Ok. You see a tree, You tell me: what, exactly, do you see? Hint. It's not, never was, never will be, the tree. — tim wood

In reply to Dfpolis, you say:

Utterly incoherent? Really? — tim wood

In your example you seem to be saying "you see a tree" but also "you do not see the tree", which is a contradiction. It's not clear what you're trying to say.

Anil Ananthaswamy's Through Two Doors at Once: The Elegant Experiment That Captures the Enigma of Our Quantum Reality also looks interesting. Especially if it lives up to the following reviewer's claims:

Ananthaswamy’s introduction of increasingly complex versions of the slit experiment proves extremely effective. Halfway through the book, even neophytes will likely find predicting the outcome of the delayed-choice quantum eraser experiment barely harder than figuring out the motions of a gear train. This approach also brings to the forefront the strengths and weaknesses of various interpretations, offering a perfectly balanced overview of each. — Science journal review

New experimental findings cast doubt on DeBroglie ‘pilot wave’ theory — Wayfarer

Nice find. It's worth noting that the walking droplet experiments provide interesting quantum analogies (and intuitions) for pilot wave theories. But a modern pilot wave theory like Bohmian Mechanics posits a hidden nonlocal mechanism for guiding the particles and doesn't depend on the outcome of those experiments.

Yes. There need not be a single ("the") causal sequence of some set of events - sometimes there are multiple causal sequences.

I think it's philosophically interesting from a language perspective. Thinking about the mathematical description of the experiment (and QM generally) and translating it into intuitive language.

And so it is not always possible to know the cause.

If the principle of causation is that every event has a cause, then the experiment is perhaps not so philosophically interesting, since what it shows is not that there are events with no cause, but that it is sometimes not possible to know the causal sequence.

So what the experiment does, is to place a limit on our knowledge such that it is not always possible for us to know the causal sequence of some set of events. — Banno

Actually not knowing the causal sequence is not the issue in this experiment. What "indefinite" means here is not "unknown causal sequence" but "no singular causal sequence".

In a classical model, the photon would travel either the first path of the interferometer (where transformation A is applied to the photon followed by transformation B) or the second path (where transformation B is applied to the photon followed by transformation A). Thus there would be a single causal sequence, whether known or unknown.

But that's not what happens. Instead the measured state of the photon shows that it must have traveled both paths in superposition (i.e., the interference pattern can't be reproduced with a single causal sequence). Thus the photon has both causal sequences in its history. For an illustration of this experiment, see https://www.youtube.com/watch?v=5hGw5jjdHO0.

It's analogous to the double-slit experiment where the interference pattern can't be reproduced classically. The photon has both slit paths in its history.

But since laws of physics don't differentiate between past and future and there is no entropic arrow of time for a particular component history, how do you know where is past and where is future for a particular component history? — litewave

Per the earlier video (from 1min:32), that is known from the experimental setup. One component history has Alice applying operation A to the photon and then Bob applying operation B, whereas the other component history has the opposite ordering.

If detectors were placed at the ends of those paths just before they merged at the final beam splitter, then a definite causal order would be observed (i.e., either the first path or the second path).

Whereas in the setup as shown, the final observer (the causal witness) does not singularly observe A occurring before B or vice-versa. The observer calculates from the interference effects that both must have happened. There is a definite causal order on a per path basis, but an indefinite causal order in aggregate.

Note that no issue need arise about a supposed failure of causality or a failure to distinguish the past from the future. The only issue is that it is a fallacy of composition to assume a single causal ordering for an aggregate of paths.

Does it even make sense to differentiate between "before" and "after" on the quantum level? I've heard that no, because the arrow of time for a quantum system only gets defined when the system decoheres into a classical system (the wave function collapses), thereby increasing entropy.

And if there is no difference between "before" and "after", what sense does it make to differentiate between cause and effect? — litewave

This probably gets into interpretation territory, but I don't think quantum systems do collapse into classical systems (for example, even if one observes a system in a precise location its momentum is still indefinite). Instead the physical context (and thus the observer's perspective) changes whenever there is a physical interaction between quantum systems. This defines an arrow of time, but it is indexed to the observer rather than being absolute. (Which is an idea we're used to with relativity anyway.)

So "before" and "after" are physically well-defined for the observer. In the case of interference effects, the history of the observed particle is the sum of the particle's component histories. "Before" and "after" are still well-defined for the particle (i.e, it goes into an interferometer, unitary processes occur and it is finally observed at a detector). However each component history must be considered separately, with cause preceding effect in each separate case. What doesn't make sense is to apply "before" and "after" in aggregate when no measurement has been performed (which would of course result in a singular observation where "before" and "after" are well-defined for that component history).

Here's an excellent video (Witnessing causal nonseparability) that demonstrates the indefinite causal order experiment that the OP describes. (It also has a nice demonstration of the Mach-Zehnder experiment.)

But with quantum mechanics, what is witnessed is violations of this simple classical model of causality "over and over and over again".

Why did the neutron decay? If its propensity to decay is steadfastly random, any moment being as good as another, then how could you assign a cause to that effect? It is a spontaneous event and so causeless in any specific triggering sense. — apokrisis

Unpredictability doesn't imply a violation of causality. Without knowledge or control of the underlying physical causes coin flips are also unpredictable.

The Schrodinger equation is deterministic and so, in principle, can predict when a particular neutron will decay. For a more practical experiment, the Schrodinger equation predicts that a beam of light sent through a Mach-Zehnder interferometer (with equal optical path lengths) will always arrive at the same detector, with certainty. Per Wikipedia:

In Fig. 3, in the absence of a sample, both the sample beam SB and the reference beam RB will arrive in phase at detector 1, yielding constructive interference. ... At detector 2, in the absence of a sample, the sample beam and reference beam will arrive with a phase difference of half a wavelength, yielding complete destructive interference. ... Therefore, when there is no sample, only detector 1 receives light." — Mach–Zehnder interferometer

As is usual in quantum experiments, the same result occurs when only one photon at a time is sent through the interferometer. Neither classical explanations nor randomness can account for that result. Both predict that a single photon should arrive at detector 1 or detector 2 with equal probability.

Strictly, the experiment shows that we cannot know if event A caused event B, or B caused A. The meaning of "cause" breaks down here. — Banno

I would say it's actually classical physical explanations that break down rather than causality.

Events A and B are independent transformations which can be ordered differently. So, for example, on one arm of the interferometer the photon is rotated left then down, on the other arm the photon is rotated down then left.

Classically, it is expected that the measured result would be consistent with the photon having traveled along only one of the interferometer arms and thus there being a definite event ordering. But each result instead indicates a combination of both orderings as if the single photon traveled along both arms simultaneously.

This is analogous to the double-slit experiment where the detected photons don't build up behind the two slits as one would expect on classical assumptions. They instead build up an interference pattern as if each photon goes through both slits simultaneously.

This is still understood causally. It's just that both arms of the interferometer necessarily contribute to the result not just one arm as per a classical explanation.

Wouldn't the cat be doing the equivalent of taking a measurement, creating a definite result? — Marchesk

Yes.

I never understood why the cat could be in a superposition, but the scientists conducting the experiments were not. — Marchesk

They can be. It just depends on which joint system is being considered.

Is the indefinite history only a product of thinking of a photon as a particle instead of a wave? — Marchesk

No. The experiment can also be considered at a macro scale using Schrodinger's cat as Banno suggests above. If QM holds true at a macro level (as most physicists expect) then the cat's history would similarly be indefinite.

It's really a matter of how one views counterfactual definiteness. If a measurement were taken after the first event on each path (whether event A or B) then a definite result (and thus history) would be obtained. It's similar to the double-slit experiment in that respect.

Well, why not? Why shouldn't a cause happen after the event? — Banno

There's no need to give up causality. The paper isn't saying that the cause can happen after the event. It's instead saying that a photon can have an indefinite causal history. The experimenters send a photon through an interferometer where one path has event A followed by event B and the other path has event B followed by event A. The paths are recombined and measurements of the photon match the predictions of quantum mechanics rather than classical mechanics (where the photon travels only one of the paths).

People are is love with the magic of infinity. It’s ideal for research as it generates all sorts of mad ideas. Anything that can happen will happen; an infinite number of times! Endless possibilities! But whilst infinity is fun I can’t help but think it is a source of confusion in many instances and is holding back scientific progress. — Devans99

Max Tegmark would agree with you.

Not only do we lack evidence for the infinite but we don’t need the infinite to do physics. Our best computer simulations, accurately describing everything from the formation of galaxies to tomorrow’s weather to the masses of elementary particles, use only finite computer resources by treating everything as finite. So if we can do without infinity to figure out what happens next, surely nature can, too—in a way that’s more deep and elegant than the hacks we use for our computer simulations.

Our challenge as physicists is to discover this elegant way and the infinity-free equations describing it—the true laws of physics. To start this search in earnest, we need to question infinity. I’m betting that we also need to let go of it. — Infinity Is a Beautiful Concept – And It’s Ruining Physics - Max Tegmark

I might have this formulation wrong but I was wondering where in Aristotle is the distinction between matter and substance? For example, I thought he made the point that mind was substance but not matter? — DS1517

These references may be a useful starting point:

In Z3, Aristotle considers the claim of matter to be substance, and rejects it. Substance must be separable and a this something (usually translated, perhaps misleadingly, as “an individual”). — Aristotle on Substance, Matter, and Form

Ζ.3 begins with a list of four possible candidates for being the substance of something: essence, universal, genus, and subject. ... In the Categories, individual substances (a man, a horse) were treated as fundamental subjects of predication. ... This horse is a primary substance, and horse, the species to which it belongs, is a secondary substance. — Aristotle's Metaphysics - SEP

As StreetlightX notes, matter and form are the paired aspects of an individual (per hylomorphism). Substance can refer either to the individual (primary substance) or the formal class of things an individual belongs to (secondary substance).

Aristotle describes mind (nous, often also rendered as “intellect” or “reason”) as “the part of the soul by which it knows and understands” (De Anima iii 4, 429a9–10; cf. iii 3, 428a5; iii 9, 432b26; iii 12, 434b3), thus characterizing it in broadly functional terms. — Aristotle's Psychology - SEP

For Aristotle, mind is a formal characteristic of individual human beings in the sense of man is a rational animal. The term distinguishes human beings from other animals in a functional sense and is not intended to denote some kind of immaterial substance or property (say, per Descartes or property dualism).

Well, there is the ancient skeptical approach. To paraphrase, the awareness of leaky compartments leads to ataraxia, in which one suspends work on leakproof compartments. After which, the leaks are no longer bothersome. — Marchesk

Like this?

It's a question of whether deflation needs to take into account meaning. — Marchesk

Only in an abstract sense. The truth schema says "p" is true iff p. You can substitute whatever you like for p as long as it is meaningful.

The snow is white is true iff the snow is white.

But then that depends on what we mean by snow, since snow-like stuff can have different chemical compositions. — Marchesk

So conventionally we mean H2O. But there's nothing prohibiting a different usage. Is there a problem here?

"What do you know, snow is white on Mars!"

But the snow is made up of carbon dioxide crystals, which melts into CO2 liquid when the temperature is low enough, which it can be near the Martian poles. Is your statement true or false? — Marchesk

As usual it depends on what the statement means. Conventionally, "snow" refers to H2O, so the astronauts are not seeing snow, they're seeing something else (dry ice, as it happens). Nonetheless snow (H2O) is white on Mars as it is on Earth. So the astronaut's statement is true.

But note in your second sentence above that you use "snow" in a different sense to refer to what the astronauts observed (dry ice). On that meaning, the astronaut's statement is true as well, since dry ice is white on Mars.

The main issue here is to avoid equivocation.

"As we have said in the previous section, in non-reflexive logics we do not accept the negation of the reflexive law of identity. Also, we don’t have to accept that it must fail in at least some interpretations. Rather, we adopt its restriction in the form of its inapplicability. Here, ‘inapplicability’ is couched in terms of identity not making sense, not being a formula, for some kinds of terms." - Arenhart

Exactly. Per the bank account metaphor, identity is not applicable to the melted coins since they are not individual coins. So to ask whether the coins are self-identical would be a category mistake (not false). What we really have is molten metal which is good for five coins when withdrawals are made.

I was talking about whether it's possible have a logic to represent the idea that some objects might not be such that Identity is applicable to them. Quoting Arendhart:

"In a nutshell, non-reflexive systems of
logic are systems that violate the so-called ‘Reflexive Law of Identity’ in the form
∀x(x = x). In its ‘metaphysical reading’, the Reflexive Law of Identity is known as a
version of the ‘Principle of Identity’, roughly stating that everything is self-identical.
Versions of this law are restricted in systems of non-reflexive logic, and those systems
are said to incorporate in a rigorous fashion the idea of entities somehow losing their
identity."

As they and others go on to point out, this is a restriction on identity by means of separating the terms of language into those to which identity applies and those of which it does not. — MindForged

That's a nice paper - here's a link to a pre-print for anyone interested.

Just to summarize the problem, Leibniz' Identity of Indiscernibles says that no two objects have exactly the same properties. However quantum mechanics says that two particles can have exactly the same properties. For example, see the Hong–Ou–Mandel effect.

A natural way to resolve this conflict is to say that Leibniz' principle is only applicable to substantial objects, that is, objects that emerge as the result of quantum interactions (or measurements). Substantial objects have identity and are always distinguishable from other substantial objects. Whereas outside an interaction, quantum particles are only accounted for in a formal sense and lack substance and identity.

A metaphor can illustrate this. Suppose that the nation's currency consists only of similarly-marked metal coins worth $1 each. Coins can be deposited at your bank where they are melted down in a furnace. At that time, the coins have no substantial existence (or identity). However, formally, if you deposit five coins, your account balance will be $5. Additionally, the molten metal materially backs your account balance. If you need coins, you can push a button and a new coin is immediately minted for your use.

So the coins in circulation have identity. But the melted coins in the bank have only an aggregate cardinality (you formally own five coins).

False, they're the same shade, which I verified with my color picker: RGB( 126,126,126 ).

The truth in this case is different than what it appears to be to us. — Marchesk

Part of the issue can also be with the perceived meaning of the question. While it says shade, perhaps some interpret it to mean natural color (which excludes shadow).

However as long as there is a standard by which the meaning and truth of claims can be decided (such as verifying with a color picker), then there is no in-principle problem.

So, whatever its unobserved state, that state is fully determined with respect to the kinds of atoms we will find. Since information is the reduction of possibility, and there is no possibility that we will find any other atoms, we can say it's atomic structure is fully informed.

So, we know there is some reality, prior to our observation, that is determinately H2O. Further, that reality is doing things. For example, it is contributing to the gravitational field. — Dfpolis

Agreed. However if there is some reality that is determinately H2O then there is some reality that determinately has three atoms. The latter is simply a logical consequence of the former. If observation is not required for the former to be true, then it is not required for the latter to be true either.

Now, what about the "threeness" of the molecule? It is also a determinate potential, but it is not doing anything that the physicality of the molecule is not doing. It has no operations of its own. — Dfpolis

Activity (and change) is a characteristic of particulars, not universals. The number of atoms is simply a function of the water molecule itself, independent of human ideas about it. It is not merely potential information, it is actual information, even if the agent doesn't count the atoms or have a concept of numbers at all.

Our discussion reminds me of a past thread entitled Is information physical. I'm curious whether or not you would agree that information is physical, in Rolf Landauer's sense.

can you prove that there are still there atoms in a water molecule regardless of an intelligent agent? — Blue Lux

No, it assumes realism.

I don't think your realistic interpretation of three is necessary to make the sentence true. The referents in the sentence are the molecule and its atoms, which, if counted, will number three. — Dfpolis

It seems to me that you could say the same thing about the particulars. That is, the referent of the sentence is the world which, if observed in a specific way, would present as a water molecule and its atoms.

Whereas on a realist premise, three atoms in a water molecule is understood to be a consequence of natural circumstances independent of humans, not of our looking or counting.

Yes, there are three atoms independently of anyone counting them, but there is no actual number independently of an agent thinking it. — Dfpolis

I would agree that there is no idea of number independent of an agent's thoughts.

Yet there would still be three atoms in a water molecule even if there were no intelligent agents in the universe. For that sentence to be true, none of the referents can depend on an agent's thoughts. So at least some universals such as three (and more generally number) are independent of mind (though not of the particulars that give them meaning).

he one fine point here, made by Aristotle in his definition of "quantity" in Metaphysics Delta, is that there are no actual numbers independent of counting and measuring operations. — Dfpolis

I can't find this - could you quote the specific text you're thinking of there?
— Andrew M

1020a "'Quantity' means that which is divisible into constituent parts, each or every one of which is by nature some one individual thing. Thus plurality, if it is numerically calculable, is a kind of quantity; and so is magnitude, if it is measurable." — Dfpolis

Thanks. So to clarify, my claim is that there are three atoms in a water molecule independent of anyone counting them or even conceptualizing numbers at all (e.g., prior to sentient life emerging on Earth). That would seem to be a premise of moderate realism about universals.

Is that your view as well? Or is it your view that there are potentially three atoms in a water molecule when no-one is thinking about or counting them? That is, that sentient life is required for there to actually be three atoms in a water molecule.

There were no actual universals prior to subjects thinking them. — Dfpolis

Isn't that conceptualism about universals rather than moderate realism?

All of these are intelligible aspects of the molecule, not actual universal ideas. If we could see on hydrogen atom, we could form the universal <hydrogen> — Dfpolis

The term universal normally refers to what particular things have in common (what you're calling the intelligible aspects). For a moderate realist the universal is immanent in the particulars, not the mind.

All of these are real and intelligible, but not actually known until someone becomes aware of them. — Dfpolis

Agreed.

The one fine point here, made by Aristotle in his definition of "quantity" in Metaphysics Delta, is that there are no actual numbers independent of counting and measuring operations. — Dfpolis

I can't find this - could you quote the specific text you're thinking of there?

So, while counting the hydrogen atoms in a water molecule will always give <2>, there is no actual number 2 floating around the molecule. — Dfpolis

Agreed. Numbers aren't particulars.

Right. It's the going out and looking which is important. — Marchesk

In this case you would be talking about assertability conditions rather than truth conditions. That is, those conditions that would warrant someone asserting (or believing) that a statement is true.

Assertability is related to knowledge/evidence/justification.

But the deflationist is leaving the satisfying of conditions off their account of truth.

The cat is on the mat is true if and only if there exists a specific cat in the world on a specific mat in the world being referred to, when making an empirical claim. — Marchesk

There does need to be a use for the statement. But the referents need not be in the actual world. The cat and mat might be in a Harry Potter book. Or you might be considering a hypothetical where it is stipulated that the cat is on the mat.

A true (or false) statement requires a concrete truth condition. The truth schema abstracts away the specifics of that truth condition.

What is it that makes, "The cat is on the mat", true? Because it's not a logical relation that does that. Not if there is reference to a cat and a mat in the world. — Marchesk

It is simply a schema for what it means for a statement to be true. In this case, it is the cat being on the mat in the world that is the condition that would obtain (or not).

Now if the statement is just a logic statement, then these three are equivalent. [...] — Marchesk

The statement is any meaningful declarative sentence that can be expressed in some context. The logical relation is the two-way entailment between the statement and the truth condition.

Which is fine for logic, but it tells us nothing about whether it's true or false that it's raining outside today in Lisbon. — Marchesk

If you want to know whether a statement is true or false, then you need to go out and look. The truth schema won't help you with that. It just tells you what condition needs to obtain in order for the statement to be true.

In ordinary usage, "The cat is on the mat" is not expressing a logical proposition, but rather is making a statement about a situation in the world. And it is that situation which makes the statement or false, not logic. That's how true and false is used outside of logic. — Marchesk

Yes, the statement can be an ordinary empirical statement. But the relation between the statement and the truth condition is a logical one.

Wha is it that makes a statement true, such that the cat is on the mat is not false or meaningless?

I'm failing to see how deflation addresses that question. — Marchesk

Regarding "p" is true iff p, the statement on the left-hand-side is true (or false) if and only if the condition on the right-hand-side obtains (or not). It's a logical relation.

If the statement "the cat is on the mat" is true then that entails that the cat is on the mat (the condition). Conversely, if the cat is not on the mat, that entails that the statement is false.

My view is that the mind is inextricably involved in every judgement about every matter, even those things that are so-called ‘mind-independent’. — Wayfarer

It is, unarguably, since you're talking about judgments. But Einstein's question is whether the mind is inextricably involved in every matter (including matters prior to life having emerged on Earth and thus prior to judgments about them).

Because questions about how we know that the snow is white are going to rear their head at this point.

Consider we're inside and the weather report says it's snowing out side. So I say,

"The snow is white".

You go out and look and say: "Nope, it's actually yellow."

And I"m like, "Bro, snow is white, stop lying!"

But then I go and look and I see that it is yellow, because you took the chance to unburden your bladder there. — Marchesk

So that is a question of what is meant by "snow is white". If you are talking about the reflective properties of snow, that is one meaning. If your friend is talking about the color of some particular patch of snow, that is another meaning. One may be conventional, another idiosyncratic. Or both may be conventional meanings, depending on context. The truth schema allows you to choose whichever meaning you like based on your metaphysical or pragmatic preferences. Which is to say, it's not an issue about truth.

I see no reason to think that universals exist independently of the minds thinking them. They have a foundation in reality, in the potential of each instance to evoke the same concept, i.e in the intelligibility of their instances. But, being potential is not being actual. — Dfpolis

I'm curious how you would describe a concrete scenario prior to sentient life emerging on Earth with respect to universals.

For example, consider a molecule of water consisting of two hydrogen atoms and one oxygen atom. Among the universals here are the kinds water, molecule and atom, the numbers one and two, and the relations between the atoms.

Philosophically, first there's the question of whether water molecules (as particulars) could have existed prior to sentient life on Earth (in a similar sense to Einstein asking whether the moon exists when nobody looks). If so, there's the second question of whether the relations between the atoms, their structure and their quantity would also have been real prior to sentient life on Earth (i..e, that a water molecule really has two hydrogen atoms independent of mind).

My reading of Aristotle's immanent/moderate realism about universals is that the answer would be "yes" to both those questions. You seem to be saying "no" to at least the latter question.

And of course, on a common sense reading, it's just looking and seeing that the cat is on the mat. — Marchesk

You said this earlier as well but it's not correct. "p" is true iff p is an expression of how the word "true" is used. On that usage, a claim can be true even if no-one looks.

Similarly for Aristotle's definition of truth - it does not mention verification.

But that's just the start of the matter, because philosophy isn't simply espousing common sense. — Marchesk

Right. Philosophy is an inquiry that starts with observation, not common sense.

They're not answering that question.
— Michael

Yeah, but it seems to me they need to. Otherwise, deflation is stating a truism. — Marchesk

"p" is true iff p is a formal rule that is derived from observing how people ordinarily use the word "true". Whether or not it does capture that use is an empirical question (which can be investigated).

Right, there isn't, as long as one isn't doing philosophy and is only speaking in ordinary terms. But at least as far back as the ancient philosophy, problems arose for our naive view of things such as truth just being a matter of checking to see whether the cat is on the mat. Why is that? Well, because of things like skepticism, relativism, and the problem of perception. — Marchesk

They aren't problems for truth though. If the referred context of a claim such as "Earth is the third planet from the sun" is our shared experience (which is generally the case in ordinary use), then it is true independently of skeptical claims about BIVs and the like. That undermines skepticism and the problem of perception. It can also be seen that relativism just involves an idiosyncratic use of "true".

A truth schema is an abstraction that allows you to plug in whatever claims you like but the schema itself doesn't itself depend on any specific metaphysical claims.

I get what the deflationist is trying to do, but it seems to me like it does so by ignoring what motivated the whole truth debate in the first place. — Marchesk

Maybe. But it can also make it easier to identify what the problems are (and whether they are substantial).

But that's a trivial observation at best. What's interesting is what makes a statement true or false. We already knew that "The cat is on the mat" was asserting a proposition. Focusing on that doesn't resolve any of the issues around truth. — Marchesk

For a deflationist, what makes "the cat is on the mat" true (or false) is for the cat to be on the mat (or not). More generally, "p" is true iff p.

The point is that a deflationist is not trying to resolve issues around meaning or verification (rightly or wrongly). They are just pointing out that there is no great mystery to the ordinary use of truth terms.

Good points, so even if ordinary language clams are empirically based, there's still a discrepancy between truth and verification. — Marchesk

Yes, they are different things. But I think the point that the deflationists are making is simply that the explicit assertion of truth about a statement doesn't add anything that wasn't already implied by the statement itself. They are not making any claims about the role of verification.

That is, if the statement "the cat is on the mat" is true (or false) then the statement "it is true that the cat is on the mat" is similarly true (or false).

This runs into a difficulty. Scientific statements are not true, they are rather confirmed by experiment and consistency with existing theory. But this is conditional upon future testing and theoretical development. Thus an empirical justification does not make statements about the world true. However, ordinary language does say that a particular cat is either on a particular mat, or it is not. That's a true or false statement in the ordinary language game, not a conditional scientific fact. — Marchesk

I think you're drawing a distinction between scientific and ordinary claims here that has its own difficulties. I don't see why scientific statements couldn't be true. Yes, they are provisional in the sense that new information may come up that cause scientists to reject them. But that's true for ordinary statements as well. You might find that there was no cat on the mat after all, it was instead a trick of the light or some such.

Per the OP, I don't think there is much difference between a deflationary view and a correspondence view in practice. The language game just is that there are things in our shared experience that we talk about (and that we generically call "the world"). If we decide to call this object a "cat" and that object a "mat" then we can also talk about the relation between them. Aristotle's, "to say of what is that it is is true..." applies equally well whether cats and mats are intrinsic features of reality, objects in the computer game we are playing, or projections within a hypothetical matrix.

Yes, absolutely, and this is specifically beyond the OP. The distributions we've been talking about have almost always been (or should have been) unknown to the player. — Srap Tasmaner

Right, the player doesn't have that perspective but we do when discussing hypotheticals with specific distributions.

The player doesn't even know that there is some selection process. There are values in envelopes. How they got there can be discussed, and that can be interesting when the player has, say, partial knowledge of that process, but it is not the source of the paradox, in my opinion. — Srap Tasmaner

What is the source of the paradox in your view?

As I see it, the source of the paradox is the idea that the player can calculate the expected gain conditional on the observed amount. That would require knowing the specific probabilities for {v/2,v} and {v,2v} which is just what she doesn't know.

On the assumption, of course, that the player takes this initial distribution to be bounded above by M for some (possibly uncknown) M; or [...] — Pierre-Normand

Yes, which I take to be a reasonable (physical) assumption.

But it is, for all that, exactly the same choice over again, and however many steps there are between beginning and end, your expected take is the average of the values of the two envelopes. If there's an example in which that is not true, I would be surprised. — Srap Tasmaner

The way I look at the problem is that the expected gain calculation depends on an agent's knowledge. Some agents may have more information than others which they should factor into their calculation.

For example, the host may know what envelope pair has been selected (rendering the initial distribution irrelevant) but not know the amount in the player's chosen but unopened envelope. For the host (as for the player), the expected gain from switching is zero. However the host calculates this by averaging the two known amounts instead of averaging the unknown X and 2X.

When the player opens the envelope revealing the amount, the host will now know the actual gain (or loss) were the player to switch. So, from the host's perspective, the expected gain just equals the actual gain. The host now has all the relevant information.

Conversely, the expected gain that the player calculates will still be the unconditional gain of zero since she doesn't know the initial distribution or both amounts in the selected envelope pair.

A further perspective is held by those who know the chosen amount and also know the initial distribution but not which envelope pair was initially selected. So for the equiprobable ({$5,$10},{$10,$20}} distribution, the expected gains from switching for $5, $10 and $20 respectively are $5, $2.50 and -$10. The $10 amount is the only amount where not all the relevant information is known (i.e., which envelope pair it belongs to). But there is enough information to recommend switching should the player see the $10 amount.

Each expected gain calculation is justified given the information the agent has. But since that information can be different, each agent can (justifiably) reach different conclusions regarding whether the player should stick, switch or be indifferent.

Newcomb's problem is more controversial, even, than the two-envelope paradox. It is also quite rich in philosophical implications. — Pierre-Normand

Definitely a good candidate for a discussion sometime!