing makes papers more horrible and that physicsworld link on superposition is one of the most horrible proofs of that I have read. It is that pop-sci stuff trying to visualize things for laymen which brings up that stuff. Real experimental papers rarely bother (or even have the space) to talk about interpretations. The math speaks for itself. See, e.g. Berthold-Georg Englerts "On quantum theory" (http://arxiv.org/abs/1308.5290) for an essay trying to make clear where physics ends and where philosophy starts.

 

[kye]

This is simply wrong. QC relies solely on the math, not on its interpretation. The math is interpreted as a "real" superposition in standard qm, but there is no need to do that for QC to work. All Bohmian mechanics does is dividing the physics into something considered a real particle and a guiding wave. Shifting the math part which leads to superposition in standard QM to the guiding wave does not change a single prediction - even without superposition.

It is stated that quantum computing can create quantum computers that can hack encryptions that can take convensionally thousands of years. Since QC relies solely on the math and even if there is no simultaneous superposition, how can you create classical algorithms or connections that can create quantum computer and hack encryptions in seconds that will year 100 years?

 

[Ken G]

Yes, the math is the key. Indeed I think there is a lot of confusion about what an interpretation of a mathematical theory really should be in the first place. In mathematics, interpretations are created for only one reason-- to help understand the mathematical structure in question. There is no sense to which one interpretation or the other is "what is really happening" in that mathematical structure, because nothing is really happening in that mathematical structure, it's just a mathematical structure. But in physics, we have an issue about what an interpretation is because we have both-- we have formal mathematical structures which allow us to prove things and derive ramifications, and we have a sense that "something is really happening." So we want an interpretation to be both things, and it just isn't. We must pick which we want it to be-- do we have a formal mathematical structure that we want to understand, which can be approached via any valid interpretation (even ones that sound wildly different from each other), or do we have a description of what is really happening, in which case we really have no right to assume it will function like a formal mathematical system in the first place. You just can't have it both ways, it's too much to ask from any interpretation. The solid ground, therefore, is to stick to the formal mathematical meaning of an interpretation, and not think of it as a description of what is actually happening. I should think we would have learned to be suspicious of the latter by now anyway.

 

[kye]

Yes, the math is the key. Indeed I think there is a lot of confusion about what an interpretation of a mathematical theory really should be in the first place. In mathematics, interpretations are created for only one reason-- to help understand the mathematical structure in question. There is no sense to which one interpretation or the other is "what is really happening" in that mathematical structure, because nothing is really happening in that mathematical structure, it's just a mathematical structure. But in physics, we have an issue about what an interpretation is because we have both-- we have formal mathematical structures which allow us to prove things and derive ramifications, and we have a sense that "something is really happening." So we want an interpretation to be both things, and it just isn't. We must pick which we want it to be-- do we have a formal mathematical structure that we want to understand, which can be approached via any valid interpretation (even ones that sound wildly different from each other), or do we have a description of what is really happening, in which case we really have no right to assume it will function like a formal mathematical system in the first place. You just can't have it both ways, it's too much to ask from any interpretation. The solid ground, therefore, is to stick to the formal mathematical meaning of an interpretation, and not think of it as a description of what is actually happening. I should think we would have learned to be suspicious of the latter by now anyway.

We were misled before. In the past we thought atoms can't exist and don't exist because the maths of Newtonian mechanics is enough. Now we can detect the pions. This is the reason many want a deeper understanding for a possible non-local hidden variables and we can't blame them for it.

In the pop-sci books. We are exposed to the concept that before measurements, the physical world or the properties don't actually exist and there is literal superposition of the objects, and our observation collapse the wave function. My question is, there is no way to refute this aint it. Those who understand the math want to just stick with the math because of experience with the electron spin not rotating in real world. The pop-sci books kinda want to (in analogy to quantum) show the public the electron spin is literally revolving twice in one revolution. Is my impression of the situation correct?

 

[bohm2]

The solid ground, therefore, is to stick to the formal mathematical meaning of an interpretation, and not think of it as a description of what is actually happening. I should think we would have learned to be suspicious of the latter by now anyway.

I don't understand this part. What is a formal mathematical meaning of an interpretation? Maybe I'm misunderstanding your point but as I see it, Fuchs, of all people, wrote a good paragraph worth regurgitating:

To take a stand against the milieu, Asher had the idea that we should title our article, “Quantum Theory Needs No ‘Interpretation’.” The point we wanted to make was that the structure of quantum theory pretty much carries its interpretation on its shirtsleeve—there is no choice really, at least not in broad outline. The title was a bit of a play on something Rudolf Peierls once said, and which Asher liked very much: “The Copenhagen interpretation is quantum mechanics!” Did that article create some controversy! Asher, in his mischievousness, certainly understood that few would read past the title, yet most would become incensed with what we said nonetheless. And I, in my naivet´e, was surprised at how many times I had to explain, “Of course, the whole article is about an interpretation! Our interpretation!”...The question is completely backward. It acts as if there is this thing called quantum mechanics, displayed and available for everyone to see as they walk by it—kind of like a lump of something on a sidewalk.

The job of interpretation is to find the right spray to cover up any offending smells. The usual game of interpretation is that an interpretation is always something you add to the preexisting, universally recognized quantum theory. What has been lost sight of is that physics as a subject of thought is a dynamic interplay between storytelling and equation writing. Neither one stands alone, not even at the end of the day. But which has the more fatherly role? If you ask me, it’s the storytelling. Bryce DeWitt once said, “We use mathematics in physics so that we won’t have to think.” In those cases when we need to think, we have to go back to the plot of the story and ask whether each proposed twist and turn really fits into it. An interpretation is powerful if it gives guidance, and I would say the very best interpretation is the one whose story is so powerful it gives rise to the mathematical formalism itself (the part where nonthinking can take over). The “interpretation” should come first; the mathematics (i.e., the pre-existing, universally recognized thing everyone thought they were talking about before an interpretation) should be secondary.

Interview with a Quantum Bayesian
http://arxiv.org/pdf/1207.2141v1.pdf

 

[strangerep]

Electron spin acts in abstract space.. because two revolutions made one turn. It has no correlate to physical world.

Nonsense. There are physical experiments you can perform in your own home that show how a rotation by $2\pi$ isn't necessarily equivalent to no rotation at all, but rotation by $4\pi$ is.

Look up "Dirac Scissors" (also known as the "belt trick" and several other names).
http://en.wikipedia.org/wiki/Plate_trick
Here's some animations referenced there:
http://vimeo.com/62228139
http://vimeo.com/62143283
This stuff serves to prove that one's natural understanding of physical 3-space, acquired in early childhood, is naive and even mistaken, in some ways.

There are also experiments involving electron interferometry where one side of the interferometer has a magnetic field which rotates the electrons on that side through $2\pi$, with the result that they cancel when the two sides are brought back together.

I wonder what Ballentine says about the higgs.

Maybe you should actually study some non-popsci books instead of making the endless crackpot suggestions that you've sprinkled like pepper throughout this thread.

 

[bhobba]

My question is, there is no way to refute this aint it.

There isn't. The junk you read in the popular press may be true. That's not the point, or why it generally makes me want to run away screaming - the point is they say it as if its the only view. A much more rational view exists - for example bog standard CI is much more rational than this observer created tripe - but they don't say it - because its not 'sensationalist' enough.

When was the last time you saw any populist book say Copenhagen assumes a world out there entirely common-sensical, trees make sounds when there is no observer, and all our every day intuition holds true? That's not going to sell is it - so they don't say it. But that is precisely what Copenhagen, and the Ensemble interpretation this thread is about says.

The key issue is how such a world emerges from a theory that only makes predictions about observations that appear in such a world. That is a very deep issue and the true quantum mystery. A lot of progress has been made - but issues still remain and more research is required before a satisfactory explanation is found. I suspect a few revolutions will occur along the way - indeed we may be in the middle of one right now - I find the following very thought provoking:
https://www.simonsfoundation.org/quanta/20130917-a-jewel-at-the-heart-of-quantum-physics/

Thanks
Bill

 

[Cthugha]

It is stated that quantum computing can create quantum computers that can hack encryptions that can take convensionally thousands of years.

Yes, at least this is what we tell the funding agencies. In real life, scaling is a problem. Few qubits are ok and we can work with them. Many are really complicated. We will see how far we can get. Rainer Blatt seems to be doing pretty well.

Since QC relies solely on the math and even if there is no simultaneous superposition, how can you create classical algorithms or connections that can create quantum computer and hack encryptions in seconds that will year 100 years?

Classical algorithms do not work. You will need quantum algorithms like Shor's algorithm and qubit states. These are superpositions from the math point of view. However, simply speaking "superposition" vs. "mixture" is just a code for "when you have two indistinguishable possible states, do the sum and take the expectation value, otherwise get the expectation values first and find their sum". Having this mathematical structure does not necessarily mean that both states are simultaneously real (like the famous "the particle is in two positions at once"). It may well be, but it does not have to. QM is a statistical theory. It does not tell us anything about what is "really" happening in a single experimental run.

 

[Nick666]

I find the following very thought provoking:
https://www.simonsfoundation.org/quanta/20130917-a-jewel-at-the-heart-of-quantum-physics/

There's something I don't understand in that article, down the page, starting at "Recently, a strange duality has been found between string theory and quantum field theory" and ending with the paragraph.

Is he referring to the duality as the discovery ? And then is he suggesting the illusion of dimensions and space-time as an answer to the cause of that duality ?

 

[Maui]

These are superpositions from the math point of view. However, simply speaking "superposition" vs. "mixture" is just a code for "when you have two indistinguishable possible states, do the sum and take the expectation value, otherwise get the expectation values first and find their sum". Having this mathematical structure does not necessarily mean that both states are simultaneously real (like the famous "the particle is in two positions at once"). It may well be, but it does not have to. QM is a statistical theory. It does not tell us anything about what is "really" happening in a single experimental run.

This makes little sense to me and seems to be another conspiracy theory. Quantum computers are real world macroscopic devices, not ideas based on math. Nobody has seen the Sun directly or visited it, but all data suggests that there is a Sun. But maybe it's not there. Perhaps it may well be, but it does not have to. QM is a statistical theory after all. Is that a sensible statement?

 

[Maui]

This criticism was already addressed in a previous thread and some links provided:

Quantum computation from a de Broglie-Bohm perspective
http://xxx.lanl.gov/pdf/1205.2563v1.pdf

Quantum Computing in the de Broglie-Bohm Pilot-Wave Picture
http://xxx.lanl.gov/pdf/1012.4843v1.pdf

And also addressed on Physics Stack Exchange: Does quantum computing rely on particular interpretations of quantum mechanics?
http://physics.stackexchange.com/qu...rticular-interpretations-of-quantum-mechanics

Personally, I find the arguments presented by those who propose that quantum theory itself is emergent from a deeper, more exact theory on a sub-quantum level as the most reasonable view, but we're not there yet, so I guess we're kind of debating which is the best means to achieve that goal (if achievable). Maybe it doesn't matter as Ken G argues. Maybe it does. But interpretations/foundations may shed light or spawn other areas of research that may shed light as pointed out by people like Lucien Hardy, Spekkens, Leifer, etc.

Those experimental results are further evidence against local theories not dBB.

You have referenced a few hundred papers just this year alone and not everyone has sufficient time to read them all in every thread. I was hoping for an explanation from your point of view how the non-local guiding wave is compatible with the superpositions of states the said guiding wave was supposed to do away with(for a somewhat classical and intuitive picture of the world). Superpositions were and are troublesome for the idea of macro realism, Bohm's idea was to restore objectivity by removing superpositions of states. He was wrong.

BTW, it's not allowed to link to blogs here. I took a look at the answers and none addressed the issue I raised above. If nobody can answer this, they are wrong and would rather believe in a conspiracy(the pilot wave has a new function - it has to perform complex conspiratorial acts to suit someone's agenda).

 

[Maui]

It feels like a superposition of states. Oh wait, we are back to standard quantum mechanics.

Yes, of course, that's why it is called an interpretation of standard quantum mechanics.

You don't understand. Bohmian mechanics makes statements about what was until recently thought to be unobserveable quantum behavior. It's observed now, it's been a decade. It's a new development and the guiding wave is in trouble with experiments. On the other hand, quantum mechanics has no problems with superpositions and quantum weirdness.

 

[bhobba]

not ideas based on math.

And neither is a weight attached to a spring.

Funny though - its behavior is well described by math.

What a mathematical model is, is very very basic to physics. But for some reason a few people get confused. I am suspicious its because they haven't actually been in a mathematical modelling, differential equation, computational modelling, or similar class where one of the activities is to check exactly how well these models describe the actual system behavior. Its very interesting taking an actual model, continually refining it and seeing exactly how well it describes a situation. If you have then its very obvious what's going on and its very simple. Once you see just how well it does work, one tends to think of the math as what's going on - its of course just a description - but works so well you tend to not think about that explicitly.

People like that are NOT saying the math is the reality - just it describes it so well you tend to think of it that way. But without doubt virtually all trained physicists, or people trained in applied math like I was, view it like that.

Thanks
Bill

 

[Cthugha]

This makes little sense to me and seems to be another conspiracy theory. Quantum computers are real world macroscopic devices, not ideas based on math.

Mathematical models are fundamental to physics. Englert's essay I linked earlier represents the foundations of physics well: formalism (the mathematical model), phenomena (experimental results) and interpretation (the link between both). And this interpretation is a minimal one: there is a wavefunction and it tells us what is happening on average for a large number of trials. Any "deeper" interpretation already makes assumptions and moves away from physics and onward into the realm of philosophy. They are not needed for actually doing experiments. Assuming that the mathematical formulation of superposition means that "particles are actually in two places at once" is such an unnecessary assumption. It does not help with the math. It does not change any predictions. It is therefore not really physics.

Nobody has seen the Sun directly or visited it, but all data suggests that there is a Sun. But maybe it's not there. Perhaps it may well be, but it does not have to. QM is a statistical theory after all. Is that a sensible statement?

I do not see the connection. The sun is considered a black body with some temperature and every single experiment will give you the same result: it will be in line with a black body at some temperature (ignoring of course atmospheric effects and other small deviations) out there in the sky. You can map the experimental results to the mathematical model directly. However, if you have any other interpretation which uses the same math and explains the same observations and is also in agreement with all the other experiments, it would of course also be valid. I am just not aware of any.

For superpositions, you can also directly map the experimental results to the mathematical model: You do a lot of measurements and the probability distribution in the ensemble average behaves as the mathematical model predicts. You cannot do so for a single measurement as qm is a statistical model and does not predict much for a single measurement. Accordingly, qm also simply does not predict that you get a particle in two places for a single experimental run. QM does not tell us anything about how to interpret superpositions for a single experiment. Claiming something else is pop-sci mumbo jumbo.

You don't understand. Bohmian mechanics makes statements about what was until recently thought to be unobserveable quantum behavior. It's observed now, it's been a decade. It's a new development and the guiding wave is in trouble with experiments.

This is of course wrong. Bohmian mechanics is not at odds with any experimental results. What people observe in experiments is that results follow the mathematical model of superposition even for quite large objects like nanomechanical cantilevers. This is pretty cool, but it is not at odds with Bohmian mechanics. Bohmian mechanics has the same math and comes to the same results in the ensemble average. You would need to create an experiment going beyond qm to rule out this interpretation. That means that you would really need to do an experiment that measures a superposition state as the result of a single experimental detection and not by backtracking from many measurements. However, nobody knows how to do that.

On the other hand, quantum mechanics has no problems with superpositions and quantum weirdness.

No, it does not because it does not care about it. Standard qm tells us way less than people often think. Standard qm does not even have collapse. It has state reduction. Interpreting that as collapse is already an unnecessary assumption. In my opinion discussing interpretations has become popular among laymen, while working physicists rather discuss physics and do not care about interpretations at all, especially in experimental physics. Most working physicists I know are already quite annoyed when another bad pop-sci summary about some nature or science article comes out claiming things being in several places at once, backward causation or fancy non-locality effect because the stuff in the pop sci summary is never claimed in the article itself and one can be sure that friends, relatives and that unknown guy on the bus who somehow heard that you do quantum physics for a living will ask you about how that works and one needs to spend a lot of time in order to undo all the damage already done by those pop-sci summaries which just try to make things sound sensational.

I recently met a guy working on nanomechanics and they got a mechanical resonator close to the ground state already a few years ago. Some journalist came over and asked him what that might be good for and he answered that the resonance frequency might change if some atoms or molecules settle on the oscillator, so one might identify some elements as a long term goal. The headline of the final article was: Scientists develop artificial nose...

 

[bhobba]

Standard qm tells us way less than people often think. Standard qm does not even have collapse. It has state reduction. Interpreting that as collapse is already an unnecessary assumption.

Ahhh. Too true. Too true.

Thanks
Bill

 

[atyy]

How does the ensemble interpretation work in cosmology? What are the multiple preparations in observing the anisotropy of the microwave background?

 

[Maui]

For superpositions, you can also directly map the experimental results to the mathematical model: You do a lot of measurements and the probability distribution in the ensemble average behaves as the mathematical model predicts. You cannot do so for a single measurement as qm is a statistical model and does not predict much for a single measurement. Accordingly, qm also simply does not predict that you get a particle in two places for a single experimental run. QM does not tell us anything about how to interpret superpositions for a single experiment. Claiming something else is pop-sci mumbo jumbo.

Experiment says so, you live in the 1940's. Small scale prototypes of quantum computers have already been implemented and I posted links earlier in the thread.

This is of course wrong. Bohmian mechanics is not at odds with any experimental results. What people observe in experiments is that results follow the mathematical model of superposition even for quite large objects like nanomechanical cantilevers. This is pretty cool, but it is not at odds with Bohmian mechanics. Bohmian mechanics has the same math and comes to the same results in the ensemble average.

That'd be all good if superpositions were not experimentally confirmed. You are completely wrong, that's why you turn this into what the maths of the BI says(it's the math that needs interpretation!). It's an interpretation, it's supposed to explain classical behavior and it does so using a pilot wave. No wonder you don't mention it anywhere.

You would need to create an experiment going beyond qm to rule out this interpretation. That means that you would really need to do an experiment that measures a superposition state as the result of a single experimental detection and not by backtracking from many measurements. However, nobody knows how to do that.

That's the same as asking for direct contact(touch) with the Sun to believe that it exists. And you know what you require is not possible but it's a shelter, when you have no other way out.

On the other hand, quantum mechanics has no problems with superpositions and quantum weirdness.

No, it does not because it does not care about it. Standard qm tells us way less than people often think.

What are you talking about? We are discussing superpositions of states and you are misinforming people that qm doesn't care about it. That's the ABC of qm, so what are you talking about?

Standard qm does not even have collapse. It has state reduction. Interpreting that as collapse is already an unnecessary assumption.

How did it get to discussing collapse? What does it have to do with what I said?

In my opinion discussing interpretations has become popular among laymen, while working physicists rather discuss physics and do not care about interpretations at all, especially in experimental physics. Most working physicists I know are already quite annoyed when another bad pop-sci summary about some nature or science article comes out claiming things being in several places at once, backward causation or fancy non-locality effect because the stuff in the pop sci summary is never claimed in the article itself and one can be sure that friends, relatives and that unknown guy on the bus who somehow heard that you do quantum physics for a living will ask you about how that works and one needs to spend a lot of time in order to undo all the damage already done by those pop-sci summaries which just try to make things sound sensational.

I recently met a guy working on nanomechanics and they got a mechanical resonator close to the ground state already a few years ago. Some journalist came over and asked him what that might be good for and he answered that the resonance frequency might change if some atoms or molecules settle on the oscillator, so one might identify some elements as a long term goal. The headline of the final article was: Scientists develop artificial nose...

That'd be great for a post of facebook but is out of place here. Can you please explain why the nonlocal guiding wave would mimic superpositions of states when a quasi-macro or macro system is isolated from the environment?

 

[kith]

I was hoping for an explanation from your point of view how the non-local guiding wave is compatible with the superpositions of states the said guiding wave was supposed to do away with (for a somewhat classical and intuitive picture of the world).

You really have to distinguish between superpositions and multiple states at the same time. In classical electrodynamics, we have superpositions as well. This doesn't imply that there are multiple states. At a time t₀, a unique state is given by the electric field E(x,t₀), the magnetic field B(x,t₀) and their derivatives. In dBB, a unique state of a particle is given by its position x₀ and its guiding field ψ(x,t₀) (note that this doesn't depend on the system being "microscopic"). It doesn't make sense to claim that dBB is proven wrong by experiments which have reconstructed a certain ψ from their measurements unless dBB predicts a different ψ for this situation.

 

[kith]

How does the ensemble interpretation work in cosmology? What are the multiple preparations in observing the anisotropy of the microwave background?

The microwave background corresponds to a mixed state which is interpreted as an ensemble in all interpretations. I'm not sure what you are getting at.

 

[Ken G]

The key issue is how such a world emerges from a theory that only makes predictions about observations that appear in such a world. That is a very deep issue and the true quantum mystery.

I agree that is the central issue, but I'd frame it differently. I don't hold that worlds ever emerge from theories, since I reject the concept that nature follows mathematics. Instead, it seems closer to what actually happens that we fit mathematics to nature like a template or a (sometimes amazingly) close approximation. Given that, it is perfectly natural to expect that all physical theories must involve predictions about observations, so the inscrutable nature of an observation should always be difficult or impossible to remove from any theory. So for me, the deep question is, what is the connection between observations and mathematics? They seem like two completely different things, but apparently they are quite deeply connected. That we cannot understand the connection is not cause to imagine it isn't there, as the success of physics shows that connection is quite clearly there. So we should not make it our goal to remove the connection, but rather to accept it, study it, and understand it better.

A lot of progress has been made - but issues still remain and more research is required before a satisfactory explanation is found. I suspect a few revolutions will occur along the way - indeed we may be in the middle of one right now - I find the following very thought provoking:
https://www.simonsfoundation.org/quanta/20130917-a-jewel-at-the-heart-of-quantum-physics/

Wow, that's potentially monumental. I would cull out this quote:“They are very powerful calculational techniques, but they are also incredibly suggestive,” Skinner said. “They suggest that thinking in terms of space-time was not the right way of going about this.”

What is the significance that one of our central conceptual tools for organizing our perceptions, space and time, is "not the right way of going about this"? It would seem that this is trying to tell us that tools we use to organize our perceptions are not always the best way to organize observations writ large. This is a bit like what Planck was quoted as saying earlier in this thread-- our ability to observe is changing, when we do modern physics we rely more and more on supplemental apparatuses than the simple perceptions we use in our daily lives. The need for new mathematics appears with the ability to do new types of observations, and the organizational milieu that worked before is no longer the most elegant approach. First it was imaginary numbers that rose to the fore, now it may be strings or amplituhedrons.

We proceed in steps-- first we have new observations that stimulate new mathematical structures, then we spend a lot of time understanding our own mathematical structures (which tend to be more profound and more elegant than we realize when we first describe them), then we get all excited we have figured out how nature really works, then come the next generation of new observations that show us it ain't. I say it's time we recognize this cycle as the natural progress of science, and stop trying to make it what it never was.

Added: The role of observation does not mean that when a tree falls, we can be unclear about if it makes noise. Instead, that role is in giving meaning to the predicate, that "a tree falls." Asserting a falling tree already asserts all that goes with it, including noise, but the assertion itself is already an observational one. That is the part people often forget. The proof is that as yet we have no idea if there is any difference between saying "a tree falls" and "a tree is observed to fall." For the time being, we mean exactly the same thing by those two phrases, as we have no other meaning for any of those words.

 

[TrickyDicky]

Really interesting thread and must say I find myself attracted the ensemble interpretation as a bare minimum interpratation of the math. However it is not without some complexities as any intepretation.
I was wondering (always from my laymen-nonexpert-naive point of view) how is this interpretation made compatible with QFT where the wavefunction can be seen as a field operator observable, the emphasis usually put in saying this operator is different from the wavefunction of a single particle, but this distinction being moot in the ensemble interpretation as the wavefunction here is never interpreted as that of a single particle if I understood correctly.

 

[Ken G]

It's a new development and the guiding wave is in trouble with experiments. On the other hand, quantum mechanics has no problems with superpositions and quantum weirdness.

As you keep saying, but you have not made the case. You keep saying that in effect, "Bohm would not have expected experiment X to come out the way it does." I think that is quite untrue, I believe there are no experiments that have ever been done that Bohm would have thought would come out any differently. Indeed, I would say this is obvious, because if there were, then you could point to the equation in BM that fails, yet the equations in BM are built to produce the equations of QM. So if such an experiment really existed, that would surprise Bohm, the project would not be to show where BM went wrong, the project would be to show where the Schroedinger equation went wrong.

 

[atyy]

The microwave background corresponds to a mixed state which is interpreted as an ensemble in all interpretations. I'm not sure what you are getting at.

If I understand correctly, the ensemble interpretation says quantum mechanics applies to many physical copies of the system. What are the many physical copies of the system when the system is the universe, eg. for the following application of quantum mechanics by Mukhanov?

Mukhanov, Physical Foundations of Cosmology, Section 8.4
"How do quantum fluctuations become classical? When we look at the sky we see the galaxies in certain positions. If these galaxies originated from initial quantum fluctuations, a natural question arises: how does a galaxy, e.g. Andromeda, find itself at a particular place if the initial vacuum state was translational-invariant with no preferred position in space? Quantum mechanical unitary evolution does not destroy translational invariance and hence the answer to this question must lie in the transition from quantum fluctuations to classical inhomogeneities. Decoherence is a necessary condition for the emergence of classical inhomogeneities and can easily be justified for amplified cosmological perturbations. However, decoherence is not sufficient to explain the breaking of translational invariance. It can be shown that as a result of unitary evolution we obtain a state which is a superposition of many macroscopically different states, each corresponding to a particular realization of galaxy distribution. Most of these realizations have the same statistical properties. Such a state is a close cosmic analog of the "Schroedinger cat." Therefore, to pick an observed macroscopic state from the superposition we have to appeal either to Bohr’s reduction postulate or to Everett’s many-worlds interpretation of quantum mechanics. The first possibility does not look convincing in the cosmological context."

 

[bohm2]

Superpositions were and are troublesome for the idea of macro realism, Bohm's idea was to restore objectivity by removing superpositions of states. He was wrong...BTW, it's not allowed to link to blogs here. I took a look at the answers and none addressed the issue I raised above. If nobody can answer this, they are wrong and would rather believe in a conspiracy(the pilot wave has a new function - it has to perform complex conspiratorial acts to suit someone's agenda).

I apologize for that. I will not post blogs again but if responses in your previous thread topic from both theoretical and experimental physicists did not convince you, then I have no hope in hell, since there's nothing I can add.

Do the SQUID experiments falsify Bohmian mechanics?
https://www.physicsforums.com/showthread.php?t=610085

 

[Ken G]

I don't understand this part. What is a formal mathematical meaning of an interpretation?

The Wiki on the logic of mathematical theories puts it pretty well I think when it says "An interpretation of a theory is the relationship between a theory and some contensive subject matter when there is a many-to-one correspondence between certain elementary statements of the theory, and certain contensive statements related to the subject matter." I'm not a mathematician, but my general impression is that a formal interpretation is basically an encoding of a theory into terms that have semantic meaning. In other words, an interpretation is a semantic picture we can attach to a theory, that contains enough information to derive the theory, but adds additional context that is not unique because it goes outside the theory proper. It is really the difference between how one proves a theorem (which is syntactic) and how one understands a theorem (which is semantic). The different roles of syntax and semantics in mathematics maps into the difference between the predictions of a physics theory, and statements about "what is happening."

Maybe I'm misunderstanding your point but as I see it, Fuchs, of all people, wrote a good paragraph worth regurgitating:

Interview with a Quantum Bayesian
http://arxiv.org/pdf/1207.2141v1.pdf

Fuchs' view is tantalizing, but it doesn't seem to be on solid formal footing. I think he is basically saying, physics is done by physicists, so whatever the physicist is picturing in their mind as they write down the equations is central to what physics is. He is also saying that our job is to understand nature, not just predict it. That's all true, but we must also bear in mind that we want objectivity in science as well. So we must tolerate different subjective interpretations of what is happening, because we cannot adjudicate them by experiment. Indeed, I should even say "embrace" rather than "tolerate." So perhaps the common ground between what I'm saying and what Fuchs is saying is, instead of saying "The interpretation should come first; the mathematics (i.e., the pre-existing, universally recognized thing everyone thought they were talking about before an interpretation) should be secondary," we should say the interpretation should come first to the individual physicist doing physics, but not necessarily the same interpretation for all. In that sense, an interpretation has some of the same status as a reference frame.

 

[Ken G]

If I understand correctly, the ensemble interpretation says quantum mechanics applies to many physical copies of the system. What are the many physical copies of the system when the system is the universe, eg. for the following application of quantum mechanics by Mukhanov?

I believe your question was answered above by bhobba, when he stressed that the ensemble is a conceptual tool, not a physical entity, in cases where there is only one realization of the system under study (like the universe). In effect, an ensemble interpretation of the CMB is a multiverse picture, but it differs from the standard multiverse picture in the sense that it does not require we view the multiverse as something real, but rather as a conceptual device. The same could be said for how the ensemble interpretation regards Everett's many worlds. One can get all the expository benefits of Everett's picture using the ensemble picture, yet without holding that decohered subspaces of the unitary superposition continue to be real even after the decoherence has assured no information can cross between them. In short, the ensemble picture is what you get when you cross many-worlds with the CI, and notice that you can eliminate all the seeming contradictions by simply throwing out everything that requires taking QM mechanics "seriously" as a description of what is actually happening.