What Constitutes Supporting Evidence?

Another book that explores quantum foundations for a lay audience: What Is Real?, by Adam Becker. Highly recommend it.

Also would highly recommend Travis Norsen’s Foundations of Quantum Mechanics for a more detailed, but still very accessible, intro to interpretive issues in QM. Undergraduate level.

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My point is, since we don’t know what kind of “substance” it might be, any so called “failed” attempts could possibly be a matter of it being humanly undetectable, or looking for the wrong kind of “substance”. Regardless, what is really meant by a “true vacuum” of space?

To say it’s “nothing” makes no sense. Whatever it is it’s still necessary for matter to exist. So whether or not we know or can know what it is, it still has to be “something”. And if it’s “something”, then it seems to make sense that there would exists absolute location within that “something”.

At least that is the only way I can make sense of it. But I’m sure we could go around it circles on this for eternity. Just seems to be one of those issues that no one can be sure about. :slight_smile:

The one that says the so called “wavefunction” doesn’t know what to be until it gets measured. Right?

Could it be that there’s a blurring of an explanation and a description here? Theories are explanations and mechanisms are descriptions, right?

What “evidence” exactly are you referring to here?

I think we all agree that spacetime coordinates would exist in a vacuum of space. What I haven’t seen is evidence that a set of coordinates defined by a specific inertial frame has primacy over others.

The way I have always thought of it is that the wavefunction is a set of probable outcomes that becomes one outcome as soon as there has to be an outcome. Until an electron interacts with something it doesn’t have to be at any one specific point in space. In my experience, “measured” injects too much anthropocentrism into the science.

Interesting. So wouldn’t it follow that absolute coordinates existing in space would entail absolute space? How can you have absolute coordinates if what they are located in isn’t absolute? Or maybe I’m not following what your point is?

Not exactly… again, if you want to get a good handle on what some of the different interpretations are saying, I really highly recommend this book.

There’s no clear dividing line there. Descriptions of phenomena are highly theory-laden, especially in fundamental physics.

I’m referring to all empirical evidence here. All the data of what we observe in the natural world around us.

It is clear from the other thread Theory of Everything? that this is something that @Jim does not appreciate. While there could be multiple “explanations” for a single equation (“mathematical description”) that is obtained from experiments, not all explanations can be made to conform to that equation.

Don’t you mean the detection methods used to detect what is being described are theory-laden? I don’t see why there’s any problem with distinguishing between explanation and description.

As far as I can tell, depending on how someone defines a theory, it’s either composed of explanations and descriptions, or it’s only the explanations and the associated descriptions are considered separate from the theory. Is that right?

However it’s defined, would it be generally correct to say that explanations are, for the most part, indirect abductive inferences based on supporting evidence of what’s being explained about processes that are, for whatever reason, beyond observation/detection?

And if verified, descriptions are, for the most part, inductive inferences based on direct observation or indirect detection of what’s being described? And if not verified are most often, at least in physics, equations that make novel predictions of phenomena that so far have yet to be observed/detected?

I assume you’re talking about supporting evidence. So of all the supporting empirical evidence, what for you is the best evidence to show that what you call the “standard” interpretation of QM is consistent with that evidence?

No, I meant descriptions.

Any kind of a description of a phenomenon that goes beyond what is strictly sense-observable is theory-laden. E.g. if you want to describe what you see in a bubble chamber as anything more than “there was a curly track here and a straight track there…” (say you want to use the terms “charged particle track” and “neutral particle track” instead) then you are going to be using theory laden language. To some extent even the descriptions of just the perceptual data is theory-laden.

“Indirect detection” is going to be theory-laden. Equations are going to have certain variables and terms in them, and even if there are different ways of interpreting those terms, the equation isn’t intelligible as referring to something in the physical world without carrying some interpretation or other, so equations are theory-laden as well.

… how about the fact that standard QM (in the way that interpretation is applied in practice) makes predictions consistent with what we observe?

Whether it makes sense to apply the standard interpretation in the way it is usually applied in practice is another question, and that is where the measurement problem, etc, comes in and where I would argue that pilot wave theory is superior. But that discussion is entirely independent of any actual observations.

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As I have noted elsewhere, physics is just a hobby for me, so I might get some of this wrong.

The way I understand absolute space is that it should result in different observations in different frames. For example, the speed of light should be different in different frames as determined by their velocity with respect to the absolute frame. In reality, all observations are the same in all non-accelerating frames of reference, including observations of the speed of light.

To put it another way, how would you know that you were moving without a different frame to compare to? If I am in a spaceship that isn’t accelerating and I have absolutely no other observable matter or energy around me, how could I measure the spaceship’s velocity?

As far as I can tell this only provides verification for what QM describes. It has nothing to say about the interpretation of QM. Before we go any further, I think it’s important that this point be clarified. I just can’t help but suspect something is awry concerning the distinction between description and explanation/interpretation.

As I understand it, QM consists of mathematical equations describing how quantum objects interact and move through space. To verify that the formulas are correct, observations are made to see if the mathematical descriptions match actual observations.

But the verification is of the formulas, i.e., the description. And if I understand correctly, the verification of the description is inductively inferred from the observations matching with the descriptions.

On the other hand, the interpretations of QM are attempts to explain how things would look if it were possible to actually observe the quantum particles and their environment. If it were possible to make this observation there would be no need for the interpretation.

But because it’s not, an attempt is made to interpret from supporting evidence what would be seen if it actually could be observed. And if I understand correctly, the interpretation is abductively inferred from the supporting evidence.

If this is correct, then the verification of QM would only apply for what’s being described, and therefore to somehow equate this verification with the interpretation would be to misapply it, unless there were an interconnection that could justify such a move. And I just don’t see any way for such to be the case.

So I’m not saying that supporting evidence doesn’t exist for the different interpretations of QM. I just don’t see how the “fact that standard QM … makes predictions consistent with what we observe”, would qualify as such. But maybe I’m missing something?

And as I’ve been saying, there line between interpretation/theory and description is blurry, so what you say here doesn’t work. What you can say is that the observational evidence doesn’t support standard QM any more than it supports other interpretations/theories that give the same predictions about observable outcomes, which is what I’ve been saying in the other direction about PWT.

No, that isn’t correct. And the reason for that is because…

… is saying “if this impossible thing were possible, then so and so would follow” which isn’t very meaningful, logically speaking (anything can follow if you assume an impossibility, or at the very least, it’s very unclear how to apply the laws of logic in impossible situations).

It’s better IMO to say that interpretations of QM are trying to provide a model or a coherent explanation of the observable results in terms of what is really happening at the microscopic level.

I am not sure what you mean by this. The supporting evidence - the evidence that supports the theory, that makes it more likely to be true in Bayesian sense - is just the correct predictions that the theory makes that other theories fail to correctly predict. It’s the observable data that we have been talking about, that you think only has to do with the “description” rather than the “interpretation.”

The difference between standard QM and PWT, and where I would say PWT is superior, is more on the level of conceptual coherence - it doesn’t have the measurement problem or the problem of vague ontology and the seemingly arbitrary divide between microscopic and macroscopic behavior. But those differences do not have anything to do with any specific, observable outcomes, being more philosophical difficulties than experimental data. Calling it “supporting evidence” is a bit of an unusual way to describe the situation.

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I’m sorry, but to make sense of this I think we just need to stick to explanation and description. There’s too much ambiguity concerning how theory, interpretation and other similar terms are used. If we examine just those two terms what I’m saying makes sense of them, but I can’t see how what you’re saying makes any sense in regards to those two terms.

Okay, I’ll try to get some clarity on what we mean.

It seems to me that when you say “explanation” you are using it to mean what I have intended to mean by “explanation”, “interpretation”, or “theory”: a model of the reality underlying our observations. And when you say “description”, you mean a kind of systematization or summary of those observations themselves, which can be represented by the physics equations under consideration. Do I understand you correctly?

I’m fine with that meaning of explanation as long as it doesn’t get used interchangeably with description. I might clarify further by saying the view I hold is “reality as in actual existence.”

However, it seems like description is a bit more of an issue. Description I think is more like a qualitative regularity of how something behaves to get from a beginning state to an ending state, e.g., mechanism, law, principle, etc.

But I think an important distinction is that description can be verifiable by inductive inference based on observation, detection, measurement, etc. Whereas explanation is about things that cannot be observed and therefore, by default, can only be abductively inferred based on supporting evidence.

Setting aside the fact that I don’t think there’s a clear division between inductive and abductive inference either (inductive reasoning is a subset of abductive reasoning), your two characteristics of “description” are somewhat in tension:

Because a lot of the regularities and laws postulated by physics are not directly observable, and can only be verified in the context of assuming a certain theory. So “descriptions” can’t be cleanly separated from “explanations”. Schrodinger’s equation is a good example: the wavefunction it governs is not something observable, nor is it even measurable without operating under certain assumptions that are part of quantum theory, which ties it up with the “explanation” side of things.

Not sure exactly what your point is. But it seems to me that with verification, using QM as an example, what’s being verified is the description (formulas) of quantum behavior as it moves through space, including any internal explanations(?) that may be involved with the description. But what’s not being verified is the explanation about what underlies the quantum realm which itself is a separate independent claim from that of the description.

I have no problem with the description with or without “internal explanations(?)” having been verified if it works as expected when applied to technology. What I’m concerned with is the explanation about the underlying reality, which as a claim is not in any way interconnected with the description that I can see, and has no possible recourse for verification, and therefore depends totally on inferences from supporting evidence.

If the explanation about what underlies the quantum realm could be verified similar to the description, the controversy over the past 100 years of which explanation is the correct explanation would have been resolved a long time ago. But even though early on the description (formulas) has been and continues to be verified over and over, and is therefore generally uncontroversial, the 100 years of intense debate over the correct explanation continues to this day.

@T_aquaticus I’ll try to get to your comment hopefully soon.

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Likewise, unfortunately. Now you are trying to draw a distinction between explanations internal to descriptions and those external to descriptions, and again I just don’t see a clean separation there.

I hope you don’t mind if I try to bring this discussion back to what started this thread: do you understand why I say the bouncing droplet experiment that you referenced is not in any way supporting evidence or confirmation of pilot wave theory?

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OK. But one last question on that point. From what I can tell there are two distinct issues here. One is epistemological in nature concerning how things behave, while the other is ontological in nature concerning what is the nature of their existence. Is that something you would agree with?

No. So far I haven’t been able to figure out why you don’t see it as evidence.

Absolutely, we have to distinguish between how we come to know about, e.g. protons and electrons and what these things are. But that doesn’t seem to me to be the description vs. explanation distinction you’ve been talking about.

Because for it to be evidence, the fact that we have observed the bouncing drop behavior would have to make it more likely that pilot wave theory is true, compared to if we had not observed the bouncing drop behavior. But it demonstrably does not:

  • Let H be the hypothesis that pilot wave theory is true.
  • Let E be the observation of the bouncing drop behavior.
  • For E to be evidence for H, the conditional probability P(H|E) must be greater than the prior probability P(H). (This is the condition that evidence for a hypothesis has to make that hypothesis more likely - otherwise it is neutral or evidence against the hypothesis.)
  • Now P(H|E) = P(H)*P(E|H)/P(E). (This is Bayes’ theorem.)
  • But P(E|H) = P(E), because you can’t directly predict the bouncing drop behavior from pilot wave theory - you have to use the fact that PWT reproduces classical physics when you get to the macroscopic level, and just use the classical fluid dynamics theory to tell you whether you will observe the bouncing drop behavior. Classical physics at the macroscopic level is part of our background knowledge whether or not PWT is true; our knowledge of the relevant macroscopic physics is established before we come to the question of whether this or that quantum theory is true. So E is independent of H.
  • This means that P(H|E) = P(H); our probability for the truth of PWT is entirely unaffected by the observation of the bouncing drop behavior.

The only way that you can say the bouncing drop experiment better supports PWT compared to a different quantum interpretation is if the other quantum interpretation fails to reproduce classical physics at the macroscopic level. And you can argue that in fact the other interpretations fail in that way (say, because of the measurement problem) - but then not just the bouncing drop experiment, but all macroscopic phenomena constitute supporting evidence for PWT, and bringing up the bouncing drop experiment is utterly superfluous. And then it is really the argument that PWT successfully reproduces classical physics at the macroscopic level (while other quantum interpretations do not) which is doing the work, rather than the observation of the macroscopic phenomena per se.

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Maybe what @Jim is missing is that the bouncing drop is merely an analogy to PWT, and does not constitute real evidence for PWT.