Is the wavefunction subjective? How?

[jlcd]

I don't have the book so I can only go on the quotes you give. The quote you gave before says the Schrodinger Equation (presumably he means the time-independent Schrodinger Equation, the one describing energy eigenstates, since his description does not fit the time-dependent Schrodinger Equation) is the quantum version of energy conservation. That sounds like he's saying it's describing something real, not just something subjective. Energy conservation is not subjective.
What "orthodox interpretation" are you talking about?

Orthodox in the sense he mentioned psi(x) had no physical meaning and only probability and squaring it stuff.

This is, as above, the time independent Schrodinger Equation, the one whose solutions describe energy eigenstates. It is not the time dependent Schrodinger Equation, the one whose solutions describe general states.
No, it doesn't. See above.
Anything relativistic. The Schrodinger Equation (either version) is a non-relativistic approximation.
It can't be because it's non-relativistic. In quantum field theory, the combination of QM with relativity, there are no wave functions except in very special cases. Quantum fields are a whole different kind of thing.

Focusing on the subject of this thread which is how the wave function is subjective. During the time of Bohr. How did he model entangled particles which didn't have wave function? How did he make entangled particles subjective too?

 

[PeterDonis]

During the time of Bohr. How did he model entangled particles which didn't have wave function?

A quantum system consisting of entangled particles does have a wave function. The particles taken individually don't, but that doesn't stop Bohr or anyone else from modeling the system using its wave function.

 

[jlcd]

A quantum system consisting of entangled particles does have a wave function. The particles taken individually don't, but that doesn't stop Bohr or anyone else from modeling the system using its wave function.

I mean in decoherence, entangled particles are not in superposition.In your Insight Article where you mentioned about more complete description (hidden variables?) if the state was subjective. Quoting it::

"For #1, the obviously true part is that we can never directly observe the state, and we can never make deterministic predictions about the results of quantum experiments. That makes it seem obvious that the state can’t be the physically real state of the system; if it were, we ought to be able to pin it down and not have to settle for merely probabilistic descriptions. But if we take that idea to its logical conclusion, it implies that QM must be an incomplete theory; there ought to be some more complete description of the system that fills in the gaps and allows us to do better than merely probabilistic predictions. And yet nobody has ever found such a more complete description, and all indications from experiments (at least so far) are that no such description exists; the probabilistic predictions that QM gives us really are the best we can do."

Reference https://www.physicsforums.com/insights/fundamental-difference-interpretations-quantum-mechanics/

Is the complete description the same as Hidden Variables? Or separate concept. If they are synonyms. Is the complete description or hidden variable describable by quantum field theory, or would it still be QM?

 

[PeterDonis]

in decoherence, entangled particles are not in superposition

Huh? I can't even make sense of this.

Is the complete description the same as Hidden Variables?

Hidden variables would be one kind of more complete description. But they would have to be nonlocal hidden variables because of Bell's Theorem.

 

[jlcd]

Huh? I can't even make sense of this.

I mean broken entangled particles are no longer in superposition. For example, in EPR, if you have entangled particles - as soon as one is observed it becomes entangled with the observational apparatus and is no longer entangled with the particle.

The math of which as Bhobba repeated many times throughout the years:

"There are standard definitions of superposition and entanglement in QM. I suggest you stick to those.
They are:

1. Superposition reflects the vector space structure of so called pure states. That is if you have a system that can be in state state |a> and state |b> then it can be in a superposition of those states ie c1*|a> + c2*|b> where c1 and c2 are complex numbers. This is called the principle of superposition and is a fundamental principle of QM. It is not an axiom because it follows from something else - but no need to go into that here.

2. Entanglement applies the principle of superposition to separate systems. Suppose you have a system that can be in state |a> or |b> and another system that also can be in state |a> or |b>. If system 1 is in state |a> and system 2 in state |b> that is written as |a>|b>. Conversely if system 1 is in state |b> and system 2 on state |a> that is written as state |b>|a>. But we can apply the principle of superposition to give a state c1*|a>|b> + c2*|b>|a>. The two systems are then said to be entangled. It is a peculiar non classical situation - system 1 is no longer in state |a> or |b> and the same with system 2 - they are entangled with each other. If you observe system 1 and find it in state |a> by the principles of QM the combined system is in state |a>|b> - so system 2 is in state |b> and conversely. Observing one system immediately has told you about another due to entanglement."

Reference https://www.physicsforums.com/threads/bells-inequality.791592/page-2#post-4975266

Hidden variables would be one kind of more complete description. But they would have to be nonlocal hidden variables because of Bell's Theorem.

I was inquiring earlier about the other equations based on your Insight Article. I was asking what kind of equations the more complete description may take. If Schroedinger Equation is only for tool for probability and subjective. So I thought your complete description mean more objective equations. It can involve Hidden Variables as you say but won't it need QFT on majority since there may be some exotic fields involved or must one focus on QM to solve for this complete equations. What do you think?

 

[PeterDonis]

Entanglement applies the principle of superposition to separate systems.

I'm not sure I would put it this way, but I see now what you meant.

 

[PeterDonis]

I was asking what kind of equations the more complete description may take.

Nobody has such a more complete description, so this question is not answerable.

 

[jlcd]

Nobody has such a more complete description, so this question is not answerable.

If someone can demonstrate that low energy physics like water and salt is enough to produce new physics. Is QM description enough or must one need QFT for water and salt? I know QFT is needed in the Large Hadron Collider, but still water and salt have electrons and electromagnetic interaction. So QFT is needed? This is the last (and critical) question as I don't want to hijack the thread, lol. So others can discuss the topics of the OP. Thanks.

 

[PeterDonis]

must one need QFT for water and salt?

Neither one involves any relativistic effects, so no.

 

[Stephen Tashi]

I see a measurement device (or any interacting part) as a kind of "information processing" object.

If we consider Nature to exist independently of human opinions about it then whether something is measuring device is subjective. For example, there can be a local phenomena that human beings agree to call a voltmeter. Sitting on a table beside it can be a local phenomena that human beings agree to call a coffee cup. Both the voltmeter and the coffee cup presumbably have inputs and outputs in the sense that humans can declare some phenomena to be external to these objects and declare other phenomena to be the objects' reactions to external pheomena.

This is one way to view the "cut" between classical and quantum systems. Is it more or less what the originators of the "cut" concept had in mind?

 

[jlcd]

I: "So these folks treat the entire Schroedinger Equation as only a tool used by humans and not necessariy ruling the objects dynamics?"

For that particular interpretation, yes, that's basically it.

Let's focus on this odd situation where QM does not necessary rule the object dynamics and what it meant.

Before the interpretation of the wave function as probability wave. Schrodinger's theory gave a complete description of the spectral lines in the hydrogen atom, reproducing touchstone Balmer formula. In addition, the splitting in electric and magnetic fields also popped right out of the wave equation.

Schrödinger was thus able to observe that the integers (number of nodes) derived from a three-dimensional wave solution precisely correspond to the three quantum numbers n, k and m from the old quantum theory.

Schrodinger actually initially thought it was literal matter waves before Henrik Lorentz made him realized key points like the fact wave packets will spread with time and the idea of representing particles completely in terms of the superposition of waves is invalid.

But can't the success of reproducing the Balmer formula tell something about the Schrodinger Equation able to describe the dynamics of objects?

Let's the case of the hydrogen atom. The interaction of the electron to the nucleus is via coulomb, and this can be described by QM. Can you give some examples showing that the Schrodinger equation doesn't necessarily describe the dynamics of objects?

I always read about Quantum Mechanics giving us so many discoveries like integrated circuits, processors, iphones, etc. So it's odd it can't even describe or rule the dynamics of objects.

And for those who take the wave function as real. Do they also say the Schrodinger Equation doesn't really rule or describe the dynamics of objects? Then why aren't any of the camps try to figure out the laws governing the real dynamics of objects instead of just this subjective thing?

 

[PeterDonis]

And for those who take the wave function as real. Do they also say the Schrodinger Equation doesn't really rule or describe the dynamics of objects?

Of course not. Those who take the wave function as real have no reason to say any such thing. But what they mean by "objects" might not be what you're thinking. See my next post.

 

[PeterDonis]

I always read about Quantum Mechanics giving us so many discoveries like integrated circuits, processors, iphones, etc. So it's odd it can't even describe or rule the dynamics of objects.

Ok, so it's odd. So are all interpretations of QM. Taking the wave function as real might fit in better with your intuitions about describing the dynamics of objects, but on that interpretation, the "objects" in question are wave functions, which if we take the Schrodinger Equation as always describing the dynamics, bear no resemblance whatever to the actual objects we observe. What you get when you just say there's the wave function evolving by the Schrodinger Equation and nothing else is the Many Worlds interpretation, which is certainly "odd" by any reasonable criterion of oddness.

 

[jlcd]

Ok, so it's odd. So are all interpretations of QM. Taking the wave function as real might fit in better with your intuitions about describing the dynamics of objects, but on that interpretation, the "objects" in question are wave functions, which if we take the Schrodinger Equation as always describing the dynamics, bear no resemblance whatever to the actual objects we observe. What you get when you just say there's the wave function evolving by the Schrodinger Equation and nothing else is the Many Worlds interpretation, which is certainly "odd" by any reasonable criterion of oddness.

I know Many world was the consequence of taking wave function as real as you emphasized in your Insight Article (i almost memorized every word of it).

But Many worlds can be tamed by simple altering unitarity. I know this needs new math and physics. But then by altering it too much. Won't it be as complex as not taking wave function as real like Bohr and just cooking up the complete descriptions?

Both need real hard work.. altering unitarity in many worlds is as Zurek put it :

"Repeatability leads to branch-like states, Eq. (13), suggesting Everettian ‘relative states’ [19]. There is no need to attribute reality to all the branches. Quantum states are part information. As we have seen, objective reality is an emergent property. Unobserved branches can be regarded as events potentially consistent with the initially available information that did not happen. Information we gather can be used to advantage—it can lead to actions conditioned on measurement outcomes [5]."

By going to Bohr and treating wave function as subjective one needs to develope more complete description. No problem as data is not lacking. But what is more elegant. Zurek idea of othe branches as information or the whole wave function as subjective and one has to cook up the complete description. But would the complete description retain some part of Zurek idea of the other branches as part information? What is the constrains for the more complete description if case 1 was true. Like in addition to discover any hidden variables. Must one produce new way of interaction that even involve spacetime. This is why I see case 1 as more elegant because there are more degrees of freedom in cooking up the new physics that involves spacetime. With wave function as real, it is not integrated to spacetime and looks a bit boring to compare to the potentiality in case 1.

Where did I go wrong in the analysis above?

Any references by say Perimeter Institute researchers about this so I can explore it further? Anyone?

 

[PeterDonis]

Many worlds can be tamed by simple altering unitarity. I know this needs new math and physics.

Yep. Which makes it out of scope for discussion unless you can give a specific reference.

as Zurek put it

Please give a reference.

 

[jlcd]

Yep. Which makes it out of scope for discussion unless you can give a specific reference.
Please give a reference.

It's in last page of Zurek paper:
https://arxiv.org/pdf/1412.5206.pdf
Say. Can Many worlds without the other worlds (even in formalism like Objective Collapse) really describe the interactions of objects (like an atom) or does it still need a more complete description just like case 1 where wave function is subjective?

 

[PeterDonis]

Many worlds without the other worlds

What does this mean?

 

[jlcd]

What does this mean?

In the paper, Zurek said "There is no need to attribute reality to all the branches. Quantum states are part information.". Meaning the other worlds are not really there. I think Zurek needs new physics to overcome unitarity. Also I think atyy mentioned something about BM is many worlds without the worlds.

Whatever, let's take first the original Many worlds. If all the worlds were real (I know they were caused by entanglement processes as you described many times.. I'm aware of the distinctions). This is enough to describe how atoms interact or how objects interact? Or there is still something missing or incomplete description? Then what is the advantage of this over Bohr subjective wave function that still require more complete descriptions?

 

[PeterDonis]

In the paper, Zurek said "There is no need to attribute reality to all the branches.

He's not talking about any version of many worlds when he says that.

If all the worlds were real (I know they were caused by entanglement processes as you described many times.. I'm aware of the distinctions). This is enough to describe how atoms interact or how objects interact?

Sure, if you define "how atoms interact" or "how objects interact" to include the existence of all of the many worlds.

 

[jlcd]

He's not talking about any version of many worlds when he says that.
Sure, if you define "how atoms interact" or "how objects interact" to include the existence of all of the many worlds.

Ok. The eigenstates from entangled processes as you described in previous messages form worlds. But I don't really like it. This was why I was exploring Zurek version all are information only. Either this or back to Born wave function as subjective.. then needs a whole new theory for the complete description. Either seems hard but that's physics. Any researchers like Zurek who is exploring the state is some kind of information only? like Wheeler It from Bit.

Oh i didnt finish the article by Lubos mentioned by the OP where he critiqued Neumaier. Ill finish reading the article later and maybe ask about it so not off topic.

 

[jlcd]

Neither one involves any relativistic effects, so no.

I understand in the LHC where particles are moving close to the speed of light. Relativistic effects are very obvious and QFT is required. But is it not in normal atom even how excited states of the electron emit a photon need QFT treatment? So not just relativistic effects? Anyway. I finished Lubos Motl many articles linked in the OP. So the bottom line is :

"Instead of specifying observables (linear operators on the Hilbert space) and calculating their eigenvalues and their probabilities of individual eigenvalues given some knowledge about the state, they keep on asking whether some "cloud here" affects another "cloud there" or whether it "collapses", assuming that the clouds objectively exist in the classical sense. That's not a good starting point to understand the essence of modern physics."

Lubos is very authorative. Right now. I wonder how large in percentage of physicists hold that view. I was so exposed to Zurek, Demystifier, Neumaier etc. views over the years I tend to ignore Lubos views which may still be the majority?

To clarify your own article when you commented "But if we take that idea to its logical conclusion, it implies that QM must be an incomplete theory; there ought to be some more complete description of the system that fills in the gaps and allows us to do better than merely probabilistic predictions."

Reference https://www.physicsforums.com/insights/fundamental-difference-interpretations-quantum-mechanics/

Let's take the double slit experiments. Lubos seemed to be emphasizing we must only focus on the output and not how the the one electron at a time version can interfere with itself. So does your "more complete description" just involved *trying* to figure out how the one electron behave when it is in between the emitter and detector or did you mean something else by "more complete description"?

And for the questions how it *interact* in Lubos or orthodox view, the answer is that it is emitted in the emitter and just appear in the detector. No interaction. Period"?

 

[PeterDonis]

is it not in normal atom even how excited states of the electron emit a photon need QFT treatment? So not just relativistic effects?

Whether you need QFT to analyze photon emission by excited states of atoms depends on how precise you want to be. A non-relativistic approximation is fine if you don't care about things like the Lamb shift.

 

[jlcd]

In msg number 79 of the thread (closed from one year of inactivity) https://www.physicsforums.com/threa...s-of-quantum-mechanics-comments.936506/page-4 you commented something I want to further inquire but can't reply there anymore so allow me to ask this here:

A better way of asking the question you might be trying to ask is, do people care about case 1 vs. case 2 because of the different ways the two cases suggest of looking for a more comprehensive theory of which our current QM would be a special case? The answer to that is yes; case 1 interpretations suggest different possibilities to pursue for a more comprehensive theory than case 2 interpretations do. Such a more comprehensive theory would indeed make different predictions from standard QM for some experiments. But the interpretations themselves are not the more comprehensive theories; they make the same predictions as standard QM, because they are standard QM, not some more comprehensive theory.

I'm aware one must draw the key distinction between interpretations of an existing theory, standard QM, and more comprehensive theories that include standard QM as a special case.

My interest in QM is towards these more comprehensive theories.

But then in the history of physics. The weak force, the strong force and EM were discovered even without upgrading QM. So even if there were another force of nature. It won't necessarily required alterations of QM. But Smolin and even Neumaier hinted quantum gravity may require more understanding of the foundation of QM.

Now let focus on these statements of yours :"case 1 interpretations suggest different possibilities to pursue for a more comprehensive theory than case 2 interpretations do. Such a more comprehensive theory would indeed make different predictions from standard QM for some experiments".

Do you have any examples in mind?

If not. Let me give an example (for sake of theoretical understanding and discussions). If someone can demonstrate a physical object like marble can be made to disappear and reappear elsewhere. Does it differentiate between case 1 and case 2? Because case 1 which just focus on the statistics of the output (the observable) is silent on what's in between and also silent on any mechanism making the entire object disappear. So if someone can demonstrate it. It can refute case 1, right? Or can one argue that is it part of the more complete description of case 1? This is very important question. There are many things Witten, Smolin, Hossenfelder and great giants of physics didn't have access to in this world. And this is a categorical statement that can be proven. But then this is just an example remember. If you can give examples about how say case 1 interpretations suggest different possibilities to pursue, please give it so I don't have to mention seemingly silly examples to get a grip of your thoughts of how case 1 or case 2 can give different possibilities of more comprehensive theories to pursue.

 

[PeterDonis]

My interest in QM is towards these more comprehensive theories.

And at this point we're getting into personal speculation, which is off limits for PF discussion.

Thread closed.