Undergrad Does a "physically real" quantum interpretation exist?

[PeterDonis]

people seem to defend their interpretation as the real one.

This often happens in the literature, yes. But such disputes are not resolvable, because there is no way to test interpretations against each other by experiment. Hence, such disputes are out of bounds here. (The guidelines for this subforum point this out.)

 

[RUTA]

Because for most people, just being able to calculate predictions for the results of experiments, and test them against actual experiments, is not enough. Most people want to be able to tell some kind of story about what is "really happening". And no interpretation of QM gives a story that everyone can accept.

Here is an excerpt from "Einstein's Entanglement: Bell Inequalities, Relativity, and the Qubit" (Oxford UP, 2024):

Quantum information theorist Chris Fuchs writes:

"What is the cause of this year-after-year sacrifice to the 'great mystery?' Whatever it is, it cannot be for want of a self-ordained solution: Go to any meeting, and it is like being in a holy city in great tumult. You will find all the religions with all their priests pitted in holy war ... . They all declare to see the light, the ultimate light. Each tells us that if we will accept their solution as our savior, then we too will see the light."

As Fuchs noted, the story from each "religion" is always, "Just give up [blank] and the mystery disappears!" Unfortunately for its advocates, everyone else considers [blank] essential to causal explanation. Maudlin agrees. Concerning what each "religion" says about the other, he writes:

"They may correctly note that according to every one of their rival theories, God was malicious, and having thus eliminated every other possibility, claim their own theory the victor. The problem is that *every* partisan can argue in this way since *every* theory posits some funny business on the part of the Deity."

 

[timmdeeg]

I think it's not a matter of taste -- we just haven't yet found the "natural" interpretation of quantum (field) theory.

There is one point, I didn't get yet. The Schrödinger equation describes the evolution of the wave function over time. But if the wave function is a mathematical description of a quantum state it can't be the quantum state of say an Elektron itself. So, if correct wouldn't it be natural to say that the wave function can't collapse because math usually doesn't collapse?

 

[WernerQH]

So, if correct wouldn't it be natural to say that the wave function can't collapse because math usually doesn't collapse?

Yes, that was Dyson's point (discussed in another thread):

A physical object can collapse when it bumps into an obstacle. But a wave-function cannot be a physical object. A wave-function is a description of a probability, and a probability is a statement of ignorance. Ignorance is not a physical object, and neither is a wave-function. When new knowledge displaces ignorance, the wave-function does not collapse; it merely becomes irrelevant.

 

[PeterDonis]

that was Dyson's point

Dyson's point is not true for all interpretations of QM. In the MWI, for example, the wave function is a direct mathematical description of the physical reality. In the Bohmian interpretation, the wave function is a direct mathematical description of part of the physical reality, the "pilot wave" that steers the particles.

 

[PeterDonis]

if the wave function is a mathematical description of a quantum state it can't be the quantum state of say an Elektron itself

It can in some interpretations--the MWI, for example.

 

[WernerQH]

As Fuchs noted, the story from each "religion" is always, "Just give up [blank] and the mystery disappears!" Unfortunately for its advocates, everyone else considers [blank] essential to causal explanation.

Does Fuchs reveal "the cause of this year-after-year sacrifice to the 'great mystery'"?

The religious analogy is perhaps amusing, but creating sects is not what scientists are striving for. And the number of interpretations (or what is passed off as such) has increased dramatically since I learnt quantum mechanics (half a century ago)! For me this is a symptom of an underlying unsolved problem. And it's only rationalization, or resignation to say that the interpretations are all equally "reasonable". It's unclear what quantum theory is about. Many people would like a better answer to the question than that it is about "wave functions", "quantum objects", or "measurements". (Of course there are also those who have given up and claim that the mathematical formalism is all that's needed.)

 

[timmdeeg]

It can in some interpretations--the MWI, for example.

So its not decidable whether the wave function describes a quantum state or just probability distributions.

If it describes a quantum state what does this mean if things like position, a definite path ... aren't describable prior to measurement?

 

[timmdeeg]

In the MWI, for example, the wave function is a direct mathematical description of the physical reality

What is the meaning of a mathematically describable "physical reality?

 

[Lord Jestocost]

What is the meaning of a mathematically describable "physical reality?

‘Physical reality’ is that what remains if the observer as a component can be eliminated from the process of knowing.

 

[timmdeeg]

‘Physical reality’ is that what remains if the observer as a component can be eliminated from the process of knowing.

And how would you describe "that what remains" using physical terms? The latter because we talk about a describable physical reality.

 

[Fra]

‘Physical reality’ is that what remains if the observer as a component can be eliminated from the process of knowing.

I think if you remove the observer from the inference process, there is no context for inference and no context of knowing.

Can we by analogy separate out and characterize "ultimate truth", from the scientific process?

I think not. Neither do I find it necessary.

/Fredrik

 

[Lord Jestocost]

And how would you describe "that what remains" using physical terms? The latter because we talk about a describable physical reality.

In principle, that boils down to one simple question. To quote Harald Atmanspacher: Can nature be observed and described as it is in itself independent of those who observe and describe – that is to say, nature as it is “when nobody looks"?

 

[timmdeeg]

Hm, supposed the wave function describes the physical reality of say an Elektron prior to measurement. Isn't this description meaningless if it doesn't refer to certain physical properties of that state of the Elektron?

 

[PeterDonis]

So its not decidable whether the wave function describes a quantum state or just probability distributions.

In the sense that there are QM interpretations that say each of those things, yes.

If it describes a quantum state what does this mean if things like position, a definite path ... aren't describable prior to measurement?

They are in some interpretations--for example, Bohmian.

In the MWI there are no "positions" of anything; the wave function is the entire physical reality.

 

[PeterDonis]

Hm, supposed the wave function describes the physical reality of say an Elektron prior to measurement. Isn't this description meaningless if it doesn't refer to certain physical properties of that state of the Elektron?

In an interpretation like the MWI, the wave function is the physical property. It's all there is.

 

[timmdeeg]

In an interpretation like the MWI, the wave function is the physical property. It's all there is.

To me its weird to identify a mathematical expression with physical properties. Physical properties are due to measurements. Which equipment do we need to measure a mathematical expression?

 

[PeterDonis]

To me its weird to identify a mathematical expression with physical properties.

This is done in every area of physics. You can't avoid it. Physics has to describe what we observe and measure using math.

What would be weird would be to insist that every mathematical expression in a physical theory must be identified with a physical property. But no theory of physics does that--not even QM with the MWI.

 

[physika]

experiments thinkable which clarify if the wave function collapses

Gravity induced collapse

“Being able to measure the time difference on such a minute scale could enable us to discover, for example, that gravity disrupts quantum coherence, which could be at the bottom of why our macroscale world is classical.”



---------
https://www.nature.com/articles/s41586-021-04349-7

 

[timmdeeg]

Thanks to everybody for helpful contributions.

 

[A. Neumaier]

To me its weird to identify a mathematical expression with physical properties. Physical properties are due to measurements.

All physical properties we talk about in physics have both a mathematical expression and a meaning in terms of measurements.

But measurements have no priority. Forces have been felt by people long before they were first measured by Galilei.

 

[timmdeeg]

All physical properties we talk about in physics have both a mathematical expression and a meaning in terms of measurements.

So leaving aside whether measurable or not which physical properties are described by the wave function?

 

[A. Neumaier]

So leaving aside whether measurable or not which physical properties are described by the wave function?

Scattering probabilities under all kinds of scattering experiments, and detection probabilities for certain kinds of measurements. These are physical properties of the sources and detectors in the experiments.

 

[martinbn]

So leaving aside whether measurable or not which physical properties are described by the wave function?

Different people may have different opinions, and different interpretations may say all kinds of things, but QM says that there isn't anything in addition to the wave function. So all properties are described by it.

 

[A. Neumaier]

Different people may have different opinions, and different interpretations may say all kinds of things, but QM says that there isn't anything in addition to the wave function. So all properties are described by it.

In addition to wave functions there must at least be measurements, since Born's rule is about them.

And we need much more to 'be there' to be able to relate wave functions to our everyday reality. We don't see, hear, or touch wave functions....

 

[timmdeeg]

Scattering probabilities under all kinds of scattering experiments, and detection probabilities for certain kinds of measurements. These are physical properties of the sources and detectors in the experiments.

If we leave everything in the context of the the probability density aside are there still other physical properties?

 

[martinbn]

In addition to wave functions there must at least be measurements, since Born's rule is about them.

And we need much more to 'be there' to be able to relate wave functions to our everyday reality. We don't see, hear, or touch wave functions....

Yes, but this is not the question! His question was what properties are described by the wave function. The fact that one needs measurments and that the particles and fields are there is somthing different.

 

[WernerQH]

So we are still pondering the question: How does the wave function relate to the real world?

 

[A. Neumaier]

So leaving aside whether measurable or not which physical properties are described by the wave function?

QM says that there isn't anything in addition to the wave function. So all properties are described by it.

Yes, but this is not the question! His question was what properties are described by the wave function. The fact that one needs measurments and that the particles and fields are there is somthing different.

???

If there isn't anything in addition to the wave function then, since there are measurements, meansurements must be described by it.

But if the only property of a wave function is the wave function itself, and nothing of it refers to reality then the wave function is irrelevant to reality, hence to physics.

 

[A. Neumaier]

If we leave everything in the context of the probability density aside are there still other physical properties?

Beyond the probabilistic properties, everything is controversial. What else is physical about it depends on the interpretation of quantum mechanics assumed.

My thermal interpretation claims that all quantum expectation values computable from it are potentially physical properties.

Bohmians think that wave functions guide particles along their paths, and therefore exert physical forces.

Those who think the wave function encode only subjective knowledge presumably have to conclude that the wave function describes certain properties of observer brains.